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Metals, Volume 8, Issue 5 (May 2018)

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Cover Story (view full-size image) Cover story: Numerically based phase transformation maps for friction stir welded aluminum 2017A [...] Read more.
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Open AccessArticle Glow Discharge Optical Emission Spectrometer Calibration Using Hydrogenated Zr-2.5Nb Alloy Standard Samples
Metals 2018, 8(5), 372; https://doi.org/10.3390/met8050372
Received: 13 April 2018 / Revised: 16 May 2018 / Accepted: 20 May 2018 / Published: 22 May 2018
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Abstract
Currently, standard samples of hydrogen-metal systems meeting the requirements of glow discharge optical emission spectrometers (GD-OES) are not available on the market. This article describes the preparation of Zr-Nb-H standard samples and the calibration of GD-OES with the usage of these samples. Samples
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Currently, standard samples of hydrogen-metal systems meeting the requirements of glow discharge optical emission spectrometers (GD-OES) are not available on the market. This article describes the preparation of Zr-Nb-H standard samples and the calibration of GD-OES with the usage of these samples. Samples of Zr-2.5Nb were chosen as the material for sample production. The creation procedure includes five main steps: sample preparation (polishing to an average roughness, Ra, of 0.04 m using sandpaper), annealing, hydrogenation, maintenance in an inert gas atmosphere, and characterization of the samples. The absolute hydrogen concentration in the samples was determined volumetrically and calculated from the weight change. The distribution of hydrogen was studied using GD-OES Profiler 2 by Jobin Yvon Emission Horiba Group. As a result of this work, calibration curves of Zr, H, Nb, O, and other elements were obtained. The calibration errors were in the range of 1–5%. Full article
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Open AccessArticle Fabrication Technology and Material Characterization of Hot Rolled Cylindrical Fe-6.5 wt. % Si Bars
Metals 2018, 8(5), 371; https://doi.org/10.3390/met8050371
Received: 28 March 2018 / Revised: 14 May 2018 / Accepted: 21 May 2018 / Published: 22 May 2018
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Abstract
Cylindrical Fe-6.5 wt. % Si bars of 7.5 mm diameter were successfully fabricated from an as-cast ingot through three rolling stages, with 10 total passes: rough rolling at 850–900 °C and 8–10 m/min; medium rolling at 800–850 °C and 10–15 m/min; finish rolling
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Cylindrical Fe-6.5 wt. % Si bars of 7.5 mm diameter were successfully fabricated from an as-cast ingot through three rolling stages, with 10 total passes: rough rolling at 850–900 °C and 8–10 m/min; medium rolling at 800–850 °C and 10–15 m/min; finish rolling at 800–850 °C and 12–18 m/min. The evolution of the microstructure, texture, and ordered structure were studied, and the mechanical properties were investigated. Results indicated that the grains were refined by the hot bar rolling. Area fractions of the {100}<011> and {011}<100> oriented grains decreased to 0 during hot bar rolling, whereas the {100}<001>, {011}<211>, and {112}<110> components increased. Furthermore, the γ fiber with {111}<110> component was dominant. After the hot bar rolling, the DO3 ordered phase was suppressed, and the B2 ordered domains were refined. Ductility of the as-rolled bar was better than that of the rotary-swaged bar, due to the absence of the DO3 ordered phase, and refinement of the grains in the rolled bar. Moreover, discontinuous dynamic recrystallization (DDRX) occurred at a high deformation rate during the rough rolling, and continuous dynamic recrystallization (CDRX) appeared at a low strain rate during the finish rolling. Hence, hot bar rolling technology is an excellent process for the fabrication of Fe-6.5 wt. % Si bars. Full article
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Open AccessFeature PaperArticle The Influence of the Electrolyte Nature and PEO Process Parameters on Properties of Anodized Ti-15Mo Alloy Intended for Biomedical Applications
Metals 2018, 8(5), 370; https://doi.org/10.3390/met8050370
Received: 26 April 2018 / Revised: 15 May 2018 / Accepted: 18 May 2018 / Published: 21 May 2018
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Abstract
Plasma electrolytic oxidation (PEO) of Ti-15Mo alloys conducted in electrolytes containing Ca and P compounds can be an efficient process with which to obtain bioactive coatings. This paper reports on the influence of the nature of the electrolyte, its concentration, and PEO process
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Plasma electrolytic oxidation (PEO) of Ti-15Mo alloys conducted in electrolytes containing Ca and P compounds can be an efficient process with which to obtain bioactive coatings. This paper reports on the influence of the nature of the electrolyte, its concentration, and PEO process parameters on the properties of anodized layers on Ti-15Mo. A wide range of Ca- and P-containing alkaline and acidic solutions was employed to incorporate Ca and P ions into the anodized layer. The efficiency of the incorporation was evaluated by the Ca/P ratio in the coating as compared to that in the electrolyte. It was found that alkaline solutions are not suitable electrolytes for the formation of good quality, uniform PEO coatings. Only acidic electrolytes are appropriate for obtaining well-adherent homogeneous layers on Ti-15Mo. However, the maximum Ca/P ratios reached in the coatings were rather low (close to 1). The variation of electrical signal (negative-to-positive current ratio, frequency) and time of electrolysis do not result in a substantial change of this value. The processing time, however, did influence the coating thickness. Despite their low Ca/P ratio, the anodized layers demonstrate good biological activity, comparable to pure microrough titanium. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Open AccessArticle Transformation Induced Plasticity Effects of a Non-Equal Molar Co-Cr-Fe-Ni High Entropy Alloy System
Metals 2018, 8(5), 369; https://doi.org/10.3390/met8050369
Received: 27 April 2018 / Revised: 13 May 2018 / Accepted: 18 May 2018 / Published: 21 May 2018
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Abstract
Metastability-engineering strategy is an important topic for high entropy alloys (HEAs), owing to the transformation-induced plasticity effect (TRIP). In this work, TRIP effects of Co-Cr-Fe-Ni HEAs are investigated. Results indicate the tensile deformation-induced martensitic transformation occurs in Co35Cr25Fe40−x
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Metastability-engineering strategy is an important topic for high entropy alloys (HEAs), owing to the transformation-induced plasticity effect (TRIP). In this work, TRIP effects of Co-Cr-Fe-Ni HEAs are investigated. Results indicate the tensile deformation-induced martensitic transformation occurs in Co35Cr25Fe40−xNix (x = 0–15 at %) HEAs. The excellent combination of tensile strength (760 MPa–1000 MPa) and elongation (65–35%) owe to solid solution strengthening of Co and Cr, and the TRIP effect. In non-equal molar Co-Cr-Fe-Ni systems, with the decrease of Ni content, the values of stacking fault energy (SFE) decrease; thus, TRIP phenomena occurs. Based on the experimental investigation in three different regions of the Co-Cr-Fe-Ni multicomponent phase diagram, the face-centered cubic structured Co-Cr-Fe-Ni HEAs with VEC of ~8.0 is more metastable, and TRIP phenomena are more likely to occur. Full article
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Open AccessArticle Numerical Study on the Influence of a Swirling Flow Tundish on Multiphase Flow and Heat Transfer in Mold
Metals 2018, 8(5), 368; https://doi.org/10.3390/met8050368
Received: 30 April 2018 / Revised: 11 May 2018 / Accepted: 18 May 2018 / Published: 21 May 2018
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Abstract
The effect of a new cylindrical swirling flow tundish design on the multiphase flow and heat transfer in a mold was studied. The RSM (Reynolds stress model) and the VOF (volume of fluid) model were used to solve the steel and slag flow
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The effect of a new cylindrical swirling flow tundish design on the multiphase flow and heat transfer in a mold was studied. The RSM (Reynolds stress model) and the VOF (volume of fluid) model were used to solve the steel and slag flow phenomena. The effect of the swirling flow tundish design on the temperature distribution and inclusion motion was also studied. The results show that the new tundish design significantly changed the flow behavior in the mold, compared to a conventional tundish casting. Specifically, the deep impingement jet from the SEN (Submerged Entry Nozzle) outlet disappeared in the mold, and steel with a high temperature moved towards the solidified shell due to the swirling flow effect. Steel flow velocity in the top of the mold was increased. A large velocity in the vicinity of the solidified shell was obtained. Furthermore, the risk of the slag entrainment in the mold was also estimated. With the swirling flow tundish casting, the temperature distribution became more uniform, and the dissipation of the steel superheat was accelerated. In addition, inclusion trajectories in the mold also changed, which tend to stay at the top of the mold for a time. A future study is still required to further optimize the steel flow in mold. Full article
(This article belongs to the Special Issue Continuous Casting)
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Open AccessArticle Microstructural and XRD Analysis and Study of the Properties of the System Ti-TiAl-B4C Processed under Different Operational Conditions
Metals 2018, 8(5), 367; https://doi.org/10.3390/met8050367
Received: 24 April 2018 / Revised: 14 May 2018 / Accepted: 17 May 2018 / Published: 21 May 2018
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Abstract
High specific modulus materials are considered excellent for the aerospace industry. The system Ti-TiAl-B4C is presented herein as an alternative material. Secondary phases formed in situ during fabrication vary depending on the processing conditions and composition of the starting materials. The
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High specific modulus materials are considered excellent for the aerospace industry. The system Ti-TiAl-B4C is presented herein as an alternative material. Secondary phases formed in situ during fabrication vary depending on the processing conditions and composition of the starting materials. The final behaviors of these materials are therefore difficult to predict. This research focuses on the study of the system Ti-TiAl-B4C, whereby relations between microstructure and properties can be predicted in terms of the processing parameters of the titanium matrix composites (TMCs). The powder metallurgy technique employed to fabricate the TMCs was that of inductive hot pressing (iHP) since it offers versatility and flexibility. The short processing time employed (5 min) was set in order to test the temperature as a major factor of influence in the secondary reactions. The pressure was also varied. In order to perform this research, not only were X-Ray Diffraction (XRD) analyses performed, but also microstructural characterization through Scanning Electron Microscopy (SEM). Significant results showed that there was an inflection temperature from which the trend to form secondary compounds depended on the starting material used. Hence, the addition of TiAl as an elementary blend or as prealloyed powder played a significant role in the final behavior of the TMCs fabricated, where the prealloyed TiAl provides a better precursor of the formation of the reinforcement phases from 1100 °C regardless of the pressure. Full article
(This article belongs to the Special Issue Processing-Structure-Property Relationships in Metals)
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Open AccessArticle Phase Diagram of near Equiatomic Zr-Pd Alloy
Metals 2018, 8(5), 366; https://doi.org/10.3390/met8050366
Received: 28 April 2018 / Revised: 16 May 2018 / Accepted: 18 May 2018 / Published: 21 May 2018
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Abstract
The exact eutectoid and peritectoid temperatures in near equiatomic Zr-Pd compositions have been determined by using the diffusion couple method and microstructure analysis. The crystal structure of Zr13Pd12 compound were estimated to be orthorhombic with a = 1.78 nm, b
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The exact eutectoid and peritectoid temperatures in near equiatomic Zr-Pd compositions have been determined by using the diffusion couple method and microstructure analysis. The crystal structure of Zr13Pd12 compound were estimated to be orthorhombic with a = 1.78 nm, b = 0.80 nm and c = 1.00 nm from the electron diffraction experiments. The Zr13Pd12 compound is formed at 1100 ± 2 K with a peritectoid reaction between Zr2Pd and ZrPd compounds. The ZrPd compound transforms to Zr13Pd12 and Zr9Pd11 compounds by a eutectoid reaction at 1028 ± 4 K. Based on these results, the phase diagram of near equiatomic Zr-Pd binary system is reconstructed. Full article
(This article belongs to the Special Issue Zirconium Alloys)
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Open AccessArticle Tensile–Shear Fracture Behavior Prediction of High-Strength Steel Laser Overlap Welds
Metals 2018, 8(5), 365; https://doi.org/10.3390/met8050365
Received: 30 April 2018 / Revised: 10 May 2018 / Accepted: 16 May 2018 / Published: 18 May 2018
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Abstract
A wider interface bead width is required for laser overlap welding by increasing the strength of the base material (BM) because the strength difference between the weld metal (WM) and the BM decreases. An insufficient interface bead width leads to interface fracturing rather
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A wider interface bead width is required for laser overlap welding by increasing the strength of the base material (BM) because the strength difference between the weld metal (WM) and the BM decreases. An insufficient interface bead width leads to interface fracturing rather than to the fracture of the BM and heat-affected zone (HAZ) during a tensile–shear test. An analytic model was developed to predict the tensile–shear fracture location without destructive testing. The model estimated the hardness of the WM and HAZ by using information such as the chemical composition and tensile strength of the BM provided by the steel makers. The strength of the weldments was calculated from the estimated hardness. The developed model considered overlap weldments with similar and dissimilar material combinations of various steel grades from 590 to 1500 MPa. The critical interface bead width for avoiding interface fracturing was suggested with an accuracy higher than 90%. Under all the experimental conditions, a bead width that was only 5% larger than the calculated value could prevent the fracture of the interface. Full article
(This article belongs to the Special Issue Laser Welding of Industrial Metal Alloys)
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Open AccessArticle An Equivalent Calculation Method for Press-Braking Bending Analysis of Integral Panels
Metals 2018, 8(5), 364; https://doi.org/10.3390/met8050364
Received: 17 April 2018 / Revised: 6 May 2018 / Accepted: 15 May 2018 / Published: 18 May 2018
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Abstract
Press-braking bending is widely applied in the manufacture of aircraft integral panels because of the advantages of strong adaptability to different contours, simplicity of bending tools, short manufacturing time and low process cost. However, a simulation of bending process requires long-time calculation and
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Press-braking bending is widely applied in the manufacture of aircraft integral panels because of the advantages of strong adaptability to different contours, simplicity of bending tools, short manufacturing time and low process cost. However, a simulation of bending process requires long-time calculation and consumes extensive computational resources. Considering the factors that the original model (ORM) of an integral panel is large and the press-braking bending is used only for the local area of integral panels with heavy thickness in practice, an equivalent calculation method for press-braking bending analysis of integral panels is proposed. The local bending area of an integral panel is simplified to a model of plate in this method. An exponential strengthening model is used to derive the equations of stress, strain and forming radius of the ORM and its simplified model (SPM). Meanwhile, the equivalent parameters of the SPM are determined and deduced based on three principles: that the material begin to be yielded simultaneously, the ultimate stress of the ORM is the same as that of the SPM at the same punch displacement, and the forming radii of neutral surfaces of the ORM and the SPM are identical after springback. The distribution of the stress and strain determined by finite element (FE) simulations are compared, and the FE simulations indicate that the contour curve of the SPM is in fairly good agreement with the profile of the ORM under the same bending process parameters, and the maximum difference is 13.17%. The computational efficiency is increased by more than 48%. Therefore, the proposed approach is quite suitable for industrial applications to improve the bending quality and efficiency of integral panels. Full article
(This article belongs to the Special Issue Modern Aerospace Materials)
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Open AccessArticle Electrodeposition of Fe-C Alloys from Citrate Baths: Structure, Mechanical Properties, and Thermal Stability
Metals 2018, 8(5), 363; https://doi.org/10.3390/met8050363
Received: 13 April 2018 / Revised: 8 May 2018 / Accepted: 16 May 2018 / Published: 17 May 2018
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Abstract
A new citrate-based electrolyte is proposed for the electrodeposition of thick Fe-C films. The structure and properties of the deposits are compared to those from another electrolyte previously reported in the literature. Both consist of a nanocrystalline single-phase structure with a grain size
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A new citrate-based electrolyte is proposed for the electrodeposition of thick Fe-C films. The structure and properties of the deposits are compared to those from another electrolyte previously reported in the literature. Both consist of a nanocrystalline single-phase structure with a grain size of 20 nm, which results in a hardness of up to 660 HV. Due to its higher growth rate, the new electrolyte is a promising candidate for the deposition of thick films. However, the codeposition of oxygen causes embrittlement, limiting the application of the deposits from both the new and the known electrolyte. On the other hand, the codeposited carbon and oxygen provide considerable thermal stability and even a hardening capacity upon annealing. The results are compared and discussed with respect to the previous investigations of electrodeposited Fe-C alloys. Full article
(This article belongs to the Special Issue Electrochemical Deposition)
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Open AccessArticle Structure and Mechanical Properties of a Copper Combustion Chamber throughout Its Life Cycle
Metals 2018, 8(5), 362; https://doi.org/10.3390/met8050362
Received: 26 April 2018 / Revised: 12 May 2018 / Accepted: 14 May 2018 / Published: 16 May 2018
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Abstract
The material of a combustion chamber is subjected to high thermal and mechanical fatigue that can result in premature failure. Nevertheless, there is very little information in the literature concerning its characterization. In this work, the study of some properties of the copper
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The material of a combustion chamber is subjected to high thermal and mechanical fatigue that can result in premature failure. Nevertheless, there is very little information in the literature concerning its characterization. In this work, the study of some properties of the copper combustion chambers in water heaters throughout their life cycle is described. The microstructure, hardness, morphology, mechanical strength and roughness were evaluated, from the pristine copper sheet to a chamber subjected to 53,000 cycles. Throughout the whole cycle, changes were detected in the organization of the crystalline structure. Both after conformation and after completing the manufacturing process, the material exhibits a preferential orientation according to the direction [110], which is the most favorable to degradation of the material by thermal fatigue. The prevalence of the less dense crystallographic planes of the material in all stages of the life cycle allowed a better diffusion of the oxidant species facilitating the corrosion of the material. The oxidation products did not form a passivated layer and detached from the bulk copper, causing a progressive deterioration of the material. Full article
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Open AccessArticle Investigation of Nanoporous Superalloy Membranes for the Production of Nanoemulsions
Metals 2018, 8(5), 361; https://doi.org/10.3390/met8050361
Received: 27 February 2018 / Revised: 7 May 2018 / Accepted: 14 May 2018 / Published: 16 May 2018
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Abstract
Premix membrane emulsification is a gentle process for producing nanoemulsions, i.e., for pharmaceutical purposes. The operating time of common membranes is short today, because of their fragility, membrane fouling and poor cleanability. In contrast, superalloy membranes are cleansable because of their high mechanical
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Premix membrane emulsification is a gentle process for producing nanoemulsions, i.e., for pharmaceutical purposes. The operating time of common membranes is short today, because of their fragility, membrane fouling and poor cleanability. In contrast, superalloy membranes are cleansable because of their high mechanical strength as well as high chemical and thermal resistances and therefore, could achieve clearly longer operating times. Their usability for premix membrane emulsification is investigated in this study. Different flow rates of the premix emulsion were tested up to 21 cycles with a small-scale extruder, three different nanoporous superalloy membrane structures have been tested in comparison to a common polymer membrane. Varying the two-phase-structure (γ- and γ′-phase) of superalloy bulk material through thermal or thermo-mechanical treatments and chemical extraction of either one of the phases, different membrane microstructures could be obtained. These membranes differ in pore size, pore structure, and porosity, resulting in different flow resistances, droplet sizes and droplet size distributions in the investigated premix membrane emulsification process. Emulsions with droplet sizes in the desired range of 100 to 500 nm and with acceptable droplet size distributions were achieved. Data display an improved process stability for superalloy membranes, however, special attention needs to be paid towards narrow droplet size distributions. Full article
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Open AccessArticle Determination of the Critical Stress Associated with Dynamic Phase Transformation in Steels by Means of Free Energy Method
Metals 2018, 8(5), 360; https://doi.org/10.3390/met8050360
Received: 30 April 2018 / Revised: 11 May 2018 / Accepted: 14 May 2018 / Published: 16 May 2018
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Abstract
The double differentiation method overestimates the critical stress associated with the initiation of dynamic transformation (DT) because significant amounts of the dynamic phase must be present in order for its effect on the work hardening rate to be detectable. In this work, an
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The double differentiation method overestimates the critical stress associated with the initiation of dynamic transformation (DT) because significant amounts of the dynamic phase must be present in order for its effect on the work hardening rate to be detectable. In this work, an alternative method (referred to here as the free energy method) is presented based on the thermodynamic condition that the driving force is equal to the total energy obstacle during the exact moment of transformation. The driving force is defined as the difference between the DT critical stress (measured in the single-phase austenite region) and the yield stress of the fresh ferrite that takes its place. On the other hand, the energy obstacle consists of the free energy difference between austenite and ferrite, and the work of shear accommodation and dilatation associated with the phase transformation. Here, the DT critical stresses in a C-Mn steel were calculated using the free energy method at temperatures ranging from 870 °C to 1070 °C. The results show that the calculated critical stress using the present approach appears to be more accurate than the values measured by the double differentiation method. Full article
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Open AccessArticle Hydrogen Evolution Reaction Property of Molybdenum Disulfide/Nickel Phosphide Hybrids in Alkaline Solution
Metals 2018, 8(5), 359; https://doi.org/10.3390/met8050359
Received: 9 March 2018 / Revised: 10 May 2018 / Accepted: 14 May 2018 / Published: 16 May 2018
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Abstract
The hydrogen evolution reaction (HER) property of molybdenum disulfide (MoS2) is undesirable because of the insufficient active edge sites and the poor conductivity. To enhance HER performance of MoS2, nickel phosphide (Ni2P) was combined with this catalyst
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The hydrogen evolution reaction (HER) property of molybdenum disulfide (MoS2) is undesirable because of the insufficient active edge sites and the poor conductivity. To enhance HER performance of MoS2, nickel phosphide (Ni2P) was combined with this catalyst and three MoS2/Ni2P hybrids (38 wt % Ni2P addition for MoS2/Ni2P-38, 50 wt % Ni2P addition for MoS2/Ni2P-50, and 58 wt % Ni2P addition for MoS2/Ni2P-58) were fabricated via a hydrothermal synthesis process. Morphologies, crystallinities, chemical components, specific surface areas, and HER properties of the fabricated MoS2/Ni2P samples in an alkaline electrolyte were characterized and tested. In addition, the insight into the HER properties of as-prepared catalysts were revealed by the density functional theory (DFT) calculation. Additionally, the stabilities of pure MoS2, Ni2P, and MoS2/Ni2P-50 samples were evaluated. The results show that the addition of Ni2P can enhance the HER property of the MoS2 catalyst. Although HER properties of the above-mentioned three MoS2/Ni2P hybrids are inferior to that of pure Ni2P, they are much higher than that of MoS2. Among as-prepared three hybrids, MoS2/Ni2P-50 exhibits the best HER performance, which may be due to its uniform morphology, large specific surface area, and excellent stability. The MoS2/Ni2P-50 hybrid shows a high cathodic current density (70 mA/cm2 at −0.48 V), small Tafel slope (~58 mV/decade), and a low charge transfer resistance (0.83 kΩ·cm2). Full article
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Open AccessArticle Texture Control of Pure Titanium Sheet by the Surface Effect during Phase Transformation
Metals 2018, 8(5), 358; https://doi.org/10.3390/met8050358
Received: 18 April 2018 / Revised: 4 May 2018 / Accepted: 15 May 2018 / Published: 16 May 2018
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Abstract
The texture evolution of cold rolled pure titanium through different annealing parameters was investigated and different processes for various textures controls were proposed for further industrial application. Columnar grains with strong {11–20}//RD (rolling direction) texture was produced through cold rolling and a cooling-controlled
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The texture evolution of cold rolled pure titanium through different annealing parameters was investigated and different processes for various textures controls were proposed for further industrial application. Columnar grains with strong {11–20}//RD (rolling direction) texture was produced through cold rolling and a cooling-controlled annealing at 1100 °C with the Ar atmosphere. The preferred nucleation on the surface and the lowest strain energy of variant pairs during grain growth caused the formation of columnar grains and variant selection. Texture inheritance was discovered both in the cold-rolled and warm rolled-pure titanium sheets following 1000 °C annealing. The stored energy during cold rolling was the main reason causing the texture inheritance. Basal texture could be produced through warm rolling and subsequent annealing. The 30°-rotated around RD from basal texture could be preserved through both recrystallized annealing and transformed annealing. Full article
(This article belongs to the Special Issue Microstructure, Texture and Properties Control in Alloys)
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Open AccessArticle Influence of Intercritical Annealing Temperature on Microstructure and Mechanical Properties of a Cold-Rolled Medium-Mn Steel
Metals 2018, 8(5), 357; https://doi.org/10.3390/met8050357
Received: 27 April 2018 / Revised: 11 May 2018 / Accepted: 14 May 2018 / Published: 15 May 2018
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Abstract
Medium-Mn steels are characterized by ultrafine-grained (UFG) duplex microstructure consisting of ferrite and a large amount of retained austenite. Intercritical annealing is of great importance to achieving the UFG duplex microstructure and adjusting amount as well as stability of retained austenite. In the
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Medium-Mn steels are characterized by ultrafine-grained (UFG) duplex microstructure consisting of ferrite and a large amount of retained austenite. Intercritical annealing is of great importance to achieving the UFG duplex microstructure and adjusting amount as well as stability of retained austenite. In the present work, the influence of intercritical annealing temperature on the microstructure and mechanical properties was investigated in a cold-rolled medium-Mn steel Fe-12Mn-3Al-0.05C. Particularly, the dependence of microstructural morphology on intercritical annealing temperature was emphasized to reveal the genesis of the microstructural morphology in medium-Mn steels. The ferrite-austenite duplex microstructure manifested an elongated morphology in the specimen annealed at 555 °C, which inherited the lath structure of the cold-rolled state. The medium-Mn steel exhibited a continuous yielding behavior and a relatively low strain-hardening rate. With an increase in intercritical annealing temperature up to 650 °C, the amount of retained austenite increased and microstructure was partially recrystallized, showing a mixture of elongated and equiaxed grain morphologies. When the intercritical annealing was applied at 700 °C, the medium-Mn steel mainly exhibited recrystallized microstructure with equiaxed morphology. The optimal balance between the amount and the stability of retained austenite led to an enhancement of strain hardening and ductility. With a further increase in the intercritical annealing temperature to 750 °C, the medium-Mn steel possessed pronounced strain-hardening behavior at the beginning of the tensile deformation with deteriorated ductility. Full article
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Open AccessArticle Plasma Electrolytic Oxidation of High-Strength Aluminium Alloys—Substrate Effect on Wear and Corrosion Performance
Metals 2018, 8(5), 356; https://doi.org/10.3390/met8050356
Received: 12 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 15 May 2018
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Abstract
With the progress in materials science and production technology and the establishment of light-weight design in many fields of the industry, the application of light metals no longer requires only mechanical strength, but also a significant protection of the material against wear and
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With the progress in materials science and production technology and the establishment of light-weight design in many fields of the industry, the application of light metals no longer requires only mechanical strength, but also a significant protection of the material against wear and corrosion. Hard and wear-resistant oxide coatings on aluminium are produced by plasma electrolytic oxidation (PEO). During PEO, a conversion of the aluminium substrate to a ceramic oxide takes place. While the role of strength-giving alloying elements like Cu, Mg/Si, Zn, and Zn/Cu on the PEO process has selectively been subject of investigation in the past, the significance of the alloy composition for the service properties of the coatings is still unknown. Therefore, the performance of PEO coatings produced on the widely used commercial high-strength alloys AlCu4Mg1 (EN AW-2024), AlMgSi1 (EN AW-6082), and AlZn5.5MgCu (EN AW-7075) is examined with regard to their behaviour in the rubber-wheel test according to ASTM G65 and the current density-potential behaviour of the substrates with undamaged and worn coatings in dilute NaCl solution. To give a reference to the unalloyed material the testings were carried out also on Al 99.5 (EN AW-1050) which was treated in an adjusted PEO process. Although differences in the conversion of intermetallic phases during PEO and the phase composition of the coatings on the various substrates are determined, the service properties are hardly depending on the alloying elements of the investigated aluminium materials. The wear rates in the rubber-wheel test are low for all the alloyed samples. The current density-potential curves show a decrease of the corrosion current density by approximately one order of magnitude compared to the bare substrate. Eventually, previous wear of the coatings does not deteriorate the corrosion behaviour. PEO layers on technically pure aluminum can resist the testing regimes if they are prepared in an electrolyte with an elevated silicate content and without additional hydroxide ions, during a longer process time. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Open AccessFeature PaperReview An Overview of Fatigue Strength of Case-Hardening TRIP-Aided Martensitic Steels
Metals 2018, 8(5), 355; https://doi.org/10.3390/met8050355
Received: 19 April 2018 / Revised: 3 May 2018 / Accepted: 5 May 2018 / Published: 15 May 2018
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Abstract
Surface-hardened layer characteristics and fatigue strength properties of transformation-induced plasticity-aided martensitic steels subjected to heat-treatment or vacuum carburization followed by fine-particle peening are revealed for automotive applications specially for powertrain parts. The as-heat-treated steels without the case-hardening process possess excellent impact toughness and
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Surface-hardened layer characteristics and fatigue strength properties of transformation-induced plasticity-aided martensitic steels subjected to heat-treatment or vacuum carburization followed by fine-particle peening are revealed for automotive applications specially for powertrain parts. The as-heat-treated steels without the case-hardening process possess excellent impact toughness and fatigue strength. When the steels are subjected to fine-particle peening after heat-treatment, the fatigue limits of smooth and notched specimens increase considerably, accompanied with low notch sensitivity. Vacuum carburization and subsequent fine-particle peening increases further the fatigue strength of the steels, except notch fatigue limit. The increased fatigue limits are principally associated with high Vickers hardness and compressive residual stress just below the surface, resulting from the severe plastic deformation and the strain-induced martensitic transformation of metastable retained austenite, as well as low surface roughness and fatigue crack initiation depth. Full article
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Open AccessArticle Effect of Pipe Flattening in API X65 Linepipe Steels Having Bainite vs. Ferrite/Pearlite Microstructures
Metals 2018, 8(5), 354; https://doi.org/10.3390/met8050354
Received: 10 April 2018 / Revised: 2 May 2018 / Accepted: 8 May 2018 / Published: 15 May 2018
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Abstract
The influence of microstructure on pipe flattening response was assessed using two different commercially produced U-ing, O-ing, and expansion (UOE) pipes from API X65 steels having either a bainitic microstructure (steel B) or a ferrite/pearlite microstructure (steel FP). A four-point bending apparatus and
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The influence of microstructure on pipe flattening response was assessed using two different commercially produced U-ing, O-ing, and expansion (UOE) pipes from API X65 steels having either a bainitic microstructure (steel B) or a ferrite/pearlite microstructure (steel FP). A four-point bending apparatus and distinctive procedure were used to minimize strain localization during flattening. The flattened specimens were sectioned at different positions through the thickness, and tensile tested in both the longitudinal (LD) and transverse directions (TD) to assess the through-thickness variation in properties. Yield strength (YS) distributions in the LD show V-shaped profiles through thickness in both steels, whereas the YS in the TD nearest the outside diameter (OD) surface is reduced. These variations in YS are due to the Bauschinger effect associated with the compressive flattening pre-strain. The uniform elongation (UE) of steel FP is almost independent of specimen position through the thickness, but for steel B there is a substantial reduction of the UE at both the inside and outside diameter positions and this reduction is greater in the LD. This work confirms that flattened pipe mechanical properties exhibit an important dependence on their microstructure type and it is postulated that the flattening procedure also influences the mechanical properties. Full article
(This article belongs to the Special Issue Development of Bainitic Steels)
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Open AccessArticle Five-Axis Milling of Large Spiral Bevel Gears: Toolpath Definition, Finishing, and Shape Errors
Metals 2018, 8(5), 353; https://doi.org/10.3390/met8050353
Received: 1 April 2018 / Revised: 9 May 2018 / Accepted: 10 May 2018 / Published: 15 May 2018
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Abstract
In this paper, a five-axis machining process is analyzed for large spiral-bevel gears, an interesting process for one-of-kind manufacturing. The work is focused on large sized spiral bevel gears manufacturing using universal multitasking machines or five-axis milling centers. Different machining strategies, toolpath patterns,
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In this paper, a five-axis machining process is analyzed for large spiral-bevel gears, an interesting process for one-of-kind manufacturing. The work is focused on large sized spiral bevel gears manufacturing using universal multitasking machines or five-axis milling centers. Different machining strategies, toolpath patterns, and parameters are tested for both gear roughing and finishing operations. Machining time, tools’ wear, and gear surface are analyzed in order to determine which are the best strategies and parameters for large modulus gear manufacturing on universal machines. The case study results are discussed in the last section, showing the capacity of a universal five-axis milling for this niche. Special attention was paid to the possible affectations of the metal surfaces, since gear durability is very sensitive to thermo-mechanical damage, affected layers, and flank gear surface state. Full article
(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)
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Open AccessArticle A Study on the Nanoparticles Evolution in Isothermally Aged Strain Glass of Ti48.7Ni51.3 Shape Memory Alloy by In Situ Small-Angle X-ray Scattering
Metals 2018, 8(5), 352; https://doi.org/10.3390/met8050352
Received: 6 March 2018 / Revised: 20 April 2018 / Accepted: 11 May 2018 / Published: 14 May 2018
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Abstract
Ni-rich nanodomains and Ti3Ni4 nanoprecipitates in the strain glass of Ni-rich Ti-Ni shape memory alloys (SMAs) play an important role in the origin and characteristic control of the strain glass transition. Ni-rich nanodomains are formed in the quenching process and
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Ni-rich nanodomains and Ti3Ni4 nanoprecipitates in the strain glass of Ni-rich Ti-Ni shape memory alloys (SMAs) play an important role in the origin and characteristic control of the strain glass transition. Ni-rich nanodomains are formed in the quenching process and dissolve during isothermal aging. Ti3Ni4 nanoprecipitates nucleate, grow and coarsen during aging. This study performed in situ small-angle X-ray scattering (SAXS) and ex situ X-ray diffraction to investigate the structural evolutions with aging time of nanoparticles in Ti48.7Ni51.3 SMA aged isothermally at 250 °C in terms of relative volume fraction, radius, thickness, orientation, lattice ordering, and morphology. The mechanism and kinetics of the concurrent phase evolutions of Ni-rich nanodomains and Ti3Ni4 nanoprecipitates are revealed and discussed in detail. Frequency-dependent storage modulus vs. temperature at different frequencies for different aging times was measured to characterize the strain glass transition. Quantitative correlation of all structural evolutions and kinetics of Ni-rich and Ti3Ni4 nanoparticles with respect to the variation and loss of the strain glass transition during aging times of 0 to 20 h is presented. The roles of different nanoparticles in causing or suppressing the strain glass behavior are also experimentally revealed. Full article
(This article belongs to the Special Issue In Situ X-Ray Diffraction on Metals and Alloys)
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Open AccessReview Microalloyed Steels through History until 2018: Review of Chemical Composition, Processing and Hydrogen Service
Metals 2018, 8(5), 351; https://doi.org/10.3390/met8050351
Received: 22 March 2018 / Revised: 20 April 2018 / Accepted: 25 April 2018 / Published: 14 May 2018
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Abstract
Microalloyed steels have evolved in terms of their chemical composition, processing, and metallurgical characteristics since the beginning of the 20th century in the function of fabrication costs and mechanical properties required to obtain high-performance materials needed to accommodate for the growing demands of
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Microalloyed steels have evolved in terms of their chemical composition, processing, and metallurgical characteristics since the beginning of the 20th century in the function of fabrication costs and mechanical properties required to obtain high-performance materials needed to accommodate for the growing demands of gas and hydrocarbons transport. As a result of this, microalloyed steels present a good combination of high strength and ductility obtained through the addition of microalloying elements, thermomechanical processing, and controlled cooling, processes capable of producing complex microstructures that improve the mechanical properties of steels. These controlled microstructures can be severely affected and result in catastrophic failures, due to the atomic hydrogen diffusion that occurs during the corrosion process of pipeline steel. Recently, a martensite–bainite microstructure with acicular ferrite has been chosen as a viable candidate to be used in environments with the presence of hydrogen. The aim of this review is to summarize the main changes of chemical composition, processing techniques, and the evolution of the mechanical properties throughout recent history on the use of microalloying in high strength low alloy steels, as well as the effects of hydrogen in newly created pipelines, examining the causes behind the mechanisms of hydrogen embrittlement in these steels. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle An Analysis of Electroplated cBN Grinding Wheel Wear and Conditioning during Creep Feed Grinding of Aeronautical Alloys
Metals 2018, 8(5), 350; https://doi.org/10.3390/met8050350
Received: 9 April 2018 / Revised: 8 May 2018 / Accepted: 9 May 2018 / Published: 14 May 2018
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Abstract
Cubic boron nitride (cBN), in addition to diamond, is one of the two superabrasives most commonly used for grinding hard materials such as ceramics or difficult-to-cut metal alloys such as nickel-based aeronautical alloys. In the manufacturing process of turbine parts, electroplated cBN wheels
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Cubic boron nitride (cBN), in addition to diamond, is one of the two superabrasives most commonly used for grinding hard materials such as ceramics or difficult-to-cut metal alloys such as nickel-based aeronautical alloys. In the manufacturing process of turbine parts, electroplated cBN wheels are commonly used under creep feed grinding (CFG) conditions for enhancing productivity. This type of wheel is used because of its chemical stability and high thermal conductivity in comparison with diamond, as it maintains its shape longer. However, these wheels only have one abrasive layer, for which wear may lead to vibration and thermal problems. The effect of wear can be partially solved through conditioning the wheel surface. Silicon carbide (SiC) stick conditioning is commonly used in the industry due to its simplicity and good results. Nevertheless, little work has been done on the understanding of this conditioning process for electroplated cBN wheels in terms of wheel topography and later wheel performance during CFG. This work is focused, firstly, on detecting the main wear type and proposing a manner for its measurement and, secondly, on analyzing the effect of the conditioning process in terms of topographical changes and power consumption during grinding before and after conditioning. Full article
(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)
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Open AccessArticle Dissolution of M23C6 and New Phase Re-Precipitation in Fe Ion-Irradiated RAFM Steel
Metals 2018, 8(5), 349; https://doi.org/10.3390/met8050349
Received: 16 April 2018 / Revised: 10 May 2018 / Accepted: 12 May 2018 / Published: 14 May 2018
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Abstract
The M23C6 precipitate plays a major role in preventing the sliding of the grain boundary and strengthens the matrix in the reduced-activation ferritic/martensic (RAFM) steel. However, its stability might be reduced under irradiation. The microstructural instability of the M23
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The M23C6 precipitate plays a major role in preventing the sliding of the grain boundary and strengthens the matrix in the reduced-activation ferritic/martensic (RAFM) steel. However, its stability might be reduced under irradiation. The microstructural instability of the M23C6 precipitates in the RAFM steels irradiated at 300 °C with Fe ions up to a peak dose of 40 dpa was investigated by transmission electron microscopy. A “Core/Shell” morphology was found for the pre-existing M23C6 and a large number of new small phases appeared in parallel near the periphery of the precipitates after irradiation. The loss of crystallinity of the M23C6 periphery due to the dissolution of carbon atoms into the interface (C-rich “Shell”) actually decreased the size of the Cr-rich “Core”. The new phase that formed around the pre-existing precipitates was M6C (Fe3W3C), which was formed through the carbide transformation of M23C6 to M6C. Full article
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Open AccessFeature PaperArticle High-Temperature Behavior of High-Pressure Diecast Alloys Based on the Al-Si-Cu System: The Role Played by Chemical Composition
Metals 2018, 8(5), 348; https://doi.org/10.3390/met8050348
Received: 1 April 2018 / Revised: 2 May 2018 / Accepted: 9 May 2018 / Published: 11 May 2018
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Abstract
Al-Si-Cu foundry alloys are widely applied in the form of high-pressure diecast components. They feature hypo- or nearly eutectic compositions, such as AlSi9Cu3(Fe), AlSi11Cu2(Fe), and AlSi12Cu1(Fe) alloys, which are used in the present study. Diecast specimens, with a thickness of 3 mm, were
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Al-Si-Cu foundry alloys are widely applied in the form of high-pressure diecast components. They feature hypo- or nearly eutectic compositions, such as AlSi9Cu3(Fe), AlSi11Cu2(Fe), and AlSi12Cu1(Fe) alloys, which are used in the present study. Diecast specimens, with a thickness of 3 mm, were used for tension tests. The short-term mechanical behavior was characterized at temperatures from 25 up to 450 °C. At temperatures above 200 °C, the tensile strength properties (YS and UTS) of the investigated alloys were severely affected by temperature, and less by chemical differences. Material hardness and ductility indexes better highlighted the differences in the mechanical behavior of these age-hardenable alloys and allowed us to relate them to the microstructure and its changes that took place at test temperatures. Thermodynamic calculations were found to be useful tools to predict phases formed during solidification, as well as those related to precipitation strengthening. By means of the performed comprehensive material characterization, deeper knowledge of the microstructural changes of Al-Si-Cu foundry alloys during short-term mechanical behavior was obtained. The gained knowledge can be used as input data for constitutive modeling of the investigated alloys. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle Template-Assisted Fabrication of Nanostructured Tin (β-Sn) Arrays for Bulk Microelectronic Packaging Devices
Metals 2018, 8(5), 347; https://doi.org/10.3390/met8050347
Received: 23 March 2018 / Revised: 8 May 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
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Abstract
In this study, uniform and ordered nanostructured arrays of pure tin (Sn) were produced by the chemical pulse plating method in potentiostatic mode. Bottom metalized anodic aluminium oxide templates were used as the substrates for holding nanostructures during deposition. The plating bath consists
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In this study, uniform and ordered nanostructured arrays of pure tin (Sn) were produced by the chemical pulse plating method in potentiostatic mode. Bottom metalized anodic aluminium oxide templates were used as the substrates for holding nanostructures during deposition. The plating bath consists of stannous sulfate (SnSO4), sulfuric acid (H2SO4), polyethylene glycol (PEG), and glutaraldehyde as a surfactant. The effect of potentiostatic potential ranging from −0.5 to −3.2 V vs. Ag/AgCl electrode was studied on the growth morphology of nanostructures that were formed. The characterization studies were accomplished by X-ray diffraction (XRD), field emission electron microscopy, and energy dispersive spectroscopy. It was found that several nanostructures were of different shapes and size when the potential was varied. Nanorods were prominent at the deposition potentials of −0.5 and −1.1 V, while a combination of nanostructures (nanorods, nanoplates, and nanoparticles) was predominant at −3.2 V. XRD results show that the nanostructures that were obtained consisted of tetragonal (Sn) structure with a crystallite size of about 20 nm. This process is economically viable and it can be scaled to produce various nanostructures through a careful control of deposition parameters. Full article
(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)
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Open AccessArticle Evaluation of Failure Pressure for Gas Pipelines with Combined Defects
Metals 2018, 8(5), 346; https://doi.org/10.3390/met8050346
Received: 11 March 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
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Abstract
The paper presents the study of the influence of mechanical damage on the safe operation of gas transmission pipelines. The main types of pipeline damage with the actual parameters and their influence on the operational parameters are analysed. The damaged fractures of the
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The paper presents the study of the influence of mechanical damage on the safe operation of gas transmission pipelines. The main types of pipeline damage with the actual parameters and their influence on the operational parameters are analysed. The damaged fractures of the section of the pipeline Kaunas (Lithuania)–Kaliningrad (Russia) were investigated in the laboratory. The main operational characteristics and the structure of the pipeline’s metal after the period of long-term operation were determined using various research and experimental methods. The influence of the pipeline’s damage was modelled by using the Finite Element Method and the ANSYS code. The predictions of the failure pressure were made, taking into consideration the actual properties of the pipeline’s metal. Techniques including the hardness and microhardness measurement, chemical analysis, the impact strength test, and metallography analysis with an optical microscope, were used in the experimental study. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
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Open AccessEditorial Valuable Metal Recycling
Metals 2018, 8(5), 345; https://doi.org/10.3390/met8050345
Received: 7 May 2018 / Revised: 7 May 2018 / Accepted: 9 May 2018 / Published: 11 May 2018
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Abstract
As the global economy grows, demand for metal continues to increase. Unfortunately, metal resources are in limited supply [...]
Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
Open AccessArticle Strengthening versus Softening of Nanotwinned Copper Depending on Prestress and Twin Spacing
Metals 2018, 8(5), 344; https://doi.org/10.3390/met8050344
Received: 7 April 2018 / Revised: 6 May 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
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Abstract
This paper addressed the prestress- and twin spacing-dependent deformation as well as the hardening-to-softening transition in nanotwinned copper (nt-Cu) using molecular dynamics simulations. The results demonstrated that the hardening-to-softening transition always occurs at any prestress with decreasing twin spacing in nt-Cu compared with
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This paper addressed the prestress- and twin spacing-dependent deformation as well as the hardening-to-softening transition in nanotwinned copper (nt-Cu) using molecular dynamics simulations. The results demonstrated that the hardening-to-softening transition always occurs at any prestress with decreasing twin spacing in nt-Cu compared with its single crystal counterpart, while it occurs at specific twin spacing with decreasing prestress. The hardening-to-softening transition induced by decreasing twin spacing or prestress is due to the same mechanism, i.e., transition in the initial plasticity mechanism from the activity of partial dislocation to twinning dislocation. Moreover, the indentation hardness increases with decreasing prestress, reaching its maximum, followed by decreases at smaller values for all nt-Cu. However, the critical prestress at the maximum indentation hardness significantly depends on twin spacing. Finally, a model was developed to explain this special deformation behavior. The present results could deepen our understanding of the deformation behavior of nt-Cu and provide a new paradigm for the design of this material under complex stress state. Full article
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Open AccessArticle Magnesium-β-Tricalcium Phosphate Composites as a Potential Orthopedic Implant: A Mechanical/Damping/Immersion Perspective
Metals 2018, 8(5), 343; https://doi.org/10.3390/met8050343
Received: 6 April 2018 / Revised: 23 April 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
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Abstract
The design and development of novel magnesium-based materials with suitable alloying elements and bio-ceramic reinforcements can act as a possible solution to the ever-increasing demand of high performance bioresorbable orthopedic implant. In the current study, Mg-β-tricalcium phosphate composites are synthesized using the hybrid
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The design and development of novel magnesium-based materials with suitable alloying elements and bio-ceramic reinforcements can act as a possible solution to the ever-increasing demand of high performance bioresorbable orthopedic implant. In the current study, Mg-β-tricalcium phosphate composites are synthesized using the hybrid powder metallurgy technique, followed by hot extrusion. The influence of addition of (0.5, 1, and 1.5) vol % β-tricalcium phosphate on the mechanical, damping, and immersion characteristics of pure magnesium are studied. The addition of β-tricalcium phosphate enhanced the yield strength, ultimate compressive strength, and compressive fracture strain of pure magnesium by about ~34%, ~53%, and ~22%, respectively. Also, Mg 1.5 vol % β-tricalcium phosphate composite exhibited a ~113% enhancement in the damping characteristics when compared to pure magnesium. A superior ~70% reduction in the grain size was observed by the addition of 1.5 vol % β-tricalcium phosphate particles to pure Mg. The response of Mg-β-tricalcium phosphate composites is studied under the influence of chloride environment using Hanks’ balanced salt solution. The dynamic passivation was realized faster for the composite samples as compared to pure Mg, which resulted in decreased corrosion rates with the addition of β-tricalcium phosphate particles to pure Mg. Full article
(This article belongs to the Special Issue Metal Matrix Composites) Printed Edition available
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