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Metals, Volume 8, Issue 6 (June 2018)

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Cover Story (view full-size image) Thermal spraying process, developed one century ago, used initially solid feedstock as powder or [...] Read more.
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Open AccessArticle Microstructural Characterization of Surface Softening Behavior for Cu-Bearing Martensitic Steels after Laser Surface Heat Treatment
Metals 2018, 8(6), 470; https://doi.org/10.3390/met8060470
Received: 12 June 2018 / Revised: 15 June 2018 / Accepted: 20 June 2018 / Published: 20 June 2018
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Abstract
The surface hardening and softening behavior of two types of medium carbon martensitic steel (AISI P20-improved and AISI P21) after laser-assisted heat treatment was quantitatively compared. The laser-assisted heat treatment was performed using a high-power diode laser with in situ temperature and laser
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The surface hardening and softening behavior of two types of medium carbon martensitic steel (AISI P20-improved and AISI P21) after laser-assisted heat treatment was quantitatively compared. The laser-assisted heat treatment was performed using a high-power diode laser with in situ temperature and laser power control (two-color pyrometer system). For AISI P20-improved steel, the peak hardness value within the hardening zone was approximately 640 HV after laser-assisted heat treatment at a temperature of 1473 K. In other words, the hardness increased by 120% from the base metal level (290 HV). However, for AISI P21 steel, the hardness within the heat-treated zone did not change from that of the base metal (410 HV), despite being accompanied by martensite transformation. Moreover, it was clearly observed that the hardness dropped below the level of the base metal at the boundary between the heat-treated zone and the base metal region, forming a softening zone. This softening behavior was strongly related to coarsening and a looser distribution of Cu precipitates compared with that of the base metal region, despite the same matrix phase (i.e., tempered martensite) existing in the softening zone and in the base metal region. Full article
(This article belongs to the Special Issue Advances in Microstructural Characterization of Metallic Materials)
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Open AccessFeature PaperArticle Techno-Economic Analysis of High-Pressure Metal Hydride Compression Systems
Metals 2018, 8(6), 469; https://doi.org/10.3390/met8060469
Received: 1 June 2018 / Revised: 16 June 2018 / Accepted: 18 June 2018 / Published: 20 June 2018
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Abstract
Traditional high-pressure mechanical compressors account for over half of the car station’s cost, have insufficient reliability, and are not feasible for a large-scale fuel cell market. An alternative technology, employing a two-stage, hybrid system based on electrochemical and metal hydride compression technologies, represents
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Traditional high-pressure mechanical compressors account for over half of the car station’s cost, have insufficient reliability, and are not feasible for a large-scale fuel cell market. An alternative technology, employing a two-stage, hybrid system based on electrochemical and metal hydride compression technologies, represents an excellent alternative to conventional compressors. The high-pressure stage, operating at 100–875 bar, is based on a metal hydride thermal system. A techno-economic analysis of the metal hydride system is presented and discussed. A model of the metal hydride system was developed, integrating a lumped parameter mass and energy balance model with an economic model. A novel metal hydride heat exchanger configuration is also presented, based on minichannel heat transfer systems, allowing for effective high-pressure compression. Several metal hydrides were analyzed and screened, demonstrating that one selected material, namely (Ti0.97Zr0.03)1.1Cr1.6Mn0.4, is likely the best candidate material to be employed for high-pressure compressors under the specific conditions. System efficiency and costs were assessed based on the properties of currently available materials at industrial levels. Results show that the system can reach pressures on the order of 875 bar with thermal power provided at approximately 150 °C. The system cost is comparable with the current mechanical compressors and can be reduced in several ways as discussed in the paper. Full article
(This article belongs to the Special Issue Metals in Hydrogen Technology)
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Open AccessArticle Ag2O Nanoparticles-Doped Manganese Immobilized on Graphene Nanocomposites for Aerial Oxidation of Secondary Alcohols
Metals 2018, 8(6), 468; https://doi.org/10.3390/met8060468
Received: 23 May 2018 / Revised: 13 June 2018 / Accepted: 17 June 2018 / Published: 19 June 2018
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Abstract
Ag2O nanoparticles-doped MnO2 decorated on different percentages of highly reduced graphene oxide (HRG) nanocomposites, i.e., (X%)HRG/MnO2–(1%)Ag2O (where X = 0–7), were fabricated through straight-forward precipitation procedure, and 400 °C calcination, while upon calcination at 300 °C
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Ag2O nanoparticles-doped MnO2 decorated on different percentages of highly reduced graphene oxide (HRG) nanocomposites, i.e., (X%)HRG/MnO2–(1%)Ag2O (where X = 0–7), were fabricated through straight-forward precipitation procedure, and 400 °C calcination, while upon calcination at 300 °C and 500 °C temperatures, it yielded MnCO3 and manganic trioxide (Mn2O3) composites, i.e., [(X%)HRG/MnCO3–(1%)Ag2O] and [(X%)HRG/Mn2O3–(1%)Ag2O], respectively. These nanocomposites have been found to be efficient and very effective heterogeneous catalysts for selective oxidation of secondary alcohols into their respective ketones using O2 as a sole oxidant without adding surfactants or nitrogenous bases. Moreover, a comparative catalytic study was carried out to investigate the catalytic efficiency of the synthesized nanocomposites for the aerobic oxidation of 1-phenylethanol to acetophenone as a substrate reaction. Effects of several factors were systematically studied. The as-prepared nanocomposites were characterized by TGA, XRD, SEM, EDX, HRTEM, BET, Raman, and FTIR. The catalyst with structure (5%)HRG/MnO2–(1%)Ag2O showed outstanding specific activity (16.0 mmol/g·h) with complete conversion of 1-phenylethanol and >99% acetophenone selectivity within short period (25 min). It is found that the effectiveness of the catalyst has been greatly improved after using graphene support. A broad range of alcohols have selectively transformed to desired products with 100% convertibility and no over-oxidation products have been detected. The recycling test of (5%)HRG/MnO2–(1%)Ag2O catalyst for oxidation of 1-phenylethanol suggested no obvious decrease in its performance and selectivity even after five subsequent runs. Full article
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Open AccessArticle Relationship between Flow Behavior and Microstructure Evolution during Isothermal Compression of near β Titanium Alloy Ti-55531 with Acicular Starting Microstructure
Metals 2018, 8(6), 467; https://doi.org/10.3390/met8060467
Received: 22 May 2018 / Revised: 14 June 2018 / Accepted: 15 June 2018 / Published: 19 June 2018
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Abstract
Near β titanium alloy Ti-55531 with an acicular starting microstructure was isothermally compressed at 750–825 °C and 10−3−1 s−1. The microstructure evolution and its influence on the flow behavior of yielding and softening were investigated. Discontinuous or continuous yielding
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Near β titanium alloy Ti-55531 with an acicular starting microstructure was isothermally compressed at 750–825 °C and 10−3−1 s−1. The microstructure evolution and its influence on the flow behavior of yielding and softening were investigated. Discontinuous or continuous yielding depends on the hindrance to the dislocation motion coming from the β grain boundary or α phase. At higher temperatures, the hindrance mainly comes from the β grain boundary. Its discontinuous action, including the piling-up and subsequent loosening of dislocations at the β grain boundary, leads to discontinuous yielding. At lower temperatures, the continuous hindrance to the dislocation motion, which is exerted by the β grain boundary and acicular α, causes continuous yielding. Sequentially, the substructures in acicular α are evolved from high-density dislocations or local shear bands, which depend on the orientation relationship between β and α. Then, the β matrix edges into the acicular α along substructure boundaries. The higher strain rate decreases the deformation time to carry out the fragmentation of acicular α, while the higher temperature decreases the dislocation density due to the recovery of β, which does not benefit the substructure formation and subsequent fragmentation of acicular α. Therefore, the retardation of acicular fragmentation and the as-resulted decreased flow softening rate are observed. Full article
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Open AccessArticle Annealing-Induced High Ordering and Coercivity in Novel L10 CoPt-Based Nanocomposite Magnets
Metals 2018, 8(6), 466; https://doi.org/10.3390/met8060466
Received: 16 May 2018 / Revised: 8 June 2018 / Accepted: 12 June 2018 / Published: 19 June 2018
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Abstract
A novel class of quaternary intermetallic alloys based on CoPt is investigated in view of their interesting magnetic properties induced by the presence of hard magnetic L10 phase. A Co48Pt28Ag6B18 alloy has been prepared by
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A novel class of quaternary intermetallic alloys based on CoPt is investigated in view of their interesting magnetic properties induced by the presence of hard magnetic L10 phase. A Co48Pt28Ag6B18 alloy has been prepared by rapid solidification from the melt and subjected to various isothermal annealing procedures. The structure and magnetism of both as-cast and annealed samples as well as the phase evolution with temperature are investigated by means of thermal analysis, X-ray, and selected area electron diffraction, scanning and high-resolution electron microscopy, and magnetic measurements. The X-ray diffraction (XRD) analysis shows that both the as-cast alloy and the sample annealed at 400 °C (673 K) have a nanocrystalline structure where fcc CoPt phase predominates. Annealing at 473 °C promotes the formation of L10 phase triggered by the disorder-order phase transformation as documented in the differential scanning calorimetry results. The sample annealed at 670 °C (943 K) shows full formation of L10 CoPt as revealed by XRD. Magnetic measurements showed coercivity values ten times increased compared to the as-cast state. This confirms the full formation of L10 CoPt in the annealed samples. Moreover, detailed atomic resolution HREM images and SAED patterns show the occurrence of the rarely seen (003) superlattice peaks, which translated into a high ordering of the L10 CoPt superlattice. Such results spur more interest in finding novel classes of nanocomposite magnets based on L10 phase. Full article
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Open AccessFeature PaperArticle Understanding the Recovery of Rare-Earth Elements by Ammonium Salts
Metals 2018, 8(6), 465; https://doi.org/10.3390/met8060465
Received: 4 June 2018 / Revised: 14 June 2018 / Accepted: 15 June 2018 / Published: 19 June 2018
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Abstract
While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis
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While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis of the compounds formed in the organic phase during the solvent extraction of REEs by [(n-octyl)3NMe][NO3] (IL). These experiments show that REE recovery using IL is a rapid process and that IL is highly durable. Karl-Fischer measurements signify that the mode of action is unlikely to be micellar, while ions of the general formula REE(NO3)4(IL)2 are seen by negative ion electrospray ionization mass spectrometry. Additionally, variable temperature 139La nuclear magnetic resonance spectroscopy suggests the presence of multiple, low symmetry nitrato species. Classical molecular dynamics simulations show aggregation of multiple ILs around a microhydrated La3+ cation with four nitrates completing the inner coordination sphere. This increased understanding is now being exploited to develop stronger and more selective, functionalized ILs for REE recovery. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessArticle Machining Distortion of Titanium Alloys Aero Engine Case Based on the Energy Principles
Metals 2018, 8(6), 464; https://doi.org/10.3390/met8060464
Received: 16 May 2018 / Revised: 7 June 2018 / Accepted: 14 June 2018 / Published: 18 June 2018
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Abstract
The simulation of a complete manufacturing process to produce an aero engine case, including forging, rolling, and machining processes, is analyzed via finite element software. The deformation of the turning and drilling processes is quantitatively studied using the energy principles. Firstly, simulations of
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The simulation of a complete manufacturing process to produce an aero engine case, including forging, rolling, and machining processes, is analyzed via finite element software. The deformation of the turning and drilling processes is quantitatively studied using the energy principles. Firstly, simulations of multi-stage forging of aero engine case and machining-induced residual stress are conducted and verified via the residual stresses test in order to provide the initial elastic strain energy condition prior to machining processes. The effects of blank forging-induced residual stress and machining-induced residual stress on the deformation of titanium alloys aero engine case are investigated. Secondly, a potential energy expression for the machining processes is developed. The predicted results of turning and drilling simulations indicate that there is an optimal process in which the deformation and potential energy decline rapidly compared with the other processes and finally, gradually stabilize at the end of the process. Full article
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Open AccessArticle Connected Process Design for Hot Working of a Creep-Resistant Mg–4Al–2Ba–2Ca Alloy (ABaX422)
Metals 2018, 8(6), 463; https://doi.org/10.3390/met8060463
Received: 12 May 2018 / Revised: 9 June 2018 / Accepted: 13 June 2018 / Published: 18 June 2018
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Abstract
With a view to design connected processing steps for the manufacturing of components, the hot working behavior of the ABaX422 alloy has been characterized for the as-cast and extruded conditions. In the as-cast condition, the alloy has a limited workability, due to the
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With a view to design connected processing steps for the manufacturing of components, the hot working behavior of the ABaX422 alloy has been characterized for the as-cast and extruded conditions. In the as-cast condition, the alloy has a limited workability, due to the presence of a large volume of intermetallic phases at the grain boundaries, and is not suitable to process at high speeds. A connected processing step has been designed on the basis of the results of the processing map for the as-cast alloy, and this step involves the extrusion of the cast billet to obtain a 12 mm diameter rod product at a billet temperature of 390 °C and at a ram speed of 1 mm s−1. The microstructure of the extruded rod has a finer grain size, with redistributed fine particles of the intermetallic phases. The processing map of the extruded rod exhibited two new domains, and the one in the temperature range 360–420 °C and strain rate range 0.2–10 s−1 is useful for manufacturing at high speeds, while the lower temperature develops a finer grain size in the product to improve the room temperature strength and ductility. The area of the flow instability is also reduced by the extrusion step, widening the workability window. Full article
(This article belongs to the Special Issue Material and Process Design for Lightweight Structures)
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Open AccessArticle Assessment of Metal Flow Balance in Multi-Output Porthole Hot Extrusion of AA6060 Thin-Walled Profile
Metals 2018, 8(6), 462; https://doi.org/10.3390/met8060462
Received: 15 May 2018 / Revised: 9 June 2018 / Accepted: 10 June 2018 / Published: 18 June 2018
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Abstract
For the porthole hot extrusion of a thin-walled tube based on metal flow, the role of the die’s structure should be focused on to achieve precision formation, especially for multi-output extrusion and/or complex cross-sectional profiles. In order to obtain a better metal flow
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For the porthole hot extrusion of a thin-walled tube based on metal flow, the role of the die’s structure should be focused on to achieve precision formation, especially for multi-output extrusion and/or complex cross-sectional profiles. In order to obtain a better metal flow balance, a multi-output porthole extrusion die was developed, including some novel features such as a circular pattern of the portholes with a dart-shaped inlet bridge, a buckle angle in the inlet side of the upper die, a two-step welding chamber, and a non-uniform bearing length distribution. Through the use of thermo-mechanical modeling combined with the Taguchi method, the underlying effects of key die features were investigated, such as the billet buckle angle, the porthole bevel angle, the depth of the welding chamber, and the type of bridge on the metal flow balance. The experimental validation showed that the developed numerical model for the multi-output porthole extrusion process had high prediction accuracy, and was acceptable for use in an industrial extrusion with a complex section. Full article
(This article belongs to the Special Issue Material and Process Design for Lightweight Structures)
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Open AccessArticle Synthesis of Core-Shell Carbon Encapsulated Fe2O3 Composite through a Facile Hydrothermal Approach and Their Application as Anode Materials for Sodium-Ion Batteries
Metals 2018, 8(6), 461; https://doi.org/10.3390/met8060461
Received: 24 May 2018 / Revised: 12 June 2018 / Accepted: 15 June 2018 / Published: 18 June 2018
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Abstract
Carbon encapsulated Fe2O3 nanoparticles (C@Fe2O3) were successfully synthesized via a facile and environmentally friendly hydrothermal method and prototyped in anode materials for sodium ion batteries (SIBs). High-resolution transmission and scanning electronic microscopy observations exhibited the formation
[...] Read more.
Carbon encapsulated Fe2O3 nanoparticles (C@Fe2O3) were successfully synthesized via a facile and environmentally friendly hydrothermal method and prototyped in anode materials for sodium ion batteries (SIBs). High-resolution transmission and scanning electronic microscopy observations exhibited the formation of a highly core-shelled C@Fe2O3 composite consisting of carbon layers coated onto uniform Fe2O3 nanoparticles with a median diameter of 46.1 nm. This core-shell structure can repress the aggregation of Fe2O3 nanoparticles, preventing the harsh volume change of the electrode, enhancing the electric conductivity of the active materials, and promoting Na-ion transformation during cycling. The electrochemical performances of the C@Fe2O3 composite, as anodes for SIBs, retained a reversible capacity of 305 mAh g−1 after 100 cycles at 50 mA g−1 and exhibited an excellent cyclability at various current densities due to the synergistic effect between the carbon layers and Fe2O3. These results suggest that C@Fe2O3 composites present much potential as anode materials for rechargeable SIBs. Full article
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Open AccessArticle Microstructure, Mechanical Properties and Wear Behavior of the Rheoformed 2024 Aluminum Matrix Composite Component Reinforced by Al2O3 Nanoparticles
Metals 2018, 8(6), 460; https://doi.org/10.3390/met8060460
Received: 3 May 2018 / Revised: 27 May 2018 / Accepted: 14 June 2018 / Published: 15 June 2018
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Abstract
The 2024 nanocomposite reinforced with Al2O3 nanoparticles was fabricated by the ultrasonic assisted semisolid stirring (UASS) method and rheoformed into a cylinder component. Microstructure, mechanical properties, and wear behavior of the rheoformed composite components were investigated. The results showed that
[...] Read more.
The 2024 nanocomposite reinforced with Al2O3 nanoparticles was fabricated by the ultrasonic assisted semisolid stirring (UASS) method and rheoformed into a cylinder component. Microstructure, mechanical properties, and wear behavior of the rheoformed composite components were investigated. The results showed that the composite components with complete filling status and a good surface were rheoformed successfully. The deformation of semisolid slurries was mainly dominated by flow of liquid incorporating solid grains (FLS), sliding between solid grains (SSG), and plastic deformation of solid grains (PDS). Mechanical properties of the rheoformed composite components were influenced by stirring temperature, stirring time, and volume fraction of Al2O3 nanoparticles. The optimal ultimate tensile strength (UTS) of 358 MPa and YS of 245 MPa were obtained at the bottom of the rheoformed composite components after a 25-min stirring of composite semisolid slurry with 5% Al2O3 nanoparticles at 620 °C. Enhancement of mechanical properties was attributed to high density dislocations and dislocation tangles and uniform dispersed Al2O3 nanoparticles in the aluminum matrix. Natural ageing led to the occurrence of needle-like Al2CuMg phase and short-rod-like Al2Cu phase. UTS of 417 MPa and YS of 328 MPa of the rheoformed composite components were achieved after T6 heat treatment. Improvement of mechanical properties is due to the more precipitated needle-like Al2CuMg phase and short-rod-like Al2Cu phase. Wear resistance of the rheoformed composite components was higher than that of the rheoformed matrix component. Wear resistance of the rheoformed composite component increased with an increase in Al2O3 nanoparticles from 1% to 7%. A slight decrease in wear rate resulted from 10% Al2O3 nanoparticles due to greater agglomeration of Al2O3 nanoparticles. A combination mechanism of adhesion and delamination was determined according to worn surface morphology. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Study of Plasma Electrolytic Oxidation Coatings on Aluminum Composites
Metals 2018, 8(6), 459; https://doi.org/10.3390/met8060459
Received: 29 April 2018 / Revised: 12 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
Coatings, with a thickness of up to 75 µm, were formed by plasma electrolytic oxidation (PEO) under the alternating current electrical mode in a silicate-alkaline electrolyte on aluminum composites without additives and alloyed with copper (1–4.5%). The coatings’ structure was analyzed by scanning
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Coatings, with a thickness of up to 75 µm, were formed by plasma electrolytic oxidation (PEO) under the alternating current electrical mode in a silicate-alkaline electrolyte on aluminum composites without additives and alloyed with copper (1–4.5%). The coatings’ structure was analyzed by scanning electron microscopy, X-ray microanalysis, X-ray photoelectron spectroscopy, nuclear backscattering spectrometry, and XRD analysis. The coatings formed for 60 min were characterized by excessive aluminum content and the presence of low-temperature modifications of alumina γ-Al2O3 and η-Al2O3. The coatings formed for 180 min additionally contained high-temperature corundum α-Al2O3, and aluminum inclusions were absent. The electrochemical behavior of coated composites and uncoated ones in 3% NaCl was studied. Alloyage of aluminum composites with copper increased the corrosion current density. Plasma electrolytic oxidation reduced it several times. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Open AccessArticle Effects of Vanadium on Microstructure and Wear Resistance of High Chromium Cast Iron Hardfacing Layer by Electroslag Surfacing
Metals 2018, 8(6), 458; https://doi.org/10.3390/met8060458
Received: 18 May 2018 / Revised: 8 June 2018 / Accepted: 11 June 2018 / Published: 15 June 2018
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Abstract
The 3.6C-20Cr-Fe-(0–2.32)V high chromium cast iron (HCCI) hardfacing layers were deposited on low alloy steel by electroslag surfacing. The microstructure of hardfacing layers were observed and the carbide types, size and area fraction were measured. In addition, the hardness and wear resistance were
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The 3.6C-20Cr-Fe-(0–2.32)V high chromium cast iron (HCCI) hardfacing layers were deposited on low alloy steel by electroslag surfacing. The microstructure of hardfacing layers were observed and the carbide types, size and area fraction were measured. In addition, the hardness and wear resistance were tested. Results show that the interface between hardfacing layer and low alloy steel is defect free. 3.6C-20Cr-Fe hardfacing layer contains primary carbides and eutectic. Increasing V wt % in the hardfacing layer, primary carbides are decreasing by increasing eutectic along with martensite formation. For 1.50 wt % of V, the microstructure contains a lot of eutectic and a little of martensite. For 2.32 wt % of V, primary austenite formed, the microstructure is primary austenite, eutectic and a little of martensite. In the V alloyed hardfacing layers, V has strong affinity with carbon than chromium, hence V can replace a part of Cr in M7C3 and (Cr4.4–4.7Fe2.1–2.3V0.2–0.5)C3 type carbides are formed. When the V is 2.32 wt %, (Cr0.23V0.77)C carbides are formed in the hardfacing layer. The hardness and wear resistance are improved by increasing V from 0 to 1.50 wt %. However, when the V is 2.32 wt %, the primary austenite has reduced the hardness and wear resistance of hardfacing layer. Full article
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Open AccessArticle Tensile Creep Characterization and Prediction of Zr-Based Metallic Glass at High Temperatures
Metals 2018, 8(6), 457; https://doi.org/10.3390/met8060457
Received: 22 May 2018 / Revised: 12 June 2018 / Accepted: 12 June 2018 / Published: 15 June 2018
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Abstract
The high temperature creep behaviors of a Zr-based bulk metallic glass (BMG) are studied by uniaxial tensile creep experiments under applied stresses of 50–180 MPa at temperatures of 660–700 K. The microstructural observations of the BMG samples after creep tests show that crystalline
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The high temperature creep behaviors of a Zr-based bulk metallic glass (BMG) are studied by uniaxial tensile creep experiments under applied stresses of 50–180 MPa at temperatures of 660–700 K. The microstructural observations of the BMG samples after creep tests show that crystalline phases can be detected under high temperature or high applied stress. Constitutive models for predicting the high temperature creep behaviors of the studied Zr-based BMG are established based on the θ projection method. The creep activation energy and stress exponent are also calculated to establish the creep model. The parameters of the established models are found to be closely associated with the applied stress and temperature. The results show an excellent agreement between the measured and predicted results, confirming the validity of the established model to accurately estimate the high temperature creep curves for the Zr-based BMG. Moreover, based on the classical diffusion creep theory, a schematic model is proposed to describe the creep behaviors of BMGs from the framework of free volume theory. Full article
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Open AccessArticle A New Cumulative Fatigue Damage Rule Based on Dynamic Residual S-N Curve and Material Memory Concept
Metals 2018, 8(6), 456; https://doi.org/10.3390/met8060456
Received: 23 May 2018 / Revised: 7 June 2018 / Accepted: 7 June 2018 / Published: 14 June 2018
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Abstract
This paper introduces a new phenomenological cumulative damage rule to predict damage and fatigue life under variable amplitude loading. The rule combines a residual S-N curve approach and a material memory concept to describe the damage accumulation behavior. The residual S-N curve slope
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This paper introduces a new phenomenological cumulative damage rule to predict damage and fatigue life under variable amplitude loading. The rule combines a residual S-N curve approach and a material memory concept to describe the damage accumulation behavior. The residual S-N curve slope is regarded as a variable with respect to the loading history. The change in slope is then used as a damage measure and quantified by a material memory degeneration parameter. This model improves the traditional linear damage rule by taking the load-level dependence and loading sequence effect into account, which still preserves its superiority. A series of non-uniform fatigue loading protocols are used to demonstrate the effectiveness of the proposed model. The prediction results using the proposed model are more accurate than those using three popular damage models. Moreover, several common characteristics and fundamental properties of the chosen fatigue models are extracted and discussed. Full article
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Open AccessArticle Theoretical Study of Particle Dissolution during Homogenization in Cu–Fe–P Alloy
Metals 2018, 8(6), 455; https://doi.org/10.3390/met8060455
Received: 18 May 2018 / Revised: 12 June 2018 / Accepted: 12 June 2018 / Published: 14 June 2018
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Abstract
The effect of temperature, soaking time and particle size on the dissolution of particles (Fe3P and Fe) during homogenization was simulated employing Thermocalc® and DICTRA software. The initial precipitate size was determined through metallographic evaluation on industrial as-cast Cu–Fe–P alloy.
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The effect of temperature, soaking time and particle size on the dissolution of particles (Fe3P and Fe) during homogenization was simulated employing Thermocalc® and DICTRA software. The initial precipitate size was determined through metallographic evaluation on industrial as-cast Cu–Fe–P alloy. The particle sizes vary from submicron (<1 μm) up to 10 μm before the heat treatment. As homogenization temperature rises, the dissolution rate increases as well, but only on temperatures above 1273 K (1000 °C) is the rate capable of completely dissolving particles effectively. At temperatures above 1273 K (1000 °C), precipitates with sizes below 5 μm dissolve completely into the Cu matrix, while larger particles only slightly decrease their size. Particles at enriched copper areas remain undissolved and slightly increase their size which is attributed to micro segregation and the local change of equilibrium conditions. The simulation results are in agreement with homogenization trials at lab scale. Full article
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Open AccessArticle Effects of Cold Swaging on Mechanical Properties and Magnetic Susceptibility of the Zr–1Mo Alloy
Metals 2018, 8(6), 454; https://doi.org/10.3390/met8060454
Received: 20 April 2018 / Revised: 23 May 2018 / Accepted: 12 June 2018 / Published: 13 June 2018
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Abstract
Zr alloy is expected to decrease the artifact volume of magnetic resonance imaging (MRI) due to its relatively small magnetic susceptibility. To improve the mechanical properties of a Zr–1mass%Mo alloy that yielded a reduced artifact volume during MRI, the alloy was melted, hot-forged,
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Zr alloy is expected to decrease the artifact volume of magnetic resonance imaging (MRI) due to its relatively small magnetic susceptibility. To improve the mechanical properties of a Zr–1mass%Mo alloy that yielded a reduced artifact volume during MRI, the alloy was melted, hot-forged, and cold-swaged with area reduction ratios of 30%, 50%, 60%, 70%, and 84%. The effects of cold swaging on the microstructure, mechanical properties, and magnetic susceptibility of the alloy were investigated. Before cold swaging, the microstructure consisted of laminated and layered α- and β-phases; however, after cold swaging, the α- and β-phases were bent and distorted, and the α-phase became oriented along the {10 1¯ 0} plane. The ultimate tensile strength and elongation to fracture of the Zr–1Mo alloy after cold swaging with an 84% area reduction were 1001 MPa and 10.7%, respectively. The alloy only experienced work-hardening when subjected to large deformations. On the other hand, the change in magnetic susceptibility with cold-swaging was small, from 13.85 × 10−9 to 14.87 × 10−9 m3·kg−1. Thus, a good balance of mechanical properties and low magnetic susceptibility in the Zr–1Mo alloy was obtained by cold swaging. Therefore, this alloy is suitable for utilization in medical devices and is expected to decrease the artifact volume. Full article
(This article belongs to the Special Issue Zirconium Alloys)
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Open AccessArticle Prediction of Resistance Spot Weld Quality of 780 MPa Grade Steel Using Adaptive Resonance Theory Artificial Neural Networks
Metals 2018, 8(6), 453; https://doi.org/10.3390/met8060453
Received: 31 May 2018 / Revised: 12 June 2018 / Accepted: 12 June 2018 / Published: 13 June 2018
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Abstract
In this study, the weld quality of 780 MPa grade dual phase (DP) steel with 1.0 mm thickness was predicted using adaptive resonance theory (ART) artificial neural networks. The welding voltage and current signals measured during resistance spot welding (RSW) were used as
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In this study, the weld quality of 780 MPa grade dual phase (DP) steel with 1.0 mm thickness was predicted using adaptive resonance theory (ART) artificial neural networks. The welding voltage and current signals measured during resistance spot welding (RSW) were used as the input layer data, and the tensile shear strength, nugget size, and fracture shape of the weld were used as the output layer data. The learning was performed by the ART artificial neural networks using the input layer and output layer data, and the patterns of learning result were classified by the setting of vigilance parameter, ρ. When the vigilance parameter is 0.8, the best-predicted results were obtained for the tensile shear strength, nugget size, and fracture shape of welds. Full article
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Open AccessArticle Formation of Multi-Type Inclusions during the Cooling and Solidification of Steel: A Trend Model
Metals 2018, 8(6), 452; https://doi.org/10.3390/met8060452
Received: 20 May 2018 / Revised: 3 June 2018 / Accepted: 11 June 2018 / Published: 13 June 2018
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Abstract
This paper presents a trend model of the competitive formation of multi-type inclusions during the cooling and solidification of steel. The model is able to predict the evolution of various inclusions, including their type, composition and size distribution. In the calculations, the thermodynamic
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This paper presents a trend model of the competitive formation of multi-type inclusions during the cooling and solidification of steel. The model is able to predict the evolution of various inclusions, including their type, composition and size distribution. In the calculations, the thermodynamic library, ChemApp, was applied to perform a thermodynamic equilibrium calculation. Homogeneous nucleation, diffusion-controlled growth and dissolution were employed to simulate the size distribution evolution. At the same time, the collision of inclusions of the same type were considered in a simplified way. The inclusion stabilities were validated by laboratory experiments, which offered a strong basis for the simulations. Using the proposed model, the influence of alloying temperature and oxygen content on the formation of multi-type inclusions was investigated. The results indicated that decreasing the alloying temperature resulted in a higher number density and finer size of different oxides. The oxygen content affected the formation of various oxides in different ways. The predictions, based on the mechanism of competitive nucleation and growth, are discussed and explained. It is believed that the calculations deepen the understanding of the competitive formation of multi-type inclusions. The predicted trends provide a valuable reference for inclusion control and experiment design. Full article
(This article belongs to the Special Issue 5th UK-China Steel Research Forum)
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Open AccessArticle Phosphorus-Containing Mineral Evolution and Thermodynamics of Phosphorus Vaporization during Carbothermal Reduction of High-Phosphorus Iron Ore
Metals 2018, 8(6), 451; https://doi.org/10.3390/met8060451
Received: 29 May 2018 / Revised: 11 June 2018 / Accepted: 11 June 2018 / Published: 13 June 2018
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Abstract
High-phosphorus iron ore is not used because of its high phosphorus content. Phosphorus is mainly present in fluorapatite. In this work, the phosphorus vaporization that occurs during the carbothermal reduction of fluorapatite was investigated. The thermodynamic principle of vaporization, which removes phosphorus during
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High-phosphorus iron ore is not used because of its high phosphorus content. Phosphorus is mainly present in fluorapatite. In this work, the phosphorus vaporization that occurs during the carbothermal reduction of fluorapatite was investigated. The thermodynamic principle of vaporization, which removes phosphorus during carbothermal reduction, was elucidated, and the mineral evolution of high-phosphorus iron ore was summarized. The results demonstrate that it was difficult to reduce fluorapatite when only carbon was added. When Al2O3, SiO2, and Fe2O3 were added, the dephosphorization of fluorapatite was stimulated, and the dephosphorization temperature decreased. A phosphorus-containing gas was generated during this process. SiO2 had the strongest effect on the dephosphorization of fluorapatite. The carbothermal reduction rate of fluorapatite accelerated when SiO2, Al2O3, and Fe2O3 were concurrently added. These oxides were advantageous for vaporization dephosphorization. The gas-phase volatiles were detected through gas-phase mass spectrometry. The volatiles were primarily P2 or PO. The temperature range of 1000–1100 °C was the optimum for vaporization dephosphorization. This article provides a theoretical and experimental basis for the development and utilization of high-phosphorus iron ore through vaporization dephosphorization. Full article
(This article belongs to the Special Issue Ironmaking and Steelmaking)
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Open AccessArticle On the Use of JMAK Theory to Describe Mechanical Amorphization: A Comparison between Experiments, Numerical Solutions and Simulations
Metals 2018, 8(6), 450; https://doi.org/10.3390/met8060450
Received: 19 April 2018 / Revised: 30 May 2018 / Accepted: 11 June 2018 / Published: 13 June 2018
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Abstract
The kinetics of amorphization during ball milling is generally analyzed using two different approaches: the classical Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory and Delogu and Cocco’s model for which a region deterministically transforms after it reaches a certain number of collisions. The application of JMAK analysis
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The kinetics of amorphization during ball milling is generally analyzed using two different approaches: the classical Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory and Delogu and Cocco’s model for which a region deterministically transforms after it reaches a certain number of collisions. The application of JMAK analysis to the latter model predicts Avrami exponents to be higher than the experimental ones (typically close to one). We develop simulations based on the probabilistic character of the nucleation phenomenon and concave growth of the amorphous phase in the core of a nanocrystal. The predictions of our simulations are in good agreement with the low Avrami exponents and with the size evolution of the remaining crystallites found experimentally. From these values, the parameters involved in the simulated model (growth rate and probability of nucleation) can be estimated. Full article
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Open AccessArticle Influence of CO2 Shielding Gas on High Power Fiber Laser Welding Performance
Metals 2018, 8(6), 449; https://doi.org/10.3390/met8060449
Received: 31 May 2018 / Revised: 31 May 2018 / Accepted: 9 June 2018 / Published: 13 June 2018
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Abstract
The weldabilities were investigated during 10 kW high-power fiber laser welding of 304 stainless steel with the shielding gases of 100% Ar, 80% Ar + 20% CO2 and 100% CO2, respectively. As the proportion of CO2 in shielding gas
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The weldabilities were investigated during 10 kW high-power fiber laser welding of 304 stainless steel with the shielding gases of 100% Ar, 80% Ar + 20% CO2 and 100% CO2, respectively. As the proportion of CO2 in shielding gas increased from 0% to 20% then to 100%, the molten pool became unstable and the optional parameter range for obtaining a good weld appearance became narrow. The defocused distance was more negative during the CO2 shielded welding, where the weld joint without apparent defect, the maximum penetration, and a necking of weld width were formed. Porosity has been suppressed and eliminated in the CO2 shielded weld joint. The highest microhardness was obtained from the Ar + CO2 shielded weld joint, because the denser δ-ferrite appeared in the Ar + CO2 shielded weld joint. The microhardness of CO2 shielded weld joints was relative low because of the oxidation of the elements of C, Si, Mn, and Cr, which reduces the solid solution hardening tendency during the welding process. Full article
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Open AccessArticle Effect of a Traveling Magnetic Field on Micropore Formation in Al-Cu Alloys
Metals 2018, 8(6), 448; https://doi.org/10.3390/met8060448
Received: 14 May 2018 / Revised: 27 May 2018 / Accepted: 5 June 2018 / Published: 12 June 2018
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Abstract
The effect of traveling magnetic fields (TMFs) on the grain and micro-pore formation in an Al alloy was studied by scanning electron microscope and X-ray microtomography in this work. The results show that with the increasing magnetic flux density, the three-dimensional morphology of
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The effect of traveling magnetic fields (TMFs) on the grain and micro-pore formation in an Al alloy was studied by scanning electron microscope and X-ray microtomography in this work. The results show that with the increasing magnetic flux density, the three-dimensional morphology of the micro-pores transformed from dendrite to a relatively equiaxed structure. Quantified results show that both the micro-pore volume fraction and the average grain size of the primary phase decreased as the TMF density increased. The analyses show that the forced convection induced by TMF can break the dendrites, refine the grain size, and promote the liquid feeding, leading to the decrease in the volume fraction of the porosity and improved mechanical property. The TMF performed at different stages during solidification reveal that the maximum effect of TMF on reducing the micro-pore formation was found when TMF was applied in the stage of nucleation and the early stage of grain growth during solidification. Full article
(This article belongs to the Special Issue Casting and Forming of Advanced Aluminum Alloys)
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Open AccessArticle Mechanical and Microstructural Features of Plasma Cut Edges in a 15 mm Thick S460M Steel Plate
Metals 2018, 8(6), 447; https://doi.org/10.3390/met8060447
Received: 4 May 2018 / Revised: 7 June 2018 / Accepted: 8 June 2018 / Published: 11 June 2018
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Abstract
In general, the thermal cutting processes of steel plates are considered to have an influence on microstructures and residual stress distribution, which determines the mechanical properties and performance of cut edges. They also affect the quality of the surface cut edges, which further
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In general, the thermal cutting processes of steel plates are considered to have an influence on microstructures and residual stress distribution, which determines the mechanical properties and performance of cut edges. They also affect the quality of the surface cut edges, which further complicates the problem, because in most cases the surface is subjected to the largest stresses. This paper studies the influence of plasma cutting processes on the mechanical behavior of the cut edges of steel and presents the characterization results of straight plasma arc cut edges of steel plate grade S460M, 15 mm thick. The cutting conditions used are the standard ones for industrial plasma cutting. The metallography of CHAZ (Cut Heat Affected Zones) and hardness profiles versus distance from plasma cut edge surface are tested; the mechanical behavior of different CHAZ layers under the cut edge surface were obtained by testing of instrumented mini-tensile 300 µm thick specimens. Also, the residual stress distribution in the CHAZ was measured by X-ray diffraction. The results for the mechanical properties, microstructure, hardness, and residual stresses are finally compared and discussed. This work concludes that the CHAZ resulting from the plasma cutting process is narrow (about 700 µm) and homogeneous in plate thickness. Full article
(This article belongs to the Special Issue Plasmas Processes Applied on Metals and Alloys)
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Open AccessArticle Improving Elevated-Temperature Strength of an Al–Mn–Si Alloy by Strain-Induced Precipitation
Metals 2018, 8(6), 446; https://doi.org/10.3390/met8060446
Received: 22 May 2018 / Revised: 7 June 2018 / Accepted: 8 June 2018 / Published: 11 June 2018
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Abstract
The coupled effect of strain-induced precipitation and stabilized substructure on the elevated-temperature strength of an Al–Mn–Si alloy and its thermal stability have been investigated. Prestrain significantly promotes the nucleation of nano-sized dispersoids, and strain-induced precipitation suppresses recrystallization, stabilizing substructure at elevated temperatures. Compared
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The coupled effect of strain-induced precipitation and stabilized substructure on the elevated-temperature strength of an Al–Mn–Si alloy and its thermal stability have been investigated. Prestrain significantly promotes the nucleation of nano-sized dispersoids, and strain-induced precipitation suppresses recrystallization, stabilizing substructure at elevated temperatures. Compared with the dispersoids formed during the heat treatment of as-cast alloy, substructure does not increase the coarsening rate of strain-induced precipitates. The strain-induced precipitation and stabilized substructure profoundly strengthen the aluminum alloy at the elevated temperature (300 °C). Full article
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Open AccessArticle Evolution of the Microstructure and Lamellar Orientation of a β-Solidifying γ-TiAl-Based Alloy during Hot Compression
Metals 2018, 8(6), 445; https://doi.org/10.3390/met8060445
Received: 11 May 2018 / Revised: 1 June 2018 / Accepted: 5 June 2018 / Published: 11 June 2018
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Abstract
A type of advanced γ-TiAl-based alloy called β-solidifying γ-TiAl has elicited remarkable research interest in the last few decadesbecause of its excellent workability and homogeneous microstructures. Thermomechanical treatments are widely applied to this alloy to obtain fine duplex microstructures. To investigate the deformation
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A type of advanced γ-TiAl-based alloy called β-solidifying γ-TiAl has elicited remarkable research interest in the last few decadesbecause of its excellent workability and homogeneous microstructures. Thermomechanical treatments are widely applied to this alloy to obtain fine duplex microstructures. To investigate the deformation behavior and microstructure evolution of Ti-44Al-4Nb-1.5Cr-0.5Mo-0.2B alloy, we conducted a series of hot compression tests at a temperature of 1473 K and a strain rate of 0.01 s−1. Scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy were performed to analyze the crystal orientation and microstructures of the alloy. During compression at 1473 K, β/B2→γ transition and α2/γ lamellae→γ+β/B2 transition occurred simultaneously, which increased the content of the γ phase and decreased the content of the α2 phase. The lamellar colonies exhibited distinct anisotropy, which could affect their hot deformation behavior. The colonies that remained after compression had strong texture components. Full article
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Open AccessArticle Tuning Low Cycle Fatigue Properties of Cu-Be-Co-Ni Alloy by Precipitation Design
Metals 2018, 8(6), 444; https://doi.org/10.3390/met8060444
Received: 17 May 2018 / Revised: 31 May 2018 / Accepted: 8 June 2018 / Published: 11 June 2018
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Abstract
As material for key parts applied in the aerospace field, the Cu-Be-Co-Ni alloy sustains cyclic plastic deformation in service, resulting in the low cycle fatigue (LCF) failure. The LCF behaviors are closely related to the precipitation states of the alloy, but the specific
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As material for key parts applied in the aerospace field, the Cu-Be-Co-Ni alloy sustains cyclic plastic deformation in service, resulting in the low cycle fatigue (LCF) failure. The LCF behaviors are closely related to the precipitation states of the alloy, but the specific relevance is still unknown. To provide reasonable regulation of the LCF properties for various service conditions, the effect of precipitation states on the LCF behaviors of the alloy was investigated. It is found that the alloy composed fully of non-shearable γ′ precipitates has higher fatigue crack initiation resistance, resulting in a longer fatigue life under LCF process with low total strain amplitude. The alloy with fine shearable γ′I precipitates presents higher fatigue crack propagation resistance, leading to a longer fatigue life under LCF process with high total strain amplitude. The cyclic stress response behavior of the alloy depends on the competition between the kinematic hardening and isotropic softening. The fine shearable γ′I precipitates retard the decrease of effective stress during cyclic loading, causing cyclic hardening of the alloy. The present work would help to design reasonable precipitation states of the alloy for various cyclic loading conditions to guarantee its safety in service. Full article
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Open AccessArticle 3D Multiphysical Modelling of Fluid Dynamics and Mass Transfer in Laser Welding of Dissimilar Materials
Metals 2018, 8(6), 443; https://doi.org/10.3390/met8060443
Received: 15 May 2018 / Revised: 5 June 2018 / Accepted: 6 June 2018 / Published: 11 June 2018
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Abstract
A three-dimensional multiphysical transient model was developed to investigate keyhole formation, weld pool dynamics, and mass transfer in laser welding of dissimilar materials. The coupling of heat transfer, fluid flow, keyhole free surface evolution, and solute diffusion between dissimilar metals was simulated. The
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A three-dimensional multiphysical transient model was developed to investigate keyhole formation, weld pool dynamics, and mass transfer in laser welding of dissimilar materials. The coupling of heat transfer, fluid flow, keyhole free surface evolution, and solute diffusion between dissimilar metals was simulated. The adaptive heat source model was used to trace the change of keyhole shape, and the Rayleigh scattering of the laser beam was considered. The keyhole wall was calculated using the fluid volume equation, primarily considering the recoil pressure induced by metal evaporation, surface tension, and hydrostatic pressure. Fluid flow, diffusion, and keyhole formation were considered simultaneously in mass transport processes. Welding experiments of 304L stainless steel and industrial pure titanium TA2 were performed to verify the simulation results. It is shown that spatters are shaped during the welding process. The thickness of the intermetallic reaction layer between the two metals and the diffusion of elements in the weld are calculated, which are important criteria for welding quality. The simulation results correspond well with the experimental results. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessArticle Fatigue Behavior of Cold-Worked High-Interstitial Steels
Metals 2018, 8(6), 442; https://doi.org/10.3390/met8060442
Received: 8 May 2018 / Revised: 5 June 2018 / Accepted: 7 June 2018 / Published: 11 June 2018
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Abstract
The austenitic high-nitrogen (AHNS) and high-interstitial steels (AHIS) with more than 0.6 weight-% N allow for a yield strength above 1.1 GPa and a tensile strength above 1.5 GPa by maintaining an elongation to fracture markedly above 30%. These steels gain their prominent
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The austenitic high-nitrogen (AHNS) and high-interstitial steels (AHIS) with more than 0.6 weight-% N allow for a yield strength above 1.1 GPa and a tensile strength above 1.5 GPa by maintaining an elongation to fracture markedly above 30%. These steels gain their prominent mechanical properties from the fact that at the chosen sum of C+N and C/N-ratios, the concentration of free electrons is higher compared to that of other steels. Thus, the capacity to dissipate plastic work under monotonic tensile loading is unique. Now, the fatigue limit of austenitic steels in general is mainly governed by the sum of interstitials and should be further improved by cold working. Unfortunately, this is not the case for the AHNS and AHIS and is in contrast to the classical CrNiC- or CrMnC-steels. Thus, tensile and fatigue tests of cold-worked samples were conducted and analyzed by scanning- and transmission-electron microscopy. This paper tries to elucidate the metallurgical reasons, as well as the material engineering aspects, of such peculiar behavior of AHNS and AHIS. Full article
(This article belongs to the Special Issue Fatigue and Wear for Steels)
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Open AccessArticle Hydrometallurgical Process for Selective Metals Recovery from Waste-Printed Circuit Boards
Metals 2018, 8(6), 441; https://doi.org/10.3390/met8060441
Received: 11 May 2018 / Revised: 28 May 2018 / Accepted: 29 May 2018 / Published: 11 June 2018
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Abstract
This paper presents an experimentally-proved hydrometallurgical process for selective metals recovery from the waste-printed circuit boards (WPCBs) using a combination of conventional and time-saving methods: leaching, cementation, precipitation, reduction and electrowinning. According to the results obtained in the laboratory tests, 92.4% Cu, 98.5%
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This paper presents an experimentally-proved hydrometallurgical process for selective metals recovery from the waste-printed circuit boards (WPCBs) using a combination of conventional and time-saving methods: leaching, cementation, precipitation, reduction and electrowinning. According to the results obtained in the laboratory tests, 92.4% Cu, 98.5% Pb, 96.8% Ag and over 99% Au could be selectively leached and recovered using mineral acids: sulfuric, nitric and aqua regia. Problematic tin recovery was addressed with comprehensive theoretical and experimental work, so 55.4% of Sn could be recovered through the novel physical method, which consists of two-step phase separation. Based on the results, an integral hydrometallurgical route for selective base and precious metals recovery though consecutive steps, (i) Cu, (ii) Sn, (iii) Pb and Ag, and (iv) Au, was developed. The route was tested at scaled-up laboratory level, confirming feasibility of the process and efficiencies of metals recovery. According to the obtained results, the proposed hydrometallurgical route represents an innovative and promising method for selective metals recovery from WPCBs, particularly applicable in small scale hydrometallurgical environments, focused on medium and high grade WPCBs recycling. Full article
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