Materials

Research

37 pages, 13639 KiB

Open AccessArticle

Design and Fabrication of New High Entropy Alloys for Evaluating Titanium Replacements in Additive Manufacturing

by Prashant Sarswat, Taylor Smith, Sayan Sarkar, Arun Murali and Michael Free

Materials 2020, 13(13), 3001; https://doi.org/10.3390/ma13133001 - 6 Jul 2020

Cited by 18 | Viewed by 3560

High entropy alloys (HEAs) were prepared using the powder bed fusion (PBF) technique. Among titanium free alloys AlCoCrFeNiMn, CoCr_1.3FeMnNi_0.7, AlCoCrFeNi_1.3, and AlCoCr_1.3FeNi_1.3 have been further investigated. A cost comparison was done for these four [...] Read more.

High entropy alloys (HEAs) were prepared using the powder bed fusion (PBF) technique. Among titanium free alloys AlCoCrFeNiMn, CoCr_1.3FeMnNi_0.7, AlCoCrFeNi_1.3, and AlCoCr_1.3FeNi_1.3 have been further investigated. A cost comparison was done for these four alloys as well as the titanium-based alloys AlCoCrFeNiTi and AlCo_0.8CrFeNiTi. Such a comparison was done in order to evaluate the performance of the titanium-free alloys as the estimated cost of these will be less than for Ti-based HEAs. Hence, we have chosen four titanium free alloys and two titanium-based alloys for further processing. All these alloys were fabricated and subsequently characterized for phase, purity and performance. Scanning electron microscopy-based images were captured for microstructure characterization. EIS-based tests and potentiodynamic scans were performed to evaluate corrosion current. Hardness tests were performed for mechanical properties evaluation. Additional testing using factorial design tests was performed to evaluate the effects of various parameters to create better PBF-based HEA samples. EBSD tests, accelerated corrosion tests (mass loss), chemical analysis after degradation, microstructure analysis before and after degradation, and mechanical property comparison for finalized samples and other similar tests were executed. The details about all these HEAs and subsequent laser processing as well as behavior of these HEAs have been included in this study. It has been observed that some of the selected alloys exhibit good performance compared to Ti-based alloys, especially with respect to improvements in elastic constant and hardness relative to commercially pure Ti. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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22 pages, 8663 KiB

Open AccessArticle

Wire Arc Additive Manufacturing (WAAM) of Aluminum Alloy AlMg5Mn with Energy-Reduced Gas Metal Arc Welding (GMAW)

by Maximilian Gierth, Philipp Henckell, Yarop Ali, Jonas Scholl and Jean Pierre Bergmann

Materials 2020, 13(12), 2671; https://doi.org/10.3390/ma13122671 - 12 Jun 2020

Cited by 70 | Viewed by 6823

Abstract

Large-scale aluminum parts are used in aerospace and automotive industries, due to excellent strength, light weight, and the good corrosion resistance of the material. Additive manufacturing processes enable both cost and time savings in the context of component manufacturing. Thereby, wire arc additive [...] Read more.

Large-scale aluminum parts are used in aerospace and automotive industries, due to excellent strength, light weight, and the good corrosion resistance of the material. Additive manufacturing processes enable both cost and time savings in the context of component manufacturing. Thereby, wire arc additive manufacturing (WAAM) is particularly suitable for the production of large volume parts due to deposition rates in the range of kilograms per hour. Challenges during the manufacturing process of aluminum alloys, such as porosity or poor mechanical properties, can be overcome by using arc technologies with adaptable energy input. In this study, WAAM of AlMg5Mn alloy was systematically investigated by using the gas metal arc welding (GMAW) process. Herein, correlations between the energy input and the resulting temperature–time-regimes show the effect on resulting microstructure, weld seam irregularities and the mechanical properties of additively manufactured aluminum parts. Therefore, multilayer walls were built layer wise using the cold metal transfer (CMT) process including conventional CMT, CMT advanced and CMT pulse advanced arc modes. These processing strategies were analyzed by means of energy input, whereby the geometrical features of the layers could be controlled as well as the porosity to area portion to below 1% in the WAAM parts. Furthermore, the investigations show the that mechanical properties like tensile strength and material hardness can be adapted throughout the energy input per unit length significantly. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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14 pages, 5637 KiB

Open AccessArticle

Towards Deterministic Computation of Internal Stresses in Additively Manufactured Materials under Fatigue Loading: Part I

by Mustafa Awd, Mhd Fateh Labanie, Kerstin Moehring, Ali Fatemi and Frank Walther

Materials 2020, 13(10), 2318; https://doi.org/10.3390/ma13102318 - 18 May 2020

Cited by 11 | Viewed by 2523

Abstract

The ongoing studies of the influence of internal defects on fatigue strength of additively manufactured metals adopted an internal crack or notch-like model at which the threshold stress intensity factor is the driving mechanism of fatigue failure. The current article highlights a shortcoming [...] Read more.

The ongoing studies of the influence of internal defects on fatigue strength of additively manufactured metals adopted an internal crack or notch-like model at which the threshold stress intensity factor is the driving mechanism of fatigue failure. The current article highlights a shortcoming of this approach and offers an alternative based on X-ray microcomputed tomography and cyclic plasticity with a hybrid formulation of Chaboche and Armstrong–Frederick material laws. The presented tessellation and geometrical transformation scheme enabled a significantly more realistic morphological representation of internal defects that yielded a cyclic strain within 2% of the experimental values. This means that cyclic plasticity models have an accurate prediction of mechanical properties without repeating a full set of experiments for additively manufactured arbitrary microstructures. The coupling with a material law that is oriented towards the treatment of cyclic hardening and softening enabled more accurate computation of internal stresses under cyclic loading than ever before owing to the maturity of tessellation and numerical tools since then. The resulting stress–strain distributions were used as input to the Fatemi–Socie damage model, based on which a successful calculation of fatigue lifetime became possible. Furthermore, acting stresses on the internal pores were shown to be more than 450% concerning the applied remote stress amplitude. The results are a pretext to a scale bridging numerical solution that accounts for the short crack formation stage based on microstructural damage. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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18 pages, 5184 KiB

Open AccessArticle

Modeling the Role of Epitaxial Grain Structure of the Prior β Phase and Associated Fiber Texture on the Strength Characteristics of Ti-6Al-4V Produced via Additive Manufacturing

by Michael D. Sangid, Andrea Nicolas, Kartik Kapoor, Eric Fodran and John Madsen

Materials 2020, 13(10), 2308; https://doi.org/10.3390/ma13102308 - 17 May 2020

Cited by 6 | Viewed by 2663

Abstract

Due to the rapid cooling and directional heat flow inherent in metal-based additive manufacturing, Ti-6Al-4V results in epitaxial grain growth and a fiber texture of the prior β phase. While Ti-6Al-4V produced via powder bed, electron beam melted processing can exhibit a range [...] Read more.

Due to the rapid cooling and directional heat flow inherent in metal-based additive manufacturing, Ti-6Al-4V results in epitaxial grain growth and a fiber texture of the prior β phase. While Ti-6Al-4V produced via powder bed, electron beam melted processing can exhibit a range of strength characteristics, recent studies have shown superior strength properties, compared to similar orientations, of conventional plate material (AMS 4911) across a range of elevated temperatures (204 to 371 °C). To investigate this phenomenon, a series of crystal plasticity models was developed for the representative grain structures of Ti-6Al-4V to rationalize if the columnar, fiber texture produced by additive manufacturing (AM) was sufficient to explain the observed strength attributes. As a first step towards understanding this behavior, the grain structure was characterized via electron backscattering diffraction for AM material taken from four specimens (with different build directions), as well as material taken from baseline plate material (along and transverse to the rolling direction), and the resulting microstructures were modeled via a crystal plasticity framework. As expected, the results showed the AM material accounting for only the α grain structure was stronger in the vertical builds and weaker in the horizontal builds compared to the conventional plate counterparts. This suggested that grain morphology and α grain orientation alone provided some information about the relative strengths, but did not explain the overall trends observed from the experiments. To account for the role of texture, the characterized α phase was converted, via variant selection, to its prior β phase for use in the simulations. The results showed that each simulation of the AM prior β phase exhibited a higher strength compared to the baseline plate material, except for one specimen (horizontally built), which had large colonies of soft microtextured regions for the prior β structure. This suggests that some variability was experienced (as anticipated), but the texture (especially of the prior β macrozones) was a key contributor for the unusually high strength observed of the AM Ti-6Al-4V material. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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26 pages, 11558 KiB

Open AccessArticle

Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting

by Hitoshi Soyama and Fumio Takeo

Materials 2020, 13(10), 2216; https://doi.org/10.3390/ma13102216 - 12 May 2020

Cited by 53 | Viewed by 4151

Abstract

Titanium alloy Ti6Al4V manufactured by additive manufacturing (AM) is an attractive material, but the fatigue strength of AM Ti6Al4V is remarkably weak. Thus, post-processing is very important. Shot peening can improve the fatigue strength of metallic materials, and novel peening methods, such as [...] Read more.

Titanium alloy Ti6Al4V manufactured by additive manufacturing (AM) is an attractive material, but the fatigue strength of AM Ti6Al4V is remarkably weak. Thus, post-processing is very important. Shot peening can improve the fatigue strength of metallic materials, and novel peening methods, such as cavitation peening and laser peening, have been developed. In the present paper, to demonstrate an improvement of the fatigue strength of AM Ti6Al4V, Ti6Al4V manufactured by direct metal laser sintering (DMLS) and electron beam melting (EBM) was treated by cavitation peening, laser peening, and shot peening, then tested by a plane bending fatigue test. To clarify the mechanism of the improvement of the fatigue strength of AM Ti6Al4V, the surface roughness, residual stress, and surface hardness were measured, and the surfaces with and without peening were also observed using a scanning electron microscope. It was revealed that the fatigue strength at N = 10⁷ of Ti6Al4V manufactured by DMLS was slightly better than that of Ti6Al4V manufactured by EBM, and the fatigue strength of both the DMLS and EBM specimens was improved by about two times through cavitation peening, compared with the as-built ones. An experimental formula to estimate fatigue strength from the mechanical properties of a surface was proposed. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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15 pages, 2714 KiB

Open AccessArticle

High Cycle Fatigue Performance of LPBF 304L Stainless Steel at Nominal and Optimized Parameters

by Mohammad Masud Parvez, Tan Pan, Yitao Chen, Sreekar Karnati, Joseph W. Newkirk and Frank Liou

Materials 2020, 13(7), 1591; https://doi.org/10.3390/ma13071591 - 31 Mar 2020

Cited by 12 | Viewed by 3354

Abstract

In additive manufacturing, the variation of the fabrication process parameters influences the mechanical properties of a material such as tensile strength, impact toughness, hardness, fatigue strength, and so forth, but fatigue testing of metals fabricated with all different sets of process parameters is [...] Read more.

In additive manufacturing, the variation of the fabrication process parameters influences the mechanical properties of a material such as tensile strength, impact toughness, hardness, fatigue strength, and so forth, but fatigue testing of metals fabricated with all different sets of process parameters is a very expensive and time-consuming process. Therefore, the nominal process parameters by means of minimum energy input were first identified for a dense part and then the optimized process parameters were determined based on the tensile and impact toughness test results obtained for 304L stainless steel deposited in laser powder bed fusion (LPBF) process. Later, the high cycle fatigue performance was investigated for the material built with these two sets of parameters at horizontal, vertical, and inclined orientation. In this paper, displacement controlled fully reversed (R = −1) bending type fatigue tests at different levels of displacement amplitude were performed on Krouse type miniature specimens. The test results were compared and analyzed by applying the control signal monitoring (CSM) method. The analysis shows that specimen built-in horizontal direction for optimized parameters demonstrates the highest fatigue strength while the vertical specimen built with nominal parameters exhibits the lowest strength. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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28 pages, 8032 KiB

Open AccessArticle

Review of Requirements for the Durability and Damage Tolerance Certification of Additively Manufactured Aircraft Structural Parts and AM Repairs

by Sudip Kundu, Rhys Jones, Daren Peng, Neil Matthews, Alankar Alankar, Singh R. K. Raman and Pu Huang

Materials 2020, 13(6), 1341; https://doi.org/10.3390/ma13061341 - 15 Mar 2020

Cited by 32 | Viewed by 4246

Abstract

The USAF requirements for the durability and damage tolerance certification for additively manufactured (AM) aircraft structural parts, which are detailed in Structures Bulletin EZ-19-01, raise a number of new and, as yet, unanswered questions. The present paper attempts to address three questions: How [...] Read more.

The USAF requirements for the durability and damage tolerance certification for additively manufactured (AM) aircraft structural parts, which are detailed in Structures Bulletin EZ-19-01, raise a number of new and, as yet, unanswered questions. The present paper attempts to address three questions: How to perform a fracture mechanics-based analysis of crack growth in an AM part so as to account for the residual stresses, how to perform a fracture mechanics-based durability analysis of a cold spray repair so as to account for both the induced residual stresses and the presence of multiple co-located cracks, and how to perform a fracture mechanics-based durability analysis of an AM part so as to account for the presence of multiple collocated surface braking cracks. In this context, the present paper reveals the potential of the Hartman–Schijve variant of the NASGRO crack growth equation to accurately predict the growth of each of the individual (collocated) cracks that arose in a cold spray-repaired specimen and in a specimen from a crack that nucleated and grew from a rough surface. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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12 pages, 9013 KiB

Open AccessArticle

Enhancing Hardness and Wear Performance of Laser Additive Manufactured Ti6Al4V Alloy Through Achieving Ultrafine Microstructure

by Yanqin Li, Lijun Song, Pan Xie, Manping Cheng and Hui Xiao

Materials 2020, 13(5), 1210; https://doi.org/10.3390/ma13051210 - 8 Mar 2020

Cited by 18 | Viewed by 3213

Abstract

Refining microstructure is an important issue for laser additive manufacturing (LAM) of titanium alloy. In the present work, the microstructures of LAM-fabricated Ti6Al4V alloy were refined using a low energy density with the combination of a small spot diameter, a low laser power, [...] Read more.

Refining microstructure is an important issue for laser additive manufacturing (LAM) of titanium alloy. In the present work, the microstructures of LAM-fabricated Ti6Al4V alloy were refined using a low energy density with the combination of a small spot diameter, a low laser power, and a high scanning speed. The microstructure, hardness, wear performance, and molten pool thermal behavior of LAM-fabricated Ti6Al4V coatings were studied. The results show that the grain sizes of both prior β and α phases are strongly dependent on the cooling rate of the molten pool. The fine prior β grains and submicron-scale acicular α phases were obtained under a low energy density of 75 J mm⁻² due to the high cooling rate of the molten pool. In addition, the as-fabricated Ti6Al4V sample with submicron-scale acicular α phase showed a very high hardness of 7.43 GPa, a high elastic modulus of 133.6 GPa, and a low coefficient of friction of 0.48. This work provides a good method for improving the microstructure and mechanical performance of LAM-fabricated Ti6Al4V alloy. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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17 pages, 5792 KiB

Open AccessArticle

Additive Manufactured Large Zr-Based Bulk Metallic Glass Composites with Desired Deformation Ability and Corrosion Resistance

by Yu Luo, Leilei Xing, Yidong Jiang, Ruiwen Li, Chao Lu, Rongguang Zeng, Jinru Luo, Pengcheng Zhang and Wei Liu

Materials 2020, 13(3), 597; https://doi.org/10.3390/ma13030597 - 28 Jan 2020

Cited by 17 | Viewed by 3231

Abstract

Zr-based bulk metallic glasses have been attracting tremendous interest of researchers because of their unique combination of mechanical and chemical properties. However, their application is limited as large-scale production is difficult due to the limitation of cooling rate. Recently, additive manufacturing technology has [...] Read more.

Zr-based bulk metallic glasses have been attracting tremendous interest of researchers because of their unique combination of mechanical and chemical properties. However, their application is limited as large-scale production is difficult due to the limitation of cooling rate. Recently, additive manufacturing technology has been proposed as a new solution for fabricating bulk metallic glasses without size limitation. In this study, selective laser melting technology was used to prepare Zr₆₀Fe₁₀Cu₂₀Al₁₀ bulk metallic glass. The laser parameters for fabricating full dense amorphous specimens were investigated. The mechanical and corrosion resistance properties of the prepared samples were measured by micro-compression and electrochemical corrosion testing, respectively. Lastly, Zr₆₀Fe₁₀Cu₂₀Al₁₀ bulk metallic glass (BMG) with dispersed nano-crystals was made, and good deformation ability was revealed during micro-compression test. The corrosion resistance decreased a bit due to the crystalline phases. The results provide a promising route for manufacturing large and complex bulk metallic glasses with better mechanical property and acceptable corrosion resistance. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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11 pages, 2668 KiB

Open AccessArticle

Strategy of Residual Stress Determination on Selective Laser Melted Al Alloy Using XRD

by Yujiong Chen, Hua Sun, Zechen Li, Yi Wu, Yakai Xiao, Zhe Chen, Shengyi Zhong and Haowei Wang

Materials 2020, 13(2), 451; https://doi.org/10.3390/ma13020451 - 17 Jan 2020

Cited by 23 | Viewed by 4501

Abstract

Selective laser melting (SLM) is known to generate large and anisotropic residual stresses in the samples. Accurate measurement of residual stresses on SLM-produced samples is essential for understanding the residual stress build-up mechanism during SLM, while a dramatic fluctuation can be observed in [...] Read more.

Selective laser melting (SLM) is known to generate large and anisotropic residual stresses in the samples. Accurate measurement of residual stresses on SLM-produced samples is essential for understanding the residual stress build-up mechanism during SLM, while a dramatic fluctuation can be observed in the residual stress values reported in the literature. On the basis of studying the influence of surface roughness on residual stress measured using X-ray diffraction (XRD), we propose a procedure coupling XRD technique with pretreatment consisting of mechanical polishing and chemical etching. The results highlight that residual stresses measured using XRD on as-built SLM-produced samples with high surface roughness are significantly lower than those measured on samples with finished surface, which is due to the stress relaxation on the spiked surface of as-built samples. Surface distribution of residual stresses and the effect of scanning strategy were systematically investigated for SLM-produced AlSi10Mg samples. Microstructural morphology was observed at the interface between sample and building platform and was linked to the surface distribution of residual stresses. This procedure can help us accurately measure the residual stresses in SLM-produced samples and thus better understand its build-up mechanism during the SLM process. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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10 pages, 3722 KiB

Open AccessArticle

Study on Microstructural and Mechanical Properties of an Al–Cu–Sn Alloy Wall Deposited by Double-Wire Arc Additive Manufacturing Process

by Shuai Wang, Huimin Gu, Wei Wang, Chengde Li, Lingling Ren, Zhenbiao Wang, Yuchun Zhai and Peihua Ma

Materials 2020, 13(1), 73; https://doi.org/10.3390/ma13010073 - 22 Dec 2019

Cited by 31 | Viewed by 2822

Abstract

In this present study, single-wire and double-wire Al–Cu–Sn alloy walls were fabricated by an arc additive manufacturing process. The surface morphology, elemental composition, and microstructure were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM) techniques. The [...] Read more.

In this present study, single-wire and double-wire Al–Cu–Sn alloy walls were fabricated by an arc additive manufacturing process. The surface morphology, elemental composition, and microstructure were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM) techniques. The mechanical properties of both the single-wire and double-wire walls were studied by mechanical property testing. The results showed that the heat input of the double-wire wall was lower than that of the single-wire wall at the same wire feeding speed. The surface microstructure of the double-wire wall showed a more uniform surface than the single-wire wall. The grains of the double-wire wall were found to be isometric crystals in the as-deposited state. The θ phase of the double-wire wall was dispersed with a smaller grain size in the grain boundary. After T6 heat treatment, the θ phase of the double-wire wall was completely dissolved into the aluminum matrix, and a large amount of θ^’ enhanced phases were precipitated with a phase spacing of about 15 nm. The mechanical properties of the double-wire wall were shown to have significantly improved performance, which further increased to 490 MPa, 420 MPa, and 12%, respectively. The transverse and longitudinal mechanical properties of the double-wire wall were consistent, and the fracture mode of both was ductile fracture. Full article

(This article belongs to the Special Issue Additively Manufactured Metallic Materials)

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