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Mechanical and Metallurgical Characterizations of Advanced Alloys
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Mechanical and Metallurgical Characterizations of Advanced Alloys

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Metals and Alloys".

Deadline for manuscript submissions: closed (10 December 2022) | Viewed by 24873

Special Issue Editor

Dr. Yong Chae Lim

E-Mail Website
Guest Editor
Materials Science and Technology Division, Oak Ridge National Laboratory, ORNL, Oak Ridge, TN, USA
Interests: advanced structural alloys; materials processing and joining; welding metallurgy; mechanical properties; advanced characterizations; corrosion of multi-material joints; residual stress measurement; neutron beam

Special Issue Information

Dear Colleagues,

The design and manufacturing of advanced materials are of great interest in many applications of automotive, aerospace, clean energy, military, and heavy industries. The addition of alloy elements and various manufacturing processes greatly influence the resulting microstructures and mechanical properties. Furthermore, microstructures and their material properties can be modified by post material processing, including shaping and forming, thermal and/or mechanical treatment, welding, and joining for the final application. In addition, residual stress after thermal and/or mechanical processing also affects mechanical performances under static or dynamic mechanical testing or in-service conditions.

This Special Issue focuses on multidisciplinary research for emerging alloy design, approaches, and theories of material processing and joining as well as advanced metallurgical characterizations and mechanical properties under static, dynamic, corrosion, high-pressure gas, or other environmental testing.

Potential topics include, but are not limited to:

  • Advanced alloy design and manufacturing
  • Advanced structural materials
  • High specific strength materials
  • Additive manufacturing
  • Thermal and/or mechanical processing
  • Solid-state processing and joining
  • Other material processing techniques to alter microstructures and mechanical properties
  • Metallurgical characterizations
  • Residual stress
  • Micro- and/or macromechanical properties
  • Material properties under various testing methods

Dr. Yong Chae Lim
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • alloy design and manufacturing
  • materials processing and joining
  • advanced materials characterization techniques
  • microstructure and mechanical properties
  • residual stress
  • material properties under various testing conditions

Published Papers (14 papers)

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Research

12 pages, 4168 KiB  
Article
Enhanced High−Temperature Wear Performance of H13 Steel through TiC Incorporation by Laser Metal Deposition
by Chengqi Lu, Zhenyu Chen, Yuqing Yan, Yuhao Zhuo, Chuanyang Wang and Qingbo Jia
Materials 2023, 16(1), 99; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16010099 - 22 Dec 2022
Cited by 4 | Viewed by 1499
Abstract
High−temperature wear failure has been a major challenge to die parts. This work provides a comprehensive study on the high−temperature wear performance of a TiC/H13 composite coating prepared by laser metal deposition (LMD). The microstructures of wrought H13 samples, LMD−processed H13 and TiC/H13 [...] Read more.
High−temperature wear failure has been a major challenge to die parts. This work provides a comprehensive study on the high−temperature wear performance of a TiC/H13 composite coating prepared by laser metal deposition (LMD). The microstructures of wrought H13 samples, LMD−processed H13 and TiC/H13 samples were systematically investigated. The refined martensite size, the uniform distribution of TiC ceramic particles, as well as their bonding with the matrix endowed the fabricated composite coating with superior hardness. The LMD−prepared TiC/H13 composite coating material demonstrated outstanding wear resistance when compared with other counterparts, mainly due to the high thermal stability and the load-transferring effect triggered by the introduced TiC ceramic particles. The dominated wear mechanism transition from severe ploughing in the wrought H13 material to mild delamination in the TiC/H13 composite coating was confirmed. The present study is expected to shed light on high-temperature wear-resistant coating material design and applications within the highly demanding mould industry. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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24 pages, 5761 KiB  
Article
Experimental and Numerical Investigation into the Stability Behaviour of Cable-Stiffened Steel Columns
by Pengcheng Li, Xuxiang Zhao, Jianyue Qiu, Jianghua Qian, Zhao Zhu, Zhigang Zhang and Lei Meng
Materials 2022, 15(24), 8813; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15248813 - 09 Dec 2022
Viewed by 722
Abstract
A cable-stiffened steel column (CSSC) possesses superior stability behaviour compared to ordinary compression columns. In the past, the research emphasis has focused on the behaviours of stiffened columns under axial compression; investigations into their behaviour under eccentric loading is scant. This study aims [...] Read more.
A cable-stiffened steel column (CSSC) possesses superior stability behaviour compared to ordinary compression columns. In the past, the research emphasis has focused on the behaviours of stiffened columns under axial compression; investigations into their behaviour under eccentric loading is scant. This study aims to examine the buckling behaviour of CSSCs under eccentric loading using experimental and numerical investigations. The effects of pretension in cables and eccentricity on stability behaviours were studied. According to the current investigation, it can be demonstrated that the capacities of CSSCs are higher than those of ordinary compression columns. It has also been illustrated that both the buckling loads and modes of CSSCs can be changed by changing the load eccentricity; however, the modes of ordinary columns cannot be changed. These results could be of theoretical and engineering significance in the exploration of the behaviours of cable-stiffened columns. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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14 pages, 5740 KiB  
Article
The Effect of Tool Geometry on the Strength of FSW Aluminum Thin Sheets
by Achilles Vairis, Markos Petousis, Nikolaos Mountakis, Charikleia Tsarouchidou and Nectarios Vidakis
Materials 2022, 15(22), 8187; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15228187 - 18 Nov 2022
Cited by 4 | Viewed by 1374
Abstract
Welding tools of different designs have been used to join friction stir welding 2-mm-thick Al 7075 sheets, to investigate the effect of the tool geometry on the weld performance. Five cylindrical tools with different pin geometries were manufactured from heat-treatable low alloy steel [...] Read more.
Welding tools of different designs have been used to join friction stir welding 2-mm-thick Al 7075 sheets, to investigate the effect of the tool geometry on the weld performance. Five cylindrical tools with different pin geometries were manufactured from heat-treatable low alloy steel WNr 1.6582/DIN 34CrNiMo6. Additionally, the effect of the welding speed was considered in the work, with six different speeds ranging from 80 mm/min to 300 mm/min. The weld tool rotational speed was kept constant at 1000 rpm and all other parameters were also kept constant in the experiments. The tensile strength was measured to investigate the mechanical properties of the weld. Results were processed with statistical analysis tools, which showed that the mechanical strength was affected by tool geometry as well as welding speed. The weld tool with the highest pin diameter achieved the highest tensile strength. The welding speed affected the tensile strength differently in the different weld tool geometries studied. The highest weld efficiency reported in the tests is 72.20%, achieved with a cylindrical pin weld tool at 250 mm/min. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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13 pages, 5877 KiB  
Article
{332}<113> and {112}<111> Twin Variant Activation during Cold-Rolling of a Ti-Nb-Zr-Ta-Sn-Fe Alloy
by Alexandru Dan, Elisabeta Mirela Cojocaru, Doina Raducanu, Anna Nocivin, Ion Cinca and Vasile Danut Cojocaru
Materials 2022, 15(19), 6932; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15196932 - 06 Oct 2022
Cited by 1 | Viewed by 1107
Abstract
Deformation twinning is a phenomenon that causes local shear strain concentrations, with the material either experiencing elongation (and thus a tensile stress) or contraction (compressive stress) along the stress directions. Thus, in order to gauge the performance of the alloy better, it is [...] Read more.
Deformation twinning is a phenomenon that causes local shear strain concentrations, with the material either experiencing elongation (and thus a tensile stress) or contraction (compressive stress) along the stress directions. Thus, in order to gauge the performance of the alloy better, it is imperative to predict the activation of twinning systems successfully. The present study investigates the effects of deformation by cold-rolling on the {332}<113> and {112}<111> twin variant activation in a Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) (TNZTSF) alloy. The Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) alloy was synthesized in a cold crucible induction levitation furnace, under an argon-controlled atmosphere, using high-purity elemental components. The TNZTSF alloy was cold-deformed by rolling, in one single step, with a total deformation degree (thickness reduction) of ε ≈ 1% (CR 1), ε ≈ 3% (CR 3), and ε ≈ 15% (CR 15). The microstructural investigations were carried out with the SEM-EBSD technique in order to determine the grain morphology, grain-size distribution, crystallographic orientation, accumulated strain-stress fields and Schmid Factor (SF) analysis, all necessary to identify the active twin variants. The EBSD data were processed using an MTEX Toolbox ver. 5.7.0 software package. The results indicated that the TNZTSF alloy’s initial microstructure consists of a homogeneous β-Ti single phase that exhibits equiaxed polyhedral grains and an average grain-size close to 71 μm. It was shown that even starting with a 1% total deformation degree, the microstructure shows the presence of the {332}<113> twinning ((233)[3¯11] active twin variant; Schmit factor SF = −0.487); at a 3% total deformation degree, one can notice the presence of primary and secondary twin variants within the same grain belonging to the same {332}<113> twinning system ((323¯)[13¯1¯] primary twin variant—SF = −0.460; (233¯)[3¯11¯] secondary twin variant—SF = −0.451), while, at a 15% total deformation degree, besides the {332}<113> twinning system, one can notice the activation of the {112}<111> twinning system ((11¯2)[1¯11] active twin variant—SF = −0.440). This study shows the {332}<113> and {112}<111> twinning variant activation during cold-deformation by rolling in the case of a Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) (TNZTSF) alloy. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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12 pages, 4437 KiB  
Article
Fracture Mode Transition during Assembly of TC4 High-Lock Bolt under Tensile Load: A Combined Experimental Study and Finite Element Analysis
by Derong Feng, Chenxi Dong, Yunpeng Hu, Yamei Wang, Jianhua Ma, Zhangdong Huang and Qiang Wan
Materials 2022, 15(12), 4049; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15124049 - 07 Jun 2022
Cited by 2 | Viewed by 1327
Abstract
Fracture during the assembly process is an important failure mode for high-lock bolts used in the aviation industry, which greatly increases the potential of unpredictable accidents during service. In the current study, the underlying reasons for fracture during the assembly of a TC4 [...] Read more.
Fracture during the assembly process is an important failure mode for high-lock bolts used in the aviation industry, which greatly increases the potential of unpredictable accidents during service. In the current study, the underlying reasons for fracture during the assembly of a TC4 high-lock bolt was investigated using a tensile test and finite element analysis (FEA). The microstructure of the as-received bolt consisted of a high proportion of α phase, some β phase, and a small amount of α′ phase formed via martensite phase transformation during the rammer process. The experimental force–displacement curves revealed an average yield load of 55.9 kN and a breaking load of 67.65 kN. The corresponding yield strength was calculated to be 0.9 GPa, which was smaller than the standard value of TC4. This was attributed to the preload-induced stress concentration on the thread surface, leading to obvious strain hardening, which can lead to crack initiation. The effect of preload was further confirmed by the fractographies in which the initial crack was observed on the thread surface. The fractographies suggested that hybrid fracture occurred on the tensile loaded bolt. The initial failure was brittle fracture on the thread surface, transforming into ductile fracture in the screw. The results can contribute to understanding the effect of preload on the load carry capacity of high-lock bolts and provide a strategy to design its assembly specification. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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12 pages, 3035 KiB  
Article
Evolution of Microstructural and Mechanical Properties during Cold-Rolling Deformation of a Biocompatible Ti-Nb-Zr-Ta Alloy
by Alexandru Dan, Mariana Lucia Angelescu, Nicolae Serban, Elisabeta Mirela Cojocaru, Nicoleta Zarnescu-Ivan, Vasile Danut Cojocaru and Bogdan Mihai Galbinasu
Materials 2022, 15(10), 3580; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15103580 - 17 May 2022
Cited by 3 | Viewed by 1625
Abstract
In this study, a Ti-32.9Nb-4.2Zr-7.5Ta (wt%) titanium alloy was produced by melting in a cold crucible induction in a levitation furnace, and then deforming by cold rolling, with progressive deformation degrees (thickness reduction), from 15% to 60%, in 15% increments. The microstructural characteristics [...] Read more.
In this study, a Ti-32.9Nb-4.2Zr-7.5Ta (wt%) titanium alloy was produced by melting in a cold crucible induction in a levitation furnace, and then deforming by cold rolling, with progressive deformation degrees (thickness reduction), from 15% to 60%, in 15% increments. The microstructural characteristics of the specimens in as-received and cold-rolled conditions were determined by XRD and SEM microscopy, while the mechanical characteristics were obtained by tensile and microhardness testing. It was concluded that, in all cases, the Ti-32.9Nb-4.2Zr-7.5Ta (wt%) showed a bimodal microstructure consisting of Ti-β and Ti-α″ phases. Cold deformation induced significant changes in the microstructural and the mechanical properties, leading to grain-refinement, crystalline cell distortions and variations in the weight-fraction ratio of both Ti-β and Ti-α″ phases, as the applied degree of deformation increased from 15% to 60%. Changes in the mechanical properties were also observed: the strength properties (ultimate tensile strength, yield strength and microhardness) increased, while the ductility properties (fracture strain and elastic modulus) decreased, as a result of variations in the weight-fraction ratio, the crystallite size and the strain hardening induced by the progressive cold deformation in the Ti-β and Ti-α″ phases. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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14 pages, 6416 KiB  
Article
Low-Power Laser Powder Bed Fusion Processing of Scalmalloy®
by Alessandra Martucci, Alberta Aversa, Diego Manfredi, Federica Bondioli, Sara Biamino, Daniele Ugues, Mariangela Lombardi and Paolo Fino
Materials 2022, 15(9), 3123; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15093123 - 26 Apr 2022
Cited by 10 | Viewed by 1921
Abstract
Among recently developed high-strength and lightweight alloys, the high-performance Scalmalloy® certainly stands out for laser powder bed fusion (LPBF) production. The primary goal of this study was to optimize the Scalmalloy® LPBF process parameters by setting power values suitable for the [...] Read more.
Among recently developed high-strength and lightweight alloys, the high-performance Scalmalloy® certainly stands out for laser powder bed fusion (LPBF) production. The primary goal of this study was to optimize the Scalmalloy® LPBF process parameters by setting power values suitable for the use of lab-scale machines. Despite that these LPBF machines are commonly characterized by considerably lower maximum power values (around 100 W) compared to industrial-scale machines (up to 480 W), they are widely used when quick setup and short processing time are needed and a limited amount of powder is available. In order to obtain the optimal process parameters, the influence of volumetric energy density (VED) on the sample porosity, microstructure and mechanical properties was accurately studied. The obtained results reveal the stability of the microstructural and mechanical behaviour of the alloy for VEDs higher than 175 Jmm−3. In this way, an energy-and-time-saving choice at low VEDs can be taken for the LPBF production of Scalmalloy®. After identifying the low-power optimized process parameters, the effects of the heat treatment on the microstructural and mechanical properties were investigated. The results prove that low-VED heat-treated samples produced with an LPBF lab-scale machine can achieve outstanding mechanical performance compared with the results of energy-intensive industrial production. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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12 pages, 3070 KiB  
Article
Effect of SiC Nanoparticles on AZ31 Magnesium Alloy
by Murugan Subramani, Song-Jeng Huang and Konstantin Borodianskiy
Materials 2022, 15(3), 1004; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15031004 - 28 Jan 2022
Cited by 29 | Viewed by 3223
Abstract
Magnesium alloys are attractive for the production of lightweight parts in modern automobile and aerospace industries due to their advanced properties. Their mechanical properties are usually enhanced by the incorporation with reinforcement particles. In the current study, reinforced AZ31 magnesium alloy was fabricated [...] Read more.
Magnesium alloys are attractive for the production of lightweight parts in modern automobile and aerospace industries due to their advanced properties. Their mechanical properties are usually enhanced by the incorporation with reinforcement particles. In the current study, reinforced AZ31 magnesium alloy was fabricated through the addition of bulk Al and the incorporation of SiC nanoparticles using a stir casting process to obtain AZ31-SiC nanocomposites. Scanning electron microscope (SEM) investigations revealed the formation of Mg17Al12 lamellar intermetallic structures and SiC clusters in the nanocomposites. Energy dispersive spectroscopy (EDS) detected the uniform distribution of SiC nanoparticles in the AZ31-SiC nanocomposites. Enhancements in hardness and yield strength (YS) were detected in the fabricated nanocomposites. This behavior was referred to a joint strengthening mechanisms which showed matrix-reinforcement coefficient of thermal expansion (CTE) and elastic modulus mismatches, Orowan strengthening, and load transfer mechanism. The mechanical properties and wear resistance were gradually increased with an increase in SiC content in the nanocomposite. The maximum values were obtained from nanocomposites containing 1 wt% of SiC (AZ31-1SiC). AZ31-1SiC nanocomposite YS and hardness were improved by 27% and 30%, respectively, compared to AZ31 alloy. This nanocomposite also exhibited the highest wear resistance; its wear mass loss and depth of the worn surface decreased by 26% and 15%, respectively, compared to AZ31 alloy. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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11 pages, 2265 KiB  
Communication
Simulation of the Peritectic Phase Transition in Fe-C Alloys
by Hui Fang, Qianyu Tang, Qingyu Zhang, Yiming Fan, Shiyan Pan, Markus Rettenmayr and Mingfang Zhu
Materials 2022, 15(2), 537; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15020537 - 11 Jan 2022
Cited by 1 | Viewed by 1251
Abstract
In this work, a multi-phase cellular automaton (CA) model is extended for the quantitative simulation of peritectic phase transition. First, the effects of cooling rate/supersaturation and temperature on the peritectic transformation kinetics in Fe-C alloys are investigated by utilizing the present CA model. [...] Read more.
In this work, a multi-phase cellular automaton (CA) model is extended for the quantitative simulation of peritectic phase transition. First, the effects of cooling rate/supersaturation and temperature on the peritectic transformation kinetics in Fe-C alloys are investigated by utilizing the present CA model. The CA simulations show that supersaturations in the parent phases (liquid and δ-ferrite) increase the L/γ interface growth velocity remarkably, but tinily for the δ/γ interface migration velocity. There exists a transition supersaturation for isothermal transformations, at which the growth rates of the two interfaces are equal. The transition supersaturation is found to increase with decreasing temperature. Microstructural evolution at different cooling rates during peritectic transformation is simulated using the experimental conditions. At low cooling rates, the δ/γ interface propagates at a higher velocity than the L/γ interface. At high cooling rates, however, the γ-phase grows more into the L-phase with a cellular morphology. Then, the proposed CA model is applied to simulate the microstructural evolution during peritectic reaction. It is observed that the γ-phase propagates along the L/δ interface and finally encircles the δ-phase. Meanwhile, the intervenient γ-phase grows in thickness through peritectic transformation. The CA simulations are compared reasonably well with the experimental data and analytical calculations. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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14 pages, 5919 KiB  
Article
The Effect of Cold Swaging of Tungsten Heavy Alloy with the Composition W91-6Ni-3Co on the Mechanical Properties
by Paweł Skoczylas, Olgierd Goroch, Zbigniew Gulbinowicz and Andrzej Penkul
Materials 2021, 14(23), 7300; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14237300 - 29 Nov 2021
Cited by 6 | Viewed by 1625
Abstract
The paper presents the results of studies on the effects of heat treatment and cold-work parameters on the mechanical properties and microstructure of the tungsten heavy alloy (WHA) with the composition W91-6Ni-3Co. Tungsten heavy alloy (WHA) is used in conditions where strength, high [...] Read more.
The paper presents the results of studies on the effects of heat treatment and cold-work parameters on the mechanical properties and microstructure of the tungsten heavy alloy (WHA) with the composition W91-6Ni-3Co. Tungsten heavy alloy (WHA) is used in conditions where strength, high density, and weight are required. The material for testing as rod-shaped samples was produced by the method of powder metallurgy and sintering with the participation of the liquid phase and then subjected to heat treatment and cold swaging. The study compares the effect of degree deformation on the strength, hardness, microhardness, and microstructure of WHA rods. The conducted tests showed that heat treatment and cold-work allowed to gradually increase the strength parameters, i.e., tensile strength σuts, yield strength σys, elongation ε, hardness, and microhardness. These processes made it possible to increase the tensile strength by over 800 MPa (from the initial 600 MPa after sintering to the final value of over 1470 MPa after heat treatment with cold swaging deformation with reduction of 30%) and the hardness from 32 to 46 HRC. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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12 pages, 4181 KiB  
Article
Interface Joint Strength between SS316L Wrought Substrate and Powder Bed Fusion Built Parts
by Jason M. Weaver, John R. Linn and Michael P. Miles
Materials 2021, 14(11), 3041; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14113041 - 03 Jun 2021
Viewed by 1971
Abstract
Metal powder bed fusion (PBF) additive manufacturing (AM) builds metal parts layer by layer upon a substrate material. The strength of this interface between the substrate and the printed material is important to characterize, especially in applications where the substrate is retained and [...] Read more.
Metal powder bed fusion (PBF) additive manufacturing (AM) builds metal parts layer by layer upon a substrate material. The strength of this interface between the substrate and the printed material is important to characterize, especially in applications where the substrate is retained and included in the finished part. Ensuring that this interface between the original and the printed material has adequate material properties enables the use of this PBF AM process to repair existing structures and create new parts using both AM and conventional manufacturing. This paper studies the tensile and torsional shear strengths of wrought and PBF-built SS316L specimens and compares them to specimens that are composed of half wrought material and half PBF material. These specimens were created by building new material via PBF onto existing wrought SS316L blocks, then cutting the specimens to include both materials. The specimens are also examined using optical microscopy and electron backscatter diffraction (EBSD). The PBF specimens consistently exhibited higher strength and lower ductility than the wrought specimens. The hybrid PBF/wrought specimens performed similarly to the wrought material. In none of the specimens did any failure appear to occur at or near the interface between the wrought substrate and the PBF material. In addition, most of the deformation in the PBF/wrought specimens appeared to be limited to the wrought portion of the specimens. These results are consistent with optical microscopy and EBSD showing smaller grain size in the PBF material, which correlates to increased strength in SS316L due to the Hall–Petch relationship. With the strength at the interface meeting or exceeding the strength of the original wrought material, this process shows great promise as a method for adding additional features or repairing existing structures using metal PBF AM. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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15 pages, 11275 KiB  
Article
Mitigation of Galvanic Corrosion in Bolted Joint of AZ31B and Carbon Fiber-Reinforced Composite Using Polymer Insulation
by Jiheon Jun, Yong Chae Lim, Yuan Li, Charles David Warren and Zhili Feng
Materials 2021, 14(7), 1670; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14071670 - 29 Mar 2021
Cited by 7 | Viewed by 2423
Abstract
The use of polymer insulation to mitigate galvanic corrosion was examined for bolted joints of AZ31B Mg alloy and carbon fiber-reinforced composite. To assess the corrosion behaviors of bolted joints with and without polymer insulation, solution immersion and salt spray exposure (ASTM B117) [...] Read more.
The use of polymer insulation to mitigate galvanic corrosion was examined for bolted joints of AZ31B Mg alloy and carbon fiber-reinforced composite. To assess the corrosion behaviors of bolted joints with and without polymer insulation, solution immersion and salt spray exposure (ASTM B117) tests were conducted, and the corrosion depths and volumes were determined for the joint specimens after the tests. The polymer-insulated bolted joints exhibited much lower corrosion depths and volumes, highlighting the effective mitigation of galvanic corrosion. The reductions of joint strength in the post-corrosion joint specimens were relatively small (up to ~10%) in the polymer-insulated group but greater (up to 90%) in the group with no insulation. Cross-sectional characterization of post-corrosion joints with polymer insulation revealed local pits developed on AZ31B under galvanic influence, indicating that limited galvanic attack (that did not decrease the joining integrity significantly) could still occur during a long salt spray exposure (~1264 h) owing to the permeation of an aqueous corrosive medium. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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17 pages, 4819 KiB  
Article
Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations
by Baohui Zhu, Zhenzhen Chen, Yanfei Cao, Yanchang Liu, Xiuhong Kang, Yun Chen, Hongwei Liu, Paixian Fu, Yikun Luan and Dianzhong Li
Materials 2021, 14(4), 796; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14040796 - 08 Feb 2021
Cited by 5 | Viewed by 1674
Abstract
Channel segregation (CS) is the most typical defect during solidification of NbTi alloy. Based on numerical simulation and experimental characterizations, we deeply elucidated its characteristics, formation mechanism, effecting factor and prediction criterion. According to acid etching, industrial X-ray transmission imaging, 3D X-ray microtomography [...] Read more.
Channel segregation (CS) is the most typical defect during solidification of NbTi alloy. Based on numerical simulation and experimental characterizations, we deeply elucidated its characteristics, formation mechanism, effecting factor and prediction criterion. According to acid etching, industrial X-ray transmission imaging, 3D X-ray microtomography and chemical analysis, it was found that in a casing ingot, by He cooling, finer grain size, weaker segregation and slighter CS can be obtained compared with air-cooled ingot. The simulation results of macrosegregation show that CS is caused by the strong natural convection in the mushy zone triggered by the thermo-solutal gradient. Its formation can be divided into two stages including channel initiation and growth. In addition, due to the stronger cooling effect of the He treatment, the interdendritic flow velocity becomes smaller, consequently lowering the positive segregation and CS and improving the global homogenization of the final ingot. Finally, to predict the formation of CS, the Rayleigh number model was proposed and its critical value was found to be 15 in NbTi alloy for the first time. When it is lower than the threshold, CS disappears. It provides an effective tool to evaluate and optimize the solidification parameters to fabricate the homogenized NbTi ingot in engineering practice. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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14 pages, 14993 KiB  
Article
Microstructure and Mechanical Properties of Intercritically Treated Grade 91 Steel
by Yiyu Wang, Wei Zhang, Yong Chae Lim, Yanli Wang and Zhili Feng
Materials 2020, 13(18), 3985; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13183985 - 10 Sep 2020
Cited by 1 | Viewed by 1731
Abstract
Premature creep failures at the intercritical heat affected zone (ICHAZ) of creep-resistant steel weldments have been frequently reported. However, the creep degradation mechanism of different microstructure constituents in ICHAZ is complicated and needs further clarification. In this work, Grade 91 steel was intercritically [...] Read more.
Premature creep failures at the intercritical heat affected zone (ICHAZ) of creep-resistant steel weldments have been frequently reported. However, the creep degradation mechanism of different microstructure constituents in ICHAZ is complicated and needs further clarification. In this work, Grade 91 steel was intercritically heat-treated at a temperature (860 °C) between the critical temperatures AC1 and AC3, and a correlation between microstructure and mechanical properties of the heat-treated specimen was built. The effects of austenitization and tempering resulting from the intercritical treatment (IT) differentiated the local strain energies between the two microstructure constituents: newly transformed martensite (NTM) and over-tempered martensite (OTM). The formation of NTM grains led to a hardness increase from 247 HV0.5 in the base metal to 332 HV0.5 in the IT specimen. The ultimate tensile strength (UTS) increased from 739 MPa in the base metal to 1054 MPa in the IT specimen. Extensive growth of the OTM grains and rapid recovery of NTM grains took place simultaneously in the IT specimen during a typical tempering at 760 °C. These microstructure degradations led to a lowered hardness of 178 HV0.5, a reduced UTS of 596 MPa, and a poor creep resistance with a minimum creep strain rate of 0.49 %/h at 650 °C in an IT + tempering (ITT) specimen. Full article
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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