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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (10 November 2021) | Viewed by 27245

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Prof. Hyokyung Sung

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Gyeongsang National University, Jinju, South Korea

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Dear Colleagues,

The history of the alloy materials dates back to the Bronze Ages. From that point on, mankind has been trying to make alloys by combining metals with one or more other elements to obtain the desired mechanical properties. The demands for advanced materials have been emphasized to meet the increasing requirements of industry in the form of high-performance structural materials. Among ferrous alloys, high-Mn steels were recently highlighted for their excellent combination of strength and ductility, led by twinning-induced plasticity (TWIP) or transformation-induced plasticity (TRIP) behavior. For non-ferrous lightweight alloys, such as magnesium, aluminum, and titanium alloys, their mechanical properties have been improved by employing solid solution and precipitation hardening mechanisms. Moreover, recently developed high-entropy alloys (HEA) have suggested new concepts by which the random occupation of alloying elements in a crystalline structure can be understood.

Alloy design is the knowledge-based approach to develop new metal materials. Generally, more than a thousand types of metallic alloys are used for alloy design. When the alloy design is determined, the microstructure of the material is controlled through manufacturing methods. Nowadays, simulation modeling and artificial intelligence have been used for advanced alloy design, and powder metallurgy and additive manufacturing have been applied in advanced processing techniques. Electron backscatter diffraction (EBSD), X-ray diffraction, and transmission electron microscope (TEM) are the most effective methods used for microstructure characterization and texture analysis. Thus, microstructure associates the chemical composition and manufacturing process of materials to their mechanical properties. In this Special Issue, we will cover the subjects of alloy design, material processing, microstructure characterization, and mechanical properties (strength, ductility, toughness, fatigue resistance, etc.) of advanced alloy materials. In addition, articles dealing artificial intelligence materials and additive manufacturing are also welcome.

It is my pleasure to invite you to submit full papers, communications, and reviews related to “Advances in Alloy Materials”.

Prof. Hyokyung Sung
Guest Editor

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Keywords

alloy design
microstructure characterization
structural materials
mechanical properties
artificial intelligence
additive manufacturing

Published Papers (12 papers)

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Research

6 pages, 1395 KiB

Open AccessArticle

Effect of Sn and Mo on Microstructure and Electrochemical Property of TiZrTaNb High Entropy Alloys

by Qiaoyu Li, Tengfei Ma, Yuliang Jin, Xiaohong Wang, Duo Dong and Dongdong Zhu

Crystals 2021, 11(12), 1527; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11121527 - 07 Dec 2021

Cited by 3 | Viewed by 2135

Abstract

The effects of Sn and Mo alloying elements on the microstructure and electrochemical properties of TiZrTaNb high entropy alloys were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemistry. TiZrTaNb, TiZrTaNbMo and TiZrTaNbSn alloys with equal atomic ratio were prepared by the arc melting method. The results showed that the microstructure of the high entropy alloys was dendritic structure with single BCC structure. The addition of Mo and Sn elements promoted the growth of the dendritic structure and accelerated the interdendritic segregation of the TiZrTaNb alloy. The TiZrTaNbMo alloy exhibited excellent corrosion properties compared to TiZrTaNb and TiZrTaNbSn alloys based on corrosion parameters I_corr, φ_corr, I_pass. The corrosion mechanism is discussed based on the corrosion morphology. The alloying elements have an important effect on the microstructure and electrochemical properties of a high entropy alloy. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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11 pages, 4796 KiB

Open AccessArticle

The Influence of Ni-Added Fe-Based Pre-Alloy on Microstructure Evolution and Lifetime Extension of Diamond Tools

by Juan Pu, Yubo Sun, Weimin Long, Mingfang Wu, Dashuang Liu, Sujuan Zhong and Songbai Xue

Crystals 2021, 11(11), 1427; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11111427 - 21 Nov 2021

Cited by 1 | Viewed by 1457

Abstract

Diamond tools were prepared by sintering Fe-Cu-Sn-Zn-Ni pre-alloyed powders and diamonds. The effects of Ni contents in pre-alloyed powders on microstructure evolution of Fe-based matrix, the properties of Fe-based matrix and the service life of diamond tools were investigated. The results showed that adding 3~15 wt.% Ni into the Fe-Cu-Sn-Zn pre-alloyed powders refined the microstructure of the Fe-based matrix and improved its density and hardness gradually. The addition of Ni reduced the loss of low melting liquid phase at a low sintered temperature, thus resulting in a decrease of the pores, an increase of the density and hardness of Fe-based matrix. When the Ni content is less than 9 wt.%, the bending strength of Fe-based matrix and diamond tools, together with the holding force of Fe-based matrix to diamonds increases sharply. They reached up to the optimal value with the Ni content of 9 wt.%. At this sintering powder ratio, the sufficient Fe-Cu-Sn-Zn-Ni liquid phase had a good wettability on the surface of diamonds, thus the optimal performance of sintered matrix and diamond tools was obtained. The service life of diamond tools was prolonged greatly owing to the excellent bonding capacity between matrix and diamonds. Once the Ni content exceeded 9 wt.%, the corresponding value decreased gradually. The fracture morphologies of the matrix changed from the brittle fracture into brittle-ductile fracture, then ductile fracture (with the Ni content of 9 wt.%), brittle-ductile mixed fracture and brittle fracture. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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11 pages, 13150 KiB

Open AccessArticle

Kappa Carbide Precipitation in Duplex Fe-Al-Mn-Ni-C Low-Density Steel

by Jaka Burja, Barbara Šetina Batič and Tilen Balaško

Crystals 2021, 11(10), 1261; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11101261 - 18 Oct 2021

Cited by 2 | Viewed by 2173

Abstract

The microstructural evolution of a Fe-Mn-Al-Ni-C low-density steel was studied. The lightweight low-density steels are a promising material for the transportation industry, due to their good mechanical properties and low density. The base microstructure of the investigated steel consists of ferrite and austenite. Thermo-Calc calculations showed the formation of an ordered BCC (body-centred cubic) B2 phase below 1181 °C and kappa carbides below 864 °C. The steel was produced in a vacuum induction furnace, cast into ingots and hot forged into bars. The forged bars were solution annealed and then isothermally annealed at 350, 450, 550, 650, 750, and 850 °C. The microstructure of the as-cast state, the hot forged state, solution annealed, and isothermally annealed were investigated by optical microscopy and scanning electron microscopy. The results showed the formation of kappa carbides and the ordered B2 phase. The kappa carbides appeared in the as-cast sample and at the grain boundaries of the isothermally annealed samples. At 550 °C, the kappa carbides began to form in the austenite phase and coarsened with increasing temperature. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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11 pages, 4265 KiB

Open AccessArticle

Effect of Interdendritic Precipitations on the Mechanical Properties of GBF or EMS Processed Al-Zn-Mg-Cu Alloys

by Sangeun Park, Saif Haider Kayani, Hyungrae Kim, Im Doo Jung, N.S. Reddy, Kwangjun Euh, Jae Bok Seol, Jung Gi Kim and Hyokyung Sung

Crystals 2021, 11(10), 1162; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11101162 - 24 Sep 2021

Cited by 4 | Viewed by 2700

Abstract

The effects of nanoprecipitations on the mechanical properties of Al-Zn-Mg-Cu alloys after GBF (gas bubbling filtration) and EMS (electromagnetic stirring) casting were investigated. Dendritic cell structures were formed after GBF processing, while globular dendritic structures were nucleated after EMS processing. Equiaxed cell sizes were smaller in the EMS-processed specimens compared to the GBF-processed specimens, confirmed by EBSD (electron backscatter diffraction) analysis. Nanoprecipitations of η′ phases inside of dendrites were observed by TEM (transmission electron microscope), and other Fe-bearing compounds were located in the dendritic boundaries. The yield strength of the T4 and T6 heat-treated specimens was close to 400 MPa and 500 MPa, respectively. Fractographic analysis was performed to investigate the effect of precipitations on tensile fracture. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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16 pages, 3577 KiB

Open AccessArticle

Numerical Alloy Development for Additive Manufacturing towards Reduced Cracking Susceptibility

by Benjamin Wahlmann, Dominik Leidel, Matthias Markl and Carolin Körner

Crystals 2021, 11(8), 902; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11080902 - 31 Jul 2021

Cited by 7 | Viewed by 3035

Abstract

In this work, we investigated the viability of established hot cracking models for numerically based development of crack-resistant nickel-base superalloys with a high γ′ volume fraction for additive manufacturing. Four cracking models were implemented, and one alloy designed for reduced cracking susceptibility was deduced based on each cracking criterion. The criteria were modeled using CALPHAD-based Scheil calculations. The alloys were designed using a previously developed multi-criteria optimization tool. The commercial superalloy Mar-M247 was chosen as the reference material. The alloys were fabricated by arc melting, then remelted with laser and electron beam, and the cracking was assessed. After electron beam melting, solidification cracks were more prevalent than cold cracks, and vice versa. The alloys exhibited vastly different crack densities ranging from 0 to nearly 12 mm⁻¹. DSC measurements showed good qualitative agreement with the calculated transition temperatures. It was found that the cracking mechanisms differed strongly depending on the process temperature. A correlation analysis of the measured crack densities and the modeled cracking susceptibilities showed no clear positive correlation for any crack model, indicating that none of these models alone is sufficient to describe the cracking behavior of the alloys. One experimental alloy showed an improved cracking resistance during electron beam melting, suggesting that further development of the optimization-based alloy design approach could lead to the discovery of new crack-resistant superalloys. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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9 pages, 38613 KiB

Open AccessArticle

Significant Improvement of Strength in Wrought 945A Ni-Based Superalloy by Aging Treatment

by Haiding Liu, Dongzhe Wang, Linping Zhou, Jia She and Wei Wu

Crystals 2021, 11(6), 627; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11060627 - 31 May 2021

Cited by 1 | Viewed by 2106

Abstract

Ni-based superalloys have attracted much attention due to their good resistance to high-temperature and -pressure environments. Compared with the traditional 718 Ni-based superalloy, 945A Ni-based superalloy with a lower Ni content showed better performance in terms of precipitated hardening and corrosion resistance. In this study, the aging behavior and the evolution of mechanical properties of the wrought 945A Ni-based superalloy were investigated. Microstructures were analyzed by scanning electron microscopy (SEM), bright field transmission electron microscopy (TEM), high-resolution TEM and high-angle annular dark field scanning TEM. Mechanical properties were measured by tensile and compressive tests. The results illustrated that the compressive yield stress was significantly improved by increasing aging time from 229 to 809 MPa. The increase was greater than 220%. This improvement was mainly attributed to the precipitates of the

γ'

phase and carbides during the aging treatment. The residual dislocations generated by the plastic processes stimulated the formation of these precipitates. The precipitation behavior and the strengthening mechanism are discussed in detail. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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13 pages, 4274 KiB

Open AccessArticle

Determination of Al-2.18Mg-1.92Li Alloy’s Microstructure Degradation in Corrosive Environment

by Franjo Kozina, Zdenka Zovko Brodarac, Sandra Brajčinović and Mitja Petrič

Crystals 2021, 11(4), 338; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11040338 - 27 Mar 2021

Viewed by 1762

Abstract

The utilization of aluminum-lithium-magnesium (Al-Li-Mg) alloys in the transportation industry is enabled by excellent engineering properties. The mechanical properties and corrosion resistance are influenced by the microstructure development comprehending the solidification of coherent strengthening precipitates, precipitation of course and angular equilibrium phases as well as the formation and widening of the Precipitate-free zone. The research was performed to determine the microstructure degradation of Al-2.18Mg-1.92Li alloy in a corrosive environment using electrochemical measurements. The solidification sequence of the Al-2.18Mg-1.92Li alloy, obtained using Thermo–Calc software support, indicated the transformation of the α_Al dendritic network and precipitation of AlLi (δ), Al₂LiMg (T), and Al₈Mg₅ (β) phase. All of the phases are anodic with respect to the α_Al enabling microstructure degradation. To achieve higher microstructure stability, the sample was solution hardened at 520 °C. However, the sample in as-cast condition showed a lower corrosion potential (−749.84 mV) and corrosion rate (17.01 mm/year) with respect to the solution-hardened sample (−752.52 mV, 51.24 mm/year). Higher microstructure degradation of the solution-hardened sample is a consequence of δ phase precipitation at the grain boundaries and inside the grain of α_Al, leading to intergranular corrosion and cavity formation. The δ phase precipitates from the Li and Mg enriched the α_Al solid solution at the solution-hardening temperature. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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8 pages, 1394 KiB

Open AccessArticle

Magnetic Phase Transition, Elastic and Thermodynamic Properties of L1₂-(Ni,Cu)₃(Al,Fe,Cr) in 3d High-Entropy Alloys

by Li Ma, Zhi-Peng Wang, Guo-Hua Huang, Jin-Li Huang, Ping-Ying Tang and Tou-Wen Fan

Crystals 2020, 10(12), 1102; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10121102 - 02 Dec 2020

Cited by 1 | Viewed by 1780

Abstract

The phase stability and elastic properties of paramagnetic (PM), ferromagnetic (FM) and antiferromagnetic (AFM) phases in L1₂-(Ni,Cu)₃(Al,Fe,Cr) alloy are first investigated using the exact muffin-tin orbitals (EMTO) method in combination with the coherent potential approximation (CPA). The result shows the AFM structure phase of the three is the most stable in the ground state. Calculated elastic constants show that all the phases are mechanically stable, and have uncovered that L1₂-(Ni,Cu)₃(Al,Fe,Cr) can achieve good strength and ductility simultaneously. Then, crucial thermal properties are described satisfactorily using the Debye–Grüneisen model, showing heat capacity, Gibbs free energy G, the competitive contribution of entropy −TS and enthalpy H exhibiting significant temperature dependences. Moreover, the magnetic phase transition thermodynamics was studied, which suggests that −TS has a primary contribution to Gibbs free energy and may play a key role in the phase transition. The present results can benefit the understanding of the mechanical, thermodynamic and magnetic properties of the L1₂ structure phase in 3d high-entropy alloys. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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12 pages, 7800 KiB

Open AccessArticle

Application of Hydride Process in Achieving Equimolar TiNbZrHfTa BCC Refractory High Entropy Alloy

by Bhupendra Sharma, Kentaro Nagano, Kuldeep Kumar Saxena, Hiroshi Fujiwara and Kei Ameyama

Crystals 2020, 10(11), 1020; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10111020 - 09 Nov 2020

Cited by 6 | Viewed by 2113

Abstract

For the first time, an equiatomic refractory high entropy alloy (RHEA) TiNbZrHfTa compact with a single-phase body-centered cubic (BCC) structure was fabricated via a titanium hydride (TiH₂) assisted powder metallurgy approach. The constituent pure Ti, Zr, Nb, Hf, and Ta powders were mechanically alloyed (MA) with titanium hydride (TiH₂) powder. The resultant MA powder was dehydrogenated at 1073 K for 3.6 ks and subsequently sintered through spark plasma sintering (SPS). Additionally, TiNbZrHfTa counterparts were prepared from pure elements without MA with TiH₂. It was observed that the compact prepared from pure powders had a chemically heterogeneous microstructure with hexagonal close packed (HCP) and dual BCC phases. On the other hand, despite containing many constituents, the compact fabricated at 1473 K for 3.6 ks via the hydride approach had a single-phase BCC structure. The Vickers microhardness of the TiNbZrHfTa alloy prepared via the hydride process was Hv 520 (±30). The exceptional microhardness of the alloy is greater than any individual constituent, suggesting the operation of a simple solid-solution-like strengthening mechanism and/or precipitation hardening. In addition, the heat treatments were also carried out to analyze the phase stability of TiNbZrHfTa prepared via the hydride process. The results highlight the substantial changes in the phase as a function of temperature and/or time. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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13 pages, 2780 KiB

Open AccessArticle

Effects of Mg Content on the Microstructural and Mechanical Properties of Al-4Cu-xMg-0.3Ag Alloys

by Talal T. Alshammari, Hamad F. Alharbi, Mahmoud S. Soliman and Muhammad F. Ijaz

Crystals 2020, 10(10), 895; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10100895 - 02 Oct 2020

Cited by 6 | Viewed by 2140

Abstract

The aim of the present research is to manipulate the amenability between composition-microstructure-property relationships in two kinds of Al-4Cu-xMg-0.3Ag alloys (where x = 0.4 and 1.4) having different Cu/Mg ratios (~9.54 and ~2.87). The effect of artificial ageing (T6) on the precipitation hardening behavior and resulting mechanical properties were also assessed and compared to two different scenarios of composition. Experimental results revealed that the modification in Magnesium concentration from 0.4 to 1.4 wt.% has a marked effect in increasing the micro hardness, ultimate tensile stress, and elongation of the alloy. Based on the microstructural analysis, the enhancement in mechanical properties was explained and addressed by considering the dual role of Mg content in the base alloy. On one hand, a large size of Mg atom produces a solid solution hardening effect, while on the other hand, a high content of Mg further promotes the formation of second phase S-type precipitate (Al₂CuMg) with various mixed morphologies. This unraveling co-precipitation phases within the matrix provide an obstacle for the dislocation glide thereby increasing mechanical strength and strain hardenability. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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12 pages, 3672 KiB

Open AccessArticle

Study on the Softening Behavior of Cu–Cr–In Alloy during Annealing

by Yunqing Zhu, Linsheng Tang, Weibin Xie, Huiming Chen, Hang Wang and Bin Yang

Crystals 2020, 10(4), 312; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10040312 - 17 Apr 2020

Cited by 3 | Viewed by 2056

Abstract

The softening behavior of a cold-drawn Cu–Cr–In alloy was investigated during annealing between 450 °C and 700 °C. The properties and microstructure evolution of the alloy were characterized using a microhardness tester, electron back-scatter diffraction, and transmission electron microscopy. Elemental In addition was found to hinder the dislocation movement and delay the recovery and recrystallization of the Cu–Cr–In alloy. The experimental data were analyzed using the Johnson–Mehlv–Avramiv–Kolmogorov model. The activation energy of recrystallization of the 60% cold-drawn Cu0.54Cr0.17In alloy was 188.29 ± 18.44 kJ/mol, and the recrystallization mechanism of the alloy was attributed mainly to Cu self-diffusion. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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16 pages, 5045 KiB

Open AccessArticle

Manufacturing of Ti-6%Al and Ti-6%Al-4%V Alloys and Their Corrosion in Sodium Chloride Solutions

by Hany S. Abdo, El-Sayed M. Sherif and Hamed A. El-Serehy

Crystals 2020, 10(3), 181; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10030181 - 07 Mar 2020

Cited by 10 | Viewed by 2382

Abstract

The current research aims at the manufacturing of Ti-6%Al alloy and Ti-6%Al-4%V alloy using the mechanical alloying method and studying their corrosion behavior after various periods of immersions in 3.5% NaCl solutions. The fabricated alloys were also evaluated using spectroscopic techniques such as X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy analyses. The corrosion behavior was studied using potentiodynamic polarization, electrochemical impedance spectroscopy, and chronoamperometric current-time electrochemical methods. It is confirmed that the presence of 4% V greatly decreases the uniform corrosion of the Ti-6%Al alloy as a result of the role of V in decreasing the cathodic, anodic, and corrosion current, and the rate of corrosion along with increasing the corrosion resistance. Increasing the time of immersion to 24 h and further to 48 h highly decreased the corrosion of the alloys. The presence of 4% V and extending the time of exposure thus increase the resistance against corrosion via decreasing the corrosion of Ti-6%Al alloy in the chloride test solution. Full article

(This article belongs to the Special Issue Advance in Alloy Materials)

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