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Abstract: A series of cost effective Co-free Al x CrCuFeNi2 high entropy alloys were developed, following the valence electron concentration rule. The solidification microstructure in these alloys showed some anomalies that were rarely seen in other high entropy alloys or multi-component alloys. Specifically, submicron rod-like microstructures existed in the eutectic alloy in spite of the high volume percentage of the rod-like phase; sunflower-like microstructures existed in the hyper-eutectic alloys, with 200nm sized spinodal decomposed seed particles densely distributed in the disk floret. [Copyright &y& Elsevier]

The microstructural features and micromechanical behavior of individual phases in a cast Al0.8CoCrCuFeNi high-entropy alloy (HEA) were characterized by high-resolution scanning electron microscopy and micro-compression tests. Use of neutron diffraction enabled the detection of a new phase which was otherwise unobservable by conventional X-ray diffraction. The identified phase constitution agreed well with the compositional analysis and the micro-compression results. The delicate microscale characterization of individual phase provides new insights for the design of novel HEAs with desirable mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, a viable way to fabricate Mg alloy sound ribbons with ultra-fine-grained microstructure was presented. The hot-rolled and annealed Mg-0.4Zn (at%) alloy exhibited excellent rollability to form sound ribbons with submicrometer grains when subjected to one-pass cold rolling process. The more balanced multi-mode dislocation slips originated from the significant decrease of critical resolved shear stress for non-basal slip with the addition of solute Zn and the favorable crystallographic orientation were suggested to be responsible for the excellent cold rollability. The formation of ultra-fine-grained microstructure was attributed to low-temperature dynamic recrystallization occurring during the cold rolling process with large strain. [ABSTRACT FROM AUTHOR]

• CoCrFeMoNi alloys were prepared by vacuum arc-melting from pure elements. • The validity of new PHACOMP method for high-entropy alloys are verified. • New PHACOMP method can be used to evaluate thermal stability of high-entropy alloy. • The designed CoCrFeMoNi high-entropy alloys show competitive corrosion resistance with commercial alloy. [Display omitted] Various methods can be used to predict the phase composition of conventional alloys. However, it is relatively difficult to predict high-entropy alloys (HEAs) owing to their complexity. There remain many challenges in designing HEAs with desirable properties. In this study, two strategies were applied to design corrosion-resistant non-equal-molar CoCrFeMoNi HEAs with a single phase. The two strategies were prediction for valence electron concentration dependent structural behavior to evaluate the matrix of HEAs, and average d -orbital energy level ( M ̅ d) that was initially used to predict precipitation in superalloys under different temperatures. The validity of these two approaches was determined by thermal stability. The corrosion behaviors of the designed HEAs were investigated by polarization tests. In conclusion, the phase compositions of CoCrFeMoNi HEAs were predicted using a combination of the two approaches. The corrosion resistance was also competitive compared to that of Hastelloy C276. This research can provide a reference for the future development of corrosion-resistant HEAs with a single phase. [ABSTRACT FROM AUTHOR]

Abstract: An Al–10Ni–8Y (at.%) alloy was atomized by Ar gas and the morphology, microstructure, thermal stability, phase composition and microhardness of the as-atomized powder were investigated. Most of the powders are spherical in shape, but the surface morphology was different for powder of different size. The cross-section microstructure of powder with size below 15μm in diameter showed no detailed feature, indicating existence of amorphous phase or nanocrystalline structure. The as-atomized powder showed four distinct exothermic peaks when heated at 296, 340, 366 and 456°C. The glass transition temperature T g, crystallization temperature T x , and the temperature interval of the supercooled liquid region ΔT x (=T x −T g) were detected to be about 266, 288 and 22°C. The Al82Ni10Y8 alloy powder exhibits a high Vickers hardness of 230.6, and shows great potential for structural application. [Copyright &y& Elsevier]

Eutectic high-entropy alloys (EHEAs), as a sub-group of high-entropy alloys (HEAs), are becoming a new research hotspot in the metallic materials community because of their excellent castability, fine and uniform microstructures even in the as-cast state, high strength, and good ductility. Some of the EHEAs have shown promising potentials for industrial applications. Here, the history, interesting solidification microstructure and mechanical properties, and the design strategy of EHEAs are reviewed, and their future prospects are outlined. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • Low temperature superplasticity was obtained in a nanostructured microalloyed steel. • Tensile condition of 500 °C and 0.00005 s−1 led to a superhigh elongation of 202%. • Equiaxed ferrite kept high angle boundaries and absent of dislocations after strain. • Grain boundary sliding was the dominant mechanism of superplasticity. • Low temperature superplasticity was highly strain rate and temperature dependent. Abstract The low temperature plasticity behavior of a nanostructured microalloyed steel was studied at varied deformation temperatures and strain rates. Tensile condition of 500 °C (0.33 melting point) and 0.00005 s−1 led to superplastic flow with a low peak stress of 140 MPa and a high elongation of 202%. The ultra-fine equiaxed ferrite kept high misorientation grain boundaries and absent of dislocations subjected to superplastic strain, accounted for grain boundary sliding mechanisms. Slip deformation was required at strain rate of 0.00025 s−1 or deformation temperature of 450 °C based on a relatively high dislocation density. Low temperature superplasticity in NG/UFG steel was highly strain rate and temperature dependent. [ABSTRACT FROM AUTHOR]

Abstract Novel Fe 68 (MoWCrVCoNiAlCu) 32 (at.%) medium-entropy high-speed steel (ME-HSS) coatings, containing various carbon contents from 0.65 to 1.05 wt%, are prepared by laser rapid solidification. The newly prepared ME-HSS coatings are characterized by a hard martensitic matrix enhanced by secondary hardening, and specifically by coherent nano-sized M 2 C. The secondary hardening effect is enhanced with the increasing carbon content. The high amount of alloying elements in ME-HSS coatings results in excellent oxidative wear resistance, without leading to serious compositional segregation and coarsening of carbides. Graphical abstract Microstructure and hardness variation of novel Fe 68 (MoWCrVCoNiAlCu) 32 medium-entropy high-speed steel (ME-HSS) coatings with different C content: 0.65 wt%C (ME-HSS-065C), 0.85 wt%C(ME-HSS-085C) and 1.05 wt%C(ME-HSS-105C). Unlabelled Image Highlights • New medium-entropy high speed steel coatings exhibit excellent hot wear resistance • Secondary hardening due to coherent nano-sized M 2 C contributes to the high hardness • The secondary hardening is enhanced with the increasing C content • The C content needs to be optimized for high hardness and good hot wear resistance [ABSTRACT FROM AUTHOR]

• A crack-free AlCoCuFeNi was fabricated by spark plasma sintering and hot roling. • The specimen consisted of BCC, FCC, nano-sized L1 2 , and Al 2 O 3 phases. • The specimen possessed good anti-wear ability and good corrosion resistance. In this work, a high hardness, crack-free AlCoCuFeNi high-entropy alloy with good corrosion resistance was successfully produced by spark plasma sintering at 1000℃ and 30 MPa for 10 min, followed by hot rolling to a thickness reduction of 10 % after holding at 600℃ for 30 min. The microstructure of the alloy was composed of fine equiaxed grains of (Fe, Co, Ni, Al)-enriched BCC, Cu-enriched FCC, nano-sized L1 2 , and Al 2 O 3 phases. The maximum texture index of the material is only 1.53, indicating a low anisotropy. The alloy possessed a high hardness (599 HV), a low friction coefficient (0.1), and a low corrosion current density (1.13 μA/cm2), implying both good wear and corrosion resistance. In addition, the creep mechanism was found to be grain boundary sliding. [ABSTRACT FROM AUTHOR]

The present work is focused on synthesis and heat treatment on non-equiatomic AlCoCrFeNiTi 0.5 high entropy alloy (HEA) with a composite structure reinforced by TiC nanoparticles. The initial alloy was prepared by mechanical alloying (MA) in a planetary ball mill, compacted by spark plasma sintering (SPS) and heat treated at different temperatures. Mechano-chemical reactions during the MA process as well as the microstructure and hardness of the SPS-ed compacts prior to and after the heat treatment were investigated. During MA, Cr-based supersaturated solid solution with the BCC structure was formed. After SPS at 1100 °C, the BCC solid solution decomposed into nano-grained microstructure consisting of FCC and ordered BCC solid solutions, σ phase, and in-situ formed TiC nanoparticles. The high hardness of the alloy (762 HV) was retained after the subsequent heat treatment at 1100 °C (603 HV). It was shown that the fabrication of TiC reinforced nanocomposites from elemental powders without the use of expensive nanograined powders can be achieved. [ABSTRACT FROM AUTHOR]

In the present study, we have carried out controlled rolling followed by accelerated cooling to explore the microstructure and mechanical properties of Ti, Ti–Mo, and Ti–B microalloyed steels. The objective was to enhance the yield strength of Ti-bearing steel and simultaneously obtain good ductility and toughness. The microstructure of Ti and Ti–Mo steels consisted of polygonal ferrite and the effective grain size was reduced from 5.6 μm in Ti-bearing steel to 4.3 μm in Ti–Mo microalloyed steel, accompanied by increase in dislocation density. The microstructure of Ti–B steel was acicular ferrite with lath width in the range of ~0.2–0.4 μm. The density of precipitates of 3–5 nm size was high in all the three steels. Both strength and low temperature toughness were increased on microalloying with 0.09 wt% Mo. In steel, containing 0.002 wt% B, the yield strength was increased by ~105 MPa, and high impact energy of 53.2 J at −40 °C was obtained. The impact energy was decreased to 14.3 J at −60 °C because free-B segregated to prior austenite grain boundaries and significantly deteriorated the low temperature toughness. The evolution of fracture surface with temperature was consistent with impact energy. [ABSTRACT FROM AUTHOR]

Changes in the microstructure and mechanical properties during annealing at 800 °C have been characterized in a 90% cold-rolled AlCoCrFeNi 2.1 eutectic high-entropy alloy containing the FCC and B2 (ordered BCC) phases. In the as-rolled condition, the FCC phase is found to contain a high frequency of finely spaced deformation-induced boundaries, which provides a high driving force for recrystallization within this phase. Quantitative analysis of electron backscatter diffraction data from the annealed samples indicates that recrystallization progresses faster in the FCC phase than in B2 regions. Although recrystallization leads to substantial coarsening of the microstructure, the average recrystallized grain size remains in the submicron range even after 2 h at 800 °C. Tensile test data demonstrate that combinations of high yield strength and good ductility are obtained in partially recrystallized samples produced by annealing for 2.5–10 min. However, the work-hardening capacity of each annealed sample is lower than that of the cold-rolled sample. Furthermore, for the samples annealed for at least 5 min a yield drop is observed soon after the onset of plastic deformation. Analysis of the microstructure and mechanical behavior in several annealed AlCoCrFeNi 2.1 samples indicates a clear correlation between the magnitude of the yield drop and the recrystallized fraction. The mechanical behavior of the AlCoCrFeNi 2.1 alloy studied in this work is compared with that reported in previous publications. [ABSTRACT FROM AUTHOR]

Abstract: Fabricating nanoporous bulk thermoelectric (TE) materials with periodically arranged nanopores is highly challenging and expensive, although TE materials exhibit high power factors (α 2 σ) and low thermal conductivities (κ). Enhanced TE performance via randomly arranged nanopores is demonstrated with a YbZn2Sb2 nanoporous material (nPM) fabricated by a combination of melt quenching and two stage spark plasma sintering in less than 10h. Measurement of the electrical conductivity, Hall mobility, Seebeck coefficient, and thermal conductivity show that simultaneously enhancing α 2 σ and reducing κ can realize in the YbZn2Sb2 nPM with randomly arranged nanopores about 50–200nm in diameter. Compared with YbZn2Sb2 dense bulk materials (dBM) fabricated by a conventional method taking more than 180h, α 2 σ at 300K increases by 122%, κ at 300K decreases by 29%, and the maximum ZT value at 775K reaches 0.67, increasing by 46% for the nPM725 sample. This work shows that a periodic arrangement of nanopores is not essential for the fabrication of attractive TE materials, which offers a wider approach to nanostructure engineering to improve TE performance. [Copyright &y& Elsevier]

The microstructure and orientation relationships in five AlCoCrFeNi x alloys with eutectic (x = 2.1) and near-eutectic compositions (x = 1.9, 2.0, 2.2 and 2.3) have been characterized in this work. The eutectic and near-eutectic AlCoCrFeNi x alloys have microstructures consisting of face-centered cubic (FCC) and ordered body-centered cubic (BCC) B2 phases, where the volume fraction of the FCC phase is found to increase with increasing Ni content. It is found that each eutectic colony consists of several parallel lamellae in the colony center and peripheral irregular labyrinth-like structures. The frequency of the irregular structures appears to be higher in the near-eutectic alloys than in the eutectic alloy. The ratio of the average widths of FCC and BCC lamellae is observed to be sensitive to the chemical composition and increases with the increasing Ni content. The two phases in the studied alloys display relationships close to the Kurdjumov-Sachs orientation relationship. The distribution of misorientation angles between the interphase boundaries changes as a function of the Ni content. The result of this change is a small increase in the average misorientation angle across the FCC/BCC interphase boundaries with increasing Ni content. The differences in the morphological crystallographic characteristics between the alloys are briefly discussed. • Microstructure and orientation relationship are investigated in near-eutectic HEAs. • each eutectic colony consists of regular parallel lamellae and irregular structures. • Ratio of the widths of FCC and BCC lamellae increases with increasing Ni content. • Two phases in all alloys display the Kurdjumov-Sachs orientation relationship. • Misorientation angle across interphase boundaries increases at higher Ni content. [ABSTRACT FROM AUTHOR]

The state-of-the-art metallic biomaterials are 316L, CoCrMo and Ti6Al4V but they all suffer from known issues relating to biocompatibility, wear resistance and corrosion resistance. Therefore, there is always the motivation to identify novel superior metallic biomaterials to 316L, CoCrMo and Ti6Al4V. The concept of refractory high-entropy alloys (RHEAs) provides an interesting research direction towards developing novel metallic biomaterials, initially because RHEAs consist of purely biocompatible elements, but a systematic study of the performance of RHEAs targeting biomedical applications, while comparing to that of the state-of-the-art 316L, CoCrMo and Ti6Al4V, was not existing before and constitutes the theme of the current work. Two exemplary RHEAs that are studied in detail in this work, TiZrTaHfNb and Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 , show highly promising characteristics as novel superior metallic biomaterials in that they possess a desirable combination of wear resistance, wettability and pitting and general corrosion resistance, outperforming 316L, CoCrMo and Ti6Al4V almost in all these important aspects. In addition, it is also shown in this work that how appropriate alloying in RHEAs can be utilized to fine-tune their performance as better metallic biomaterials, such as the correlation between lattice strain and corrosion resistance. Image 1 • As-cast TiZrTaHfNb and Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 were composed of a single BBC phase. • Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 showed lower lattice strain than TiZrTaHfNb. • RHEAs exhibited higher H and E ratios compared to 316L, CoCrMo and Ti6Al4V. • TiZrTaHfNb and Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 revealed no pitting effect. • Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 has more resistance of barrier oxide than TiZrTaHfNb. [ABSTRACT FROM AUTHOR]