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Two classes of new materials, i.e. high entropy alloys (HEAs) and metallic nanocomposites offer processing related challenges, while showing significant promise for an array of ...technological applications requiring wear and irradiation resistance. This review addresses those challenges together with microstructure-property correlations. In particular, the main focus of this review is to demonstrate the efficacy of the superfast densification route, i.e., spark plasma sintering (SPS) as an effective consolidation route for these two classes of materials.
To start with, this review will critically analyze the influence of conventional solidification on the microstructure and property of Cu-based bearing alloys. Using nanocrystalline Cu-Pb and Cu-Pb-TiB2, Cu-Pb-cBN (cubic boron nitride) as model systems, various aspect of the microstructure-property correlation and enhancement of the tribological properties will be highlighted. A thorough understanding of the processing related issues and stability of the nanoscale/ultrafine microstructure obtained via SPS will be illustrated.
A significant part of this review will further discuss the development of novel nanostructured HEAs and HEA-based composites for wear and irradiation resistance applications. The efficacy of SPS route to prepare bulk HEAs with high sinter density will be demonstrated, together with property enhancement in single phase and two-phase HEAs. HEA-based nanocomposites containing soft metallic dispersoids (Bi, Pb, Ag) and ceramic lubricating phases (MoS2, CaF2/BaF2) for wear resistance application will be highlighted. Finally, oxide dispersed and refractory HEAs via MASPS route for irradiation resistance application will be discussed to elucidate the effective usage of the design and development of HEAs for technologically critical applications.
Single-phase equiatomic face centre cubic based MnFeCoNiCu multi principle multi-component high entropy alloy was subjected to thermo-mechanical processing followed with state of the art ...microstructural and mechanical characterization and crystal plasticity simulations to establish the complete processing-microstructure-texture-property paradigm for the newly developed alloy. A characteristic Brass type texture with strong {110} Goss and {110}<11¯2> Brass component was observed in 90% cold rolled sample. Microstructure of the deformed sample was characterized by absence of twinning for different rolling reductions and micro-scale shear bands were observed in the 90% rolled sample. Annealing treatment at 1173K for different duration showed negligible change in texture and completely recrystallized microstructure with annealing twins was observed. Hardness and tensile test indicated high strength for the rolled sample and lower strength with higher ductility was observed for the annealed samples. The unique Goss-Brass deformation texture is explained on the basis of operation of partial {111}<112¯> slip along with conventional {111}<11¯0> octahedral slip by crystal plasticity simulations. The operation of partial slip is attributed to short range ordering in the solid solution alloy which contributes to planar character of slip and leads to Goss-Brass deformation texture. The deformation texture is retained on recrystallization due to insignificant driving force for formation of nuclei of particular orientation and sluggish diffusion during recrystallization.
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The design and development of single phase multi-component high entropy alloy (HEA) using conventional hit and trial method is a challenging job due to the large number of experimental trials ...required to find the right alloy composition from possible combinations of various alloying elements in the multi-component system. Present investigation reports a novel CALculation of PHAse Diagram (CALPHAD) based approach, which can significantly reduce number of experimental trials in a very time effective manner to find single phase HEAs. Here, 1287 equiatomic five-component alloy systems were studied using both parametric and CALPHAD approaches to find single phase fcc and bcc HEAs. The parametric approach reduced the number of trials to 124 whereas; CALPHAD approach reduced the number of alloy compositions to 10. Further, the experimental investigation on the 10 alloy systems reveals that six of them form single phase HEAs. In addition, Thermo-Calc software was also used effectively to draw the isothermal pseudo ternary sections at 1000 K varying all constituents elements from 5 to 35 atomic percent for the CoCuFeMnNi alloy system. Experimental evidences confirmed that the isothermal pseudo ternary diagrams are very useful to design non equiatomic single phase as well as multiphase HEAs in the absence of phase diagram for the five component systems.
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•CALPHAD is effectively used to develop a method to design single phase HEAs with minimum effort.•Only nine experimental trials produce five brand new single phase equiatomic HEAs.•Pseudo isothermal ternary diagram is drawn to design non-equiatomic HEAs.•Success rate in design of HEAs is 60%.
The preparation of aluminium nanoparticles in large quantity is a challenge for most of the synthesis processes available. The present investigation reports a top down approach, known as cryomilling ...to synthesize large quantity of aluminium nanoparticles (Al NPs). The cryomilling is known to be for ultra refinement of particles size as well as suppress of the rate of oxidation during synthesis. Aluminum is a reactive metal and highly prone to oxidization/nitridation in nanoscale. Therefore, a novel cryomill has been used to prepare large quantity Al NPs in which, the powder has been milled at extremely low temperature (<123K). This technique does not leave any hazardous by-product and is known to be environment friendly. The ultra refined Al NPs are promising candidate for application in various including explosive formulation, nanofluids, pigments, heat shield coating of aircrafts, etc. Thus, the bulk synthesis of Al NPs by cryomilling will satisfy the increasing demands of Al NPs on an industrial scale. The prepared nanoparticles have been characterized by host of advanced techniques to obtain shape, size, dispersion stability, and purity of the Al NPs. The results indicate that it is possible to prepare Al NPs having size ranging from 5 to 15nm. Additionally, the thermal stability of nanoparticles has been probed and Al NPs have been found to be thermal stable till 150°C. The results have been discussed using currently available theories.
We present a brief review and perspective on the development of eutectic alloys, emphasizing the emergence of complex microstructures during eutectic solidification of ternary and higher-order ...multicomponent alloys. Such alloys' abundant existence promises a large domain in the alloy development space for newer materials suitable for high-temperature applications. Hence the review explores these developments in eutectic alloys based on aluminum, titanium, nickel, intermetallics, and recently developed high entropy alloys. While the importance of fundamental understanding and various functional properties of the eutectic alloys cannot be ignored, this paper focuses primarily on the microstructure and their mechanical properties. The possibilities of ultrafine eutectics and multiscale variation of length scale and morphologies are emphasized. It highlights the potential for the future emergence of these alloys as high-strength structural materials for engineering applications.
Conversion of carbon dioxide into selective hydrocarbon using a stable catalyst remains a holy grail in the catalysis community. The high overpotential, stability, and selectivity in the use of a ...single-metal-based catalyst still remain a challenge. In current work, instead of using pure noble metals (Ag, Au, and Pt) as the catalyst, a nanocrystalline high-entropy alloy (HEA: AuAgPtPdCu) has been used for the conversion of CO2 into gaseous hydrocarbons. Utilizing an approach of multimetallic HEA, a faradic efficiency of about 100% toward gaseous products is obtained at a low applied potential (−0.3 V vs reversible hydrogen electrode). The reason behind the catalytic activity and selectivity of the high-entropy alloy (HEA) toward CO2 electroreduction was established through first-principles-based density functional theory (DFT) by comparing it with the pristine Cu(111) surface. This is attributed to the reversal in adsorption trends for two out of the total eight intermediates*OCH3 and *O on Cu(111) and HEA surfaces.
The advancement of nanotechnology demands large-scale preparation of nanocrystalline powder of innovative materials. High-entropy alloys (HEAs) exhibit unique properties: mechanical, thermal, ...magnetic etc., making them potentials candidates for applications in energy, environment and biomaterials etc. Thus, there is a need to develop novel synthesis methods to prepare nanocrystalline high-purity HEAs in large quantity. Conventional mechanical alloying of the multicomponent metallic powder mixture requires larger milling time and it is prone to contaminations and phase transformation. The present investigation reports a unique approach, involving casting followed by cryomilling, leading to formation of nanocrystalline HEAs powder, which are relatively contaminations free with narrow size distribution. Using examples of two FCC and one BCC single-phase HEAs, it has been shown that large-scale nanocrystalline HEAs powder can be prepared after few hours of cryomilling at 123 K. The formation of nanocrystalline HEAs during cryomilling has been discussed using theoretically available approaches.
The near equimolar and non-equimolar high entropy alloys (HEAs) having five or more major components along with their mingled sites over the surface have made them unique materials for various ...catalytic reactions involving renewable energies. HEAs provide a platform to tune the surface microstructure and chemistry by selecting and controlling the elements, opening up vistas to design new materials for catalysis. The present perspective aims to provide the correlation between HEAs' structure and catalytic performance in various applications with views on challenges and unique opportunities. The scientific and technological curiosity needs to dig deep into the multicomponent phase space to discover various new materials with unique catalytic properties.
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•HEAs provide a platform to tune the surface microstructure and chemistry by selecting and controlling the elements, opening up vistas to design new materials for catalysis.•The present perspective aims to provide the correlation between the structure and catalytic performance of HEAs in various applications with views on challenges and unique opportunities.•The scientific and technological curiosity needs to dig deep into the multicomponent phase space to discover various new materials with unique catalytic properties.
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•EBSD investigation on low cycle fatigue tested CoCuFeMnNi high entropy alloy.•Increase in intragranular misorientation and GND density with strain amplitude.•Intergranular cracking ...at high strain amplitude.•Dislocation interaction with solute environment & nano-cluster retard reversibility.•Coherent annealing twins act as barrier for crack propagation.
Low cycle fatigue behavior of equiatomic CoCuFeMnNi high entropy alloy was investigated under fully reversible strain control mode followed with detailed microstructural characterization using electron back scatter diffraction. There is an increase in the intragranular misorientation and geometrically necessary dislocation density with increase in the strain amplitude that leads to accumulation of damage and intergranular cracking. The interaction of dislocations with copper rich nano-clusters, solute environment and grain boundaries affect slip reversibility, thereby deciding cyclic deformation behaviour. Annealing twin boundaries are resistant to damage and increasing their population density by grain boundary engineering can improve performance of CoCuFeMnNi alloy.
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