Processing and Consolidation of Nanocrystalline Cu-Zn-Ti-Fe-Cr High-Entropy Alloys via Mechanical Alloying
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INTRODUCTION
THE discovery of the multicomponent high-entropy alloys (HEAs) by Yeh et al.,[1] subsequently followed by other groups[2–5] across the globe, has stimulated intense research activity in many research laboratories in the past few years. This is mainly due to the interesting fundamental physics these alloys exhibit as well as the technological promise they possess. It is to be noted that the HEAs are multicomponent alloys (at least five elements) having equiatomic or near equiatomic compositions showing the presence of solid-solution phases with simple crystal structure, in particular FCC and/or BCC.[1] Earlier, it has been anticipated that a variety of intermetallic phases with complex crystal structure would form in case of multicomponent alloys, making the processing of these alloys extremely difficult. On the contrary, the multicomponent HEAs are found to be consisting of simple phases with FCC and/or BCC crystal structure. This is reported due to high-configurational entropy, lattice distortion, sluggish diffusion, cocktail effect, etc.[1,6–8] In addition, these alloys are reported to exhibit versatile and interesting properties, such as high strength, good ductility, as well as
SANGHITA MRIDHA, SUMANTA SAMAL, P. YOUSAF KHAN, Research Scholars, and KRISHANU BISWAS, Associate Professor, are with the Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India. Contact e-mail: [email protected] GOVIND, Scientist E, is with the Materials Science Division, Vikram Sarabhai Space Centre, Indian Space Research Organization (ISRO), Trivandrum 695022, Kerala, India. Contact e-mail: [email protected] Sumanta Samal and Yousaf Khan made equal contribution. Manuscript submitted February 14, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
reasonably good resistance to oxidation, corrosion, and wear, making them suitable candidates for a myriad of potential engineering applications. The HEAs can be prepared by a host of experimental techniques, such as rapid solidification, mechanical alloying (MA), and thin film deposition. However, the multicomponent HEAs containing elements with varying melting temperatures, synthesized by rapid solidification route, show segregation and inhomogeneous microstructure.[9] To circumvent this limitation, MA[10,11] has been utilized. MA renders the formation of microstructure at room temperature with better homogeneity compared with rapid solidification route.[10] In addition, the process of MA allows for the formation of nanocrystalline grains in the alloyed powders. To reap the benefits of nanocrystals formed in the mechanically alloyed powders, the fieldassisted sintering technique (FAST), such as spark plasma sintering (SPS), can be applied to obtain bulk nanocomposites. SPS has widely been used as a rapid densification tool in a variety of material systems.[12] There are many advantages of using SPS including shorter holding time (due to faster heating rate) and lower processing temperature compared with the conventional sintering tech
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