High-entropy alloys by mechanical alloying: A review
- PDF / 1,122,152 Bytes
- 23 Pages / 584.957 x 782.986 pts Page_size
- 6 Downloads / 274 Views
FOCUS ISSUE
NANOCRYSTALLINE HIGH ENTROPY MATERIALS: PROCESSING CHALLENGES AND PROPERTIES
High-entropy alloys by mechanical alloying: A review Mayur Vaidya1, Garlapati Mohan Muralikrishna1, Budaraju Srinivasa Murty1,a) 1
Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India Address all correspondence to this author. e-mail: [email protected]
a)
Received: 6 September 2018; accepted: 23 January 2019
Mechanical alloying (MA) followed by sintering has been one of the most widely adopted routes to produce nanocrystalline high-entropy alloys (HEAs). Enhanced solid solubility, room temperature processing, and homogenous alloy formation are the key benefits provided by MA. Spark plasma sintering has largely been used to obtain high-density HEA pellets from milled powders. However, there are many challenges associated with the production of HEAs using MA, which include contamination during milling and high propensity of oxidation. The present review provides a comprehensive understanding of various HEAs produced by MA so far, with the aim to bring out the governing aspects of phase evolution, thermal stability, and properties achieved. The limitations and challenges of the process are also critically assessed with a possible way forward. The paper also compares the results obtained from high-pressure torsion, another severe plastic deformation technique.
Introduction Materials development has always been at the forefront of technological innovations, which have governed the growth of human civilizations since ancient times. Alloys have been an integral part of materials evolution, since their first accidental discovery (arsenic bronze, 3000 BCE) in the primeval cave fires [1]. The conventional alloy design strategy involved adding one or more elements to a parent metal to achieve enhancement in desired properties. A plethora of currently used alloys, like steels, bronzes, aluminum alloys, and magnesium alloys, were developed using this traditional approach. It followed that the exploration of phase diagrams was largely limited to three dimensions and terminal composition range. However, a shift in this paradigm occurred more than a decade ago when parallel works of Cantor et al. [2] and Yeh et al. [3] marked the beginning of a new class of multicomponent alloys termed high-entropy alloys (HEAs). HEAs are defined as multicomponent alloys containing 5 or more constituents in equiatomic or near equiatomic ratio [1]. They tend to exhibit solid solution structures, instead of complex phases, stabilized by their high configurational entropy of mixing. HEAs have shown some fascinating properties, like high strength [4], high fracture toughness at cryogenic temperatures [5], enhanced thermal stability [6], superior oxidation [7, 8], and corrosion resistance [9]. The advent of HEAs has also generated a lot of fundamental curiosities and led to the investigation of
ª Materials Research Society 2019
hitherto unexamined questions: atomic occupancy in a multicomponent latti
Data Loading...
