Nearly full-density pressureless sintering of AlCoCrFeNi-based high-entropy alloy powders
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FOCUS ISSUE
NANOCRYSTALLINE HIGH ENTROPY MATERIALS: PROCESSING CHALLENGES AND PROPERTIES
Nearly full-density pressureless sintering of AlCoCrFeNibased high-entropy alloy powders Sahil Rohila1, Rahul B. Mane1, Govind Ummethala1, Bharat B. Panigrahi1,a) 1
Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Sangareddy, Telangana 502285, India Address all correspondence to this author. e-mail: [email protected]
a)
Received: 30 September 2018; accepted: 3 January 2019
AlCoCrFeNi is among the promising high-entropy alloys (HEAs) that possess high strength with considerable ductility. Powder sintering is one of the competitive routes for the production of HEA powders. However, sintering of HEA powders under a pressureless condition is difficult. The present work aims to produce highdensity components from mechanically alloyed AlCoCrFeNi HEA powders through the pressureless sintering method. Nearly full density was achieved at 1275 °C. Sintering was performed in the presence of a viscous phase in the temperature range of 1200–1250 °C, which was confirmed through differential scanning calorimetry and dilatometric measurements. This viscous phase was found have a Cr-rich composition, detected by interrupting the sintering and quenching of the sample. The powder initially contained the BCC phase with a small fraction of FCC and other phases. During sintering, a significant fraction of the FCC phase and nanosized B2 phase were formed. Sintered sample had a hardness of 679 ± 20 Hv.
Introduction Traditional metallurgical theories suggest that multiple alloying elements in an alloy may lead to the formation of multiple compounds with some complex microstructures [1, 2]. The development of high-entropy alloys (HEAs) adds a new dimension to the alloy design strategy [3, 4, 5]. HEAs have gained a considerable attention in the last decade, due to their outstanding properties, such as higher strength at ambient as well as elevated temperatures, wear resistance, irradiation resistance, and good chemical passivity against corrosive and oxidizing atmospheres [6, 7, 8, 9, 10, 11, 12, 13, 14]. Many of the HEAs were reported to exhibit exceptionally high tensile as well as compressive strengths (over 2 GPa [1, 2, 14]). Several hypotheses have been proposed about the characteristics of HEAs and correlating their properties [1, 2, 3, 4, 5, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]. Initially, it was believed that singlephase solid solutions could be formed only when constituents were taken in the equiatomic ratio; however, lately, several alloys have been reported with non-stoichiometric compositions [1, 2, 3, 4, 5]. It has also been realized that producing a 100% pure single-phase alloy has not been an easy task in most of the cases. Alloys often have some secondary phases, sigma phases or lave phases, and as a result, HEAs with dual
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phases and multiphases have been widely reported [1, 2, 13, 14, 15, 16, 17, 18, 19, 20]. This class of alloys has a huge
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