Design of a low density refractory high entropy alloy in non-equiatomic W–Mo–Cr–Ti–Al system. (November 2020)

• Record Type: Journal Article
• Authors: Naser-Zoshki, Hamed; Kiani-Rashid, Ali-Reza; Vahdati-Khaki, Jalil
• Is Part Of: Vacuum. Volume 181(2020)
• Publication Date: 2020-11
• Subjects: Refractory high entropy alloy -- Non-equiatomic -- Low density -- Solid solution -- Vacuum arc melting -- Hardness -- Compression strength; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2020.109614
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: A new refractory high entropy alloy (RHEA) with non-equiatomic composition of W10 Mo27 Cr21 Ti22 Al20 was designed based on empirical rules and CALPHAD approach. Calculated results showed that W10 Mo27 Cr21 Ti22 Al20 RHEA had lower density and higher melting temperature than that of equiatomic alloy. The designed alloy was prepared by vacuum arc melting then the crystal structure, microstructure, chemical composition, density, hardness and compressive strength had been evaluated. The alloy exhibited a BCC solid solution as major phase with typical dendritic microstructures. The experimental results confirmed calculated results, suggesting a BCC solid solution phase. The density of the alloy was 7.48 g/cm 3, which was approximately close to the calculated value, 7.61 g/cm 3 . However, the measured hardness value (511 kg/mm 2 ) was significantly higher than the calculated value (125 kg/mm 2 ), indicating the effect of solid solution strengthening. This alloy had compressive yield strengths of 1245 MPa at room temperature, 510 MPa at 600 °C, 201 MPa at 1000 °C and 105 MPa at 1200 °C. Compressive strain of the alloy was limited at room temperature, but it increased significantly to above 60% at 1000 °C and 1200 °C. Comparing with four conventional superalloys Inconel 718, Waspaloy, Hastaloy X and Haynes 230, the studied RHEA shows lower density and superior high-temperature yield strength. Highlights: The composition optimization was performed on the W–Mo–Cr–Ti–Al alloy system to achieve minimum ρ and maximum Tm. A new non-equiatomic RHEA, W10 Mo27 Cr21 Ti22 Al20, was designed as optimal composition. The CALPHAD results, in agreement with the experimental results, confirmed the formation of BCC solid solution phase. The measured hardness was about four times the calculated hardness of the alloy. The studied refractory HEA has lower density and higher high-temperature yield strength than conventional superalloys.