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Experimental Investigations of Phase Equilibria in the Ta-V-Cr Ternary System X. J. Liu1,2 • P. Yang1 • S. Y. Yang1 • J. J. Han1 • Y. Lu1 • Y. X. Huang1 J. B. Zhang1 • C. P. Wang1

•

Submitted: 18 August 2020 / in revised form: 25 October 2020 / Accepted: 3 November 2020 Ó ASM International 2020

Abstract The phase equilibria and microstructure of the Ta-V-Cr ternary system at 1200 and 1300 °C were studied by x-ray diffraction and electron probe microanalysis. The isothermal section at 1200 °C consists four single-phase regions, four two-phase regions and one three-phase region. In addition, the C15 phases of aV2Ta and Cr2Ta(LT) exhibit complete mutual solid solubility at 1200 °C, while the C15(Cr2Ta(LT)) phase containing a large solubility of V is identified at 1300 °C. Keywords isothermal section
phase equilibrium
Ta-VCr

1 Introduction Alloys containing Laves phase have excellent mechanical properties, and their potential as high temperature structural materials is prospected.[1-4] The Laves phase formed by alloy element Cr and refractory metal not only has high melting point and proper density, but also has excellent high-temperature oxidation resistance, hot corrosion resistance, high-temperature strength and creep resistance due to the presence of a large number of Cr.[5-7] Ta was taken into account in this experimental investigation, for Cr2Ta & C. P. Wang [email protected] 1

College of Materials and Fujian Provincial Key Laboratory of Materials Genome, Xiamen University, Xiamen 361005, People’s Republic of China

2

Department of Materials Science and Engineering, Harbin Institute of Technology, Shenzhen 518055, Guangdong, People’s Republic of China

Laves phases have the potential as high temperature structural materials.[8-10] However, the room temperature brittleness of the Cr2Ta Laves phase alloy is still serious, and the fracture toughness is still very low, which can not meet the practical requirements. Therefore, another key element V should be considered given its unique property of being the only known element forming complete solid solution with Cr, and it plays an important role in improving the ductility of Cr by alloying.[11-15] Therefore, the investigations on the Ta-V-Cr ternary system can provide data support for the future application of Laves phase in superalloys. The Ta-V-Cr ternary system consists of three subsystems: Ta-V,[16] Ta-Cr[22] and V-Cr[23] binary systems, as shown in Fig. 1. For the Ta-V binary system, according to previous work,[16-19] high temperature continuous solid solution bcc-(V,Ta) and low temperature mesophase (V2Ta) were determined. In 1972, Savieky et al. reported that the mesophase (V2Ta) might have high temperature polymorphism.[16] Later, Danon et al. presented a Ta-V phase diagram containing the TaV2 phase polymorphic transition by thermodynamic calculation.[18] Many investigators have carried out experimental and thermodynamic studies on the phase diagram of the Ta-Cr binary system.[21-23] An overview of the Ta-Cr system was performed by Venkatraman et al