Improvement of Mechanical Properties with Non-Equimolar CrNbTaVW High Entropy Alloy

Francisco Antão,Eduardo Alves,Marta Dias,António Pereira Gonçalves,José Ygnacio Pastor,Rui Coelho Da Silva,Elena Tejado,Ricardo Martins,José Brito Correia

doi:10.3390/cryst12020219

Abstract

CrNbTaVWx with (x = 1 and 1.7) high entropy alloys have been devised for thermal barriers between the plasma-facing tungsten tiles and the copper-based heat sink in the first wall of fusion nuclear reactors. These novel materials were prepared by ball milling and consolidated by Upgrade Field Assisted Sintering Technology at 1873 K under an applied pressure of 90 MPa for 10 min. In this work, the structural and mechanical properties of these materials were evaluated. Consolidated samples presented a major phase with a bcc-type structure with lattice parameter value of 0.316 nm for CrNbTaVW and CrNbTaVW1.7 compositions. Moreover, observation of the microstructures evidences also two minor phases: Ta-Nb-Cr and Ta-V rich (in which carbon is detected). Despite the similarity in the structural properties of these two alloys, their mechanical properties are distinct. The flexural stress for the sample with higher amount of W (CrNbTaVW1.7) is higher by 50% in the 298–873 K range, with an increased strain to fracture, which can be associated with reduced brittleness caused by the additional W incorporation.

Highlights

Tungsten is considered the best candidate for plasma facing tiles due to its endurance for high temperature and irradiation resilience and resistance, high melting point, low sputtering rate, and low tritium retention [1]
One approach to solve this issue is the use of high entropy alloys compatible with both W and the CuCrZr alloys which can work as a thermal barrier interlayer capable of minimizing the thermal mismatch between both materials, keeping them in their required work temperature intervals
A novel CrNbTaVW and CrNbTaVW1.7 high entropy alloys were successfully synthesized by a combination of mechanical alloying and ultra-fast fieldassisted sintering technique

Summary

Introduction

Tungsten is considered the best candidate for plasma facing tiles due to its endurance for high temperature and irradiation resilience and resistance, high melting point, low sputtering rate, and low tritium retention [1]. The material selected for heat sink behind the plasma-facing components is a CuCrZr alloy with a service temperature limited to ~623 K [3]. These two materials, W and CuCrZr alloy, show a large mismatch in working temperatures, demanding resourcefulness solutions for their joint operation. Despite the numerous studies on refractory HEAs, only a few recent works have been devoted to the high temperature class of alloys, with output on microstructure characterization and mechanical properties [10,11]. The study of the effect of the increasing W content, on the equiatomic CrNbTaVW in terms of structural and mechanical properties, is the goal of the present work

Experimentals

Results and Discussion

Conclusions

22. Rate Processes in Plastic Deformation of Materials