Microstructure and Composition Evolution of a Fused Slurry Silicide Coating on MoNbTaTiW Refractory High-Entropy Alloy in High-Temperature Oxidation Environment.

Jiesheng Han,Bo Su,Youzhi Wu,Junhu Meng,Aijun Zhang

doi:10.3390/ma13163592

Abstract

In this paper, the Si-20Cr-20Fe coating was prepared on MoNbTaTiW RHEA by a fused slurry method. The microstructural evolution and compositions of the silicide coating under high-temperature oxidation environment were studied. The results show that the silicide coating could effectively prevent the oxidation of the MoNbTaTiW RHEA. The initial silicide coating had a double-layer structure: a high silicon content layer mainly composed of MSi2 as the outer layer and a low silicon content layer mainly contained M5Si3 as the inner layer. Under high-temperature oxidation conditions, the silicon element diffused from the silicide coating to the RHEA substrate while the oxidation of the coating occurred. After oxidation, the coating was composed of an outer oxide layer and an inner silicide layer. The silicide layer moved toward the inside of the substrate, led to the increase of its thickness. Compared with the initial silicified layer, its structure did not change significantly. The structure and compositions of the oxide layer on the outer surface strongly depended on the oxidation temperature. This paper provides a strategy for protecting RHEAs from oxidation at high-temperature environments.

Highlights

Refractory high-entropy alloys (RHEAs) are considered to be a new generation of high-temperature materials, because they have the advantages of both high-entropy alloys (HEAs) and refractory metals (RMs), such as high-temperature strength, high hardness, and good phase stability at high temperatures [1,2,3,4,5,6,7]
The Si-20Cr-20Fe coating was prepared on the surface of MoNbTaTiW RHEA by a fused slurry method
(1) The Si-20Cr-20Fe coating was prepared on the surface of MoNbTaTiW RHEA by a fused slurry

Summary

Introduction

Refractory high-entropy alloys (RHEAs) are considered to be a new generation of high-temperature materials, because they have the advantages of both high-entropy alloys (HEAs) and refractory metals (RMs), such as high-temperature strength, high hardness, and good phase stability at high temperatures [1,2,3,4,5,6,7]. The neutron diffraction analysis of those alloys after annealing at 1400 ◦ C for 19 h shows that no changes have occurred to their phase structures Their compression yield strengths are much higher than that of Inconel 718 alloy at temperatures above 800 ◦ C.

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Conclusion