High-Temperature Deformation Behaviors of the C-Doped and N-Doped High Entropy Alloys

Hailong Yi,Yifan Zhang,Daixiu Wei,Mengyuan Bi,Renyi Xie

doi:10.3390/met11101517

Abstract

High entropy alloys (HEAs) containing multi-principal metallic constituents have attracted much attention. A good understanding of their hot-deformation behavior and recrystallization mechanism is the prerequisite for microstructures tuning and for optimizing mechanical performance. Here, the flow behavior and recrystallization mechanism of the N-doped and C-doped face-centered cubic phase HEAs are produced at high temperatures by hot-compression at 1123–1273 K, with strain rates of 0.1–0.001 s−1. Constitutive equations were successfully constructed to reveal flow behavior, and stress-strain curves were predicted using strain compensated polynomial functions. Discontinuous and continuous dynamic recrystallization proceeded concurrently when compressed at a low temperature and high strain rate, whereas discontinuous recrystallization, which occurs at primary grain boundaries, became predominant at a high temperature and low strain rate, significantly contributing to the refinement and homogenization of the grains. For this reason, a relatively high temperature and a low strain rate, in which the recrystallized grains exhibit equiaxed morphology and very weak texture, are more suitable for refining grains. The average size of the grains was approximately 10 μm. This study sheds light on grain optimization and mechanical properties through thermomechanical processing.

Highlights

high entropy alloys (HEAs) contain more than four principal elements, where the atomic percentage of each element is between 5 at% and 35 at% [1,2]
We aimed to reveal the microstructure evolution, grain refinement, hot-deformation of C-doped and N-doped HEAs/medium entropy alloy (MEA) by conducting hot-compression tests at various conditions and by constructing the corresponding constitutive relationships
Ingots of the C-doped HEA and the N-doped HEA with a diameter of 50 mm were prepared by vacuum induction melting and casting

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. A minor addition of Mo could increase the lattice constant and decrease the SFE and elastic modulus [10] Based on these findings, a series of novel high-performance Co-rich non-equiatomic HEAs and MEAs were developed and exhibit tensile properties that are superior to other reported FCC single-phase HEAs or MEAs. The Co-rich HEAs/MEAs show an enhanced strain hardening behavior, which can be attributed to either the TWIP effect or the FCC → HCP TRIP effect [8,9,10]. Cold processing is not appropriate for alloys with the TRIP effect due to the poor workability of the deformation-induced HCP-phase For this reason, thermomechanical processing, which has been devoted to producing excellent products with precious dimensions and optimal mechanical properties, is an alternative candidate for refining the grain structures of hard materials [20,21,22,23]. The present study will shed light on the thermomechanical processing of interstitial solidsolution strengthened HEAs and MEAs in order to optimize grain structure and mechanical properties

Materials and Methods

The forfor hot-compression tests of the CFigure

Comparison

Microstructure

Findings

Conclusions