Effects of Cr Content on Microstructure and Mechanical Properties of AlCoCrxFeNi High-Entropy Alloy

Tao-Tsung Shun,Wei-Jhe Hung

doi:10.1155/2018/5826467

Abstract

In this study, we investigated the effects of Cr content on the crystal structure, microstructure, and mechanical properties of four AlCoCrxFeNi (x = 0.3, 0.5, 0.7, and 1.0, in molar ratio) high-entropy alloys. AlCoCr0.3FeNi alloy contains duplex phases, which are ordered BCC phase and FCC phase. As the Cr content increases to x = 1.0, the FCC phase disappears and the microstructure exhibits a spinodal structure formed by a BCC phase and an ordered BCC phase. This result indicates that Cr is a BCC former in AlCoCrxFeNi alloys. With increasing Cr content, the alloy hardness increases from HV415 to HV498. AlCoCr0.3FeNi, AlCoCr0.5FeNi, and AlCoCr0.7FeNi exhibit a high compressive fracture strain of about 0.24 because of the formation of the FCC phase in the BCC matrix. Moreover, the highest yield stress of 1394 MPa and compressive strength of 1841 MPa presented by AlCoCrFeNi alloy are due to the existence of a nano-net-like spinodal structure.

Highlights

For a long time, the designs of traditional alloys, such as Al, Mg, Fe, Ni, and Co-based alloys, were mainly based on the use of one element as a principal component and the addition of minor elements for improving properties
Studies [2,3,4,5,6,7,8,9] mostly focused on AlxCoCrCuFeNi high-entropy alloys which exhibited face-centered cubic (FCC) and/or body-centered cubic (BCC) crystal structure
At higher Al content (x > 0.8), duplex FCC and BCC phases form in the interdendrite, and the spinodal phase exists in the dendrites

Summary

Introduction

The designs of traditional alloys, such as Al-, Mg-, Fe-, Ni-, and Co-based alloys, were mainly based on the use of one element as a principal component and the addition of minor elements for improving properties It is because conventional metallurgical theories suggest that the use of multi-principal-element alloys may result in the formation of numerous complex structures and intermetallic compounds, which make them difficult to analyze microstructure and cause deterioration of mechanical properties. Previous studies [3, 10] have shown that Cu has a larger positive mixing enthalpy with other elements It segregates in interdendritic regions, resulting in deterioration of mechanical properties. We investigated such e ects on the crystal structure, microstructure, and mechanical properties of four high-entropy alloys with a nominal composition of AlCoCrxFeNi (x 0.3, 0.5, 0.7, and 1.0, in molar ratio)

Material and Methods

B: BCC F: FCC

Conclusions