Microstructure, Mechanical Properties and Tribological Properties of NiAlComposites Reinforced by CrMnFeCoNiHigh-Entropy Alloy.

Shuqiang Zhou,Xinyu Liu,Yi Xu

doi:10.3390/ma11101850

Abstract

NiAl-based composites reinforced by CrMnFeCoNi high-entropy alloy (HEA) particles were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructure, mechanical, and tribological properties of the NiAl-HEA composites were investigated. Microstructural analyses show that after SPS, the HEA phase homogenously distributed in the NiAl matrix. Non-uniform diffusion of various elements occurred during the high temperature sintering process. Transmission electron microscope (TEM) observation of the composites revealed that many nano particle of Al2O3 generated at the grain boundary. The yield strength significantly increased after adding HEA particles. The compressive strength of the composites increased with the contents of HEA increasing, which should be attributed to the second phase hardening effect of HEA particles and fine grain strengthening effect. The composite of 10 wt.% HEA exhibited significant room temperature compressive properties, with the ultimate compressive strength of 2692 MPa and the compressive strain of 34.2%, respectively. The results of the wear tests show that the addition of HEA will reduce the wear resistance of composites to some extent and slightly increase the coefficients of friction (COFs) of the composites.

Highlights

The NiAl intermetallic has been recognized as a candidate of high temperature structural materials, due to its excellent physical and mechanical properties, such as low density (5.9 g/cm3 ), high melting points (1911 K), and excellent oxidation resistance up to 1573 K, as well as good thermal conductivity (2–4 times higher than conventional nickel-based alloys) [1,2,3,4]
The diffraction peaks of NiAl ((100), (110), (111), (200), (210), (211)), and CrMnFeCoNi high-entropy alloy (HEA) ((110), (200), (220)) can be observed, and no diffraction peaks belonging to additional phases can be detected
These changes indicated that there was no reaction between the NiAl matrix and reinforcement, or the amounts of new phase was too low to be detected by X-ray diffraction diffraction (XRD)

Summary

Introduction

The NiAl intermetallic has been recognized as a candidate of high temperature structural materials, due to its excellent physical and mechanical properties, such as low density (5.9 g/cm3 ), high melting points (1911 K), and excellent oxidation resistance up to 1573 K, as well as good thermal conductivity (2–4 times higher than conventional nickel-based alloys) [1,2,3,4]. Two major weaknesses limited its applications due to the poor ductility at ambient temperature and low strength at high temperature [5]. High entropy alloys (HEAs), which are a new class of materials, are known for their good structural stability, high ductility, and exceptional high-temperature strength. It usually contains four or five metallic elements with nearly equiatomic ratios. They are recognized as the promising candidate for structural application [11]

Methods

Results

Conclusion