Effect of Al content in CoCrFeNiAlx HEA on mechanical properties and high temperature oxidation resistance of WC-10%CoCrFeNiAlx hard alloy

Abstract

The CoCrFeNiAl high-entropy alloy, with varying Al compositions, was utilized as the bonding phase in this study to fabricate WC-10%CoCrFeNiAlx (where x represents the mole ratio of Al element, ranging from 0 to 1) hard alloys using the Spark Plasma Sintering method. The investigation focused on elucidating the influence mechanism of microstructure and properties of CoCrFeNiAlx high-entropy alloys on the mechanical properties of WC-10%CoCrFeNiAlx hard alloys. Isothermal oxidation testing was subsequently conducted to examine the impact of Al content on the high-temperature oxidation resistance of WC-10%CoCrFeNiAlx hard alloys. Finally, a comparison was made between the mechanical properties and high temperature oxidation resistance of WC-10%CoCrFeNiAlx hard alloys and conventional WC-6Co cemented carbide. The findings suggest that as the Al content increases, the CoCrFeNiAlx high-entropy alloy undergoes a transition from a single Face-Centered Cubic (FCC) phase to a combination of FCC and Body Centered Cubic (BCC) phases, ultimately transforming into a BCC phase. This evolution results in a gradual enhancement in hardness. The mechanical properties of WC-10CoCrFeNi hard alloy exhibit exceptional characteristics when the Al content is eliminated, with hardness, fracture toughness, and bending strength reaching 1702 MPa, 13.0 MPa·m1/2, and 1378 MPa respectively. As the Al content increases in WC-10%CoCrFeNiAlx hard alloys, there is a corresponding increase in hardness while fracture toughness and bending strength gradually decrease. Furthermore, an enhancement in high temperature oxidation resistance is observed. Finally, in comparison to the conventional WC-6Co hard alloy, the mechanical properties of WC-10CoCrFeNiAlx hard alloys exhibit similarity while demonstrating a significant enhancement in oxidation resistance.