Effect of Heat Treatment Temperature on the Microstructure and Mechanical Properties of Cu0.3Cr2Fe2Ni3Mn2Nbx High-Entropy Alloys

The effects of heat treatment temperature on the microstructure and mechanical properties of Cu0.3Cr2Fe2Ni3Mn2Nbx high-entropy alloys (HEAs) were studied. Results indicate that in the as-cast state, an Nb0 alloy is composed of a single FCC phase, and a Laves phase gradually forms as Nb content increases. After heat treatment at 800 degrees C, BCC solid solution phases rich in Cr, Fe, and Mn form in all alloys. The BCC phases in the Nb-0.2 and Nb-0.4 alloys decompose after heat treatment at 900 and 1000 degrees C, respectively, and the microhardness of the as-cast Cu0.3Cr2Fe2Ni3Mn2Nbx HEAs increases from 127 to 203 HV with increasing Nb content. After heat treatment, the microhardness of the alloys considerably improves, and the Nb-0.4 alloy has the highest microhardness after heat treatment at 800 degrees C (approximately 346 HV). After heat treatment at 900 and 1000 degrees C, the microhardness of the three alloys decreases. The yield strength of the as-cast Cu0.3Cr2Fe2Ni3Mn2Nbx HEAs increases with Nb content and shows a trend of first increasing and then decreasing with increasing heat treatment temperature. The strengthening mechanism of the heat-treated alloys is mainly attributed to the second-phase strengthening of the Laves phase and the solid solution strengthening of the BCC phase.