Effects of boron on microstructure and properties of microwave sintered FeCoNi1.5CuY0.2 high-entropy alloy

Abstract The mechanical properties of high-entropy alloys (HEAs) containing rare earth are improved by adding boron element. Under the condition that the content of rare-earth is fixed, FeCoNi1.5CuY0.2Bx high-entropy alloy with different boron atom ratios (x= 0, 0.2, 0.4, 0.6, 0.8 and 1.0) is prepared by advanced microwave sintering process. The effect of boron addition with different atomic ratios on the phase evolution, microstructure, compressive mechanical properties and magnetic properties of the FeCoNi1.5CuY0.2 high-entropy alloy is emphatically studied. The results show that the phase transformation temperature decreases with the increase of boron content, which is conducive to the rapid sintering at low temperature. When boron content is less than 0.4 atomic ratio, the alloy is dominated by FCC base phase and BYO3, eliminating the oxidation phase of Y2O3. When boron adding amount as x=0.4, it has the largest maximum compression ratio. When the amount of boron exceeds 0.4 atomic ratio, boride precipitates in the alloy, which increases the strength and hardness and at the cost of plasticity and soft magnetism. When the amount of boron is x=1, the hardness arrives at utmost, and the compressive strength, yield strength and hardness are 1546MPa, 1112MPa and 367.1HV, respectively, which are 150%, 129% and 29.03% higher than those of boron-free sample. The improvement of mechanical properties is due to the fact that boron with small atomic size is easy to solute into the FCC base phase, forming interstitial solid solution, which results in lattice distortion and solid solution strengthening effect. And BY12 particles precipitated in BYO3 have dispersion strengthening effect on the alloy.