Abstract CoCrFeNiAl0.25Ti0.5 high entropy alloy alloys (HEA), produced by powder metallurgy were subjected to boriding to improve their mechanical properties. Sintering was carried out at 1200 °C for 2 h in Ar, and boriding was performed at 900, 1000 and 1100 °C for 2 h using a 90 wt% B4C + 10 wt% NaBF4 boriding powder mixture. Microstructures, densities, surface roughnesses, and mechanical properties (hardness, fracture toughness and nanoindentation responses) of the samples were investigated. FCC, BCC and sigma phases had been observed after sintering, whereas complex metal borides were formed on the surfaces after boriding. Relative density values were between 85% and 90%. Significant increases in surface hardness were observed after boriding due to formation of hard, silicide-free boride layers. The boride layer thickness and hardness increased with increasing boriding temperature. The elastic modulus of the surface of the sintered sample (47.07 GPa) increased with the boriding process to values in the range of 140–151 GPa. Fracture toughness values between 3.57 and 4.25 MPa m1/2 were obtained in borided samples, and increasing the boriding temperature reduced the fracture toughness.

中文翻译：

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粉末冶金硼化CoCrFeNiAl0.25Ti0.5高熵合金的组织和力学性能

摘要 对粉末冶金法生产的CoCrFeNiAl0.25Ti0.5高熵合金(HEA)进行渗硼处理以提高其力学性能。烧结在 1200 °C 下在 Ar 中进行 2 小时，并使用 90 wt% B4C + 10 wt% NaBF4 硼化粉末混合物在 900、1000 和 1100 °C 下进行硼化 2 小时。研究了样品的微观结构、密度、表面粗糙度和机械性能（硬度、断裂韧性和纳米压痕响应）。烧结后观察到 FCC、BCC 和 sigma 相，而硼化后在表面形成复杂的金属硼化物。相对密度值在 85% 和 90% 之间。由于形成坚硬的无硅化物硼化物层，在硼化后观察到表面硬度显着增加。硼化物层厚度和硬度随着硼化温度的升高而增加。烧结样品表面的弹性模量 (47.07 GPa) 随硼化过程增加到 140-151 GPa 范围内的值。硼化样品的断裂韧性值介于 3.57 和 4.25 MPa m1/2 之间，提高硼化温度会降低断裂韧性。