热处理工艺对AlCoCrFeNiTi_(0.5)高熵合金的显微组织和硬度的影响

Effect of heat treatment on microstructure and hardness of AlCoCrFeNiTi_(0.5) high entropy alloy

为了探索热处理工艺对AlCoCrFeNiTi0.5高熵合金的显微组织和硬度的影响,采用水冷铜坩埚真空感应悬浮熔炼法制备合金,然后对合金样品进行不同温度、不同冷却方式和不同保温时间的热处理,研究合金的显微组织和硬度的变化规律。结果表明:AlCoCrFeNiTi0.5高熵合金制备态相结构为两种成分不同的BCC相,微观组织由树枝晶、枝晶间和共晶组织(α+β)组成,共晶组织α相上弥散分布着大量纳米粒子。经过热处理后,合金中析出σ相,硬度均大于660.00 HV,其中800℃退火2 h后合金硬度达最大值773.28 HV,高出制备态合金硬度176.22 HV。炉冷比空冷和水冷更能提高合金的硬度。首次发现合金具有晶界硬化现象,晶界硬度均比晶粒硬度大140.00 HV左右。合金试样在800℃下保温480 h后,其组织结构和硬度均无太大变化,具有良好的热稳定性。

AlCoCrFeNiTi0. 5 high entropy alloy was prepared by cold crucible levitation melting and heat treated in different conditions, including different temperatures, time and cooling methods, to explore the effect of heat treatment on microstructure and hardness. The results show that the as-pre-pared sample is composed of two BCC phases with different compositions and its microstructure con-sists of dendrite, interdendrite and eutectic structure （α＋β） ,and there are a lot of nanoparticles dif-fusely distributing on α phase. The hardnesses of all the annealed samples exceed 660. 00HV, due to the precipitation of σ phase. The maximum hardness reaches 773.28 HV when annealed at 800 ℃, 176.22 HV higher than that of the as-prepared alloy. Furnace cooling is more effective to increase the hardness of the alloy than air cooling and quenching cooling. Grain boundary hardening phenomenon was observed for the first time, for which the hardness of grain boundary is about 140.00 HV higher than that of the grains. It was found that the microstructure and hardness of the＆amp;nbsp;alloy have no noticeable changes even after annealed at 800 ℃ for 480 h, showing good thermal sta-bility of AlCoCrFeNiTi0. 5 high entropy alloy.