Al0.8CoCrFeNiTi0.2高熵合金铸态及退火态组织和性能研究

Studies on the microstructure and properties of the as-cast and annealed Al0.8CoCrFeNiTi0.2 high-entropy alloys

摘要:

采用真空电弧熔炼法熔炼出Al0.8CoCrFeNiTi0.2高熵合金，并在600 ℃、800 ℃、1000 ℃下进行了真空退火热处理。利用X射线衍射仪（XRD）、光学显微镜（OM）、电子探针（EPMA）、硬度计、万能试验机以及电化学工作站对合金铸态和不同温度退火态的微观组织结构、硬度、压缩机械性能和在3.5wt.%的NaCl溶液、0.5mol/L的H2SO4溶液中的耐蚀性进行了研究。组织分析表明退火处理使合金的相组成和组织形貌都发生了改变，铸态下合金由BCC和FCC两相固溶体组成， 600 ℃、800 ℃和1000 ℃退火态下合金由BCC、FCC和σ相三相组成，800 ℃退火态中σ相析出最多。随着退火过程的进行，铸态下的单相固溶体树枝晶转变为了细小层片状的两相混合组织。在800 ℃及以下温度范围，退火温度越高，混合组织越细小，成分均匀性越好。但1000℃退火态有大块状单相固溶体析出，导致元素偏析重新加剧。硬度试验和压缩试验结果表明合金在铸态和三种温度退火态下都有较高的硬度、屈服强度、断裂强度和塑性变形量，表现出了良好的综合机械性能和抗回火软化能力。800 ℃退火态的硬度、屈服强度和断裂强度最高，铸态的塑性最好。电化学腐蚀试验表明铸态和三种温度退火态下的合金在3.5% NaCl溶液和0.5mol/L H2SO4溶液中都表现出了良好的耐蚀性， 800 ℃退火态的耐蚀性最好。

Abstract:

Al0.8CoCrFeNiTi0.2 high entropy alloys were prepared by vacuum arc melting and were treated by vacuum annealing at 600 ℃, 800 ℃ and 1000 ℃ for 10h. The microstructure, mechanical properties and corrosion resistance of the as-cast and annealed alloys were studied using XRD, OM, EPMA, hardness tester, universal testing machine, and electrochemical workstation. Microstructure analysis shows that the Annealing treatments have changed the phase composition and microstructure morphology of the alloys. The as-cast alloy consists of BCC and FCC solid solutions, while the 600 ℃, 800 ℃ and 1000 ℃ annealed alloys consist of BCC, FCC and σ phase. In the 800 ℃ annealed alloy, the σ phase precipitates the most. During the annealing process, the single-phase solid solution dendrites in the as-cast shift to the thin layer-flake two-phase mixed structure. In the temperature range of 800 ℃ and below, the higher the annealing temperature, the mixed structure is finer and the composition uniformity is better. But the 1000 ℃-annealed alloy has a large block single-phase solid solution precipitation, causing elements segregation to intensify. Hardness and compression tests show that all of the as-cast and three kinds of annealed alloys have high hardness, yield strength, fracture strength and plastic deformation, showing good comprehensive mechanical properties and resistance to temper softening. The 800 ℃-annealed alloy has the highest hardness, yield strength and fracture strength, but the as-cast alloy have the best plasticity. Electrochemical corrosion tests show that the as-cast and three kinds of annealed alloys all have good corrosion resistance in the 3.5wt.% NaCl solution and 0.5 mol/L H2SO4 solution and the corrosion resistance of the 800 ℃-annealed alloy is best.