铸态Ti-22Al-25Nb合金的结构特征与力学性能

Structural features and mechanical properties of as-cast Ti-22Al-25Nb alloy

摘要:

Ti2AlNb基合金是目前有望在650-800℃温度范围内取代高温镍基合金的金属间化合物。利用水冷铜坩埚感应悬浮熔炼法，通过调控熔炼工艺，制备了主相分别为B2/?相和O相 Ti-22Al-25Nb合金铸锭，通过XRD、SEM等手段进行了合金结构特征的表征，通过室温拉伸试验、室温压缩试验、纳米压痕试验测试了合金的力学性能并分析了断口形貌。研究表明，铸态Ti-22Al-25Nb合金晶粒尺寸达到数百微米。相组成对铸态Ti-22Al-25Nb合金的力学性能有一定影响，铸态O相合金的极限抗拉强度达到了1125MPa，超过了铸态B2/?相合金的1031MPa，但粗大晶粒导致合金塑性较差（铸态B2/?相与铸态O相合金的延伸率分布为1.82%与1.32%）。铸态Ti-22Al-25Nb合金的拉伸断口与压缩断口均具有明显的解理断裂特征，拉伸断口主要表现为沿晶断裂，压缩断口主要表现为穿晶断裂。

Abstract:

Ti2AlNb-based alloy is a kind of intermetallic compound. It is expected to replace Ni-based superalloys for high-temperature structural applications with a temperature range of 650-800 ℃. In this work, a Ti2AlNb based alloy with a nominal composition of Ti-22Al-25Nb is prepared by water-cooled copper crucible induction floating melting method. The structural features of the as-cast Ti-22Al-25Nb alloy are characterized by XRD and SEM. It is found that the main phase of the as-cast Ti-22Al-25Nb alloy can be B2/? phase or O phase, depending on its melting and casting process parameters. The grain size of the as-cast Ti-22Al-25Nb alloy reaches several hundred microns. The mechanical properties of the as-cast Ti-22Al-25Nb alloy are investigated by tensile, compressive and nanoindentation tests at room temperature. The ultimate tensile strength of the as-cast Ti-22Al-25Nb O phase alloy and B2/? alloy reaches 1125 MPa and 1031 MPa respectively, with the elongation of 1.32% and 1.82%. The nanoindentation hardness of the as-cast Ti-22Al-25Nb O phase alloy is slightly higher than that of the as-cast B2/? phase alloy. The tensile fracture and compression fracture of as-cast Ti-22Al-25Nb alloy show obvious cleavage fracture characteristics. In addition, the tensile fracture is mainly intergranular, while the compression fracture is mainly transgranular.