研究了 TC17 钛合金电子束焊接接头的显微组织与力学性能. 研究表明, 焊接接头由熔合区(FZ)、热影响区(HAZ)和母材区(BM)组成. 焊态下, FZ 由 β 柱状晶组成, HAZ 由针状 α/α′相、等轴 α 相和亚稳态 β 相组成. 在 630~800 ℃范围焊后热处理后, FZ 和 HAZ 中的亚稳态 β 相分解, 生成 α 相和 β 相, 随着焊后热处理温度的升高, FZ 和 HAZ 中的 α 相板条厚度增加, 晶界 α相发生粗化. 焊态和 800 ℃, 2 h, A.C.焊后热处理条件下, FZ 在 450 ℃高温拉伸过程中会析出次生 α 相板条, 导致熔合区抗拉强度升高, 屈强比降低. 焊接接头的拉伸断裂优先发生于屈服强度低的区域, 接头各区域屈服强度相差不大时, 最终断裂发生在硬度较低的区域. TC17 钛合金电子束焊接接头的最佳焊后热处理制度为 630 ℃, 2 h, A.C., 此时焊接接头具有良好的拉伸强度和塑性匹配.
Most titanium alloys have been designed for aeronautical applications, where their excellent specific properties are fully employed and weldability is a classic problem with Ti and its alloys. Microstructure and mechanical properties of the electron beam weldments of TC17 alloy were investigated in this study. The results showed that there exhibited three zones across the TC17 electron beam weldment: the fusion zone (FZ), heat affected zone (HAZ) and base metal (BM). It was also observed that the as-welded FZ consisted of metastable β columnar grains, while the HAZ consisted of acicular α/α′ phase, equiaxed α phase and metastable β phase. Furthermore, it was indicated that the transformation from metastable β phase to α + β phase happened when the FZ and HAZ were post-weld heat treated at 630~800 ℃, the coarsening of α laths and the grain boundary α were also observed when the heat treatment temperature increased. The increasing of 450 ℃ ultimate tensile strength of FZ was ascribed to the precipitation of secondary acicular α platelets during tensile testing in the as-welded and 800 ℃ heat treated conditions, which led to the low yield ratio of FZ. The tensile failure location of the weldments was found to occur in preference in the low tensile yield strength area, or in the low hardness area when the difference between yield strength across the weldments is very small. It was concluded that the optimal post-weld heat treatment for the TC17 alloy weldment was 630 ℃, 2 h, A.C., at which the weldments showed good combination of tensile strength and elongation.
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