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利用SEM原位观察技术研究了近片层Ti-45Al-8Nb-0.2W-0.2B-0.1Y合金在750℃疲劳蠕变交互作用下的裂纹萌生及扩展行为,循环实验采用在最大拉应力保载的梯形波.结果表明,裂纹主要在片层团界面萌生,裂纹萌生方式包括蠕变空洞和疲劳微裂纹.片层团界面处的微裂纹先通过吞并蠕变空洞或在裂纹尖端应力集中作用下沿片层团界面进行扩展,然后相互连接长大;当裂纹扩展受到不同取向的片层团界面阻碍时,受阻的裂纹开始沿试样厚度方向扩展,且附近伴随出现垂直于载荷方向的微裂纹;最终受阻的裂纹相互连接直至合金断裂.将实验结果与该合金在相同条件下疲劳变形和蠕变变形的原位观察结果进行了比较.结合实验结果建立了高铌TiAl合金在疲劳蠕变交互作用下裂纹萌生及扩展示意模型.
The crack initiation and propagation behavior of near-layer Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy under the fatigue-creep interaction at 750 ℃ was studied by SEM in situ observation. The cyclic experiment was carried out under the conditions of maximum tensile stress The results show that the crack initiation mainly occurs at the lamellar interface, and the crack initiation modes include creep voids and fatigue micro-cracks.The microcracks at the lamellar interface first cohere with creeping voids or stress concentration at the crack tip Then propagate along the lamellar interface and then connect with each other. When the crack propagation is hindered by lamellar interface with different orientations, the hindered crack begins to spread along the thickness of the specimen, Cracks and finally hindered cracks were connected to each other until the alloy was broken.The results of in-situ observation were compared with those of in-situ fatigue deformation and creep deformation under the same conditions.According to the experimental results, A schematic model of crack initiation and propagation under interaction.