全层TiAl合金裂纹扩展阻力的研究

Study on Crack Propagation Resistance of Fully Lamellar TiAl Alloy

本文通过对直缺口两个层团厚度拉伸试样的扫描电镜原位拉伸实验、相应的断裂表面观察以及有限元计算研究了全层铸状TiAl基合金组织的裂纹扩展机理。研究表明:为了扩展主裂纹,外加载荷需要增加。外加载荷的增加一方面归功于试样表面观察到的主裂纹并没有穿透整个试样厚度,另一方面因为应力场由缺口控制,只有随着外加载荷的增加,扩展的裂纹尖端才保持一定的应力。当两个层团的位向使裂纹从沿层扩展过渡到穿层扩展时,裂纹扩展阻力才提高。

The study was done using notched two-colony thick tensile specimens of a directionally solidified cast fully lamellar TiAl alloy. In situ-observations of fracture processes in scanning electron microscope （SEM） were combined with section-to-section related observations of fracture surfaces to investigate the crack growth process. Finite element method （FEM） calculations are carried out to evaluate the stresses for propagating cracks. The results reveal that： the reason why enhancement of applied load is required to propagate the main crack, on the one hand was attributed to that the main crack observed at the surface did not extend all the way through the specimen＇s thickness, on the other hand the stress field was still controlled by the notch, in which a definite stress required for extending a crack tip should be kept by increasing the applied load. Crack propagation resistance is enhanced at colony boundaries, only when a change occurs from an inter-lamellar propagation to a trans-lamellar propagation.