TiAl基合金双态组织原位拉伸-卸载试验研究

Experimental investigation of in-situ tensile-unloading of duplex TiAl alloy

通过对TiAl基合金不同类型的缺口试样进行原位拉伸-卸载实验及其SEM断裂表面观察,研究了TiAl基合金的断裂机理.研究发现,对于缺口试样,裂纹起裂于缺口根部,其断裂过程主要是主裂纹首先起裂、扩展并最后断裂.对于双态组织,由于晶粒尺寸小,应力集中出现在缺口根部,裂纹沿晶粒边界和层间起裂并扩展,裂纹路径比较平直.在拉伸过程中,试样产生微裂纹导致材料发生损伤,随后卸载再加载时,与先前相比,裂纹更易扩展.预损伤加快了裂纹的产生和扩展,使损伤进一步加重,促使材料抵抗裂纹产生、扩展的能力下降.

By means of in-situ tensile-unloading test on different notched specimens of duplex TiAl-based alloys and SEM observation upon their fracture surface, the fracture mechanism of TiAl alloys was investigated. It was found by investigation that cracks were initiated at the notch root for the straight notch specimens. The main crack was initiated first, then propagated, and fractured finally. For duplex microstructure, because the grain size was very fine, the stress concentration appeared at the notch root, then the cracks was initiated and propagated along grain boundary and lamellar interfaces, so that the main crack propagation path was straighter. Microcracks produced in the tensile process induced the damage of materials. With subsequent unloading and reloading, the microcracks were easier to propagate than those before reloading. Pre-damage would accelerate crack initiatiofi and propagation, and aggravate the damage, making the ability of crack initiation and propagation decrease.