孔洞对双晶TiAl合金断裂行为影响的声发射响应

本文基于分子动力学方法,对含孔洞的双晶TiAl合金试样进行了单轴拉伸模拟,在纳米尺度下研究了材料变形和断裂过程中的缺陷演化行为及其声发射响应。研究发现：孔洞大小和位置对材料的弹性模量影响较小,屈服强度随孔洞尺寸的增大而降低；进入塑性变形后,孪晶界对孔洞边缘连续发射的位错有阻碍作用,使晶体强度增加；达到屈服应力时,含晶界孔洞的试样更容易产生稳定的位错结构,阻碍其他位错运动,从而提高了晶体强度；通过对拉伸过程中的声发射信号进行分析,发现声发射信号主要来源于晶格振动,并且具有较大的功率值范围和较低的中值频率；位错滑移的声发射信号表现出宽频域的特点,位错增殖和位错塞积的声发射信号表现出低功率的特点；裂纹扩展的声发射信号属于突发型信号,表现为高频率、高功率的特征。

Acoustic Emission Response on Effect of Voids on Fracture Behavior of Bicrystal TiAl Alloy

Based on the molecular dynamics method, the uniaxial tensile simulation of the bicrystal TiAl alloy containing voids is performed. The evolution behavior of defects and acoustic emission(AE) response on the deformation TiAl alloy and fracture of the TiAl alloy are studied at nanometer scale. The results show that the size and location of the voids have little influence on the elastic modulus of the TiAl alloy and the yield strength decreases with the increase of the void size. After plastic deformation, twin boundary can block dislocation emitted continuously at the edge of void, and increase crystal strength. When yield stress is reached, the TiAl alloy with voids at grain boundary is more likely to produce stable dislocation structure, which hinders the movement of other dislocations, thus improving the crystal strength. Through the analysis of the AE signals during the stretching process, it is found that the AE signals mainly come from lattice vibration, and has a large power range and a lower median frequency. The AE signals of dislocation slip reveal the characteristics of wide frequency domain, and the AE signals of dislocation proliferation and dislocation accumulation display the characteristics of low power. The AE signals of crack propagation belongs to the burst signal, which is characterized by high frequency and high power.