Study On The Mechanism Of Crack Healing In Titanium Alloy

The study on the mechanism of crack healing of materials can help us elimate the cracks in materials and will improve the performance of materials. By this way we can recycle many materials we can not use before. This has an important economic value. And by understanding the mechanism of crack healing we can find the reasons of the appearance of cracks and its diffusion way. In the production it can provide theoretical guidance for avoiding crack.The molecular dynamics method is used to simulate healing of an sphere crack inside titanium under compressive stress. The result shows that dislocations are emitted firstly from the sphere crack and move along the close-packed planes. The generation of dislocation is accompanied by the stacking fault. The sphere crack becomes smaller and smaller until it is healed through dislocation emission, motion and annihilation. After crack healing, there are a residual dislocation net and some vacancy sites. It seems that the cavity inside the sphere crack is transferred through dislocation emission, motion, and annihilation.In order to study the effect of grain boundaries on void healing under compression,this experiment using molecular dynamics simulation method, simulate the healing process of void in double crystal of titanium. The simulation comparies three kinds of relations of grain boundaries and void positions and the different mechanisms of healing. The relationships between these three groups are: the void is far from the grain boundary, near the grain boundary and on the grain boundary. The result shows that: in the condition of compression under constant temperature, the void which is far from the grain boundary is the most easy to be healed with dislocation rings emissioning at both edges of void. The void near the grain boundary, is the second one to be healed with only one dislocation ring emissioning. The void on the grain boundary, with no dislocation ring around, but linear dislocations along closing packed surface in two different grains finally heals.By the research of the effect of strain, temperature, strain rate, grain boundary on the healing of cracks in titanium alloys, it suggest:(1) as the strain increases, the crack oftitanium alloy in place along the close packed surface outward dislocation emission,accompanied by the stacking faults, finally healing crack;(2) the temperature had a great effect on the speed of crack healing, and the healing mechanism at the crack is mainly formed with healing mechanism of bond between the healing mechanism of diffusion atoms heat and close atomic;(3) high strain rate leads to the dislocation after initiation and development lag that strain rate sensitivity is due to the lag of the dislocation;(4) other conditions are the same, should not conducive to crack healing gear ratio.