Crack Propagation In Single Crystal Gamma-TiAl Alloy By Molecular Dynamics

There are series of excellent properties of γ-TiAl alloy which used in aviation, aerospace and automobile. During manufacture process various inevitable defects such as porosity, impurities and micro cracks would exist. It is easy to cause deformation, cracking and even fracture failure of components during working. Crack propagation is the main reason which leads to material failure. In practice, there exist a variety of defects instead of a single defect. So, it is necessary to know and understand in detail about the mechanism and process of crack propagation and fracture. Molecular dynamics method is adopted to study the crack propagation and fracture mechanism.The main contents of this paper are as follows:(1) Effects of defect on the properties of γ-TiAl specimen at room temperature and temperature on crack propagation are studied. The influence of crack on γ-TiAl specimen properties is analyzed by two models which with and without crack. The results show that when there is no crack on the model, not only dislocation emit and concentration occur, but also appears slip band, which lead to fluctuating of total energy, while slip band doesn’t appear at model with crack, after specimen fracture the total energy keep balance. The existence of the crack will accelerate the fracture and reduce the strength of the specimen. In addition, effect of temperature on crack propagation is studied, the results follow that: the higher the temperature is, the lower the yield strength of specimen is, and modulus of elasticity would decrease with increasing of temperature. Dislocation emits easily from crack tip. And the more the dislocation emits, the higher the total energy is, it lead to the system unstable at high temperature. It is prone to appear plastic deformation, but the tendency of total energy will not affected by temperature. Though temperature is different, the mechanism of crack propagation is similar. But the time which crack initiation and first dislocation emits is different, the rate of crack propagation would slow down and the path would become complicate with of increasing temperature.(2) Effect of holes size on crack propagation is studied. The mechanism of crack propagation is analyzed at three different radius of hole. The results show that the initiation stress would decrease with increasing of holes size. As the radius of holes are different, the position of crack initiation and crack propagate mechanism are different after holes combine with crack. In addition the crack propagation is inhibited by the hole. Stress distribution and total energy is affected by dislocation which appears during crack propagation.(3) Crack propagation rule of parallel double crack is studied. The mechanism of crack propagation rule and effect of each other under four different crack length ratios is analyzed. the results show that there are influence between two cracks and inhibition between each other. The time of the first dislocation emits, crack begins to propagate, and the numbers of dislocation are different when crack length ratio is different. At the condition of two cracks not equal, the shorter of the short crack is, the greater of the strength of the specimen is. Besides, there is a good consistence between energy curve and stress-strain curve, due to the change of dislocation and slip band appearing and moving.