Tial Intermetallic Compound Of Damage Mechanisms

This paper focuses on the studying of damage mechanisms of TiAl-based alloys of fully lamellar and duplex. The damage mechanism of lamellar and duplex TiAl alloys has been investigated in tensile-unload experiments and situ SEM experiments. The studies indicate that, if the displacement-controlled is applied, the fiat tensile process produces microcracks which result in damage of materials. With load increasing, microcracks will propagate and at the same time, a lot of new microcracks will come into being. Pre-damage will increase the initiation and propagation of cracks as well as the degree of damage. Pre-damage at different degrees will decrease the material elastic module and the ability against crack initiation and propagation; but the pre-damage has no effect on the ultimate fracture properties. If the load-controlled is applied, the microcracks will not come into being easily, even if they have, they will have no time to propagate. So the damage has no influence on the elastic module, the stress of fracture, the strain of fracture and yielding stress. In addition, the result of in-situ tensile-unload experiment indicates: during the tensile-unload process, the fracture process is completely different because the damage mechamsm is different to specimens with notch and flat specimens. To the specimens with notch (pre-fracture), the process of causing fracture is the one that is initiated by the main fracture which will propagate and fracture because of the centralization of stress in the root of notch; while, to the flat specimens, it is many microcracks that will fist come into being, and they will propagate with the increasing of stress. At the moment that facture and stress interact with each other and cause the further propagation of microcracks, the specimens will cleavage fracture.