The Microstructure Evolution And The Crack Initiates And Propagates Mechanism Of TC11 Alloy During Hot Process

As an important aerospace material, TC11 alloy is aα+βdual phase titanium alloy with the phasetransfer temperature between 998 and 1020℃. Because of its excellent properties such as high strength andfatigue resistance, it becomes an ideal material to make parts of aerospace engine. However, the applicationof TC11 alloy was so limited now because of the easily occurred defects such as fracture and fold duringforging process and the problem cannot be solved completely only by the present try- and -error method.So possible effective prediction of fracture can improve the efficiency and quality of the forged TC11 alloyparts and then promote the development and application of TC11 alloy. In this work, a damage evolutionmodel based on continuum damage mechanics theory was proposed to be used for fracture prediction. Andthe effect of microstructure and the microstructure parameters on the fracture process was analyzed. Thenthe fracture mechanism of TC11 alloy was discussed.First the stress-strain curves were obtained by physical simulation experiments and the effects ofdeformation conditions (temperature. strain rate)on the deformation behaviors were discussed and then theconstitutive equation was established. On this basis, the damage evolution model at high temperature wasestablished based on the continuum damage mechanics theory considering the effects of deformationconditions (temperature,strain rate) on damage evolution. Then the parameters of the model weredetermined by hot tensile tests. Finally, the proposed model was used to predict the fracture behaviorsduring upset forging. The results indicated that the model can predict the fracture successfully.The effects of the microstructure and the microstructure parameters on the fracture process werediscussed and fracture mechanism of TC11 alloy was studied. First, different microstructures were obtainedby changing heat treatment conditions and the microstructure evolution was analyzed. Then the relationshipbetween the volume fraction and size ofαphase and the heat treatment conditions were built up. Therelationship between the microstructure parameters and the mechanical properties were also discussed asthe damage evolution rate was proposed. At last, the facture mechanism of TC11 alloy was investigatedbased on some micro telescope observation. It is found that incompatibility of deformation between theαandβphases could be the main cause of fracture. It begins with some cavities and then those cavitiescoalescence and growth and finally the fracture happen.