Investigation Of High Temperature Deformation Behaviors And Microstructure Mechanical Properties Of High Nb Containing TiAl Allly With MO

As one of the light-weight structural materials, TiAl alloys has many excellent properties such as high temperature mechanical properties( high temperature toughness of metal and high temperature property of ceramics ), low density, good oxidation resistance, high creep resistance and excellent high temperature intensity. These characteristics make them becaming one of the most promising novel light-weight structural materials in engineering application. So far, many countries have achieved fruitful resultes in the preparation and processing of TiAl alloys in order to obtain high performance. However, TiAl alloys have poor hot-working abilility and low plasticity at room temperature due to a small number of movable dislocation, large burgers vector of super dislocation and difficultiies to cross-slip. The hot-working abilility and room temperature plasticity has becoming the key point that restrict the application of TiAl alloys, so the deformation mechanism of TiAl alloys should be researched.Through thermal compression simulation experiment, high temperature deformation behavior and microstructural evolution of Ti-45Al-5Nb-0.8Mo-0.3Y alloy were studied and the hot processing map was also drewd in this paper. The corresponding results of thermal simulation were used as the guidance of canning extrusion. The thermal simulation experiments show that the flow-stress of the casted Ti-45Al-5Nb-0.8Mo-0.3Y alloy rised as increasing strain rate or reducing temperature. Calculated theraml activationg energy Q=385.107 KJ/mol. In the early stages of thermal processing of the cast Ti-45Al-5Nb-0.8Mo-0.3Y alloy, the deformation mechanism is based on twinning and dislocation silp ofγphase near the lamellar crystal group, while slip of the unstableβphase played a coordinating role. Deformation increases to a certain extent , dislocation slip of dynamic recrystallizationγgrain is primary deformation mechanism, and dislocation slip ofβphase is secondary. Dynamic recrystallization ofγphase and dynamic recovery ofβphase are the softening mechanism. The hot processing map can be divided into flow instability region and security zone according the power dissipation efficiency in different regions. Then the reasonable process parameters of sheath extrusion were established. Furthermore, the deformation mechanism in different regions was analyzed based on the hot processing map.At high temperature and room temperature, the tensile properties on cast and extrused alloy were analyzed and compared. The results show that: the property of alloy has greatly improved after hot extrusion. The room temperature fracture of the casted and extrused alloy were influenced by the microstructure. The room temperature fracture of the casted alloy was brittle intergranular fracture, while the extrused alloy was intergranular fracture. When temperature exceeds the brittle-ductile transition point, the fracture mechanism of the cast and extruded alloy have changed.The cast alloy changed from brittle intergranular fracture to quasi-cleavage fracture, with a very small amount of ductile fracture characteristics. The extruded alloy has a transition form intergranular fracture to ductile fracture.The hot-working abilility was improved by the intorduction of unstableβphase, which also made a worse plasticity at room temperture. In order to improve the ductility, the heat treatment of the extrusion alloy was studied and the reasonable thermal process parameters were established. At last, the tensile properties at room temperature after heat treatment and the tensile fracture were analyzed.