Study On Process And Structures Of Tial-basedalloy In The Shellmold Directional Solidification

TiAl-base alloys cater the requirement of speed due to their low density, high specific strength, better oxidation and creep resistance at evaluated temperature. However, because of their low room fragility and highly chemical reactivity in Melton state their industrialization process was limited. Although cold crucible directional solidification technology can solve the problem of pollution, Processing problem remains unresolved.In this paper, we used the shell mold method in directional solidification of TiAl based alloy, and determined the process parameters of through numerical calculation and thermocouple. Meanwhile, we also determined the optimum of Φ15Ti-45Al-2Cr-1.3Nb process parameters which was heating power21kW and speed1.Omm/min by the analysis of the influence of Heating power and speed on directional solidification micro structure. We observated and analyzed the maro and microstructure of Ti-45Al-2Cr-1.3Nb in directional solidification, the growing region can be divided into the initial growing region, the growth interface and transforming growth region. The stable grow zone composed by a2+y.And there region which was rich Cr and less Al. But, in the upper of stable growing region with less β segregation type, the number of Y2O3increased. Thermal analysis about the shell mould directional solidification technologies had been done and a simple growth model was established. The above work explained the reason of its flat growth morphology. Take maximum advantage of directional solidification shell mould technology,29mmx9mm square shape directional solidification sample was prepared.Then, we chosen representative TiAl alloy, for example High niobium TiAl alloy, High niobium TiAl alloy contained B and Ti-48Al-2Cr-2Nb, and experimented in the optimum process. We also analyzed directional effect, organization, and defects of the directional solidification experiment. There were beta segregation rich Nb and less Al segregation in three yuan titanium aluminum alloy with high Nb, and four yuan titanium aluminum alloy containing Cr and Nb mainly exist beta segregation, but less rich Cr and Al segregation, and segregation area is located in the isometric gamma phase. When content of Al was higher, the beta type of segregation reduced in a certain extent.In the process, B elements mixed with Y2O3existed in thslice layer. In addition, directional solidification sample of Ti-48Al-2Cr-2Nb was prepared. And summarized directional ability of the shell mould directional solidification technology.Mechanical properties-micro hardness and fracture toughness-of each component after directional solidification was analyzed. We also analyzed influence of different growth stages and alloying elements of TiAl alloy on micro hardness and fracture. The hardness of directional growth stable region was significantly greater than non-directional zone. When the content of Al from43increased to52for three element TiAl-based alloys, the micro hardness of growth direction of the cross-sectional from494.4downed to365.5, and the fracture toughness13.6down to5.6.We calculated the content of aluminum of multicomponent TiAl-based alloys by the aluminum equivalent method. When the content of Al from41.2increased to50.2, the fracture toughness gradually reduced in overall. But there was fluctuation point in47%.