The microstructures and mechanical properties of Ti Al alloys are directly linked to micro-segregation which cannot be avoided during solidification. So a thorough understanding of the micro-segregation should be a gr...The microstructures and mechanical properties of Ti Al alloys are directly linked to micro-segregation which cannot be avoided during solidification. So a thorough understanding of the micro-segregation should be a great help to further enhance the mechanical properties of the cast products. Theoretical analysis and experiments have been used to predict the micro-segregation, but it is very difficult to observe and determine the dendritic segregation in the micro region. Phase-field method has been employed for the simulation of dendritic growth. However, due to the complicated quasi-sub regular solution model for Ti-45Al(at.%) alloy, the classic phase-field models have difficulty to deal with the free energy. In this work, a phase-field model by linking thermodynamic calculation was used to simulate solidification dendritic segregation of Ti-45 Al alloy for Liquid→Liquid+β(Ti). The free energies of solid phase and liquid phase for Ti-45 Al alloy were calculated by Thermo-Calc and then coupled with the phase-field equations. The simulation results show the dendritic morphology and Al content variations between liquid and growing solid phase for Ti-45 Al alloy. With the growth of the β(Ti), dendritic segregation is formed in the liquid and solid phases due to the solute partitioning and rejection into the liquid. As a result, the dendrite arms are depleted of Al element, while the inter-dendrites are enriched. The dendritic tip growth velocity decreases with the progress of solidification, whereas the segregation ratio increases.展开更多
Dislocation structures in the γ phase grains of Ti 45Al 10Nb specimens have been characterized after tensile tests at room temperature. In addition to ordinary dislocations with b=1/2〈110], a certain density of supe...Dislocation structures in the γ phase grains of Ti 45Al 10Nb specimens have been characterized after tensile tests at room temperature. In addition to ordinary dislocations with b=1/2〈110], a certain density of superdislocations and faulted dipoles were observed, which are rarely present in the conventional two phase TiAl base alloys of normal impurity. This difference was attributed to the solution of high Nb in the γ phase, which may increase the CRSS for 〈110] ordinary slip.展开更多
文摘The microstructures and mechanical properties of Ti Al alloys are directly linked to micro-segregation which cannot be avoided during solidification. So a thorough understanding of the micro-segregation should be a great help to further enhance the mechanical properties of the cast products. Theoretical analysis and experiments have been used to predict the micro-segregation, but it is very difficult to observe and determine the dendritic segregation in the micro region. Phase-field method has been employed for the simulation of dendritic growth. However, due to the complicated quasi-sub regular solution model for Ti-45Al(at.%) alloy, the classic phase-field models have difficulty to deal with the free energy. In this work, a phase-field model by linking thermodynamic calculation was used to simulate solidification dendritic segregation of Ti-45 Al alloy for Liquid→Liquid+β(Ti). The free energies of solid phase and liquid phase for Ti-45 Al alloy were calculated by Thermo-Calc and then coupled with the phase-field equations. The simulation results show the dendritic morphology and Al content variations between liquid and growing solid phase for Ti-45 Al alloy. With the growth of the β(Ti), dendritic segregation is formed in the liquid and solid phases due to the solute partitioning and rejection into the liquid. As a result, the dendrite arms are depleted of Al element, while the inter-dendrites are enriched. The dendritic tip growth velocity decreases with the progress of solidification, whereas the segregation ratio increases.
文摘Dislocation structures in the γ phase grains of Ti 45Al 10Nb specimens have been characterized after tensile tests at room temperature. In addition to ordinary dislocations with b=1/2〈110], a certain density of superdislocations and faulted dipoles were observed, which are rarely present in the conventional two phase TiAl base alloys of normal impurity. This difference was attributed to the solution of high Nb in the γ phase, which may increase the CRSS for 〈110] ordinary slip.
