The microstructure and mechanical property of TiAl alloy containing β-stabilizer

Abstract

In this study, TiAl alloy with the nominal constitution of Ti45Al2Cr2Nb and Ti45Al4Cr2.5Nb were prepared by the cold crucible directional solidification method, the microstructure and mechanical property were investigated by means of XRD, SEM as well as tensile test. The different microstructure of the two TiAl alloy was analyzed, the main reason of the difference is their different segregation pattern, in the Ti45Al2Cr2Nb alloy the s-segregation is the dominating pattern while in the Ti45Al4Cr2.5Nb β-segregation is the dominating pattern, which cause the discrepancy distribution of B2 phase and independent γ phase in the two alloy. In the Ti45Al2Cr2Nb the B2 phase distribute in the lamellar colony and in the Ti45Al4Cr2.5Nb the B2 phase distribute in the boundary of the lamellar colony. Besides, the different microstructure also influence the mechanical property, the brittle B2 phase in the lamellar colony break the continuity of the lamellar and the boundary of B2 could act as the source of the crack during deformation. In the tensile test the ultimate tensile strength of the Ti45Al2Cr2Nb and Ti45Al4Cr2.5Nb alloy are 347 MPa and 539 MPa respectively. Interestingly, the Young modulus that is the intrinsic property of TiAl alloy and not affected a lot by the microstructure also gets higher, which means that the Cr, Nb element strengthen TiAl alloy not only by optimizing the microstructure but also by strengthening the matrix.