Superplasticity and superplastic diffusion bonding of a fine-grained TiAl alloy

Abstract

Superplasticity and superplastic diffusion bonding in a TiAl alloy with a fine-grained duplex microstructure have been investigated in order to fabricate TiAl alloy products using a combination process of superplastic forming with diffusion bonding. Superplastic tensile tests were carried out at temperatures ranging from 1000 to 1100°C, and at strain rates ranging from 10 -5 to 10-3 s-1. A low superplastic flow stress of less than 25 MPa was observed at 1100°C and at a strain rate of 8.3 × 10-5 s-1. Under this condition, a tensile elongation of 300% and a strain rate sensitivity coefficient of over 0.5 were obtained. Furthermore, superplastic diffusion bonding under a low pressure of 10 MPa was conducted. Defect-free bonds were achieved at 1100°C for holding 1 h. It is suggested that the low superplastic flow stress at 1100°C allows a significant plastic flow between the two contacted surfaces, resulting in a full contact of the surfaces, which is necessary for the sound bonds. Finally, a two-sheet part of spherical dome was successfully produced from this alloy. © 2005 The Japan Institute of Metals.