Diffusion bonding of investment cast gamma-TiAl

Intensive alloy development studies on intermetallic gamma (gamma) based al loys in recent years has led to the development of several aerospace engine components using advanced gamma-TiAl based alloys by ingot and powder meta llurgical routes. These materials are of great interest to the aerospace in dustry owing to their very low density and good high temperature properties . Further application of this material will require the development of succ essful joining and cost effective fabrication methods. Joining of this inte rmetallic alloy by fusion joining processes, however, requires very careful process controlling, i.e. low cooling rates and very high preheat temperat ures. On the other hand, solid state joining processes, particularly diffus ion bonding, brazing, and friction welding, can readily be used to join thi s material. In the present work, successful application of solid state diff usion bonding to weld investment cast gamma-TiAl alloys has been demonstrat ed. A series of diffusion bonds were produced without using an interlayer a t temperatures ranging from 950 to 1100 degrees C with different pressure l evels and holding times. Bonds have been characterized using optical and sc anning electron microscopy. Defect-free bonds were achieved for all the con ditions studied. The bond qualities were assessed by shear testing at room temperature. Reasonable shear strength levels were obtained by bonding at 1 000 and 1100 degrees C for 3 h at pressures of 20 and 40 MPa, respectively. The bonds were also post bond heat treated at 1430 degrees C for 30 min, w hich improved the bond quality in all cases. (C) 1999 Kluwer Academic Publi shers.