Diffusion bonding of investment cast #gamma#-TiAl

Intensive alloy development studies on intermetallic gamma (#gamma#) based alloys in recent years has led to the development of several aerospace engine components using advanced #gamma#-TiAl based alloys by ingot and powder metallurgical routes. These materials are of great interest to the aerospace industry owing to their very low density and good high temperature properties. Further application of this material will require the development of successful joining and cost effective fabrication methods. Joining of this intermetallic alloy by fusion joining processes, however, requires very careful process controlling, i.e. low cooling rates and very high preheat temperatures. On the other hand, solid state joining processes, particularly diffusion bonding, brazing, and friction welding, can readily be used to join this material. In the present work, successful application of solid state diffusion bonding to weld investment cast #gamma#-TiAl alloys has been demonstrated. A series of diffusion bonds were produced without using an interlayer at temperatures ranging from 950 to 1100 C with different pressure levels and holding times. Bonds have been characterized using optical and scanning electron microscopy. Defect-free bonds were achieved for all the conditions studied. The bond qualities were assessed by shear testing at room temperature. Reasonable shear strenght levels were obtained by bonding at 1000 and 1100 C for 3 h at pressures of 20 and 40 MPa, respectively. The bonds were also post bond heat treated at 1430 C for 30 min, which improved the bond quality in all cases. (orig.)First published in Journal of Materials Science 34 (1999) 3345-3354SIGLEAvailable from TIB Hannover: RA 3251(99/E/58) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman