Interfacial structures and diffusion studies in solid state bonded TZM (Mo-0.5Ti-0.1Zr) specimens using multilayers

TZM alloy has excellent high temperature mechanical properties, high recrystallization temperature and good resistance to liquid metals and hence this alloy finds application in missile technology, fusion reactors and also as structural material for high temperature nuclear reactors. Practical application of this alloy requires joining at low temperature. Diffusion bonding technique was used for joining TZM alloy with Ti, Mo and Ta as interlayer and thickness of these foils was in the range of 100 - 200 μm. Specimens were bonded in the temperature range of 900 to 1200 deg C for 2 hrs at a pressure of 50 MPa. The cross-sections of the annealed specimens were characterized using optical microscope, scanning electron microscope (SEM) and electron probe micro analyser (EPMA). The microstructure of the TZM base material consisted of large elongated grains with carbide precipitates along the grain boundaries. All the interlayers Ti, Mo and Ta produced excellent contact at the interface and the microstructure revealed absence of discontinuities or micropores along the interface. A bonding temperature of about 1200 deg C was essential for joining TZM using Ta and Mo interlayers and 1000 deg C was suitable using Ti as an interlayer. The concentration profiles of Ti and Mo for TZM/Ti/TZM specimens joined at 1000 deg C were asymmetric about the Matano Interface and Mo was found to diffuse to about 50-70 μm into Ti and the diffusion of Ti into Mo was generally less than 20 μm. The paper presents details of microstructure, diffusion parameters and the advantages of using Ti as an interlayer for joining TZM alloy. (author)