Diffusion bonding of the Mo-base alloy TZM with interlayers

Abstract

Abstract Molybdenum-base alloys have excellent high temperature mechanical properties and joining of these alloys as heat sink materials is envisaged in many structural applications of fusion reactors. TZM is an important Mo-base alloy and diffusion bonding experiments were carried out in a hot vacuum press by sandwiching interlayers, Ti, Ni, Mo and Ta between two pieces of the TZM alloy in the temperature range 900 to 1200 °C. Detailed metallurgical analysis was carried out using optical microscopy, scanning electron microscopy and by electron probe microanalyser. All the sandwiched diffusion couples consisting of TZM/X/TZM, (X = Ti, Ni, Mo, Ti) showed defect-free microstructures at the bonded interface at the optimised bonding conditions. Ti seems to be a more suitable interlayer compared to other interlayers in terms of bonding temperature and applied pressure. The TZM/Ni interface was marked by the presence of the intermetallic compound NiMo. The concentration profiles for diffusion couples TZM/Ti were asymmetric, whilst TZM/Mo and TZM/Ta were symmetric about the Matano Interface. The interdiffusion coefficients calculated using the Boltzmann–Matano method for TZM/Ti diffusion couples showed decreases in the values with increase in the Mo concentration.