Karanam Bhanumurthy

Friction stir welding (FSW), a solid-state joining technique, is being extensively used in similar as well as dissimilar joining of Al, Mg, Cu, Ti, and their alloys. In the present study, friction stir welding of two aluminium alloys—AA6061 and AA5052—was carried out at various combinations of tool rotation speeds and tool traverse speeds. The transverse cross-section of the weld was used for optical as well as electron microscopy observations. The microstructural studies were used to get an indication of the extent of material mixing both at the macro- and microscales. It was observed that, at the interface region, both materials exhibited similar texture despite the nonrigorous mixing of the materials in the nugget. The extent of interdiffusion of alloying elements at the interface was studied using electron probe microanalysis. The tensile testing evaluation of these specimens showed good mechanical properties. The interdiffusion of alloying elements and development of similar orientations in the nugget could have contributed to the better tensile properties of the friction-stir-welded AA5052-AA6061 specimens.

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.