TWI

Friction stir processing (FSP) experiments were undertaken on three Ni-based alloys (Alloy 625 (Ni, 21.6%Cr, 8.6%Mo, 3.7%Fe), Alloy 718 (Ni, 23.7%Fe, 18.1%Cr, 3.1%Mo, 1%Ti) and Hastelloy X (Ni, 21.3%Cr, 19.2%Fe, 8.3%Mo)) using a W-Re tool, process parameter windows were defined, and the microstructure and mechanical properties of processed specimens were investigated. FSP was conducted using an Accustir gantry style friction stir welding machine. Alloy coupons were embedded with type K thermocouples to record thermal histories during processing. FSP parameters were varied in situ so that interactions between the process inputs (travel speed, tool rotation rate and plunge depth) and forces (normal force, path force and torque) could be monitored for each alloy. Microstructure was observed by optical microscopy, SEM and energy dispersive spectroscopy. Mechanical properties were characterised by hardness measurements and longitudinal sub-size tensile tests. Issues discussed include grain refinement, hardness profiles in stir zone and TMAZ (thermomechanically affected zone), and the relationship between grain size and mechanical properties.

9th International Symposium, 15-17 May 2012, Session 8A: Nickel Alloys, Paper 01