Interface structure in a Fe–Ni friction stir welded joint

Friction stir welding of commercially pure iron and nickel was carried out using a polycrystalline cubic boron nitride tool. The macroscopic flow of the two phases generally corresponded to that predicted by the mixing models proposed in the literature. The interface region, however, revealed striations of the phases suggesting a complex flow pattern. Transmission electron microscopy and high resolution Auger analyses revealed that the width of the inter-diffusion zone was about 1.5 μm in single pass and 1.8 μm in double pass joints. The measured concentration profiles could be fitted using calculated profiles generated with static diffusion rates reported for iron and nickel. The diffusion profiles also indicated stabilization of the austenite phase at the interface, which it is proposed are the result of high levels of plastic strain.