The microstructure and strength properties of MA957 nanostructured ferritic alloy joints produced by friction stir and electro-spark deposition welding

The nanostructured ferritic alloy (NFA) MA957 was joined by friction stir welding (FSW) and electro-sparked deposition (ESD) welding. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) characterization studies showed a uniform fine-scale equiaxed ferrite structure with a high dislocation density and slightly coarsened nm-scale particles in the joint region of the FSW weld compared to the base metal. Microhardness and tensile measurements on the FSW showed a modest reduction in the strength of the joint compared to the as-processed MA957. In contrast, the ESD-welds contained considerable porosity and the nm-scale particles dissolved or coarsened significantly, resulting in a larger degradation of the joint region strength. Thus FSW is a promising method for joining NFAs.