Friction stir processing parameters and property distributions in cast nickel aluminum bronze

Abstract

Cast nickel-aluminum bronze (NAB) alloy is specified for many marine applications, including ship propellers, due to its excellent corrosion-resistance combined with acceptable mechanical properties. Friction stir processing (FSP) can be used to improve the alloyâ s mechanical properties by localized microstructure modification in the cast material. FSP converts an as-cast microstructure to a wrought condition in the absence of macroscopic shape change, closes porosity, and provides a means to surface harden the castings. The closure of porosity near the surface of the material may shorten the manufacturing and processing time for ship propellers. The surface hardening of cast NAB alloy can be used to increase the wear life of ship propellers. Rockwell Scientific Corporation (now Teledyne Scientific Corporation) supplied three Nickel Aluminum Bronze alloy plates which have been friction stir processed in a raster pattern under a Defense Advanced Research Project Agency (DARPA) project. Each plate had been processed using a different tool RPM and IPM (inches per minute of transverse) combination. Miniature tensile samples were sectioned from the FSP zone and surrounding base metal and mechanical property distributions were determined in these regions. The material within the FSP zone exhibited consistently higher yield strengths, ultimate tensile strengths, and ductilities than the as-cast base metal.