Analysis of microstructure refinement during single-pass and multi-pass friction stir processing of NiAl propeller bronze

Abstract

High strength, corrosion resistance, ductility, and toughness are material properties required for United States Navy (USN) Propellers. Propellers for both surface ships and submarines in the USN are currently made from cast Nickel Aluminum Bronze (NAB) Wrought NAB exhibits strength, corrosion resistance, high dampening capacity, low friction coefficients, and good fracture toughness for a wide range of temperatures [1]. Casting NAB into large structures lowers some of the qualities seen in wrought material and sought after for the propellers. After casting, some of the structure exhibits high porosity and an undesirable grain structure. Friction Stir Processing (FSP) can be used to refine grain structures and remove pores created during casting. This would reduce or eliminate the need for heat treatment and fusion welding currently being used to prepare Navy propellers. Orientation imaging microscopy was used to aid understanding of friction stir process's effects on grain structure evolution and processes of recrystallization in Nickel Aluminum Bronze. Observations were made about the grain orientation, size, and texture within the stir zone, thermal-mechanically affected zone, and the heat-affected zone for both a single-pass and a multi pass processed pieces of bronze.