Microtextural Characterization of Shear Textures in the Thermo- Mechanically Affected Zone of Friction Stir Processed Nickel Aluminum Bronze

摘要

Cast nickel-aluminum bronze (NAB) is used in the production of the Navy's marine propellers for both surface and submersible platforms. Improving the properties of NAB will facilitate new designs. Friction Stir Processing (FSP) is a solid state, thermo-mechanical process to achieved surface hardening of cast NAB by use of a rotating tool that is plunged into and traversed across the material surface. The subsequent 'stirring' action produces local yielding/ softening of the material by frictional as well as adiabatic heating. The softened regions experience extensive shear deformations resulting in refinement and homogenization of the local microstructure. In essence, FSP can be used to achieve a wrought microstructure from as-cast nickel-aluminum bronze in the absence of macroscopic shape change. There is a region known as the Thermo- mechanically Affected Zone, or TMAZ, in material that has experienced FSP. This region, similar to the heat affected zone (HAZ) common in fusion welding, displays a microstructure characteristic of one affected by diffusion of heat, as well as deformation induced by the rotating tool resulting in the development of shear textures. Using Orientation Imaging Microscopy (OIM) these shear textures were analyzed and characterized for two separate FSP conditions. Through OIM, shear textures in the TMAZ were characterized to be of the C-type, with varied lattice orientations. Shear directions were predominately in the direction of tool advance for one processing condition, while tangent to the tool interface for the other.