Orientation structural mapping and textural characterization of a CP-Ti/HA surface nanocomposite produced by friction-stir processing

Abstract

In this study, hydroxyapatite (HA) nanoparticles (~120 nm, 3 vol%) are incorporated within a subsurface layer based on commercial pure titanium using multi-step friction-stir processing (FSP) to fabricate an CP-Ti/HA surface nanocomposite. A combination of electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM) analyses are used to developed a correlation between microstructural features and crystallographic texture formed by material flow and dynamic restoration phenomena in the processed titanium versus CP-Ti/HA surface nanocomposite. An equiaxed ultra-fine grained structure with a mean size <1.4 μm forms on the surface of both samples caused by N and O absorption into the structure of the titanium substrate during high-temperature severe plastic deformation via FSP. The annealed BM does not contain any preferred orientation and its texture is completely random. However, the scenario is significantly altered by FSP treatment due to martensitic phase transformation as well as the absorption of impurities on the titanium surface, the incorporation of HA inclusions, and thermo-mechanical treatment. This results in new crystallographic textures consisting of weak shear and strong prismatic P-fiber dominant components on the surface and center of the processed zone respectively.