Fabrication of TiCp/Ti–6Al–4V surface composite via friction stir processing (FSP): Process optimization, particle dispersion-refinement behavior and hardening mechanism

After the process optimization experiments according to a series of principles stated in the paper, the TiC particle-reinforced surface composites were successfully fabricated via friction stir processing (FSP) method on the Ti–6Al–4V alloy substrates, using a surface-reservoir reinforcement placement method for embedding TiC powder into the substrate. A relatively uniformed dispersion and an ultra-refined average size of the introduced TiC reinforcements were obtained. The reinforcement behaviors of dispersion and refinement were investigated in consideration of the plasticized Ti-matrix material-flow characteristics during FSP. Nano-sized martensite-α′ phase and ultra-refined TiC particles were found in the TiCp/Ti–6Al–4V surface composites. The average micro-hardness of the produced surface composites was 680Hv0.2. The thicknesses of hardening surface layer with the hardness upon 650Hv0.2 reached 900 μm. It was further discussed on the hardening mechanisms including ceramic particle strengthening, nano-sized refinement pinning effect and matrix martensite-α′ influence.