Surface modification of Ti-6Al-4V alloy via friction-stir processing: Microstructure evolution and dry sliding wear performance

The friction-stir processing (FSP) method was employed to the surface modification of Ti-6Al-4V alloy applying different processing parameters. The defect-free friction-stir processed surface layers with ~ 2.5 mm thickness, with final microstructures of β-regions with acicular-α and GB-α, or Martensite-α′ phase, were obtainable. The FSP processing thermal cycles, macro/micro-structures, phase evolutions, microhardness measurements, and dry-sliding wear performance of the processed surface layers were investigated. Considering to the basic laws of Ti-6Al-4V microstructure evolutions during the FSP procedures, the relations between processing parameters and produced microstructure characteristics were further elucidated. It was found that a relatively lower processing peak temperature and a fast enough cooling rate benefited the formation of the fine β-regions with ultra-refined acicular-α phase and/or even needle-typed Martensite-α′. The microstructures favored the improvement of hardness and wear performance of the processed surface layers, in comparison with those properties of the base material.