A surface Ti-WC composite was fabricated on CP-Ti by surface friction stirring(SFS)using a pinless WC-Co tool at a processing window of 800-2500 r/min and 8-50 mm/min.At 1600 r/min-50 mm/min,a defect-free composite layer with an average hardness of～HV 1170 is formed.The hardness was increased by WC and TiN reinforcing particles,dissolved Co atoms in Ti,and the formation of ultrafine grains.WC particles were incorporated into the Ti substrate owing to the intense frictional interaction/heating at the tool-plate interface(～1000 ℃),which led to strength loss and wear of the tool.The Williamson-Hall analysis of the XRD peaks of the SFSed sample confirmed a significantly small crystallite size(～100 nm).Wear tests showed that the wear resistance of the composite structure was about 4.5 times higher than that of the CP-Ti.Friction analysis revealed a significant reduction in average value and fluctuations of the friction coefficient.
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