Characterization of microstructure and mechanical properties for Ti-6Al-4 V processed by rotary ultrasonic roller burnishing

Ultrasonic assisted surface plastic deformation can significantly improve the mechanical properties of metal material by grain refinement and crystallographic texture. This paper investigated the effect of microstructure evolution on the microhardness and residual stress for Ti-6Al-4 V treated by rotary ultrasonic roller burnishing. The microstructure evolution of α and β phases was explained from grain size, crystallographic texture, misorientation, grain boundary and recrystallization. Crystallite rotation caused by ultrasonic vibration introduced strong crystallographic textures on the cross-sections of Ti-6Al-4 V samples. When ultrasonic amplitude was 7 μm, a strong {0001} texture appeared on the cross-section. The strength of α grain with {0001} texture orientation was larger than that of α grains with other texture orientations. The mean grain size of Ti-6Al-4 V cross-sectional sample was 7.39 μm at an ultrasonic amplitude of 7 μm. The corresponding maximum microhardness value 392.4 HV was larger than that measured at other ultrasonic amplitudes. However, the maximum compressive residual stress affected depth was obtained at an ultrasonic amplitude of 10 μm. The high microhardness of Ti-6Al-4 V was attributed to the grain refinement and crystallographic texture distribution of α and β phases in RURB. The high compressive residual stress affected depth was related to the fraction of deformed grain for α and β phases in RURB. •Various ultrasonic amplitudes could form different crystallographic texture.•The maximum microhardness appeared with the {0001} texture of α phase.•Residual stress affected depth increased with the fraction of deformed grain.•The maximum microhardness increased with the fraction of low angle grain boundary.•The maximum microhardness appeared with the minimum mean grain size.