Formation mechanism of nano-crystal on the blade surface produced by low-plasticity ultrasonic rolling strengthening process

This paper proposes a low-plasticity ultrasonic rolling strengthening process (URSP) to form a surface hardened layer of titanium alloy blade. The process principle of low-plasticity URSP is firstly analyzed, and then the mechanism of titanium alloy blade surface grain refinement is revealed based on the SEM, TEM and EBSD experiment. The mechanical properties of strengthen layer caused by the grain refinement are finally analyzed on macroscopic and microscopic scales. The results showed that the low-plasticity URSP reduced the volume of the grain and formed nano-crystal with clear grain boundary distribution on the blade surface. The low-plasticity URSP formed a hardened layer with the depth of 70 μm caused by grain refinement and the nano-hardness is increased by 26 %.