Nanocrystallization of interfacial microstructure of deformed particles in cold sprayed Ti6Al4V deposits

Abstract

The low temperature solid deposition characteristics of cold spraying technology are conducive to the remanufacturing/repair of oxidation sensitive titanium alloy in the atmosphere. Ti6Al4V alloy deposits prepared by cold spray (CS) usually show porous microstructure due to insufficient plastic deformation of Ti6Al4V alloy particles. The interfacial bonding and the microstructural evolution mechanisms of Ti6Al4V particles during cold spray are still unclear. In this study, the Ti6Al4V deposits were prepared by cold spray with nitrogen as process gas at a temperature of 800 °C and a pressure of 4 MPa. The micron CT results show that the porosity is 8.25%. The deformation ultrafine grain zone and un-deformation martensitic laths zone at the bonding interface between Ti6Al4V particles were observed. The EBSD results show that the grain orientation signal was only detected at the edge of the particles deformation area and the 23% of grain sizes detected by EBSD are less than 500 nm, which indicates that the nanocrystallization induced by dynamic recrystallization occurs at the inter-particle boundaries between cold-sprayed Ti6Al4V particles. The TEM and SADPs demonstrate a gradient structure consisting of equiaxed nanograins zone, crushing dendrites transition zone and original martensitic laths zone from the interface to the core of particles.

Keywords

• Cold spray
• Titanium alloy
• Interface
• Microstructure
• Nanocrystallization