Influence of powder properties and processing gas on the microstructural evolution of Armstrong CP-titanium and Ti6Al4V powders processed by cold spray

Abstract

This paper studies the microstructural evolution of commercially pure titanium (CP-Ti) and Ti6Al4V powders manufactured by the Armstrong process deposited by cold spray with nitrogen and helium. The unique, coral-like morphology of the powders resulted in high density deposits sprayed with both nitrogen and helium carrier gasses. The plastic deformation of the CP-Ti and Ti6Al4V particles upon impact leads to refinement of the equiaxed grains present in the starting powder. CP-Ti deposits sprayed with nitrogen result in a grain size of 1 ± 0.6 μm while deposit processed with helium results in a grain size of 0.7 ± 0.2 μm with no clear difference between the grain size at particle interiors and at prior particles boundaries. The low levels of intragranular misorientation in the CP-Ti helium deposit indicated the presence of recrystallized grains. The higher grain refinement when using helium as carrier gas resulted in a weak basal plane (0001) fiber texture. Regions of ultrafine grains are also identified in the microstructure of Ti6Al4V analyzed by SEM. Microhardness values of the deposits made with these coral-like morphology powders were similar to CP-Ti and Ti6Al4V cold sprayed deposits produced with spherical powders. • The microstructure was refined in both the cold sprayed CP-Ti and Ti6Al4V deposits. • Recrystallized grains were identified in the cold sprayed CP-Ti deposit sprayed with helium gas. • EBSD of CP-Ti sprayed with helium gas revealed a weak texture in the basal <0001> direction. • The vanadium-rich regions presented in the Ti6Al4V powder are retained in the cold spray deposit.