Deposition behavior and microstructural development of TiNi powder particles in low temperature-HVOF spraying process

•LT-HVOF was developed from conventional HVOF process with properties of low temperature and high velocity for plume.•TiNi alloy particles were deposited on the substrate in solid state along with severe deformation in this process.•The grain refinement at the high deformed region of a splat was researched by TEM observation. TiNi alloy particles were deposited at high velocity on Q235 steel substrate in thermally softened solid state by the modified high-velocity oxygen fuel spraying process (so called low temperature HVOF). Microstructural developments and deposition behaviors of a deposited single particle were observed by high resolution scanning electron microscopy and transmission electron microscopy. A single TiNi particle sprayed onto the substrate was severely deformed and the jetting-out phenomenon occurred in the margin of the splat. Extremely fine grains were observed along the interfacial boundary of the deposited particles where the most severe deformation had taken place. The grain refinement at the high deformed region of a splat was arisen from dynamic recrystallization of heavily deformed grain during deformation.