Xiao-Bo Bai

Deformation Behaviors of Cold-Sprayed WC-Co Particles

In the present work, the WC-Co particles with different sizes and contents of WC particle were deposited on the stainless and WC-Co substrate in different accelerating gas temperatures. The deformation mechanisms of incident WC-Co particles and impacted substrates, and especially their interactions were characterized via scan electron microscopy (SEM) observations of both surface morphologies and cross-sectional microstructures of individual splats, and splat/substrate interface with the assistance of focus ion beam (FIB). The effects of feedstock powder structure, i.e., WC particle size and Co content, and temperature of accelerating gas on plastic deformation were comprehensively studied. It was revealed that the splats on stainless steel exhibited ellipsoid shape with a comparative integrated contour similar to original powder, and there were some revers on substrate around splats. In contrast, splats on WC-Co substrate exhibited more flattened pie shape with some ejectas on its periphery in the radial direction. The more curved interface convex to stainless steel substrate appeared compared to that of WC-Co substrate. Deformation of WC-Co splats was enhanced by the increment of substrate hardness and increment of Co binder and reduction of WC size of incident particles.

Deposition Behavior of Nanostructured WC–23Co Particles in Cold Spraying Process

The nanostructured WC–23Co particles were deposited on three kinds of substrates in different accelerating gas temperature by using cold spraying process. The morphologies of nanostructured WC–23Co splats attached on the polished surface of different substrates were characterized via scanning electron microscopy. It is revealed that the splats are partially embedded in Q235 and stainless steel with a comparative integrated contour similar to that of the original particles. There exist some revers around the splats and some corrugations or ripples on the Q235 and stainless steel substrates. In contrast, the splats on the surface of WC–12Co substrate present clearly a flat shape with central hump surrounded by a ringy band. By comparison of the morphologies of splats deposited on three kinds of substrates with the accelerating gas temperature of 850 ± 10°C and 750 ± 10°C, it can be found that the deformation of nanostructured WC–23Co particles is enhanced by the increment of substrate hardness and gas temperature.

Microstructures and Properties of Cold Spray Nanostructured HA Coatings

Nanostructured hydroxyapatite (nHA) coatings on implant surface are highly desirable owing to their excellent osteoconductive properties in association with intrinsic small crystals. Low processing temperature of cold spray makes it an ideal technique to prepare nHA coatings with nanostructured feedstock. This work demonstrated that dense and thick nHA coatings were achievable by cold spraying nanostructured feedstock onto TC4 alloy surface. Coating formation mechanisms were explored by investigating the deposition of individual particles. Microstructures, mechanical profiles and biological properties of the coatings were comprehensively investigated. A porous Ti buffer layer significantly enhanced the bonding between nHA coatings and the substrate. As-deposited nHA coatings exhibited a high wear resistance when slid against polyurethane or polycarbonate and a strong apatite-forming ability when being immersed in simulated body fluid (SBF). Findings of this work will contribute to a comprehensive understanding of building mechanisms, structures and properties of cold sprayed nHA coatings.