Cold spray is a complex process where many parameters have to be considered in order to achieve optimized material deposition and properties. In the cold spray process, deposition velocity influences the degree of material deformation and material adhesion. While most materials can be easily deposited at relatively low deposition velocity (<700 m/s), this is not the case for high yield strength materials like Ti and its alloys. In the present study, we evaluate the effects of deposition velocity, powder size, particle position in the gas jet, gas temperature, and substrate temperature on the adhesion strength of cold spayed Ti and Ti6Al4V splats. A micromechanical test technique was used to shear individual splats of Ti or Ti6Al4V and measure their adhesion strength. The splats were deposited onto Ti or Ti6Al4V substrates over a range of deposition conditions with either nitrogen or helium as the propelling gas. The splat adhesion testing coupled with microstructural characterization was used to define the strength, the type and the continuity of the bonded interface between splat and substrate material. The results demonstrated that optimization of spray conditions makes it possible to obtain splats with continuous bonding along the splat/substrate interface and measured adhesion strengths approaching the shear strength of bulk material. The parameters shown to improve the splat adhesion included the increase of the splat deposition velocity well above the critical deposition velocity of the tested material, increase in the temperature of both powder and the substrate material, decrease in the powder size, and optimization of the flow dynamics for the cold spray gun nozzle. Through comparisons to the literature, the adhesion strength of Ti splats measured with the splat adhesion technique correlated well with the cohesion strength of Ti coatings deposited under similar conditions and measured with tubular coating tensile (TCT) test.

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A modified ball bond shear test was developed to measure the adhesion of cold sprayed splats to both bulk substrates and cold sprayed coatings. The technique was applied to the deposition of Ti feedstock powder (spherical morphology, 29 m average dia.) onto a commercially pure bulk Ti plate and onto Ti coatings prepared with the same feedstock powder as the splats. Both an adhesion strength and adhesion energy were measured, with trends in adhesion examined as a function of in-air particle velocities between 580 and 825 m/s.Comparisons between cold spray splat on bulk materials versus coatings were conducted for two deposition conditions (694 and 825 m/s). Generally, the adhesion for splats deposited at the higher deposition condition were insensitive to the substrate material, while splats deposited at the lower deposition condition adhered better to the bulk material than to the coatings.3

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Third body behavior during dry sliding of cold-sprayed Al-Al₂O₃ composites : in situ tribometry and microanalysis Shockley, J. Michael; Descartes, S.; Irissou, É.; Legoux, J.-G.; Chromik, R. R.