Microstructural Analysis of Cold-Sprayed Ti-6Al-4V at the Micro- and Nano-Scale

Birt, Aaron; Champagne, Victor K.; Sisson, Richard D.; Apelian, Diran

doi:10.1007/s11666-015-0288-1

Cited by 48 publications

(30 citation statements)

References 30 publications

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“…Besides, the current work also shows that the coating porosity level can be reduced with a small addition of He gas in the N 2 gas. The Ti64 coating sprayed with 20 vol.% addition of He gas to the N 2 gas successfully achieves a lower coating porosity in comparison with other reported works [22,42,[47][48][49]51,[76][77][78]. There are several reasons for the densification of the coatings: (1) the increase in particle velocity provides sufficient impact energy for the particles to deform and seal the pores, and (2) the increase in preheated temperature allows the particles to have more thermal softening.…”

Section: Particle Velocity Analysismentioning

confidence: 79%

“…As shown in Figure 1a, plasma-atomized spherical Ti64 ELI (Grade 23) powder with an average size ranging from 15 to 45 µm was used as the feedstock powder. The backscattered electron image (BEI) of an unetched powder cross-section is shown in Figure 1b and consists of martensitic α'-Ti lathes due to its quenching process [48]. The particle size distributions measured by laser diffraction (ASTM B822-10) [52] for D10, D50 and D90 were 19, 33 and 45 µm, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…For the porosity measurement, at least 10 continuous cross-section images (optical, ×100 magnification) were taken from the coating top, middle and near-interface regions. These images were stitched (per location) and processed using the open source software ImageJ (NIH, Bethesda, MD, USA) [48].…”

Section: Microstructural and Mechanical Characterisationmentioning

confidence: 99%

“…The "textured" region continues to shrink and the transition between the "textured" and "smooth" regions eventually becomes unclear as seen in the particles deposited with a velocity of 855 m/s (Figure 6e). The "textured" region is believed to be made up of broken martensitic lathes with varying degrees of fragmentation as well as the remnant martensitic microstructure from the parent powder (Figure 1b), as indicated in the difference in contrast within the region [19,48]. The "smooth" region appears rather featureless, which generally contains more refined grains than the martensitic lathes, resulting in the grain refinement of the parent microstructure due to the adiabatic shear instabilities upon impact [48,81].…”

Section: Particle Velocity Analysismentioning

confidence: 99%

“…The hardness of the coatings increases with particle velocity from 330 to 394 HV as shown in Figure 7. A higher particle impact velocity results in a larger deformation of the particles, and also the occurrence of adiabatic shear instability forms refined polycrystalline nanograin zones [48,81]. These refined nano-grains increase the hardness of the coating by the grain boundary strengthening effect and decrease the dislocation mobility across grain boundaries, as described in the Hall-Petch equation [82].…”

Section: Cross-section Analysismentioning

confidence: 99%

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Influence of Particle Velocity When Propelled Using N2 or N2-He Mixed Gas on the Properties of Cold-Sprayed Ti6Al4V Coatings

et al. 2018

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Cold-spraying is a relatively new low-temperature coating technology which produces coatings by the deposition of metallic micro-particles at supersonic speed onto target substrate surfaces. This technology has the potential to enhance or restore damaged parts made of light metal alloys, such as Ti6Al4V (Ti64). Particle deposition velocity is one of the most crucial parameters for achieving high-quality coatings because it is the main driving force for particle bonding and coating formation. In this work, studies were conducted on the evolution of the properties of cold-sprayed Ti64 coatings deposited on Ti64 substrates with particle velocities ranging from 730 to 855 m/s using pure N2 and N2-He mixture as the propellant gases. It was observed that the increase in particle velocity significantly reduced the porosity level from about 11 to 1.6% due to greater densification. The coatings’ hardness was also improved with increased particle velocity due to the intensified grain refinement within the particles. Interestingly, despite the significant differences in the coating porosities, all the coatings deposited within the velocity range (below and above critical velocity) achieved a high adhesion strength exceeding 60 MPa. The fractography also showed changes in the degree of dimple fractures on the particles across the deposition velocities. Finite element modelling was carried out to understand the deformation behaviour of the impacting particles and the evolutions of strain and temperature in the formed coatings during the spraying process. This work also showed that the N2-He gas mixture was a cost-effective propellant gas (up to 3-times cheaper than pure He) to deliver the high-quality Ti64 coatings.

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