Effect of Nozzle Geometry on the Microstructure and Properties of HVAF-Sprayed WC-10Co4Cr and Cr3C2-25NiCr Coatings
Thermally sprayed hard metal coatings are the industrial standard solution for numerous demanding applications to improve wear resistance. In the aim of improving coating quality by utilising finer particle size distributions, several approaches have been studied to control the spray temperature. The most viable solution is to use the modern high velocity air-fuel (HVAF) spray process, which has already proven to produce high-quality coatings with dense structures. In HVAF spray process, the particle heating and acceleration can be efficiently controlled by changing the nozzle geometry. In this study, fine WC-10Co4Cr and Cr3C2-25NiCr powders were sprayed with three nozzle geometries to investigate their effect on the particle temperature, velocity and coating microstructure. The study demonstrates that the particle melting and resulting carbide dissolution can be efficiently controlled by changing the nozzle geometry from cylindrical to convergent–divergent. Moreover, the average particle velocity was increased from 780 to over 900 m/s. The increase in particle velocity significantly improved the coating structure and density. Further evaluation was carried out to resolve the effect of particle in-flight parameters on coating structure and cavitation erosion resistance, which was significantly improved in the case of WC-10Co4Cr coatings with the increasing average particle velocity.
KeywordsHVAF < processing HVOF < processing HP/HVOF < processing WC-CO-Cr < feedstock chromium carbide < feedstock cavitation erosion < properties diagnostics < processing
The authors would like to thank Mr. Mikko Kylmälahti (Tampere University of Technology) for the assistance with HVAF spraying of the coatings and Mr. Leo Hyvärinen (Tampere University of Technology) for carrying out the XRD measurements. The authors gratefully acknowledge Tekes (Finnish Funding Agency for Technology and Innovation), the participating companies of the HYBRIDS research programme, and DIMECC Ltd. for financial support. MSc Matikainen acknowledges the personal grant from Finnish Cultural Foundation.
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