WC Decomposition Phenomena in ID-HVOF-Sprayed WC-CoCr Coatings Using Fine Powder Feedstock

Wolfgang Tillmann,Michael Paulus,Leif Hagen,Ingor Baumann

doi:10.3390/coatings12020124

Wolfgang Tillmann, Michael Paulus + Show 2 more

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https://doi.org/10.3390/coatings12020124

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Journal: Coatings	Publication Date: Jan 23, 2022
Citations: 1	License type: CC BY 4.0

Affiliation: TU Dortmund University

Abstract

Over the last few decades, the high velocity oxygen fuel (HVOF) spraying of WC-CoCr for internal diameter (ID) coating has attracted much interest for hard chrome replacement. Current demands for the ID coating of small cylindrical parts necessitates the use of specialized spray gun equipment and powder feedstocks with small particle size fractions. Due to the limited spray distance inside cylindrical parts with small IDs, the process control, spraying fine WC-CoCr powders, meets new challenges to avoid significant WC decomposition, which increases the risk of mechanical degradation. Within the scope of this study, ID-HVOF spraying using a fine-structured WC-CoCr (−15 + 5 μm) feedstock with a mean WC particle size of 400 nm is examined with respect to the WC decomposition phenomena using X-ray diffraction (XRD). Hence, a statistical design of experiments (DoE) is utilized to systematically analyze various spray parameter settings along with their interaction as part of the WC to W2C conversion.

Highlights

Thermal spraying processes meet new challenges when it comes to the coating of inner surfaces of cylindrical components with small diameters, internal bore hole features, or hard-to-reach undercuts
A conventional high velocity oxy-fuel (HVOF) spray gun utilizes stand-off distances of 200 to 400 mm, which are not feasible given the limited accessibility of the internal diameter (ID) of cylindrical parts unless the dimensions are quite large
Only a few studies have been conducted with regard to ID applications using ID-HVOF spraying systems, such systems are already available for small IDs of up to 43 mm [1]

Summary

Introduction

Thermal spraying processes meet new challenges when it comes to the coating of inner surfaces of cylindrical components with small diameters, internal bore hole features, or hard-to-reach undercuts. Process limitations are mainly related to the perpendicularly directed particle spray jet used in thermal spraying processes, the large build-up of common spray guns, as well as the long stand-off distances required to ensure a sufficient heat and momentum transfer of spray particles. Current demands for ID coatings with small diameters require the use of a compact spray gun. The use of a fine-structured feedstock, i.e., fine particle-sized spray powder, enables the sufficient heat and momentum transfer of spray particles even at short stand-off distances [1,2]

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