Fabrication of erosion resistant WC-Ni based coatings using cold gas dynamic spaying
Date
2019
Authors
Lioma, Dineo Boitumelo Thansanqa
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Abstract
This paper provides a review on cold gas dynamic spraying (CGDS) and its application to produce WC-based wear resistant coatings. CGDS is a deposition technique, in which fine, solid powder particulates are accelerated to supersonic speeds by means of a pressurized carrier gas. The high velocity particles are impacted onto a surface to form dense coatings. Severe plastic deformation of the particles during deposition is required to achieve sufficient adhesion and coating build-up. This process involves limited to no melting during coating deposition, thus, the chemical composition and bulk properties of the coatings typically remain identical to the feedstock powders. Substrate and particle adhesion occur as a result of highly localized adiabatic shearing, and the formation of a material jet of the ductile material, allowing for material interlocking and mechanical bonding. Deposition of WC-based coatings has been achieved using high pressure CGDS systems, with dense coatings having thickness and hardness values comparable to HVOF coatings. It is generally challenging to achieve the adhesion of WC-based coatings using low pressure CGDS systems; the addition of a ductile binder metal such as Cu, Ni and Al in the form of a MMC is generally required to facilitate deposition. Limited studies have been done on the wear resistance of cold sprayed WC-based coatings. To date it has been shown that WC-based coatings deposited using both high and low CGDS systems, possess higher sliding and abrasive wear resistances compared to coatings deposited using some HVOF techniques. The typical wear mechanisms observed are plastic deformation of the ductile metal matrix with minimal damage of the hard WC grains. Changes in wear mechanisms during wear have also been noted and appear to be influenced by the amount of WC present
Description
A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the
Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering.
Johannesburg, 2019