Effect of preplaced graphene and graphite films on the substrate of Stellite 6 metallurgical coatings processed by PTA

Abstract

Protective coatings contribute to a longer and improved service life of equipment motivating the search for better coatings with new materials and efficient processing techniques. Carbon-based compounds are materials widely studied for their unique properties due to a variety of atomic arrangement. Tailoring metal matrix composites to improve performance through the distribution of carbon compounds in the matrix offers a competitive route to process coatings. Graphite and graphene powders were manually brushed on a rough substrate steel to modify Co based coatings processed by Plasma Transferred arc (PTA). An atomized Co based alloy was deposited on pre-placed films of graphene and graphite, respectively. The impact of the C compounds in hardfacing coatings was assessed by the geometry, dilution, microstructure, hardness and scratch tests. Results show similar microstructures and phases in coatings regardless of the presence of the preplaced C films. However, Co based coating deposited on preplaced graphene films exhibit larger dilution, lower hardness and a larger scratch scar compared to those processed without the C film. In contrast, depositing the Co based alloy on graphite films resulted on coatings with a higher hardness and scratch resistance inspite of the similar dilution to that of coatings processed on the stainless steel substrate. The measured behavior is associated with differences in the heat transfer at the interface with the substrate due to the thermal conductivity of the C film and its interaction with the plasma arc. Changes in the heat affected zone of each coating further sustain this understanding.