Carbide composites are routinely sprayed as wear resistant coatings, BUT they always lose some carbon during the coating process. Loss of carbon leads to a multitude of negative consequences – formation of sub-stoichiometric carbide phases which have poorer wear characteristics, embrittlement of the metallic binder and loss of ductility etc. The feedstock powder compositions have been defined by traditional sintered carbide composites, where the carbon content can be accurately controlled during production within very tight tolerances in order to avoid the problem above. However, no one has attempted to address the carbon loss issue through the addition of carbon to the starting powder. We have attempted this in a previous years project – however this was largely unsuccessful due to the method of carbon addition which dissolved away a lot of the metallic binder. In the current project we have added carbon directly to the powder during spray drying production specifically to overcome this issue. One project added carbon alone to the WC-17Co powder, while the second project added a combined composite powder of Ni+graphite (i.e. the two compositions will be split between a pair of students).
Three different concentrations of carbon/(Ni+graphite) have been added to investigate the carbon concentrations below, at and above the stoichiometric concentration. The as-sprayed coatings will be analysed to determine if the carbon dissolved into the metallic binder during plasma spraying and if it protected the carbide grains from undergoing decarburisation. Coatings will be analysed by combined DSC and TGA to determine the energy changes that occur due to compositional developments with heat treatment. These will be compared to previous studies on the conventional starting powder without carbon addition. Heat treatment trials below and above each characteristic DSC peak will enable ethe change in composition to be determined through XRD/EDS and SEM analysis. Longterm heat treatment (125 hours) at 900°C will enable the coating compositions to reach equilibrium and determine if the concept of carbon addition was successful in being able to maintain the desired phase composition in the coating.
Undergraduate
None
No lab has been assigned to this project