Modelling and Characterisation of Electrical Discharge TiC-Fe Cermet Coatings

Abstract

The creation of coatings via Electrical Discharge (ED) methods can enhance the functionality of components which are subject to prior ED machining process steps. However, the industrial application of these methods has been limited due to poor understanding of the fundamental interaction between energy source and material. In this paper, for the case of a TiC sacrificial electrode deposited onto a stainless steel, 2D transient heat transfer is modelled and solved by a finite difference method to estimate the effective fraction of total energy transferred to the workpiece, as well as heat distribution and expected microstructure upon ED coating (EDC). The model was validated via comparison with experimental data, as well as data in literature. In addition, a TiC coating was tested under dry sliding wear conditions to evaluate its tribological properties against an Al2O3 counter face sphere using ball-on-flat geometry. The effective amount of energy transferred to the workpiece is predicted to vary between 17% and 23% for increasing current, from 2 to 19 A, at fixed pulse-on time of 8μs; and between 7% and 53% for increasing pulse-on time, from 2 to 64μs, at fixed current of 10 A. Backscattered electron (BSE) imaging showed that the coatings comprised a metal matrix composite, with a complex banded fine-grained microstructure and different cooling rate across the coating. A TiC-based ED coating on 304 stainless steel (304-SS) yielded a wear rate two orders of magnitude lower than that of the substrate only.