In this chapter, the authors provide the phase field model formulation to the tungsten-carbon-cobalt ternary system. Rather than apply the phase field equations to usual dendrite morphology during solificiation growth, they opt to demonstrate the model's applicability to the dissolution of tungsten carbide (WC) in a cobalt matrix during thermal spray coating deposition. Tungsten carbide-cobalt is a metal matrix composite consisting of hard WC particles and a softer Fcc cobalt matrix. It is commonly applied as a thermal spray coating to improve the wear resistance of a surface in harsh conditions. The chapter shows the results of simulations of the ternary grand potential phase field model presented in the previous section that demonstrate the dissolution of tungsten-carbine into a cobalt matrix.