This paper is based on results described earlier and is concerned with the mathematical simulation of parameters which could influence the structural characteristics of the coating and the interfacial region of the substrate during the high velocity oxy-fuel thermal spraying of WC-Ni powder. The variations in the solidification velocity, the thermal gradients and the cooling velocity in the first layer of the coating were determined. Similar parameters were determined for the substrate but in this case attention was also given to the melting velocity. The influence of these parameters on the formation of amorphous and nanocrystalline structure in the coating is discussed together with the development of fine crystalline structures in the interfacial region of the substrate. The results agree well with those obtained by direct metallographic examination of the coating and the interfacial region of the substrate.