In recent years, the thermal spray technique has emerged as the most useful method for developing a wide variety of coatings which enhance the performance and durability of engineering components exposed to diverse forms of wear. Among the thermal spray techniques, detonation spray coating (DSC) has retained its position as one of the best available techniques for obtaining dense, wear-resistant coatings. Notwithstanding the advantages of the DSC technology over other thermal spray variants, the understanding of the fundamental aspects of this technology is still extremely limited. In view of the above, a major programme has been undertaken in this laboratory to assess the parametric impact of the key DSC process variables (oxy-fuel ratio, spray distance, powder feed rate and shot frequency) on the mechanism of coating formation and the properties of the resulting coating. As a part of the above exercise, the key DSC process variables have been varied systematically employing a statistical design and the properties of the WC-12Co coatings so obtained have been evaluated. The results of such a study are presented in this paper. In particular, it has been demonstrated that useful conclusions regarding the influence of process parameters on the properties of the WC-12Co coating cannot be reached unless the scatter in the experimentally measured coating property data is also simultaneously taken into account.

Thermal sprayed chromium carbide (Cr3C2)-25% NiCr (Ni-20%Cr) coatings are extensively used in wear resistant applications especially under conditions wherein operating temperatures are likely to be higher than 500°C . The performance of the Cr3C2-NiCr coatings under such conditions depend on a variety of coating properties like the porosity, microstructure, extent of decarburization of Cr3C2 phase and hardness. One of the parameters which affects the above mentioned coating properties is the characteristics of the powder utilized for thermal spraying. In the present study, Cr3C2-25% NiCr powders obtained from four different sources has been utilized to form Cr3C2-NiCr coatings on steel substrates utilizing the detonation spray coating (DSC) system. The Cr3C2-NiCr powders utilized vary from each other in terms of manufacturing route employed (sintered and crushed, pre-alloyed, blended, etc.), particle size distribution, particle shape and even phases present. The influence of each of these powder characteristics on the coating microstructure, porosity, hardness, extent of carbide dissolution and ultimately on coating performance (i.e. sliding and abrasive wear resistance) has been evaluated.