Development of Ni–TiC and Ni– (Ti,W)C composite powders for high velocity oxy-fuel (HVOF) coating and characterisation of coatings M. Karbasi*, A. Saidi and M. R. Zamanzad Ghavidel The main objective of this research work was to develop Ni–TiC and Ni–(Ti,W)C composite powders for high velocity oxy-fuel (HVOF) coating and characterisation of the coatings. For this purpose, two kind of composite powders were produced by the self-propagation high temperature synthesis (SHS) method (Ni–TiC and Ni–(Ti,W)C composites). Subsequently composite powders were used as feedstock for HVOF coating. Also, as reference sample, similar coating was prepared using Ni and TiC powders mixture. Samples were characterised by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy and adhesion tests. According to results, Ni–TiC and Ni–(Ti,W)C composite powders were developed via the SHS method yield appropriate HVOF coatings with dense, homogeneous, rounded, fused carbide distribution as well as suitable adhesive strength and high crack resistance. With an initial powder mixture of Ni and TiC for HVOF coating, TiC oxidation and Ti 2 O 3 formation occurred; the microstructure of the coating was heterogeneous and irregular morphology having sharp facets. This coating had a low density and low adhesive strength and low crack resistance. Keywords: Ni–TiC, Ni–(Ti, W)C, Composite, SHS, HVOF, Coating Introduction Combustion synthesis, also known as self-propagation high temperature synthesis (SHS), is a favoured method for producing ceramics, composites and intermetallics. According to this method, a compacted pellet of reactant materials is ignited by an external heating source. Heat released from the exothermic reactions creates a self-propagation combustion front. Passing over this combustion wave, reactant materials convert to final products. The high production rate and low energy consumption are some of the advantages of the method. 1,2 The equipment required for the SHS process is simple and this dramatically reduces the cost of primary production. 3 Self-propagation high temperature synthesis process is employed for production of X–TiC powders (composite powders of TiC as hard phase with a metallic phase as binder or matrix). These powders are favourable materials for thermal spray coatings. Thermal spraying is an ever expanding area in surface engineering technology, which involves the deposition of molten or semimolten droplets of powders on a substrate to form a coating. 4,5 High velocity oxy-fuel (HVOF) thermal spraying is characterised by a high flame velocity up to 2000 m s 21 . 6 In the HVOF thermal spray technology, oxygen and liquid fuel are combusted under high pressure in a chamber and the combustion products are accelerated through a converging–diverging nozzle. 7–9 The powder, fed into the hot stream of gases, can be oxidised due to hot temperature and oxidising condition in HVOF process. X–TiC powders (composite powders of TiC as hard phase with a metallic phase as binder or matrix) produced by SHS method can be used. On the other hand, the performance of HVOF coatings also strongly depends on the coating micro- structure which, in turn, depends on the characteristics of powder feedstock. Titanium carbide has a high hardness and can be readily compounded with tungsten carbide [(Ti,W)C]. The novel and additional characteristic of this double carbide is its higher thermal stability for high tempera- ture applications. 1 In addition, (Ti,W)C powder and cermets have been demanded by hard material industries since the 1980s. 10,11 Despite the fact that numerous recent studies have been focused on the production and examination of the microstructure of thermal sprayed coatings of TiC and (Ti,W)C, an adequate understanding of this topic is yet to be obtained. 2,3,12 The present study aims to investi- gate the development of Ni–TiC and Ni–(Ti,W)C composites powders to be used as suitable feedstock powder HVOF coatings. Department of Materials Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran *Corresponding author, email m_karbasi@cc.iut.ac.ir ß 2011 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 5 July 2009; accepted 22 August 2009 DOI 10.1179/026708309X12512744154289 Materials Science and Technology 2011 VOL 27 NO 4 839