journal of materials processing technology 209 ( 2 0 0 9 ) 3172–3181 journal homepage: www.elsevier.com/locate/jmatprotec Effect of WC on the residual stress in the laser treated HVOF coating Z.Y. Taha-al a , M.S. Hashmi a , B.S. Yilbas b,* a School of Mechanical and Manufacturing Engineering, DCU, Dublin, Ireland b ME Department, KFUPM, Dhahran, Saudi Arabia article info Article history: Received 18 February 2008 Received in revised form 3 July 2008 Accepted 12 July 2008 Keywords: HVOF Diamalloy 1005 Inconel 625 WC Residual stress abstract HVOF coating of diamalloy 1005 containing WC particles onto steel (304) is considered and laser melting of the coating is carried out. The effect of WC content on the residual stress formed in the coating is examined. Temperature rise and the temperature gradient devel- oped in the coating is modeled and predicted. XRD technique is used to measure the residual stress in the coating while the analytical formulation is used to predict the residual stress at the coating base material interface. The indentation tests are carried out to measure the Young’s modulus and fracture toughness of the coating with and without WC content. It is found that existing of WC modifies temperature rise and the temperature gradient in the coating; in which case, increasing WC content reduces the temperature gradient. The Young’s modulus, the magnitude of the residual stress, and the fracture toughness of the coating increase with increasing WC content in the coating. © 2008 Elsevier B.V. All rights reserved. 1. Introduction HVOF coating finds application in power industry to protect the metallic surfaces from high temperature and corro- sive environments. The most commonly used HVOF coating powder is diamalloy 1005, which provides reasonably resis- tive surfaces to severe environments. However, the blend of tungsten carbide in the powder improves further the wear resistance of the surface (Hamatani, 2002). HVOF coating is involved with thermal spraying and mechanical anchor- ing of the powders sprayed onto the base material. Since the powders are in molten or in semi-molten states (splats) at different sizes, the coating structure becomes inhomoge- neous. Moreover, thermal integration of splats in the coating can be possible through the control melting. This can be achieved through using the laser heating source. Although the laser heating improves the structural integrity of the coat- ing, the metallurgical changes due to heating and cooling ∗ Corresponding author. Tel.: +966 3 860 4481; fax: +966 3 860 2949. E-mail address: bsyilbas@kfupm.edu.sa (B.S. Yilbas). rates modify the residual stress levels in the coating. Conse- quently, investigation into thermal process during the laser heating and the resulting residual stress levels as well as metallurgical changes in the laser irradiated region becomes essential. Considerable research studies were carried out to exam- ine the HVOF coating and the laser melting process. The microstructure of HVOF tungsten carbide coating was inves- tigated by Verdon et al. (1998). They showed that tungsten carbide grains in the coating were smaller than those in the unsprayed powder and this fluctuated through the coating cross-section. The fracture toughness and the crack mor- phologies in eroded WC–Co–Cr HVOF coating were examined by Lopez Cantera and Mellor (1998). They showed that the cracks produced by indentation testing and erosion tend to propagate along the boundaries between the splats. The rolling contact fatigue failure mechanisms in HVOF sprayed W–Co coatings were investigated by Nieminen et al. (1997). 0924-0136/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2008.07.027