Materials Science and Engineering A 371 (2004) 187–192 Effects of structure and processing technique on the properties of thermal spray WC–Co and NiCrAl/WC–Co coatings Jun Wang a,b,∗ , Ke Li a , Da Shu a , Xin He a , Baode Sun a , Qixin Guo b , Mitsuhiro Nishio b , Hiroshi Ogawa b a School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, China b Venture Business Laboratory, Saga University, Saga 840-8502, Japan Received 14 August 2003; received in revised form 18 November 2003 Abstract Single-layered coatings of WC–Co and multi-layered coatings of NiCrAl/WC–Co were manufactured by high-velocity oxy-fuel (HVOF) and detonation spraying (DS) techniques. The residual stress, mechanical properties, and wear resistance of these coatings were evaluated and the effects of coating structure and spraying method on coating properties were analyzed. Experimental results show that the coatings made by HVOF excel corresponding DS coatings with respect to mechanical and thermal shock properties. Both the spraying method and coating structure affect the residual stress markedly. Compared with the single-layered coatings, multi-layered ones exhibit better wear resistance under light-load conditions. © 2003 Published by Elsevier B.V. Keywords: Detonation spray; High-velocity oxy-fuel; Coating structure; Coating property 1. Introduction Cermet thermal spray coatings are widely used in many anti-wear areas because they combine several advantages such as resistance to abrasion, erosion, high temperature and corrosive atmospheres. Many efforts have been applied to improve the properties of coatings such as developing new spray methods, minimizing the size of the spray powder. It has also been shown that the multi-layered and gradi- ent structure have potential applications for decreasing the discontinuity of physical and mechanical properties within coatings [1–4]. WC–Co cermet has been applied in a variety of industrial environments. The effects of factors such as carbide grain size, cobalt and carbon content on the performance of the sintered cermet have been researched in detail [5–7]. To study the effects of coating structure and spraying method on coating properties, single-layered WC–Co coatings and multi-layered coatings consisting of WC–Co and NiCrAl ∗ Corresponding author. Tel.: +86-21-6293-2870; fax: +86-21-6447-6867. E-mail address: junwang@sjtu.edu.cn (J. Wang). manufactured by detonation spraying (DS) and high-velocity oxy-fuel (HVOF) are analyzed in this work, including their mechanical and anti-wear properties. 2. Experimental The low carbon steel contained 0.08 wt.% C, 0.31 wt.% Mn, and 0.015 wt.% Si is used as substrate material. WC–12%Co and NiCrAl (75%Ni–20%Cr–5%Al) commer- cial agglomerated sintered powders are used for present study. The particle sizes of the above powders are in the range of 15–45 m. Coatings of two structures were prepared, i.e., single-laye- red and multi-layered coatings. The single-layered is ob- tained by spraying WC–Co directly on the substrate surface. The multi-layered coatings is made of four layers, which were sprayed successively by using mechanically mixed powders of NiCrAl and WC–Co. The chemical content of every layer is shown in Fig. 1. The thickness of the entire coating was fixed at 300 m. In this paper, DS-s and DS-m stand for the single-layered and multi-layered coating prepared by detonation spraying, respectively. The abbreviations HVOFs and HVOFm are used to indicate 0921-5093/$ – see front matter © 2003 Published by Elsevier B.V. doi:10.1016/j.msea.2003.11.045