Original article Effect of carburizing and annealing processes in improving the Ni/WC–Co adhesion strength AW Hassan 1,2 , MY Noordin 1 , S Izman 1 and K Denni 1 Abstract Heat treatment processes have a positive impact in improving the adhesion strength of different interlayer/substrate materials. However, information regarding the effect of these processes in enhancing the adhesion strength of an electroplated nickel interlayer on tungsten carbide substrate for diamond deposition is lacking. In this study, the effect of carburizing and annealing process conditions in enhancing the adhesion strength of the electroplated nickel interlayer was investigated. The heat treatment processes were designed and modeled by the design of experiments technique. The heat-treated specimens were characterized by the field-emission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques. The adhesion of the interlayer before and after the heat treatment was assessed by the scratch test. The results show that the adhesion of the electroplated nickel interlayer was remark- ably improved by both processes. The mathematical models for predicting the adhesion strength of the carburized and annealed nickel interlayer within the specified ranges were developed. The maximum adhesion strength of 30 N was obtained from the nickel interlayer annealed at the highest process condition of temperature and time. Keywords Design of experiments, nickel interlayer, tungsten carbide, annealing, carburizing, critical load, adhesion Date received: 23 June 2016; accepted: 24 April 2017 Introduction Application of interlayer on hard metal (WC–Co) is advantageous especially for the purpose of diamond deposition. It can promote the nucleation and growth of well-defined diamond crystals on tungsten carbide by suppressing or reducing cobalt diffusion. 1–4 Moreover, it can accommodate for the large mismatch in the coefficient of thermal expansion between diamond and the hard metal, and conse- quently residual stresses between them can be relieved. 5,6 Nickel is considered as a good interlayer material candidate for diamond deposition on tungsten carbide. Its low yield strength and small lattice mis- match with diamond enable the interfacial thermal stresses with the hard metal substrate as well as with diamond to be relieved. 7,8 However, nickel material as an interlayer on tungsten carbide for diamond depos- ition has not been given full attentions. In this study, the nickel interlayer was deposited on the carbide substrate by electrodeposition process from Watt’s solution. Unlike physical vapor deposition (PVD) or chemical vapor deposition (CVD) coating techniques, electroplating is more economical, easy to manipulate its deposition parameters in order to obtain good quality coating, 9–11 and can deposit the interlayer with minimum possible residual stresses due to its low processing temperature. However, the weak adhe- sion strength of the electroplated nickel interlayer to the WC–Co substrate is a major issue. Nevertheless, the interface adhesion of this interlayer–substrate system can be improved by heat treatment process. Previously reported works demonstrated the effective- ness of annealing heat treatment in enhancing the adhesion strength of different interlayer/substrate materials through the initiation of solid-state diffusion between these materials. 12–14 Therefore, in this study, two different heat treatment processes that are carbur- izing and annealing were proposed for improving the Ni/WC–Co interface adhesion. Proc IMechE Part E: J Process Mechanical Engineering 0(0) 1–11 ! IMechE 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954408917710144 journals.sagepub.com/home/jpme 1 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia 2 Faculty of Engineering and Technical Studies, University of Alimam Almahdi, Kosti, Sudan Corresponding author: MY Noordin, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor Bahru 81310, Malaysia. Email: noordin@fkm.utm.my