Wetting and brazing of Ni-coated WC-8Co cemented carbide using the Cu-19Ni-5Al alloy as the filler metal: Microstructura
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n Qiaob) School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China; and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China (Received 7 February 2018; accepted 2 April 2018)
The wetting of Cu–19Ni–5Al alloy on Ni-coated WC–8Co substrates with different coating thicknesses was investigated, and the brazing of Ni-coated WC–8Co to SAE1045 steel was performed by using the Cu–19Ni–5Al alloy as the filler metal. All the Cu–19Ni–5Al/Ni-coated WC–8Co systems present excellent wettability with a final contact angle of ;10°. The thicknesses of the b 1 c phase enriched with Co, Ni, and Al at the two joint interfaces increase and decrease with the Ni coating thickness, brazing temperature, and holding time increasing, respectively. The joint shear strength increases first and then decreases with the increase of Ni coating thickness, brazing temperature, or holding time. The maximum joint shear strength of ;328 MPa is obtained while Ni plating for 90 min and brazing at 1210 °C 5 min.
I. INTRODUCTION
WC–Co cemented carbides, consisting of hard WC grains embedded in the ductile Co-rich binder, have been widely used in many fields including tools, structural components, and wear parts due to high strength and hardness in combination with high wear resistance.1–3 In general, the WC–8Co cemented carbide needs to be joined with steel or other metals because of its low plasticity and ductility. In the past decades, much work has been done to get a sound joint between cemented carbide and steel via brazing,4–12 diffusion bonding,13–17 fusion welding,18,19 and transient liquid-phase bonding.20 Among which, brazing has become one of the main methods for joining cemented carbide to steel in terms of simple process and low cost. However, it remains challenging to obtain a high strength joint due to the great differences between cemented carbide and steel in physical and chemical properties. Presently, there are two challenging problems in the brazing process. One is how to improve the wettability of cemented carbides. As we know, the wettability of substrates by molten filler metals and the brazing process (i.e., brazing temperature and holding time) are recognized as the critical parameters in determining the mechanical properties of brazed joint.21–23
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2018.101
A few investigations are concerning the wetting and spreading of metals on the cemented carbides.11,24–26 For instance, Silva et al.25 investigated the wetting behavior of molten Cu on WC–3.5Co, WC film, and WC at 1080 °C by the sessile drop method and obtained the lowest final contact angle of 6° on the WC–3.5Co surface. Mirski et al.26 reported that the wettability of Cu48ZnNi alloys/cemented carbide system can be enhanced by selective electrolytic etching of the WC phase, with the contact angle decreasing from 120° to 30° at 1100 °C and from 70° to 4° at 1180 °C in nitrogen atmo
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