Reliability of dual compounds “carbide composite+steel” produced by diffusion welding H. Klaasen a,1 , J. Kübarsepp a,2 , A. Laansoo a,3 , M. Viljus b, ⁎ a Department of Materials Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086, Tallinn, Estonia b Centre for Materials Research, Tallinn University of Technology, Ehitajate tee 5, 19086, Tallinn, Estonia abstract article info Article history: Received 23 December 2009 Accepted 29 March 2010 Keywords: Diffusion welding Brazing Carbide composite Hardmetal Cermet This paper focuses on the reliability (strength and residual welding stresses) of the dual compound of TiC-based composite+steel and WC-based hardmetal+steel produced by diffusion bonding (welding). Vacuum brazing was used as a reference technology. The influence of some metallurgical factors on the properties and structure of joints was investigated by SEM and EPMA. It was found that the TiC-based cermet and diffusion welding used instead of a WC-based hardmetal and vacuum brazing in the production of the dual compound of carbide composite+steel results in remarkable improvements of joint reliability. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Carbide composites – hardmetals and cermets – enable the service life of tools and wear parts to be prolonged. Tungsten carbide-based hardmetals bonded with cobalt are most widely used because of their excellent combination of wear resistance and strength-toughness [1,2]. In many cases tools for finish machining (particularly turning of special alloys) [1,3] and tools working in the conditions of prevailing adhesion wear are made from so-called tungsten free carbide composites (cermets). Cermets based on TiC cemented with Ni or Fe alloys have found their applications [3,4] because of properties such as low density, high specific strength, high oxidation resistance and low (close to steels) thermal expansion coefficient. A series of TiC-based cermets cemented with Fe–Ni alloys have been elaborated at Tallinn University of Technology (TUT). Some of such composites TiC–FeNi – grades T70/14, T75/14 – have demon- strated their superiority as tool materials over tungsten carbide-based hardmetals in metalforming operations [5,6]. To save expensive carbide composites and simplify the design of complicated tools resulting in improved reliability, and to reduce manufacturing costs, application of dual compounds of a carbide composite + steel is of interest. Such bimaterial structures (hybrid materials), in particular cutting tools production have commonly used brazing as a bonding technique [7,8]. However, brazing does not ensure fair reliability in complicated working conditions [5,8]. The amorphous alloys developed for use as filler materials in brazing are prospective due to their good compatibility with hardmetals. To ensure high quality high vacuum during brazing is to be applied [9,10]. Diffusion welding developed as an alternative joining technology has proved successful in the production of diverse compound parts of various metallic alloys [11,12]. Some preliminary results related to the properties of WC-hardmetal+steel diffusion welded joints are reported in [13,14]. The application of bimetallic compounds of WC-20%Co+steel in the production of metalforming tools has been found relatively successful [15]. Attempts to use this technology in the production of more complicated tools and tools of enhanced wear resistance (utilization of hardmetals with WC content N 85 wt.% in a bimetallic tool) have not been so successful. This could be explained by higher brittleness and higher sensitivity to welding residual stresses of such cemented carbides [14,16]. Due to their favourable properties, i.e. lower modulus of elasticity than that of hardmetals and a thermal expansion coefficient close to steel TiC-based cermets are prospective as a counterpart in the dual compound of carbide composite+steel produced by diffusion welding or vacuum brazing. However, information concerning the prospects of diffusion welding and brazing technology for joining of TiC-based cermets to steel is comparatively restricted [13,14,17–19]. The present study is focused on the influence of alternative joining techniques (diffusion welding, brazing) and some relevant metallur- gical factors (carbide composite composition, composition of inter- layer material, process parameters) on reliability characteristics (shear strength of joint, level of residual stresses) of bimaterial Int. Journal of Refractory Metals and Hard Materials 28 (2010) 580–586 ⁎ Corresponding author. Tel.: + 372 620 3150; fax: + 372 620 3153. E-mail addresses: heinrich.klaasen@ttu.ee (H. Klaasen), jakob.kubarsepp@ttu.ee (J. Kübarsepp), andres.laansoo@ttu.ee (A. Laansoo), marty@staff.ttu.ee (M. Viljus). 1 Tel.: +372 620 3359; fax: +372 629 3196. 2 Tel.: +372 620 2006; fax: +372 620 2020. 3 Tel.: +372 620 3354; fax: +372 620 3196. 0263-4368/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2010.03.005 Contents lists available at ScienceDirect Int. Journal of Refractory Metals and Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM