Sintering shrinkage of WC–Co materials with different compositions A. Petersson * , J. A ˚ gren Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Received 11 November 2004; accepted 24 May 2005 Abstract The composition of cemented carbides affects not only the properties of the finished product, but also changes the sintering behaviour. In this work the sintering of medium–coarse WC–Co materials has been investigated. Descriptions of the constitutive behaviour, uniaxial viscosity, viscous PoissonÕs ratio and sintering stress, obtained from dilatometry experiments under uniaxial load were extended to cover different material compositions. The proposed models were used to express the linear shrinkage rate, and the model parameters fitted to shrinkage data from materials with different carbide grain size, cobalt content and carbon content. The influence of grain size distribution was also investigated. Finally, the shrinkage rate was used to numerically integrate for sintering shrinkage under different thermal cycles. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Cemented carbides; Sintering; Shrinkage; Modelling 1. Introduction Cemented carbides is a class of composite materials with tremendous practical importance and are often used in wear resistant applications. In the simplest case, tungsten carbide (WC) is the hard phase providing hard- ness and wear resistance while cobalt (Co) is the matrix phase, in cemented carbides often referred to as the bin- der phase, providing strength and toughness. It is possi- ble to obtain different mechanical properties of the material through variations in composition. However, the composition determines also the sintering behaviour, which will be addressed in the present work. It has long been realised that even though cemented carbides normally are sintered for a significant time in the presence of a liquid phase, much shrinkage can occur during the heating sequence and even at temperature where the binder phase still is in the solid state. The mechanisms through which the solid state densification occurs are however typical liquid phase sintering pro- cesses with rearrangement and solution-reprecipitation [1]. Cobalt particles become packed with carbide frag- ments during mixing, milling and compaction. Upon heating to sufficiently high temperature, the cobalt-rich phase spreads over the surrounding carbide surfaces providing a capillary-like attraction that rearranges and pulls carbide particles together, cementing them into growing clusters [2]. When then cobalt-rich phase melts an additional rearrangement is possible due to the increased carbide solubility. The higher mobility of the cobalt phase in the liquid state also leads to a spa- tially more homogenous binder distribution [3]. Linear shrinkage during sintering of these materials is in the order of 15–20%, but powder compaction nor- mally results in spatial variations to the green density, which in turn leads to heterogeneous shrinkage. This has to be accounted for in compaction-tool design. International Journal of Refractory Metals & Hard Materials 23 (2005) 258–266 www.elsevier.com/locate/ijrmhm 0263-4368/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2005.05.016 * Corresponding author. Present address: Department of Ceramics and Materials Engineering, Rutgers, The State University of New Jersey, 607 Taylor Road, Piscataway, NJ 08854, USA. Tel.: +1 732 445 5616; fax: +1 732 445 3258. E-mail address: andersp@rci.rutgers.edu (A. Petersson).