Production of nanostructured WC–Co powder by ball milling M.H. Enayati * , G.R. Aryanpour, A. Ebnonnasir Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415483111, Iran article info Article history: Received 26 March 2008 Accepted 20 June 2008 Keywords: WC–Co Nanocrystalline Ball milling Mechanical alloying abstract Formation of nanostructured WC compound by ball milling process was investigated through two differ- ent routes. First route involved the ball milling of preformed WC-17 wt.% Co powder while in second route the mechanical alloying of W–Co–C powder mixture was used. The results showed that ball milling of WC-17 wt.% Co readily led to nanocrystalline WC particles with a crystallite size of 15 nm. Annealing of this structure however caused a transition from WC phase to undesirable Co 6 W 6 C phase. Mechanical alloying of W–Co–C powder mixture did not yield WC phase whereas it was possible to produce nano- crystalline WC phase with a crystallite size of about 10 nm by mechanical alloying of W–C powder mixture. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Extreme hardness, high elastic modulus and flexure strength of cemented tungsten carbide materials make them useful in the manufacture of cutting, machining and abrasive tools as well as for wear and bearing applications [1,2]. These materials often exhi- bit a Co binder phase which enables sintering at relative low tem- peratures while the ductile Co phase provides a relative high toughness and transverse rupture strength. The microstructure of conventional WC–Co material consists of angular WC particles sur- rounded by Co binder [2]. Metal carbides are usually prepared by powder metallurgy route. The metal or oxide powder is reacted with carbon, pressed, and sintered. Very high temperatures (>1000 °C) and good vacuum conditions or highly purified gases are generally required for prep- aration of homogeneous material [3]. One recently developed method for preparing metal carbides is ball milling. In this process the starting powder is charged into a suitable ball mill and pro- cessed for several hours depending on experimental conditions as well as desired microstructure and properties. The ball milling processes which involve mass transfer between the components is known as ‘‘mechanical alloying” (MA). Such cases can occur dur- ing milling of multi-component powders (e.g. a mixture of elemen- tal or dissimilar alloy powders) and are associated with compositional changes of powder particles. During the milling process powder particles are trapped be- tween colliding balls and undergo severe plastic deformation. Ball–powder–ball collisions lead to the following events [3];I– cold welding and fracturing of particles which result in mixing of constituents and formation of composites of powders, II – creation of a high density of lattice defects, in particular dislocations, in- duced by intensive plastic deformation. It has been shown that a dense dislocation network forms even in nominally brittle inter- metallics like Nb 3 Sn under ball milling conditions [4] and III – material transfer by diffusion of components. Diffusion during ball milling is significantly accelerated by lattice defects [5] and by a momentary increase in temperature of particles trapped between colliding balls [3]. The occurrence of mass transfer during ball milling makes it possible to synthesize the commercial high melting metal carbides directly at room temperature by either milling of pure elements or milling of metal powders with hydrocarbons [6,7]. Although a sub- sequent heat treatment was reported to be necessary to obtain car- bide compounds in some alloy systems [8,9]. Ball milling process has the advantage over other fabrication techniques as the final product has a nanocrystalline structure with superior properties to those of conventional coarse grain materials [8]. Nanostructured WC–Co materials have been previously pro- duced and applied as protective coatings and cutting tools. In both applications the enhanced hardness, wear resistance as well as toughness of the nanostructured WC–Co were observed in compar- ison to the conventional coarse-grained WC–Co materials [10,11]. Although Stewart et al. [12] found that nanocomposites HVOF- sprayed WC–Co coating had a poorer abrasive wear resistance than the conventional coating. They explained the differences in the wear behaviour of the coatings in terms of differences in powder characteristics, the extent of reaction and decarburisation during HVOF spraying and the development of a Co-rich amorphous phase during rapid solidification of splats. This work investigates the possibility of producing WC–Co nanocomposite powder by ball milling through two different 0263-4368/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2008.06.005 * Corresponding author. Tel.: +98 311 3915730; fax: +98 311 3912752. E-mail address: ena78@cc.iut.ac.ir (M.H. Enayati). Int. Journal of Refractory Metals & Hard Materials 27 (2009) 159–163 Contents lists available at ScienceDirect Int. Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM