Reciprocating sliding friction and wear behavior of electrical discharge machined zirconia-based composites against WC–Co cemented carbide K. Bonny a, * , P. De Baets a , J. Vleugels b , O. Van der Biest b , A. Salehi b , W. Liu c , B. Lauwers c a Department of Mechanical Construction and Production, Ghent University (UGent), IR04, Sint-Pietersnieuwstraat 41, B-9000 Gent, Belgium b Department of Metallurgy and Materials Engineering, Catholic University Leuven (K.U. Leuven), MTM, Kasteelpark Arenberg 44 (bus 2450), B-3001 Leuven, Belgium c Department of Mechanical Engineering, Catholic University Leuven (K.U. Leuven), PMA, Celestijnenlaan 300 B (bus 2420), B-3001 Leuven, Belgium article info Article history: Received 27 April 2008 Accepted 2 July 2008 Keywords: ZrO 2 composite WC–Co cemented carbide Wire-EDM Dry reciprocating sliding wear abstract The tribological characteristics of hot pressed zirconia-based composites containing 40 vol.% of WC, TiC 0.5 N 0.5 or TiN and surface finished by electrical discharge machining (EDM) were evaluated by per- forming linearly reciprocating pin-on-flat sliding experiments against WC–Co cemented carbide under unlubricated conditions. The wear tests were executed on a Plint TE77 tribometer using normal con- tact loads of 15 N up to 35 N and a sliding velocity of 0.3 m/s. The ZrO 2 -40 vol.% WC grade displayed an undoubtedly better wear resistance compared to the ZrO 2 -40 vol.% TiCN and ZrO 2 -40 vol.% TiN com- posites. The morphology of the worn surfaces and the wear debris was investigated by scanning elec- tron microscopy (SEM) and X-ray diffraction (XRD), revealing several wear mechanisms such as polishing and abrasion, mainly depending on the imposed contact load and the material compo- sition. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Engineering ceramics display exceptional properties of hard- ness, chemical stability, refractoriness and resistance against ero- sion/friction, which make them extremely adequate for tribological applications where high wear resistance is required [1]. In recent times, yttria stabilized tetragonal zirconia (Y-TZP) ceramics have been recognized as one of the strongest and tough- est single phase oxides owing to the stress-induced phase transfor- mation from tetragonal to monoclinic zirconia [2,3]. Additionally, the capacity to preserve these properties in a wide range of tem- peratures together with the excellent chemical inertness and low specific density has brought zirconia ceramics to the front end material to meet a large number of industrial applications [4] in the fields of manufacturing, cutting and tools [5,6], punches [7] and biomedical applications [8–13]. A growing trend in the devel- opment of advanced ceramics is the introduction of a secondary phase into the microstructure combined with grain size refinement towards nanometer scale with the aim of improving mechanical properties [14–16] and wear resistance [17]. The beneficial effect of grain refinement on the sliding wear resistance in ceramics can be explained by the fact that cumulative material removal dur- ing the sliding wear of non-transforming polycrystalline ceramics occurs by two successive mechanisms – dislocation plasticity, fol- lowed by fracture – which are both controlled by the grain size [18,19]. In sliding wear, an initial period of mild wear can be fol- lowed by a transition to severe wear promoted by the formation of surface fractures [20–22]. The incorporation of hard metallic phases such as WC, TiC 0.5 N 0.5 or TiN into a ZrO 2 matrix not only improves the hardness but also reduces the electrical resistivity of the resulting compos- ites [23–26], making them suitable to be machined by electrical discharge machining (EDM) [27–31] and therefore avoiding the expensive grinding operation for final shaping and surface finish- ing of these otherwise hard to machine materials. This paper fo- cuses on self-developed ZrO 2 -based composites with 40 vol.% WC, TiC 0.5 N 0.5 or TiN addition and grain sizes in the sub-microm- eter and nanometer range. Flat samples of ZrO 2 -40 vol.% WC, ZrO 2 - 40 vol.% TiCN and ZrO 2 -40 vol.% TiN composites were produced by hot pressing and were surface finished by wire-EDM in deionized water. Their tribological behavior against WC–Co cemented car- bide was investigated in dry reciprocating sliding experiments on a pin-on-plate testing rig using distinctive normal contact loads. Post-mortem obtained wear volume and volumetric wear rate were correlated to real-time recorded penetration depth as well as to mechanical properties, microstructure and contact load. The worn surfaces and the wear debris of the zirconia composites were analyzed thoroughly by scanning electron microscopy and X- ray diffraction analysis in order to identify the occurring wear mechanisms. 0263-4368/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2008.07.004 * Corresponding author. Tel.: +32 485523004; fax: +32 92643295. E-mail addresses: koenraad.bonny@ugent.be, koenraad.bonny@gmail.com (K. Bonny). Int. Journal of Refractory Metals & Hard Materials 27 (2009) 449–457 Contents lists available at ScienceDirect Int. Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM