Microstructure and tribo-mechanical properties of ultrafine Ti(CN) cermets E.T. Jeon, J. Joardar, S. Kang * School of Materials Science and Engineering, College of Engineering, Seoul National University, Kwanak-ku, Seoul 151-742, South Korea Received 18 June 2001; accepted 30 November 2001 Abstract Role of Ti(CN) particle size on the microstructure of the Ti(CN)–WC–Ni cermets has been evaluated. The systems containing ultrafine grade Ti(CN) shows better structural homogeneity and a large volume fraction of rim phase in the core-rim structure when compared to the coarse Ti(CN) cermets. Measurable shift in the lattice parameter of the Ti(CN) core occurs in the ultrafine grade cermet possibly due to the diffusion of W and/or Ni. The improved structural features in the ultrafine grade led to considerably enhanced tribo-mechanical properties of the cermets. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Ti(CN); Cermets; Ultrafine; Microstructure; Wear 1. Introduction Development of Ti(CN) cermets has received signifi- cant research thrust in the field of cutting tool materials in recent years. The excellent wear resistance of Ti(CN), accompanied by good chemical stability at elevated tem- perature ensures enhanced cutting efficiency and tool life [1–3]. The Ti(C 1x N x ) hard phases have been used in- variably, with WC, Mo 2 C and other secondary carbides to improve the sinterability, abrasion resistance and mechanical properties. In addition, Co, Ni, Fe, or a mixture of them, have been incorporated as binder for providing adequate toughness to the tool inserts [4–7]. The dissolution and reprecipitation of these carbides in binder phases lead to the formation of a typical core-rim structure [1,8–11], which is envisaged to be critical in controlling the material properties. The role of NbC, HfC, TaC, WC and other carbides in the Ti(CN) cer- mets has been studied in this regard in previous works [11–14]. However, the size effect of ultrafine Ti(CN) on the formation of the core-rim structure in Ti(CN)–WC– Ni cermets, and its influence on the mechanical prop- erties is not known yet. The present work investigates into the role of sub-micron Ti(C 0:5 N 0:5 ) particles on the evolution of the microstructure in Ti(CN)–WC–Ni cer- mets containing 0.4 lm WC particles, and its impact on the tribo-mechanical properties. 2. Experimental The various compositions investigated in the present study are enlisted in Table 1. Three different sets of samples, with Ti(CN) particle sizes of 0.7–0.95 (H.C. Starck GmbH), 1.4 and 3–5 lm (Kennametal Inc.) were blended with WC (Nanodyne Inc.; 0.4 lm) and Ni (INCO; 4.1 lm) in a horizontal ball mill at a ball- to-powder weight ratio of 5. Milling was performed for 24 h under acetone using WC–Co balls. The milled powders were dried and compacted under uniaxial load of 100 MPa and were subsequently sintered in vacuum for 1 h at 1783 K. The sintered samples were examined for Vickers hardness, H v , under indentation load of 20 kg and the fracture toughness was calculated from H v using the expression derived by Shetty et al. [15]. Relative density of the sample was determined by Ar- chimedes principle to assess the degree of porosity. The microstructural features were studied using SEM (JEOL JSM-5600) in back scattered mode and the vol- ume fractions of the various phases were estimated by image analysis. X-ray diffraction (XRD) studies using Cu Ka radiation in M18XHF (MacScience Co.) system was also performed to monitor the phase evolution and/ or change in lattice constants during sintering. The wear International Journal of Refractory Metals & Hard Materials 20 (2002) 207–211 www.elsevier.com/locate/ijrmhm * Corresponding author. Tel.: +82-2-880-7167; fax: +82-2-884-1578. E-mail address: shinkang@plaza.snu.ac.kr (S. Kang). 0263-4368/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0263-4368(02)00004-5