414 International Journal of Mechanical and Materials Engineering (IJMME), Vol.6 (2011), No.3, 414-418 MACHINING PERFORMANCE AND WEAR MECHANISM OF TiAlN-COATED INSERT R.J. Talib, H.M. Ariff and M.F. Fazira AMREC, SIRIM Bhd,.Lot 34, Jalan Hi-Tech 2/3 Kulim Hi-Tech Park, 09000 KULIM, Malaysia Email address: talibria@sirim.my Received 2 December 2011, Accepted 26 December 2011 ABSTRACT Titanium Aluminum Nitride (TiAlN)-coated cutting tool inserts were subjected to turning of carbon steel at two cutting speeds (75 mm/min and 120 mm/min), whereas depth of cut and feed rate is kept constant at 0.5 mm and 0.06 mm/rev, respectively. The objective of this work is to investigate the microstructural changes on the flank of the insert and effect of cutting speed on the machining performance of the coated insert. Microstructural examinations revealed the following phenomenon during turning process; (i) two-way transfer of material on worn surfaces of the insert and workpiece, (ii) formation of mechanically alloying transferred material, (iii) plastic flow of coated material, and (iv) abrasion wear mechanism. Test results also show that the flank wear reduced as the cutting speed increased due to good oxidation resistance properties of TiAlN coating layer at high temperatures generated during turning process. Keywords: 3-5 TiAlN-coated insert, Turning, Wear, Performance, SEM 1. INTRODUCTION Hard coating is used to increase microhardness, wear resistant, corrosion resistant, tool life properties of engineering components. Hard coating can be applied to cutting tool, mold and dies, machine elements, automotive parts, and electrical components. The commercial coatings of TiN, TiCN, TiAlN, Al 2 O 3 are frequently used in tools industry for machining and drilling of metals (Che-Haron et al., 2001; Sproul, 1996; Talib et al., 2007). Previous study by earlier researchers showed that an increase in tool life may be due to increase in hardness (Zeng et al., 1998), greater bonding energy of the coating elements (Lin et al., 1997), and lower friction coefficient (Sedlacek, 1982). In case of TiAlN coating, the improvement in the cutting performance is due to the oxidation resistance of TiAlN properties at higher temperature (Munz, 1986); Leyendecker et al., 1991). High wear resistance even at high temperatures is the outstanding property of TiAlN (Munz, 1986), a characteristic that makes this coating appropriate to cut abrasive work piece material such as cast iron, aluminium silicon alloys and composite materials at high speeds. The generations of thermal fatigue crack on the substrate are due to the phenomena of thermal cycling coupled with thermal shock during machining (Ghani et al., 2002). During machining process, wear mechanism also take place, depending on the machining parameters setting, coating materials employed, and type of work piece used. In the study on failure mechanisms of TiAlN-coated insert, Khrais and Lin (2007) identified that the micro- wear mechanisms in operation during machining of AISI 4140 steel were edge chipping, microabrasion, micro- fatigue, micro-thermal, and micro-attrition. This work will discuss the wear mechanism operated on the tool insert during turning process and the effect of cutting speed on the performance of the tool insert. 2. METHODOLOGY The investigations were carried out on the tool inserts made from the TiAlN coated on the tungsten carbide substrate. Cutting tests were carried out on a CNC milling machine model EXCEL SL 360/600I with cutting fluid of metal cut emulsion (SELSO). Cutting ability of the TiAlN coated insert was conducted at two cutting speed (75 mm/min and 120 mm/min), while feed rate of 0.06 mm/rev, and depth of cut 0.5 mm were kept constant (Table 1). The tests were conducted on 100 mm diameter and 140 mm long medium carbon steel rod (1.25 % C, 0.23% Si, 0.12% Mn, 0.24 %, 5.39% Cr, 0.47 % Mo, 0.93 % V, 0.011% W, 0.075% P and balance Fe) with hardness of 38 HRC. Figure 1 and Figure 2 show the microstructure of the workpiece and TiAlN coating film deposited on WC substrate, respectively. After subjected to turning test, the cutting edges of the inserts were examined using a field emission scanning electron microscope (FESEM) model LEO 1525 equipped with energy dispersive X-ray (EDX). FESEM operated at 15 kV, using secondary electrons mode. Sample for microstructural investigation were ultrasonically cleaned for 30 minutes. Table 1: Machining parameters Depth of cut (mm) Feed Rate (mm/rev) Cutting Speed (mm/min) 0.5 0.06 75 0.5 0.06 120