Journal of Materials Processing Technology 166 (2005) 188–192 The effect of machining on surface integrity of titanium alloy Ti–6% Al–4% V C.H. Che-Haron a,∗ , A. Jawaid b a Department of Mechanical and Materials Engineering, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia b School of Engineering, Coventry University, Coventry CV1 5FB, UK Received 28 January 2002; received in revised form 6 July 2004; accepted 13 August 2004 Abstract This paper gives the investigation on surface integrity of rough machining of titanium alloy Ti–6% Al–4% V with uncoated carbide cutting tools. The experiments were carried out under dry cutting conditions. The cutting speeds selected in the experiment were 100, 75, 60 and 45 m min -1 . The depth of cut was kept constant at 2.0 mm. The feed rates used in the experiment were 0.35 and 0.25 mm rev -1 . Two types of insert were used in the experiments. For a range of cutting speeds, feeds, and depths of cut, measurements of surface roughness of machined surface, microhardness and work hardening backed up with scanning electron microscope were taken. The surface of titanium alloy is easily damaged during machining operations due to their poor machinability. The machined surface experienced microstructure alteration and increment in microhardness on the top white layer (≤10 m) of the machined surface. Severe microstructure alteration was observed when machining with the dull tool. In addition, surface roughness values obtained were within the limit (<6 m) stipulated by ISO for rough machining. © 2004 Elsevier B.V. All rights reserved. Keywords: Surface integrity; Titanium alloy; Carbide tool 1. Introduction Titanium alloys are extremely difficult to machine materi- als. The machinability of titanium and its alloys is generally considered to be poor owing to several inherent properties of materials. Titanium and titanium alloys have low thermal con- ductivity and high chemical reactivity with many cutting tool materials. Its low thermal conductivity increases the temper- ature at the cutting edge of the tool. Hence, on machining, the cutting tools wear off very rapidly due to high cutting tem- perature and strong adhesion between tool and workpiece material. Additionally, the low modulus of elasticity of ti- tanium alloys and its high strength at elevated temperature further impair its machinability. Machining of titanium alloys at higher cutting speed will cause rapid chipping at the cutting edge which leads to catas- ∗ Corresponding author. Fax: +60 3 8259 659. E-mail address: chase@eng.ukm.my (C.H. Che-Haron). trophic failure of the inserts [1]. A higher cutting speed also results in rapid cratering and/or plastic deformation of the cutting edge. This is due to the temperature generated which tends to be concentrated at the cutting edge closer to the nose of the inserts. The heat affected zone is very small when cutting titanium alloys. The smaller heat affected area pro- duced is as a result of the shorter chip/tool contact length. It is mainly for this reason that the cutting speeds are limited to about 45 m min -1 when using straight grade cemented car- bides (WC–Co) [2]. The rapid tool failure and chipping at the cutting edge has resulted in poor surface finish of the ma- chined surface. It has caused not only higher surface rough- ness values but also higher microhardness values and severe microstructure alteration. Titanium alloys are generally used for a component, which requires the greatest reliability, and therefore the surface in- tegrity must be maintained. According to Field and Kahles [3], when machining any component it is essential to satisfy surface integrity requirements. However, during machining 0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.08.012