Please cite this article in press as: W.Y.H. Liew, Low-speed milling of stainless steel with TiAlN single-layer and TiAlN/AlCrN nano-multilayer coated carbide tools under different lubrication conditions, Wear (2010), doi:10.1016/j.wear.2010.06.012 ARTICLE IN PRESS G Model WEA-99547; No. of Pages 15 Wear xxx (2010) xxx–xxx Contents lists available at ScienceDirect Wear journal homepage: www.elsevier.com/locate/wear Low-speed milling of stainless steel with TiAlN single-layer and TiAlN/AlCrN nano-multilayer coated carbide tools under different lubrication conditions W.Y.H. Liew ∗ School of Engineering and Information Technology, Universiti Malaysia Sabah, Locked Bag 2073, Kota Kinabalu, Sabah 88999, Malaysia article info Article history: Received 12 January 2010 Received in revised form 16 June 2010 Accepted 21 June 2010 Available online xxx Keywords: Fracture Steel Cutting tools Electron microscopy abstract This paper evaluates the performance of TiAlN/AlCrN nano-multilayer coated, TiAlN single-layer coated and uncoated carbide tools in low-speed milling of STAVAX (modified 420 stainless steel) under flood and mist lubrication. Scanning electron microscope, energy dispersive X-ray analysis system and Raman spectroscopy were used to examine the tool wear and determine the type of oxide formed on the tool surface during machining. In machining STAVAX with a hardness of 40 HRC, the coated tools were sub- jected to delamination, attrition and abrasive wear throughout the duration of testing. During machining STAVAX with a hardness of 55 HRC, three distinct stages of tool wear occurred, (i) initial wear by delami- nation, attrition and abrasion, followed by (ii) cracking at the substrate and (iii) the formation of individual surface fracture at the cracks which would then enlarge and coalesce to form a large fracture surface. The TiAlN/AlCrN coated tool exhibited higher resistance against delamination and abrasive wear than the TiAlN coated tool. The cracking resistance and hardness of the coating, and oxidation of the coating during machining appeared to have significant influences on the resistance of the tool against these wear mechanisms. A longer cutting distance was required to cause TiAlN/AlCrN coated tool to crack and frac- ture. This was due to the substrate receiving greater protection against cracking and fracture as a result of the coating being removed at a slower pace by abrasion and delamination. The likeliness of the uncoated tool to chip, crack and fracture, and the severity of abrasion increased with an increase in the hardness of the workpiece. Small quantity of mineral oil sprayed in mist form was effective in reducing the severity of delamination and abrasive wear, and delaying the occurrence of cracking, fracture and chipping. The influence of the ductility of the workpiece, tool wear and the lubricants on the surface finish are also discussed. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Many researchers had studied the wear of cutting tools in milling steel. Attrition, chipping, and cracking and fracture due to impact between the tool and the workpiece were the dominant wear mechanisms at low speeds. At high speeds, the tool wear was governed by thermal cracking and thermo-chemical wear such as diffusion and oxidation [1–7]. In milling process, the tool is heated during cutting and cooled when it leaves the cutting zone. Tem- perature variation can cause periodic expansion and contraction of the tools leading to the formation of thermal cracks which is also known as comb cracks. Thermal cracks are more likely to form at high speeds since the amplitude of the temperature variation increases with increasing speed [8,9]. Coating can effectively improve the tool life in milling steel. It is generally accepted that coating enhances the oxidation resis- ∗ Tel.: +60 88 320000; fax: +60 88 320348. E-mail address: wyhliew@ums.edu.my. tance and lubricity of the tool, protects the tool against diffusion wear, and reduces the temperature variation in the tool, rendering it less susceptible to crack [3,10,11]. Liu et al. [4] reported that when the lubricity of the TiC-based cermets tool was improved by TiN nano-powder addition, the severity of attrition wear was reduced. Endrino et al. [12] found that diffusion of aluminium to the surface of nano-crystalline AlTiN resulted in the formation of an alumina protective layer that subsequently reduced the adhesion between the stainless steel and the tool surface, and hence attrition wear. The experimental results obtained in low-speed milling of stainless steel showed that TiAlN coating enhanced the abrasive and crack- ing resistance of the cutting tool, and prevented edge chipping and catastrophic failure [13]. Many researchers demonstrated that AlCrN coating, which had been developed recently, gave better wear protection than TiAlN coating. Kalss et al. [14] and Lin et al. [15] reported that in machining steel where tool wear was governed by abrasion, fracture, ther- mal cracking and attrition, AlCrN coated tools exhibited higher wear resistance than TiAlN coated tools. This was due to the AlCrN coating having higher cracking resistance and lower ther- 0043-1648/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2010.06.012