Wear 274–275 (2012) 442–451 Contents lists available at SciVerse ScienceDirect Wear j o ur nal ho me p age: www.elsevier.com/locate/wear Tool life and wear mechanism of coated and uncoated Al 2 O 3 /TiCN mixed ceramic tools in turning hardened alloy steel K. Aslantas a,∗ , ˙ I. Ucun b , A. C ¸ icek c a Afyon Kocatepe University, Faculty of Techonolgy, Department of Mechanical Engineering, Afyonkarahisar, Turkey b Afyon Kocatepe University, Technical Education Faculty, Department of Mechanical Education, Afyokarahisar, Turkey c Düzce University, Faculty of Technology, Department of Manufacturing Engineering, Düzce, Turkey a r t i c l e i n f o Article history: Received 22 July 2011 Received in revised form 23 November 2011 Accepted 28 November 2011 Available online 13 December 2011 Keywords: Cutting tool Steel Engineering ceramic Hard materials PVD coatings a b s t r a c t The focus of this paper is the continuous turning of hardened AISI 52100 (∼63HRc) using coated and uncoated ceramic Al 2 O 3 –TiCN mixed inserts, which are cheaper than cubic boron nitride (CBN) or polycrystalline cubic boron nitride (PCBN). The machinability of hardened steel was evaluated by mea- surements of tool wear, tool life, and surface finish of the workpiece. Wear mechanisms and patterns of ceramic inserts in hard turning of hardened AISI 52100 are discussed. According to the results obtained, fracture and chipping type damages occur more frequently in uncoated tools, whereas crater wear is the more common type of damage in TiN coated tools. Most important result obtained from the study is that TiN coating and crater wear affect chip flow direction. In uncoated ceramic tool, the crater formation results in decrease of chip up-curl radius. Besides, uncoated cutting tool results in an increase in the temperature at the tool chip interface. This causes a thermal bi-metallic effect between the upper and lower sides of the chip that forces the chip to curl a smaller radius. Chips accumulate in front of the tool and stick to the workpiece depending on the length of the cutting time. This causes the surface quality to deteriorate. TiN coating not only ensures that the cutting tool is tougher, but also ensures that the surface quality is maintained during cutting processes. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Hard turning is a turning operation which is applied on high- resistance alloy steels (45 < HRC < 65) to obtain surface roughness values that are close to those obtained in grinding (R a ∼ 0.1 m). The workpiece materials involved include various hardened alloy steels, tool steels, case-hardened steels, superalloys, nitrided irons and hard-chrome-coated steels, and heat-treated powder metal- lurgical parts [1]. Although this production method is a new subject, there are quite a few studies by several researchers in the literature. These studies mostly concern the turning of AISI 52100 bearing steel, H11–H13 hot work tool steel, and AISI 4130–4340 low alloy steel using CBN, ceramic, and coated carbide tools. The most common problem encountered in the hard turning process is tool wear. Therefore, ceramic, PCBN, and CBN cutting tools are generally used for hard turning processes [2–5]. The use of alumina based ceramic tools in hard machining is an attrac- tive alternative to grinding in order to reduce processing costs, improve material properties, and for the environmental benefits [6]. Advances in ceramic processing technology have resulted in ∗ Corresponding author. Tel.: +90 272 228 13 11; fax: +90 272 228 13 19. E-mail address: aslantas@aku.edu.tr (K. Aslantas). a new generation of high performance ceramic cutting tools that exhibit properties such as fracture strength, toughness, thermal shock resistance, hardness, and wear resistance. Therefore ceramic tools are used in the machining of various types of steels and hard materials. There are different classifications of tool wear in the metal cutting process such as abrasion, adhesion, fatigue, diffusion, and chemical wear [7]. In hard turning, not only tool geometry and cut- ting conditions but also the cutting tool type and composition and hardness of the workpiece materials are important factors influ- encing wear mechanisms. Cutting type (continuous or intermittent turning) is also an important factor affecting tool wear behavior. Results on intermittent turning using a cemented carbide cutting tool showed that the wear type that generally occurred was flank wear, and the wear mechanisms were abrasion, adhesion, and oxi- dation [8]. The most prominent mechanisms of tool wear in typical hard turning applications have been found to be abrasion, adhe- sion, and diffusion [9]. Numerous studies have been carried out to describe the tool wear and wear mechanisms in the hard turn- ing process. These studies can be categorized into four groups: (a) workpiece material type; (b) cutting tool type; (c) cutting edge geometry; (d) wear type and mechanisms. An extensive studies were performed by [10–14] to investi- gate the tool wear mechanisms of CBN cutting tools in turning the 0043-1648/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2011.11.010