ORIGINAL ARTICLE Experimental investigation on chip morphologies in high-speed dry milling of titanium alloy Ti-6Al-4V Anhai Li & Jun Zhao & Yonghui Zhou & Xiaoxiao Chen & Dong Wang Received: 9 September 2011 /Accepted: 9 December 2011 /Published online: 23 December 2011 # Springer-Verlag London Limited 2011 Abstract An experimental investigation of chip morphologies in high-speed dry milling of Ti-6Al-4V alloy was conducted over a variety of different cutting conditions. Observation on the multi-view characterization of the chips was carried out which includes free surface, back surface, and cross-section of top surface. Structure and shape alterations of the free and back surfaces were analyzed using an optical microscope and a scanning electron microscope (SEM). The microstructural analysis indicated that the chip morphology when dry milling Ti-6Al-4V alloy in high-speed range exhibited a serrated shape for a wide range of cutting conditions. The degree of chip serration is more pronounced and evident with the increase in cutting speed, feed, and depth of cut. A significant variation in the microstructure of the chip including the thickness of the shear bands and the serrated tooth structure for different cutting speeds has been identified. The higher chip serration ratio (CSR) in high cutting speed range may facilitate appropriate machining condition for the occurrence of well-broken chips. Moreover, chip formation takes place by the mechanism of catastrophic thermoplastic shear from the observation of the shear bands using metallurgical analysis techniques. X-ray diffraction results indicated that no evidence of phase transfor- mation was found in the shear localized chips. The variation in chip serration and metallurgical microstructure inside the shear bands and the tool/chip contact zone should be attributed to the reinforcement of coupled thermo-mechanical behavior in the cutting process with the increase in machining parameters. Keywords High-speed milling . Titanium alloy . Chip morphology . Saw-tooth chip . Phase transformation 1 Introduction Application of titanium alloys in the aerospace industries has received great attention from many industrialist and researchers due to their attractive properties such as high specific strength (strength-to-weight ratio) maintained at elevated temperature, superior fracture resistant characteristics, and exceptional resistance to corrosion [1]. However, titanium alloys are known as difficult-to-machine materials, and machining of titanium alloys has been an issue that needs to be improved. Specifically, Ti-6Al-4V alloy has low elasticity modulus and exhibits severe plastic deforma- tion, severe wear, and breakage in high-speed machining. On the other hand, this important alloy is characterized by low thermal conductivity in combination with high chem- ical reactivity with tool materials, leading to increased tool cutting loads and temperatures, as well as to extreme abrasion [2]. Nowadays, in order to reduce the costs of production and to make the processes environmentally safe, the aeronautical manufacturers move toward dry cutting by eliminating or minimizing cutting fluids. Generally speaking, water-based cooling lubricants are used in conventional cutting of titanium and its alloys with carbide tools. High-speed machining may be a possibility to switch from wet to dry cutting [3]. For continuous high-speed turning, carbide tool for titanium has to be cooled with a great flow of water-based coolant to achieve better results in terms of tool wear. In discontinuous high- A. Li (*) : J. Zhao : Y. Zhou : X. Chen : D. Wang Key Laboratory of High Efficiency and Clean Mechanical Manufacture of MOE, School of Mechanical Engineering, Shandong University, 17923 Jingshi Road, Jinan 250061, People’s Republic of China e-mail: liahsea@163.com J. Zhao e-mail: zhaojun@sdu.edu.cn Int J Adv Manuf Technol (2012) 62:933–942 DOI 10.1007/s00170-011-3854-9