# Thermal Behavior of Single-Crystal Diamonds Catalyzed by Titanium Alloy at Elevated Temperature
## 1 Introduction  
Single-crystal diamonds are often used in ultra-precision machining for components where an optical-grade surface finishes Are generally required. Titanium alloy has a series of advantages such as high specific strength, high temperature resistance and corrosion resistance. Hence, titanium alloys could be used to provide additional value in optical applications. Ti-6 Al-4V is a commonly used titanium alloy that is very suitable for aircraft engines and airframe components. For example, integral blade rotors must be made of hard-to-cut alloys (Ti-6 Al-4V and Inconel 718). It is difficult to machine due to elevated cutting forces, high temperature, limited cutting conditions and excessive tool wear [1]. Thin-wall structures are usually manufactured out of aluminum and titanium alloys and are widely used in the aeronautical sector. However, their machining presents serious challenges such as vibrations because of excessive tool wear and high cutting force [2]. The critical problem faced during the machining process of these superalloys is the concentration of heat in the cutting zone and the difficulty in dissipating it. The concentrated heat in the cutting zone has a negative influence on the tool life [3]. [PERSON] carried out an experimental to study the effect of lubricant pressure and material heat treatment on cutting forces and tool wear evolution on turning of super alloys [4]. [PERSON] et al. conducted dry-cutting experiments of titanium alloy with cemented carbide, CBN and PCD toolsand measured the critical bonding temperatures of three tool materials and workpiece materials with quasi-static contact method to be 760 \({}^{\circ}\)C, 740 \({}^{\circ}\)C and 900 \({}^{\circ}\)C, respectively [5]. [PERSON] et al. [6] classified titanium alloy as non-diamond turnable because of excessive tool wear. As Ti-6 Al-4V has a low thermal conductivity (about 15 W/(m\({}^{\circ}\)C)), the cutting temperature on the interface is very high. High cutting temperature will exacerbate the reactivity between the titanium and diamond. This serves to accelerate the tool wear rate as stated by [PERSON] et al. [7]. Therefore, it is necessary to research the tool wear of Ti-alloy cutting with diamond tools.  
A number of researchers have reported so far on wear characteristics of diamond tool in machining of Ti-6 Al-4V.  
[PERSON] et al. [8] studied the wear of single-crystal diamond tools in the ultra-precision cutting of titanium alloys. The results show that the cutting temperature and pressure on the contact surface between the diamond tool and the titanium alloy are the main causes of the diamond tool wear. The wear mechanism of the diamond tool is the graphitization of the diamond. [PERSON] et al. [9] studied the wear mechanism of a polycrystalline diamond (PCD) cutting tool when machining titanium alloy Ti-6 Al-4V. He pointed out that the wear form of the PCD cutting tool is crater-wear of the rake face and uniform wear and groove wear of the flank face. The wear mechanism is adhesion, diffusion and oxidation under high temperature, and indicates that the groove on the PCD tool is caused by diamond phase-transition. [PERSON] et al. [10] used PCD tool to carry out cutting experiments on titanium alloy Ti-6 Al-4V. It was found that the main failure mode of PCD tool when cutting titanium alloy is flank wear. The wear mechanism of PCD tool is mainly adhesion and attrition. The study mentioned above suggest that the wear mechanism is not mechanical, but thermochemical one. Graphitization of diamond is the main form of diamond tool wear when cutting Ti alloy with a diamond tool.  
Based on the above analysis, in this work, a series of thermochemical experiments were carried out to simulate the process of diamond wear during Ti alloy-cutting with diamond tools, in order to study the thermochemical wear mechanism of diamond at elevated temperature under the catalytic of titanium alloy. The findings of this research could provide a theoretical basis for reducing tool wear in cutting Ti alloy with a diamond tool.