Comparing the performance of several tool coatings in turning of commercially pure titanium grade 4

Abstract

The increasing use of titanium and its alloys in the manufacture of implants results from the simultaneous presence of excellent biocompatibility, relatively low density, high mechanical properties, and corrosion resistance. Unlike the excellent application characteristics, titanium is classified as a difficult-to-machine material. Therefore, one constant challenge for implant manufacturers is to correctly choose turning tools for each application. This work aims to compare the useful life of the uncoated insert with other three types of coatings on carbide tools, titanium aluminum nitride (TiAlN), aluminum chromium nitride (AlCrN), and titanium nitride/titanium carbonitride multilayer coating (TiN + TiCN). Turning experiments were performed using grade 4 commercially pure titanium (typically used in dental implants), testing two cutting speeds for each tool used. The tests were carried out in a CNC rotary head lathe, using cutting fluid in abundance. The results showed that the uncoated insert achieved the shortest life due to its worst properties (lower surface hardness, higher friction coefficient, and lower maximum working temperature), even with its supposedly higher chemical stability with titanium. On the other hand, the tool with the TiN + TiCN multilayer coating obtained the longest tool life among the four tested inserts. The main novelty of this work is that the tool that showed the longest life (TiN + TiCN coating) did not have the best properties among the tested coatings. In fact, it had both the lowest hardness and working temperature. However, this tool has a low coefficient of friction and a multilayer structure coating, which increases its resistance against the wear mechanism that occurred predominantly in this application, which was attrition. Even with the increased cutting speed, this coating also achieved the best result. Therefore, during the machining of titanium, the most important characteristics of the tool are low coefficient of friction and resistance against the pull out of particles.