Evaluation of Refined Tribological Properties of Diamond Coated Cutting Tools Used in Machining of High-Strength Aluminum Alloys : Master thesis report regarding refined frictional & wear behavior of uncoated & CVD diamond coated WC-Co cemented ca

Abstract: High strength aluminum alloys have for a long time been a popular material utilized in the automotive and aerospace sector due to coveted mechanical properties in terms of weight, strength, fatigue, and corrosion. However, tribological mechanisms such as tribo-film formation and material transfer during the metal cutting manufacturing process of aluminum impose significant reduction of machining and tool-life performance. Additionally, environmental aspects associated with metal cutting manufacturing has got more interest and pushed cutting tool development in new directions to meet increased customer demands. One possible way of achieving this, is the implementation and utilization of diamond based cutting tools which has been shown to perform well in machining of high strength aluminum. However, in depth knowledge regarding the tribological properties of diamond based cutting tools is currently lacking. Thus, the aim of this master thesis has been to investigate the refined tribological characteristics and properties of WC-Co cemented carbide cutting tools coated with synthetically grown CVD diamond. Tribological testing methods, such as frictional scratch/sliding, pin-turning, contact-zone temperature measuring, and longitudinal turning have been conducted to acquire extensive amount of research material in the form of test samples and data information. Furthermore, pin-turning tests were performed using a newly developed Tribojan pin-turning equipment and the performance of this was evaluated as a subgoal task. Specimen sample analysis have primarily been performed through LOM and SEM/EDS microscopy techniques. The results acquired from testing, microscopy analysis and data set evaluation have showed promising results in terms of frictional characteristic and material transfer properties regarding CVD diamond coated surfaces. The average CoF of CVD diamond sliding against an Alumec 89 aluminum alloy surface were somewhat lower as compared with similar sliding of a conventional uncoated WC-Co cemented carbide material. Furthermore, the frictional behavior and characteristic of CVD diamond appears to be more consistent and regular over longer sliding distances. The contact interaction between the CVD diamond coated surface and Alumec 89 appears to have a more abrasive nature due to the rough surface structure and material properties of the coating. The corresponding tribo-pair contact interaction with WC-Co cemented carbide shows more adhesive tendencies. Additionally, the contact-zone temperature development during pin-turning is shown to be somewhat lower during CVD diamond/Alumec 89 surface interactions. Regarding material transfer properties, CVD diamond are shown to perform well when interacting with high-strength aluminum. The amount of material adherence is significantly reduced on CVD diamond coated surfaces. During longitudinal turning using CVD diamond coated cutting tools, no significant wear was observed. On the other hand, evidence of both adhesive and abrasive wear was observed during turning using conventional uncoated WC-Co cemented carbide tools. Finally, tribological mechanisms acting during Tribojan pin-turning tests was shown to be relatively comparable with an actual machining operation, which indicate that the testing method perform well as compliment to standard frictional sliding and machining testing.