Comparing the adhesion of aluminum to nanocrystalline diamond and tungsten carbide: Consequences for micromanufacturing

Abstract

Tungsten carbide (WC) micro end mills exhibit a high wear rate, and when cutting soft materials such as aluminum, the chips tend to adhere to the cutting tool increasing the cutting force and leading to clogging and eventually tool failure. Diamond has outstanding properties such as high hardness, high thermal conductivity, chemical inertness, extremely low friction, low wear, and low adhesiveness, making it an ideal coating for cutting tools. However, it has been a challenge to grow uniform, conformal diamond films on WC tools with good adhesion due to the presence of cobalt which suppresses the diamond nucleation and reduces adhesion between the tool and diamond film. We present results for nanocrystalline diamond (NCD) films deposited onto WC micro end mills. Improved growth methods led to a high density of diamond nucleation sites at the surface, and enhanced tool performance cutting Al. We discuss the dramatic reduction of adhesion between Al and the tool that is observed when the diamond coating is present. To understand the origin of this behavior in more detail, atomic force microscopy was used to measure the work of adhesion for Al when in contact with both bare WC and NCD. It was observed that adhesion between Al and diamond is far lower than for Al and WC, illustrating that the macroscopic reduction of adhesion during micro machining is manifested at the nanoscale single asperity level.