Tribological behaviors of diamond films and their applications in metal drawing production in water-lubricating condition

Abstract

The frictional and wear performance of the microcrystalline diamond (MCD), nanocrystalline diamond (NCD) and MCD/diamond-like carbon (DLC) bi-layered film are comparatively investigated under water-lubricating conditions. A full factorial experimental plan is conducted with four sliding velocities ranging from 0.126 to 0.503 m/s and four normal loads from 2 to 8 N. The duration of each sliding process is 24 h. The results show that although the MCD/DLC film shows the lowest stable coefficient of friction ranging from 0.025 to 0.12, the top-layered DLC film does not show beneficial effect on enhancing the sliding stability of single-layered diamond films. Comparatively, the MCD film exhibits the superior sliding stability and wear resistance, which are regarded as the more critical characters that determinate the lifetime and performance of a metal drawing die. Therefore, a drawing production of aluminum pipes is conducted in the water-lubricating condition using the MCD-coated drawing die. A novel drawing device is designed for the water-lubricating metal drawing production. It is capable of providing a fully immersed drawing environment for the metal pipe and thus guarantee the lubrication and cooling effects. The result of the drawing production shows that utilizing the diamond-coated drawing die in the water-lubricating condition could elevate the production of a drawing die by over 100 times compared with using the tungsten carbide drawing dies in oil-lubricating condition. Moreover, good surface quality and geometrical precision could also be obtained by the diamond-coated drawing dies in the water-lubricating drawing.