PCD after cobalt leaching reinforced by high temperature annealing: Tribological properties and graphitization evolution

Polycrystalline diamond (PCD) is widely used in drill bits and bearings of downhole tools for oil drilling because of its excellent tribological properties. However, the graphitization of PCD caused by downhole high temperature and the reduction of wear resistance are urgent problems that need to be solved. Cobalt at high temperature is the main factor leading to graphitization. Therefore, this experiment improves the tribological properties of PCD at high temperatures by leaching Co treatment. An annealing experiment was conducted in a box-type resistance furnace, and the PCD after high-temperature annealing for Co leaching was studied by X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, and Raman spectroscopy. Results of Raman spectroscopy show that Co leaching is conducive to the significant reduction of graphitization. The results show that the area of the transfer films increases with the increase of the annealing temperature, and the formation of the transfer films may result from the complex chemical reaction or the combined effect of the transfer film mechanism, passivation mechanism, and graphitization mechanism of the friction pairs in the flash temperature state. Thus, the tribological properties of PCD annealed at high temperatures with the Co leaching are greatly improved.

Automated summary

This study improves the tribological properties of PCD at high temperatures through cobalt leaching treatment. The results show that cobalt leaching contributes to the reduction of graphitization. Additionally, the area of transfer films increases with increasing annealing temperature, leading to improved tribological properties of PCD.