Study on the effectiveness of WS2 and CaF2 on the performances of self-lubricating micro impregnated diamond bits

Abstract

Self-lubricating micro impregnated diamond bits (IDBs) were manufactured for the first time via hot-pressing powder metallurgy to investigate the effectiveness of two promising solid lubricant additives, WS2 and CaF2, in improving IDBs' self-lubricating and drilling performances through laboratory drilling test and micro analyses. It was found that, with increase in lubricant concentration, the rate of penetration (ROP) of WS2 IDBs increased exponentially, while that of the CaF2 IDBs decreased monotonically from its maximum value at 6 vol% CaF2 concentration. For WS2 IDBs, the increase in ROP was at the sacrifice of substantial deterioration of IDBs' service life, while the service life of CaF2 IDBs gradually increased to surpass that of lubricant-free IDBs at 8 vol% CaF2 addition and continued to grow. Micro analyses, including measurement of diamond protrusion height and micro morphological analysis of IDBs' worn surface, were conducted using a confocal laser scanning microscopy (CLSM). The 10 vol% CaF2 IDBs were found under good protection from either matrix or diamond wear. By contrast, the surface of the 6 vol% WS2 IDBs suffered severe wear. Based on CLSM images, it was inferred that the high ROP and low service life of WS2 IDBs were a result of enhanced three-body abrasive wear by breakaway diamond grits. In general, self-lubricating IDBs with 10 vol% CaF2 addition acquired best overall performances in that they achieved longest service life while having higher ROP than lubricant-free IDBs.