Characterization and Performance Evaluation of Mono-grain and Bi-modal PCD Grade in Machining of MMC

The aim of this investigation is to study the influence of different parameters such as grain size and cobalt content on the tool performance in the machining of metal matrix composite (MMC) using different polycrystalline diamond (PCD) tools. The experimental tests were conducted with four different PCD grades in dry the milling of Aluminium-Silicon carbide (Al-SiC) composite containing 20% wt of SiC as a workpiece material. The SEM study shows that PCD grades I and II have a bimodal grain size distribution. Rietveld refinement of the XRD spectra for these grades indicates that grade I contains larger amount of Co compared to grade II. The difference in performance between these grades can be explained by the Co content. PCD grade III is a coarse grain grade while grade IV is a fine grain grade. An XRD analysis shows that the main difference between the mono- grain and bimodal grain PCD is the presence of WC in the mono-grain grades which is believed to be added to the raw material of PCD as a grain growth inhibitor. In the XRD pattern for the bimodal grades the peaks in the WC phase are completely absent. The results indicate that the tool performance in terms of wear development is influenced by grain size distribution, cobalt content and the presence of WC; where the abrasive wear is the main wear mechanism which determines the tool life of the diamond grades in milling MMC. The results also indicates that the MMC can be machined with any diamond grade at the low range of cutting speed (≤ 400 m/min) while at a higher range of cutting speed (> 400 m/min) the selection of the diamond grade should be based on the chemical composition and grain size distribution. The presence of grain growth inhibitor also has a significant effect on the tool performance in machining MMC at cutting speeds above 400 m/min.