FIB/TEM/EELS micro/nanometric investigations of the effects of laser ablation on the diamond/binder structure in polycrystalline diamond composites

Abstract

Laser ablation of diamond composites is of high interest for a wide range of industries for making high wear resistant tools/components. In this context, the paper studies the effects of pulsed laser ablation on a polycrystalline diamond composite (CMX850, average grain size 2μm, Cobalt binder volume, circa 15%) by identifying the residual carbonic allotropes and metallic binder traces in the ablation region. For this study, grooves were first laser (DMG LASERTEC 60 HSC Q-switched Nd:YAG, pulse duration 20μs, frequency 10kHz) ablated into the surface of the polycrystalline diamond structure, then, by using Focused Ion Beam (FIB) techniques, a thin section across the groove was extracted, which allowed the identification of the distinct microstructural characteristics below the ablated surfaces at sites that experienced high and low laser fluence. Using Transmission Electron Microscopy (TEM) imaging and Electron Energy Loss Spectroscopy (EELS) scans, the extracted lamella revealed that amorphous carbon and graphitic structures were formed as a consequence of the ablation process and an abrupt interface graphite to polycrystalline diamond was evident showing an undisturbed polycrystalline diamond (PCD) composite substructure below the graphitic boundary. Furthermore partially evacuated pockets containing traces of the Cobalt binder were identified within the amorphic/graphitic regions of the lamella. The examination of local high and low laser fluence ablated sites has revealed that the extent of residual deposits (amorphic and graphitic carbon) is related to the level of fluence/thermal activity during ablation.