Laser finishing of polycrystalline diamond as strengthening mechanism

Polycrystalline diamonds are widely used in the cutting tool industry for machining of aluminium alloy and metal matrix composites as they exhibit superior wear resistance. However, their wear characteristics are dependent on their microstructural features (i.e. percentage of binder phase and size of grains) which are defined during the sintering process. Low-energy fibre laser process of polycrystalline diamond composites with different grain dimensions is proposed to promote microstructural changes, enhance their hardness, and retain surface finish. Specimens were processed with a nanosecond pulsed fibre laser (ytterbium-doped) at a wavelength of 1064 nm. Samples treated at various fluences, beam speeds and pulse durations were characterised via 3D interferometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and microindentation hardness test. At a fluence below the composite’s ablation threshold (i.e. 20 J cm 2), the investigated finishing/polishing process for a coarse grain polycrystalline diamond resulted in a change of diamond grain size, a surface integrity of 140 nm and increased micro hardness (i.e. 240 GPa). The laser treatment caused plastic deformation of the grains, changing the intergranular boundaries area therefore impeding dislocation movements and enhancing hardness.