Effects of Laser Surface Modification of Cemented Carbide and Bionic Microtexture on Properties of Boron-doped Diamond Coatings

The mismatch between the coefficients of thermal expansion of diamond and WC-Co cemented carbide causes hot filament chemical vapor deposition (HFCVD) diamond coating tools to be prone to coating flaking and wear, which severely limits their promotion in the field of ultra-precision machining. In this work, in order to prepare high performance diamond coating applied in the field of ultra-precision machining, different types of bionic microtexture were fabricated on the surface of carbide tools by laser technology, and boron-doped diamond (BDD) coatings were deposited on the surface of tools by HFCVD method. The effect of laser microtexture on the deposition quality of BDD coatings on hard alloy substrates was investigated, and the improvement effect and reasons of different types of bionic microtexture on substrate-coating bonding strength and cutting performance of tools were analyzed. The surface hardness of samples was studied by digital rockwell hardness tester (HRS-150). The surface morphology and elemental composition of the samples were observed by super depth 3D microscope (VHX-5000), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The roughness of coatings was measured by white light interferometer. The composition of coatings was analyzed by Raman spectroscopy. The effects of different microtextures on coating adhesion strength and cutting performance were studied by indentation and milling tests. Surface hardening occurred at the edge of microtexture, and the hardening effect decreased sharply when the distance from the edge exceeded 75 μm. After laser treatment, the content of Co element increased from 3.3% to 4.6%, while after combination with acid-base two-step method, the content of Co element decreased from 0.7% to 0.5%. After laser zone deposition of BDD coating, surface defects were significantly reduced and diamond grains were denser in texture. After the deposition of BDD coatings in the laser microtexture regions, the surface defects of the substrate were significantly reduced, and the diamond grains in the texture were denser, and the deposition quality was improved. In particular, the slope of diamond particles at the edge of triangle texture (TT) was the slowest. Different types of textured BDD coatings had different roughness, diamond purity, cutting performance and adhesion strength and coating adhesion was positively correlated with surface hardness. The performance of untextured BDD coated tools was better than that of untextured groove textured (GT) tools, and that of textured BDD coated tools are better than those of the former two, among which the boron-doped triangular textured (BDTTD) coated tools had the best cutting performance. The following conclusions can be drawn from the above phenomena: the acid-base two-step method combined with laser technology creates a good substrate environment for HFCVD diamond growth. The texture can improve the deposition quality of BDD coatings, and the edge and interior of the texture have higher secondary nucleation rate of diamond. The existence of texture can improve the adhesion strength and tool performance of BDD coatings and the coating adhesion at the texture edge is the strongest, which benefits from the hardening of cemented carbide surface and the repair of the inherent defects of BDD coatings by laser bionic micro-texture. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.