CVD diamond coating can give full play to the excellent properties of diamond to protect the substrate material, has a high surface hardness, can enhance the wear resistance of the substrate material, improve the lubrication of the substrate surface, and extend the service life of the material. However, the deposition of CVD diamond coating on various substrates generally has the problem of poor film-based adhesion, which seriously affects the use effect of CVD diamond coating, so the pretreatment of substrate materials is adopted to enhance the film-based adhesion. The pretreatment methods used for different substrate materials also vary. Let me give you a brief introduction.
1. Pretreatment of cemented carbide substrates
1) Cobalt removal treatment on the surface
HCI, HNO3, H2SO4 and other acids were selected to etch the cobalt elements in the outer surface of the substrate. Hydrogen plasma or oxygen-containing hydrogen plasma is used to etch cobalt elements; Chemical reagents, passivation and other methods are used to make the cobalt element in the outer surface of the substrate lose its activity.
2) Stack the transition layer
Pre-stacked between the CVD diamond coating and the substrate, the intermediate transition layer satisfies the criteria of modest thermal expansion coefficient, stable chemical characteristics, excellent adhesion with cemented carbide and diamond, and may react with cobalt to generate stable compounds. The existence of the intermediate transition layer allows the internal stress generated by lattice mismatch and thermal expansion coefficient difference between the diamond film and the cemented carbide substrate to be eliminated, so preventing the excessive penetration of carbon into the substrate and the diffusion of cobalt elements from the depth of the substrate to the surface, so improving the nucleation density and adhesion.
3) Implantation treatment on the surface
The surface of the cemented carbide substrate is sonicated with a suspension containing diamond powder (such as acetone) or the nano-scale diamond powder is evenly distributed with the surface of the substrate through acetone, and then heated with a laser to embed the diamond powder into the surface adhesive phase, which can improve the nucleation density.
2. Pretreatment of copper substrate appearance
The nickel transition layer was pre-stacked on the copper substrate by the chemical vapor phase stacking method, and the copper-nickel cocrystals formed between the nickel and the copper substrate under high temperature annealing conditions enhanced the film-based bonding. Studies have also shown that the use of a titanium transition layer on copper can also effectively improve the adhesion of the film base.
3. Pretreatment of the appearance of steel or iron substrate
Tungsten plating on the surface of steel, silicon carbide on high-speed steel, nickel plating on stainless steel, and copper/rhenium coating on iron substrate can eliminate the graphitization effect of iron and obtain CVD diamond coating with good film-based adhesion.
4. Silicon substrate surface pretreatment
Because silicon has the same lattice structure as diamond, silicon is of great significance as a heteroepitaxial matrix material. However, due to the large surface energy of diamond and the large lattice mismatch between substrates, the nucleation rate of diamond on a smooth silicon matrix is very low. The deposition of diamond epitaxial film on the silicon substrate can be realized by mechanical grinding of diamond powder, ultrasonic cleaning, pretreatment of the substrate and silicon carbide transition layer on the silicon substrate, and strict control of the test conditions.
The aim is to enhance the bonding interaction between the substrate material and the CVD diamond coating as a quick explanation of the pretreatment technique of CVD diamond coating substrate reveals that the pretreatment of various substrates is very varied. Please get in touch with us if you like more information.