Academics and industry have sought after combining the exceptional properties of diamonds with the toughness of steel. Since the early 1990s several partial solutions have been found but chemical vapor deposition (CVD) diamond deposition on steel substrate continues to be a persistent problem. The main drawbacks are the high carbon diffusion from gas phase into substrate, the transition metals on the material surface that catalyze sp 2 bond formation, instead of sp 3 bonds, and the high thermal expansion coefficient (TEC) mismatch between diamond and steels. An intermediate layer has been found necessary to increase diamond adhesion. Literature has proposed many efficient intermediate layers as a diffusion barrier for both, carbon and iron, but most intermediate layers shown have not solved TEC mismatch. In this review, we briefly discuss the solutions that exclusively work as diffusion barrier and discuss in a broader way the ones that also solve, or may potentially solve, the TEC mismatch problem. We examine some multilayers, the iron borides, the chromium carbides, and vanadium carbides. We go through the most relevant results of the last two and a half decades, including recent advances in our group. Vanadium carbide looks promising since it has shown excellent diffusion barrier properties, its TEC is intermediary between diamond and steel and, it has been thickened to manage thermal stress relief. We also review a new deposition technique to set up intermediate layers: laser cladding. It is promising because of its versatility in mixing different materials and fusing and/or sintering them on a steel surface. We conclude by remarking on new perspectives.
In this work an interface is studied and proposed for chemical vapour deposition (CVD) diamond films on sintered carbides and steel substrates, the most relevant tooling materials for mechanical applications. It consists of a thermoreactive deposited and diffused vanadium carbide layer. This interface presents good characteristics for diamond films deposition: high adherence to substrates, favourable thermal expansion coefficient, high hardness and high mechanical strength. Good quality and adherent diamond films are obtained and its characteristics are evaluated by SEM, X-ray diffraction, Raman spectroscopy and indentation tests. For sintered carbides substrates, typical Raman shift of 4·1 cm−1 is obtained, equivalent to compressive residual stresses of 1·4 GPa applied from the substrate to CVD diamond films through vanadium carbide interlayer. For steel substrates, Raman shift reached 20·1 cm−1, corresponding to 6·93 GPa compressive stress applied from substrate to diamond films through VC interlayer, evidencing the mechanical strength of the VC diamond film coatings.
Silicon Nitride is largely used as the base material to manufacture cutting tools. Due to its low thermal expansion coefficient it is ideal candidate for CVD diamond deposition. In this work, we functionalized the surface of silicon nitride inserts (Si3N4) with a polymer (PDDA Poly (diallyldimethylamonium chloride - Mw 40000)) to promote seeding with nanodiamond particles. The seeding was performed in water slurry containing 4 nm diamond particles dispersed by PSS Poly (sodium4-styrenesulfonate) polymer. CVD diamond films, with high nucleation density, were deposited in a hot filament reactor. Film morphology was characterized by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Diamond film quality was determined by Raman Spectroscopy. CVD diamond film adherence was evaluated using Rockwell C indentation.
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