Microstructure and properties of multilayer coatings with covalent bonded hard materials

Abstract

Single layer thin films of, preferably, covalent hard coatings SiC, Si3N4 have been deposited by non-reactive r.f. and reactive d.c. magnetron sputtering. By sequential deposition they are combined with metallic hard coatings (TiC, TiN) to multilayer systems with an individual layer thickness of 1–500 nm of alternating covalent and metallic hard material layers on cemented carbide or quarz substrates. The reactive deposition was carried out at 400°C in an atmosphere of N2 or CH4 containing Ar by elementary targets (Si, Ti). The non-reactive deposited films were grown by the use of stoichiometric targets (SiC, Si3N4, TiN, TiC) between room temperature and 550°C.The constitution of the single layer and multilayer thin films was studied by XRD, EMPA and HRTEM in dependence on the deposition parameters (substrate temperature, reactive gas flow) and related to the mechanical properties (hardness, adhesion). SiC films deposited by non-reactive sputtering in a stochiometric composition at temperatures between 200 and 550°C show an amorphous structure in XRD-studies. The microhardness was measured to 2600HV0.05 and the critical loads of failure in the scratch test below 30 N for hardmetal/SiC composites. The composition of SiCx thin films deposited by reactive magnetron sputtering has been varied up to x≤1.5. The deposition rate of 0.17 nm/s is weakly dependent on the CH4 gas flow. The films show a hardness up to 3500HV0.05 and critical loads of failure in the scratch test of 70 N. Using XRD studies in Bragg–Brentano geometry, the (102) line of hexagonal SiC has been found at a substrate temperature of 400°C.