Microstructure and property changes caused by diffusion during CVD coating of steels

Abstract

Abstract The interdiffusion of carbon and titanium between a substrate and coating during chemical vapor deposition (CVD) coating of steels influences the microstructures and properties of the coating/substrate compounds. The CVD parameters atmosphere, temperature and pressure as well as the composition of the steel substrates were investigated systematically to optimize the properties of the coating/substrate compounds. The tool and carbon steels AISI H13 (DIN X40CrMoV5-1), AISI A2 (DIN X100CrMoV5-1), AISI 1045 (DIN Ck45) and ∼AISI 1095 (DIN 100V1) were coated by high-temperature CVD TiN, low-pressure CVD TiN and moderate-temperature CVD TiCN. Chemical compositions of coatings and substrates were measured by glow discharge optical spectroscopy (GDOS) and electron probe microanalysis (EPMA). Substrate and coating microstructures were examined in taper sections by light microscopy. Further, the substrate hardness was investigated in the taper sections. In an earlier work, carbon diffusion near the interface was investigated. Low coating pressures combined with high temperatures and high carbon activities of the substrates promoted the diffusion process. In this work, the investigations were extended to deeper substrate regions and to the titanium diffusion. From the carbon profiles in coatings and substrates, a carbon balance was set up for the diffusion from the substrate to the coating during CVD.