Microstructure and property changes caused by diffusion during CVD coatingof steels

The interdiffusion of carbon and titanium between a substrate and coating d uring chemical vapor deposition (CVD) coating of steels influences the micr ostructures and properties of the coating/substrate compounds. The CVD para meters atmosphere, temperature and pressure as well as the composition of t he steel substrates were investigated systematically to optimize the proper ties of the coating/substrate compounds. The tool and carbon steels AISI H1 3 (DIN X40CrMoV5-1), AISI A2 (DIN X100CrMoV5-1). AISI 1045 (DIN Ck45) and s imilar to AISI 1095 (DIN 100V1) were coated by high-temperature CVD TiN, lo w pressure CVD TiN and moderate-temperature CVD TiCN. Chemical compositions of coatings and substrates were measured by glow discharge optical spectro scopy (GDOS) and electron probe microanalysis (EPMA). Substrate and coating microstructures were examined in taper sections by light microscopy. Furth er, the substrate hardness was investigated in the taper sections. In an ea rlier work, carbon diffusion near the interface was investigated. Low coati ng pressures combined with high temperatures and high carbon activities of the substrates promoted the diffusion process. In this work, the investigat ions were extended to deeper substrate regions and to the titanium diffusio n. From the carbon profiles in coatings and substrates, a carbon balance wa s set up for the diffusion from the substrate to the coating during CVD. (C ) 1999 Elsevier Science S.A. All rights reserved.