ARC DEPOSITION OF TI-C AND TI-C-N USING ACETYLENE AS A REACTIVE GAS

Thin hard coatings on cutting tools and metal-forming dies now contribute substantially to the reduction of tool wear. They permit cost-effective machining processes and open the way to new tool applications. Titanium carbonitride physical vapour deposition (PVD) coatings have demonstrated their high performance potential in interrupted cut machining. Hitherto, however, production applications have been limited, due to technical difficulties. On the basis of detailed research into the stability of the PVD arc evaporation process, the paper demonstrates that Ti-C and Ti-C-N coatings can be deposited successfully and reproducibly on cemented carbides, using acetylene as the carbon-containing gas. The structures and properties of the coatings are described as a function of dominant process parameters. It can be shown that substrate temperatures of approximately 500-degrees-C are required for titanium to react with carbon. Arc-PVD coatings produced with acetylene consequently attain high hardness values. Due to high internal compressive stress, however, pure TiC coatings tend to spall. Conversely, very little internal stress occurs in Ti-C-N coatings, resulting in good coating-substrate adhesion.