Mladen Stupnišek

Novelty in Diffusion Coating Technology

Diffusion forming of a hard carbide layer has been used for many years, mostly in Japan (Toyota Diffusion Process, TDR) and in the USA (Thermoreactive Deposition, TRD) but not so much in Europe. Carbide layers on constructive parts and tools formed by a diffusion process, especially a vanadium carbide layer, have excellent tribological properties and some technical and economical advantages in comparison with carbide layers formed by chemical vapour deposition (CVD) and physical vapour deposition (PVD) processes. Diffusion formed layers are thicker with very strong bond to steel substrate and are produced using significantly cheaper equipment than for deposition coating. The process has one disadvantage: partial decarburization of the steel surface beneath the carbide layer reducing hardness and loading capacity of the surface. This disadvantage is eliminated by a developed and patented duplex process introducing previous carburizing to prevent decarburization and to form a hardened case under layer beneath the carbide layer. The new developed process should contribute to widely application of diffusion carbide coating for automotive industry. Mathematical model and program for optimization of process is presented as well as some examples of application: extruders for medium with very abrasive particles, aluminium die casting moulds, etc.

Improvements in thermo reactive deposition of carbide layers

Abstract This paper presents developments contributing to the improvement of the process of producing hard carbide layers, with special attention to the application on tools and dies. The quantitative impact of the chemical composition of the steel and the process temperature on the kinetics of the carbide layer formation has been determined. In conventional processes of diffusion formation of carbide layers the phenomenon of partial decarburisation of steel occurring beneath the carbide layer during the process of its formation has been dealt with by the introduction of controlled precarburisation. Diffusion formation of carbide layers has been improved by the development of duplex processes that enable the formation of a case hardened layer which is harder than the core. Thus, the substrate for the hard and brittle carbide layer is improved. This development should contribute to the improvement of properties of the surface layers produced by the diffusion formation of carbide layers. In this way this process can be applied to the manufacturing of tools and dies.