Functionally Graded Coatings of Carbon Reinforced Carbon by Physical and Chemical Vapour Deposition (PVD and CVD)

Abstract

This paper reflects our R&D results in the field of functionally graded coating processes. For industrial applications a special architecture for coatings is necessary: because the surface has to withstand environmental attacks, specific physical and mechanical functions and characteristics are required. In the interface region to the substrate additional stresses and strains occur due to the different materials combined. Consequently, the coatings have to be chemically and mechanically adjusted to the substrates. For this challenging problem, a concept named Materials Adapter has been developed within the frame of different research programs at MPA. For optimisation of the interface region an ion bombardment-activated inter-diffusion process ("ion mixing") was employed by using ion assisted electron beam PVD (IA EB PVD). Several Cr, Ti, Al and Zr coatings have been produced. An automated precursor inlet has been installed for CVD processes to obtain preset composition profiles for graded systems. Especially multilayer stacks of PyC-SixCy-SiC-Si3N4-Al2O3 have been deposited in a single growth process. The structure and composition of the coatings and interfaces were investigated by XRD, AFM, SEM, EDX, EPMA, ESCA and the micro-Raman spectroscopy. The characterisation confirms the gradual transition between Si and Cr, as well as between Cr and Al deposited by IA EB PVD and between C and Si grown by CVD.