DUPLEX SURFACE-TREATMENT OF MOLDS FOR PRESSURE CASTING OF ALUMINUM

The subject of this paper is the technology of the production of compo site-nitrided case/TiN coatings. This technology is used for improving the lifetime of tools operating at heavy thermal and mechanical loads and at conditions of intensive abrasive wear. In the case of such too ls, the standard methods of improving the surface properties by therma l treatment, thermo-chemical treatment or by deposition of anti-wear m onolayers [e.g. TiN, Ti(C, N)] do not lead to the desired increase in tool life. This goal can be achieved only by the application of a dupl ex surface treatment which involves beside the deposition of mono and multilayers, a therms-chemical treatment (for example, nitriding), and determining the structure and properties of the tool's surface layer. As a result of a duplex treatment, a multi-layer composite is obtaine d, which in terms of anti-wear properties outdoes both diffusion layer s obtained by thermo-chemical treatment and multilayers deposited by P APVD methods. The chemical composition and internal structure of the c omposite must be selected with regard to its final application. The te chnology of duplex surface treatment was used to improve the durabilit y of moulds for aluminium injection moulding. (C) 1997 Elsevier Scienc e S.A.