DEPOSITION AND STRUCTURAL-PROPERTIES OF 2-COMPONENT METAL COATINGS FOR TRIBOLOGICAL APPLICATIONS

Advanced vacuum deposition processes are gaining increasing importance in material manufacturing. This paper describes the deposition of imm iscible metal-metal systems by magnetron sputtering. Two basic deposit ion modes, codeposition from a multicomponent target and sequential de position from two separate targets, are discussed. We show that it is possible to obtain a film structure of soft metal particles homogeneou sly dispersed in a tough metal matrix. In practical, e.g. tribological , applications, the tough matrix takes high mechanical loads, while th e soft particles act as a solid lubricant. The dependence of the film structure on the process parameters and him composition is discussed w ith respect to the different deposition modes. A thermodynamic model, which describes the roughness evolution and phase distribution of a sy stem consisting of a layer-forming matrix and an island-forming inclus ion component, is presented for the sequential deposition mode. The re sults are compared with quantitative atomic force microscopy (AFM) mea surements of the surface roughness. For the codeposition mode, the pha se distribution in the film can be described by a dynamic model of str uctural evolution based on the far-from-equilibrium process of diffusi on-limited aggregation (DLA). The complex morphological properties of the soft phase are qualitatively well matched with the structures obta ined from the model. In conclusion, we discuss a practical application of metallic two-component films as coatings for plain bearings in hig h performance diesel engines. These bearings are always oil lubricated during the operation of the engine to prevent metal-metal contact. Ne vertheless, they are exposed to severe pressures and pressure gradient s. Therefore the coating has to resist extremely high and time-depende nt mechanical loads. The wear properties of aluminum-tin films, which are currently manufactured by high rate post magnetron sputtering in a n industrial process, are compared with conventional bearing designs a nd are found to be superior to all alternative surface- modified desig ns.