MICROSTRUCTURE AND ADHESION MECHANISMS OF TIN COATINGS ON METALLIZED ACRYLONITRILE-BUTADIENE-STYRENE

Metallized plastics are used in various applications, ranging from the packaging of microelectronic devices to the coatings used in automotive, aircraft and space industries. Coating metallized plastics with hard metal compounds results in materials which combine the properties of high wear resistance and low density. Titanium nitride films (0.7 mu m and 5 mu m thickness) were deposited by plasma-assisted magnetron sputtering on metallized acrylonitrile-butadiene-styrene (ABS). The microstructure, interfacial morphology, composition, preferred orientation and internal strains were studied. The analytical techniques applied were transmission and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, Auger electron spectroscopy and X-ray diffraction. The microstructure of the TiN films was found to be heterogeneous. Near the interface with the metallic layer, oriented columnar grains developed whereas, near the free surface, randomly oriented grains were formed. The preferred orientation in the films was found to be {111} and {422} for the thicker(5 mu m) film. The strain in the layer was found to be compressive in nature and in the range of 5 x 10(-3) for the thinner film and 2 x 10(-3) for the thicker film. Direct deposition of TiN on the ABS substrate failed because of adhesion problems, demonstrating that an intermediate metallic layer is crucial to assure an adherent coating. The correlations between the microstructure, the interfacial morphology, the strain and the preferred orientation developed in the films are discussed.