PROPERTIES OF MAGNETRON-DEPOSITED POLYCRYSTALLINE TIN LAYERS

Polycrystalline TiNx layers were magnetron sputtered on substrates of high speed steel, sintered carbide and low carbon steel in an ArN2 atmosphere with various N2 partial pressures and bias voltages, the deposition rate being from 0.5 mm min-1 (metallic mode) to 0.1 mm min-1 (reactive mode). The stoichiometry of the layers was evaluated on the basis of thermogravimetric analysis of separated coatings, Auger electron spectroscopy investigation and X-ray powder patterns. The relationship between the X-ray powder diffractograms of coatings on a substrate and separated coatings allowed the role of the thermally based stress in the coatings to be estimated. Maximum values of the compressive stresses were found at biases of -200 to -250 V; for UB > -60 V tensile stresses were observed. The colour coordinates exhibited a strong dependence on N2 flow rate with an apparent threshold at 35 standard cm3 min-1, which corresponds to the stoichiometric compound. An increase in the bias voltage leads to an increasing yellow and red tint of the coating. Drilling tests revealed the highest durability for slightly superstoichiometric coatings. The optimum bias was found to be -100 V, because of the very low or zero internal stress in the TiNx layer. © 1990.