THE COATING OF INTERNAL SURFACES BY PVD TECHNIQUES

The development of a PVD technique for the coating of steel tubes is described. Experiments were conducted using small samples both planar and rifled, mounted in trapezoidal slots within a 120 mm bore, stainless steel tube. Various plasma etching techniques, using d.c., r.f. and reactive etching with hydrogen chloride containing gases, were investigated in order to remove damaged surface layers and machining marks from the samples. D.c. argon sputtering was shown to be the most satisfactory method. A triode sputter ion plating system was developed in which an axial d.c. post magnetron was used to coat both small samples and gun steel sections with chromium, niobium and a chromium niobium alloy. Variations in coating thickness and structure on rifled substrates were investigated. Further development is necessary to increase deposition rates and to obviate certain effects produced by the magnetic field of the post magnetron.