Studies of steered arc motion and macroparticle production in PVD processing.
During the past decade the production industry has constantly strived to improve performance and cut costs, this has been aided by the development of high performance tools. The advancement of these tools has been accomplished by the application of hard wearing, low friction, coatings. A key process in the production of such coatings is Physical Vapour Deposition (PVD). Interest in such thin films has led to much research effort, both academic and industrial, being devoted to the area. In order that these advancements in technology continue, research into the fundamental aspects of PVD is required. This thesis describes research and experimental studies which have been performed to study the effect of "steering" an electric arc on various aspects of its behaviour. "Steering" of the arc is achieved by applying external magnetic fields which allow the guidance of the path of the arc. Work by earlier authors has aimed to control the arc more fully. The research presented here is based of a novel electromagnetic three coil steering array of cylindrical geometry. With such coils it is possible to vary the field profiles to a greater degree than has been previously achieved, permitting a greater range of steering arrangements/fields to be applied. The research presented is divided into two distinct areas: Firstly a number of experiments were performed to assess the effectiveness of the new steering coils on the motion of the arc. A personal computer was used here along with new arc motion monitoring electronics. This enabled the simultaneous measurement of the orbital transit times and also the degree of travel perpendicular to the steered direction of motion of the arc, as it traversed the surface of the cathode. Such information was then used to produce values for standard deviation of the arc from its steered path, velocity of the arc and a diffusion constant related to the motion of the arc. Such values then allowed evaluation of the stochastic model of arc motion proposed by Care'. Secondly the effect of changes in magnetic field on the production, ejection angle and size of macroparticles(small molten droplets of the cathode material) was studied. This was accomplished by the design, production and usage of new sample holding equipment. This equipment allowed the coating of highly polished samples at a number of angles in relation to the cathode, with all samples being held equidistant from the arc track. Once such samples coatings had been produced they were then analysed using a Scanning Electron Microscope(SEM) to give macroparticle density figures.
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Sheffield Hallam University (United Kingdom).