Weakly ionized plasmas produced by gas discharge are widely used in material processing. Production and control of such plasmas are current interests. In this paper, methods of producing plasma by gas discharge are classified into three groups-electron beam, do diode and ratio frequency (including microwave) -in accordance with the main characteristics of the discharge based on plasma physics. Some comments on various methods of producing plasma and of controlling plasma parameters are also discussed.
Hydrogenated amorphous Si(a-Si:H) film has excellent photoconductivity, and the electrical properties of the film can be controlled over a wide range by doping with substitutional impurities. Intense interest has been shown towards the application of a-Si:H, for example to solar cells, photoreceptors, thin film transistors, image sensors. Amorphous-Si:H films can be prepared by plasma CVD (glow discharge), reactive sputtering, photo CVD and other methods. In this report, characterisitics of plasma CVD a-Si:H which has been most widely studied are reviewed.
The plasma spray process can be used to produce coatings on metals, ceramics, etc., and as a result of recent technical innovations, new plasma systems-the high-power plasma system and low-pressure plasma-spray coating (LPC) -have been introduced to the market. LPC makes it possible to spray in inert atmospheres, there by utilizing higher-velocity plasma jets and enlarging the high-temperature zone. Thus coatings are virtually free of oxides, pores and trapped dust, and high-density coatings can be produced, so that such high-quality coatings can be applied as hot corrosion protection or a thermal barrier on gas turbine parts. It is also possible to make a free-standing object by removing the substrate after spraying -a process known as spray casting -in which a material having new properties is produced through formation of a super saturated solid solution and micronization of particles of precipitate and crystals.
Conditions for CVD of an SiO2 single coating and an SiO2/Si double coating to the inner walls of alloy tubes were examined in order to obtain a material that would resist corrosion by concentrated H2SO4 at 1173K. Uniform SiO2 films were coated on Incolloy 800 from Si(O-Et)4-N2-O2-Ar at 1053-1073K under 9.2KPa. Si undercoating films obtained from SiH4-Ar at 903K under 6.6KPa followed by annealing at 1273K markedly improved the adhesion of the film to substrate. The SiO2-Si coated Incolloy 800 tubes exhibited high resistance to corrosion by concentrated H2SO4 at 1173 K for 10h. EPMA line-analysis showed that the Si undercoating films turned to Si-Ni-Cr-Fe alloy during annealing and the alloy then changed to metal and SiO2 film during CVD of SiO2.
Studies were made on ion nitriding of aluminum at 400-650°C in 3.8 Torr nitrogen atomosphere by dc glow discharge. An aluminum nitride layer was formed on aluminum surface at temperatures as low as 450°C as a result of argon sputtering prior to the nitriding. The argon sputtering removed aluminum oxide layers from the initial surface and resulted in production of conical protrusions a few micrometers in height on the surface. Sputtering with nitrogen or hydrogen did not cause surface changes that occurred in argon sputtering and no aluminum nitride layers were formed. Microvickers hardness testing showed layer hardness to be about Hv (0.01) 1000.
The drawability of zinc vapor deposited and galvannealed steel sheet, and the powdering behavior of the deposited layer during drawing were investigated. Heat treatment to form an alloy layer may be conducted either at higher temperatures (450-550°C) for short periods or at lower temperatures (280-340°C) for longer periods. The iron content of the deposited layer varied with heat treatment conditions from 9 to 15wt. %. When the ζ phase remains in the surface layer of the deposit, the degree of powdering decreases and drawability declines, but when the phase disappears, the layer peels easily and drawability improves. This may result from a decrease in the friction coefficient during drawing due to peeled powders. The ζ phase tends to remain in the deposited layer, when treatment is at lower temperatures, and little powdering occurs in these cases even though the iron content of the deposited layer is much higher than in the other cases.
The hydrogen embrittlement of 145kgf/mm2-class high strength steel was evaluated, with the concomitant measurement of hydrogen absorbed during pretreatment and zinc plating of the steel using zincate bath with or without suspended silica particles. It was found that almost all of the absorbed hydrogen was located in the plated zinc layer and at the zinc/steel boundary layer of a thickness of less than 100μm. During a series of tensile tests conducted using a notched tensile test piece at strain rates of from 4.2×10-5 to 4.2×10-3sec-1, a clear relationship was established between hydrogen content and tensile strength. Thus it was concluded that the tensile test can be used as a quick method of evaluating hydrogen embrittlement. When 0.018μm silica particles were codeposited with zinc in an amount of only 0.2wt%, the notch-tensile strength as well as elongation were much greater than with plain zinc coated steel. This effect may be ascribed to the dispersed particles lowering the diffusion barrier height for hydrogen diffusion.
Structural changes of 1μmα-Al2O3 particles in Watt's Ni matrix during annealing at 1000°C were examined by X-ray diffraction to account for the increase in tensile strength that occurs after an induction period of 10 hours. On annealing at 1000°C, an NiAl2O4 phase layer was found to form as a result of the reaction between the Al2O3 particles and the NiO layer which adheres on the particle, and the particles changed into a composite, NiO /NiAl2O4/Al2O3. The reaction-induced particle growth, after the induction period of 10 hours, was found to fill up the space between the particles and the matrix, which arose from heating the composite. The strengthening of the composite after the induction period of 10 hours was found to be described by the Orowan mechanism. Evidence of a compressive stress region around the particles is presented.