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The plasma torch is a modified Komatsu Fine Plasma cutting torch, with throat diameter of 1mm. Modifications include the addition of a Laval contour diverging section of exit-to-throat area ratio 4.5, the installation of a tungsten tip on the cathode, and arc operation in non-transferred mode. The nozzle has an internal powder injector of 1 mm diameter inclined at an angle of 30° to the horizontal and located such that its centerline intersects the nozzle contour 1.2 mm upstream of the exit plane.
The powder feeder was designed and built in order to achieve stable average feed rates, variable from 0.06 g/min to 0.8 g/min using 316L stainless steel powder of 5-45 μm size distribution.
All gas flow rates are metered and measured with thermal mass flow controllers. All three independent cooling water loops have flow rates measured with calibrated rotameters, and the temperature rise in each loop is measured with a K-type thermocouple circuit using the inlet temperature as reference, allowing calorimetry to be performed on the three cooled regions (anode/cathode, nozzle diverging section, and substrate). The arc current is measured with a Hall effect current sensor. Arc voltage is measured with a voltmeter protected by a 20X voltage probe and a fast-acting rectifier circuit for shunting high-voltage spikes to ground. Process chamber pressure and powder feeder manifold pressure are measured with capacitance diaphragm gauges of 15 kPa and 150 kPa ranges, respectively. Powder feeder screw rotation rate is measured by tachogenerator output, which is calibrated to average feed rate for each powder prior to running an experiment. The stability of average powder feed rate has been tested by continuous sampling during deposition of powder onto a 50-gram capacity load cell. The analog signals from all the sensors are continuously scanned and stored digitally on a PC during an experiment.
Plasma Spraying Facility
Our vacuum microplasma spray (VMPS) system has the same elements as a conventional VPS system, with the exception of a translation stage for either the spray torch or the substrate. Also, different from many installations, the plasma jet axis is directed downward with respect to gravity.The plasma torch is a modified Komatsu Fine Plasma cutting torch, with throat diameter of 1mm. Modifications include the addition of a Laval contour diverging section of exit-to-throat area ratio 4.5, the installation of a tungsten tip on the cathode, and arc operation in non-transferred mode. The nozzle has an internal powder injector of 1 mm diameter inclined at an angle of 30° to the horizontal and located such that its centerline intersects the nozzle contour 1.2 mm upstream of the exit plane.
The powder feeder was designed and built in order to achieve stable average feed rates, variable from 0.06 g/min to 0.8 g/min using 316L stainless steel powder of 5-45 μm size distribution.
All gas flow rates are metered and measured with thermal mass flow controllers. All three independent cooling water loops have flow rates measured with calibrated rotameters, and the temperature rise in each loop is measured with a K-type thermocouple circuit using the inlet temperature as reference, allowing calorimetry to be performed on the three cooled regions (anode/cathode, nozzle diverging section, and substrate). The arc current is measured with a Hall effect current sensor. Arc voltage is measured with a voltmeter protected by a 20X voltage probe and a fast-acting rectifier circuit for shunting high-voltage spikes to ground. Process chamber pressure and powder feeder manifold pressure are measured with capacitance diaphragm gauges of 15 kPa and 150 kPa ranges, respectively. Powder feeder screw rotation rate is measured by tachogenerator output, which is calibrated to average feed rate for each powder prior to running an experiment. The stability of average powder feed rate has been tested by continuous sampling during deposition of powder onto a 50-gram capacity load cell. The analog signals from all the sensors are continuously scanned and stored digitally on a PC during an experiment.