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5179 |
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High velocity atmospheric plasma sprayer |
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Yuri Chivel* / MerPhotonics, France |
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The electromagnetic plasmadynamic systems (EMAPS) is a simple, efficient, compact, and mechanically robust device that utilizes the Lorentz J×B force to accelerate plasma to high velocity 3-5Å103m/s. These systems have advantages - large action spots and combined thermal and shock action. However, these systems operate stable only under vacuum or under low (1-100 Torr) pressure. A two-stage atmospheric EMAPS (AEMAPS) with the first stage in the form of a three DC plasma torch with power 7 kW and plasma flow temperature ~ 8000 at atmospheric pressure, and with the second stage in a form of a coaxial plasma accelerator has been devised. The plasma flows with duration 200-300 µs and plasma temperature up to 1,5 103K were obtained. Several AEMAPS are developed with energy of pulsed flow 6 - 24 kJ and frequencies up to 1- 4 Hz. In the AEMAPS, being considered , the transition regime from vacuum to atmospheric pressure regime of plasma current sheath acceleration is realized. At high pressure the movement of plasma sheath can be considered in the framework of the subsonic radiation wave when gasdynamic pressure in plasma sheath in together with the radiative flux and heat conduction afford movement of plasma sheath along with shock wave with the velocity several km/s. The results of the use of this plasma source for the acceleration of powder particles (10-30 ¼m) up to 2 km/s as well as for powder coating modification are presented . Powder particles are injected into gas, compressed by leading shock wave up to 20-40 bar, thereby resulting high drug coefficient . Pulse- periodic plasma flow action on plasma sprayed coating NiCr Fe +50% Cr3C2 results in decreased porosity, increased microhardeness , amorphous phase formation. Amorphizm of structure contributes to an increase of wear resistance. |