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1577 |
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Tuesday, June 03, 2008, Room 08 10:10 AM Fe-based Materials 1 Due to the worldwide rise of material costs Fe-based materials are becoming more and more a suitable alternative to established hard phase coatings |
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Arc sprayed coatings obtained from iron based cored wires under high temperature abrasive wear conditions |
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Hanna Pokhmurska* / Institute of Composite Materials, Chemnitz University of Technology , Germany Mykhajlo Student/ G.V. Karpenko Physico-Mechanical Institute of National Academy of Sciences of Ukraine, Ukraine Yaryna Sirak/ G.V. Karpenko Physico-Mechanical Institute of National Academy of Sciences of Ukraine, Ukraine Bernhard Wielage/ Institute of Composite Materials, Chemnitz University of Technology, Germany, Germany Thomas Grund/ Institute of Composite Materials, Chemnitz University of Technology, Germany, Germany |
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Two cored wires in steel cover with Fe-Cr-B-Al and Fe-Cr-N-Al filling are proposed as an alternative choice for self fluxing and cermet coatings that are considered nowadays for protection of screen tubes of boilers of power stations that are operated under the temperatures 500-600 °Ñ. Oxidation behavior of arc sprayed coatings under the temperatures up to 800°Ñ is estimated by gravimetric measurements. Abrasive wear resistance at elevated temperatures after 1 hour is investigated by means of laboratory unit that alloys a rotation of coated specimens in heated quartz sand. The transverse velocity of samples of 5.7 m/s and temperature of 550 °Ñ correspond to operating conditions of coatings. It is shown that due to the high crystallisation rates during arc spraying a large amount of supersaturated solid solution and even amorphous phase is observed in as sprayed coatings. During annealing at 550 °Ñ the precipitation of phases, which cause disperse strengthening effect, occurs. In the case of coatings bases on the Fe-Cr-B-Al system these phases are mainly iron borides and intermetallic phase Fe3Al. Micro hardness depends on boron content and increases from 4000 MPa for a coating sprayed with cored wire with 2 mass.% B in filling mixture to 7000 MPa for 3.6 mass.% B. After 1 hour of exposure at 550 °Ñ a 10% increase of microhardness is noted. For coating based on Fe-Cr-N-Al system approximately 2 times increase of microharness after 1 hour exposure at 550 °Ñ occurs (2500 MPa and 4500 MPa respectively) due to additional formation of CrN and AlN phases. It is shown that abrasion wear lost of carbon steel increases 1.5 times when test temperature increases from 20 °Ñ to 550 °Ñ. For all investigated coatings the 20-25% decrease of wear lost is observed at higher temperature. Arc sprayed coatings of both investigated systems improve significally the abrasive wear resistance of carbon steel. At room temperature the improvement by factor 1.35-2.2 times and at the temperature 550 °Ñ by factor 2.75-4.6 is observed depending on chemical composition of coatings. |