Study On Structure And Properties Of FeCoCr Coatings Produced By Supersonic Electric Arc Spraying

High temperature corrosion and erosion of the boiler pipes has been becoming one of major issues which puzzled security and stability of power plant for generations. Especially in recent years, with development of industrial and the increasing of power consumption, the larger capacity generators emerged. At the same time, the low quality coal was used to reduce the cost of power generation, which result the corrosion speed of the pipeline greatly increased. In order to improve the power plant boiler pipe the capability of corrosion-resistant, anti-erosion at high temperature. Preparing FeCoCr coatings on the surface of20steel used the supersonic electric arc thermal spraying technology. The high temperature oxidation, vulcanization and wearing of coatings were tested. Metallographic microscope, X ray diffraction, scanning electron microscope and micro hardness tester etc were used to test and analysis. Draw the following conclusions:(1)The supersonic electric arc spraying FeCoCr coatings were obvious layer structure, the thickness was about230μ m and the organization was dense. The pore rate of coatings was about5%. The coating is mainly composed of metal compounds of CoFe,(Cr, Fe) and a little of SiO2.(2) The bond strength of FeCoCr coatings and the substrate is about19MPa. Heated and air-cooled at700℃for600times, there were no significant spalling and cracks in the coatings, indicating that the coatings’ roperty of thermal-shock resistance was well and coatings matched with the substrate material well.(3) Samples oxidized at700℃for100hours, substrate weight gained of20steel was about230μg/mm2and FeCoCr coatings was about60μg/mm2. The weight gained of the20steel as more than3times as the FeCoCr coatings specimen. The high temperature oxidation resistance of20steel was improved obviously by FeCoCr coatings. It benefits from the dense Cr2O3and CoO oxidized film on the surface of coatings. So the way of oxidation gradually transformed into the mass transfer reactions from the initial interface reaction and corrion was decelerated. The substrate of20steel has been interface reaction, so corrosion faster.(4) Samples vulcanized at700℃for100hours,700℃heat curing100hours, substrate weight gained of20steel was about1400μg/mm2and FeCoCr coatings was about400μg/mm2. The weight gained of the20steel as more than3times as the FeCoCr coatings specimen. The high temperature vulcanization resistance of20steel was improved obviously by FeCoCr coatings. It benefits from the dense CoCr2O4, CoFe2O4and CrO3oxide film on the surface of coatings. They protected the internal metal.(5)The coating micro-hardness was about615N/mm2. The friction coefficient of FeCoCr coatings was about0.33heated at700℃for100hours. The friction coefficient without heat treatment was about0.4. The friction coefficients of the substrate of20steel always were approximately0.5even heated for100hours. Heat treatment of coatings changed wear morphology from the "tear" and "furrows" into minor injury, but it didn’t change the wear morphology of20steel.