High-temperature oxidation resistance of laser cladding CoCrFeNi and AlCoCrFeNi medium-entropy coatings
CoCrFeNi and AlCoCrFeNi medium-entropy alloy coatings were successfully prepared on the surface of H13 steel by laser cladding technology.Microstructure,composition distribution and phase composition of the coatings were analyzed by means of scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).On this basis,the high-temperature steady-state oxidation and cyclic oxidation performance of the coatings were studied,and the oxidation mechanism was analyzed.The results show that there is a good metallurgical bonding between the laser cladding CoCrFeNi and AlCoCrFeNi medium-entropy alloy coatings and the substrate.The coatings exhibit a single-phase FCC structure,and their microstructure is mainly composed of columnar and equiaxed grains.After high-temperature oxidation at 700,800 and 900 ℃ for 60 h,the oxide layer thickness of the CoCrFeNi and AlCoCrFeNi coatings is much smaller than that of the H13 steel,and the oxidation resistance is significantly better than that of the H13 steel.After 6 times of cyclic oxidation at 600 ℃,the surface of the AlCoCrFeNi coating shows almost no oxidation,while the surface of the CoCrFeNi coating forms an extremely thin oxide layer after 5 cycles.Although the surface oxide layer of the H13 steel is relatively thin during cyclic oxidation at 600 ℃,its structure is relatively loose and easy to peel off,which cannot provide protection for the interior of the alloy.This indicates that the CoCrFeNi and AlCoCrFeNi medium-entropy alloy coatings have excellent high-temperature oxidation resistance.
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