激光熔覆CoCrFeNi和AlCoCrFeNi中熵合金涂层的高温抗氧化性能

High-temperature oxidation resistance of laser cladding CoCrFeNi and AlCoCrFeNi medium-entropy coatings

采用激光熔覆技术在H13钢表面成功制备了CoCrFeNi和AlCoCrFeNi中熵合金涂层。利用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射(XRD)对涂层的微观组织、成分分布和相组成进行分析;在此基础上,重点研究涂层的高温稳态氧化和循环氧化性能,分析涂层的氧化机理。结果表明:激光熔覆CoCrFeNi和AlCoCrFeNi中熵合金涂层与基体之间呈良好的冶金结合,涂层呈现单相FCC结构,其微观组织以柱状晶和等轴晶为主。在700、800和900℃高温氧化60 h后,CoCrFeNi和AlCoCrFeNi涂层的氧化层厚度远小于H13钢的氧化层厚度,抗氧化性能显著优于H13钢。在600℃经历6次循环氧化后,AlCoCrFeNi涂层表面几乎无氧化,CoCrFeNi涂层经历了5次循环后表面形成了极薄的氧化层;600℃循环氧化时虽然H13钢表面氧化层较薄,但结构比较疏松易剥落,对合金内部无法起到保护作用。表明CoCrFeNi和AlCoCrFeNi中熵合金涂层具有优异的高温抗氧化性能。

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.