超声振动辅助激光熔覆IN718-Hf涂层的抗高温氧化性能

High-temperature Oxidation Resistance of IN718-Hf Coating by Ultrasonic Vibration-assisted Laser Cladding

目的基于航天航空领域对IN718合金的抗高温氧化性能需求,通过活性元素(RE)掺杂与物理场辅助,提升IN718合金的抗高温氧化性能。方法采用超声振动辅助激光熔覆工艺,在IN718合金表面制备IN718-Hf熔覆层,研究涂层的微观结构演变,以及在800℃下长达100 h的氧化行为。利用扫描电子显微镜(SEM)、电子探针显微分析仪(EPMA)研究涂层的显微组织、氧化膜结构和元素分布。通过X射线衍射仪(XRD)分析物相。结果在不同Hf含量(均以质量分数表示)的涂层中,IN718-Hf(0.3%)涂层中的氧化层最薄、最均匀。Hf的高化学活性使得它很容易与其他元素发生反应,增加了成核粒子数量,使涂层中的微观结构细化。超声振动的施加提升了熔池的过冷程度,同时打碎了熔池中粗大的柱状枝晶,从而达到了细化晶粒的目的。晶粒细化有利于形成致密均匀的氧化层,从而增强材料的抗高温氧化性。氧化层具有双层结构,外层为MnCr_(2)O_(4)尖晶石,内层为Cr_(2)O_(3)。Hf的掺杂和超声振动的施加促进了MnCr_(2)O_(4)尖晶石氧化物和Cr_(2)O_(3)的优先生成。超声振动辅助IN718-Hf涂层的氧化增量(0.349 mg/cm^(2))、氧化速率常数(1.21×10^(–3)mg^(2)·cm^(–4)·h^(–1))与IN718涂层相比,分别减少了46%、69%。结论Hf的掺杂和超声振动促进了涂层微观结构的细化,提升了抗高温氧化性能,扩展了IN718合金在航天航空领域的运用。

To improve the high-temperature oxidation resistance,the doping of Reactive Element(RE)and physical field are used to treat the surface of IN718 alloy,since the aerospace field has higher requirements for its high-temperature oxidation resistance.In this experiment,the IN718-Hf coating was fabricated on IN718 alloy by ultrasonic vibration-assisted laser cladding.The microstructure evolution and oxidation behavior of multiple coatings at 800℃for 100 h were investigated.The microstructure,morphologies of oxide film,elemental distribution,and phase composition were studied by scanning electron microscopy(SEM),electron probe microanalyzer(EPMA),and X-ray diffractometer(XRD).The results indicated that the scale thickness of the IN718-0.3wt.%Hf coating was the thinnest and the oxide film was the most uniform among the coatings with different Hf contents(0,0.3wt.%,0.6wt.%,0.9wt.%).With higher Hf content,more HfO2 was generated in the oxide scale,resulting in higher scale thickness and slight scale peeling.The excessive formation of HfO2 particles allowed rapid inward transport of oxygen,leading to an increase in the thickness of the oxide film.The high chemical activity of Hf made it easy to react with other elements and form new compounds in the molten pool,thereby increasing the number of nucleating particles during solidification and refining the microstructure of the coatings.The application of ultrasonic vibration increased the degree of supercooling of the molten pool,and at the same time broke the coarse columnar dendrites in the molten pool to further achieve grain refinement.The grain refinement was conducive to the formation of a more dense and uniform oxide layer,thereby improving the high-temperature oxidation resistance of the IN718 cladding layer.The oxide layer had a double-layer structure.The outer layer was MnCr_(2)O_(4),and the inner layer was Cr_(2)O_(3).The doping of Hf element and the application of ultrasonic vibration promoted the preferential formation of MnCr_(2)O_(4)spinel oxide and Cr_(2)O_(3).During this oxidation process,Hf prevented the outward diffusion of cations,but it did not prevent anions from diffusing inward.As a result,the growth of the oxide film changed from the outward diffusion of Cr3+to the inward diffusion of O2–,which decreased the oxide film growth rate.Ultrasonic vibration further refined the microstructure of the coatings and induced a more uniform distribution of elements.It also increased the grain boundary density of the coating surface.Increased grain boundary density led to faster diffusion of Cr^(3+)in the coatings.Consequently,a stable,continuous,and compact Cr_(2)O_(3)oxide film was formed over a short time.At the same time,the oxide nodules formed on the surface of the oxide film were more uniform and finer.Compared with the IN718 coating,the oxidation weight gain(0.349 mg/cm^(2))and oxidation rate constant(1.21×10^(–3)mg^(2)·cm^(–4)·h^(–1))of the ultrasonic vibration-assisted IN718-Hf coating were reduced by 46%and 69%respectively.The doping of Hf element and the application of ultrasonic vibration promote grain refinement,improve the high-temperature oxidation resistance,and expand the application of the IN718 alloy in the aerospace field.