激光熔覆Hastelloy C276涂层组织及抗热震性能研究

Microstructure and Thermal Shock Resistance of Laser Cladding Hastelloy C276 Coating

目的 针对微晶玻璃压延辊在服役过程中因表面频繁承受较大的温度梯度而开裂的问题,研究一种抗冷热疲劳性能突出的高性能防护涂层来延长压延辊服役寿命。方法 采用激光熔覆技术,以扫描速度为800 mm/min、送粉量为26 g/min、光斑直径为4 mm、搭接率为50%、激光功率为2 200 W的工艺参数,在2Cr13基体上熔覆Hastelloy C276镍基合金涂层。采用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)研究熔覆涂层的微观组织和热震失效裂纹微观形貌、元素分布以及涂层相组成。利用箱式电阻炉对Hastelloy C276熔覆涂层与2Cr13基体进行热震试验。结果 Hastelloy C276熔覆涂层表面无裂纹、成形良好,涂层与基体之间为冶金结合。涂层由γ-Ni、M_(6)C和M_(23)C_(6)相组成。熔覆涂层从基体结合处至表面依次形成了平面晶、胞状组织、柱状树枝晶以及等轴树枝晶,碳化物相均在树枝晶间析出。Hastelloy C276熔覆涂层抗热震失效次数约为2Cr13基体的3倍,最高抗热震次数可达到202,Hastelloy C276熔覆涂层具有良好的抗热震性能。结论 由于HastelloyC276涂层与2Cr13基体结合紧密且存在热膨胀系数差异,热震时在熔覆结合界面产生了较大热应力,因此裂纹最先在熔覆结合界面处萌生,然后逐渐扩展至涂层表面最终失效。Hastelloy C276涂层的裂纹萌生扩展机制使裂纹在涂层表面出现较晚,有效延长了2Cr13微晶玻璃压延辊抗冷热疲劳寿命。

The surface of the glass-ceramics calender roll is frequently subject to steep temperature gradient,causing cracks.It is expected to obtain a high-performance protective coating with outstanding thermal fatigue resistance to prolong the service life of glass-ceramics calender roll.In this study,Hastelloy C276 nickel base alloy coating was prepared on martensitic stainless steel 2Cr13 substrate by laser cladding technology.The thermal shock resistance of Hastelloy C276 coating was compared with that of 2Cr13,a commonly used material for glass-ceramics calendar roll.The Hastelloy C276 coating was prepared by laser cladding technology with a scanning speed of 800 mm/min,a powder feeding rate of 26 g/min,a spot size of 4 mm,an overlap ratio of 50%and a laser power of 2200 W.The microstructure,elemental distribution and phase compositions of the cladding coating were analyzed by scanning electron microscopy(SEM),energy dispersive X-Ray spectroscopy(EDS)and X-Ray diffraction(XRD).SEM and EDS were also used to study the microstructure and element distribution at the crack due to thermal shock failure.The thermal shock tests of Hastelloy C276 coating and 2Cr13 substrate were carried out by a box-type resistance furnace.The test results showed no crack on the Hastelloy C276 coating,and the good forming indicated that the coating and the substrate maintained metallurgical bonding.The coating was composed ofγ-Ni,M_(6)C and M_(23)C_(6) phases.The planar,cellular,columnar dendrites and equiaxed dendrites were formed in the cladding coating from the base joint to the surface,and the carbide phases were precipitated in the dendrites.The thermal shock resistance of Hastelloy C276 coating was superior to that of 2Cr13 substrate based on the thermal shock test results.The thermal shock failure cycles of Hastelloy C276 coating were about 3 times of that of 2Cr13 substrate,and the maximum thermal shock failure cycles of Hastelloy C276 coating could reach 202.After the cross-sectional morphology of the crack of Hastelloy C276 coating was observed,it could be inferred that,in the process of thermal shock,the crack initiated at the bonding interface of the cladding,then gradually propagated to the coating surface and finally failed.By scanning the elemental distribution near the cracks,the enrichment of oxygen was detected.It was supposed that crack propagation was also affected by oxidation during the thermal shock tests.According to the analysis,because Hastelloy C276 coating was tightly bonded to 2Cr13 substrate and there was a difference in thermal expansion coefficient between the coating and substrate,large thermal stress was generated at the cladding interface during thermal shock.The crack initiated at the cladding interface.At the same time,the cracks gradually propagated to the coating surface and finally failed.The crack initiation and propagation mechanisms of Hastelloy C276 coating make the crack appear late on the coating surface,which effectively prolongs the thermal fatigue life of 2Cr13 glass-ceramics calender roll.This study has significance for the improvement of thermal fatigue resistance of glass-ceramics calender roll to some extent.