多弧离子镀NiCrAlY涂层与搪瓷基复合涂层的抗热震行为对比研究

Comparative Study of Thermal Shock Behavior of the Arc Ion Plating NiCrAlY and the Enamel Based Composite Coatings

以K444镍基高温合金为基体,采用多弧离子镀法制备了NiCrAlY涂层、喷涂-烧结法制备了搪瓷基复合涂层,并对比研究了2种涂层的抗热震性能。热震实验高温段温度为900℃。高温段保温1.5h后经水或空气冷却为一个热震循环。结果表明,NiCrAlY涂层的抗热震性能较差。当冷却介质为水时,水淬热震30cyc后,涂层表面氧化膜开裂明显,且有个别裂纹已穿透氧化膜,扩展至涂层内部;而搪瓷基复合涂层的抗热震性能非常优异。热震后,涂层表面及内部均未发现裂纹,涂层和基体界面结合良好。经分析,其优良的抗热震性能源于:(1)搪瓷釉热膨胀系数与高温合金基体匹配度高;(2)纳米Ni和NiCrAlY金属颗粒的加入进一步增大涂层热膨胀系数的同时,还提高了搪瓷的韧塑性。

From the view of material point, high-temperature protective coatings are divided into the following two categories： ceramic coating and metallic coating. Metallic coating possesses higher toughness and bond strength to the alloy substrate than ceramic coating does. Its protectiveness relies on the formation of a slow-growing and adherent oxide scale at high temperatures. However, with increasing the oxidation time, the oxide scale will experience cracking and spalling as it has grown to the critical thickness. Ceramic coating due to its chemical inertness has been used in many corrosive environments for protection. But the weak interfacial bond and big mismatch of coefficient of thermal expansion with the al- loy substrate limit its application in thermal shock environments. Since glass-ceramics combine the generally superior properties of crystallite ceramics with the easy processing of glasses, it is expected that glass-ceramic coating should show a higher spallation resistance than ceramic one under thermal shock. Cast K444 superalloy is widely used in advanced aircraft engine and gas turbine. Its protection from high- temperature oxidation under thermal shock becomes a critic issue. In this work, NiCrAIY and enamel based composite coatings on the K444 superalloy substrate by arc ion plating and spray-firing methods were prepared, respectively. Thermal shock behavior from 900 ℃ to room temperature of these two coatings was studied comparatively. One cycle of thermal shock contained the holding of samples at 900℃ for 1.5 h and the following cooling down in air or water. Results indicated that thermal shock resistance of the NiCrAIY coating was low. As the NiCrAIY coating was thermal shocked by water, its oxide scale cracked severely after 30 cyc, and certain crack had already transported the scale and penetrated into the interior of the underlying metallic coating; for the enamel based composite coating, however, its thermal shock resistance was high. No cracks were detected at the coating surface or interior after thermal shock test. Besides, the enamel coating still adhered well with the alloy substrate. The high resistance to thermal shock of the enamel based composite coating originated from： （1） the coefficient of thermal expansion of the enamel based composite coating matched well with that of the alloy substrate; （2） the addition of nano-sized Ni and NiCrAIY metallic particles improved the toughness of the enamel coating, in addition to enhancing its coefficient of thermal expansion.