热处理对多层复合增韧涂层的微观结构及力学性能的影响

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Multilayer Composite Toughened Coatings

AT40陶瓷涂层与黏结层界面裂纹萌生、扩展是导致涂层失效的主要原因,制备多层陶瓷/金属低应力涂层为陶瓷涂层增韧的方法之一。利用APS(大气等离子喷涂)在Q235上制备AT40-NiAl-AT40-NiAl四层复合多层涂层并对复合多层进行热处理。使用SEM、EPMA、3PB等表征手段研究热处理对四层复合金属-陶瓷涂层的微观结构及涂层断裂韧性的影响。结果表明,热处理过程中陶瓷层-黏结层界面、陶瓷层富Al相富Ti相界面均发生了元素扩散;热处理后陶瓷层硬度增加30%,复合涂层断裂韧性提高。热处理过程中元素扩散形成的氧化物一方面在黏结层与陶瓷层之间形成钉扎效应增强黏结性,另一方面填充涂层中的孔隙、裂纹等缺陷提高涂层的硬度,降低裂纹扩展的面积从而提升涂层的断裂韧性。多层金属陶瓷沉积形成的复合陶瓷涂层及对其使用热处理的方法能有效提升AT40等陶瓷涂层的断裂韧性,对解决铁基零部件表面耐磨陶瓷容易脆断失效和扩展陶瓷涂层的应用范围提供了新的思路。

Coating failure principally leads to crack initiation and propagation at the interface between the AT40 ceramic coating and the bond coat.One of the methods of toughening ceramic coatings is to make a multilayer ceramic and low-metal-stress coating.A four-layer AT40-NiAl-AT40-NiAl composite coating is prepared on Q235 using APS(Atmospheric Plasma Spray)and all the composite multilayer should be engaged in heat treatment.SEM,EPMA,3PB and other characterization methods are then used to study the effects of heat treatment on the microstructure of the four-layer metal-ceramic composite coating and the fracture toughness of the coating.The results show that element diffusion occurrs at the interface between the ceramic layer and the bond coat and at the Al-rich phase-Ti-rich phase interface of the ceramic layer during heat treatment;the hardness of the ceramic layer increases by 30%,and the fracture toughness of the composite coating improves after the heat treatment.On the one hand,the oxide formed by element diffusion during the heat treatment causes a pinning effect between the bond coat and the ceramic layer to improve the cohesion;and on the other hand,filled pores,cracks and others in the coating to improve the hardness of the coating and reduce the area of crack propagation to improve the fracture toughness of the coating.The composite ceramic coating formed by the deposition of multi-metal ceramics,together with the use of heat treatment thereon,can effectively improve the fracture toughness of ceramic coatings such as AT40.This creates a new idea for avoiding the possible brittle fracture failure of surface abrasion-resistant ceramics of iron-based components and expanding the range of application for ceramic coatings.