Study On The Structure And Properties Of Laser Cladding MCrAlY/YSZ Gradient Thermal Barrier Coating

In order to meet the design requirements of advanced aeroengine with high thrust,high efficiency,low fuel consumption and long life,the high temperature protection performance of thermal barrier coatings is increasingly demanded.Since the development of thermal barrier coatings,the preparation technology has a direct impact on the microstructure,thermodynamic properties and service life of coatings.Therefore,the continuous improvement of preparation methods and processes is also one of the important development directions of thermal barrier coating preparing technology.Due to the complexity of the laser cladding process and the close relationship between material characristics and cladding process,it is of great significance to study the relations among the process,micro-structure and properties of thermal barrier coatings prepared by laser cladding.The main work of this paper is as follows:Firstly,single-path CoCrAlSiY coatings and single-path CoCrAlSiY/YSZ coatings were cladded on TC4 substrates with various laser process parameters.The laser cladding CoCrAlSiY and CoCrAlSiY/YSZ coatings were compared and analyzed in terms of forming condition,surface quality and microstructure.The samples prepared by different processes were evaluated by microhardness test.The results show that the overall quality of CoCrAlSiY coating is the best when the laser power is 1600 W and the scanning speed is 10mm/s.When laser power is 1800 W and the scanning speed is 10mm/s,the overall quality of CoCrAlSiY/YSZ coating is the best.Secondly,the effects of E on the densification,microstructure,microhardness and friction and wear properties of multi-layer CoCrAlSiY/YSZ composite coatings prepared by laser cladding were studied.The results show that when E = 200 kJ,the densification degree is the highest,the columnar crystals with uniform distribution are formed,the microhardness distribution is the most uniform and the mean value is the largest,and the friction coefficient and wear rate are the smallest.The gradient CoCrAlSiY/YSZ composite coatings were prepared using the optimized process parameters and evaluated.The coatings are well formed,and there is no obvious interface between gradient layers.Ceramic and metal layers have good metallurgical bondings.The regularity of change from substrate to top layer is irregular massive structure,dendritic structure,skeleton structure,petal structure and white massive structure.Finally,the oxidation and thermal shock resistance of gradient coatings at high temperature were studied,and the failure mechanism at high temperature was analyzed.The results show that the gradient coating can improve the cracking of the coating caused by thermal stress due to the inconsistency of thermal expansion coefficient.