Abstract
To effectively improve the properties of a mullite coating and its interfacial bonding with the substrate, a Ni–P layer is deposited on the surface of mullite powders by electroless plating. The original mullite powders and coated mullite powders are then deposited onto stainless-steel substrates by plasma spraying. The growth mechanism of the Ni–P layer during the plating, the microstructures of the coated powders and mullite coating and the properties of the mullite coatings are characterized and analyzed. The results indicate that the Ni–P layer on the surface of the mullite powder has cell structures with a dense uniform distribution and grows in layers on the surface of the mullite powder. The crystallization behavior of Ni-P amorphous layer is induced by heat treatment. Compared to the original mullite coating, the coating prepared by the coated mullite powders has better manufacturability, stronger adhesion to the substrate, lower porosity (7.40%, 65% of that of the original coating), higher hardness (500.1 HV, 1.2 times that of the original coating), and better thermal cycle resistance (two times that of the original coating). The method of preparation of high-temperature thermal barrier coatings with coated mullite powders has a high application value.
Highlights
High-temperature components used in modern aerospace applications, aircraft manufacturing, and internal combustion engines usually bear high thermomechanical loads
Film acted as an activation center, where a new island-shaped Ni nucleus was formed at the position of a Pd site
A good Ni–P layer was formed on the surface of the mullite powder by orthogonal test
Summary
High-temperature components used in modern aerospace applications, aircraft manufacturing, and internal combustion engines usually bear high thermomechanical loads. To improve the properties and service lives of high-temperature components, thermal barrier coatings (TBCs) are often fabricated on the surface of the metallic substrate [1,2,3,4]. Plasma spraying has a high commercial application value owing to its high deposition rate, low economic cost, and high coating speed. Among the various thermal barrier materials, mullite is often used as a material for TBCs of diesel engines owing to its low thermal conductivity, high-temperature resistance, creep resistance, and chemical stability [9,10]. The thermal stress accumulation between the mullite coating and metallic substrate at high temperatures (around 1000 ◦ C) can peel off the coating. Some researchers used the method of designing gradient coating and introducing a secondary phase to solve the above problems [12,13,14,15]
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