Characterization of Plasma Sprayed Layered Coatings

• Main Authors: Louh, Shi Ping, 駱世平
• Other Authors: Lin, Chung Kwei
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/22575395462337526340

碩士 === 逢甲大學 === 材料科學學系 === 89 === Plasma sprayed thermal barrier coatings have received much attention notably in the advanced gas turbine and diesel engine applications. However, the significant differences in properties between ceramics and metals, as well as the severe environments that these materials have to operate, present challenging scientific problems. One problem is the thermal expansion mismatch between bond coat and ceramic layer which leads to delamination and spalling of coating. Functionally graded coating presents one solution to the problem by lowering peak stresses and eliminating stress singularities at certain crack sensitive locations. In this study, we prepared four kinds of air plasma sprayed coatings with various compositions and layers, including pure bond coat, ceramic, duplex thermal barrier coating and functionally graded coatings. SEM, XRD, hardness test, tensile adhesion test and four-point bending test with in-situ acoustic emission inspection characterized these coatings. Thee samples after bending tests were also examined by liquid penetration test, thus the crack patterns can be revealed better. The results show that fracture modes of plasma sprayed coatings related to the spraying parameters. Mutil-layered coatings exhibit better mechanical properties and less visible surface cracks than single layer coatings. The AE results show that higher AE energy events and AE event rates recorded during four-point bending test controlled macro-crack distribution and crack modes of plasma sprayed coatings, which may result in final delamination and spalling of coatings.