Comparison of vacuum and atmospheric plasma sprayed ZrO_27Y_2O_3 thermal barrier coatings

摘要

Yttria partially stabilised zirconia (YPZ) thermal sprayed coatings have a very good heat insulation properties but they have still insufficient life time. A common failure mechanism of TBC's on thermal cycling is delamination of the ceramic coating due to high local thermal stresses [1,2,3]. Thermal stresses can be reduced by means of perpendicular cracks (segmentation of ceramic coatings. Segmented coatings can better tolerate mismatch in elongation of substrate and TBC's. An example for segmentation is the columnar structure. Such structure exhibit coatings produced by electron beam-physical vapor deposition (EB-PVD) procedure [4, 5]. But the EB-PVD equipment and process are very expensive and so are the coatings. Therefore, cheaper plasma sprayed TBC's are still interesting. Cracks in plasma sprayed ceramic coatings are not only in perpendicular direction but often parallel to the substrate surface. The parallel cracks are dangerous, it can result in coating detachment. To avoid parallel cracks it is necessary to improve bonding between splats and especially between the layers. Such coatings with a better cohesion/adhesion properties is possible to achieve among others by vacuum plasma spraying (VPS). According to theoretical considerations, using VPS and APS procedure is possible to deposit TBC's with a columnar structure [6, 7].