Abstract
Laser surface re-melting (LSR) is a well-known method to improve the properties of atmospheric plasma-spraying thermal barrier coatings (APS TBCs) by eliminating the voids, incompletely melted particles and layered-structure. Laser energy density should be carefully selected to reduce the exposed thermal damage of the underlying single crystal (SX) matrix. Therefore, the purpose of this paper was to identify the effect of introducing induction heating to laser modifying of APS TBCs coated on Ni-based SX superalloy. The results indicated that the preheating of the substrate can lower the laser energy threshold that is required for continuously re-melting the coating. It proved that, in LSR processing of a APS TBCs/ SX matrix multilayer system, the combined method of adopting the low laser energy and preheating at elevated temperature is an effective means of minimizing the cracking susceptibility of top ceramic coating, resulting from decreasing the mismatch strain between the re-melted layer and residual APS TBCs, which can significantly improve the segmented crack condition in terms of crack dimension and crack density. Moreover, this combined method can remarkably lower heat input into an SX matrix and correspondingly the interface stored energy induced by pulsed laser thermal shock, which can effectively lower the tendency for surface recrystallization after the subsequent heat treatment.
Highlights
Thermal barrier coatings (TBCs) are commonly applied to the surface of turbine blades to protect them from high temperature exposure and eventual damage
TBCs systems consist of a thermally-insulating ceramic top coating, a thin thermally-grown oxide layer, and an aluminium-rich metallic bond coating [1,2], which are used as gas turbine components to prevent the underlying materials from exposure to extreme environments
It was found that a TC with a thickness of about 250 ± 10 μm and a BC with superalloy a thickness of about 100 ± 10 μm are deposited on the SX superalloy substrate
Summary
Thermal barrier coatings (TBCs) are commonly applied to the surface of turbine blades to protect them from high temperature exposure and eventual damage. TBCs systems consist of a thermally-insulating ceramic top coating, a thin thermally-grown oxide layer, and an aluminium-rich metallic bond coating [1,2], which are used as gas turbine components to prevent the underlying materials from exposure to extreme environments. The typical TBCs material comprise 7–8 wt %. Plasma spraying has become one of the most common manufacturing methods to fabricate TBCs [7]. The TBCs will degrade in long-term serve at extremely environment, such as at high heat flux, thermal cycling and hot gases environment contained sulfur, Materials 2019, 12, 3088; doi:10.3390/ma12193088 www.mdpi.com/journal/materials
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