Abstract
The axial injection of the suspension in the atmospheric plasma spraying process (here called axial suspension plasma spraying) is an attractive and advanced thermal spraying technology especially for the deposition of thermal barrier coatings (TBCs). It enables the growth of columnar-like structures and, hence, combines advantages of electron beam-physical vapor deposition (EB-PVD) technology with the considerably cheaper atmospheric plasma spraying (APS). In the first part of this study, the effects of spraying conditions on the microstructure of yttria partially-stabilized zirconia (YSZ) top coats and the deposition efficiency were investigated. YSZ coatings deposited on as-sprayed bond coats with 5 wt % solid content suspension appeared to have nicely-developed columnar structures. Based on the preliminary results, the nicely developed columnar coatings with variations of the stand-off distances and yttria content were subjected to thermal cycling tests in a gas burner rig. In these tests, all columnar structured TBCs showed relatively short lifetimes compared with porous APS coatings. Indentation measurements for Young’s modulus and fracture toughness on the columns of the SPS coatings indicated a correlation between mechanical properties and lifetime for the SPS samples. A simplified model is presented which correlates mechanical properties and lifetime of SPS coatings.
Highlights
Thermal barrier coatings (TBCs) are widely used in aircraft and industrial gas-turbine engines to improve the durability and efficiency of engines [1,2]
It has been reported that the vertical cracks in the atmospheric plasma spraying (APS) TBCs can improve the strain tolerance of TBCs during thermal cycling [34]
Thermal barrier coatings with different microstructures were deposited with axial suspension plasma spraying
Summary
Thermal barrier coatings (TBCs) are widely used in aircraft and industrial gas-turbine engines to improve the durability and efficiency of engines [1,2]. The ceramic top coat is typically made of 7–8 wt % yttria partially-stabilized zirconia (YSZ). Due to the refractory nature of YSZ with a melting point of ~2700 ◦ C, high temperature materials processing technology is required [4]. The two primary widely-used methods for depositing TBCs are electron beam-physical vapor deposition (EB-PVD) and atmospheric plasma spraying (APS) [5]. During the EB-PVD process, a high-energy electron beam is used to melt and evaporate ceramic ingots in a vacuum chamber. The vapor deposits onto a preheated substrate at a deposition rate of, typically, several μm/min. Due to the vapor phase condensation and shadowing effect [5], columnar-structured
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