Dysprosia stabilized zirconia (DySZ) is a promising candidate to replace yttria stabilized zirconia (YSZ) as a thermal barrier coating due to its lower inherent thermal conductivity. It is also suggested in studies that DySZ may show greater stability to high temperature phase changes compared to YSZ, possibly allowing for coatings with extended lifetimes. Separately, the impurity content of YSZ powders has been shown to influence high-temperature sintering behavior. By lowering the impurity oxides within the spray powder, a coating more resistant to sintering can be produced. This study evaluates high purity and standard purity dysprosia and yttria stabilized zirconia coatings and their performance after extended heat treatment. Coatings were produced using powders with the same morphology and grain size; only the dopant and impurity content were varied. Samples were heat treated for up to 400 hours at 1150 °C and thermal conductivity measurements were plotted to show the evolution of thermal properties with respect to time. Thermal conductivity is compared to coating microstructure and porosity in order to track structural changes due to sintering.

Lightweight gamma titanium aluminide (γ-TiAl) intermetallic alloys have recently found application in low-pressure turbine blades in the aviation industry, but their use is currently limited to around 700 °C due to oxidation. This study evaluates the potential of various multilayer coating systems to increase the operating temperature range of γ-TiAl. The coating systems tested are based on a CoNiCrAlY topcoat for oxidation protection and a YSZ diffusion barrier, both applied by atmospheric plasma spraying using a three-cathode torch. Two bond coats, NiCrBSi and CoNiCrAlY, were also tested. Test specimens with bond coats withstood 1000 h of exposure at 900 °C without delamination and no detectable oxygen at the coating-substrate interface. Samples produced with varying feed rates showed that graded coatings can be achieved using the APS process.

Atmospheric plasma spray parameters were developed for a three-cathode torch with a high-velocity nozzle and MCrAlY powders of different particle size fractions. The main objectives of the work are to achieve bond coats with low oxygen content and porosity. Other goals are achieving sufficient surface roughness at high deposition rates and efficiencies. The oxidation behavior of the sprayed coatings was characterized by thermal gravimetric analyses and isothermal heat treatments.

This study investigates the effects of plasma spray parameters on the microstructure and porosity of yttria-stabilized zirconia coatings. In the experiments, the torch was held in place perpendicular to the substrate to produce cone or stalagmite shaped deposits. Stand-off distance (80, 90, 120 mm) and spray time (15, 30, 60 s) were varied to assess their effect on microstructure-property relationships as well as particle temperature, velocity, and impact angle. The shapes of the deposits were recorded using a CMM and surface topography and roughness were measured with a 3D optical profiler.

The durability of columnar TBCs produced by PS-PVD are strongly influenced by the compatibility of the metallic bond coat and ceramic topcoat. Studies have shown that a smooth bondcoat surface improves thermal cycling performance and that further improvements are possible by optimizing the formation of the thermally grown oxide layer. In this work, preheating and the deposition of the first coating layer are varied in order to adjust oxide growth. The results show that thermal cycling lifetimes can be more than doubled without a major increase in manufacturing time.

This study compares the accuracy of 2D and 3D models for determining the thermal conductivity of thermally sprayed ceramic coatings. Although the overall dependency of relative thermal resistance on microstructural parameters is similar for the two models, the detailed dependency is quite different and is more accurate in the 2D model. With increasing unit size and decreasing splat thickness and bonding ratio, the 2D model is more effective than the 3D model due to its more appropriate assumption of splat thickness relative to the distance between cracks.

In previous work, it was observed that atmospheric plasma sprayed bond coats perform better than their HVOF counterparts, which is contrary to current literature data. The objective of this work is to understand the observed difference with the aid of finite-element modeling. Different thermally grown oxide layer thicknesses and surface topographies are evaluated and the modeling results are compared with current theories based on simplified sinusoidal profiles. It is shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.

The processing conditions, microstructural and tribological characterizations of plasma sprayed CoNiCrAlY-BN high temperature abradable coatings are reported in this manuscript. Plasma spray torch parameters were varied to produce a set of abradable coatings exhibiting a broad range of porosity levels (34-62%) and superficial Rockwell hardness values (0-78 HR15Y). Abradability tests have been performed using an abradable-seal test rig capable of simulating operational wear at different rotor speeds and seal incursion rates. These tests allowed determining the rubbing forces and quantifying the blade and seal wear characteristics for slow and fast seal incursion rates. Erosion wear performance and ASTM C633 coating adhesion strength test results are also reported. For optimal abradability performance, it is shown that coating hardness needs to be lower than 70 and 50 HR15Y for slow and fast blade incursion rate conditions, respectively. It is shown that the erosion wear performance, as well as, the coating cohesive strength is a function of the coating hardness. The current results allow defining the coating specifications in terms of hardness and porosity for targeted applications.

This study investigates the effect of plasma spray parameters on the erosion rate of abradable seals used for clearance control in gas turbine engines. Coating samples were sprayed using YSZ powder containing polyester that was entrapped in the deposit then subsequently removed by heating. Test results show that erosion behavior is influenced by gun voltage and spray distance. A higher voltage results in a denser coating with a lower erosion rate. Increasing spray distance, on the other hand, increases porosity, which results in a higher erosion rate. Further analysis shows that the erosion rate is proportional to the inverse square of the spray distance and the square of the gun voltage.