This study investigates the effect of thermal cycling on cold-spray chromium coatings deposited on steel substrates. First, equilibrium stress states are determined for different coating thicknesses. Next, the potential for crack initiation and growth is simulated based on periodic heating and cooling cycles. The corresponding crack driving forces are characterized using interface stresses and energy release rate as a function of the thermal cycles. The effects of coating thickness, embedded microcracks, and initial residual stress on the driving forces are investigated systematically to demonstrate the risk of coating fracture and delamination.

Yttrium aluminum garnet (YAG) has desirable properties for a thermal barrier coating (TBC), although there are two production challenges. One, YAG has a relatively low thermal expansion coefficient which leads to large thermal mismatch stresses, and two, amorphous phases are produced by atmospheric plasma spraying. Solution precursor plasma spraying (SPPS) has to potential to solve both problems. First off, it produces no amorphous phases. Secondly, it can produce a cracked microstructure that mitigates the CTE mismatch issue. To judge the adequacy of the properties of SPPS YAG, a summary of the properties of common TBCs is presented. It is shown that the properties of SPPS YAG fall within desirable or usable ranges. Current efforts described in this paper focus on improving the efficiency and rate of deposition.

Thermal barrier coatings typically incorporate a YSZ topcoat and a metallic bond coat. During service, a reaction zone consisting of different thermally grown oxides forms at the interface. Although most such oxides are detrimental, one (α-Al 2 O 3 ) improves service life due to its barrier effect on oxygen diffusion. In this study, Al and AlOx films are deposited on metallic bond coats by dc magnetron sputtering prior to topcoat deposition. The resulting TBCs were thermally cycled to determine the effect of the interlayer films on service life and TGO formation. It is shown that the Al films transform in situ into dense Al 2 O 3 layers that act as oxygen diffusion barriers. TBCs with interlayer alumina, whether deposited directly or formed in situ, showed less cracking and were more mechanically stable during thermal cycle tests.

This investigation evaluates the microstructure and properties of thermal barrier coatings produced by suspension plasma spraying. A YSZ suspension was injected axially into a plasma jet and deposited on a superalloy substrate with a CoNiCrAlY bond coat. SEM examination revealed a columnar microstructure with a network of vertical segmentation cracks and horizontal branching cracks. In furnace cycle testing, the TBCs withstood 166 thermal shock cycles with failure attributed to partial spallation of the columnar segments initiating at the edge and center of the coatings. The TBCs were also subjected to burner rig tests to assess thermal insulation properties and to heat treatments up to 1600 °C to evaluate thermal stability based on phase composition, grain size, and microhardness.

The lifetime of casting molds in the aluminum industry is strongly limited by the corrosiveness of aluminum melts and alternating thermal and mechanical loads. With the added protection of sintered tungsten pseudoalloy inlays, casting molds have been known to last as much as 1000 times longer, and the work presented here indicates that it may be possible to replace the massive liners with a twin wire arc or plasma sprayed coating that can be tailored by varying spraying parameters.

Coating operations over glass ceramic substrates represent a new field for thermal spray applications. Due to the unique thermal and mechanical properties of glass ceramics, especially the low or even negative CTE, coating processes must be adapted to reduce the distribution of thermal stresses in the system and to not damage the substrate. This study investigates the deposition of a complex-shaped ceramic-metallic multilayer coating system that could potentially serve as a heating element in a glass ceramic cooking plate. To ensure coating adhesion, the substrates are preheated and their surfaces are grit blasted. In order to minimize stresses associated with the deposition of metal, the movement of the spraying mechanism was automated with robot control and new masking concepts were developed to ensure the accuracy of the shape and placement of the coating. The influence of spraying parameters on coating properties and residual stress distribution is analyzed as well.

During the past few years thermally sprayed ceramic coatings deposited from nanostructured feedstock powder have often demonstrated improved properties relative to coatings produced from convention powder. Nanostructured or bimodal structured ceramic coatings have been reported to exhibit better wear resistance and adhesion strength. For thermal barrier coatings, key properties include thermal conductivity and thermal stability. In this study thermomechanical properties of plasma sprayed, bimodal structured, yttria stabilized zirconia coatings were investigated. The thermal stability was examined by measuring the hardness and elastic modulus of free standing coating layers before and after heat treatments in air at 600-800 °C. The creep behaviour was investigated using free standing coating layers loaded in the four point bending configuration at temperatures of 1000 °C in air. The results for bimodal structured coatings have been compared with the behaviour of conventional plasma spray coatings under the same test conditions.

Plasma spraying was used to produce continuously graded and layered structures of molybdenum disilicide and alumina. These microstructures were achieved by manipulating the powder hoppers and plasma torch translation via in-house created computer software. The resultant microstructures sprayed uniformly and were crack free. The mechanical and thermal performance of these sprayed materials will be evaluated through C-ring tests and thermal cycling experiments respectively. The purpose of this study is two fold; firstly to demonstrate the ability of produce such composite ceramic microstructures using a conventional plasma spraying process, and secondly to quantify the improvements in thermo-mechanical performance provided by these composite microstructures over conventional monolithic microstructures.