Columnar structured coatings, due to their high strain tolerance, are well suited for thermal shock applications and thermal cycling service. In this study, plasma spray-physical vapor deposition (PS-PVD) was used to produce YSZ coatings with quasi-columnar microstructure. Thermal cycling and thermal shock tests were performed, and coating microstructure, phase composition, and residual stresses were evaluated before and after testing. Coatings obtained prior to process optimization, on average, made it to 623 cycles at 1250 °C before 10% of the coating surface showed signs of spallation.

Thermal cycling tests were performed on thermal barrier coatings (TBCs) to evaluate the influence of temperature gradients in the ceramic topcoat on overall lifetime and performance. The coating system tested consists of an Inconel 738 substrate, a cold-sprayed NiCoCrAlTaY bond coat, and an atmospheric plasma sprayed YSZ topcoat. YSZ surface temperatures were 1150, 1200, and 1250 °C, corresponding to temperature gradients of 150, 200, and 250 °C across the 250 µm thick layer. Heating and cooling times were set at 120 sec for each thermal cycle. The results of the study show that lifetime decreases with increasing temperature gradient, although the gradient has little effect on the failure mode.

In this work, a LCA based on Eco-indicator 99 methodology was used to compare the environmental impacts and benefits of thermal spraying (including APS, HVOF, Flame and Cold Spray) carried out with materials which could be used in application to resist against wear and/or corrosion. The comparison was carried out using the SimaPro 7.2 software, and it was focused on all stages necessary to build the coating, i.e. extraction of raw materials, production of powder, transport, surface preparation, thermal spray operating, until the end of life, as well as emissions (solid, liquid and gaseous) at each stage of a process. As a major result, it appears that the lifetime of the coatings plays a high role. If a coating needs to be regularly replaced or if failure of the coating decreases the lifetime of the component, this almost impact on the LCA. Moreover, there is an influence on the nature of the resources used to build the coating, as well as on the end of life strategies.

Electroplated chromium improves corrosion resistance while providing resistance to wear, fatigue and impact. However, hard chromium plating uses chromic acid, which releases fumes containing carcinogenic chromium +6 ions into air during the process. Therefore, numerous efforts have been carried out worldwide in the last decade to develop alternatives and several applications and processes were validated, among which trivalent chromium plating, electroless nickel and nickel alloy coatings, micro-welding, PVD, CVD, and thermal spraying. Nevertheless, these finishing processes have impacts on human health, ecosystems and resources. In this work, a Life-cycle assessment (LCA) methodology based on Eco-indicators 99 was used to compare the environmental impacts and benefits of thermal spraying (including APS- and HVOF-sprayed WC-Co coatings and TWEA- and APS-sprayed hard steel coatings) to conventional chromium plating.

A thermal cycling test rig and procedure was designed in order to predict the life expectancy of Thermal Barrier Coatings (TBC) under thermal cycling conditions similar to those meet in combustion chambers. Two 2kW-halogen lamps highly focused on the TBC were used to expose the surface of the coating to an intense heat flux. A 25x100 mm TBC is Air Plasma Sprayed (APS) centered onto a substrate 25x370 mm. The thermal cycling can be done either under inert or oxidizing atmosphere in order to separate oxidation-induced acoustic emissions from that resulting from the mismatch of the Coefficient of Thermal Expansion (CTE) of the coating compared to that of the substrate. Two transducers located at each end of the substrate monitor the Acoustic Emission (AE) signals emitted by crack initiation and/or propagation, were recorded and analyzed in order to deduce available information about TBC behavior under thermal load. The use of two transducers with a time of flight approach provides a valuable means of identifying both the crack formation and its location. This thermal cycling test is adequate for the study of various samples, like welded substrates coated with TBC or TBC coated around holes. The presence of cracks is observed using metallography preparation and microscopic observation.