In recent studies, crack formation was observed in oxidized areas of wire-arc sprayed Zn-Al coatings. As corrosion tests show, these cracks allow electrolyte to penetrate the coating, reducing effective service lifetime. Wire-arc sprayed coatings usually exhibit tensile residual stresses with the potential to cause such cracking. To determine the extent of that potential, the stress state of Zn-Al coatings was measured and correlated with corrosion test results. Residual stress was obtained using the sin2ψ method based on XRD analysis and the results are combined with those of previous studies, forming a hypothesis for the root cause of crack formation in wire-arc sprayed Zn-Al coatings, its effects, and its control.

In this investigation, an air plasma sprayed TBC system consisting of a CoNiCrAlY bond coat (BC) and a YSZ topcoat (TC) is produced with a PVD AlOx interlayer in order to study its effect on thermally grown oxides. For comparative purposes, a reference TBC without the AlOx interlayer was also prepared and studied. A cyclic thermal load was applied to both systems and the coatings were examined after 6, 12, 24, 40, and 80 cycles. Crack lengths were measured in the YSZ layer and TGO thicknesses were assessed at the BC-TC interface. An examination of coating microstructures revealed the expected mixed-mode failure in both TBCs. In comparison to the reference TBC, the system with the AlOx interlayer showed reduced crack formation in the TC and slowed TGO formation at the BC-TC interface both during and after thermal treatment.

This study assesses the corrosion performance of aluminum-manganese (Al-Mn) coatings deposited on 42CrMo4 steel by atmospheric plasma spraying and (APS). Al-Mn alloy powder containing 25 at% Mn was gas atomized under nitrogen atmosphere using pure Al and Mn as starting materials. The powder was characterized by laser granulometry and SEM-EDX analysis. A fraction with particle sizes ranging from 10 to 60 μm was used as the feedstock powder. The APS coatings were characterized by optical image analysis, Vickers hardness measurements, and salt-spray testing. The Al-Mn coatings exhibited significantly higher hardness in comparison to pure aluminum. Red rust appeared after 240 h of salt-spray testing, leading to local coating detachment after 1000 h. The corrosion attack starts at coating defects such as microcracks, which can be attributed to the brittleness and nonuniform melting behavior of the powder and possibly inhomogeneities in the spraying process.

The aim of this study is to better understand the formation of nonbonded splat-to-splat interfaces in thermally sprayed ceramic coatings. To that end, the surfaces between splats in plasma-sprayed La 0.5 Sr 0.5 CoO 3 (LSCO) coatings were examined and compared to free splat surfaces. The results show that free splat surfaces are relatively smooth, while adjacent surfaces at intersplat interfaces are quite rough. The observation implies that nonbonded splat-to-splat interfaces were never bonded, having fractured due to interface shear stress generated during splat cooling.

This study investigates the microstructure of coating-substrate interfaces formed by vacuum cold spraying. Commercially available TiO 2 nanopowder was deposited on SnO 2 -glass substrates using a lab-developed vacuum cold spray system. For comparison, TiO 2 coatings were also prepared by screen printing followed by mechanical pressing. Coating surfaces and interfaces were evaluated by means of TEM and SEM imaging and XRD analysis. SEM images show that screen-printed coatings have a crack-rich morphology, while mechanical pressed and vacuum cold sprayed coatings have no obvious cracks. TEM images, on the other hand, show the extent of bonding between TiO 2 nanoparticles and the glass substrate. Very little interface bonding was observed in screen-printed coatings in contrast to their vacuum cold sprayed and mechanical pressed counterparts. The difference is attributed to the higher pressures achieved by mechanical pressing and the high-velocity impact of vacuum cold spraying.

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 thermomechanical properties of plasma-sprayed deposits strongly depend on residual stress distribution. This latter is mainly attributed to the relative torch/substrate velocity as well as to the cooling system location and efficiency. The determining of both quenching and thermal stresses, which are generated respectively during spraying stage and cooling stage, is then required to improve coatings quality. A rather simple apparatus, which consists in monitoring the curvature of a beam substrate during the whole deposition process, has been developed to work under industrial conditions. It has been applied to partially stabilized zirconia coatings performed onto stainless steel and cast iron substrates. Spraying temperature and plasma gun velocity have been selected as relevant parameters for this study about stress generation and mechanical release. Finally, four point bend tests have been performed on deposited samples to measure coating mechanical properties and to evaluate damage level.

Two different W-Co-C powders were used in three deposition devices, the Super D-Gun, Jet Kote, and JP-5000 to produce coatings for laboratory immersion tests in molten zinc and %55Al-Zn. Resistance was evaluated as time to failure. Scanning electron microscopy and X-ray diffraction were used to characterize the structures ssid failure mechanism. All coatings were found to fail when the molten metal breached the coating thickness at weak spots and spread out over the underlying interface to lift the coating away from the underlying 316L substrate. These weak spots were "pits" on one Super D-Gun coating (the most resistant coating) and cracks on all the other coatings. No diffusion of zinc through the tungsten carbide coatings was observed.