Thermally sprayed coatings can be used in structural health monitoring devices where the coatings can reveal defects in the real-time integrity of the component through changes in mechanical, thermal or modal properties during service. In this emerging application, the mechanical properties of the coating are strongly affected by the interfacial bond between the coating and the substrate. This paper presents an analytical study of the interfacial stress distribution based on piezoresistive-stress constitutive relation of a coating layer. Both a single layer coating- and a bilayer coating-substrate system were considered. An analytical solution of the interfacial stress was developed by solving a Fredholm-Volterra singular integro-differential equation of a coating-substrate model using Chebyshev polynomials. Numerical simulation was conducted to analyze the effects of geometric and effective material properties of the coating-substrate system on the interfacial stress distribution. It was found that the susceptibility of the piezoresistive layer to delamination primarily relies on thicknesses of the coating layers and the stiffness of the intermediary insulating layer and substrate.

In this work, finite element analysis is used to investigate the effect of pore size on the stress intensity factor (SIF) of plasma sprayed coatings. Test samples with different pore sizes were obtained by spraying wollastonite powders with particle sizes of 60-75 μm, 75-95 μm, and 95-150 μm onto Ti 6 Al 4 V coupons. The results show that coating stress varies in proportion to the length of 2D pores and to a lesser extent the diameter of 3D pores. This implies that reducing the length of 2D pores may be considered as a way to increase the fracture resistance of plasma sprayed coatings.

This study deals with two new material deposition processes in which raw materials are in the form of a thixotropic slurry. In one case, the slurry (Al 2 O 3 nanoparticles in an acrylic resin) is misted into an arc plasma jet and sprayed on a stainless steel substrate. By varying the volume content of nanoparticles and slurry supply rates, investigators were able to achieve uniform droplets, resulting in fine Al2O3 layers free of microcracks and pores. In the other process evaluated, pure aluminum particles were dispersed in a photosensitive resin, producing a slurry that was spread on stainless steel substrates then patterned with a UV laser. The patterned metal particles were heat treated, creating iron-aluminide intermetallic phases through reaction diffusions. The microstructure and composition of the patterned lines are analyzed by SEM and XRD and surface stress distributions associated with a Hilbert fractal pattern are simulated via finite element analysis.