Thermal wave characterization of inhomogeneities in sprayed coatings

Abstract

Des couches métallisées par projection thermique ont été examinées par des ondes thermiques et leurs chaleurs spécifiques et conductivités thermiques ont été évaluées. Les déviations des résultats expérimentaux de la théorie des milieux homogènes dans le domaine des basses fréquences servent à déterminer l'influence des différentes espèces de défauts. Les rôles des pores et des barrières thermiques ont été étudiés en comparant les résultats avec des modèles des milieux inhomogènes et on a trouvé que l'influence des barrières thermiques sur les propriétés des couches métallisées par projection est la plus importante. Abstract. 2014 Thermally-sprayed metal coatings were investigated with thermal waves and their specific heats and thermal conductivities were determined. The deviations of the experimental results from the theory of homogeneous solids at low frequencies served to determine the influence of different types of defects. The roles of the pores and the thermal barriers were studied by comparing the results to models of inhomogeneous media and the thermal barriers were found to affect significantly the coating properties.

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“…Insufficient fusion between the grains may affect significantly thermal wave propagation within samples [7]. In order to avoid thermal wave scattering on these thermal barriers, samples sintered at high temperature are investigated, for which fusion between grains is expected to be good.…”

A complex investigation of structure and properties of thermally sprayed Ni and Cu-based coatings

“…In the first case one can find out from the thermal parameters, obtained in [5], that even at 10 Hz the thermal diffusion length in the coating is more than 10 times smaller than its thickness. The presence of pores is found not to affect significantly the photoacoustic signal in this case [5]. Thus the phase shift is attributed to the thermal barriers (domains with very low thermal conductivity) between the different grains.…”

“…Other studies have been performed on the bonding mechanism between the sprayed coating and the substrate [2,3]. The thermal diffusivity and thermal effusivity coefficients as well as the thermal conductivity and the specific heat of the coatings have been estimated in [4,5]. The influence of the coating properties on the sensitivity of the thermal-wave testing techniques is investigated in [4].…”