Influence of Substrate Removal Method on the Properties of Free-Standing YSZ Coatings

Abstract

Thermally sprayed ceramic coatings are often tested as free-standing layers to investigate different properties such as thermal expansion coefficient, thermal conductivity, sintering, mechanical behavior, corrosion resistance, gas tightness, or electrical properties. In this paper, four different substrate removal methods were used to obtain free-standing YSZ coatings. At first, spraying on a steel substrate and subsequent dissolution of the substrate-coating interface by hydrochloric acid (HCl) was used. Second, the steel substrate was removed by applying an electrical field via electrochemical corrosion of the surface of the substrate. In a third method, the coating was sprayed on a salt (NaCI) interlayer, which was removed later by dissolution in water. At last, the coating was sprayed on a graphite substrate and the substrate was removed by heat treatment. After the preparation of free-standing coatings, these were characterized using scanning electron microscopy, mercury porosimetry, indentation tests, and room temperature three-point bending tests, which allowed the determination of Young’s modulus and viscosity. The results revealed measurable differences in coating properties as a result of the substrate removal methods, i.e., HCl method led to higher porosity and lower modulus in the YSZ coating.

Systematic Approach to Optimize Technological and Economical Aspects of Atmospheric Plasma Sprayed Thermal Barrier Coatings

“…The heat treatments performed to investigate changes in the coating properties during operation were carried out with free‐standing coatings. These were detached electrochemically from the substrate following a procedure described by Vaßen et al [ 31 ] The sintering process was carried out in a furnace under air atmosphere for 100 h at 1200 °C.…”

“…Therefore, rectangular samples with a length of 15 mm and a width of 4 mm were cut out of free‐standing coatings using a diamond saw. The coatings were detached electrochemically as described by Vaßen et al [ 31 ] The exact thickness of each sample, which was kept uniform by adjusting the number of passes to the coating parameters, was determined using the CT 350T profilometer from Cyber Technologies via a double‐sided measurement with a chromatic white light sensor. The elastic properties and viscoplastic deformation of the free‐standing coatings were investigated in the TMA dilatometry facility Setsys TMA‐18 of the company Setaram Inc.…”