Plastic Flow in Plasma Sprayed Ceramics
Ceramics plasma sprayed onto metal substrates have a considerable potential application in gas turbine engines and other high temperature devices as thermal/mechanical insulation since plasma spraying is convenient and widely available. However, there is disturbing evidence of expulsive shedding of the ceramic after cyclic heating to approximately 1000° C. Analyses were made and experiments were designed to measure the effect of tensile and compressive strain in the ceramic when at temperature in order to determine the cause of failure. Plastic flow was predicted and inelastic behavior measured for plasma sprayed binary oxide ceramics both on metal substrates and also when stripped from the substrate before exposure to temperature. Differential expansion between the metal substrate and plasma sprayed materials ZrO2-Y2O3, ZrO2-CaO or Al2O3-TiO2results in irreversible flow. Loading of the stripped binary oxide ceramic sheet materials at temperatures up to 1200° C also produced plastic flow, but annealing before loading eliminated the inelastic behavior. The conclusion is that plasma spraying of binary oxide ceramics results in a metastable state which is inelastic at temperature but can also be stabilized or devitrified through heat treating, so as to decrease plastic properties. Mechanical properties of the as-plasma sprayed and devitrified binary oxide ceramic sheet materials have been measured. Stresses associated with sheet formation and component applications have been calculated using the finite element codes MARC and ADINA/ ADINAT. These studies point to significant inelastic behavior at elevated temperatures.
Materials Science Research
Padovan, J.; McDonals, G.; Hendricks, Robert C.; Mullen, R. L.; Chung, Benjamin T.F.; and Braun, Minel J., "Plastic Flow in Plasma Sprayed Ceramics" (1984). Mechanical Engineering Faculty Research. 1049.