THERMAL SHOCK STRENGTH OF THERMAL SPRAYED COATINGS SUBJECTED TO LOCAL IMPULSE HEATING

摘要

Ceramic coatings by thermal spraying coating are attracting attention in the development of space planes, aircraft and nuclear fusion reactors because they have excellent wear and heat-resistant characteristics. In some applications, it is anticipated that they will be exposed to very high temperature environments of the order of thousands of degrees. Therefore, it is very important to investigate their thermal shock characteristics. In this report, the distributions of temperatures and thermal stresses of cylindrically shaped Al_2O_3 ceramic coatings under irradiation by laser beams are analyzed using the finite element method with 8 nodes and arbitrary quadrilateral axisymmetric ring elements. The relationships between spot diameters of laser beams and maximum values of thermal stresses are derived for various laser power densities. From these relationships, a critical fracture curve was obtained based on the strength of ceramic coatings. Tentatively several experiments were done using CO_2-laser.