Stationary gas turbines have been used for several decades for energy supply. In order to save the environment and to use resources more efficiently, an attempt is made to improve the efficiency of such gas turbines by means of a higher working temperature and a reduced cooling capacity. The used materials must withstand these new conditions. In this case, a high thermal and mechanical strength, low specific weight, high toughness and high chemical resistance of the material is required. Silicon nitride is a promising material for these application. In this work, the creep behavior of five different Si3N4 ceramics is investigated. Two of the materials are not intended for high temperature applications and served as comparative materials and for optimizing the experimental design. The other three materials have been specially developed for use in stationary gas turbines. Accordingly, it is expected that the creep resistance of these materials clearly exceeds those of the comparative materials. To investigate the creep behavior, four-point bending creep tests were carried out on bending samples (45 × 4 × 3 mm) of the various materials. As expected, the performance of the comparative materials was a lot worse than that of the high-temperature ceramics. The high-temperature ceramics show an approximately linear relationship between applied stress and creep rate. The determined creep rates differ only slightly between these materials. The activation energies of these materials are approximately in the range of 220 – 240 kJ/mol. Furthermore, a study of the surface and the resulting creep damage was carried out after the creep tests. The surface changes strongly, oxidation and precipitate formation can be observed. Creep damage such as pores and cavities was present in the interior of the material. Fractographic investigations revealed fracture-inducing defects in the various materials. On some fracture surfaces areas in which slow crack growth has occurred were found.
|Translated title of the contribution
|Creep behaviour of different silicon nitride ceramics
|28 Jun 2019
|Published - 2019
Bibliographical noteembargoed until null
- silicon nitride
- high-temperatur behaviour