Methodology for analysing the degradation of Mg-PSZ

For expanded applications and ease of manufacture, joining ceramics to other ceramic and metal components is a subject of intense interest, especially for heat engine applications. Magnesia partially stabilized zirconia (Mg-PSZ) is one possible material for various desired applications, due to its toughness and thermal and mechanical shock resistance. During processing of the join and during the lifetime of the ceramic component, thermal and chemical potential gradients are expected to cause complex reactions at the zirconia-metal interface. Particularly important reactions are the oxidation of the metal-joining agents and their diffusion/migration into the ceramic. Because of the small spatial scales of both the complex reactions and the interface, identifying mechanisms of degradation due to particular metals or metal oxides would be difficult. This research focuses on a methodology to identify whether the reaction of the metal oxides with Mg-PSZ would cause degradation. The methodology for investigating these reactions of Mg-PSZ to oxidized metals was developed by adapting a conventional metallurgical technique known as the temperature-time-transformation diagram. The metals selected for investigation were copper, tin and zinc (typical brazing agents), titanium and aluminium (reactive metals), and cobalt and nickel (super alloys and typical interlayer metals). To model the reaction at the interface layer, oxides of the metals were mixed with Mg-PSZ powder and its effect on precipitation analysed. All metal oxides accelerated the precipitation rate of the tetragonal phase, thereby shifting the nose of the temperature-time-transformation diagram to shorter times as compared to undoped Mg-PSZ. Additionally, these oxides enhanced growth of the monoclinic phase with increasing time at temperature.