Role of oxidation in creep and high temperature failure of silicon nitride
Creep and stress rupture behaviour of a HPSW (9 wt% Y(2)O(3)) was studied in air and nitrogen at 1400 C. This material has an excellent creep and subcritical crack growth resistance in comparison with other silicon nitrides. The intergranular phase consists of a crystalline silicon-yttrium-oxynitride with apatite structure. Cavitation at triple grain junctions is not observed after testing. Steady-state creep rates are only marginally influenced by the testing environment or by preoxidation, whereas lifetime is strongly influenced by these factors. At a stress of about 300 MPa, a static fatigue limit exists under inert conditions. Under oxidising conditions, lifetime may be curtailed by formation of oxidation pits. Formation of these pits during preoxidation further reduces life. After lifetimes longer than 100 secs in air, another crack initiation mechanism appears, which may be related to formation of a porous layer underneath the oxide scale. The implications of the observations with respect to in-service behaviour and design of improved materials is discussed.
Bibliographic Reference: Paper presented: 3rd International Symposium "Ceramic Materials & Components for Engines", Las Vegas (US), Nov. 27-30, 1988
Availability: Available from (1) as Paper EN 34479 ORA
Record Number: 198910164 / Last updated on: 1994-12-01
Original language: en
Available languages: en