Tensile creep behavior of a ytterbium silicon oxynitride-silicon nitride ceramic

Tensile creep behavior of hot pressed silicon nitride on the Si3N4-Yb4Si2O7N2 tie line was investigated at temperatures of 1300 and 1400 degreesC under an applied stress of 125 to 200 MPa. During the tests, the creep strain increased with time and the creep rate monotonically decreased both with time and strain. On the basis of minimum strain rates, the stress exponents for 1300 and 1400 degreesC were determined to be 3.1 and 1.7, respectively. All the specimens tested at 1400 degreesC lead to failure while exhibiting a large scatter in the time-to-failure data. The activation energy was determined to be 879 kJ/mol from a comparison between creep rates at different temperatures. The creep mechanism is discussed on the basis of the creep parameters and creep damage observation. (C) 2002 Published by Elsevier Science Ltd.