Tensile Creep in an in Situ Reinforced Silicon Nitride

Abstract

The tensile creep of an in situ reinforced silicon nitride is described in terms of the rheological behavior of the thin intergranular film present in this liquid-phase sintered silicon nitride. The high stress exponents and apparent activation energies (at constant stress) can be explained assuming non-Newtonian flow behavior of the film during grain boundary sliding. Time-to-failure is related to the minimum creep rate, even for samples which fail by slow crack growth. In addition, the primary creep region and the relaxation effects observed on unloading are described in terms of grain boundary sliding modified by the presence of a grain boundary phase with a lower elastic modulus than silicon nitride.

Compressive Creep and Creep Failure of 8Y2O3/3Al2O3‐Doped Hot‐Pressed Silicon Nitride

“…Such a macroscopic asymmetric creep behavior between tension and compression, with slower creep rates and higher creep failure strains in compression, appears to be a general feature of Si 3 N 4 containing a residual grain-boundary glassy phase. [22][23][24][25] At higher levels of applied stress, Ͼ 300 MPa, steady-state creep was almost absent. Accelerated creep started immediately, resulting in a short lifetime and lower creep strain.…”

Creep mechanisms in quasi-plastic silicon nitride by instrumented indentation

“…[13][14][15][16] They were accompanied by intensive cavitation in the core, strong oxidation enhanced by stress in surface layers and intensive cracking of these layers. 13 The obtained strains were up to five times higher than those in the standard silicon nitride grades, [17][18][19][20] however, at least half order of magnitude lower than the strains obtained during superplastic deformation. 21 Superplastic deformation is usually observed at temperatures above 1500 • C in inert atmosphere when cavitation is suppressed.…”

High-temperature elastic properties of in situ-reinforced Si3N4

“…The ISR Si 3 N 4 is known to experience grain rotation and grain boundary sliding during creep, resulting in an increased alignment of its acicular grains along the loading axis. 2,3 This phenomenon is then expected to induce an increase in peak breadth as well as hkl-dependent residual strains, especially for the (00•l) reflections, due to the elastic anisotropy of the material. 3 In the present study, the comparison of roomtemperature diffraction data collected at the beginning and end of the investigation yielded no appreciable change in peak breadth and very low residual strains ͑the maximum was 190 for the (00•2) reflection-here ϭ10 Ϫ6 strain͒.…”