A New Model for Tensile Creep of Silicon Nitride

Abstract

The tensile creep rate of most commercial grades of Si 3 N 4 increases strongly with stress. Although the usual powerlaw functions can represent the creep data, the data often show curvature and systematic variations of slope with temperature and stress. In this article, we present a new approach to understanding the creep of ceramics, such as Si 3 N 4 , where a deformable second phase bonds a deformation-resistant major phase. A review of experimental data suggests that the rate of formation and growth of cavities in the second phase controls creep in these materials. The critical step for deformation is the redistribution of the second phase away from the cavitation site to the surrounding volume. The effective viscosity of the second phase and the density of active cavities determine the creep rate. Assuming that the hydrostatic stresses in pockets of the second phase are normally distributed leads to a model that accurately describes the tensile creep rate of grades of Si 3 N 4 . In this model, the creep rate increases exponentially with the applied stress, is independent of Si 3 N 4 grain size, is inversely proportional to the effective viscosity of the deformable phase, and is proportional to the cube of the volume fraction of the deformable phase.

Mecanismos de deformación plástica en policristales cerámicos con fases secundarias vítreas

“…Como ejemplo, la figura 2 muestra este hecho en materiales a base de nitruro de silicio, deformados en compresión y en tracción (7,(15)(16)(17); un comportamiento análogo ha sido identificado en cerámicos a base de SiC (18) o de Al 2 O 3 (19) con fases secundarias. En cambio, los materiales monofásicos exhiben el mismo comportamiento en compresión y en tracción (14).…”

“…En tracción, en cambio, la deformación se produce generalmente por cavitación acomodado por el deslizamiento relativo de los granos (7,16,17) o por un mecanismo combinado (7,21). Esta afirmación está apoyada por la observación sistemática de que la fracción volumétrica de cavidades aumenta linealmente con la deformación (7,(15)(16)(17)20).…”

Sintering behaviour and properties of YAlSiO and YAlSiON glass-ceramics

“…Furthermore, yttrium aluminosilicate glassy compounds containing a little nitrogen are the typical grain boundary compositions of sintered Si 3 N 4 -based ceramics, which usually dictates their mechanical properties at high temperatures [17][18][19][20][21][22]. In this case, viscosity is a critical parameter.…”

Creep mechanisms in quasi-plastic silicon nitride by instrumented indentation

“…The progress in understanding cavitation creep allows us to incorporate oxidation and other effects into quasi-plastic creep model at least at qualitative level. 8,24 Thus, the aim of the work is to elucidate possible tensile creep mechanisms in quasi-plastic silicon nitride including oxidation and other effects with the emphasis on the analysis of the data obtained by instrumented indentation.…”