Evaluation of the Strength and Creep–Fatigue Behavior of Hot Isostatically Pressed Silicon Nitride

Abstract

High Temperature Materials Iaboratory, Oak Ridge National Laboratory, Oak Ridge, TennesseeThe strength of a commercially available hot isostatically pressed silicon nitride was measured as a function of temperature. To evaluate long-term mechanical reliability of this material, the tensile creep and fatigue behavior was measured at 1150", 1260", and 1370°C. The stress and temperature sensitivities of the secondary (or minimum) creep strain rate were used to estimate the stress exponent and activation energy associated with the dominant creep mechanism. The fatigue characteristics were evaluated by allowing individual creep tests to continue until specimen failure. The applicability of the four-point load geometry to the study of strength and creep behavior was also determined by conducting a limited number of flexural creep tests. The tensile fatigue data revealed two distinct failure mechanisms. At 1150"C, failure was controlled by a slow crack growth mechanism. At 1260" and 1370"C, the accumulation of creep damage in the form of grain boundary cavities and cracks dominated the fatigue behavior. In this temperature regime, the fatigue life was controlled by the secondary (or minimum) creep strain rate in accordance with the Monkman-Grant relation.

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.…”

Creep of Hi-Nicalon S Ceramic Fiber Tows at 800 deg C in Air and in Silicic Acid-Saturated Steam

“…In more recent times, this same relationship has been shown to apply to creep of ceramic materials as well [4,46,[187][188][189][190]. The Monkman-…”

“…Ferber and Jenkins [190] investigated the creep performance of hot isostatcially pressed silicon nitride at temperatures from 1150 to 1370…”

Effect of Sintering Aid Composition on the Processing of Si3N4/BN Fibrous Monolithic Ceramics

“…[9][10][11][12] Based on this understanding, it was hypothesized that the high-temperature flexure properties of fibrous monoliths could be improved by using only Y 2 O 3 as a sintering aid in the cells of Si 3 N 4 . Thus, fabrication of 4-wt%-Y 2 O 3 -Si 3 N 4 /BN fibrous monoliths (4Y-FMs) was investigated.…”