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

Abstract

The compressive creep properties of hot-pressed Si 3 N 4 -purpose, compressive creep tests were performed at temperatures of 1543-1603 K in air. Flexural dynamic and static fatigue 8Y 2 O 3 -3Al 2 O 3 (wt%) have been investigated in the temperature range of 1543-1603 K in air. The stress exponent, n, of tests also were conducted in the temperature range of 1373-1573 K and will be analyzed in detail in a later paper. 20 A the power creep law was determined to be 1.5, and the activation energy was determined to be 650 kJ/mol. Transmajor part of our attention was directed to the high-temperature mechanisms that control the creep and failure of this material. mission electron microscopy observations showed that grain-boundary sliding occurred with cavitation formation Furthermore, microstructural observations allowed us to distinguish the dominant cavitation process that occurs during comin the grain-boundary glassy phase. The quasi-steady-state creep results were consistent with that of the diffusionpressive creep-rupture tests. controlled solution-diffusion-precipitation creep mechanism, and the distinguished failure mechanism was II. Materials and Testing cavitation creep damage controlled by the viscosity of the boundary glassy phase. The compressive creep failure time,The selected material, designated as RAY 38 SM, was prepared by mechanically mixing an ␣-Si 3 N 4 powder (S-Stark LC obtained at 1573 K, in the stress range of 175-300 MPa, followed the Monkman-Grant relation, indicating that cav-12 SX, H. C. Starck, New York, NY) with 8 wt% Y 2 O 3 and 3 wt% Al 2 O 3 as sintering aids. The powder mixture was uniaxiity growth was mainly controlled by the creep response of the material.ally hot-pressed in an induction-heated graphite die under a pressure of 30 MPa at 1983 K for 1 h. X-ray diffractometry (XRD) of the as-sintered material revealed that the main phases I. Introductionwere ␤-Si 3 N 4 with ϳ10% residual ␣-Si 3 N 4 . The density was evaluated by the Archimedes method and S ILICON NITRIDE (Si 3 N 4 ) has an exceptionally high strength at room temperature, but its strength degradation can be was 3.27 g/cm 3 . The material was considered to be fully dense. Specimens with dimensions of ϳ3 mm ϫ 3 mm ϫ 9 mm significant at high temperatures. Thus, despite its high and quasiinvariant fast-fracture strength to temperatures up to 1173-were deformed during compressive creep tests performed in air in a constant-load machine. 21 The variation of specimen length 1273 K, silicon nitride is susceptible to slow crack growth, which limits long-term reliability for structural components. [1][2][3][4][5][6] was determined by an extensometer system constituted by an Al 2 O 3 probe connected to a linear-variable differential transConsequently, the use of silicon nitride in high-temperature strength applications has motivated numerous studies on fatigue former (LVDT). Temperature monitoring was performed by using a Pt/Pt-10% Rh thermocouple. Most of the compressive behavior. 7-15 These studies have shown that creep rupture also...

Fabrication of Heat-Resistant and Plastic-Formable Silicon Nitride

“…It is obvious that the accommodation process here is the solution-precipitation process because of the slight grain growth and elongation of β-Si 3 N 4 grains. Furthermore, the present experimental activation energy of 571.8 kJ/mol, which corresponds to that for the diffusion of nitrogen ions through the grain boundary glassy phase [36], is similar to other values reported for the deformation of Y 2 O 3 /Al 2 O 3 -doped silicon nitride materials for the grain boundary sliding mechanism accommodated by a diffusion-controlled solution-precipitation process [36,37]. The solution-precipitation process in fine-grained ceramics can be controlled by either an interface reaction or by diffusion in the liquid.…”

Cavitación durante la fluencia de policristales de Si₃N₄

“…Por último, la evidencia de disminución del daño inducido por cavitación al aumentar la temperatura es un argumento adicional que siguiere que este fenómeno no está controlado por difusión. Estos resultados son consistentes con estudios previos en cerámicos de nitruro de silicio (5,15,16).…”

“…La fluencia de estos compuestos en compresión y en tracción ha sido investigada en un gran número de estudios (1)(2)(3)(4)(5), que han puesto de manifiesto que la fluencia estacionaria del nitruro de silicio está controlada por cavitación en tracción (6) y por disolución -reprecipitación en compresión (7).…”

The creep behavior of Si3N4/SiC nanocomposites

“…Similar data were also found in Si 3 N 4 monoliths. [26][27][28] The volume of data is insufficient to make a conclusion as to whether the basic creep mechanism in micro-nanocomposites is the same as in silicon-nitride monoliths. The best one can say at this point is that there has not been any evidence that the creep mechanism in silicon-nitride/siliconcarbide micro-nano is different from that in silicon-nitride monoliths.…”