Partial Devitrification of Sintered Silicon Nitride During Static Fatigue Testing

1992 ◽  
Vol 287 ◽  
Author(s):  
W. Braue ◽  
G. D. Quinn
Keyword(s):  
Fatigue Testing ◽  
Fatigue Behavior ◽  
Slow Crack Growth ◽  
Stress Rupture ◽  
Secondary Phase ◽  
Boundary Phase ◽  
Static Fatigue ◽  
Phase Assemblage ◽  
Transmission Electron ◽  
Stress States

ABSTRACTThe static fatigue behavior of sintered Y2O3/A12O3-fluxed Si3N4 in air is controlled by slow crack growth or creep fracture. Partial devitrification of the amorphous grain boundary phase at 1000°C and 1100°C improves the static fatigue resistance with specimens surviving up to 1500 hrs. during stress rupture experiments. In this study the early stages of partial devitrification during static fatigue testing at 1000°C are investigated by conventional and analytical transmission electron microscopy with emphasis on nucleation and growth of δ-Y2Si2O7 and X1-Y2SiO5 and possible constraints from different stress states. The results show that the stress state does not affect the nature of the secondary phase assemblage. However, the amount of crystallization is higher within the tensile region of the flexural specimens than in areas which experienced compressive stresses.

scholarly journals Static Fatigue of SiC Multifilament Tows at Temperatures up to 1200 °C in Air

Ceramics ◽  
2019 ◽  
Vol 2 (3) ◽  
pp. 426-440 ◽  
Author(s):  
Jacques Lamon
Keyword(s):  
High Temperatures ◽  
Fatigue Behavior ◽  
Slow Crack Growth ◽  
Stress Rupture ◽  
Constant Load ◽  
Rupture Time ◽  
Static Fatigue ◽  
Probability Relation ◽  
Time Relation ◽  
Increasing Temperature

SiC-based fibers are sensitive to delayed failure under constant load at high temperatures in air. Static fatigue at intermediate temperatures < 800 °C was attributed to slow crack growth from flaws located at the surface of fibers, driven by the oxidation of free carbon at grain boundaries. The present paper examines the static fatigue behavior of SiC-based Hi-Nicalon fibers at high temperatures up to 1200 °C and Hi Nicalon S fibers at intermediate temperatures (500–800 °C). The degradation of stress- rupture time relation of multifilament tows with increasing temperature was investigated. Predictions of tow lifetime based on critical filament-based model of tow failure were compared to experimental stress-rupture time diagrams. Critical filaments are characterized by strength–probability relation. The critical filament-based model was found to describe satisfactorily the static fatigue behavior of fiber tows at these temperatures. The influence of various factors on lifetime as well as the origins of variability is analyzed.

Microvoid formation in the grain boundary phase of a sintered Si-Al-O-N ceramic after static fatigue testing

1986 ◽  
Vol 44 ◽  
pp. 490-491
Author(s):  
M. R. Hughes ◽  
T. A. Nolan ◽  
J. Chang
Keyword(s):  
Silicon Nitride ◽  
Elevated Temperatures ◽  
Fatigue Testing ◽  
Slow Crack Growth ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Static Fatigue ◽  
Gas Turbine Engines ◽  
Sintering Aid ◽  
Intergranular Phase

Sintered silicon nitride materials are currently being considered for use in hot flow-path components of gas turbine engines because of their good thermal shock and oxidation resistance as well as strength at high temperatures. These materials, however, have been shown to be susceptible to slow crack growth (SCG) and creep at elevated temperatures. The high-temperature properties are largely determined by the intergranular phase which is composed of the sintering aid residue and may be either amorphous or crystalline depending on sintering and annealing parameters. The silicon nitride examined in this study had reportedly been sintered with Y2O3 (5.86%) and Al2O3 (2.2%) to produce a composite of β'Si3N4 crystals in an amorphous Y-Si-Al-O-N matrix. Static fatique tests performed on test bars of this material resulted in failures originating, via SCG and creep within the intergranular phase, above certain stress loads at 1000°C. These sites and other areas through the cross section of the test bars were examined by SEM and AEM to determine the microstructure and chemistry related to these failure phenomena.

scholarly journals Static Fatigue of SiC/SiC Minicomposites at High Temperatures up to 1200 °C in Air: Multiscale Approach

2021 ◽  
Vol 5 (3) ◽  
pp. 67
Author(s):  
Jacques Lamon ◽  
Adrien Laforêt
Keyword(s):  
Crack Growth ◽  
High Temperatures ◽  
Fatigue Behavior ◽  
Slow Crack Growth ◽  
Stress Rupture ◽  
Rupture Time ◽  
Cumulative Distribution ◽  
Initial Stresses ◽  
Static Fatigue ◽  
Time Relation

The present paper investigates the static fatigue behavior of Hi-Nicalon fiber-reinforced SiC–SiC minicomposites at high temperatures in the 900–1200 °C range, and under tensile stresses above the proportional limit. The stress–rupture time relation was analyzed with respect to subcritical crack growth in filaments and fiber tow fracture. Slow crack growth from flaws located at the surface of filaments is driven by the oxidation of free carbon at the grain boundaries. Lifetime of the reinforcing tows depends on the statistical distribution of filament strength and on structural factors, which are enhanced by temperature increase. The rupture time data were plotted in terms of initial stresses on reinforcing filaments. The effect of temperature and load on the stress–rupture time relation for minicomposites was investigated using results of fractography and predictions of minicomposite lifetime using a model of subcritical growth for critical filaments. The critical filament is the one whose failure by slow crack-growth triggers unstable fracture of the minicomposite. This is identified by the strength–probability relation provided by the cumulative distribution function for filament strength at room temperature. The results were compared to the fatigue behavior of dry tows. The influence of various factors related to oxidation, including multiple failures, load sharing, and variability, was analyzed.

Methodology to Predict Delayed Failure Due to Slow Crack Growth in Ceramic Tubular Components Using Data From Simple Specimens

1993 ◽  
Vol 115 (2) ◽  
pp. 204-210 ◽  
Author(s):  
O. M. Jadaan ◽  
R. E. Tressler
Keyword(s):  
Crack Growth ◽  
Fatigue Testing ◽  
Slow Crack Growth ◽  
Stress Rupture ◽  
Scaling Analysis ◽  
Rupture Data ◽  
Threshold Stress Intensity Factor ◽  
Using Data ◽  
Tubular Components

The methodology to predict the liftime of sintered α-silicon carbide (SASC) tubes subjected to slow crack growth (SCG) conditions involved the experimental determination of the SCG parameters of that material and the scaling analysis to project the stress rupture data from small specimens to large components. Dynamic fatigue testing, taking into account the effect of threshold stress intensity factor, of O-ring and compressed C-ring specimens was used to obtain the SCG parameters. These SCG parameters were in excellent agreement with those published in the literature and extracted from stress rupture tests of tensile and bend specimens. Two methods were used to predict the lifetimes of internally heated and pressurized SASC tubes. The first is a fracture mechanics approach that is well known in the literature. The second method used a scaling analysis in which the stress rupture distribution (lifetime) of any specimen configuration can be predicted from stress rupture data of another.

scholarly journals Influence of testing environment on static fatigue behavior of a glass and a polycrystalline ceramic

2021 ◽  
Vol 32 (3) ◽  
pp. 56-64
Author(s):  
Sara Fraga ◽  
Gabriel Kalil Rocha Pereira ◽  
Luís Felipe Guilardi ◽  
Liliana Gressler May ◽  
Luiz Felipe Valandro ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Fatigue Test ◽  
Fatigue Behavior ◽  
Slow Crack Growth ◽  
Lithium Disilicate ◽  
Static Fatigue ◽  
Distilled Water ◽  
Step Size ◽  
Test Environment ◽  
Time To Fracture

Abstract It aims on evaluate the effect of the test environment on static fatigue behavior of lithium disilicate-based (LD), and yttrium oxide-stabilized zirconia (YSZ) ceramics. Specimens of LD (IPS e.max CAD, Ivoclar Vivadent) and YSZ (IPS e.max ZirCAD MO, 3 mol% Y2O3, Ivoclar Vivadent) were randomly allocated into three groups: tested in air, inert (paraffin oil, Sigma Aldrich) or distilled water. The static fatigue test (n=15) was performed using a piston-on-three ball assembly, adapted from ISO 6872, as follows: starting load 100 N for LD and 300 N for YSZ; loading application time set to 1 hour for each loading step; step size of 50 N for LD and 100 N for YSZ, applied successively until fracture. Data from static fatigue strength (MPa) and time to fracture (hours) were recorded. Fractographic analysis was executed. Survival analysis corroborates absence of influence of environment on static fatigue outcomes (fatigue strength, time to fracture and survival rates) for YSZ. For LD, specimens tested in air presented statistically superior survival rate and static fatigue strength (p= 0.025). In regards of time to fracture, LD tested in air were superior than when tested in distilled water (p=0.019) or inert (p=0.017) environments. No statistical differences for Weibull modulus were observed. Failures started on the tensile stress surface. Thus, the test environment did not affect slow crack growth (SCG) mechanisms during static fatigue test of YSZ ceramics, but it plays a significant role for the static fatigue behavior of lithium disilicate-based glass ceramics, indicating a high susceptibility to SCG.

Evaluation of Tensile Static, Dynamic, and Cyclic Fatigue Behavior for A Hiped Silicon Nitride at Elevated Temperatures

1992 ◽  
Vol 287 ◽  
Author(s):  
Chih-Kuang Jack Lin ◽  
Michael G. Jenkins ◽  
Matitison K. Ferber
Keyword(s):  
Silicon Nitride ◽  
Cyclic Loading ◽  
Crack Growth ◽  
Failure Mechanism ◽  
Fatigue Behavior ◽  
Slow Crack Growth ◽  
Cyclic Fatigue ◽  
Creep Rupture ◽  
Static Fatigue ◽  
Dynamic Fatigue

ABSTRACTTensile fatigue behavior of a hot-isostatically-pressed (HIPed) silicon nitride was investigated over ranges of constant stresses, constant stress rates, and cyclic loading at 1150-1370°C. At 1150°C, static and dynamic fatigue failures were governed by a slow crack growth mechanism. Creep rupture was the dominant failure mechanism in static fatigue at 1260 and 1370°C. A transition of failure mechanism from slow crack growth to creep rupture appeared at stress rates ≤10−2 MPa/s for dynamic fatigue at 1260 and 1370°C. At 1 150-1370°C, cyclic loading appeared to be less damaging than static loading as cyclic fatigue specimens displayed greater failure times than static fatigue specimens under the same maximum stresses.

Estimation of Static Fatigue Behavior of Ceramic Materials as Candidate Overpack Materials

1993 ◽  
Vol 333 ◽  
Author(s):  
Masamichi Obata ◽  
Akira Honda ◽  
Hirohisa Ishikawa ◽  
Tadashi Mano
Keyword(s):  
Titanium Oxide ◽  
Life Prediction ◽  
Growth Parameters ◽  
Fatigue Behavior ◽  
Slow Crack Growth ◽  
Prediction Method ◽  
Ceramic Materials ◽  
Localized Corrosion ◽  
Static Fatigue ◽  
Stabilized Zirconia

ABSTRACTStatic fatigue behavior is one of the important factors for life prediciton of ceramic materials. In this study, SCG (slow crack growth) parameters were measured under atmosphere conditions, and the static fatigue behavior of alumina, PSZ (partially stabilized zirconia), and titanium oxide was examined.According to the results of the evaluatin of the static fatigue behavior, the destruction probability after 1,000 years would be less than 1/40,000 when tensile stresses occurring in the material were less than 79.4, 241.3, 8.0 MPa for alumina, PSZ, and titanium oxide, respectively. However titanium oxide could not be used because of the wall thickness that would be needed to accomplish this stress. The life prediction method includes only tht effect of preexisting flaws so the method to estimate the effect of localized corrosion is required for the future examination of the application of ceramic materials.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Observation of solid-state reaction between a thin yttria film and a (0001) α-alumina substrate

1994 ◽  
Vol 52 ◽  
pp. 644-645
Author(s):  
J. R. Heffelfinger ◽  
C. B. Carter
Keyword(s):  
Electron Microscopy ◽  
Solid State ◽  
Solid State Reaction ◽  
Yttrium Aluminum Garnet ◽  
Secondary Phase ◽  
Ceramic Composites ◽  
Alumina Substrate ◽  
Transmission Electron ◽  
Alumina Fibers ◽  
Optical Applications

Transmission-electron microscopy (TEM), scanning-electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) were used to investigate the solid-state reaction between a thin yttria film and a (0001) α-alumina substrate. Systems containing Y2O3 (yttria) and Al2O3 (alumina) are seen in many technologically relevant applications. For example, yttria is being explored as a coating material for alumina fibers for metal-ceramic composites. The coating serves as a diffusion barrier and protects the alumina fiber from reacting with the metal matrix. With sufficient time and temperature, yttria in contact with alumina will react to form one or a combination of phases shown by the phase diagram in Figure l. Of the reaction phases, yttrium aluminum garnet (YAG) is used as a material for lasers and other optical applications. In a different application, YAG is formed as a secondary phase in the sintering of AIN. Yttria is added to AIN as a sintering aid and acts as an oxygen getter by reacting with the alumina in AIN to form YAG.

A computer-control program for TEM in situ fatigue experiments

1989 ◽  
Vol 47 ◽  
pp. 620-621
Author(s):  
Kenneth S. Vecchio ◽  
John A. Hunt
Keyword(s):  
Slow Crack Growth ◽  
Computer Control ◽  
Control Program ◽  
Video Tape ◽  
Computer Control System ◽  
Transmission Electron ◽  
In Situ Experiments ◽  
Tremendous Amount ◽  
And Control

In-situ experiments conducted within a transmission electron microscope provide the operator a unique opportunity to directly observe microstructural phenomena, such as phase transformations and dislocation-precipitate interactions, “as they happen”. However, in-situ experiments usually require a tremendous amount of experimental preparation beforehand, as well as, during the actual experiment. In most cases the researcher must operate and control several pieces of equipment simultaneously. For example, in in-situ deformation experiments, the researcher may have to not only operate the TEM, but also control the straining holder and possibly some recording system such as a video tape machine. When it comes to in-situ fatigue deformation, the experiments became even more complicated with having to control numerous loading cycles while following the slow crack growth. In this paper we will describe a new method for conducting in-situ fatigue experiments using a camputer-controlled tensile straining holder.The tensile straining holder used with computer-control system was manufactured by Philips for the Philips 300 series microscopes. It was necessary to modify the specimen stage area of this holder to work in the Philips 400 series microscopes because the distance between the optic axis and holder airlock is different than in the Philips 300 series microscopes. However, the program and interfacing can easily be modified to work with any goniometer type straining holder which uses a penrmanent magnet motor.

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