Performance of CVD Mullite Coatings on Silicon Nitride under High Temperature High Load Conditions

2005 ◽  
Vol 287 ◽  
pp. 457-470 ◽  
Author(s):  
S.M. Zemskova ◽  
Hua Tay Lin ◽  
Mattison K. Ferber ◽  
A.J. Haynes
Keyword(s):  
Silicon Nitride ◽  
Slow Crack Growth ◽  
Ambient Air ◽  
Fatigue Tests ◽  
Static Fatigue ◽  
Strength Increase ◽  
Test Procedures ◽  
Flexure Strength ◽  
Mullite Coatings ◽  
Dynamic Fatigue

Previous studies have demonstrated that dense coatings of CVD mullite (3Al2O3×2SiO2) provide excellent oxidation protection for Si3N4 and SiC in a high pressure, steam environment. In this study the mechanical properties of CVD mullite coated silicon nitride materials from different vendors (AS800, NGKSN88, Kyocera SN281) were evaluated following ASTM test procedures. The dynamic fatigue tests werep erformed in ambient air at temperatures of 850 and 1200°C under fast (30 MPa/s) and slow (0.003 MPa/s) load rates. The static fatigue tests were carried out at a constant load of 350 MPa for 1000h at 1200°C. The cyclic fatiguetests at 850°C consisted of a loading ramp from 20 to 400 MPa in 30 seconds followed by unloading ramp from 400 to 20 MPa. A total of 10,000 cycles were applied to the fatigue test specimens before fast fracture tests were conducted at room temperature. The strength test results indicated that CVD mullite coatings showed excellent adhesion during dynamic fatigue tests and exhibited no creep behavior. Minor flexure strength reduction observed at low stressing rate and at high temperatures appeared to be related to Si3N4 properties such as SCG (slow crack growth) susceptibility. During cyclic and static fatigue tests, a glassy silica/aluminosilicate phase was formed due to oxidation. This resulted in localized coating separation and buckling. However, accumulation of this corrosion layer was not critical since the coated specimens showed a flexure strength increase of ~7-9.5%.

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.

Slow Crack Growth of a Pyroceram Glass Ceramic Under Static Fatigue Loading: Commonality of Slow Crack Growth in Advanced Ceramics

2014 ◽  
Author(s):  
Sung R. Choi ◽  
D. Calvin Faucett ◽  
Brenna Skelley
Keyword(s):  
Crack Growth ◽  
Glass Ceramic ◽  
Life Prediction ◽  
Elevated Temperatures ◽  
Slow Crack Growth ◽  
Static Fatigue ◽  
Fatigue Data ◽  
Prediction Approach ◽  
Applied Stresses ◽  
Dynamic Fatigue

An extensive experimental work for Pyroceram™ 9606 glass-ceramic was conducted to determine static fatigue at ambient temperature in distilled water. This work was an extension and companion of the previous work conducted in dynamic fatigue. Four different applied stresses ranging from 120 to 170 MPa was incorporated with a total of 20–23 test specimens used at each of four applied stresses. The slow crack growth parameters n and D were found to be n = 19 and D = 45 with a coefficient of correlation of rcoef = 0.9653. The Weibull modulus of time to failure was in a range of msf = 1.6 to 1.9 with an average of msf = 1.7±0.2. A life prediction using the previously-determined dynamic fatigue data was in excellent agreement with the static fatigue data. The life prediction approach was also applied to advanced monolithic ceramics and ceramic matrix composites based on their dynamic and static fatigue data determined at elevated temperatures. All of these results indicated that a SCG mechanism governed by a power-law crack-growth formulation was operative, a commonality of slow crack growth in these materials systems.

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.

Slow Crack Growth of a Pyroceram Glass Ceramic Under Static Fatigue Loading—Commonality of Slow Crack Growth in Advanced Ceramics

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Sung R. Choi ◽  
D. Calvin Faucett ◽  
Brenna Skelley
Keyword(s):  
Crack Growth ◽  
Glass Ceramic ◽  
Life Prediction ◽  
Elevated Temperatures ◽  
Slow Crack Growth ◽  
Static Fatigue ◽  
Fatigue Data ◽  
Prediction Approach ◽  
Applied Stresses ◽  
Dynamic Fatigue

An extensive experimental work for Pyroceram™ 9606 glass–ceramic was conducted to determine static fatigue at ambient temperature in distilled water. This work was an extension and companion of the previous work conducted in dynamic fatigue. Four different applied stresses ranging from 120 to 170 MPa was incorporated with a total of 20–23 test specimens used at each of four applied stresses. The slow crack growth (SCG) parameters n and D were found to be n = 19 and D = 45 with a coefficient of correlation of rcoef = 0.9653. The Weibull modulus of time to failure was in a range of msf = 1.6–1.9 with an average of msf = 1.7 ± 0.2. A life prediction using the previously determined dynamic fatigue data was in excellent agreement with the static fatigue data. The life prediction approach was also applied to advanced monolithic ceramics and ceramic matrix composites (CMCs) based on their dynamic and static fatigue data determined at elevated temperatures. All of these results indicated that a SCG mechanism governed by a power-law crack growth formulation was operative, a commonality of SCG in these materials systems.

High Temperature Fatigue Properties of Silicon Nitride in Nitrogen Atmosphere

1992 ◽  
Vol 287 ◽  
Author(s):  
Yasuhiro Shigegaki ◽  
Takashi Inamura ◽  
Akihiko Suzuki ◽  
Tadashi Sasa
Keyword(s):  
Silicon Nitride ◽  
Fatigue Behavior ◽  
Cyclic Fatigue ◽  
Nitrogen Atmosphere ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Static Fatigue ◽  
Four Point Bending ◽  
Bending Mode ◽  
Sintered Silicon

ABSTRACTCyclic and static fatigue properties of pressure-less sintered silicon nitride were evaluated at 1000° C in air and in nitrogen using four-point bending mode. The data of cyclic fatigue tests or static fatigue tests and the morphology of the fractured surfaces in nitrogen were compared with those in air. The cyclic fatigue behavior was remarkably influenced by the atmosphere, while the static fatigue was less influenced. Crack healing effect due to the oxidation around the crack are thought to be the most probable mechanism to affect the cyclic fatigue rate in air.

Dynamic Fatigue of CVD-Mullite Coated SN88 Silicon Nitride

2003 ◽  
Author(s):  
H.-T. Lin ◽  
M. K. Ferber ◽  
T. P. Kirkland ◽  
S. M. Zemskova
Keyword(s):  
Silicon Nitride ◽  
Mechanical Testing ◽  
Mechanical Performance ◽  
Damage Zone ◽  
Surface Region ◽  
Lifetime Performance ◽  
Mullite Coating ◽  
Mullite Coatings ◽  
Dynamic Fatigue

Studies of dynamic fatigue were carried out on CVD-mullite coated and uncoated of SN88 silicon nitride at 850°C and at 30 MPa/s and 0.003 MPa/s in air. The objective of the studies was to evaluate the effect of thin CVD-mullite coatings on the mechanical reliability and lifetime performance of SN88 subjected to mechanical loading conditions. Mechanical results showed that the CVD-mullite coated SN88 samples exhibited similar strength degradation and lifetime performance to those uncoated samples under similar test conditions. SEM examinations of both coated and uncoated samples after mechanical testing also showed similar development of damage zone (i.e., pores and cracking were generated in SN88 surface region) due to oxidation reaction. Results of mechanical testing and SEM examinations indicated that the CVD-mullite coating could not environmentally protect SN88 to ensure a long-term mechanical performance and lifetime in gas turbine environments.

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.

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.

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