Effect of Mechanical and Thermal Loading Histories on Residual Properties of SiCf/SiC Ceramic Matrix Composites

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Effect of Mechanical and Thermal Loading

Histories on Residual Properties of

SiC

f

/SiC Ceramic Matrix Composites

Presented at the 12th Pacific Rim Conference on Ceramic and Glass Technology (PACRIM 12)

May 21-26, 2017 Waikoloa, Hawaii

Research Supported by the NASA Transformational Tools and Technology Project

Amjad Almansour, Doug Kiser, and Craig Smith

NASA Glenn Research Center, Cleveland, OH

Ram Bhatt

Ohio Aerospace Institute (at NASA GRC), Cleveland, OH

Dan Gorican and Ron Phillips

Vantage Partners, LLC (at NASA GRC), Cleveland, OH

Terry McCue

SAIC (at NASA GRC), Cleveland, OH

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Motivation

Objective

Approach

Materials and Properties

Experimental Set Up

High-Temperature Results

Room-Temperature Results

Fracture Surface Analysis

Summary & Conclusions

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SiCf/SiC Ceramic Matrix Composites (CMCs) are candidates for high-temperature applications such as the new generations of aircraft engines for:

Reduced component weight (1/3 density of superalloys)

Higher temperature capability/increased thermal margin

Reduced cooling requirements

Improved fuel efficiency

Reduced emissions (NO

x

and CO

2

)

Motivation

Further increase with 2700°F CMC components

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Objectives

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 Evaluation of CVI SiC/SiC Composites for High Temperature Applications.

 Establish stress-dependent and temperature-dependent parameters for modeling SiC/SiC composite creep behavior.

 Assess durability at 2200°F (1200°C) to 2700°F (1482°C) in air while under different mechanical loadings for up to several hundreds of hours.  Determine post-creep retained mechanical properties.

Approach

 Conduct CMC constant temperature and stress creep, variable

temperature creep, variable stress creep and sustained peak low-cycle fatigue testing from 2200°F (1200°C) to 2700°F (1482°C)—with a limited number of specimens.

 Apply stresses below the onset of matrix cracking stress.

 Examine samples that survived during the 2700°F (1482°C) testing (run-out condition) and characterize their residual properties / integrity at

room temperature with the use of acoustic emission composites health monitoring technique.

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 2D CVI (chemical vapor infiltration) SiC/SiC reinforced with ~30% SylramicTM-iBN SiC fabric. ~11% Porosity

(Variable throughout samples).

Muiltilayered CVI-SiC Matrix.

 Machined tensile samples were CVI SiC seal-coated to seal the coupons’ edges.

 Made by Hyper-Therm (Rolls-Royce HTC Now)(via NASA LaRC-funded SBIR Phase II Contract NNX11CB63C).

Relevant material system, especially for 2700°F applications.

CMC Material

CVI-SiC Layers

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S2-4 (As-Fabricated Sample)

Prepped for Resistivity Measurement

2D CVI SiC/SiC Reinforced with Sylramic

TM

-iBN:

Testing at Room Temp.: As-Rec. and Following Creep in Air

Used various characterization approaches (Acoustic emission (AE), resistivity, hysteresis testing, metallography and fractography)

S2-6 (Post-creep)

Unique Acoustic Emission (AE) Set-up

25 m

m

25 m

m

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Determination of CMC Stress Dependence Creep at 2700 °F

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 50 100 150 200 250 300 350 Cr ee p Stra in , %

Exposure Time, Hours

Sylramic

TM

iBN/BN/CVI-SiC Creep in Air

2200 °F, 86.2 MPa

2D CVI SiC/SiC Reinforced with Sylramic

TM

-iBN:

Creep in Air— Results of 5 different testing conditions

• No failures occurred due to creep

• All tests were run-outs: discontinued as-planned

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2D CVI SiC/SiC Reinforced with Sylramic

TM

-iBN:

Creep and SPLCF in Air at 2700°F (1482°C)

S2-2 S2-1 S2-6

SPLCF, R = 0.5, 5 / 10 ksi

• Strain rate measured at end of each test

2700°F, 10 ksi for 100 hrs

2700°F, 12.5 ksi for 300 hrs

Held at T without loading following test to observe elastic creep recovery

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www.nasa.gov 9 0 0.05 0.1 0.15 0.2 0.25 0.3 0 50 100 150 200 250 300 350 C reep Str ai n , %

Exposure Time, Hours

SylramicTMiBN/BN/CVI-SiC Creep at 2700°F in Air

103.4 MPa 86.2 MPa

69 MPa

S2-3

10 Ksi 12.5 Ksi 15 Ksi

Determination of CMC Creep Stress-Dependence

2D CVI SiC/SiC Reinforced with Sylramic

TM

-iBN:

Creep in Air at 2700°F (1482°C)—

Exposed to 3 stresses

• Strain rate measured at end of each 100 hr segment Sample 100 hr 200 hr 300 hrVery similar to S2-1 creep curve

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2D CVI SiC/SiC Reinforced with Sylramic

TM

-iBN:

Creep in Air at 2700°F (1482°C)

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Determination of CMC Stress Dependence Creep at 2700 °F

y = 9.72E-17x3.48E+00 R² = 9.77E-01 1E-10 2E-10 4E-10 8E-10 1.6E-09 60 70 80 90 100 110 C reep Str ai n R ate, S -1 Stress, MPa

Sylramic/BN/CVI-SiC Stress Dependence at 2700 °F

= B

B is a constant =9.72 *10-15

n is the stress exponent ~ 3.5

10 Ksi

15 Ksi

12.5 Ksi

2700 °F 69 MPa 86.2 MPa 103.4 MPa Sample S2-3 C reep Strai n R ate at 100 h rs , S -1

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Determination of CMC Stress Dependence Creep at 2700 °F

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 50 100 150 200 250 300 350 Creep Strain, %

Exposure Time, Hours

SylramicTMiBN/BN/CVI-SiC Creep under 86.2 MPa in Air

2200 °F 2460 °F 2700 °F

S2-5

Examination of CMC Creep Temperature-Dependence at 2200-2700 °F

Held at 2700º F to assess creep

recovery (No Load); broke during cool-down

• Strain rate measured at end of each 100 hr segment 1200°C 1350°C 1482°C Sample Heating / expansion

2D CVI SiC/SiC Reinforced with Sylramic

TM

-iBN:

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2D CVI SiC/SiC Reinforced with Sylramic

TM

-iBN:

Creep in Air, 12.5 ksi (86.2 MPa)—Exposed to 3 Temperatures

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Determination of CMC Stress Dependence Creep at 2700 °F

y = -12849x - 13.423 R² = 0.9681 -22.4 -22.2 -22 -21.8 -21.6 -21.4 -21.2 -21 -20.8 -20.6 -20.4

5.50E-04 6.00E-04 6.50E-04 7.00E-04

LN( Creep Strain Rate) , S -1 1/T(K-1)

SylramicTMiBN/BN/CVI-SiC Temperature Dependence

2200-2700 °F under 86 MPa in Air

Slope = (− )/

R= Gas Constant= 8.314 J/K.mol Q= Activation Energy= 107 KJ/mol

13 2200°F 1200°C 2460°F 1350°C 2700°F 1482°C • Activation Energy is

dependent on when strain rate is measured (hrs of creep completed)

• Contribution from Primary Creep leads to low Activation Energy

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CMC Creep Dependence on Mechanical and Thermal Loading Histories

After: 12.5 ksi: 100 hrs at 2200°F, 100 hrs at 2460°F, 100 hrs at 2700°F

Example of How Measured Strain Rate Depends on Loading History

After: 100 hrs at 2700°F (10 ksi), 100 hrs at 2700°F (12.5 ksi) and 100 hrs at 2700°F (15 ksi) After: 12.5 ksi: 300 hrs at 2700°F S2 -6 S2 -3 S2 -5

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RT FF Tensile Tests with Hysteresis Loops Results

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 Post creep RT FF UTS results were similar to that for as-received sample.  No fiber degradation.

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Test Results Summary

 Samples from gage sections were cut and polished and crack

densities were measured.

 AE provided good estimate for the stress at the onset of CVI-SiC

matrix cracking.

Differences in the elastic modulus and matrix cracking stresses could be due to:

 Different creep and fatigue loading histories.

 Different porosity content.

 Difference in fibers content in loading direction.

Specimen ID

Test Condition (Temperature °F, Stress MPa, Time

Hours) Elastic Modulus, GPa Residual UTS, MPa Ultimate Creep Strain, % σth, MPA ρc, mm -1 Ultimate Strain, % Stress at Onset of Matrix Cracking, MPa Thickness, mm Fiber Content, % 1520-S2-1 2700 °F, 69 MPa for 100 Hours 302 341 0.15 50 9.53 0.26 145 2.53 15.69 1520-S2-2 2700 °F, SPLCF, R=0.5, 34/69 MPa for 100 Hours 365.9 355 0.12 60 9.35 0.18 163 2.62 15.15 1520-S2-3 2700 °F, 69 MPa for 100 Hours, 86 MPa for

100 Hours, 103 MPa for 100 Hours 281 311 0.26 55 8.11 0.28 157 2.5 15.88 1520-S2-4 RT Tensile test 261.7 341 0 40 9.16 0.33 119 2.73 14.54 1520-S2-5 2200 °F, 86 MPa for 100 Hours, 2460 °F, 86

MPa for 100 Hours, 2700 °F, 86 MPa for 100 Hours - Broke upon cooling 0.34 (0.2) - - - - 2.64 15.03 1520-S2-6 2700 °F, 86 MPa for 300 Hours 296 325 0.26 52 8.37 0.31 150 2.6 15.27

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RT Fast Fracture Tensile Tests Results:

Stress & Acoustic Emission Vs. Strain

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 Samples were cut from gage sections and polished, and crack densities were measured.

 AE provided a good estimate for the onset and progression of damage.

 Crack Density Evolution of SylramicTM

iBN/BN/CVI-SiC was obtained from the

multiplication of the normalized AE evolution by the measured CVI-SiC crack density at failure. Cracks linking up through-thickness AE Onset

90

° tow

AE Crack Density

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RT Post Creep Fast Fracture Tensile Tests Results

S2-1

S2-3

 Compressive residual stress values were obtained using the intersection of the tangents of the loading portions of the hysteresis loops*.

*Steen M, Valles JL. ASTM STP 1309. In: Jenkins MG et al., editors. West Conshohocken, PA: American Society for Testing and Materials; 1997. p. 49–65.

Crack Density Crack Density CVI-SiC Cracks CVI-SiC Layers Loading Direction

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AE Energy Evolution of Sylramic

TM

-iBN/BN/CVI-SiC with

Different Creep Loading Histories

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 AE provided good estimate for the onset and progression of damage.

 Absolute AE energy evolution of SylramicTM iBN/BN/CVI-SiC samples correlates with stress

dependent matrix cracking after different creep loading histories.

 Cracking evolution of SylramicTM-iBN/BN/CVI-SiC is dependent on the different creep loading

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Creep and Low-Cycle Fatigue at 2700°F Effect

on the Stress at the Onset of CVI-SiC Cracking

 Creep and low-cycle fatigue exposure at 2700°F (1482°C) induced additional compressive thermal residual stress on the CVI-SiC which may have caused the increase in the stress at the onset of CVI-SiC matrix cracking in post

creep FF testing.

• AE Onset~based on AE characterization of the onset of matrix cracking

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Fracture Surfaces

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2700 °F 69 MPa for 100 Hours 86 MPa for 100 Hours 103 MPa for 100 Hours Typical Limited Fibers pull-out

2700 °F SPLCF, R=0.5

34/69 MPa for 100 Hours Oxidation

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Summary and Conclusions

 CVI SiC/SiC CMCs incorporating SylramicTM-iBN SiC fiber were evaluated via tensile creep testing to determine creep parameters for modeling. A stress exponent was determined at 2700°F, and an activation energy was calculated.

 Post creep RT FF ultimate tensile strength results were similar to that for as-received samples (no fiber degradation).

 Acoustic emission energy data analysis provided a good estimate for the onset and evolution of damage during RT FF testing.

 Creep resistance differential between the constituents of SylramicTM-iBN/BN/CVI-SiC

induced compressive thermal residual stress, which may have caused the increase in the stress at the onset of CVI-SiC matrix cracking in post creep FF testing.

 Examination of fracture surfaces indicated CVI-SiC microcrack formation and oxidation during low cycle fatigue testing at stresses below the RT matrix cracking stress.

Figure

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