Bhatt, Ramakrishna T.

Raj, Sai V.

Singh, M.

NASA Technical Reports Server

NASA Aeronautics Research Institute 
Development of Engineered Ceramic  
Matrix Composites  
S. V. Raj1 (PI), R. Bhatt2 and M. Singh2  
1) Glenn Research Center, Cleveland, OH 
2) Ohio Aerospace Institute, Cleveland, OH 
Acknowledgements  
Technicians: Mr. Ray Babuder; Mr. Robert Angus; Mr. Ronald Phillips & 
Mr. Daniel Gorican  
Program Manager: Dr. Koushik Datta 
Funding: NASA’s ARMD Seedling Fund Phases I & II  
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
https://ntrs.nasa.gov/search.jsp?R=20140006748 2019-08-29T13:49:55+00:00Z
NASA Aeronautics Research Institute 
Introduction 
• Advanced aircraft engines require the use of 
reliable, lightweight, creep-resistant and 
environmentally durable materials. 
• Silicon carbide-based ceramic matrix composite 
(CMC) technology is being developed to replace 
nickel-based superalloy blades and vanes. 
 Near term 1589 K (2400 ºF) (cooled). 
 Medium term 1755 K (2700 ºF) (cooled). 
 
February 20, 2014 NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar 
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Factors Affecting Composite Properties 
 

Composites are engineered systems, whose properties depend on:  
• Fiber properties 
• Matrix properties 
• Interfacial properties 
• Volume fractions of the constituents 
• Processing 
• Fiber weave architecture 
• Fiber coatings 
• Protective coatings (e.g. EBCs, TBCs) 
MMCs & IMCs 
CMCs 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Typical Microstructures of As-Processed 
BN-Coated Hi-Nicalon MI SiC Composites 
Density ~ 96-97 % 
fiber 
SiC 
10 m 
Si 
SiC 
40 m 
Porosity 
(Courtesy M. Singh) 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Current SiC/SiC CMC Matrix Capabilities 
• Brittle at all temperatures. 
• No crack tip blunting – fast crack propagation. 
• No self-healing. 
• Oxygen ingress to fibers shortens fiber life. 
• Free Si in the matrix limits temperature usage 
(melting point of Si: 1687 K; 1414 ºC; 2577 ºF). 
• Matrix fills space and provides a 
thermally conductive path. 
• Fracture toughness due to crack 
bridging and interface debonding. 
• Relatively low matrix cracking 
strength - design < proportional limit  
SiC fibers 
SiC + Si 
matrix 
Crack 
Interface 
debonding 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Recession of BN and Formation of Glassy Phase 
in BN-Coated Hi-Nicalon MI SiC Composites 
T = 973 K;  = 250 MPa;1000 h in air 
2BN (s) + 3/2 O2 (g) = B2O3 (l) +N2 (g) 
B2O3 - SiO2: Low eutectic temperature of 372 ºC 
Glass 
5 mm 
BN 
10 m 
Glass 
(Courtesy M. Singh) 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Important Question 
 
Can the matrix constituents be suitably engineered to develop 
a new generation of Engineered Matrix (Ceramic) Composites 
(EMCs) with improved properties and tailored for a specific 
component?  
 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Crack Tip Blunting and Self-Healing 
SiC fibers 
Engineered 
matrix 
Crack 
Crack blunting 
due to matrix 
plasticity slows 
crack growth 
SiC fibers 
Engineered 
matrix 
Crack 
Self-healing of 
fine cracks 
minimizes 
oxygen ingress 
to fibers 
  
Increased  reliability and 
load carrying capacity 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Innovation and Expected Impact 
 High temperature matrix - greater than 1589 K (1315 ºC/2400 ºF) 
 Matrix plasticity - increased reliability, compliant matrix. 
 Chemical and thermal strain compatibility with the coated SiC fibers. 
 Self-healing matrix - prevents or minimizes oxygen ingress. 
 Low free Si - reduces fiber attack, reduces incipient melting, increased 
high temperature capability. 
 Dense matrix - high thermal conductivity.  
 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Historical Perspective 
Monolithic 
ceramics 
Ceramic matrix  
composites (CMCs) 
Engineered matrix  
composites (EMCs) 
Pre-1980s Current Concept 
Low toughness 
Low strength 
Higher toughness 
Higher strength 
Free silicon 
Crack blunting & 
self-healing 
Low free silicon 
Higher toughness 
Higher strength 
Higher temperature 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Technical Approach 
• Plasticity – Introduce a chemically stable metallic silicide.  
• Temperature capability – Choose silicides with melting points 
higher than that of Si (m.p. 1687 K; 1414 ºC; 2577 ºF). 
• Thermal expansion – Match thermal expansion of the 
engineered matrix (EM) with the SiC fibers. 
• Self-healing capability – Add constituents to heal cracks with 
low viscosity oxides or silicates. 
• Low Si – Melt infiltrate with silicide instead of Si. 
• Dense EMCs – Slurry infiltration and melt infiltration. 
 
 February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Silicide Additives 
• CrSi2 
• MoSi2 
• TiSi2 
• WSi2 
• CrMoSi alloy 
 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Matching Thermal Strains: 
 Theoretical Concept 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Matrix Design Concept 
Concept Vsilicide (%)  VSiC (%) VSi3N4 (%) 
Traditional 0 100 0 
Present 
investigation 
x (100-x-y) y 
(L/L0)fiber = (L/L0)EM = Vsilicide(L/L0)silicide + V SiC(L/L0) SiC+ VSi3N4 (L/L0) Si3N4 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Objectives 
 Evaluate different engineered matrices based on theoretical 
concepts. 
 Proof of concept: Demonstrate thermal strain compatibility 
with SiC. 
 Evaluate bend and oxidation properties. 
 Evaluate self-healing compositions. 
 Fabricate and test engineered matrix composites. 
 
 
 
 February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Matrix Processing Steps 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Hot-Pressed Plate and  
Optical Micrograph
50 x 50 x 4 mm Optical micrograph
CrMoSi/SiC/Si3N4 (CrMoSi-EM) 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Back Scattered Image and Energy Dispersion 
Spectra: CrMoSi/SiC/Si3N4 (CrMoSi-EM) 
Si 
C 
Si 
N O 
Si 
Mo 
Cr 
Cr Cr 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Proof-of-Concept: Thermal Strains 
Disilicides / 
(Cr,Mo)3Si 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Macrograph of the Surface of a Thermally Cycled 
CTE MoSi2/SiC/Si3N4 Specimen 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
• MoSi2/SiC/Si3N4 engineered matrix dropped from the program. 
NASA Aeronautics Research Institute 
Isothermal Oxidation Behavior of  
Engineered Matrices 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
TiSi2/SiC/Si3N4 and WSi2/SiC/Si3N4 engineered matrices dropped 
from the program  
NASA Aeronautics Research Institute 
Four-Point Bend Stress-Strain Curves for a  
CrSi2 Engineered Matrix 
Air tested 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
• Crack blunting due to crack tip plasticity increases bend strength  
NASA Aeronautics Research Institute 
Four-Point Bend Stress-Strain Curves for a  
CrMoSi Engineered Matrix 
Air tested 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
CT Scan and a Schematic of the  
BN-Coated SiC/SiC Preform 
CT Scan 
Schematic of 
void distribution 
 
Void volume 
fraction ~ 25% 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Steps in Engineered Matrix Composite Fabrication 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Epoxy pressure infiltration unit 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Microstructures of TiSi2-EM-Infiltrated  
SiC Fiber Preform  
Particulates 
Coated 
Preform 
Fibers 
tows 
Voids 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
CT Scans of TiSi2/SiC/Si3N4  
Particulate Epoxy and Si- Melt Infiltrated Preform 
Particulate 
Infiltrated 
Area fraction of 
porosity ~ 0.9% 
As-received 
Preform 
Area fraction of 
porosity ~ 21-23% 
Pyrolized 
Area fraction of 
porosity ~ 6.6% 
Si Melt 
Infiltrated 
Area fraction of 
porosity ~ 1.8% 
The red 
regions are 
voids 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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TiSi2/SiC/Si3N4 epoxy infiltrated preforms 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
400 m 
Bright Field Fluorescent 
Epoxy 
Particulates 
Porosity 
NASA Aeronautics Research Institute 
CrMoSi/SiC/Si3N4 Epoxy Infiltrated Preforms 
Epoxy – 
Particulate mixture 
Fibers 
Fibers 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Particulate and Silicon Melt Infiltrated 
SiC/SiC Preforms 
Si 
Unfilled 
Particulates 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Room Temperature Bend Stress-Strain Curves for 
CrMoSi EMCs 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Preliminary Studies:  
Bend Strengths of CrMoSi-SiC-Si3N4-Si EMCs 
unfilled 
Si 
Fibers 
Heat treated in air at 1600 K for 50 h 
Air tested 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Preliminary Studies:  
Bend Strengths of CrMoSi-SiC-Si3N4-SiGe EMCs 
Heat treated in air at 1600 K for 50 h 
Fibers 
SiGe 
unfilled 
Air tested 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Assessment of the Self-Healing Characteristics of 
Different Additives to CrMoSi-SiC at 1600 K  
• CrB2 addition shows the best ability to heal scratches 
Before Oxidation 
CrB2 
CrB2 
Ge 
Ge 
Y 
Y 
ZrSiO4 
ZrSiO4 
After Oxidation for 24 h 
Pre-drilled hole 
~ 1 mm dia.  
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Self-Healing of CrMoSi-SiC with 5%CrB2 at  
1700 K after 100 h  
Top Face 
1.0 mm 
Rear Face 
1.2 mm 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Self-Healing Characteristics of CrMoSi-SiC-
CrB2 Oxidized at 1700 K for 100 h 
Si 
O 
100 m 
Si 
O 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
NASA Aeronautics Research Institute 
Self-Healing Studies (in progress) 
Cracks emanating from a  
Vickers indent 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
Perform qualitative healing 
studies on indented matrices 
to demonstrate crack healing. 
NASA Aeronautics Research Institute 
Dynamic Loading Studies (in progress) 
Notched specimens will 
be tested in air and inert 
gas to demonstrate that 
the air-tested specimens 
are stronger than those 
tested in inert gas due to 
self-healing of cracks.    
NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  February 20, 2014  
X 
X 
Time 
S
t
r
e
s
s
 
Air 
Argon 
Proportional 
limit 
Fracture 
Fracture 
T = 1700 K 
NASA Aeronautics Research Institute 
Optical Micrographs of Single Edge Pre-
Cracked Beam (SEPB) Specimens Studies 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
Unoxidized Unoxidized 
Oxidized 
Top 
Surface 
Oxidized 
Bottom 
Surface
NASA Aeronautics Research Institute 
Cr-Si Binary Phase Diagram 
1414 0C 
1490 0C 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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CrSi2-Melt Infiltrated Tyranno SA Preforms 
CrSi2 
fibers 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Composition Analysis of the  
CrSi2-SiC Fiber Interface 
Cr 
Cr 
Si 
B 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
No reaction of CrSi2 with SiC – consistent with thermodynamic 
calculations 
NASA Aeronautics Research Institute 
Summary and Conclusions 
• A concept for developing a new class of high temperature engineered 
matrix composites (EMCs) with crack blunting, self-healing and low Si 
capabilities using intermetallic silicides is proposed.  
• The following concepts have been demonstrated: 
 Thermal expansion of the engineered matrix can be matched with that of SiC. 
 Increased matrix ductility can lead to higher bend strengths due crack blunting. 
 Promising self-healing additives have been identified.  
 CrSi2/SiC/Si3N4 and CrMoSi/SiC/Si3N4 engineered matrices have been identified for 
1589 K (2400 ºF) and 1755 K (2700 ºF).  
• Several new compositions have been formulated for further studies. 
• Fabrication of dense EMCs has proved to be challenging due to 
insufficient particle infiltration in the coated SiC/SiC woven preforms 
and due to poor capillarity action of the Cr-Si alloys.  
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Distribution and Dissemination 
• Applied for US Patent (May 30, 2013) –NASA Docket No:  LEW 18964-1 
Title:  Engineered Matrix Self-Healing Composites 
S/N: 13/905,333; Filed:  5/30/13 
Inventors: Sai Raj, Mrityunjay Singh, Ramakrishna Bhatt 
• S. V. Raj, M. Singh and R. Bhatt, “High-Temperature, Lightweight, Self-Healing 
Ceramic Composites for Aircraft Engine Applications”, NASA Tech Briefs, vol. 
37, No. 2, p. 40 February 2013;  
http://www.techbriefs.com/component/content/article/5-ntb/tech-
briefs/materials/15663-lew-18964-1. 
• S. V. Raj, M. Singh and R. Bhatt, “Preliminary Studies on the Development of 
Engineered Matrices for SiC Fiber-Reinforced Ceramic Composites”, 38th 
Annual Conference on Composites, Materials and Structures, Cocoa Beach, FL 
Jan 26-30, 2014 
• Journal paper submitted for DAA 1676 management approval. 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  
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Next Steps 
• The research has been transferred to ARMD’s Aero Sciences 
Program (FY 14). 
• Methods to increase particulate loading and silicide melt 
infiltration of the preforms are being studied. 
• Dynamic fracture toughness tests are underway to quantify the 
self-healing capabilities of several engineered matrices. 
• Bend and tensile creep tests of several engineered matrix 
specimens are planned. 
 
February 20, 2014  NASA Aeronautics Research Mission Directorate 2014 Seedling Technical Seminar  


Development of Engineered Ceramic Matrix Composites

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