● Development of oxide-based ceramic matrix
composites with high thermal stability
Advanced Materials Research Laboratory, TOSOH Corporation

Yushi NAWATA
Ikuya OHTA
Yo HIRATAKA
Isao YAMASHITA

tolerance of CMCs is achieved by clack deflection along

1．Introduction

the weak fiber–matrix interface, uncollected fiber failure

Ceramic matrix composites (CMCs) exhibit anand energy dissipation during fiber pullout.

interesting combination of low density, damage

Oxide-based CMCs (Ox/Ox) composed of oxide

tolerance, and high-temperature mechanical properties.

fibers and an oxide matrix involve a simpler preparation

Thus, these materials have potential application inprocess, have a lower cost, and exhibit good corrosion

thermal resistance materials, aircraft engines, andresistance compared to SiC-based CMCs6. Thus, Ox/

power generation turbines as conventional nickel superOx are promising for high-temperature applications in

1–3alloys.

For aircraft gas turbine engines, the efficiency

various oxidizing environments7.

improvement obtained using CMCs is 〜6.5% due toHowever, the primary limitation of Ox/Ox in

fuel efficiency improvements, and approximately 100

practical applications is their thermal stability. Previous

million tons of CO 2 reduction is expected by 2035
due to the use of CMCs4. Figure 1 shows monolithicceramics and CMCs after performing a nail penetration
test. The monolithic ceramics exhibit fully brittle
failure; however, the CMCs maintain their shape dueto their high damage tolerance. Figure 2 shows thedamage tolerance mechanism of the CMCs. Three
microstructural concepts are considered for enabling

Monolithic ceramics

Fig.１

crack deflection at fiber–matrix interface5. High damage

CMCsNail penetration test

CoatingDebond
crackMatrix（b）Pullout

Porousmatrix
DebondcrackMatrix crack（c）Debonding ／ sliding

Interfacegap（a）

Fig.２（d）
5Damage tolerance mechanism of CMCs85

TOSOH Research & Technology Review Vol.66（2022）

commercially available Ox/Ox degrade after long-doping element in mullite fibers. The doped element

term thermal exposure at up to 1200 ℃. The bending

is distributed uniformly and segragated in the grain

stresses of UMOXWHIPOXTMTM(EADS Innovation Works),

boundary.

(DLR), and OXIPOL (DLR) are reduced

by approximately 20%–50% after thermal exposure

Non－treated fiber

at 1200 ℃ temperatures for 50 h 8. Additionally, thetensile strength of Ox/Ox (Composite Horizons, 3M

Grain

Company, and Axiom Materials, Inc.) are reduced by〜 25% after being exposed to a temperature of 1200 ℃

Thermalexposure

9for 500 h . The tensile strength of N610/AS and N720/

Grain growth⇒ Strength reduction

AS (ATK-COIC) is reduced by approximately 68%–79%

UDM－treated fiberafter exposure at 1200 ℃ for 100 h10 and that of N720/
A (ATK-COIC) is reduced by 12% after exposure at 1200

As－received fiber℃ for 1000 h11,12. The tensile strength of Nextel610 /dopinginhibitor
element
Suppression of grain growth⇒ Keep Strengthmonazite/alumina composite (Air Force ResearchLaboratory) is reduced by 38% after exposure at 1200 ℃
for 1000 h13. The degradation of Ox/Ox after thermal

Fig.３

Concept of uniform doping methods（UDM）

exposure is due to the enhancement of the fiber–matrix
interface bonding and, most importantly, thermal

Fiber surface

degradation of the reinforcing fibers. Fiber degradationDopingelement

due to grain growth is the most essential problem foroxide fibers. The size of crack inducing flaws correlate
well to the grain size of oxide fibers. Fiber strength ofNextel 610, Nextel650, Nextel720 (3M Company) is
clearly affected by grain size14.

Inside the fiberThus, we have developed the uniform doping method(UDM) to suppress the grain growth of oxide fibers
and novel Ox/Ox that exhibit high thermal stability.
In this report, the proposed UDM for oxide fibers andFig.４

High resolution TEM－EDS mappingof doping element in mullite fiber

the mechanical properties of the developed Ox/Ox aresummarized. The purpose of our development is toFigure 5 shows the relative single-filament tensile

achieve Sustainable Development Goal 7 (Affordable

strength of fibers treated using the proposed UDMand Clean Energy) and contribute to society bycompared to untreated fibers. The tensile strength ofproviding novel Ox/Ox.

fibers was evaluated following JIS R1657. Here, weapplied UDM treatment to alumina fiber and mullite

2．Proposed UDM for oxide fibersfiber. The tensile strength of the alumina and mullite
fibers was improved after thermal exposure at 1300

The proposed UDM is based on the uniform doping℃ for 100 h with the proposed UDM. Figure 6 showsof a grain growth inhibitor element into ceramics fibera scanning electron microscope (SEM) image of the(Figure 3). During thermal exposure, grain growthsurface of UDM-treated alumina fiber after thermal

occurs, which reduces strength, and the fibers treatedexposure at 1300 ℃ for 100 h and a SEM image ofby the proposed UDM exhibit suppressed grain grown

the untreated fiber. Many abnormal grain growths

and retained strength. Figure 4 shows a high-resolution

are observed in the untreated fiber, whereas thetransmission electron microscopy with energy-

suppression of grain growth can be observed in thedispersive spectroscopy (TEM-EDS) mapping of thefiber treated by the proposed UDM.

86

東ソー研究・技術報告第 66 巻（2022）

Non－treated fiber
Relative fiber strength（UDM－treated ／ non－treated）

1.5

After1300℃－100h thermal exposure

1.4
1.3
1.2
1.1

UDM treated fiber

1.0
0.9
0.8

Fig.５

Alumina fiber

Mullite fiber

Relative fiber strength after thermal exposure
at 1300℃ for 100h

Fig.６

Surface appearance of alumna fiber
after thermal exposure at 1300℃ for 100h

Top view
80mm
220mm

MatrixSectional view

MatrixFiber

Fiber bundle

2mm

Optical microscope image

Fig.７

SEM－EDS image

Optical image and microstructure of Ox／Ox using UDM－treated fiber

3．Appearance and microstructure of Ox/Ox
using UDM-treated fibersof the test specimen. Here, TCA-01 is an alumina fiberbased CMC, and TCM-01 is mullite fiber-based CMC
using UDM-treated fibers. In this study, density of theOx/Ox were developed using UDM-treated fibers

composite was measured following the Archimedes

and an alumina-based matrix fabricated by slurry

method, and the tensile modulus, tensile strength, andinfiltration and sintering process. Figure 7 shows

proportional limit (0.05% offset) were evaluated following

optical and SEM-EDS images of a fabricated plate type

the American Society for Testing and Materials (ASTM)

of Ox/Ox. The plate of five woven layers Ox/Ox had

C1275 standard. Tensile tests were carried out using a220 by 80 mm rectangular shape with a thickness of
2 mm. Additionally, matrix phase filled between thepiled woven layers and inside the fiber bundles. The
developed CMCs can be fabricated into various shapes,e.g., a cylindrical shape (Figure 8 ), using slurry
infiltration and sintering process.

4．Mechanical properties of Ox/Ox at roomtemperature
The mechanical properties at room temperature of
the developed Ox/Ox are given in Table 1. Figure 9shows stress–strain curves and shape and dimension

Fig.８

Cylindrical shape of Ox ／Ox87TOSOH Research & Technology Review Vol.66（2022）

Table１

Mechanical properties of Ox ／Ox using UDM treated fiber at room temperature

Young’s
Proportional
Densitymodulus1）
limit1）2）
3［g ／cm ］
［GPa］
［MPa］
2.75
73290
TCA－01（Alumina fiber－based）
2.62
64
140
TCM－01（Mullite fiber－based）
CMC

Tensilestrength1）
［MPa］
295
1831）Following ASTM C1275，2）0.05％ Offset Method，350
TCA－01Stress［MPa］

300
250
200

TCM－01150100
50000.001

0.002

0.003

0.004

0.005

0.006

Strain（a）Stress－strain curves（b）Appearance of tensile test specimenFig.９(a) Stress-strain curves of Ox/Ox and (b) appearance of tensile test specimen

screw-driven type universal mechanical test machine
TM(MTS Criterion

20 mm

Model 45 MTS Systems Corporation)

Ox/Ox exhibited low thermal conductivity (5.6 W/(m·K) for TCA-01, 3.3 W/(m·K) for TCM-01) .

and a strain gauge (Model 632.13F-20 MTS SystemsCorporation). Here, the constant displacement rate
was 0.50 mm/min. Dog bone shaped specimens (200mm total length with an 8-mm wide gauge section and a

5．Mechanical properties of Ox/Ox at hightemperature

thickness of 2 mm) were used. In TCA-01, Young’s

High-temperature (1200 ℃) tensile tests weremodulus is >70 GPa, and the tensile strength andconducted based on the ASTM C1359 standard in air

proportional limit is >250 MPa. In TCM-01, Young’s

using mechanical test machine (MTS808 MTS Systems

modulus is >60 GPa, the tensile strength is >150 MPa,

Corporation) and a strain gauge (MTS632.59F-71 MTS

and the proportional limit is >100 MPa. Furthermore,System Corporation). The constant displacement rate

thermal conductivity of the developed Ox/Ox waswas 3.00 mm/min. The mechanical properties of thecalculated from thermal diffusivity evaluated followingOx/Ox at 1200 ℃ are listed in Table 2. Figure 10

ASTM E1461, specific heat, and density. The developed

shows stress–strain curves of TCA-01 and TCM-01. The

Table２Mechanical properties of Ox ／Ox using UDM－treated fibers at 1200℃

Young’s
Proportionalmodulus1）
limit1）2）
［GPa］
［MPa］
83
92
TCA－01（Alumina fiber－based）
56
130
TCM－01（Mullite fiber－based）
CMC1）Following ASTM C1359，2）0.05％ offset method，

88Tensilestrength1）
［MPa］
188
177

東ソー研究・技術報告

The fracture surface clearly exhibits uncorrelated fiber

250
Stress［MPa］

第 66 巻（2022）

200

TCA－01

failure and bundle unite fiber pull-out. Thus, both of the150

TCM－01developed oxide-based CMCs exhibit damage tolerance
after thermal exposure at 1200 ℃ for 1000 h. Figure100

13 shows tensile strength as processed and retention

500

rate of tensile strength after thermal exposure of TCM0

0.001

0.002

0.003

0.004

0.005

0.006

StrainFig.10

Stress-strain curves of Ox/Ox at 1200℃shape of the test specimen was the same as that usedin the room temperature test. The tensile strength and

01 and previous commercially available Ox/Ox usingmullite fiber. TCM-01 shows higher retention rate oftensile strength than that of others, and high tensile
strength as processed.

7．Notch sensitivity test of Ox/Ox

proportional limit of TCA-01 is degraded compared toA notch sensitivity test of the Ox/Ox after thermal

the results obtained in the room temperature test. Theexposure at 1200 ℃ for 1000 h was also conducted using

tensile strength of TCM-01 at 1200 ℃ was almost same

tensile specimens containing double-edge notches, as

as that that of TCM-01 at room temperature.

shown in Figure 14(a). Figure 14(b) shows the relativetensile strength of the notched and unnotched Ox/

6．Thermal exposure test of Ox/Ox

Ox at different 2a/W (a: notch length and W: specimenwidth) and the theoretical curve of the relative strength

A thermal exposure test was also performed usingof monolithic ceramics. Note that the strength ofdog bone shaped specimens 200 mm total length withmonolithic ceramics depends on the size of the defects

an 8 mm wide gauge section and a thickness of 2 mma( σ ＝ KI f wπaa( ) , K is stress intensity factor, f ( w ) isI

at 1200 ℃ for 1000 h in air. Here, the temperatureshape function) 15 ; thus, the relative strength ofduring thermal exposure was controlled precisely using

monolithic ceramics decreases rapidly as 2 a / W

an R type thermocouple. Figure 11 shows the tensile

increases. Here, no remarkable reduction in thestrength of developed Ox/Ox as processed and after

relative tensile strength of the developed Ox/Ox was

thermal exposure at 1200 ℃ for 1000 h. No remarkable

observed with 2a/W. Thus, these results confirm that

reduction in tensile strength was observed for both

the developed Ox/Ox exhibit damage tolerance after

TCA-01 and TCM-01 after 1200 ℃ for 1000 h. Retention

thermal exposure at 1200 ℃ for 1000 h.

rates of TCA-01 and TCM-01 are 96% and 103%. Figure
12 shows the fracture surface of the tensile test
specimens after thermal exposure at 1200 ℃ for 1000 h.

TCA－01350Tensile strength［MPa］

300

Retention rate：96％

As processed
After 1200℃－1000h

250
Retention rate：103％

200

TCM－01150
100
500Fig.11

TCA－01

TCM－01

Tensile strength of developed Ox/Ox as processed
and after 1200℃ for 1000h thermal exposure

Fig.12Fracture surface of tensile test specimen after
1200℃－1000h

89

TOSOH Research & Technology Review Vol.66（2022）

Retention rate of tensile strength［％］120

Mullite fiber based Ox ／ Ox
TCM－011200℃－1000h

10080

N720A
COIC
1200℃－1000h11,1260

N720 OxOx
3M Axiom C.H.
1200℃－500h940200

N720/ASCOIC
1200℃－100h10
100150200250Tensile strength as processed［MPa］

Tensile strength as processed and retention rate of tensile strength after thermal
exposure of TCM-01 and previous commercially available Ox/Ox using mullite fiber

Relative tensile strength［－］(Net strength of notched CMC/Unnotched)

Fig.13（a）Fig.14

1.2
1
0.8
0.6

TCA－01
TCM－01Monolithic ceramics

0.4

Theoretical curve σ∝1/√a0.2
00（b）

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

2a/W［－］(a)Schematic of test specimen(b)Notch sensitivity of Ox/Ox after thermal exposure at
1200℃-1000h and theoretical curve of monolithic ceramics,

8．Conclusion

developed Ox/Ox can be employed in energy relatedmaterials, particularly thermal resistance materials,

In this report, we have described a method toaircraft turbines, and power turbines, where long-term

improve the thermal stability of oxide fibers and thethermal stability and high mechanical properties aredevelopment of two oxide-based CMCs that exhibit highrequired.

thermal stability. We found that TCA-01 demonstrated
high tensile strength and proportional limit (>250 MPa)at room temperature, and TCM-01 maintained a highAcknowledgments

tensile strength and proportional limit even at 1200 ℃.

The authors thank Professors Yutaka Kagawa andAdditionally, the developed CMCs did not demonstrate

Yoshihisa Tanaka at The Center for Ceramics Matrix

a reduction in tensile strength after thermal exposure atComposites at Tokyo University of Technology for

1200 ℃ for 1000 h. The developed Ox/Ox also exhibitedthe use of their evaluation equipment and useful

low thermal conductivity (5.6 W/(m·K) for TCA-01,discussions.

3.3 W/(m·K) for TCM-01). Thus, we consider that the90東ソー研究・技術報告第 66 巻（2022）

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