The thermal shock resistance of Si2N2O refractory material was studied. The thermal expansion coeff. is 3.55x10 to the -6th power at 20 to 800 C and 2.86x10 to the -6th power m/m/deg at 20 to 200 C. The breaking loads are high at high stress. Young's modulus E and the shear modulus G decrease linearly with increasing porosity. For dense material E sub o approx. = 216,500 N/mm2 and G approx = 90,600 N/mm2. The Vickers hardness of the dense material is comparable to that of sapphire. The results on thermal shock show that R, the breaking load, stays constant for T  T sub c, the first cracks appear and R decreases sharply for T=T sub c. As the severity of the thermal shock is increased at T  T sub c, a small no. of new, large-size cracks appears. The shock's cumulative effect is negligible, and repeated shocks do not change the cracks. The low values of the thermal expansion coefficient and Young's modulus and the high tension breaking load are considered. Sintered Si2N2O with 5% MgO shows excellent cracking resistance under thermal shock

Boch, P.

Glandus, J. C.

English

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JNASA TECHNICAL MEMORANDUM	 NASA TM-76665
THE THERMAL SHOCK RESISTANCE OF SILICON OX`_'NiTPIDE
J. C. Glandus and P. Boch
(NASA-Ttl-76665)
	
THERMAL SHOCK RESISTANCE OF	 N82-20249
SILICON OYYNITRIDE (National Aeronautics and
Space Administration) 12 F HC A02/BF A01
	
CSCL 11D	 Onclas
G3/i4 09391
Translation of "Etude de la r6sistance aux chocs thermiques de 1 1 oxy-
nitrure de silicium
t,
 , Silicates Industriels, Vol. 45, No. 2, 1980,
 pp. 45-48.
\` 4 
v9JG
APR 1°E2
RECEIVED
NASAill RAM
AOCESS WT.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
	 DECEMBER 1981
STANDARD TITLF PAGE
1.	 Report No. 2. Government Accession No. 3.	 Recipient's Catalog No.
NASA TM-76665
4.	 Title and Subtitle S. Report Date_
THERMAL SHOCK RESISTANCE OF SILICON December 1081
OXYNITRIDE d.	 Performing Organization Code
7.	 Auther(s) •.	 Performing Organization Report No.
J. C. Glandus and P. Boch _^
Center for Ceramic Research, Univ. . of 10.	 work Unit No
	
f
Limoges	 (France, I
9.	 Perlorm:ng Organization Nome and Address 11.	 Contract or Grnt Vo.
NASw-3541Leo Kanner Associates
1 3.	 Type of Report and Period Covered
ERedwood City, Californ ia 94063
Translation
	 f12. Sponsoring Agency Name and Address
National Aeronautics and Space Adminis—
tration, Washington, D.C.	 20546 id.	 Sponsoring Agency Code
15.	 Svpplementory Notes
Translation of "'Etude de la resistance aux chocs thermiques
de 1'oxynitrure de silicium", Silicates Industriels, Vol. 	 45,
No.	 2,	 1980,	 pp._45-48.
16.	 Abstract
The thermal shock resistance of Si 2N 20 refractory material
was • studied.	 The thermal expansion coeff. is 3.53x10 -6 at
20-800 and 2.86x10 -6 m/m/ 0 at 20-200 1 .	 The breaking loads
are high.at high stress. Young's modulus E and the shear mod-
ulus G decrerse linearly with increasing porosity.
	
For dense
material Eo = 216,500 N/mm 2 and G~90,600 N/mm 2 .	 The Vickers
hardness of the dense material is comparable to that of sap-
phire. • The exptl. results on thermal shock show that R, the
breaking load, stays const.
	
f-or T<Tc	 (Tc~225 0 ),	 the first
crack3 appear and R decreases sharply for T=Tc. -As the se-
verity of the thermal shock is increased at T>Tc, a small no.
of new,•large-size cracks appears.
	
The shock's cumulative
effect is ne ;-liSible, and repeated shocks do not change the
.cracks.
	
It ins difficult to describe quant. the degrdn. in-
duced by there,:al shock at T>Tc, but the low values of thermal
expan coeff, and Young's,'mod. 	 and the high tension breaking
lnAa Arp considered -	Sinferee	 Si-)N20 with 5% McrQ shnws excel-
lent cracking resistance un — 18.	 Distribution Statement
der thermal shock.
Unclassified - Unlimited
19.	 Security Clossil. (of this report) 	 20.	 Security Classil, (of this page) 11. No. of Pages :2.
Unclassified
	 Unclassified 12
or dell tin
	 i^
THE THERMAL SHOCK RESISTANCE OF SILICON OXYNITRIDE
J. C. Glandus and P. Boch
Laboratory of Vibrational Physics
Center for Ceramic Research
University of Limoges, France
1. Introduction	 /45*
Nitride ceramics are currently the subject of a large number of
studies because of their refractory characteristics [1]. Mainly
because of their mechanical performance at high temperatures, a vast
field of application awaits these new ceramics: Increasing the
efficiency of heat engines involves running them at as high a temper-
ature as passible, and in the majority of cases, the materials employed
are the limiting factor holding down that temperature.
At present, silicon carbide, SiC, and silicon nitride, Si3N4,
are the main candidates for such uses. Silicon carbide, which was
developed a long time ago, has reached a level of quality that seems
difficult to improve upon significantly. In contrast, the nitrides
are making rapid progress. Besides Si 3N4 , research is concentrating
on the SiAlON system: These "sialons" currently are a center of
attraction for those concerned with energy and high temperature
materials problems [1,2].
Alumina, &&1 203 , has many advantages: ease of production and
forming, good refractoriness, and perfect resistance in oxidizing
atmospheres. Unfortunately, its thermal shock resistance is mediocre,
which rules out its use in heat engines that often undergo extreme
temperature cycles. It is known [3] that, all other things being
equal, the higher the coefficient of thermal expansion is, the more
marked is the degradation provoked by thermal shocks. In this area,
Al203 does relatively poorly: Between 0 and 1000°C the average
*
Numbers in the margin indicate pagination in the foreign text.
value of a is 8 x 10 -6
 m/m/°C [4), compared to 4.5 [5] for SiC and
3 to 3.5 for the nitrides [6]. In addition, the higher the Young's
modulus is, the earlier the first cracks appear. Here again, Al2O3
does not do well: E = 400,000 N/mm 2
 [7), and SiC likewise:
E = 400,000 N/mm `
 [8], whereas the nitrides have more favorable
figures, less than 300,000 N/mm 2
 [9) -- these figures being for
completely nonporous materials. Let us add that in certain cases
the nitrides hold up well in the face of appreciable surface energies
[10). We are interested in this thermal shock resistance for a new
refractory material, silicon oxynitride.
2. Silicon Oxynitride
In contrast to oxides, which are stable in oxidizing atmospheres,
nitrides degenerate at high temperature in such atmospheres. The
advantage of silicon nitrides (and also of SiC) is that they act to
create a protective layer of silica. Along these lines, silicon
oxynitride, Si 2N 2O (which is located at one of the boundaries of the
SiAlON field), merits particular examination. This refractory
material first made its appearance in 1958 [11], but it was only in
1975 that it became a directly usable material, as a result of its
preparation in the form of high purity powders and the use of
sintering to mold it. The samples available to us were prepared by
the Limoges Laboratory of Mineral Chemistry and Heterogeneous
Kinetics (ERA no. 539), which was the group that perfected Si 2N 2O in
the first place [12,13]. The powder (95% Si 2N2O, 5% MgO) was sintered
under a load of 33 N/mm 2
 in a nitrogen atmosphere and at temperatures
that reached 1560°C. The cycle of sintering operations is schematized
in figure 1. It is thus possible to obtain a 100% densification.
	 /46
Unless specifically stated otherwise, our tests were conducted with
3
a dense material, p = 2.83 g/cm.
3. Experimental Techniques, Results, and Discussion
The study we made of Si 2N 2O's thermal shock resistance produced
a set of complementary measurements.
A
, n
2
Figure 1
1) The coefficient of thermal expansion was determined by differ-
ential dilatometry using prismatic test pieces with a 6 x 6 cm square
cross section, a length of 35 mm, and zero porosity. (This
coefficient is only very slightly affected by porosity [141). The
average value between 20 and 800°C was 3.55 x 10 -6 m/m/°C and
2.86 x 10 -6
 between 20 and 200°C (figure 2). This low figure ranks
with the smallest values found for the nitride family [6]. The
essentially covalent nature of the atomic bonding seems to account
for the small coefficient of expansion obtained [14].
A%.
L35mm 
a: 3,5 5.10
3-	 _
Figure 2
2) The breaking load was determined for compression and biaxial
bending (15). The latter stress led to the value for the tensile
breaking load (dc = 950 N/mm 2 ). The compression test specimens were
cubes 6 mm on a side, and those for biaxial beading were disks
30 mm in diameter and 2.5 mm thick. A Zwick 1461 machine was used
in both cases, with a deformation speed of 0.2 mm/min. The values
obtained for breaking were high for both compressive and tensile
stresses and comparable to those found for hot-pressed Si N 4 [101.
The material's surface energy was not measured, but this work is in
progress. For Si3N 4 , the value of y can reach 70 J/m 2 [1,10].
3) The elasticity moduli were evaluated with particular care,
and a detailed description of the results will be published elsewhere.
-- Measurements were made using an ultrasonic "pulse-echo
overlap" (PEO) technique [16] with transverse and longitudinal waves
at frequencies N of 6 and 10 MHz. The samples were cylindrical ones
(diameter: 20 mm, length: 16 mm).
-- A "phase comparison" ultrasonic technique [17] checked
samples similar to the ones used in the bending tests at N = 10 MHz
and 20 MHz.
-- These last test specimens (diameter: 30 mm, thickness: 2
to 3 mm) also participated in plate resonance tests [181, at
around 30 kHz.
-- Finally, the dilatometry test speciii.ens were used for making
bar resonance measurements, also at around 30 kHz.
This group of tests involved samples of varying porosity P
(0%, 0.3%, 3%, 8%, 9.[illegible]$, 12%, 16.5%, 21%, 26.5%).	 The
different techniques employed showed that the samples' anisotropy was
very slight, and that the material's texture did not have a preferred
orientation. Youn g's modulus E and the shear modulus G decreased
linearly as P increased:
G = 1-2.51 P.Go
The Poisson ratio u remained constant at 0.2.
For dense material:
Eo
 = 216,500 N/mm2 ;	 G = 90,600 N/mm2.
These low moduli (compared to those of Si 3N4 ) auger well for
the thermal shock resistance of Si2N2O.
4) The dense material's Vickers hardness was measured, and the /47
results were comparable to those obtained for a sapphire sample
under the same conditions.
SiN2O2
	 HV10N	 1,550
Sapphire
	 HvlON = 1,800
Other measurements have shown that the hardness increases when
the MgO additive is replaced by Y2O3.
5) The actual study of thermal shocks was carried out on the
samples (diameter: 20 mm, length: 16 mm) used for the PEO ultra-
sonic measurements. The specimens were exposed to increasing temper-
atures in an oxidizing atmosphere for a period of one hour. They were
then plunged into 20°C water and agitated.
The conventional technique for checking degradation engendered
by thermal shocks is to evaluate the breaking load R of test specimens
subjected to increasingly severe shocks. As long as the temperature
T remains below a critical value T c , R is constant. For T = T c the
first cracks appear and R decreases sharply [20]. For T > Tc,
Hasselman's theory gives a good explanation of cracking [211. This
technique has two disadvantages: The destructive tt-:sts require a
large number of samples, and it is impossible to examine the cumul-
ative effect of multiple shocks. We therefore limited such tests to
5
a few cases, preferring .instead to work with ultrasonic nondestructive
tests [22,231. The same sample underwent successive shocks, of
constant or increasing severity, and we measured the propagation
speed V  of longitudinal ultrasonic waves and the acoustic attenuation
A after each cooling in the water bath. We once again resorted to
the PEO method, this time at 6 MHz, for these measurements. Our
results were compatible with the preceding data [22,23), in that V 
was not appreciably affected by thermal shocks, in contrast with
A. Figure 3 shows that for dense Si 2N 20, A does not vary (0.4 dB/us)
until Tc = 225°C, where it registers a sharp increase (A = 2.4 dB/us).
The attenuation remains constant as T increases above Tc . Crack
detection confirmed that cracking appeared at Tc : There were a
few .large cracks extending across the sample. As the severity
of the shocks increased, new cracks appeared at T > Tc . They
were still few in number and of large size. Repeated shocks did
not appreciably alter the cracking, which agrees with Hasselman's
conclusions [211. We have started to check the damage caused by
destructive compressive stress breaking tests. The usual appearance
	 +
of the curve obtained is given in figure 4. It has been pointed out
that a certain amount of porosity has a beneficial effect on thermal
shock resistance [24]. We therefore testes: samples with P = 8% and
16.5% (figure 3). The values obtained for Tc did not differ signif-
icantly from those observed in the dense material.
aldbtysl -- --- — ----T-- — T— —
• P 0'a	 o
• P 8'X	 /p--b—o 	 •o
• P 16 5,.	 J	 •	 s
A7—	 _ _ _ _•,^ i ^^
	 Fig .3
o
tco	 '.200	 300	 ^4no	 Tc VC),
Figure 3
6
Xc
o
2	 Fig.4
io	 J00	 2oo	 t3oo Tl°C)
Figure 4
Calculation of the critical temperature T  was based on the
sample's thermal and mechanical characteristics. T  does not play
a direct role; rather it is the difference T 
	
Tbath - AT  that
does. In fact, it has been mentioned [25] that dipping a sample at
temperature T in water leads to a AT = T - 100. The boiling point
of water imposes a temperature of 100°C on the sample's surface, and
the initial temperature of the bath is irrelevant. The relationship /48
between AT  and the other parameters is given by [26]:
AT	 at ( 1-v)	 (at, v, E, and a have already been defined.)
c	 3EaT	 t
y -1 = 1.50 + 3 'S 5 - 0.5exp S6,
a = hd/k (a = Biot number, h = coefficient of thermal exchange,
d= average dimension of the sample, k = thermal conductivity). For
dipping in water, h = 1 CGS unit [25,20]; d = 0.8; measurement of our
sample's thermal conductivity is in progress, but for impure i2N2O,
a figure of k = 1.38 x 10 -3 cal-cm-1 - O C -1 - sec - l has been obtained [27],
which is a low value. This leads to B > 500. The thermal shock is
thus very sharp, and T = 1. Here, therefore, oT c = 125°C, which
implies that a t = 287 N/mm 2 , which is in very reasonable agreement
with the value of 250 N/mm 2 found in biaxial bending. The term
W.
7
AT  characterizes the "initiation" of the crack, and must be
considered for parts in which no degradation is tolerable. The
actual degradation engendered by a shock at T > T  is difficult. to
describe quantitatively. Meanwhile, the area of the cracks remains
the least arbitrary method of evaluation. We have undertaken such
measurements, and they will complete those of surface energy, which
are also in progress.
While awaiting these results,it is possible to argue that, given
its smell coefficient of thermal expansion, its low Young's modulus,
and its high tensile breaking load, silicon oxynitride that contains
5% MgO and is scintered under load is a refractory material with
excellent resistance under thermal shock.
4. Acknowledgement s
	i
This study would not have been possible without the samples
prepared by Mr. Dumazaud, the description of them done by the
University Center for Electron Microscopy, and the aid received
from Dr. Goursat and Prof. Billy. This work was done under a
contract with the Ministry of Industry and Research.
8
REFERENCES
1. For example: NATO Advanced Study Institute, Canterbury, G.B.,
1976.
2. For example: "Mechanical Properties of Ceramics", Numbers 22
and 25, British Ceramic Society, 1973 and 1975.
3. Hasselman, D.P.H., Am. Ceram. Soc. Bull. 49, 1033 (1970).
4. Gitzen, W.H., "Alumina as a Ceramic Material", Chapter 6,
American Ceramic Society, 1970.
5. Restall, J.E. and C.R. Gostelow, In: "Mechanical Properties of
Ceramics", Number 22, British Ceramic Society, 1973.
6. Wills, R.n., R.W. Stewart, and J.M. Wimmer, Am. Ceram. Soc. Bull.
55/11, 975 (1976).
7. Anderson, O.L. and R.C. Liebermann, Physical Acoustics, Volume IV,
Part B, Chapter 16, Academic Press, 1968.
8. Rosinger, H.E., I.G. Ritchie, and A.J. Shillinglaw,_Katerials
Science and Engineering, 16, 143 (1974).
9. Glandus, J.C. and P. Boch, "Elastic and Anelastic Properties of
Some Nitrogen Ceramics", NATO Advanced Study Institute, Canter-
bury, G.B., 1976.
10. Lange, F.F., J. Am. Ceram. Soc., 56/10, 518 (1973).
11. Forgeng, W.D. and B.F. Decker, Trans. Metall. Soc. A.I.M.E.,
212/3, 343 (1958).
12. Mary, J.P., P. Lortholary, P. Goursat, M. Billy, and J. Mexmain,
Bull. S.F.C., 105/3 (1974).
13. Lortholary, P., Thesis for the University of Limoges, 1975.
14. Kirby, R.K., "Mechanical and Thermal Properties of Ceramics",
Wachtman N.B.S. (1969).
15. Wachtman, J.B., W. Capps, and J. PZandel, J. of Mat., 7/2,
188 (1972).
16. Papadakis, E.P., J. Acous. Soc. Am., _'2/3 (1972).
17. McSkimin, H.J., J. Acous. kn., 34, 404 (1962).
18. Nardzewski, J.R., Rev. Roum. Sci. Techn., 15/5, 1079 (1970).
19. Glandus, J.C., and P. Boch, C.R.A.S. Paiis A2275, 1972.
20. Hasselman, D.P.H., J. Am.Ceram. Soc., 53/9, 490 (1970).
21. Hasselman, D.P.H., J. Am. Ceram. Soc., 52/11, 600 (1969).
22. Coppola, J.A. and R.C. Bradt, J. Am. Ceram. Soc., 56/4, 214 (1973).
23. Boisson, J., F. Platon, and P. Boch, Ceramurgia, 2, 74 (1976).
24. Hasselman, D.P.H., J. Am. Ceram. Soc., 52/4, 215 (1969).
25. Davidge, R.W. and G. Tappin, Trans. Brit. Ceram. Soc., 66/8, 405
(1967) .
26. Mai, Y.W., J. Am. Ceram. Soc., 59/11, 491 (1976).
27. Washburn, M.E., Am. Ceram. Soc. Bull., 46/7, 667 (1967).
uo
10


Thermal shock resistance of silicon oxynitride

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