The operation of rocket engine turbine pumps is limited by the temperature restrictions of metallic components used in the systems. Mechanical strength and stability of these metallic components decrease drastically at elevated temperatures. Ceramic materials that retain high strength at high temperatures appear to be a feasible alternate material for use in the hot end of the turbopumps. This project identified and defined the processing parameters that affected the properties of Si3N4, one of candidate ceramic materials. Apparatus was assembled and put into operation to hot press Si3N4 powders into bulk material for in house evaluation. A work statement was completed to seek outside contract services to design, manufacture, and evaluate Si3N4 components in the service environments that exists in SSME turbopumps

Hall, W. B.

English

NASA Technical Reports Server

Prepared By:
Academic Rank:
University and Department:
NASA/ASEE SUMMER FACULTY RESEARCH FELLOWSHIP PROGRAM
MARSHALL SPACE FLIGHT CENTER
THE UNIVERSITY OF ALABAMA
STRUCTURAL APPLICATION OF HIGH STRENGTH,
HIGH TEMPERATURE CERAMICS
William B. Hall, Ph.D.
Professor
Mississippi State University
Department of Chemical Engineering
NASA/MSFC:
Division:
Branch:
MSFC Counterpart:
Date:
Contract No:
Non-Metallic
Ceramics & Coatings
Marshall King
August 9, 1982
NGT 01-002-099
The University of Alabama
XVlII-i
https://ntrs.nasa.gov/search.jsp?R=19830009106 2020-03-22T00:14:37+00:00Z
STRUCTURALPPLICATIONOF
HIGHSRENGTH,HIGHTEMPERATUREC RAMICS
BY
William B. Hall, Ph.D.
Professor of Chemical Engineering
Mississippi State University
Mississippi State, Mississippi
ABSTRACT
The operation of rocket engine turbine pumps is limited by the
temperature restrictions of metallic components used in the systems.
Mechanical strength and stability of these metallic components decrease
drastically at elevated temperatures. Ceramic materials that retain
high strength at high temperatures appear to be a feasible alternate
material for use in the hot end of the turbopumps. This project
identified and defined the processing parameters that affected the
properties of Si_ N4, one of the candidate ceramic materials. Appa-
ratus was assembled and put into operation to hot press Si 3 N4 powders
into bulk material for in house evaluation. A work statement was com-
pleted to seek outside contract services to design, manufacture, and
evaluate Si^ N components in the service environments that exists in
4
SSME turbopumps.
XVIll-ii
INTRODUCTION
The Space Shuttle Orbiter is the heart of NASA'sspace transpor-
tation system during the decadeof the eighties. This reusable vehicle
trims the cost of space travel while increasing NASA's capabilities in
space. The system can carry a crew of three, four scientists, and a sixty
five thousand pound load into orbit. This Orbiter returns to earth like
an airplane and it is anticipated that it can makeone hundred round
trips into space and back. Although the Shuttle System utilizes the most
advanced aerospace technology available to date to achieve economical
and useful space flight, it is anticipated various improvementswill be
madeon the system as experience is gained and new technologies emerge.
Marshall Space Flight Center has the main responsibility for the Space
Shuttle main engine and solid rocket boosters used in this system.
One area in which improvement is desired is in the high-pressure
turbopumps, both fuel and oxidizer, in the Space Shuttle main engine.
The operation of these pumpsis limited by temperature restrictions of
the metallic componentsused in these pumps. Spot melting, oxidation,
and erosion-corrosion are someof the problems encountered in the turbo-
pumps.
High strength refractory ceramics are being considered for use as
structural materials in these turbopumps. This will alleviate the prob-
lems mentioned above and in addition permit a several hundred degree
fahrenheit increase in operational temperatures. This increase in tem-
perature will increase the overall efficiency of the space shuttle main
engines, which in turn will permit a larger pay load. This ceramic
material which appears to have the best possibility of being utilized is
silicon nitride, Si 3 N4.
XVIII-I
OBJECTIVES
The objectives of this two year study were:
l.
o
Identify and define the processing parameters that affect the properties
of Si 3 N 4 ceramic materials.
Design and assemble equipment required for processing high strength
ceramic.
.
.
Design and assemble test apparatus for evaluating the high temperature
properties Si 3 N 4.
Conduct a research program of manufacturing and evaluating Si 3 N 4
materials as applicable to rocket engine applications.
ENGINEERING ANALYSIS
Silicon nitride has the desired properties for utilization as a high
temperature structural material. These properties include high strength,
low coefficient of friction, high decomposition temperature, good corrosion
resistance, good oxidation resistance, high wear resistance and good ther-
mal shock resistance. These positive features have been known for two
decades and slowly silicon nitride is approaching the fulfillment of its
potential. Two problems have slowed the use of silicon nitride. The first
is the fabricating of suitable or useful shapes with the desirable proper-
ties. The second is the brittleness of silicon nitride, and indeed, all
ceramic materials. Traditionally, all engineering design compromises on
the selection of a material to use in an application, taking into conside-
ration the total cost of a material and the use properties of that material.
The evaluation of these compromises in design generally show that a metal-
lic material has a higher net profit. Because of this, there is very little
design experience with structural applications of silicon nitride or other
brittle ceramics. It is being considered at this time because of the great
need for the potential of Si_ N and the development of computer capability
4
to define the stresses as required for brittle material design.
PROCESSING PARAMETERS
There are three basic methods of forming bulk Si 3 N 4. The first of
these three is called "reaction-bonded" Si_ N_ whereby formed piece of
ressed s11icon owder ..... _ 4
P o " p s Is nltrlded in nltrogen gas in the range of 1300-
1400 C. During this nitridation process, the silicon powders are reacted
with N 2 gas to form a mixture of _- and S-Si_ N 4. The second method is
l! V!
called hot-pressed Si N This process entails the nitriding of Si
3 4"
powders to form _-Si N powders. These Si 3 N powders are mixed with de-4
sirable additives an_ t_en pressed into a compact in a graphite mold, under
2 o
a pressure of 1-2 tons/in , at a temperature of 1700-1800 C. This results
in a high strength, high density S-Si_ N 4 product. The third process is
called "sintered" Si_ N 4. In the sin_ered product, _-and/orSSi_ N 4J
powders are mixed wi_h desirable additives and then pressed into the
desired shape. This pressed bulk is then sintered in a controlled
XVIII-2
atmosphere at 1800-1911°C for a considerable length of time. The product
i!n!_!:d:!!!!_gr_Ptu![!!i°_!_;ii!!!!Y aeBnS-diSnith3SeNnt4ingi!a_ !i!na_!d!! :!i! d
oS_flig_dnil!yden_ilS :h°nlg200Octrr°g m tedPtheantU_el_ndo_mSrtre_g;hd .falslince
reaction bonded and sintered silicon nitride both have lower room tempera-
tur_hst[2ogoth thal4h0_cPreSSerdange, therTehe exacits c°nsiderabslet ength andVerlaoPther propertie° sf strengths n
this range is very dependent on the starting materials and other processing
parameters, such as the specific sintering aid utilized.
In addition to the above parameters, there are two hexagonal crystal
structUreuSnlte cell bein°gf siliC°apn roximatenlyi ride' twi_ 3 Nh4eandzBe-S_3tN4'j-_huther_ -Stn[tctu[l-
Since either structure can be produced from the other by rotation of two
basal planes, requiring breaking and forming primary bonds, the _-8 trans-
formation requires time and energy. Two possible methods are _olutloning-
precipitation and volatillzation-condensation. Both structures can be
formed over a wide range of temperatures and both are relatively stable,
iii: :h°
favours the B-Structure formation. The morphology of the formed crystals
is important with the fibrous B-Structure preferred because it enhances
the strength and toughness of the resulting bulk material.
The processing parameters that are controlled to obtain the desired
properties in the silicon nitride include:
a. Initial particle size and size distribution
b. Impurities
c. Milling and Mixing procedures
d. Sintering aids
e. Reaction (sintering) temperature
f. Reaction (sintering) pressure
g. Reaction (sintering) time
h. Reaction (sintering) atmosphere
i. Post heat treatment
Not all of these parameters apply to each of the three types of bulk
present in the combined state such as oxides, silicides or silicates.
An excellent article on how all of the above variables affect the
final physical properties of the silicon nitride is given in the paper
by Larsen et al (Ref. i) which was presented in 1981.
_VIII-3
EQUIPMENTASSEMBLY
Equipmentwas assembledand checked out to hot press silicon nitride
powders into a bulk shape. The equipment utilized was as follows:
Lepel High Frequency Induction Furnace, model T-20-3-KC-E-H,
45 KVA, 20KWRadio Frequency Output, 180-450 KC Frequency
range, water cooled at a rate of ten gallons per minute.
Corning Precision Deviation Controller model 8810.
Leeds and Northrup Automatic Optical Pyrometer.
BLHElectronics Universal Transducer Indicator, BLHmodel 350,
25,000 pound load cell at 100%.
Graphite Dies, 1½inch diameter.
Cavity, dual plungers 1½diameter and 4 inches in length, outside
shell 3½inch diameter and a height of 6 inches.
Silicon nitride powders, Cerac Pure, Cerac Incorporated,
Milwaukee, Wisconsin, -325 mesh, mixture of alpha and beta.
Phases, about 2 micron average diameter, 99.9%pure, nitrogen
content 38%.
Several runs were completed utilizing this equipment with the final
bulk density of the silicon nitride being 99.4% of theoretical. Two
problem areas requiring additional effort are:
The sintered silicon nltride bonds to the plungers during the sin-
tering process. It is suggested that small sacrificial dish be
inserted between the powders and the plungers.
Water pressure variations causes the safety switch to activate
cutting off the Induction Furnace during low pressure periods.
Larger lines, or a large surge tank should alleviate this problem.
DESIGN,MANUFACTURINGANDEVALUATIONOFSi3 N4
AS A STRUCTURALCOMPONENTOFTHESSME
This portion of the objectives of this research project was
beyond the scope of the ASEE-NASAprogram, and a request for proposal was
prepared. The work statement of the RFPfollows.
General
It is requested that a contract be negotiated to define the parameters
affecting the use of high temperature, high strength ceramics as structural
components of the Space Shuttle Main Engine. This contract should be nego-
tiated on a noncompetitive basis and awarded as a cost-plus fixed fee con-
tract.
XVIII-4
Background
Operation of the Space Shuttle on a more efficient basis of providing
more thrust without additional fuel consumption should directly result in
an increase in payload capacity. One means of achieving this increased
efficiency is to increase the operational temperature of the turbopumps.
The operational temperatures of the turbopumps are presently limited by
the capabilities of the superalloys in the turbopump. The sue of struc-
tural ceramic materials should permit operation of the turbopumps up to
2500°F.
Several materials systems are being developed that may provide the
properties necessary for the higher temperature operation. Silicon nitride,
silicon carbide, transformation toughened zirconia, and fiber reinforced
ceramics appear promising as candidate materials systems for structural
applications. The material for this application must possess the proper-
ties of high strength at elevated temperatures, good fracture toughness,
and thermal shock resistance.
Work Statement
Phase I - Environment Definition
Definition of the environment that the ceramic components of a turbo-
pump will be exposed to will acutely effect the material, processing, and
design of the components. The contractor shall define in detail the
environments in the turbopumps during start-up, operation, and shut down.
The environmental parameters of interest are as follows:
l.
2.
3.
4.
5.
6.
7.
8.
9.
i0.
ii.
12.
13.
14.
15.
16.
Temperature Extremes
Rate of Temperature Change
Heat Flux Extremes
Rate of Change of Heat Flux
Gas Mass Flow
Gas Composition
Combustion Products Composition
Change in Gas Composition Ratios
Uniformity of Gas Composition Relative to Location
Temperature Profile
Stress Levels
Rotational Speed
Pressure Extremes
Rate of Change of Pressure
Other Stress Sources and their levels
Any Other Parameter that would Affect
This data shall be compiled and be available for use in the following
phases of this program.
Phase II - Components Study
Based on the data generated in Phase I and knowledge of structural
ceramics, the contractor shall conduct a study to identify the components
that appear to be candidates for being fabricated from high strength
refractory ceramic materials. The rationale utilized to reach these
XVIII-5
conclusions shall be provided. Acceptable design criteria such as Wiebull
Modulus or other accepted techniques shall be utilized to establish an
acceptable degree of reliability for the candidate structures/materlals.
Phase III - Design Parameters
The contractor shall apply the results of Phase I and Phase II of
this work statement to identify and quantify the critical design parameters
of selected components. Included should be the area of utilizing brittle
materials as a structural member,where someattention given to:
I.
2.
3.
4.
.
6.
Method of attachment of components
Method of joining of components
Design concepts to eliminate point contacts
Design concepts to maximize compressive loading of ceramics
and minimize other types of loading
Design concepts to minimize thermal shock effects
Design concepts to minimize impact potential and effect
The contractor will also identify any other potential problem areas
expected to be encountered and suggest design concepts to minimize these
problems. This phase of the project will require the expertise of expe-
rienced design personnel in the field of utilization of brittle materials
as structural members.
Phase IV - Design Variables
The contractor upon completion of Phase III shall supply a format for
the preparation of ceramic components for the turbopumps to be utilized in
the Space Shuttle Main Engine. This format shall contain, but not limited
to, the following:
i.
2.
The selected shapes of the components
Materials characterization
a. Starting Powders
i. size
2. shape
3. purity
b. Required alpha or beta Phase Ratio
c. Suppliers
3. Processes
ao Forming
Sintering
Final Shaping Tolerance
4. Attachment Techniques
XVIII-6
5. Special Handing Required
6. Required Specifications of as Completed Components
This phase will require the collaboration of design personnel and
material personnel.
CONCLUSIONS AND RECOMMENDATION:
Si_ N 4 is a viable material candidate for utilization in high
temperature structural applications. However, it must be fully evaluated
under use conditions and environments before utilization. Main areas
of concern are thermal shock, methods of attachment, and reactive atmos-
phere when considering application in rocket engine turbine. It is recom-
mended that these areas be studied and evaluated under actual environments
existing in the turopumps early in the program. These evaluation should
continue throught the life of the program as long as any change is made
in the Si 3 N4 processing parameters. Additional studies could include:
a. Creep and strength improvement based on different sintering aids
b. Forming techniques
c. New processing techniques such as reaction-bonding followed by
sintering
d. Basic studies on the glass bond formed during sintering
XVIII-7
References
le
e
Be
e
De
e
Q
8.
9.
i0.
ii.
12.
13.
14.
Larsen, D. C., Adams, J. W., Bortz, S. A. and Ruh, R., Evidence of
strength degradation by subcritical crack growth in Si 3 N 4 and Si C.,
International Symposium as Fracture Mechanics of Ceramlcs, Penn. State
University, 1981.
Larsen, D. C., and Bortz, S. A., Properties of structural ceramics,
S_MPE Journal, January, February, 1981.
Larsen, D. C. and Ruh, R., The Nature of Si C for use in Heat Engines
as compared to Si^ N4: An overview of Properties Differences, NATO
Advanced Study Institute of Nitrogen Ceramics, Univeristy of Sussex,
U. K., 1981.
Heitman, P. W. Development of Ceramic Gas Turbine Components Detroit
Diesel Allison, NASA Contract: Den. 3-17, 1981.
Byrd, J. A., Ceramic Applications in Turbine Engines, Detroit Diesel
Allison, NASA Contract: Den. 3-17, 1981.
Edington, J. W., Rowcliffe, D. J., and Henshall, J. L., The Mechanical
properties of Silicon Nitride and Silicon Carbide, Powder Metallurgy
International, Vol. 7, No. 2, 1975.
Exempt Vol. 7, No. 3, 1975.
Jack, K. H., Nitrogen Ceramics, 17th Mellor Memorial Lecture, 1973.
Guha, J. P., Goursat, P., and Billy, M., Hot Pressing and Oxidation
Behavior of Silicon Nitride with Ceria Additive, Journal of the
American Ceramic Society, Vol. 63, No. 1-2, 1980.
Jennings, H. M., Danforth, S. C., and Richman, M. H., On a Growth
Mechanism for B phase Silicon Nitride, Journal of Materials Science
Vol. 14, 1979.
Dervisbeqovic, H., and Riley, F. L., The Influence of Iron and Hydrogen
in the Nitridation of Silicon, Journal of materials Science, Vol. 14,
1979.
Lindley, M. W., Elias, D. P., Jones, B. F. and Pitman, K. C., The
Influence of Hydrogen in The Nitriding Gas on the Strength, Structure
and Composition of Reaction-Sintered Silicon Nitride Journal of
Materials Science, No. 14, 1979.
Elias, D. P., and Lindley, M. W., Reaction Sintered Silicon Nitride,
Part i, Journal of Materials Science, No. 14, 1979.
Jones, B. F., and Lindley, M. W., Reaction Sintered Silicon Nitride,
Part 2, Journal of Materials Science, No. 14, 1979.
XVIII-8
15.
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26o
Katz, R. Nathan, High Temperature Structural Ceramics, Science,
Vol. 208, 1980.
Greskovich, C., and Rosolowski, J. H., Sintering of Covalent Solids,
Journal of the American Ceramic Society, Vol. 59, No. 7-8, 1976.
Vasilos, T., Cannon, R. M., and Wvench, B. J., Improving the Stress
Rupture and Creep of Silicon Nitride, Final Report NASA Contract
NAS 3-20088, March, 1979.
Richman, M. H., Effect of Processing Parameters on Reaction Bonding
of Silicon Nitride, Final Report, NASA Contract NSG-311$1, October, 1980.
Jack, K. H., Sialons and Related Nitrogen Ceramics, Journal of
Materials Science, No. ii, 1976.
Longe, F. F., Silicon Nitride Polyphase Systems: Fabrication,
Microstructure, and Properties, International Metals Reviews,
No. i, 1980.
Vasilo, T., and Cannon, R. M. Jr., Improving and Toughness of Refrac-
tory Compounds, Final Report, NASA Contract NAS3-17768, November, 1975.
Palm, J. A., and Greskovich C. D., Silicon Nitride for Airborne
Turbine Applications, Final Report, Naval Air Systems Command Con-
tract No. 0019-77-C-0259 July, 1978.
Sikara, P. F. and Yeh, H. C., Consolidation of Silicon Nitride Without
Additives, NASATechnical Memorandum NASATM 73693, 1976.
Williams, R. M., Linear Thermal Expansim of Hot-Pressed Si^ N,, The
Journal of the American Ceramic Society, Vol. 63, No. i-2,J19§0.
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Properties, Journal of Materials Science, No. 14,1979.
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Columbus; Tom Miller, NASA-Lewis.
XVIII-9


Structural application of high strength, high temperature ceramics

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