NASA / TMm2001-210684

One-Step Tape Casting of Composites

via Slurry on Fiber

Henry C. de Groh III

Glenn Research Center, Cleveland, Ohio

February 2001
The NASA STI Program Office... in Profile

Since its founding, NASA has been dedicated to

the advancement of aeronautics and space

science. The NASA Scientific and Technical

Information (STI) Program Office plays a key part

in helping NASA maintain this important role.

The NASA STI Program Office is operated by

Langley Research Center, the Lead Center for

NASA's scientific and technical information. The

NASA STI Program Office provides access to the

NASA STI Database, the largest collection of

aeronautical and space science STI in the world.

The Program Office is also NASA's institutional

mechanism for disseminating the results of its

research and development activities. These results

are published by NASA in the NASA STI Report

Series, which includes the following report types:

TECHNICAL PUBLICATION. Reports of

completed research or a major significant

phase of research that present the results of

NASA programs and include extensive data

or theoretical analysis. Includes compilations

of significant scientific and technical data and

information deemed to be of continuing

reference value. NASA's counterpart of peerreviewed formal professional papers but

has less stringent limitations on manuscript

length and extent of graphic presentations.

TECHNICAL MEMORANDUM. Scientific

and technical findings that are preliminary or

of specialized interest, e.g., quick release

reports, working papers, and bibliographies

that contain minimal annotation. Does not

contain extensive analysis.

CONTRACTOR REPORT. Scientific and

technical findings by NASA-sponsored

contractors and grantees.

CONFERENCE PUBLICATION. Collected

papers from scientific and technical

conferences, symposia, seminars, or other

meetings sponsored or cosponsored by

NASA.

SPECIAL PUBLICATION. Scientific,

technical, or historical information from

NASA programs, projects, and missions,

often concerned with subjects having

substantial public interest.

TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific

and technical material pertinent to NASA's

mission.

Specialized services that complement the STI

Program Office's diverse offerings include

creating custom thesauri, building customized

data bases, organizing and publishing research

results.., even providing videos.

For more information about the NASA STI

Program Office, see the following:

• Access the NASA STI Program Home Page

at httpY/www.sti.nasa.gov

• E-mail your question via the Internet to

help@sti.nasa.gov

• Fax your question to the NASA Access

Help Desk at 301-621-0134

• Telephone the NASA Access Help Desk at

301-621-0390

Write to:

NASA Access Help Desk

NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076
NASA / TM--2001-210684

One-Step Tape Casting of Composites

via Slurry on Fiber

Henry C. de Groh III

Glenn Research Center, Cleveland, Ohio

National Aeronautics and

Space Administration

Glenn Research Center

February 2001
Trade names or manufacturers' names are used in this report for

identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National

Aeronautics and Space Administration.

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Price Code: A03

Available from

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Price Code: A03

Available electronically at http://gltrs.grc.nasa.gov/GLTRS
One-Step Tape Casting of Composites via Slurry on Fiber

Henry C. de Groh III

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, OH 44135

Executive Summary

A major contributor to the continued advancement of aircraft engine performance is the

development of less dense and stronger engine materials. Metal matrix composites (MMC) are

being considered by many for jet engine applications in an effort to make improvements in these

areas. Tape casting in particular is being developed in an effort to develop MMC's. The objectives

of this paper are: to present a one step tape casting process and a supporting computer code; to

assess the flexibility and controllability of the one step process; and to compare this one step

technique to other tape casting and composite production techniques. The process is termed "onestep" because the green tape containing the fibers and matrix is made in one casting - where the

binder and matrix are laid down on the fibers in one step. The general tape casting process consists

of winding the fiber on a rotating drum; mixing the solvent, copolymer binder, and powder; casting

the slurry onto the fibers using the dozer blade set at a specific height above the drum; casting flat

matrix-only tapes; and stacking, and hot pressing.

In Tcast2 - the FORTRAN program developed to assist in tape casting - the fiber

architecture in the final composite is expressed as and controlled through c_, the ratio of the drum

fiber spacing to the fiber spacing between the plies. Fiber spacing through the width is controlled

through the winding of the fiber on the drum. The fiber spacing through the thickness (between

plies) is controlled by the dozer blade height and slurry characteristics. Easy control of fiber

volume fraction and architecture through drum winding and blade height are the primary result of

this work. When a new fiber and powder system is being tape cast for the first time, the first

preparatory step is characterization of the green tape which results from the casting of the bindersolvent-powder mixture. With a particular fiber and slurry chosen, and the resulting green tape

characterized, the Tcast2 program can be used to determine the dozer blade heights and fiber

spacings needed to produce whatever fiber architecture and fraction fiber desired in the composite.

A wide variety of fibers have been successfully used to make tape cast composites at NASA

Glenn. Initial studies were made using 0.005 inch diameter W fiber. Various castings have been

made with the carbon core, carbon coated, silicon carbide fibers SCS-6 and SCS-9. Saphikon single

crystal aluminum oxide (0.00478 inch diameter) fibers as well as the very fine tow fibers (Nextel

610) have been used in tape casting. Tow fibers are run through a powder slurry as they are wound

on a drum.

Many different alloys and powder size distributions have been examined. Composites have

been made using -140 mesh Ti-24A1-11Nb (at%), -100 mesh Ti-6A1-4V, -325 mesh Fe-24Cr-4A1-

1Y (wt%), and -325 mesh MoSi2-30Si3N 4 (vol%) powders, as well as others. Since blade heights

are typically in the range of about 0.01 tO 0.04 inches, -70 mesh is expected to be the coarsest

powder reasonable for tape casting.

NASA/TM--200I-210684 1
Different binders were examined, and qualitatively assessed on the basis of tape strength,

ductility, warpage, and ease of mixing - casting - and removal from the substrate; other aspects of

the binders quantitatively examined were burn-out cleanliness and temperatures, and toxicity (of

binder and solvents, based on literature data). The binders examined were each cast on a variety of

substrates. Thermal Gravimetric Analysis (TGA) in vacuum was performed on all of the binder

mixes. Ultimately, the copolymer mix of PIBlo w and PMMAhig h was chosen and used in

subsequent tape casting.

The ultimate room temperature tensile strength and strain at failure of the 4-ply, 0 ° tape

cast, Ti-24Al-I INb/SCS-6, 32voi% fiber composite were: _trrs = 215 ksi (1477 MPa), and ef =

1.15%. The results of the room temperature 0 - 120 ksi, v -- 0.3 Hz fatigue test on the 4-ply Ti24A!-! 1Nb/SCS-6, 32vo1% fiber tape cast composite were: Number of cycles to failure, Nf202,205 and maximum strain on the 100th cycle, Ae -- 0.43%), which indicates the room

temperature fatigue properties to be good and similar to above average Ti-24A1-11Nb composites

made using other techniques.Though the above mechanical property tests are not exhaustive, they

support the feasibility of tape casting.

Introduction

A major contributor to the continued advancement of aircraft engine performance is the

development of less dense and stronger engine materials. Density, creep and tensile strength,

toughness and high temperature durability are all of concern; metal matrix composites (MMC) are

being considered for jet engine applications in an effort to make improvements in these properties.

For such parts as fan blades - continuous fiber MMC's have received much interest.l'2'3 In

continuous fiber composites, fiber lengths are of the same order as the part, and usually placed in

specific directions relative to the geometry of the part and the stresses expected. Processing steps

commonly include the consolidation of a multi-ply layup of fiber and matrix materials. Several

processing techniques, such as foil-fiber-foil, 4 arc spray, 5 powder cloth, 6 and tape casting] have

been developed, and have successfully produced quality continuous fiber MMC test plates. Each

of these techniques has different advantages and disadvantages. 3Tape casting in particular is being

developed in an effort to improve composite quality, and decrease costs as compared to the other

techniques. 7,8,9 The objectives of this paper are: to present a one step tape casting process and a

supporting computer code; to assess the flexibility and controllability of the one step process; and

to compare this one step technique to other tape casting and composite production techniques.

Efforts are in place at several companies to produce titanium matrix composites suitable for

use near the cooler, front end of jet engines. Fan blades and fan frame applications are two

possibilities for use of titanium matrix composites. Many of the fabrication techniques, such as hot

isostatic pressing and hot pressing, for the production of basic air foil shapes from multi-ply layups

are similar and have been presented elsewhere, 8'1° and will not be discussed in detail here. Several

variants of tape casting have been developed including the following. Edd and Niemann (Alcoa

Laboratories and McDonnell Douglas respectively) have presented what will be referred to here as

a two-step tape casting procedure where a matrix-only green tape is made separate from a fiber only

tape. 7,s In this two-step process binders are mixed with matrix powder and cast to make the green

matrix tape. Then fiber is wound on a drum and binder applied onto the fibers to make the fiber

mat. Spear (Atlantic Research Corp.) is examining a similar two-step tape casting technique. I1

Textron Systems Division (formerly Textron Specialty Materials) has developed a technique to

NASA/TM--2001-210684 2
produce green fiber-matrix-binder mats by which matrix-only and binder only tapes are made

separately and then combined in a continuous fashion with fibers fed through a spacer (or creeling

device); this might be viewed as a three step process where two castings are made and then the

fibers sandwiched between them. Chesnutt, et al., have shown excellent results using a hybrid

approach which combines foil/fiber/foil and tape casting techniques. 12 At the NASA Glenn

Research Center we have been developing and using a "one-step" tape casting process in which the

green tape is made in one step by casting the powder slurry directly onto the fibers - the results and

details of this process are presented in this paper. In particular, a FORTRAN computer program

which assists tape casting will be presented. Though the details of a similar "one-step" process,

referred to as "Tape-Cast Powder Monotape'" have not been found in the literature, the process of

casting a powder slurry onto fibers was used in a collaboration among Pratt & Whitney, Atlantic

Research Corp., and Rockwell International Science Center (with credit for initial development of

the process given to the Alcoa Technical Center under the auspices of the National Aerospace Plane

Materials and Structures Augmentation Program).13'14 Figure 1 shows a schematic of the one-step

tape casting process of winding the fiber on a rotating drum; mixing the solvent, copotymer binder,

and powder; casting the slurry onto the fibers using the dozer blade set at a specific height above

the drum; casting fiat matrix-only tapes; and stacking, and hot pressing.

Development of Tape Casting Procedures

Fibers and Drum Winding

Fiber locations in the composite are determined largely by the initial winding on the drum;

the drum spacing is maintained through subsequent steps which will be discussed later. A wide

variety of fibers have been successfully used to make tape cast composites at NASA Glenn. Initial

studies were made using 0.005 inch diameter W fiber. Various castings were made with the carbon

core, carbon coated, silicon carbide fibers SCS-6 and SCS-9. Saphikon single crystal aluminum

oxide (0.00478 inch diameter) fibers as well as the very fine tow fibers (Nextel 610 and Hi-Nicalon)

have been used in tape casting. All fibers are wound on a smooth drum prior to casting. In all cases

the drum is clad with release paper prior to winding. Tow fibers (strings of approximately 500

filaments) are spread out, hand-wound in large groups on a drum and infiltrated with matrix

slurry. 15'16 We have not found a fiber which could not be used in tape casting.

Specific fiber spacings on the drum are computer controlled (except in the case of tow

fibers) by accurately controlling the movement of the feed arm across the drum and the drum

rotation. The consistency of fiber spacing in the end composites is first dependent upon the quality

of the winding. A poor winding - one in which the interfiber spacing varies too much, or results in

fibers touching while on the drum, will result in poor fiber spacing in the composite. A key

advantage of casting the powder slurry directly onto the fibers is that there is much less movement

of fibers during consolidation and thus better fiber spacing control within the plies and better fiber

row retention. What is meant by row retention is that fibers within each ply are nicely lined up in

a straight line, as they were on the drum. Fibers were typically wound at a drum rotation rate of 15

rpm; on a 16 inch diameter drum, this translates to a rate of 63 feet of fiber laid down on the drum

per minute. The average fiber spacing was found to be accurate to about +2.5%, with the average

fiber spacing being consistently on the low side. For example, the requested value of 124 fibers/

inch resulted in an actual, measured value of 121 fib/in. Preparation of the fiber wound drum is a

time consuming step in the production of the green tapes. Improvements made here, such as

NASA/TM--2001-210684 3
increasingtherotationrateusedto wind thefiberonthedrum,will haverelativelylargeeconomic

utility. All windingsfor 0° compositesweremadetwoincheswide fortheproductionof 2 x 6inch,

four ply plates.It takesabout 17min. to wind thedrumat 124fibers/inch,two incheswide.Prior

to winding thedrumhowever,thedrummustbecleaned,clad with releasepaper,andthefiber

attachedto it; thistakesabout10min.For the90degreecomposite,acastingsix incheswidewas

made.

Fiber

/ rum 

(a)

Binder

+

Solvent Powder

\ /

Matrix tape --_\ _ Heat

\

(b)

Dozer blade;-_.

%..

"_- Heat

(c)

Fiber mats --_ _-_

_-- Matrix mat T

Hot press

(d) (e)

Figure 1 .----Schematic of "one-step" tape casting process. (a) winding the fibers, we use about 15 rpm

on a 16 inch diameter drum; (b) mixing solvent (toluene), copolymer binder (PIB and PMMA), and

powder; (c) two views of the casting of the powder slurry onto the fiber wound drum and heat to

quicken curing of the fiber/matrix mats, we let the tape cure for about I hour without heat; (d) fiat

continuous casting of the matrix-only end plies on release paper, we do this in small batches using

the excess slurry from the drum casting; (e) stacking of the fiber/matrix mats with a matrix-only end

ply to cover the exposed fibers, and vacuum hot pressing to give the fully dense composite.

Since fiber spacings have been excellent and row retention nearly perfect in finished tape

cast composites, it is believed that the fiber spacing on the drum is locked in and retained through

consolidation due to significant penetration of the powder between the fibers during slurry casting.

This superior fiber spacing and row retention yields greater flexibility by enabling the volume

fraction of fiber to be more accurately controlled by both drum fiber spacing and fiber row spacing.

A good winding and excellent retention of that spacing enables the fiber volume fraction to be

raised further, as compared to other processes, without the fear of problems such as fibers touching.

And since the architecture can be controlled accurately (drum fiber spacing and fiber row spacing)

coarser powders may be possible because wider fiber spacings can be used while maintaining high

NASA/TM--2001-210684 4
fiber volume fractions. As can be seen in Fig. 4 of reference 3, other processes such as foil-fiberfoil, plasma-spray, and powder cloth may rely on high within ply (drum) fiber spacings to achieve

the desired volume fraction fiber - resulting in a large number of fibers touching and a non-square

architecture. Though the degree of any degradation (or enhancement) of properties due to a nonsquare architecture is not clear - fibers touching has been found to degrade composite properties

through fiber damage. Arc-spraying has been found to damage the fibers. 5'17 Tape casting is

considered to be more gentle on fibers than powder cloth (because several of the processing steps

are similar and there is less movement of fiber and powder during consolidation) - and powder cloth

has been found to not damage fibers. 18

In Tcast2 - the FORTRAN program developed to assist in tape casting - the fiber

architecture is expressed as the ratio, or, of the drum fiber spacing, fs, to the fiber spacing between

the rows (through the composite thickness); both in units of fiber per inch. For a ratio of c_ = 1 the

architecture will be square, thus the fiber spacing will be the same through the width of the

composite and its thickness. The density and diameter of the fiber are needed to accurately tape

cast composites and are a required inputs to Tcast2. In situations were fiber diameter varies

significantly (such as in the case of the 0.00478 inch dia. Saphikon alumina fibers mentioned above

which varied by about +/- 0.001 inch) a representative average diameter is needed. Some densities

of fibers are given in Table 1.

Table 1 Densities and approximate diameters of various fibers used in Tape Casting.

SCS-6 SCS-9 Saphikon, A120 3 W, W218 Hi-Nicalon

Density, g/cc 3.00 2.8 3.97 19.3 2.3

Diameter, inches 0.00566 0.0031 0.00478 0.004 5.5-7.9x 10 -4

Diameter, microns 144 79 121 102 14-20

Powders

Several different alloys and powder size distributions have been examined. Composites

have been successfully made using -140 mesh Ti-24Al-11Nb (at%), -100 mesh Ti-6A1-4V, -325

mesh Fe-24Cr-4A1-1Y (wt%), and -325 mesh MoSi2-30Si3N 4 (vol%) powders, as well as other

powders examined which produced good green tapes. We have not found a powder which could

not be used in tape casting - though tape casting has definite constraints on the maximum powder

size.

The maximum powder size must be less than the dozer blade height; since blade heights are

typically in the range of about 0.01 to 0.04 inches (250 - 1000 _m) -70 mesh is expected to be the

coarsest powder reasonable for tape casting. It is economically most desirable to use very coarse

powder because it is the least expensive; coarser powders have lower surface area and are therefore

cleaner, and thus pose less risk of significant contamination of the composite from impurities such

as oxygen and carbon. From a processing point of view however, it is desirable to have the powder

size maximum be less than or equal to the average edge-to-edge fiber spacing; thus promoting

better filling of the spaces between the fibers, and enabling consolidation of the green tapes with a

minimum of powder and fiber movement. Minimizing powder and fiber movement during

consolidation, and locking in the drum fiber spacing with good filling, results in a more gentle

NASA/TM--2001-210684 5
consolidation,andhelpstoinsuregoodfiber spacingandpropertiesin thefinal composite.Forfour

ply compositesusingSCS-6fiber at 35vol% anda squarearchitecture,theedge-to-edgefiber

spacingis about.0.0026inches;thususeof apowdersievedto -230meshwouldinsurenearlyall

thepowderto belessthantheaverageedge-to-edgefiber spacing.Thoughgoodgreentapeshave

beenmadeusing-100meshpowder- ourexperienceindicatesthat goodfilling of thespaces

betweenthefibersis aidedby asignificantamountof fines(-325mesh)in thepowder.Though

usingacoarsesizedistributionsuchas-80to +200meshmayresultin usabletapesandacceptable

composites,retentionof finepowders(using-100meshfor example)will resultin a more

aestheticallypleasingtapeandlessmovementof fiber andpowderduringconsolidation.Table2

listssomepowdersandtheiridealdensities.Thedensityof thematrixisarequiredinputin thetape

castingprogram,Tcast2.

Table2 Densitiesin g/cm3of variousmatrixalloys,in weight percent unless marked; density

variations expected to be about +/- 1%; *at%.

Ti6A14V Ti24AI11N'b* Ti21A123Nb* Fe24Cr4AIiY

Density 4.43 4.5 5.1 7.2

MoSi230vol%Si3N 4

4.92

Binders and Slurry Development

Table 3 lists the different binders examined and the tape casting recipe developed. Initial

binder selection was based on previous experience with the powder cloth 6 process and the

literature. 7 Factors most important to final binder selection were tape strength, burn-out

cleanliness, and toxicity. Many matrix-only, fiat castings were made and qualitatively assessed on

the basis of tape strength, ductility, warpage, and ease of mixing - casting - and removal from the

substrate; other aspects of the binders quantitatively examined were burn-out cleanliness and

temperatures, and toxicity (of binder and solvents using literature data). The binders examined

were each cast on a variety of substrates including stainless steel, glass, Teflon, and a heavy, glossy

release paper. Thermal Gravimetric Analysis (TGA) in vacuum was performed on the binder

mixes. TGA included measurement of burn-out temperatures, mass of residual ash, and visual

inspection of the TGA crucible. The crucibles were alumina, the heating rate was 20 K/min and the

initial weight of cured binder samples was 25 g. While testing the different binders, materials were

mixed in glass beakers, pored in front of a dozer blade and cast on fiat substrates by pulling the

dozer by hand at a rate of about 6 in/s. Green tape properties and TGA results are presented later

'When modifying the recipes in Table 3 through use of other powders, it is recommended

that the weight of powder used be scaled such that both volume and surface area of powder in the

slurry are considered; the volume being considered through the matrix density and the surface area

of the powder by its average particle size (diameter). For example, when using -325 mesh Fe based

powders and the copolymer mix of PIBlo w and PMMAhig h the weight percent of Fe powder

recommended in the slurry is 82.5%. When switching to a -100 mesh Ti based powder, a ratio of

the matrix densities will help maintain a similar volume of powder in the slurry (82.5%PTi/PFe%),

and a ratio of sphericalsurface area to volume ratios will help maintain constant powder surface

area (82.5%dTi/dFe). The density ratio, about 0.6, shows that less powder (by weight) is needed to

make a similar volume of powder in the slurry; but the ratio of the surface area to volume ratios of

the powders, estimated to be about 2, indicates that since the Ti powder is coarser a higher weight

NASA/TM--2001-210684 6
fractionpowderin theslurry canbetoleratedwhile still coatingtheparticles.TheTi andFematrix

densitiesbeingrepresentedby PTi and PFe respectively. Since the surface area to volume ratio of a

sphere is 3/radius, the ratio of the surface area to volume ratios of the two spheres can be

represented by their diameters, where in this case dTi and dFe are the average particle diameters of

the -100 mesh and -325 mesh powders respectively.

Slurries were prepared by first dissolving the binder in the solvent. This sometimes took

several hours. After a good binder solvent mixture was made - the powder was added to it and

mixed by hand using a spatula just before tape casting. Mixing was fast enough to overcome

particle settling and slow enough to avoid the production of too many bubbles in the slurry. Ball

milling, to mix the powder and dissolved binders, was not necessary. Large quantities of the binder

solvent mixture can be made in advance and stored if precautions are made to prevent the loss of

solvent from the mix; we have had success using glass containers with Teflon-lined screw-on caps.

Ultimately, as will be discussed later, the copolymer mix of PIBlo w and PMMAhig h was

choscn and used in subsequent tape casting because it had the best combination of green tape

properties and burn-out cleanliness. The solvent used with this PIB, PMMA mix is toluene, which

is onc of the more benign industrial solvents. Wet chemical analysis was preformed on a FeCrA1Y/

W libcr composite to determine carbon and oxygen pickup during processing; the results of which

arc presented in the results section, as are the results of binder properties, burnout (TGA) and green

tape properties

Table 3 Binders examined, all percents are weight percents based on -325 mesh FeNiCrA1 powder.

Met h_.-cl '".* 20-214. A cellulose based binder soluble in water with unique gelling capabilities. To

pre_ ent premature gelling and promote dispersion of the powder - ingredients are mixed separately

and heated. A = [mix and heat to 50 °C 11.4% water, 1.14% glycerin, 0.43% polyglycol, then add

57. Ir, powder], B = [heat to 90 °C 28.5% water, add and mix 1.43% Methocel]. Combined A and B,

mi\. and cool to about 18 °C.

Nc,_'r3 I. B-700. From ICI Resins US, this methacrylate polymer has what is referred to as a glass

tran,ition temperature of 48 °C. Dissolve 4.3% NeoCryl in 9.4% 2-ethoxyethyl acetate, add 86.3%

po_ dcr and mix.

N coCr) 1. A-614. This binder comes in solution and has a glass transition temperature of-10 °C. Mix

88ri powder in 12% NeoCryl A-614 solution.

PIB. polvisobutylene, a synthetic rubber available in a variety of average molecular weights. M.W.

4.2x 105:'dissolve 1.7% PIBIo w in 9.5% toluene, and mix with 88.8% powder. M.W. 1.2x106: dissolve

2c,,i PIBme d in 21% toluene, and mix with 76% powder. M.W. 4.7x10°: dissolve 0.5% PIBhig h in 17%

toluene, and mix with 82.5% powder.

PMMA. poly(methyl methacrylate), a plastic available in a variety of weight-average molecular

weights. M.W. 1.5x10'_: dissolve 6% PMMA,- w in 10% toluene, and mix with 84% powder. M.W.

1.2x105: dissolve 4% PMMAme d in 12% toluene, and mix with 84% powder. M.W. 9.96x105:

dissolve 4.5% PMMAhig h in 18% toluene, and mix with 77.5% powder.

PVP, polyvinylpyrrolidone, a water soluble binder. Dissolve 3.7% PVP in 17% ethanol, and mix with

79.3% powder.

Copotymer mix of PIBlo w and PMMAhig h. Dissolve 1.3% PIBlo w and 1.2% PMMAhi h in 15%

toluene, and mix with 82.5% powder. In use with Ti base powders we dissolve 2.2% P_low and 1.7%

PMMAhig h in 21% toluene, and mix with 75% Ti alloy powder.

*Trademark of The Dow Chemical Company

NASA/TM--2001-210684 7
Tape Casting Development and Procedures

The goal of this paper is to present efficient tape casting methods by which the fiber

spacing, through both the width and thickness of sheet composites, can be independently

controlled; thus both fiber volume fraction and cross-section architecture are controlled. Fiber

spacing through the width is easily specified through the winding of the fiber on the drum. The fiber

spacing through the thickness (between plies) is controlled by the dozer blade height and the

characteristics of the slurry and subsequent consolidation processing. Easy control of fiber volume

fraction and architecture through drum winding and blade height are presented below and are

the primary result of this work.

When a new fiber and powder system is being tape cast, the first step is characterization of

the green tape which results from the casting of the binder-solvent-powder mixture.

Characterization of the green tape includes experimentally measuring the matrix-only (fiber free)

green tape density, pg, and the thickness shrinkage, S, from the wet to green state of the tape. The

shrinkage, S, is defined as

(BH- Tg)

s - (l)

BH

where BH is the dozer blade height above the substrate, and Tg is the thickness of the cured, matrixonly, green tape. Initial estimates of Pg and S are made by tape casting a matrix-only tape on a flat

surface (or on the tape casting drum). These preliminary estimates and measurements must

however be checked and corrected using measurements from a tape casting on a fiber wound drum.

The density and shrinkage of the matrix-only green tape is determined from the tape containing

fibers through rule of mixture calculations as follows:

(pfg- Vfg(pf)) (2)

Pg = 1 - Vfg

and since there is no shrinkage in the fibers,

Sf S - (3)

(J - rig)

where Vfg is the volume fraction of fibers in the green tape, pf is the density of the fiber, pfg is the

density of the green tape with fibers, and Sf is the thickness shrinkage of the fibrous green tape,

( BH f - T fg)

Sf = BHf

(4)

where Tfg is the thickness of the green tape with fibers and BHf is the blade height used to cast it.

The fiber volume fraction in the green tape is calculated using the measured thickness Tfg, the drum

fiber spacing fs (in units of fibers/inch) and the fiber diameter d:

NASA/TM--2001-210684 8
rcd2(fs)

VZ8 - 4 Tfg

(5)

Now with the density of the matrix-only green tape 9g, and tape shrinkage S, the blade heights for

different drum fiber spacings and composite architectures can be determined by the Tcast2

program. Figure 2 is a schematic of cross-sections and is included to help clarify some of the

variables.

Wet tape Four ply composite

. ....

_ O_ O_ O_ 0_0

BHf "-_QQQQ

I"

l_d _ oooo_41--_l/fs

;ooooo

odfs

(odfs)-d

(a) (b) (c)

Figure 2.mCross-section schematics of (a) the wet tape after tape casting

but before curing showing the dozer blade height BHf and the fiber diameter d; Co)the green tape after curing showing fiber spacing as the

reciprocal of the number of fibers per inch 1/fs, and the thickness of the

green tape Tfg; and (c) a four ply composite plate showing the thickness

of matrix on the outer surface (edfs)-d, and the fiber spacing between

fiber rows edfs.

In subsequent efforts using Tcast2 to solve equations (2) through (5) we see an additional

independent equation is needed since there are five unknown variables (pfg, Vfg, Sf, BHf, and Tfg)

and only four equations. Since volume changes throughout processing of the sheet or plate are

accomplished through changes in thickness only, a relation among composite density Pc, green tape

density, drum fiber spacing, cross-section architecture, and green tape thickness can be developed.

The architecture is brought in as a variable, o_, in the dense ply thickness; _x is the ratio of the drum

fiber spacing to the fiber spacing desired between the plies. In a square architecture, the thickness

of a single fully dense ply is equal to the reciprocal of the drum fiber spacing (fs, in units of fibers/

inch). The thickness of the green ply with fibers can thus be expressed as,

(6)

The fully dense composite density Pc, and fiber volume fraction, Vfc, can be found directly from

o_, fs, and d,

r_d2 fs(p)

Vf¢ =

4(_(p/1) d),and (7)

NASA/TM--2001-210684 9
Pc = PfVfc + Pro( 1 - Vfc ) ,

(8)

where p is the number of (fibrous) plies. An assumption used in (7) and (8) is that the thickness of

matrix on the outer surfaces of the composite is equal to the distance between the fiber edges

through the thickness (that is, equal to (_/fs) - d).

With a particular fiber and slurry chosen, and the resulting green tape characterized, the

Tcast2 program can be used to determine the dozer blade heights needed for different situations.

Table 4 outlines the input and output of the code. The Tcast2 code and an example of it in use are

included in the Appendix.

Table 4 Outline of input and output of the tape casting helper Tcast2 program.

Inputs Outputs

Variable

Drum fiber spacing, fib/in, fs

Number of plies, p

Architecture ratio, c_

Constanl

Matrix density, g/cc, Pm,

Fiber density, g/cc, pf

Fiber diameter, inches, d

Wet to Green Shrinkage, S

Fiber free Green Tape Density, Pg

Composite fiber volume fraction, Vfc

Dozer blade height for fiber mat, BHf

Dozer blade height for matrix-only end ply, BH e

Composite density, Pc

Thickness of green mat with fibers, Tfg

Thickness of green matrix-only end ply, Yeg

Thickness of final composite, T c

With the slurry prepared, drum wound, and blade height set, castings were made under a

fume hood by pouring the slurry in front of the dozer blade and rotating the drum at a rate of 2 rpm.

The drum circumference was 50 inches - thus the casting rate was 8.3 ft/min. Rotation of the drum

continued during the room temperature curing of the tape. No attempts have been made to

accelerate the 15 to 30 rain. curing time typically used. Wet tapes were cast two inches wide

and green tapes trimmed to 1.937 inch. Of the 50 inch drum circumference, about two inches

are lost in the start up and take offof the dozer blade. Thus there is about 4% of the fiber lost

and 7% of the powder. The tape is cut from the drum with a razor blade and then cut with a

shear to 1.937 x 6 inch sheets.

The excess slurry from the drum casting was immediately used to cast matrix-only tapes on

a flat, release paper clad substrate. Figure 1(d) shows how the matrix-only tapes might be made in

a continuous process. One of these matrix-only mats were then used to cover the exposed fibers on

the end ply (see Figures l(e) and 2(c)). As part of my examination of surface porosity and

NASA/TM--2001-2 i0684 10
embrittlement,anextramatrix-onlyply wasaddedto theoutersurfaceof thetopandbottomplies.

Thisextracladdingcouldthenbeengroundoff if desired.

Consolidation of Green Tapes and Mechanical Testing

After layup of the matrix-only and four fibrous plies, the green tapes were vacuum hot

pressed (VHP). Pressing conditions, several of which are listed in Table 5, varied depending on the

matrix. Most materials, including Ti based composites, are hot pressed between sheets of Mo foil.

The Mo foil is etched off using nitric acid after pressing. Vacuum hot pressing produced fully dense

composite plates from which dog bone samples were machined for mechanical testing using either

EDM or water jet cutting. Table 6 summarizes the tape cast plates analyzed. Figure 3 shows the

details of the dog bones made for mechanical testing. In the case of Hi-Nicalon/MoSi2-Si3N4

composites, hot pressing was done in two steps: first at 2100 °F, 20 ksi for 2 hours, then at 2550 °F,

10ksi for 2 hours.

Table 5 Vacuum Hot Pressing conditions used to produce fully dense 4 ply composite plates. Plates

were approximately 2" x 6" by 0.037" thick. Alloys in wt% or marked *at%.

Matrix and fiber Conditions

Time, min. Pressure, ksi Temp. °F

Ti-6A1-4V/SCS-6

Ti-24A1-11Nb*/SCS-6

Ti-21A1-23Nb*/SCS-6

Fe-24Cr-4A1-1Y/SCS-6

120. 15 1650

60 18 1900

60 15 2000

60 15 1950

Table 6 Tape Cast composites presented, all were 4-ply, and used SCS-6 fiber.

Sample Alloy Powder size Fiber spacing Volume % fiber Orientation

fibers/inch

32vo1% Ti-24Al-I1Nb -200mesh 120 32 0 °

35vo1% Ti-21A1-23Nb -140 +325 121 35 0 °

HDH* Ti-6A1-4V -170 +325 122 26 0 °

Coarse HDH Ti-6A1-4V -80 +200 122 25 0 °

45vo1% Ti-24Al-llNb -100mesh 133 45 0 °

90 ° Ti-24Al-llNb -140mesh 120 32 90 °

*Hydride dehydried

NASA/TM--2001-210684 11
41

=.3 _1_.95_1_

_._ j

.25 I

_- 6 radius

1.5

__ .03 (as -received) .04

Figure 3.mDogbone specimen used for tensile and fatigue tests, in units of inches.

Room temperature fatigue and tensile tests were done on a 4-ply, 0 ° tape cast Ti-24AI1 INb/SCS-6 composites, with fibers wound at 120 fib/in and a fiber volume fraction of 32%. Extra

matrix-only plies were added to the exterior - thus making the matrix a little thicker (thicker than

tz/fs -d) on the outer surface of the plate, and intentionally making Vfc a little lower than that given

by equation (7). Stress during fatigue was from 0 to 120 ksi (825 MPa) at 0.3 Hz. Room

temperature tensile tests were done on two HDH samples and two HDH samples heat treated at 800

°F for 300 hours.

Results and Discussion

Microstructure and Fiber Spacing

As can be seen in the micrographs shown in Figures 4 through 8, and later in the fiber

spacing histograms, tape casting produces composites that are nearly free of touching fibers. The

superior ability of tape casting to maintain and control within ply fiber spacing and the spacing

between plies enables composites of relatively high volume fraction fiber to be made, such as that

shown in Figure 7 at 45voi% fiber. Fiber volume fraction was determined using the actual average

fiber diameter, fiber spacing and composite plate thickness, such that Vol. Frac. Fiber = r_d2fs/

thickness. Figure 4 shows the cross section of sample 35vo1% (see Table 5) which is characteristic

of structures resulting from tape casting; as indicated in Table 5, this 4-ply, 0 °, 35 vol% fiber

composite was made using Ti-21A1-23Nb, -140 +325 powder and SCS-6 fiber at 121 fibers/inch.

Figure 5 shows sample HDH, a 4 ply, 26 vol% fiber composite plate made using Ti-6A1-4V powder

provided by Concurrent Technology Corp.; this -170 +325 powder (-80+200 for Coarse HDH) is

known as hydride-dehydried (HDH) due to the novel and inexpensive techniques used to

manufacture it. HDH powder is very irregular and nonspherical. Figures 6 through 8 show sections

transverse to the fibers in samples Coarse HDH, 45voi%, and 90 °.

For comparison, Figures 9, 10 and 11 show typical within-ply fiber spacing histograms for

composites fabricated by the powder cloth, foil-fiber-foil, and low-pressure plasma spray

techniques respectively, all taken from reference 3. The spacing resulting from powder cloth and

foil-fiber-foil techniques is poor, with a large portion of the fibers touching. Plasma spraying

resulted in fewer fibers touching, and a rather wide distribution of fiber spacings, indicating poor

control over the within-ply fiber spacing.

NASA/TM--2001-210684 12
(a)

00)

Figure 4a and b.---Cross-section of 0.036 inch thick

35 vol% fiber tape cast composite, 0°, Ti-21AI-23Nb,

-140 + 325 powder and SCS-6 fiber at 121 fibers/

inch.

Figure 5._Cross-section of 0.046 inch thick 26 vol%

fiber tape cast composite made uslng HDH, -170 +

325 mesh powder, Ti-6AI-4V.

NASA/TM--2001-210684 13
Figure 6._Cross-section of 0.048 inch thick Coarse

HDH tape cast composite, 25 vol% fiber, 0°,

Ti-6AI-4V, -80 + 200 mesh powder, 122 fibers/inch.

Figure 7.--Cross-section of 0.028 inch thick 45 vol%

fiber, 0° tape cast composite, Ti-24AI-11Nb, -100

mesh powder, 133 fibers/inch.

Figure 8.--Longitudinal section of 0.039 inch thick 90 °

tape cast composite, Ti-24AI-11Nb, -140 mesh, 120

fibers/inch, 32 vol% fiber.

NASA/TM--2001-210684 14
40--

35

3O

o_ 25

g 2o

H

10

m

m

m

m

m

Powder Cloth

0 I I I 1

5 15 25 35 45 55 65 75 85 95 105 115 125 135 145 155

Edge-to-edge spacing, p.m

Figure 9.--Histogram of typical within-ply SCS-6 fiber spacing in an approximately

28 vol% fiber composite made using the Powder Cloth technique, indicating

large numbers of fibers touching 3.

40--

35

3O

25

0

2O

10

i

I---"1 Foil-fiber-foil

n

m

F

[ _ I I I I 1_ I I I I--I--I

5 15 25 35 45 55 65 75 85 95 105 115 125 135 145 155

Edge-to-edge spacing, I*m

Figure 10.mHistogram of typical within-ply SCS-6 fiber spacing In an approximately

31 vol% fiber-foil-fiber composite, showing large numbers of fibers touching 3,

40--

35

3O

25 --

20 -

_'15 -- "I 10

5

0

r"--i Plasma Spray

5 15 25 35 45 55 65 75 85 95 105 115 125 135 145 155

Edge-to-edge spacing, i_m

Figure 11 ._l-listogram of typical within-ply SCS-6 fiber spacing in an approximately

28 vol% fiber composite made using low-pressure Plasma Spray, showing some

fibers touching 3.

NASA/TM--2001-210684 15
Figures 12 through 16 show the fiber spacing histograms for the tape cast composites.

Figure 12 shows the edge-to-edge fiber spacing to be narrowly grouped around the theoretical ideal

(l/fs - d) of 66 _tm for the 35vo1% composite, with 84% of the fibers spaced within 15 lam of the

theoretical ideal. The composite made by plasma spraying, in Fig. 11, has at best 42% of the fibers

within 15 lam of the spacing intended. The spacing shown in Fig. 15 for this very high volume

fraction fiber composite is not as good as in the other tape cast composites, but is still better than

the other fabrication techniques represented in Figure 9-11. Improvements could be made in

similar high volume fraction composites by decreasing the between ply spacing (thereby enabling

the within row spacing to be increased), and by double casting. In double casting the slurry pile in

front of the blade is maintained while the drum goes two times around, so after the tape is made

(but is still wet) the slurry pile and dozer blade pass over it again - working the powders deeper into

the spaces between the fibers. Double casting was used to make the six inch wide 90 ° composite,

Fig. 16, resulting in excellent spacing.

40--

35

30

25

0

g 2o

 '15

tl.

10

D

m

m

35 vol% fiber

] I I _l I. I ,--_ , I I I I I

5 15 25 35 45 55 65 75 85 95 105 115125135145 155

Edge-to-edge spacing, i_m

Figure 12.--Histogram of SCS-6 within-ply fiber spacing in the 35 vol% fiber, tape

cast composite (see Table 5).

40 m

35

3O

o_ 25

O

10

5

0

m

n

m

m

m

m

5 15 25 35 45

"--1

|

,

m

- I--

|

I 1 II

55 65 75

Edge-to-edge

Figure 13._Histogram of SCS-6 within-ply fiber

posite, 26 vol% fiber (see Table 5).

[Z_ HDH

i -T-t-T-11 J J I I

85 95 105 115 125 135 145 155

spacing, _m

spacing In the HDH, tape cast cornNASA/TM--2001-210684 16
4O

35

30

°_ 25

¢J

2O

_'15

10

i

m

m

r_l Coarse HDH

-----4

--L-I-]--_ ! I I 1 I I _ _ I I I

5 15 25 35 45 55 65 75 85 95 105 115 125 135 145155

Edge-to-edge spacing, i_m

Figure 14.--Histogram of SCS-6 within-ply fiber spacing in the coarse HDH, tape

cast composite, 25 vol% fiber (see Table 5).

40 _--

35

30

_ 25

® 20

U.

10

5

0

I--"1 45 vol% fiber

n

w

N

I 1 _ I I 1 I I 1 I__

5 15 25 35 45 55 65 75 85 95 105 115 125 135 145 155

Edge-to-edge spacing, _m

Figure 15.--Histogram of SCS-6 within-ply fiber spacing in the 45 vol% fiber, tape

cast composite (see Table 5).

40--

35--

30--

=_ 25 --

o

20 -

i15 --

U.

10--

5--

0

m

90 degree

I.I I 1 t I I I 1 I I I

15 25 35 45 55 65 75 85 95 105 115 125 135 145 155

Edge-to-edge spacing, p.m

Figure 16.--Histogram of SCS-6 within-ply fiber spacing in the 90 degree, tape cast

composite, 32 vol% fiber (see Table 5).

NASA/TM--2001-210684 17
Mechanical Properties

Tension and fatigue properties were measured using samples cut from the 32vo1% four-ply

SCS-6/Ti-24A1-1 INb plate (Table 5). The goal of these tests was to indicate whether panel quality

was similar to that obtained from other fabrication techniques. The room temperature ultimate

tensile strength and strain at failure of the 4-ply Ti-24A1-11Nb/SCS-6, 32vo1% fiber tape cast

composite were:

GUT S = 215 ksi (1477 MPa), and _ 1.15%,

which indicates the quality of the tensile properties to be good and similar to above average Ti24A1-11Nb composites made using powder cloth, 18'19 plasma spray, 2°'21 and foil-fiber-foil 22'23'24

techniques. For example, in reference 19 the best SiC/Ti-24Al-11Nb powder cloth sample had a

room temperature tensile strength of GUT s = 217 ksi (1496 MPa), and ef = 0.97%; the average stress

and strain of the, 31 to 36 fiber volume percent, powder cloth samples being GUTS = 179 ksi (1232

MPa), and ef = 0.77%.19 The results of the room temperature 0 - 120 ksi, v = 0.3 Hz fatigue test on

the 4-ply Ti-24A1-11Nb/SCS-6, 32vo1% fiber tape cast composite were:

Number of cycles to failure, Nf = 202,205 and

Maximum strain on the 100th cycle, Ac = 0.43%),

which indicates the room temperature fatigue properties to be good and similar to above average

Ti-24A1-11Nb composites made using other techniques. Hall et al. 23 showed Nf _ i00,000 in Ti24A1-11Nb/SCS-6 foil-fiber-foil composites of about 39 vol.% fiber, in load control at 1034 MPa

(150 ksi), R = 0.1, v = 0.33 Hz. Larsen 24 similarly showed Nf _= 100,000 in Ti-24AI-11Nb/SCS-6

foil-fiber-foil composites of about 35% fiber, in a stress range of 825 MPa (120 ksi), v = 0.33 Hz.

Using the fiber elastic modulus from Brindley, et al., of 400 GPa, the modulus at the

elastic limit of matrix-only Ti-24AI-11Nb of 108 GPa 19, and rule-of-mixture calculation, the ideal

modulus (near the elastic limit) of the Ti-24AI-1 INb/SCS-6, 32vo1% fiber tape cast composite was

201.4 GPa. At similar strain (0.43%) this tape cast composite had a modulus of 192 GPa, which is

95% of the rule-of-mixture value.

Though the above mechanical property tests are not exhaustive, they support the feasibility

of tape casting.

Tape Casting Process Feasibility Comparisons

Comparison of the "one-step" tape casting process detailed here with other processes is

difficult due to the lack of published data. However, my best attempt will be made on the basis of

what I have found in the literature, personal communications, and a per square foot basis of 4-ply

33 vol% fiber composite of square architecture using 0.00566 inch dia. SCS-6 fiber. At this fiber

diameter and desired volume percent fiber, the fiber spacing is 119 fiber/inch.

Even though drum wound tape casting is considered a batch process - it is still considered

to be economically feasible because of its: fast casting rate, excellent fiber spacing and architecture

control, low labor costs, and low waste of fiber and powder. Also, the process of casting the slurry

directly onto the fibers results in a simpler process with fewer steps.

The fiber winding rate on our 50 inch circumference drum is 15 rpm, equal to 63 ft/min.

Little effort has been invested in maximizing this rate - faster wind rates are believed feasible. At

this rotation and fiber spacing, fiber sheets are laid down at the rate of 0.044 ft2/min (or 22.7 rain

NASA/TM--2001-210684 18
ft2). TO put the slurry down on the fibers, a casting rate of 6 rpm was used. At 2 inches wide this is

a casting rate of 4.2 ftZ/min. However, we have also made castings 6 inches wide, showing the

feasibility of a casting rate of 12.6 ftZ/min (or 0.0794 rain/ft2). Curing time for the wet tape is

generally independent of the length and width. We let our tapes cure under hood ventilation

conditions without heat for about 20 min. No attempts have been made to accelerate curing - thus

for comparison purposes only (based on a 12 inch wide by 100 inch long casting curing in 20 min)

the curing rate will be assumed to be 0.4 ftZ/min (or 2.5 min/ft 2) for all applicable cases. Thus, the

total time to make the Tape Cast green tape is approximately (22.7 + 0.079 + 2.5 rain/ft 2) 25.3 rain/

ft 2 (or 0.04 ft2/min).

The creeling techniques used at Textron Specialty Materials 25 can be used to make

composite green tapes from the integration of matrix-only green tape - binder only tape - and fibers.

A rough estimate of the productivity of this technique based on 1994 procedures follows. First

matrix-only and binder only tapes are "tape cast" without fibers onto release paper. The casting rate

for these matrix and binder tapes is believed to be limited by the curing time, since the tape is cast

and must dry before it reaches the roll-up spool. By contrast, in tape casting on a drum, the entire

tape is curing at about the same time. Assuming it takes 10 min. to cure, a 1 ft. wide tape on a drying

table 10 ft. long would result in the production rate 1 ft2/min. (or 1 min/ft 2) for the matrix-only and

binder only tapes, each. In creeling, each fiber is fed through a spacer and into the sandwich area

between the matrix and binder tapes. Each fiber is fed from a spool hung on a large rack. For a 1

inch wide tape, at 119 fibers/inch, 119 fibers are fed one at a time through spacers, from 119 spools

all hanging on the spool rack and feeding into the casting area at the same time. It was estimated

that it takes about 1 minute to take a fiber from the spool and feed it into the sandwich area through

the spacers. Thus about 119 min/inch to feed the fibers in. The casting process is continuous once

all fibers are fed in, and done in 500 ft. lots. Thus to get the process started represents a rate of 0.34

ft2/min (or 2.86 min/ft2). Now the matrix and binder tapes are fed at a rate of 0.5 ft/min with the

fibers sandwiched between them with some heat. Assuming a width of 1 ft., this represents a rate

of 0.5 ft2/min (or 2 min/ft2). Thus the total time to make the green tape by creeling is about (2 x 1

+ 2.86 + 2 min/ft 2) 8 min/ft2(or 0.125 ft2/min). Which is a production rate about 3 times faster than

drum wound tape casting as done at NASA Glenn.

Considering the accuracy of these production estimates the values for drum wound tape

casting seem plausible, in particular since about 90% of the time in the process is used winding the

fiber on the drum. Simple and immediate improvements may be achieved by increasing the rate at

which fiber is put on the drum, and by having several drums working at the same time. There may

be labor advantages to tape casting also. Tape casting requires one person for the entire process.

And that person does not even need to be there during the most time consuming step, fiber winding.

Thus, in labor, tape casting takes less than about 0.4 hrlft 2 for production of the green tape. Creeling

takes 3 or 4 people during the creeling and at least one during the making of matrix and binder only

tapes. Thus, in labor, creeling takes about (2 tapes @ lmin/ft 2 x 1 person + 4.86 min/ft 2 x 4 people)

20 min./ft 2, or 0.33 hr/ft 2 for the production of the green tape. Thus these estimates of production

rate in terms of man hours for tape casting (0.4 hr/ft 2) and creeling (0.33 hr/ft 2) are comparable.

Binders

The physical characteristics of the matrix-only castings using the different binder recipes

developed are listed in Table 7. Due to glue-like bonding, tapes made with PIB could not be

removed from the substrate, thus castings were made on thin Mylar films, the Mylar then becoming

NASA/TM--2001-210684 19
partof thegreentape.Textronusesheatto helpwith removalof tapesusingPIB fromthesubstrate.

UndesirablewereNeoCrylB-700andPMMA dueto their strengthandwarpage.It wasfoundthat

mixing PIB andPMMA resultedin astrong,adequatelyflexibletapethatreleasedeasilyfrom the

substrate.

Table7 Characteristicsof matrix-onlytapecastingusing-325meshFeCrA1Yandadozerblade

0.04inchesabovethesubstrate.Referto Table3for slurryrecipedetails.[gg] = g/cm3,[S] = %

Binder Properties Substrate/removal Shrinkage, S Green density, pg

Methocel Strong, flexible, S. Steel, glass 75. 4.

like paper. Teflon/very easy

NeoCryl, Brittle, warped Teflon/easy 47. 4.5

B-700

NeoCryl, Strong, flexible Teflon/very easy 37 4.1

A-614

PIBIo w Strong, flexible on Mylar film/ 38 4.1

p = 0.92g/cm 3 not removed

PMMAhig h Weak, brittle, Teflon/very easy 52 4.1

warped

PVP Strong, flexible Teflon/easy 70 4.2

Copolymer, Strong, flexible Teflon/very easy 50 4.

PIB + PMMA

Table 8 lists the results of the Thermal Gravimetric Analysis. Although some of the TGA

data related to cleanliness are qualitative, and contamination specifications were not available, it is

known that oxygen content in the matrix can significantly reduce matrix strain at failure. 19 To

prevent undesirable contamination of the composite, only clean "burning" binders are desired; thus

Methocel, NeoCryl A-614, PIBIo w on Mylar, and PVP were judged unacceptable. The copolymer

mixture of PIBlo w + PMMAhig h gave the best combination of physical properties and cleanliness

and was thus the binder used to tape cast composites for mechanical testing. Burnout is also

complete below 455 °C, the temperature titanium oxide is absorbed into the matrix.12 Others use

PIB and have shown it to be clean when used with metal powders. 7,12

Oxygen and carbon pickup in a FeCrA1Y/W fiber composite were examined using a double

dose of the PIB + PMMA binder in the green mats. All of the O and C were assumed to be in the

matrix, and weight percents calculated on the basis of the matrix-only (with the mass of the fibers

removed). The virgin powder had 0.18 and 0.011 wt% O and C respectively - while the matrix, after

vacuum hot pressing, had 0.128 and 0.027 wt% O and C respectively in the matrix. It is clear that

oxygen is not a problem - since O is lower in the composite than in the virgin powder. Carbon

pickup of 0.016% C (160ppm) is also low and compares well with other clean processes noted in

the literature. 6.'8

*It is believed, due to prior use of the convention, that the % C contamination noted in Table IV of reference

6 for W/NiA! is on the basis of the composite mass. If the C is assumed to be in the matrix there is about

0.017% C for W/NiA1 (pickup of 150ppm C).

NASA/TM--2001-210684 20
Table8Resultsof ThermalGravimetricAnalysisof binders.SeeTable3for recipesused.Nometal

powderwasusedin theTGA tests.

Binder Residualmass,mg Cruciblecondition Burnouttemperatures,°C

Methocel 0.4 Poor, black, dirty

NeoCryl, B-700 0.1 Excellent

NeoCryl, A-614 0.2 Fair, black

PIBIo w 0.0 Excellent

Mylar 1.7 Poor, black, dirty

PMMAhig h 0.2 Very good

Copolymer, 0.0 Excellent

PIB 1+ PMMA h

PVP 0.27 Poor, black

single mass loss peak at 350

mass loss peaks at 125, 280, 350

last mass loss at 350 to 400

last mass loss at 365

single mass loss peak at 420

mass loss peaks at 125, 260, 340

mass loss peaks at 130, 265,365

single mass loss peak at 430

The toxicological properties of PIB and PMMA have not been thoroughly investigated. PIB

was developed as a synthetic rubber, and PMMA is, among other uses, a paint additive. Many here

at NASA Glenn have handled these materials with no known negative health effects. These

materials however should never be inhaled or ingested. Contact with bare skin should be avoided.

As with most polymers, these materials are suspected carcinogens to tissues around an implant

sites where ever retention may occur, such as in the skin, lungs, or organs. 26 The disposal of PIB

and PMMA should be by mixing with a combustible solvent and burning in a chemical incinerator

with afterburner and scrubber. The toxicity of toluene, the solvent used with PIB and PMMA, can

be summarized as moderate through oral, inhalation and intraperitoneal routes and low via

absorption through the skin. 26 Acute poisoning, resulting from exposures to high concentrations of

toluene vapors are rare. Commercial grades of toluene usually contain small amounts of the

poisonous and accumulative benzene as an impurity. With proper venting, toluene does not pose a

toxicological problem. Similarly, no outstanding toxicology problems were found for any of the

other binders.

The copolymer mixture of PIBlo w and PMMAhig h listed in Table 3 was the best binder.

PIBlo w was chosen over the two higher molecular weight PIB's available because PIBlo w took less

time to dissolve in the solvent and formed a more stable binder/solvent mix. Matrix-only tapes

made with PIB are extremely flexible with nearly no stiffness; resulting in a cloth analogous to silk,

with no strength in compression, like a chain. Tapes made with PIBlo w by itself could not be

removed without damage from the substrate. PMMAhig h was chosen over the two lower molecular

weight PMMA's available because PMMAhig h made smoother and flatter matrix-only tapes. Tapes

made with PMMAhig h alone were too weak and brittle. Mixing PIBlo w and PMMAhig h resulted in

a tape with adequate strength and flexibility and good release properties from the substrate.

NASA/TM--2001-210684 21
Improvementscanbemadeto theTable3PIB+PMMA recipe.I believethatimprovements

instrengthandflexibility canbeachievedby increasingtheamountofPIBanddecreasingPMMA.

Theseimprovementsmayenableadecreasein theamountof binderused.Theincreased

flexibility of a PIB basedbindermayalsohelpwith theproductionof morecomplexshapes.

PMMA is addedsimply toimprovethereleasepropertiesof thePIB;otherbindersmayalsodothis

well. A groupat TextronSpecialtyMaterialsusesaPIB-10%NeoCrylbindermix. Futureefforts

will attemptto improvethebinderby increasingthePIB:PMMA ratio in therecipe.

Thedensityof fiber free,matrix-only,tapecastgreentapes,Pg, and the wet to green

shrinkage, S, for different metal powders are listed in Table 9. The green tape densities and

shrinkage data listed in Table 9 are averages of fiber free tape castings and of tapes with fibers cast

on a drum (see eq. 2 and 3). Most castings were made with fibers using a blade height very close

to that needed for a 35 vol% fiber composite (about 0.020" blade height). It is worth noting however

that P_ and S were found to vary slightly as a function of blade height. Other more significant

threats to the accuracy of the blade height are: one of the dozer blade sides running over a fiber,

and ovcrlapping release paper. In developing a Tape Casting program however, it is recommended

to quantify how Pg and S vary with blade height. In castings made with FeCrA1Y, Pg and S were

5q louver than the average at the smallest blade heights (0.015") and 5% larger at the larger blade

heights 10.030"). Variation in blade height, from that determined from the mean, was found to be

about 0.001 inch.

Table 9 Average fiber free green tape density, Pg, and wet to green shrinkage, S, for different metal

po_vdcrs, all using PIBlo w + PMMAhig h binder (recipe given in Table 3). All powders were

spherical except for the Ti-6AI-4V, HDH powder; this hydride-dehydride powder was very rough,

irregular, and nonspherical.

Pox_ der pg, g/cm 3 Shrinkage, S, %

"15-21AI-23Nb at%, -140 +325 mesh 2.12

Ti-24AI-i 1Nb at%, -140 and -200 mesh, 2.02

Ti-6AI-4V wt%, - 100 mesh 1.74

Ti-6AI-4V, HDH -80, +200 and -170, +325 mesh 1.6

MoSi2-30Si3N 4 vol%, -325 mesh, 1.1

Fe-24Cr-4AI- 1Y wt%, -325 mesh 3.6

Fe-25Ni-29Co-5.5Cr-0.5A1 wt%, -325 mesh, Pm=8.25 3.2

Fe-11.7AI- 1.53V-0.29C-0.5Mn wt%, -325 mesh, pro=6.7 3.1

43

42

30

18

46

5O

62*

61"

*Not averaged, based on a single measurement.

NASA/TM--2001-210684 22
Conclusions

A process by which metal matrix composites can be made was presented. The process

involves putting a powder slurry on fibers to make a precursor green tape. These green tapes are

cut, stacked and hot pressed to form the fully dense composite. A computer program was presented

which enables compIete quantification and control of the process. Once some easily obtained

properties of the slurry and its behavior are determined (such as the shrinkage from the wet to green

state, and the density of the green tape) modification of the fiber spacing and blade height give the

maker precise control of fiber volume fraction, and fiber architecture in the composite. The process

was shown to be accurate and flexible through the production of a wide variety of volume fraction

fiber composites made from a wide variety of fibers and powders. The most time consuming step

of the tape casting process (other than hot pressing) was winding the fiber on the drum. The tape

casting techniques developed resulted in high quality metal matrix composites, with ultimate

tensile strength in the range of 215 ksi (1477 MPa), a strain at failure of 1.15%, and in fatigue at

room temperature 0 - 120 ksi, v = 0.3 Hz, a 4-ply Ti-24Al-11Nb/SCS-6, 32vo1% fiber tape cast

composite lasted 202,205 cycles with a maximum strain on the 100th cycle of 0.43%.

References

1) HITEMP. Review 1992, Vol. II: Compressor/Turbine Materials (MetaFIntermetallic Matrix

Composites), Proc. of the 5th Ann. HITEMP Review, Oct. 1992, NASA Conf. Pub. 10104.

2) HITEMP. Review 1993, Vol. ]I: Compressor/Turbine Materials-MMC's/IMC' s, Proc. of the 6th

Ann. HITEMP Review, Oct. 1993, NASA Conf. Pub. 19117.

3) "Continuous Fiber-Reinforced Titanium Aluminide Composites," by R.A. MacKay, EK.

Brindley and EH. Froes, JOM, Vol. 43, No.5, May 1991, pp. 23-29.

4) "Titanium Aluminides for Aerospace Application" High Temperature Aluminides and

Intermetallics, ed. S.H. Whang et al., Warrendale, PA, TMS, 1990, pp. 521-556.

5) "Relationship among Processing, Surface Structure, and Properties of Arc Sprayed Fibers and

Composite," by J.W. Pickens, J.W. Smith, and B.A. Lerch, HITEMP. Review 1992, Vol. II:

Compressor/Turbine Materials, 1992, NASA Conf. Pub. 10104, pp. 31-1 - 31-17.

6) "Fabrication of Intermetallic Matrix Composites by the Powder Cloth Process," by J.W. Pickens,

R.D. Noebe, and G.K. Watson, 1989, NASA TM 102060.

7) "Fabrication of Titanium-Aluminide Composites by Tape Casting," by J.T. Niemann and J.E

Edd, in Titanium Aluminide Composites, ed. P.R. Smith et al., 1991, Wright Laboratory, WL-TR91-4020, pp. 300-314.

8) "Scale-Up of a Tape Casting Process for Continuous Fiber-Reinforced Metal and Intermetallic

Matrix Composites," by J.E Edd and J.T. Niemann, pp. 158-173.

9) "processing of Ceramic-Matrix/Platelet Composites by Tape Casting and Lamination," by T.

Claal3en and N. Claussen, Jol. of the Euro. Ceramic Soc., vol. 10, 1992, pp. 263-271.

10) "NASP Materials and Structures Augmentation Program Final Report", Titanium Matrix

Composites, Vol. IV - Fabrication Development, by J.T. Niemann, S.M. Sullivan, D.J. Thies et al.,

1993, NASP Contractor Report 1145, Vol. IV, Report MDC 91B0487 Vol. IV.

NASA/TM_2001-210684 23
11)S.Spear,Atlantic ResearchCorp.,presentationat the HPC Program Workshop, 1994.

12) "Material behavior modeling for understanding and controlling microstructure evolution- Task

4.1.6 (orthorhombic titanium composite processing)," by J.C. Chesnutt et al., WL-TR-95-4020,

1995, Wright Laboratory, WPAFB, Ohio, p. 46-50.

13) "Modeling of Titanium Matrix Composite Consolidation," by C.C. Bampton, 1993, interim

report, WL-TR-94-4009, Wright Laboratory, WPAFB, Ohio.

14) "Modeling of Titanium Matrix Composite Consolidation" by C.C. Bampton, K. Newell, and

W.L. Morris, 1994, WL-TR-94-4098, Wright Laboratory, WPAFB, Ohio.

15) "Strong, Tough, and Pest Resistant MoSi2-Base Hybrid Composite for Structure

Applications," by M.G. Hebsur and M.V. Nathal, 1997, NASA TM 107471.

16) "Development and characterization of SiC(fcqVIoSi2-Si3N 4(p) hybrid composites," by Mohan

Hebsur, 1999, Mat. Sci. and Eng. A261, pp. 2-37.

17) "Wire Arc Spray Fabrication of Superalloy MMC's Reinforced by Single Crystal Sapphire:

Fiber Damage Considerations," by J.W. Pickens and I.E. Locci, HITEMP Review 1994, Vol. ]I,

NASA Conf. Pub. 10146, pp. 47-1 to 47-12.

18) "Factors which Influence Tensile Strength of a SiCfri-24Al-1 I Nb (at%) Composite," by P.K.

Brindley, S.L. Draper, M.V. Nathal, and J.I. Eldridge, in Fundamental Relationships Between

Microstructure and Mechanical Properties of Metal-Matrix Composites, ed. by P.K. Liaw and M.

N. Gungor, TMS, 1990, pp. 387-401.

19) "The Effect of Temperature on the Deformation and Fracture of SiCffi-24-11Nb," by P.K.

Brindley et al., Metall. Trans. A, Vol. 23A, 1992, pp 2527-2540.

20) J.J. Jackson and D.R. Spriffs, Air Force Contract F33657-86-C-2136, Wright-Patterson AFB,

OH, 1988, Interim Report No. 3.

21) D.R. Pank, A.M. Ritter, R.A. Amato, and J.J. Jackson, in Titanium Aluminide Composites, P.R.

Smith, S.J. Balsone, and T. Micholas, eds., WL-TR-91-4020, Wright-Patterson AFB, OH, 1991,

pp. 382-98.

22) M.L. Gambone, WRDC-TR-89-4145-vol-2, Wright-Patterson AFB, OH, 1990.

23) "Damage Tolerance Concepts for Titanium-Aluminide Composites," J.A. Hall et al., Sept.

1993, 8th Interim Report for Contract No. F33615-89-C-5621, p. 38-40, 68.

24) "Titanium Aluminide Composites for Aerospace Applications," by J.M. Larsen et al. in

Titanium Aluminide Composites, ed. P.R. Smith et al., 1991, Wright Laboratory, WL-TR-91-4020,

pp. 363-381.

25) Personal communication, Bill Grant and Mr. Lewis, Textron Specialty Materials, Sept. 14,

1994.

26) "Dangerous Properties of Industrial Material" 5th Edition, N. Irving Sax, Litton Educational

Pub. Inc., 1979, p. 329, 921, 1035.

NASA/TM--2001-210684 24
Appendix A

The FORTRAN 77 program Tcast2 is designed to assist tape casting of a powder slurry onto fibers.

The program can also be used for tape casting of fiber free green mats. The source code, Tcast2.f,

was compiled using a Lahey FORTRAN compiler to produce an executable file. The executable

file is Tcast2.exe. Any IBM compatible PC with an 80286 or better processor running DOS 3 can

be used. What follows are the code prompts, an example of inputs and displayed output.

This program estimates the fiber volume fraction

of tape cast composites, and the dozer blade

heights needed to produce them. It is assumed that

a powder slurry will be cast onto regularly spaced

fibers. The program will need the density of the

fibers, the matrix density, and that of the green

mat without fibers. The density of the green mat

can be found by weighing and measuring a sample

fiber free casting. The program will also request

D1 the percent shrinkage in thickness from the wet to

the green state for the fiber free tape. This

allows the program to estimate the dozer blade

heights. This program can also help with the casting of fiber free mats. To use the code for a

fiber free system - use a very, very small fiber

diameter and a fiber spacing equal to the

number of green plies used plus 1, divided by the

final thickness wanted in the plate, that is,

fs=(p+ 1)/Tc); with the drum: between ply fiber

spacing ratio equal to 1.

D2 Input the density of the fully dense matrix in g/cc.

Enter zero to QUIT.

D3

4.5

Input the density of the fibers in g/cc.

D4

3.00

Input the diameter of the fibers in units of inches.

D5

0.00568

Input the fiber spacing in fibers/inch.

D6

123

Input the numbers of plies used in the composite, not

including the fiber free end ply.

D7

4

Input the ratio of the drum fiber spacing

(in fiber/in) to the desired spacing between

the plies (in fib/in).

NASA/TM--2001-210684 25
D8

1

Thevolumefractionfiberin thecompositeis,VF=

Thedensityof thecompositeis, Dc= 3.96526

Inputthedensityof thegreentapewithout fibers.

0.356494

D9

D10

2.0

Thethicknessof thegreentapewith fibersis,

Tgf= 3.69839E-02cm

Input theshrinkageexpectedfor a fiberfreeply from

thewetto greenstate,thatis, thefractiondecrease

in thicknessbetweenthewet ascasttapeandafter

thesolventhasleft thebindermakingthegreentape.

With adozerbladeheightof BH andagreenfiberfree

ply thicknessof Tg, theshrinkageexpectedis,

S=(BH-Tg)/BH.

Dll

0.42

Thedozerbladeheightneededfor thepliescontaining

fibersat 123.000fiber/inis,BHf= 5.52081E-02cm

Thebladeheightneededfor theendply is,

BHe= 2.41417E-02cm

D13 Summarizingresults:

Volumefrac.fibersin thedensecompositeis

VF= 0.356494

Bladeheightw/fibers = 2.17355E-02in

Bladeheightfor endply (nofibers)= 9.50462E-03in

Densityof fully densecomposite= 3.96526g/cc

Thicknessof greentapew/fibers,

Tgf= 1.45606E-02in

Thicknessof greenendply, nofibers,

Tge= 5.51268E-03in

Thicknessof thedensecomposite= 3.49704E-02in

D14 Input thedensityof the fully dense matrix in g/cc.

Enter zero to QUIT.

The first thing that comes up after the initiation of the executable file Tcast2.exe are the displays

marked above as D 1 and D2. In D 1, fs is the fiber spacing in units of fibers per inch, p is the number

of plies, and Tc is the thickness you wish the final plate to be. When considering a fiber free system,

as when using the code to make fibrous composites, p does not include the needed matrix-only end

ply. Thus when making a "4-ply" plate, with or without fiber, 5 plies are actually used. The drum:

between ply fiber spacing ratio is ct, see (6).

NASA/TM--2001-210684 26
Appendix B

The FORTRAN Tcast2 code.

10

ii

20

Program Tcast

implicit real (j-n)

by

Henry C. de Groh III

NASA m.s.105-1

Cleveland OH 44135

(216) 433-5025

Last modified Sept. 26, 1994

write i* *)

write * *)

write * *)

write * *)

wrlte * *)

write * * )

write * *)

write * *

write * *

write (* *

write (* *

write(* *

write(* *

write (* *

write (* *

write (* *

write (* *

write (* *

write (* *

write (* *

write (* *

Dm, density of the matrix

Dm=0

Df, Density of the fiber

Df=0

This program estimates the fiber volume fraction'

of tape cast composites, and the dozer blade'

heights needed to produce them. It is assumed that'

a powder slurry will be cast onto regularly spaced'

fibers. The program will need the density of the'

fibers, the matrix density, and that of the green'

mat without fibers. The density of the green mat'

can be found by weighing and measuring a sample'

fiber free casting. The program will also request'

the percent shrinkage in thickness from the wet to'

the green state for the fiber free tape. This'

allows the program to estimate the dozer blade'

'heights. This program can also help with the cast-'

'ing of fiber free mats. To use the code for a'

'fiber free system - use a very, very small fiber'

'diameter and a fiber spacing equal to the'

'number of green plies used plus i, divided by the'

'final thickness wanted in the plate, that is,'

'fs=(p+l)/Tc; with the drum:between ply fiber'

'spacing ratio equal to I.'

ir

23

* di, diameter of the fiber in inches

25 di=0

* d, fiber diameter in cm

d=0

* fsi, fiber spacing in fibers per inch

fsi=0

* fs, spacing in fibers/cm

fs=0

* ps, the inerply to interply fiber spacing ratio, drum fiber

* spacing in fibers/in :to: fiber spacing through the thickness

ps=0

* p, number of plies in the composite

p=0

* Dg, density of the fiber free green tape

30 Dg=0

* VFg, volume fraction fiber in the green tape

NASA/TM--2001-210684 27
33

4O

45

5O

55

60

*65

*

68

VFg:0

Dgf, density of the green tape with fibers

Dgf=0

Tgf, thickness of the green ply with fibers

Tgf=0

S, fractional shrinkage from wet to green for fiber free tapes

S=0

Sc, fractional shrinkage from wet to green with fibers

Sc=0

write(*,*)'Input the density of the fully dense matrix in g/cc.'

write(*,*)'Enter zero to QUIT.'

write(*,*)' '

read(*,*) Dm

If(Dm.eq.0) go to 109

write(*,*)'Input the density of the fibers in g/cc.'

write(*,*)' '

read(*,*) Df

write(*,*)'Input the diameter of the fibers in units of inches.'

write(*,*)' '

read(*,*) di

d=di*2.54

write(*,*)'Input the fiber spacing in fibers/inch.'

write(*,*)' '

read(*,*) fsi

fs=fsi/2.54

write(*,*) 'Input the numbers of plies used in the composite, not'

write(*,*)'including the fiber free end ply.'

write(*,*)' '

read(*,*) p

write(*,*)'Input the ratio of the drum fiber spacing'

%Tite(*,*)' (in fiber/in) to the desired spacing between'

write(*,*)'the plies (in fib/in).'

write(*,*)' '

read(*,*) ps

VF is the volume fraction of fibers expected in the composite.

Note that the thickness of the dense plies containing fibers is ps/fs.

VF=3.1416*d*d*p*fs/4.0/((p+l)*ps/fs-d)

write(*,*)'The volume fraction fiber in the composite is, VF=',VF

Dc is the density of the matrix plus fiber composite.

Dc=VF*Df+(I.0-VF)*Dm

write(*,*)'The density of the composite is, Dc=',Dc

Dg is the desity of the fiber free green tape.

wTite(*,*) 'Input the density of the green tape without fibers.'

write(*,*)' '

read(*,*) Dg

The density of the green tape WITH the fibers will be needed for later

calculations,Dgf, but, this density will vary with fiber spacing. Thus

a system of two equations (with two unknowns) will be set up and solved.

VFg is the volume fraction of fibers in the green tape (single ply with

fibers). In the first equation for VFg, Dg is used as a starting point,

later, Dg is replaced by Dgf, the density of the green tape with fibers.

VFg=3.1416*d*d/4.0*fs*fs*Dg/Dc/ps

a=VFg

Dgf=Df*VFg+Dg*(I.0-VFg)

NASA/TM--2001-210684 28
7O

76

8O

*87

VFg=3.1416*d*d/4.0*fs*fs*Dgf/Dc/ps

If(abs(a-VFg) .GT. 0.00001) go to 68

Tgf is the thickness of the green ply with fibers.

Tgf=Dc/Dgf/fs*ps

wrlte(* * 'The thickness of the green tape with fibers is,'

write(* * 'Tgf=',Tgf, 'cm'

write(* * 'Input the shrinkage expected for a fiber free ply from'

wrlte(* * 'the wet to green state, that is, the fraction decrease'

wrlte(* * 'in thickness between the wet as cast tape and after'

write(* * 'the solvent has left the binder making the green tape.'

write(* * 'With a dozer blade height of BH and a green fiber free'

write(* * 'ply thickness of Tg, the shrinkage expected is,'

write(* * 'S=(BH-Tg)/BH.'

write(* * ' '

read(*,*) S

Sc is the thickness shrinkage expected in the ply with fibers.

Sc=VFg*0.0+(I-VFg)*S

Sc also equals (BHf-Tgf)/BHf, where BHf is the blade height needed for

the composite ply containing the fibers.

BHf=Tgf/(l.0-Sc)

write(*,*)'The dozer blade height needed for the plies containing'

90 write(*,*)'fibers at',fsi,' fiber/in is, BHf=',BHf, 'cm'

* BHe is the blade height needed for the powder cloth end ply.

* Te is the thickness of the fully dense end ply (no fibers).

* Tge is the thickness of the green end ply.

Te=ps/fs-d

Tge=Te*Dm/Dg

96 BHe:Tge/(I.0-S)

* Tc is the thickness of the of the dense multiply composite.

Tc=(ps/fs*p+Te)/2.54

write(*,*)'The blade height needed for the end ply is,'

wTite(*,*) 'BHe=',BHe,'cm'

write(*,*)' '

write(*,*) 'Summarizing results:'

write(*,*)'Volume frac. fibers in the dense composite is'

write(*,*) 'VF=',VF

i00 BHfi=BHf/2.54

write(*,*)'Blade height w/ fibers =',BHfi,'in'

BHei=BHe/2.54

write(*,*)'Blade height for end ply (no fibers) =',BHei,'in'

104 wTite(*,*) 'Density of fully dense composite =',Dc, 'g/cc'

Tgfi=Tgf/2.54

write(*,*)'Thickness of green tape w/ fibers,'

write(*,*)'Tgf=',Tgfi,'in'

Tgei=Tge/2.54

write(*,*)'Thickness of green end ply, no fibers,'

write(*,*)'Tge=',Tgei, 'in'

write(*,*)'Thickness of the dense composite =',Tc,'in'

write(*,*)' '

go to 23

109 stop

end

NASA/TM--2001-210684 29
Form Approved REPORT DOCUMENTATION PAGE

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated_to average 1 hour per response, including the time for reviewing instructions, seamhing existing data sources,

gathering and maintaln|ng the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202_1302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

February 200 l

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

One-Step Tape Casting of Composites via Slurry on Fiber

6. AUTHOR(S)

Henry C. de Groh III

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

3. REPORT TYPE AND DATES COVERED

Technical Memorandum

WU-708-31-13--00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-12611

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--2001-210684

11. SUPPLEMENTARY NOTES

Responsible person, Henry C. de Groh HI, organization code 5120, Mail Stop 105-1, E-mail: henry.degroh@grc.nasa.gov,

URL: http://cmI.grc.nasa.gov/degroh, 216--433-5025.

12=. DISTRIBUTIO N/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category: 24 Distribution: Nonstandard

Available electronically at http;//gltrs.grc.nasa.gov/GLTRS

This publication is available from the NASA Center for AeroSpace Information, 301-621_)390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

A process by which metal matrix composites can be made was presented. The process involves putting a powder slurry on

fibers to make a precursor green tape. These green tapes are cut, stacked and hot pressed to form the fully dense composite. A computer program was presented which enables complete quantification and control of the process. Once some

easily obtained properties of the slurry and its behavior are determined (such as the shrinkage from the wet to green state,

and the density of the green tape) modification of the fiber spacing and blade height give the maker precise control of fiber

volume fraction, and fiber architecture in the composite. The process was shown to be accurate and flexible through the

production of a wide variety of volume fraction fiber composites made from a wide variety of fibers and powders. The

most time consuming step of the tape casting process (other than hot pressing) was winding the fiber on the drum. The

tape casting techniques developed resulted in high quality metal matrix composites, with ultimate tensile strength in the

range of 215 ksi (1477 MPa), a strain at failure of 1.15 percent, and in fatigue at room temperature 0 to 120 ksi, n = 0.3

Hz, a 4-ply Ti-24A1-11Nb/SCS-6, 32 vol% fiber tape cast composite lasted 202,205 cycles with a maximum strain on the

100th cycle of 0.43 percent.

14.

17.

SUBJECT TERMS

Metal matrix; MMC; Continuous fiber; Processing manufacture

SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION

OF REPORT OF THIS PAGE OF ABSTRACT

Unclassified Unclassified Unclassified

15. NUMBER OF PAGES

_5

16. PRICE CODE

20. LIMITATION OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102