Michael C. Halbig and Joseph E. Grady

Glenn Research Center, Cleveland, Ohio

Mrityunjay Singh

Ohio Aerospace Institute, Brook Park, Ohio

Jack Ramsey, Clark Patterson, and Tom Santelle

Rapid Prototyping+Manufacturing (rp+m), Avon Lake, Ohio

A Fully Nonmetallic Gas Turbine Engine Enabled by 

Additive Manufacturing

Part III: Additive Manufacturing and Characterization of Ceramic Composites

NASA/TM—2015-218892

December 2015
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Michael C. Halbig and Joseph E. Grady

Glenn Research Center, Cleveland, Ohio

Mrityunjay Singh

Ohio Aerospace Institute, Brook Park, Ohio

Jack Ramsey, Clark Patterson, and Tom Santelle

Rapid Prototyping+Manufacturing (rp+m), Avon Lake, Ohio

A Fully Nonmetallic Gas Turbine Engine Enabled by 

Additive Manufacturing

Part III: Additive Manufacturing and Characterization of Ceramic Composites

NASA/TM—2015-218892

December 2015

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

The authors would like to thank Drs. Mike Dudley and Koushik Datta from NASA Aeronautics Research Institute for their continuous 

support and encouragement. The authors would also like to thank Ron Phillips (Vantage Partners, LLC) for mechanical testing,

Joy Buehler (Vantage Partners, LLC) for epoxy mounting and polishing of samples, and Gerald Hurd (NASA GRC) for conducting 

1450 °C heat treatment furnace runs. This work was supported by the NASA Aeronautics Research Institute (NARI) Program.

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This report is available in electronic form at http://www.sti.nasa.gov/ and http://ntrs.nasa.gov/
NASA/TM—2015-218892 1 

A Fully Nonmetallic Gas Turbine Engine Enabled by 

Additive Manufacturing 

Part III: Additive Manufacturing and Characterization of 

Ceramic Composites 

Michael C. Halbig and Joseph E. Grady 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Mrityunjay Singh 

Ohio Aerospace Institute 

Brook Park, Ohio 44142 

Jack Ramsey, Clark Patterson, and Tom Santelle 

Rapid Prototyping+Manufacturing (rp+m) 

Avon Lake, Ohio 44012 

Abstract 

This publication is the third part of a three part report of the project entitled “A Fully Nonmetallic 

Gas Turbine Engine Enabled by Additive Manufacturing” funded by NASA Aeronautics Research 

Institute (NARI). The objective of this project was to conduct additive manufacturing to produce ceramic 

matrix composite materials and aircraft engine components by the binder jet process. Different SiC 

powders with median sizes ranging from 9.3 to 53.0 m were investigated solely and in powder blends in 

order to maximize powder packing. Various infiltration approaches were investigated to include 

polycarbosilane (SMP-10), phenolic, and liquid silicon. Single infiltrations of SMP-10 and phenolic only 

slightly filled in the interior. When the SMP-10 was loaded with sub-micron sized SiC powders, the 

infiltrant gave a much better result of filling in the interior. Silicon carbide fibers were added to the 

powder bed to make ceramic matrix composite materials. Microscopy showed that the fibers were well 

distributed with no preferred orientation on the horizontal plane and fibers in the vertical plane were at 

angles as much as 45°. Secondary infiltration steps were necessary to further densify the material. Two to 

three extra infiltration steps of SMP-10 increased the density by 0.20 to 0.55 g/cc. However, the highest 

densities achieved were 2.10 to 2.15 g/cc. Mechanical tests consisting of 4 point bend tests were 

conducted. Samples from the two CMC panels had higher strengths and strains to failure than the samples 

from the two nonfiber reinforced panels. The highest strengths were from Set N with 65 vol% fiber 

loading which had an average strength of 66 MPa. Analysis of the fracture surfaces did not reveal pullout 

of the reinforcing fibers. Blunt fiber failure suggested that there was not composite behavior. The binder 

jet additive manufacturing method was used to also demonstrate the fabrication of turbine engine vane 

components of two different designs and sizes. The binder jet method has benefits over the conventional 

manufacturing of CMCs in that prototype and production parts can be fabricated quickly and 

economically with no tooling and extensive hand layup. 

Introduction 

Ceramic matrix composites (CMCs) with their continuous fiber reinforcement, high fracture 

toughness, and favorable strengths are very promising materials for high temperature structural 

applications. The elevated temperature capability and lower cooling requirements of CMCs make them 

particularly beneficial for replacing metallic components in turbine engine applications. These capabilities 

allow for improved fuel efficiency and reduced emissions. Silicon carbide fiber reinforced silicon carbide 
NASA/TM—2015-218892 2 

Figure 1.—Conventional manufacturing of CMCs compared to the newly emerging area of additive manufacturing. 

matrix (SiC/SiC) materials are a leading CMC for such applications (Refs. 1 to 6). However, the cost of 

the materials, the complexity in processing, and the limitations in obtaining complex geometries with 

current CMC fabrication approaches, requires alternative fabrication methods to be investigated such as 

additive manufacturing (AM). 

Additive manufacturing allows custom designed parts to be fabricated layer by layer with much 

greater complexity into 3D shapes than traditional manufacturing methods. Compared to conventional 

manufacturing, additive manufacturing of CMCs is in the early stages of development as shown in 

Figure 1. The efforts in conventional manufacturing of CMCs started over 30 years ago and have 

continued to progress over the years. The materials are just now reaching maturity and are getting ready 

to enter service. However, due to high cost of the materials (fibers and coatings) and of the many 

processing steps (hand layup, fiber coatings, and matrix infiltration), it is not cost effective to conduct 

small processing runs. Also, with the manual hand layup processes and the use of 2D fiber architectures 

in cloth form, it is very challenging to obtain large, complex shaped parts for turbine engine components, 

especially those that require internal channels and 3D geometries. The conventional processing methods 

tend to restrict the components toward structural rather than multifunctional applications. Additive 

manufacturing can offer several significant benefits over conventional processing. Prototypes can be 

rapidly manufactured, small batches can be produced economically, and tooling and molds are not 

required, since it is a freeform fabrication approach. AM has been demonstrated for metals and polymers 

and is at higher technology readiness levels (TRL) than for ceramics. While research into the additive 

manufacturing of ceramics is starting to increase, there has been even less activity reported in the 

literature for the additive manufacturing of ceramic matrix composites. While there are many additive 

manufacturing approaches (Refs. 7 and 8), most do not allow the versatility to include fiber reinforcement 

additions except laminated object manufacturing (LOM) and power bed processing methods. 

LOM is a very promising method for fabricating continuous fiber reinforced CMCs that are most 

similar to current CMCs which have 1D or 2D fiber architectures. In the LOM process, layers of green or 

adhesive-coated laminates are cut with a laser and then successively stacked and then bonded or glued 

together to form the part from the bottom to the top. There are only a few references that appear in the 

literature for the laminated object manufacturing of SiC-based ceramics and fiber reinforced ceramic 

composites. Windsheimer and Travitzky et al. (Refs. 9 and 10) have demonstrated the fabrication of a 

nonfiber reinforced material using preforms derived from preceramic paper to obtain a Si-SiC material. 
NASA/TM—2015-218892 3 

Also, biomorphous SiSiC composites have been fabricated by Weisensel et al. (Ref. 11) by LOM in 

which pyrolyzed paper sheets and phenolic resin were used to make biocarbon preforms. The biocarbon 

preforms had a 34 percent reduction in weight after pyrolysis, and the 69.4 percent porous preforms were 

further densified by a silicon (Si) liquid infiltration step. Upon analysis, it was found that the materials 

had 16 vol% unreacted carbon and 23 vol% residual silicon that had infiltrated into the porous regions of 

the laminates. It should be noted that when considering such materials and processes for high temperature 

and turbine engine applications, the residual silicon is not desirable since it will limit the use temperatures 

to below 1300 °C. 

As far as the LOM of CMC materials, Klosterman et al. (Ref. 12) have reported on the use of bilayer 

materials that had ceramic grade Nicalon (CG-Nicalon) fiber prepregs stacked in alternating layers with 

monolithic ceramic tapes. Composite properties suffered due to weak interlayer bonding. Also, low 

flexural strength was observed due to an insufficient fiber coating and poor high temperature stability of 

the SiC (CG-Nicalon) fibers. In recent work by the authors (Ref. 13), laminated object manufacturing of 

SiC/SiC composites was reported. High temperature silicon carbide fiber prepregs were developed and 

processing parameters were optimized to give the desired SiC/SiC compositions with single step 

conversion to SiC matrix. Due to the high conversion to SiC, secondary infiltration steps to further 

densify the composite are not required, and the material will be suitable for use temperatures above 

1300 °C, since it does not contain any free silicon. 

The other additive manufacturing techniques that are well suited for fabricating CMCs are those 

methods which use powder bed processing, since micron sized chopped fibers, nano sized fibers, and 

nanotubes can be easily added to the powder mix. Powder bed processing techniques include selective 

laser sintering, electron beam sintering, and binder jet 3D printing. These techniques, as with most AM 

techniques, start with a representation of the part in the form of a computer-aided design (CAD) file 

which is converted to a stereolithography (STL) file. The STL file represents the part in cut layers which 

are to be printed as the part is built up. One of the powder bed approaches, binder jet, is illustrated in 

Figure 2 (Ref. 14). A binder is dispensed from the nozzle of a print head and selectively deposited onto 

the powder bed surface and coats the powders so that they bond to one another. As each cross-section is 

complete, the build platform is lowered slightly, and a new layer of powder of a designated thickness is 

spread over its surface. The process is repeated until the whole part is completed. 

Figure 2.—Illustration of the binder jet additive manufacturing process (Ref. 14). 
NASA/TM—2015-218892 4 

All three of the powder bed approaches are similar in that the part is formed in a build box filled of 

loose powder. The main difference is in the way the powders are solidified to form the shape. Selective 

laser sintering is a thermal method in which a highly focused laser beam is used to densify powders by 

causing necking between adjacent powders and further consolidation due to volume diffusion and 

sintering (Ref. 15). Selective laser sintering of SiC powders without binders but with secondary silicon 

(Si) infiltration has been demonstrated (Ref. 16). Laser micro sintering was used to form micron sized 

shapes from a blend of Si, SiC, and carbon (C) powders (Ref. 17). Also, a lower temperature process 

called selective laser curing was demonstrated on a mix of polymethylsilsesquioxane (PMS) preceramic 

powder mixed with SiC powder (Ref. 18). The porous Si-O-C/SiC material was densified with liquid 

silicon and turbine wheel shapes were demonstrated. In the electron beam sintering method, the process 

occurs under a vacuum using a high-energy electron beam as the heat source for melting and fusing 

powders (Ref. 19). In the binder jet method, instead of a heat based approach, a binder is dispensed from 

the nozzle of a print head. Schlier et al. demonstrated the 3D binder jet printing of lattice structures of 

silicon infiltrated silicon carbide for reactors in piston engines (Ref. 20). In our work presented here, we 

advance the technology beyond the current state of the art by pursuing additively manufactured SiC 

materials which contain no remaining free silicon and include the addition of SiC fiber reinforcement for 

higher temperature capability and improved mechanical properties. 

The additive manufacturing work reported here is the third part in a series of reports. The 

corresponding first report in the series provided details on a system study to determine the benefits of 

replacing metallic turbine engine components with polymer and ceramic matrix composite materials. 

System benefits were reported for weight reduction and reduced fuel consumption when material 

replacements were done for critical turbine engine components (Ref. 21). The objective of this work was 

to develop a processing approach for additively manufacturing ceramic matrix composite materials using 

the binder jet method. Since there was not a basis within NASA GRC or rp+m, as well as within the 

wider scientific community, the technology had to be developed from a fundamental level. Different SiC 

powders with median sizes ranging from 9.3 to 53.0 m were investigated solely and in bimodal powder 

blends in order to maximize powder packing. Small SiC fibers were added to the powder bed for the 

fabrication of ceramic matrix composites. Various infiltration approaches were investigated. Densities 

were determined for printed coupons. Microstructural analysis was conducted on polished cross-sections 

using optical and scanning electron microscopes. Mechanical properties of select materials were 

evaluated in four point bend tests. The additive manufacturing of complex turbine vanes shapes of two 

sizes was demonstrated using the binder jet 3D printing method. 

Experimental Details 

To conduct binder jet printing of SiC ceramics and CMCs, a M-Flex print machine by ExOne was 

used as illustrated in Figure 3. The powder bed was filled with SiC powders to first manufacture 

unreinforced materials. In the second phase of development, SiC fibers were added to the powder bed 

powder mix to manufacture fiber reinforced CMCs. The powders that were utilized to fill the powder bed 

were Carborex SiC grit powders (Washington Mills AS) in grit sizes of F220, F240, F360, and F600. The 

particle size distributions and composition are shown in Table 1 (Ref. 22). The particle size distribution 

for F220 was not provided but was added according to the standard of the Federation of the European 

Producers of Abrasives (FEPA) which is followed by Washington Mills AS. Figure 4 shows the shape 

and size distribution for the F240 and F360 powders. It can be seen that the powders had a coarse 

irregular shape rather than a spherical shape. The powders were used singularly and in bimodal powder 

distributions to investigate particle packing. Fiber additions, ranging from 25 to 75 vol%, were added to 

the powder mix to manufacture fiber reinforced composite materials. The fiber reinforcement was SiTUFF SiC fiber (Advanced Composite Materials, LLC). The manufacturer reports fiber dimensions of 7 

m mean diameter by 65 to 70 m mean length (Fig. 5). 
NASA/TM—2015-218892 5 

Figure 3.—The ExOne M-Flex print machine. 

TABLE 1.—DETAILS OF SIC POWDER USED IN PRESENT WORK 

SHOWING PARTICLE SIZE DISTRIBUTION AND 

CHEMICAL ANALYSIS (REF. 22) 

Grit designation dS3-value 

max. 

μm 

Median grain size 

dS50-value 

μm 

dS94-value 

min. 

μm 

F220 75 53.03.0 45 

F240 70 44.52.0 28 

F360 40 22.81.5 16.5 

F600 19 9.31.0 3 

Particle size distribution measured on Beckman Coulter Multisizer 3, 

according to FEPA 42-2:2006. 

Grit range % 

SiC 

% 

Free C 

% 

Si 

% 

SiO2

% 

Fe 

F240 to F600 99.20 0.15 0.25 0.40 0.07 

Chemical analysis (in weight percent) according to FEPA 45-1986, 

R1993 resp. ISO 9286. 

 
NASA/TM—2015-218892 6 

(a) SiC powders (Carborex F240) 

(b) SiC powders (Carborex F360) 

Figure 4.—Optical micrographs at the same magnifications of the SiC F240 (a) and F360 (b) powders on a glass slide. 

Figure 5.—Si-TUFF SiC fibers (Advanced 

Composite Materials, LLC). 

Two sizes of samples were additively manufactured. The first size was used for microstructural 

analysis and secondary infiltration trials and had dimensions of approximately 12.7 mm wide by 25.4 mm 

long by 4.0 mm thick. The second, relatively larger size of coupon, had dimensions of approximately 50.8 

by 50.8 by 4.0 mm and was used for mechanical testing. As each layer is built up in the ExOne 

M-Flex machine, an ExOne binder that is a polymer based ink is used to rigidly link the powders as the 

green body is formed. Following green body printing, the samples were infiltrated under vacuum with 
NASA/TM—2015-218892 7 

either a polycarbosilane or a phenolic resin. The polycarbosilane that was used was SMP-10 (Starfire 

Systems) which is a pre-ceramic polymer with a carbon-silicon backbone that is converted to SiC during 

pyrolysis. The phenolic resin was loaded with nanoparticles and provided a source of carbon during 

pyrolysis. Pyrolysis of all printed and infiltrated samples was conducted in a tube furnace under flowing 

argon with a 30 min. hold at 1000 °C. Other infiltration approaches were investigated for further 

densifying the coupons. One approach was to load the SMP-10 infiltrant with either 0.7 μm or 0.8 μm 

average grain size SiC powders and then conduct vacuum infiltration into the green printed coupons. 

Another approach was to conduct multiple iterations of the polycarbosilane vacuum infiltration and 

pyrolysis steps. In another approach, pure silicon was melt infiltrated into selected coupons at 1450 °C in 

vacuum to fill in the porous interior to demonstrate full densification of the coupons. Several print runs 

were conducted to investigate the various combinations of constituents to include single powder and two 

powder blends with phenolic infiltrant or SMP-10 infiltrant with and without 0.7 m and 0.8 μm SiC 

powder loading, and with and without the addition of reinforcing Si-Tuff SiC fibers added to the powder 

bed at volume percentages of 25 to 75 vol%. 

Microstructural analysis of polished cross-sections of printed samples was conducted using optical 

and field emission scanning electron microscopes. Selected microscopy will be presented in the results 

section to illustrate the effects of different constituents and processing steps. Several of the larger samples 

(50.8 by 50.8 by 4.0 mm) underwent 2 to 3 extra infiltration and pyrolysis cycles where SMP-10 was 

vacuum infiltrated into the samples to further fill the porous interior and increase the density. These 

coupons were then surface ground to a flat surface and bend bars were machined with dimensions of 

50 mm long by 4 mm wide and roughly 2.5 mm thick. There were variations in thickness among the 

material sets due to different print runs and powder beds. The bend bars were used to assess mechanical 

properties of the materials through 4 point bend tests. The binder jet method was used to demonstrate the 

additive manufacturing of two vane shapes of different sizes. 

Results and Discussion 

Coupons were printed during several print runs each with variations in the constituents and infiltrants. 

An example of coupons from one set is shown in Figure 6. Four of the smaller coupons (12.7 mm wide by 

25.4 mm long by 4.0 mm thick) and two of the larger coupons (approximately 50.8 by 50.8 by 4.0 mm) 

were printed during each run. The dimensions and weight of the coupons were measured to determine the 

bulk density of the coupons in their green state after an infiltration step. The dimensions and weight were 

taken again after a furnace run to pyrolyze the samples at 1000 °C in flowing argon with a 30 min hold. 

The average density of the six samples from each set are shown in Table 2. The specific details of each 

material set (powder sizes, powder blends, infiltrant, and infiltrant loading) will not be divulged due to 

proprietary issues. However the main point of Table 2 is that the densities of the samples are much lower 

than the theoretical density of bulk SiC which is ~3.2 g/cc. Only trends will be discussed. Initially binder 

jet processing with single powders was investigated followed by powder blends. It was observed that the 

larger F240 SiC powders gave higher densities than the smaller F360 SiC powders. Also the SMP-10 

infiltration gave higher densities than the phenolic infiltration. Going to a powder blend of two powder 

sizes as in set F may have provided a slight improvement in density. Adding 25 vol% of 0.7 m SiC 

powders to the SMP-10 infiltrant improved the density as noted in comparing sets F, H, and J with no 

additions in the infiltrant to G, I, and K which had the addition of the 25 vol% SiC powders of 0.7 m in 

diameter. For the CMC materials, sample sets M, N, and O show that as the vol% of SiC fiber increases 

from 35 to 45 to 65, respectively, the density remains about the same. For sets R to U which were 

phenolic infiltrated samples, the densities were relatively low. It was noted that after pyrolysis, there was 

excessive flaking at the surface which was assumed to be an overcoat of the phenolic. Microscopy will be 

conducted in the future to determine the extent that the phenolic infiltrated the interior of these samples. 

In order to further densify the samples, optimized processing steps and other processing approaches need 

to be investigated to include multiple infiltration cycles and melt-infiltration. 
NASA/TM—2015-218892 8 

Figure 6.—An example of one of the coupons sets that is printed 

during a binder jet print run. 

TABLE 2.—AVERAGE DENSITIES OF THE 

SAMPLE SETS IN THEIR GREEN STATE 

AND AFTER PYROLYSIS 

Sample densities (g/cc) 

 Green Pyrolyzed 

Set A 1.60 1.55 

Set B 1.54 1.47 

Set C 1.21 1.26 

Set D 1.01 1.02 

Set E 1.54 1.53 

Set F 1.71 1.66 

Set G 1.95 1.94 

Set H 1.68 1.62 

Set I 1.78 1.80 

Set J 1.57 1.48 

Set K 1.73 1.68 

Set L 1.47 1.44 

Set M 1.65 1.60 

Set N 1.51 1.53 

Set O 1.53 1.57 

Set P 1.50 1.49 

Set Q 1.36 1.27 

Set R 1.08 0.92 

Set S 0.99 0.93 

Set T 0.91 0.86 

Set U 0.87 0.87 

 

Set M 

After Pyrolysis 
NASA/TM—2015-218892 9 

Microstructural analysis of polished cross-sections of a sample from each material set was conducted 

using optical and scanning electron microscopy. Micrographs from select samples are presented to illustrate 

the results obtained from using the different constituents and infiltration methods. The cross-section of a 

sample from Set A is shown in Figure 7. This sample was printed from Carborex F360 SiC powder and had 

the SMP-10 infiltration. Macro views of the cross-section at the ends and center of the sample are shown in 

Figure 7(a). It should be noted that the three macro-views represent only about 40 percent of the full length 

of the cross-section. The two black arrows in-between the three views represents the 60 percent of the crosssection that is not shown. Figure 7(b) shows a higher magnification view of the interior of the sample. 

Larger pockets of porosity are seen in the macro view while the micro view shows that the individual 

powders are not tightly packed, and there is minor contact between the SiC powders. The sample underwent 

one infiltration with SMP-10 followed by pyrolysis. It is seen that the infiltrant does not uniformly coat the 

powders but rather is a relatively thick deposit on some portions of the powder surfaces. Similar micrographs 

are shown in Figure 8 which was made from F240 Carborex SiC powders. Main points, compared to Figure 5, 

are that a gap between printed layers was observed at the right edge of the sample cross-section (Fig. 8(a)), and 

the powders seem a little more elongated in one-dimension and narrow in the other (Fig. 8(b)). 

Figure 7.—Polished cross-section of a sample from Set A: Carborex F240 

SiC powders with SMP-10 infiltration. Optical micrographs of sections at 

the ends and middle of the cross-section (a) and a scanning electron 

micrograph from the middle of the cross-section (b). 

(a) 

SiC powder 

SiC 

powder 

SMP-10 

(b) 
NASA/TM—2015-218892 10 

Figure 8.—Polished cross-section of a sample from Set B: Carborex F360 SiC powders with SMP-10 infiltration. 

Optical micrographs of sections at the ends and middle of the cross-section (a) and a scanning electron micrograph 

from the middle of the cross-section (b). 

 

(a) 

SiC 

powder 

SMP-10 

d

Porosity 

(b) 
NASA/TM—2015-218892 11 

The microstructure of a sample from Set C is shown in Figure 9 which was made from the F240 SiC 

powder and was infiltrated by the powder loaded phenolic. The SiC powders were not tightly packed and 

the single infiltrant step only slightly filled in the porosity. The infiltrant was more concentrated at the 

sample edge but it was also observed further into the interior. The close-up view of a concentrated region 

of the infiltrant shows detail of its powder loading. 

The densest set of samples was Set G, which had an average density of 1.94 g/cc. Figure 10 shows the 

microstructure of a sample from Set G, which was made from a blend of 90 vol% F240 and 10 vol% F360 

Carborex SiC powders. The SMP-10 infiltrant was loaded with 25 vol% 0.7 m SiC Powder. As seen in 

the figure on the left, the one infiltration of the loaded SMP-10 gave a much better result in densifying the 

porous interior and surrounding the F240 SiC powder than compared to the results in Sets A and B which 

did not have powder loaded SMP-10. The figure on the right shows greater detail of how the 0.7 m 

powders and the SMP-10 fill in around and have good contact with the larger Carborex powder. 

 

Figure 9.—Polished cross-section of a sample from Set C: Carborex F240 SiC Powders with phenolic infiltration 

showing scanning electron micrographs at the edge of the sample (left) and a close up view (right). 

Figure 10.—Polished cross-section of a sample from Set G: 90 vol% F240 and 10 vol% F360 Carborex SiC powder 

blend with SMP-10 infiltration loaded with 25 vol% of 0.7 m SiC powder. Scanning electron micrographs of the 

interior of the sample (left) and a close up view (right). 

 

SiC 

powder 

Powder Loaded 

Phenolic 

Powder Loaded 

SMP-10 

SiC 

powder 
NASA/TM—2015-218892 12 

Figure 11.—Polished cross-section of a sample from Set C: Carborex F240 SiC powders with phenolic infiltration 

followed by a secondary silicon melt infiltration step. Optical micrographs of the edge of the sample (left) and a 

close up view (right). 

In order to demonstrate how well the printed coupons have the potential to be more fully infiltrated 

and densified, select coupons from the sets underwent a silicon melt infiltration step. Figure 11 shows the 

cross-section of a sample from Set C that was first infiltrated with phenolic resin and was then infiltrated 

with liquid silicon during a furnace run in vacuum. As seen in the figure on the left, the silicon completely 

infiltrated from the edge to the interior. Excess silicon did build up around the exterior of the sample. This 

effect can be addressed by further optimizing the infiltration step or by doing some post-infiltration 

machining. The figure on the right shows that the silicon completely surrounded the powders, and no 

porosity was observed. While good densification results with silicon were observed, the use temperatures 

of the materials will be restricted to below 1316 °C due to the melt temperature of silicon. Ideally, similar 

results need to be achieved with the polycarbosilane and phenolic infiltration approaches or melt 

infiltrations need to be done with higher temperature phases. 

Once experience was gained in fabricating only powder loaded materials using the binder jet method, 

SiC fibers were introduced into the powder bed to begin making fiber reinforced composite materials. 

Micrographs are shown in Figure 12 of a polished cross-section from Set L which had 65 vol% of a 

90 wt% F240 and 10 wt% Carborex F360 SiC Powder mix and 35 vol% of Si-Tuff SiC fiber followed by 

infiltration by SMP-10. The top micrographs of Figure 12(a) are images from the edge to progressively 

higher magnifications which shows detail of the Si-Tuff SiC fibers distributed in with the powders. The 

two bottom images from two additional locations, Figure 12(b), illustrate how the fibers appear in general 

within the material. The cross sectional views are through the thickness of the sample with the sample 

being built layer on top of layer in the vertical direction. It can be seen that within the material, the fibers 

are well distributed with non-preferred orientations. On the horizontal plane fibers are in both the 0° and 

90° directions. While it will be difficult to print materials with fibers fully upright, fibers at as much as 

45° from horizontal are observed in the vertical plane. The good distribution of fibers in different 

orientations is expected to contribute to beneficial composite properties for the material. 

In order to further densify the materials, extra infiltration steps were conducted for 50.8 by 50.8 mm 

panels from several of the materials sets. Beyond the infiltration as indicated in Table 2, additional 

iterations of SMP-10 vacuum infiltration followed by pyrolysis in a furnace were conducted. Figure 13(c) 

shows the starting density and the density of the panel after the 2 to 3 additional infiltration iterations. The 

extra infiltrations increased the densities by 0.20 to 0.55 g/cc. Most of the increase in density occurred in 

the first two infiltrations with less effect from the third infiltration. An example of a panel that has been 

further densified and bend bars that were machined from the panel are shown in Figure 13(a) and (b). 

 

SiC 

powder 

Silicon 

Infiltration 
NASA/TM—2015-218892 13 

Figure 12.—Polished cross-section of a sample from Set L: 65 vol% of 90 wt% F240 and 10 wt% Carborex F360 SiC 

Powder mix and 35 vol% of Si-Tuff SiC fiber with an infiltration of SMP-10. Scanning electron micrographs of the 

edge of the sample and a close up view are shown (a) with additional views at other locations showing detail of the 

Si-Tuff SiC fibers (b).

Figure 13.—An example of a 50.8 by 50.8 mm panel that had undergone extra infiltrations (a) and bend 

bars that had been machined from the panel which had been surface ground (b). The improvements 

in panel densities with infiltration iterations is shown where the legend correlates to the material set 

and the print run sample number (c). 
NASA/TM—2015-218892 14 

 (a)

(b)

Figure 14.—Plots of stress versus strain for the results of three bend bar tests from each panel for the nonreinforced 

materials (a) and the Si-Tuff SiC fiber reinforced materials (b). 

The results from four point bend tests are given in Figure 14 for two nonreinforced panels, Sets I and 

G, and two fiber reinforced panels, Sets N and O. Three bend bars from each panel were tested at room 

temperature. Overall, the fiber reinforced ceramic matrix composite materials had much higher strengths 

and strains to failure compared to the non-fiber reinforced materials. One bend bar from Set I had a 

relatively high strength and strain to failure which was comparable with results of the reinforced 

materials. The highest strains to failure were from Set O which had 45 vol% fiber loading. The highest 

strengths to failure were from Set N which had 65 vol% fiber loading. 

Fractography was conducted on tested samples to observe for composite behavior. The bend tests 

showed improvements in the stress and strain to failure for fiber reinforcements. However, composite 

behavior would more truly be demonstrated from the presence of fiber pullout from fracture surfaces. 

Figure 15 shows the fracture surface of a bend bar from Set N. The material does appear dense due to the 

three extra infiltration steps. Fiber pullout was not observed. Instead areas of fibers bridging porous 

regions were observed (Fig. 15(a) and (c)). Only in rare cases was fiber pullout observed (Fig. 15(b)). It 

should be noted that the fibers were uncoated. In ceramic matrix composite materials, the observance of 

composite properties is dependent on an interfacial fiber coating. For the materials presented here, the 

fibers are rigidly bonded to the matrix due to the absence of an interphase. This can cause the material to 

behave more like a monolithic material with the fibers providing little benefit. In future work, fiber 

coatings will be investigated for improving the composite behavior of the material. 

0

10

20

30

40

50

0.00 0.02 0.04 0.06 0.08

Stress (MPa)

Strain (%)

0

10

20

30

40

50

60

70

0.00 0.02 0.04 0.06 0.08 0.10 0.12

Stress (MPa)

Strain (%)

45 vol% SiC Fiber Reinforced SiC - Set O

0

10

20

30

40

50

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

Stress (MPa)

Strain (%)

0

10

20

30

40

50

60

70

80

0.00 0.02 0.04 0.06 0.08 0.10

Stress (MPa)

Strain (%)

65 vol% SiC Fiber Reinforced SiC - Set N
NASA/TM—2015-218892 15 

(a) Location 1

(b) Location 2 

(c) Location 3 

Figure 15.—FE SEM of a fracture surface at three locations for a sample from Set N with 65 vol% SiC fiber. 

 
NASA/TM—2015-218892 16 

(a) (b) 

Figure 16.—Demonstration of the additive manufacturing of turbine engine CMC components (20 vol% SiC fiber). 

Two smaller first stage nozzle segments in addition to two high pressure turbine nozzle segments for a cooled 

doublet vane (a). Aligned cooled double vane sections (b). 

The ability for the binder jet method to be used to fabricate relevant shapes for turbine engine component 

applications was demonstrated. Two different sizes of turbine vanes were printed to include larger size high 

pressure turbine nozzle segments for a cooled doublet vane and two smaller first stage nozzle segments 

(Fig. 16(a)). Two cooled double vane sections were aligned to illustrate how the sections are placed to form a 

vane ring section (Fig. 16(b)). While the material processing may need further optimization to improve the 

properties, it is encouraging that such complex and relevant shapes can be made. 

Conclusions 

Binder jet 3D printing was used to fabricate ceramic matrix composite materials. Silicon carbide 

powders of different sizes and blends were used in the powder bed to investigate the printability during the 

printing process such as powder spreading and layer build up and the print quality that resulted by 

conducting microscopy to look at powder packing, porosity, and infiltration. Single infiltrations of SMP-10 

and phenolic only slightly filled in the interior. When the SMP-10 was loaded with sub-micron sized SiC 

powders, the infiltrant gave a much better result of filling in the interior. Silicon carbide fibers were added to 

the powder bed to make ceramic matrix composite materials. Microscopy showed that the fibers were well 

distributed with no preferred orientation on the horizontal plane, and fibers in the vertical plane were at 

angles as much as 45°. Secondary infiltration steps were necessary to further densify the material. Two to 

three extra infiltration steps of SMP-10 increased the density by 0.20 to 0.55 g/cc. However, the highest 

densities achieved were 2.10 to 2.15 g/cc. This is still much lower than the density of fully dense monolithic 

SiC (~3.00 to 3.20 g/cc) depending on the manufacturing process used for these materials. 

Mechanical testing results show that two CMC panels had higher strengths and strains to failure that 

the samples from the two non-fiber reinforced panels. The highest strengths were from Set N with 

65 vol% fiber loading which had an average strength of 66 MPa. Analysis of the fracture surfaces did not 

reveal pullout of the reinforcing fibers. Blunt fiber failure suggested that there was not composite 

behavior. The binder jet additive manufacturing method was used to demonstrate the fabrication of 

turbine engine vane components of two different designs and sizes. The binder jet method has benefits 

over the conventional manufacturing of CMCs in that prototype and production parts can be fabricated 

quickly and economically with no tooling and extensive hand layup. Future work will focus on improving 

the density of the materials by optimizing the powder packing and infiltration. Fiber coatings will need to 

be investigated. 
NASA/TM—2015-218892 17 

References 

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C/SiC, and SiC/SiC Composites,” Adv. Eng. Mater., (2002) 4: 903–912. 

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above,” In Handbook of Ceramic Composites, pp. 77–98. Springer US, 2005. 

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Preceramic-Paper-Derived Si-SiC Composites,” Advanced Materials, 19 (2007) 4515–4519. 

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Ceram. Soc., 91, 11 (2008) 3477–3492. 

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Composites Fabricated by Laminated Object Manufacturing,” Composites, Part A, 29 A (1998) 

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NASA/TM—2015-218892 12 

Figure 11.—Polished cross-section of a sample from Set C: Carborex F240 SiC powders with phenolic infiltration 

followed by a secondary silicon melt infiltration step. Optical micrographs of the edge of the sample (left) and a 

close up view (right). 

In order to demonstrate how well the printed coupons have the potential to be more fully infiltrated 

and densified, select coupons from the sets underwent a silicon melt infiltration step. Figure 11 shows the 

cross-section of a sample from Set C that was first infiltrated with phenolic resin and was then infiltrated 

with liquid silicon during a furnace run in vacuum. As seen in the figure on the left, the silicon completely 

infiltrated from the edge to the interior. Excess silicon did build up around the exterior of the sample. This 

effect can be addressed by further optimizing the infiltration step or by doing some post-infiltration 

machining. The figure on the right shows that the silicon completely surrounded the powders, and no 

porosity was observed. While good densification results with silicon were observed, the use temperatures 

of the materials will be restricted to below 1316 °C due to the melt temperature of silicon. Ideally, similar 

results need to be achieved with the polycarbosilane and phenolic infiltration approaches or melt 

infiltrations need to be done with higher temperature phases. 

Once experience was gained in fabricating only powder loaded materials using the binder jet method, 

SiC fibers were introduced into the powder bed to begin making fiber reinforced composite materials. 

Micrographs are shown in Figure 12 of a polished cross-section from Set L which had 65 vol% of a 

90 wt% F240 and 10 wt% Carborex F360 SiC Powder mix and 35 vol% of Si-Tuff SiC fiber followed by 

infiltration by SMP-10. The top micrographs of Figure 12(a) are images from the edge to progressively 

higher magnifications which shows detail of the Si-Tuff SiC fibers distributed in with the powders. The 

two bottom images from two additional locations, Figure 12(b), illustrate how the fibers appear in general 

within the material. The cross sectional views are through the thickness of the sample with the sample 

being built layer on top of layer in the vertical direction. It can be seen that within the material, the fibers 

are well distributed with non-preferred orientations. On the horizontal plane fibers are in both the 0° and 

90° directions. While it will be difficult to print materials with fibers fully upright, fibers at as much as 

45° from horizontal are observed in the vertical plane. The good distribution of fibers in different 

orientations is expected to contribute to beneficial composite properties for the material. 

In order to further densify the materials, extra infiltration steps were conducted for 50.8 by 50.8 mm 

panels from several of the materials sets. Beyond the infiltration as indicated in Table 2, additional 

iterations of SMP-10 vacuum infiltration followed by pyrolysis in a furnace were conducted. Figure 13(c) 

shows the starting density and the density of the panel after the 2 to 3 additional infiltration iterations. The 

extra infiltrations increased the densities by 0.20 to 0.55 g/cc. Most of the increase in density occurred in 

the first two infiltrations with less effect from the third infiltration. An example of a panel that has been 

further densified and bend bars that were machined from the panel are shown in Figure 13(a) and (b). 

 

SiC 

powder 

Silicon 

Infiltration