Geometric characterization of additively manufactured polymer derived ceramics

Accepted Manuscript Title: Geometric Characterization of Additively Manufactured Polymer Derived Ceramics Authors: Jacob M. Hundley, Zak C. Eckel, Emily Schueller, Kenneth Cante, Scott M. Biesboer, Brennan D. Yahata, Tobias A. Schaedler PII: DOI: Reference:

S2214-8604(17)30014-3 http://dx.doi.org/10.1016/j.addma.2017.08.009 ADDMA 210

To appear in: Received date: Revised date: Accepted date:

23-2-2017 6-6-2017 22-8-2017

Please cite this article as: Jacob M.Hundley, Zak C.Eckel, Emily Schueller, Kenneth Cante, Scott M.Biesboer, Brennan D.Yahata, Tobias A.Schaedler, Geometric Characterization of Additively Manufactured Polymer Derived Ceramics (2010), http://dx.doi.org/10.1016/j.addma.2017.08.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Geometric Characterization of Additively Manufactured Polymer Derived Ceramics Jacob M. Hundley1,*, Zak C. Eckel1, Emily Schueller1, Kenneth Cante1, Scott M. Biesboer1, Brennan D. Yahata1 and Tobias A. Schaedler1 1

Architected Materials Department, HRL Laboratories LLC. 3011 Malibu Canyon Rd,

Malibu CA 90265 * Corresponding author, [email protected]

1.0 Abstract The high hardness, melting temperature and environmental resistance of most ceramic materials makes them well-suited for propulsion, tribilogical and protective applications. However, these same attributes pose difficulties for manufacturing and machining of ceramics and ultimately limit the achievable design space of these materials. Recently, a new class of preceramic photopolymers has been developed that enables additive manufacturing of ceramics using commercially available stereolithography systems. By consolidating preceramic monomers via layer-wise exposure to ultraviolet light and subsequently pyrolyzing under an inert atmosphere to form a ceramic, this method allows for complex geometry parts that cannot be produced with traditional sintering, pressing or vapor infiltration processes. In order to retain geometric fidelity and generate flaw-free microstructures, volumetric and gravimetric changes during the polymer-to-ceramic conversion must be quantified.

To this end, we present x-ray micro-computed

tomography (micro-CT) measurements of the dimensional stability and uniformity of additively manufactured silicon-based ceramics as a function of geometry and processing conditions.

1.1 Introduction Monolithic ceramics and ceramic matrix composites offer several important benefits that cannot be achieved from engineering polymers or metal alloys. The high strength, hardness, thermal stability and chemical inertness intrinsic to most ceramics has led to their continued implementation in armor, combustion, industrial filtration, friction, wear and power generation applications [1-2].

However, design flexibility for ceramic

components in each of these cases is limited by practical difficulties in their manufacture © 2017 HRL Laboratories, LLC. All Rights Reserved

and processing. Currently, most high performance ceramics are produced via powder pressing, slip casting, vapor infiltration or film deposition methods that cannot accommodate high aspect ratio structures or internal features such as conformal cooling channels [2-3]. Furthermore, the time and cost required to fabricate fully-dense ceramics from gaseous or powder feedstock renders these components suitable only for niche, high value markets (e.g. high end automotive brakes). Conversely, machining of ceramic components is complicated by their low fracture toughness, which often leads to chips or cracks that severely limit the utility of flaw-sensitive ceramics [3]. Due to the complexity and cost of processing and machining high performance ceramics, additive manufacturing has been identified as a promising route to reduce cycle times, increase part yield and limit overhead tooling burdens. Furthermore the ability to form optimized ceramic configurations in net-shape will enable ceramics to be used more widely and in new applications, as has been demonstrated with polymer and metal additive manufacturing processes.

In comparison to these metal and polymer processes however, additive manufacturing of ceramics is relatively new, with only a handful of three-dimensional (3D) printers currently capable of producing ceramic components [4]. In the vast majority of these systems, ceramic powders are mixed with an organic binder that is then consolidated in a layer-bylayer fashion to form a green body. The sacrificial binder phase is then removed through a firing or de-binding step and the residual ceramic powder is sintered under heat and pressure to form the finished part.

Examples of these binder-assisted sintering

approaches include laminated tape casting, stereolithography of ceramic particulates dispersed in a UV-sensitive resin and binder-jetting, in which liquid binder materials are selectively deposited onto a bed of ceramic particulates [5].

In all of these binder-assisted sintering approaches, the main challenge lies in producing a fully-dense, crack-free material and maintaining geometric fidelity upon firing. Given that organic/inorganic composition gradients naturally occur on the millimeter length scales in the green body, non-uniform shrinkage often results from the de-binding step. After de-binding, the ceramic particles must be sintered together, which requires high © 2017 HRL Laboratories, LLC. All Rights Reserved

temperatures (>1600C) and sintering aids [6]. Additionally, removal and replacement of sacrificial organic material during these de-binding and sintering steps can lead to entrapped porosity in the consolidated ceramic due to inadequate sintering pressure or volatilization of the binder. The inability to reinforce the sintered ceramic with a secondary toughening phase presents an additional limitation in these binder-based processes. Considering the green body as a ceramic-reinforced polymer composite, elimination of polymer matrix and the requirement that all particulate reinforcement be consolidated during de-binding and sintering prevents the introduction of a second toughening phase into the ceramic and ultimately limits the fracture toughness that can be achieved via these methods.

In contrast, a new ceramic additive technique has recently been developed to enable direct conversion of a free-form preceramic polymer into a fully-dense, flaw-free ceramic (Figure 1) [7-8]. In this “binder-free” approach, UV-active functional groups such as thiols, vinyls, or epoxides are added to an inorganic polymer backbone (e.g. carbosilane, siloxane or silazane) to form preceramic monomers that can be consolidated under ultraviolet light, typically at wavelengths between 300-420nm [9].

Given that high

particulate volume loadings are not required to form the ceramic component in this approach, these radiation-curable monomers possess viscosity and UV-absorptivity comparable to commercially available 3D printing resins and can be consolidated using off-the-shelf stereolithography systems. After achieving sufficient cross-link density from the layer-by-layer SLA operation, near net-shape cured preceramic polymer components are then converted to a ceramic by driving off volatile organic species from the polymer network (e.g. H2O, CO2, CH4, etc.) at elevated temperatures (≤1000°C) in an inert atmosphere [10-11].

By removing the sacrificial binder and sintering requirements, this direct conversion method eliminates several challenges inherent in prior ceramic additive approaches. Namely, the length scale of inorganic/organic composition gradients is now reduced to the atomistic scale (10s of angstroms) and is incorporated into the polymer network itself, as opposed to micron or millimeter scale obtained via heterogeneous dispersion. This © 2017 HRL Laboratories, LLC. All Rights Reserved

enables more uniform shrinkage and dimensional stability during conversion of the green body (i.e. preceramic polymer vs. particulate loaded binder).

Furthermore, direct

conversion of a polymer precursor eliminates de-binding and sintering steps necessary to form the ceramic, allowing for lower temperature (≤1000°C) and ambient pressure processes that reduce thermal stresses and porosity generation within the structure.

However, it is essential that the improved dimensional stability and reduced porosity anticipated in binder-free, polymer-derived ceramics be validated under typical additive manufacturing conditions for representative component geometries. While composition gradients are minimized, volatile organic species are still driven off during the process and there is the potential for void formation and cracking, particularly for thick sections with long diffusion lengths (10s of centimeters) or as a result of pre-existing flaws at the preceramic polymer stage. Additionally, shrinkage and dimensional stability benefits must be quantified, particularly for designs that incorporate a mixture of high and low aspect ratio structures or internal features typical of optimized additive designs. To this end, the present study presents micro-CT measurements of dimensional stability in additively manufactured polymer-derived ceramic microstructures for several common geometric classes. These results will be used to validate the assumption of uniform shrinkage on pyrolysis and track the initiation and progression of flaws from the polymer state to the ceramic state. 1.2 Sample Preparation In this study, evaluation of the pre- and post-pyrolysis microstructures in additively manufactured ceramics was performed for several representative additive geometric classes, shown in Figure 2. All designs were scaled to fit within the maximum exposure window of the micro-CT system (27mm diameter) and are provided in the supplemental materials. The first and most basic class of structures analyzed consisted of prismatic rectangular sections extruded along the build direction of the stereolithography system, with face angle varying between each sample (Figure 2A). Design complexity was then increased by combining in-plane and through-thickness features in the impellers of Figure 2B as well as cylindrical geometries with internal features such as holes and negative © 2017 HRL Laboratories, LLC. All Rights Reserved

draft angles that were orthogonal to the build direction of the SLA (Figure 2C). Finally, cantilever beam geometries with supports attached at 45° and 90° angles were produced to quantify potential relaxation or sagging of the structure during heating and pyrolysis (Figure 2D).

All additively manufactured preceramic polymers in Figure 2 were composed of a UVcurable siloxane formulated from a mixture of (mercaptopropyl) methylsiloxane and vinylmethoxysiloxane combined with a photo-initiator active at 405nm. UV inhibitors and absorbers were also added to the preceramic resin to retain the maximum in-plane (X/Y) resolution available from the SLA printer (50um). Layer-wise additive manufacturing of the geometries in Figure 2 utilized an Autodesk Ember open architecture digital light project (DLP) stereolithography system with a 405nm source.

For all preceramic

structures, a build layer height of 50um was used and machine parameters were determined through curing single layer films under varying intensity and exposure duration [12]. After printing, the structures were rinsed with isopropyl alcohol, allowed to dry, and then subsequently post-cured using a 120W/cm Heraeus high intensity UV exposure chamber with an H BF9 style Hg bulb for a minimum of 120s.

Following printing, each of the as-manufactured preceramic polymer structures was measured via micro-CT using techniques discussed in Section 1.3. The structures were then pyrolyzed on a flat graphite plate in an argon atmosphere using a 150mm diameter tube furnace to covert the cured siloxane resin to amorphous silicon oxycarbide. In all cases, a heating rate of 1°C per minute was applied up to a maximum temperature of 1000°C as measured by a thermocouple located near the samples in the furnace. The specimens where held at 1000°C for 1 hour and subsequently cooled to room temperatre at 5°C per minute.

After pyrolysis the preceramic polymer structures converted to

amorphous silicon oxycarbide with a composition of SiO1.34C1.25S0.15 as measured by inductively coupled mass spectrometry (Figure 3). Average mass loss for each of the additively manufactured geometries in Figure 2 was measured to be 41%, which correlates well with thermogravimetric measurements obtained from bulk cured (i.e. nonadditively manufactured) preceramic resin (Figure 4) [13]. Following pyrolysis, micro-CT © 2017 HRL Laboratories, LLC. All Rights Reserved

measurements were then performed on the same set of specimens to determine dimensional stability, repeatability and flaw formation or evolution as a function of component geometry (Figure 5).

1.3 Measurement Methods X-ray micro-computed tomography measurements for the pre- and post-pyrolyzed structures in Figures 2 and 5 were obtained using a Bruker SkyScan 1172 high resolution micro-CT system. In all cases, shadow images for each sample cross section were generated over a full 360° rotation with increments of 0.47° separating each successive exposure. The total duration of exposure at each individual rotation was set at 540ms using an x-ray source voltage and current of 100kV and 100uA, respectively. Prior to exposure, aluminum and copper soft x-ray thin film filters were placed between the source and the additively manufactured samples for both the preceramic and ceramic measurements.

Shadow images were collected on an 11-megapixel camera at a

resolution of 13.4um, which was selected to be a factor of 4 smaller than the maximum resolution of the SLA system. This resulted in an effective voxel size of 2400um3 for each of the measured geometries.

After generation of the rotated two-dimensional x-ray shadow images, high resolution through-thickness cross sections for each sample were reconstructed using a cone beam processing algorithm in Bruker’s Nrecon software package, Figure 6.

Prior to

reconstruction, the vertical axis of each shadow image was adjusted to align it with the build direction of the SLA and correct for any orientation shift during mounting the samples in the micro-CT fixture. Ring and beam hardening corrections were each applied at 50% of the algorithm maximum for all shadow images in the stack. All grayscale throughthickness cross-sections reproduced from the two-dimensional shadow images were then converted to binary representations using a threshold histogram to differentiate between gas (or voids) and the preceramic or ceramic material (Figure 6C-D). The threshold cutoff intensity was calibrated using a ceramic cylindrical witness sample of known diameter that was analyzed using the same x-ray source and beam reconstruction parameters. Binary images for each preceramic and ceramic sample were then subsequently © 2017 HRL Laboratories, LLC. All Rights Reserved

assembled into a three-dimensional computer aided design (CAD) file from which comparative measurements in Section 1.4 were obtained.

1.4 Results and Discussion For each geometry printed and pyrolyzed in this study, critical geometric parameters of interest are illustrated in Figure 7. The average measured dimensions corresponding to all of these quantities are provided in Tables 1-4 for both the preceramic and ceramic states along with the as-designed CAD parameters. Data presented in the tables is also plotted for each measured linear and volumetric quantity in Figure 8A-B, respectively. Measurement identification numbers in these figures follows the ordering convention shown in Tables 1-4.

Comparison of the pre- and post-pyrolysis measurements for all geometries indicates that the average linear shrinkage upon conversion (29.7% ± 1.2%) is well aligned with that empirically determined for bulk, non-additively manufactured, preceramic resin used for compositional and TGA analyses. Furthermore, measured linear shrinkage is constant across all geometries employed in this study and is independent of feature type, aspect ratio or alignment with the SLA build direction. Volumetric changes in the parts also reflect this consistent linear shrinkage trend. The average measured volumetric shrinkage of 64.9% ± 1.6% is nearly identical to the expected 65.2% shrinkage that would occur if a uniform linear shrinkage of 29.7% were applied across a unit volume. Furthermore, the observed sample-to-sample variation in average linear and volumetric shrinkage is within measurement uncertainty imparted by the micro-CT and SLA resolution as well as the cone beam and thresholding algorithms used for reconstruction. This consistent and feature agnostic shrinkage upon pyrolysis is an important differentiation versus binderassisted sintering approaches and validates prior SEM and TEM characterization of localized crack and pore free microstructures in additively manufactured polymer derived ceramics [7].

Similarly, angular orientation between features in the additively manufactured geometries was found to remain consistent between the preceramic and ceramic states when the © 2017 HRL Laboratories, LLC. All Rights Reserved

samples were supported on a graphite plate during pyrolysis. Average dimensional changes in these supported wall, blade and draft angles was equal to 0.4% ± 0.8%, again well within measurement uncertainty. However, a non-trivial variation of 2.8% ± 0.3% was observed in all unsupported features as characterized by the cantilever angle measurements in Table 4. Upon pyrolysis, the preceramic polymer traverses its glass transition temperature and undergoes a conversion to a glassy ceramic. As the material softens, there is insufficient support in high aspect ratio sections to counteract this softening, resulting in the observed sag of Table 4. Based upon the linear shrinkage and face angle measurements for the impeller and cantilever specimens, an aspect ratio (length or width to thickness) less than 5 is required to maintain geometric fidelity without support.

Along with quantifying the linear, volumetric and orientation changes imparted during conversion of the preceramic polymer, a second aim of this study was to investigate the presence of porosity or cracking in the pyrolyzed ceramic components. This elimination of pores or voids resulting from de-binding or sintering steps is one of the primary benefits of a direct preceramic conversion route as compared to binder-based additive approaches. Figure 9 presents representative grayscale cross-sections for two sets of ceramic parts produced in this study. The upper row (Figure 9A) displays microstructure typical of components produced in this study, wherein the individual cross-sections are fully-dense, without spherical voids that would be expected from gas entrapment or high aspect ratio cracks that would likely propagate from a flaw in these unreinforced ceramics. This is corroborated by previous SEM and TEM investigations at higher resolution (<10um) in localized areas of additively manufactured ceramic structures where porosity or flaws could not be detected.

However, it is important to note that the flaw-free ceramic microstructure demonstrated in this study does not extend to cases where flaws were present in the initial preceramic polymer state. Such flaws, shown for example in Figure 9B-C, typically resulted from air entrapment in the volume of liquid resin between the cured preceramic part and the DLP exposure aperture. When these preexisting flaws were isolated from one another or a © 2017 HRL Laboratories, LLC. All Rights Reserved

free surface of the part by >400um, equivalent to 8 build layers in this study, pyrolysis did not lead to further growth of the flaw (Figure 9B). Conversely, multiple flaws located within a single build layer or separated from one another or a free surface by <400um tended to propagate through the ceramic structure during pyrolysis leading to failure of the part (Figure 9C). This difference between these stable and unstable flaws illustrates the utility of micro-CT measurements as a diagnostic tool for additive manufacturing of polymer derived ceramics provided that pyrolysis kinetics and gas evolution pathways in the component are understood [14].

1.5 Conclusions Despite their high strength, hardness, operating temperature and environmental stability, implementation of optimized ceramic geometries is often hampered by difficulties in their fabrication and machining. Ceramic additive manufacturing via direct conversion of preceramic polymer precursors offers a promising alternative to these traditional ceramic manufacturing techniques as well as prior binder-based sintering approaches. In this study, uniform linear and volumetric shrinkages of 29.7% ± 1.2% and 64.9% ± 1.6% respectively were demonstrated across multiple component geometries representative of typical ceramic applications. This repeatable conversion from a near net-shape polymer to a flaw-free ceramic is crucial to implementation of additively manufactured ceramic components, given that this uniform shrinkage allows for dimensional changes in the parts to be corrected for in the initial design. Additionally, as theorized from localized high resolution SEM and TEM microstructural evaluation, the preceramic polymer to ceramic conversion does not induce porosity or cracking in the material. However, it was observed that relaxation and flow during heating of the polymer and conversion to an amorphous ceramic was insufficient to allow for void migration during pyrolysis. Therefore, if multiple preexisting flaws exist within the preceramic polymer part they are likely to link up through propagation of cracks, even though the individual flaws remain fixed in place.

While the present study focused on a siloxane-based preceramic polymer chemistry, the results presented herein are extensible to other UV-active preceramic formulations (e.g. carbosilanes or silzanes). Additionally, the data provided in Tables 1-4 combined with © 2017 HRL Laboratories, LLC. All Rights Reserved

CAD models in the supplemental materials represent the first step towards a pyrolysis kinetics model that links pyrolysis conditions (e.g. heating rate, atmosphere) with preceramic polymer geometry to bound the feature sizes achievable for a given chemistry and set of process parameters.

1.6 Acknowledgements The authors gratefully acknowledge financial support from HRL Laboratories, LLC. and thank Professors X. Li and H.T. Hahn at the University of California, Los Angeles for use of the micro-CT system employed in this study.

1.7 References [1] Richerson, D.W. Modern Ceramic Engineering; Taylor and Francis: New York, 2006 [2] Bansal, N.P. Handbook of Ceramic Composites; Kluwer: London, 2005 [3] Kingery W.D.; Bowen H.K.; Uhlmann D.R. Introduction to Ceramics, 2nd Ed; Wiley: New York, 1976 [4] Zocca A.; Colombo, P.; Gomes, C. M.; Günster J. Additive Manufacturing of Ceramics: Issues, Potentialities, and Opportunities J. Am. Ceram. Soc. 2015, 98, 1983– 2001 [5] Deckers, J.; Vleugels, J.; Kruth, J.-P. Additive Manufacturing of Ceramics: A Review J. Ceram. Sci. Tech., 2014, 5, 245-260 [6] Schwentenwein, M.; Homa J. Additive Manufacturing of Dense Alumina Ceramics Int. J. Appl. Ceram. Technol. 2015, 12, 1-7 [7] Eckel, Z. C.; Zhou, C.; Martin, J. H.; Jacobsen, A. J.; Carter, W. B.; Schaedler, T. A. Additive Manufacturing of Polymer-Derived Ceramics Science 2016, 351, 58-62 [8] Zanchetta, E.; Cattaldo, M.; Franchin, G.; Schwentenwein, M.; Homa, J.; Brusatin, G.; Colombo, P. Stereolithography of SiOC Ceramic Microcomponents, Adv. Mater., 2016, 28, 370-376. [9] Halloran, J.W. Ceramic Stereolithography: Additive Manufacturing for Ceramics by Photopolymerization, Annu. Rev. Mater. Res. 2016, 46, 19-40

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[10] Colombo, P.; Mera, G.; Riedel, R.; Sorarù G. D.; Polymer-Derived Ceramics; 40 Years of Research and Innovation in Advanced Ceramics, J. Am. Ceram. Soc., 2010, 93, 1805-1837 [11] Greil P. Near Net Shape Manufacturing of Polymer Derived Ceramics J. Eur. Ceram. Soc. 1998, 18, 1905-1914 [12] Jacobs,

P.

F.

Rapid

Prototyping

and

Manufacturing:

Fundamentals

of

Stereolithography, Society of Manufacturing Engineers, 1992. [13] Renlund, G.M.; Prochazka, S.; Doremus R. H. Silicon Oxycarbide Glasses: Part II Structure and Properties, J. Mater. Res., 1991, 6, 2723-2734 [14] Sorarù, G. D.; Pederiva, L.; Latournerie, J.; and Raj R. Pyrolysis Kinetics for the Conversion of a Polymer into an Amorphous Silicon Oxycarbide Ceramic, J. Am. Ceram. Soc., 2002, 85, 2181-218

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1.8 Figures

Figure 1: Additive manufacturing process for fully dense ceramics (A) Formulation of UV-active preceramic polymers (B) Layer-by-layer consolidation using a stereolithography system (C) UV post-cured preceramic polymer part and (D) Post-pyrolysis conversion to ceramic

Figure 2: Geometric part classes employed in this study (A) Rectangular extrusions (B) Impellers (C) Graded cylinders and (D) Cantilever beams. CAD files for each design are provided in the supplemental materials

Figure 3:

Composition of the pyrolyzed ceramic as measured by inductively coupled plasma mass

spectrometry

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Figure 4: Thermogravimetric analysis of mass change as a function of temperature within the preceramic polymer at a heating rate of 1°C/min

Figure 5: Additively manufactured geometries resulting from pyrolysis of components in Figure 2

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Figure 6: Micro-CT analysis procedure for all pre- (top row) and post-pyrolyzed (bottom row) additively manufactured geometries (A) Components sized for micro-CT specimen chamber (B) Rotated x-ray shadow images (C) Cone beam reconstruction for as-built cross sections (D) Binarization using calibrated thresholding algorithm and (E) Assembly into CAD representation for geometry measurement.

Figure 7: Geometric measurements for each component in the pre- and post-pyrolyzed states corresponding to the results of Tables 1-4

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Figure 8: Measured shrinkage upon pyrolysis for all (A) linear dimensions and (B) component geometries included in this study with predicted values obtained from thermogravimetric analysis of neat preceramic resin. Numbering of measurement IDs follows the ordering convention in Tables 1-4

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Figure 9: Flaw generation and stabilization during pyrolysis (A) Fully-dense impeller before and after pyrolysis (B) Stable flaw in rectangular extrusion resulting from air entrapment in cured preceramic polymer and (C) Unstable flaw in a supported cylinder preceramic polymer leading to crack propagation upon pyrolysis

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Tables Table 1: Comparison of design and as-manufactured geometry for rectangular extrusions in both the preceramic polymer and pyrolyzed ceramic states 90 Degree Face Angle [mm] Feature

120 Degree Face Angle

150 Degree Face Angle

Symbol CAD

Preceramic

Ceramic

Change

CAD

Preceramic

Ceramic

Change

CAD

Preceramic

Ceramic

Change

Wall Thickness [mm]

t

1.00

1.15

0.83

28.3%

1.00

1.20

0.82

31.4%

1.00

1.17

0.81

31.1%

Face Angle [deg]

β

90.0

90.2

89.8

0.4%

120.0

120.5

120.4

0.1%

150.0

149.7

150.2

0.3%

Total Thickness [mm]

H

12.7

12.2

8.54

29.9%

12.7

12.2

8.27

31.9%

12.7

12.0

8.31

30.7%

Total Volume [mm3]

V

507

560

203

63.8%

431

451

153

66.1%

436

441

149

66.2%

Table 2: Comparison of design and as-manufactured geometry for impellers in both the preceramic polymer and pyrolyzed ceramic states Small Blade Geometry Feature

Large Blade Geometry

Symbol CAD

Preceramic

Ceramic

Change

CAD

Preceramic

Ceramic

Change

Inner Diameter [mm]

D

6.35

6.16

4.34

29.5%

6.35

6.20

4.40

29.0%

Outer Diameter [mm]

d

9.35

9.65

6.79

29.6%

9.35

9.51

6.64

30.2%

Blade Angle [deg]

ɣ

50.5

51.3

50.9

0.8%

50.5

49.9

50.1

0.4%

Blade Length [mm]

L

1.94

1.90

1.38

27.2%

2.95

2.92

2.05

29.7%

Blade Thickness [mm]

t

1.50

1.74

1.19

31.5%

1.50

1.56

1.08

31.0%

Total Thickness [mm]

H

12.7

12.0

8.58

28.4%

12.7

12.0

8.59

28.5%

V

691

728

260

64.3%

805

796

266

66.6%

3

Total Volume [mm ]

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Table 3: Comparison of design and as-manufactured geometry for graded cylinders in both the preceramic polymer and pyrolyzed ceramic states Drafted Cylinder Feature

Internally Supported Cylinder

Symbol CAD

Preceramic

Ceramic

Change

CAD

Preceramic

Ceramic

Change

Inner Diameter [mm]

D

5.33

5.42

3.93

27.6%

8.00

7.89

5.54

29.8%

Outer Diameter [mm]

d

6.67

7.06

5.09

27.9%

10.0

10.2

7.04

30.8%

Inner Wall Thickness [mm]

t

1.00

1.18

0.81

31.4%

Through Hole Diameter [mm]

p

1.00

0.99

0.69

30.6%

Inner Draft Angle [deg]

ɸ

97.3

98.4

96.8

1.7%

Total Thickness [mm]

H

8.46

8.47

5.94

29.8%

12.7

11.7

8.35

28.8%

V

169

175

64

63.7%

549

575

189

67.2%

3

Total Volume [mm ]

Table 4: Comparison of design and as-manufactured geometry for cantilever beams in both the preceramic polymer and pyrolyzed ceramic states 90 Degree Support (E) Feature

45 Degree Support (Z)

Symbol CAD

Preceramic

Ceramic

Change

CAD

Preceramic

Ceramic

Change

Cantilever Length [mm]

L

10.7

10.6

7.46

29.4%

12.7

12.9

9.17

28.8%

Cantilever Width [mm]

W

12.7

12.6

8.72

30.9%

12.7

12.3

8.75

28.9%

Cantilever Angle [deg]

ɑ

90.0

89.8

87.5

2.6%

45.0

43.8

42.5

3.0%

Cantilever Thickness [mm]

t

2.00

2.05

1.45

29.0%

2.00

2.00

1.39

30.3%

Total Thickness [mm]

H

12.7

12.7

9.07

28.7%

12.7

12.6

8.92

29.2%

V

1008

984

362

63.2%

938

919

339

63.0%

3

Total Volume [mm ]

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