"Solid Freeform Fabrication at The University of Connecticut" by S. Harrison, J.E. Crocker, T. Manzur, and H.L. Marcus, Proceedings of the 1996 Solid Freeform Fabrication Symposium, Austin, TX, August 1996, 345-348. Abstract: Gas phase solid freeform fabrication research at The University of Connecticut focuses on two main procedures, Selective Area Laser Deposition (SALD) and Selective Area Laser Deposition Vapor Infiltration (SALDVI). A SFF research laboratory is under construction at UCONN, with two new operation systems. These systems possess temperature control, data acquistion capabilities, in-situ video monitoring, and the ability to fabricate SALDVI parts up to four inches wide by four inches long. The procurement of a harmonic generating Nd:YAG six watt laser, capable of producing output at 532, 355, and 266 nanometer wavelengths, as well as a coupled effort with the Photonics Center at the University providing laser diodes at a variety of wavelengths, presents the opportunity to explore interactions involved in gas reactions driven by lasers. Investigations of material systems will include ceramic carbides, nitrides, and their composites, as well as metals.
"Solid Freeform
Fabrication: An Overview" by H.L. Marcus, S. Harrison, and J.E. Crocker, Proceedings of the Symposium on Rapid
Response Manufacturing 1996, Atlanta, GA, Nov. 17-22, 1996. Abstract:
Solid Freeform Fabrication
(SFF) has become a prominent area of interest and research in the last 10
years. SFF produces parts directly
through additive procedures, without any part-specific tooling. The design for
the part originates in a Computer Aided Design (CAD) file which is a three
dimensional representation of the part that is sectioned into thin two
dimensional layers from which the part is built. SFF vastly enhanced the
prototype production process, and now looks to make advances for short run
productions and tool and dies. This paper presents an overview of SFF, in terms
of where it has been, what it is today, and where it will go in the future.
"Recent Advances in SALD and SALDVI", by K. Jakubenas, B.R. Birmingham, S. Harrison, J.E. Crocker, J. Sanchez, and H.L. Marcus, Proceedings of the Seventh International Conference on Rapid Prototyping 1997.
"Current and Future Trends in Solid Freeform Fabrication", by D.L. Bourell, J.J. Beaman, J.W. Barlow, R.H. Crawford, H.L. Marcus, and L.E. Weiss, SPIE Proceedings Volume 2910, Rapid Product Development Technologies, Boston, MA, November, 1996.
"Selective Area Laser Deposition (SALD) of Titanium Oxide" by K.J. Jakubenas, Y.L. Lee, M.S. Shaarawi, H.L. Marcus, and J.M. Sanchez, Proceedings of the 6th European Conference on Rapid Prototyping and Manufacturing 1997, edited by P.M. Dickens, University of Nottingham, p. 119-126.
"Selective Area Laser Deposition of Titanium Oxide" by K.J. Jakubenas, Y.L. Lee, M.S. Shaarawi, H.L. Marcus, and J.M. Sanchez, Rapid Prototyping Journal, Vol. 3, No. 2, 1997, p. 66-70.
"Recent Advances in SALD and SALDVI", by K. Jakubenas, B.R. Birmingham, S. Harrison, J.E. Crocker, J. Sanchez, and H.L. Marcus, Proceedings of the Seventh International Conference on Rapid Prototyping 1997, edited by R.P. Chartoff, A.J. Lightman, M.K. Agarwala, and F. Prinz, University of Dayton, p. 60-69.
"The Use of VRML to
Integrate Design and Solid Freeform Fabrication", by Y. Wang, J. Dong, and
H.L. Marcus , Proceedings from the 1997
Solid Freeform Fabrication Symposium, Austin, TX, August, 1997,
669-676. Abstract: The
Virtual Reality Modeling Language (VRML) was created to put interconnected 3D
worlds onto every desktop. The 3D VRML
format has the potential for 3D fax and Tele-Manufacture. An architecture and
methodology of using VRML format to integrate a 3D model and Solid Freeform
Fabrication system are described in this paper. The prototype software
discussed in this paper demonstrates the use of VRML for Solid Freeform
Fabrication process planning. The path used from design to part will be
described.
"Fabrication of In-Situ
SiC/C Thermocouples by Selective Area Laser Deposition", by L. Sun, K.J.
Jakubenas, J.E. Crocker, S. Harrison, L.L. Shaw, and H.L. Marcus, Proceedings from the 1997 Solid Freeform
Fabrication Symposium, Austin, TX, August, 1997, 481-488. Abstract:
With the intrinsic nature to process small features, selective area
laser deposition (SALD) is a potential technique to fabricate complex shaped
macro-components with in-situ high-resolution micro-devices. In the study, SALD
was used to deposit in-situ SiC/C thermocouples on alumina and silicon carbide
substrates with a CO2 laser. Tetramethylsilane (TMS) and acetylene
(C2H2) were chosen as precursors for deposition of the
silicon carbide and carbon lines respectively. The electromotive force (emf) of
the deposited thermocouple was measured and found to respond sensitively to
temperature variations from room temperature to 800°C.
The effect of the deposition parameters on the product morphology was also
investigated with the SEM.
"Gas Phase SFF Control System for Silicon Nitride Deposition by SALD/SALDVI", by S. Harrison, C.F. Costa, K.J. Jakubenas, J.E. Crocker, and H.L. Marcus, Proceedings from the 1997 Solid Freeform Fabrication Symposium, Austin, TX, August, 1997, 241-246. Abstract: A closed-loop laser scanning and temperature control system has been developed for SALD/SALDVI. Temperature control is especially important in SALD/SALDVI because temperature plays a defining role in both composition and deposition rate. The control system for SALD/SALDVI is presented which provides .STL file interpretation, real time temperature control, and laser response modeling, all on a PC. This control system was utilized with the SALD/SALDVI techniques for depositing silicon nitride. Characteristics of Si3N4 fabricated shapes are discussed, including composition, morphology, and electrical properties.
"SALDVI Optimization for the Tetramethylsilane-Silicon
Carbide System", J.E. Crocker, K.J. Jakubenas, S. Harrison, L.L. Shaw, and
H.L. Marcus, Proceedings from the 1997
Solid Freeform Fabrication Symposium, Austin, TX, August, 1997,
489-496. Abstract: Selective Area Laser Deposition Vapor
Infiltration (SALDVI) of silicon carbide powder infiltrated with silicon
carbide deposited from tetramethylsilane (TMS) was studied. The effects of deposition time, temperature,
and gas precursor pressure are discussed.
The discussion centers on the efforts to properly balance these
parameters to produce multi-layered shapes with structural integrity,
particularly for use as the matrix material for shapes containing embedded devices. This includes optimizing scan speed,
deposition temperature, and gas pressure to maximize infiltration to increase
density and layer to layer bonding, and minimize excessive deposition to
maintain critical dimensions. Initial
powder properties are also optimized to minimize bulk motion in the powder bed
during deposition, which was observed and identified as a mechanism that
reduces inter-layer bonding.
"Net Shape Functional Parts Using Diode Laser", by T. Manzur, C. Roychoudhuri, P. Dua, F. Hossain, and H.L. Marcus, Proceedings from the 1997 Solid Freeform Fabrication Symposium, Austin, TX, August, 1997, 99-114.
"Rapid Prototyping and Solid Free Form Fabrication", by J.G. Conley and H.L. Marcus, Journal of Manufacturing Science and Engineering, November, 1997.
"Multiple Material Solid Free-Form Fabrication by Selective Area Laser Deposition" by K. J. Jakubenas, J.M. Sanchez, and H.L. Marcus, Materials & Design, 1997.
"Gas-Phase Selective Area
Laser Deposition (SALD) Joining of SiC Tubes with SiC Filler Material" by
S. Harrison and H.L. Marcus, Proceedings
of the 1998 Solid Freeform Fabrication Symposium, Austin, TX, August, 1998,
537-542. Abstract: The laser-driven, gas phase based SFF
technique for joining together ceramic components with ceramic filler material,
known as Selective Area Laser Deposition (SALD) Joining, was utilized in
fabricating joined silicon carbide structures. Specifically, silicon carbide
tubes were 'welded' together by depositing silicon carbide from a gas phase
reaction. Two different precursor environments were examined, one a
tetramethylsilane/hydrogen mixture and the other composed of
methyltrichlorosilane. The quality of the joints were examined by bend tests
and hermeticity measurements. In addition, the composition and morphology of
the silicon carbide deposit was studied and is discussed here.
"Preparation and Properties of In-Situ Devices Using the SALD and SALDVI Techniques" by J.E. Crocker, L. Sun, L.L. Shaw and H.L. Marcus, Proceedings of the 1998 Solid Freeform Fabrication Symposium, Austin, TX, August, 1998, 543-547. Abstract: One of the many advantages of the Selective Area Laser Deposition (SALD) and the Selective Area Laser Deposition Vapor Infiltration (SALDVI) is that they can be used to embed in-situ micro-sensors within macro-components. The single-point SiC/C thermocouple sensor embedded within SiC macro-component and electrically insulated with silicon nitride layers has been demonstrated. In many applications, multi-point sensors within a single component are needed, e.g., in monitoring temperature gradient and distribution at different positions. In this paper, the multi-point thermocouple devices are demonstrated. The macro-component is a SiC bulk shape made by infiltrating vapor deposited silicon carbide into a silicon carbide powder bed using the SALDVI technique. Multiple SiC/C thermocouples are embedded in-situ in the SiC bulk shape using the SALD technique. The transient and steady state responses of the embedded thermocouples are compared to reference thermocouples probing the surfaces of the bulk shape.
"Using SALDVI and SALD with
Multi-Material Structures" J.E. Crocker, S. Harrison, L. Sun, L.L. Shaw
and H.L. Marcus, JOM, 50, 21-23, December 1998. Abstract: Two techniques for solid freeform
fabrication using gas precursors and localized laser heating are Selective Area
Laser Deposition (SALD) and Selective Area Laser Deposition Vapor Infiltration
(SALDVI). The concepts, capabilities, and processing issues of the two
techniques are described. An example of a multiple material structure
fabricated using SALD and SALDVI illustrates the versatility of these
developing processes.
"Gas Phase Solid Free-Form Fabrication and Joining of Ceramics", by K.J. Jakubenas, J.E. Crocker, S. Harrison, L. Sun, L.L. Shaw and H.L. Marcus, Naval Research Reviews, July 1998.
"In-Situ Thermocouples in
Macro-Components Fabricated Using SALD and SALDVI Techniques: Parts I.
Thermochemical Modeling" by L. Sun, K.J. Jakubenas, J.E. Crocker, S.
Harrison, L.L. Shaw and H.L. Marcus, Materials
and Manufacturing Processes, 13,
859-882, 1998. Abstract: To
fabricate macro-structural SiC components containing an in-situ SiC/C
thermocouple using an integrated SALD and SALDVI technique, thermodynamic
analyses on the involved reactant gases have been performed with the CET89 code
based on the minimization of the system free energy. The gaseous precursors considered include tetramethylsilane (TMS)
and methyltrichlorosilane (MTS) for the deposition of silicon carbide, and methane,
ethylene, and acetylene for the deposition of carbon. Reactions between disilane and acetylene and between TMS and
ammonia have also been thermodynamically calculated for the deposition of
silicon carbide and silicon nitride (for use as an insulation layer between the
thermocouple and the matrix), respectively.
Based on these analyses, four characteristic temperature zones have been
defined for the decomposition of silicon carbide from TMS. A silicon nitride deposition map has been
built for the TMS and ammonia system.
The deposition temperature range of silicon nitride is found to increase
with the total pressure of TMS plus ammonia and the addition of hydrogen, and
be affected by the ratio of TMS to ammonia.
The addition of hydrogen also introduces a stable silicon carbide and
silicon nitride mixture zone that otherwise does not exist. The co-deposition of graphite with silicon
carbide and silicon nitride is found in the TMS-containing systems at certain
conditions. However, the threshold temperature
at which graphite co-deposition occurs can be increased by the addition of
hydrogen, thereby eliminating or reducing the graphite co-deposition. Based on these thermodynamic analyses, the
gaseous precursors for the deposition of silicon carbide, silicon nitride and
carbon have been selected for further experimental evaluation, the result of
which is reported in part II of this series.
"In-Situ Thermocouples in Macro-Components Fabricated Using SALD and SALDVI Techniques: Parts II. Evaluation of Processing Parameters" by L. Sun, K.J. Jakubenas, J.E. Crocker, S. Harrison, L.L. Shaw and H.L. Marcus, Materials and Manufacturing Processes, 13, 883-907, 1998. Abstract: In order to fabricate well-controlled in situ SiC/C thermocouples embedded within macro-structural SiC components using an integrated selective area laser deposition (SALD) and the selective area laser deposition and vapor infiltration (SALDVI) technique, the major processing parameters affecting the crystal structure, the deposition rate, surface morphology of deposits, and shapes and sizes of the cross section of deposited lines are evaluated. It is found that the growth rate of SiC deposits increases with temperature and tetramethylsilane (TMS) gas pressure over the temperature and pressure range studied. The apparent activation energy for depositing SiC from TMS is 61 kJ/mole in the temperature range from 700 to 1200°C and independent of the TMS gas pressure ranging from 20 to 60 Torr. The shape and size of the cross section of SiC lines depend strongly on the deposition temperature. XRD examination indicates that the deposition product using a C2H2 precursor at 900°C is crystalline graphite. The crystallinity of Si3N4 deposits is affected by the substrate material even though the deposition temperature and other process parameters are the same. These phenomenon have been explained in terms of the growth controlling mechanisms of deposits, the temperature distribution induced by an incident laser beam, and the thermal conductivity of the substrate.
"In-Situ Thermocouples in Macro-Components Fabricated Using SALD and SALDVI Techniques: Parts III. Fabrication and Properties of the SiC/C Thermocouple Device " by L. Sun, K.J. Jakubenas, J.E. Crocker, S. Harrison, L.L. Shaw and H.L. Marcus, Materials and Manufacturing Processes, 13, 909-919, 1998.
"Investigation on Morphology and Microstructure of SALD SiC," L. Sun, J.E. Crocker, L.L. Shaw, and H.L. Marcus, MRS Symposium Proceedings Series, Vol. 542, 37-42, 1998. Abstract: In this work, the deposition of silicon carbide using a tetramethylsilane (TMS) precursor was investigated. Effects of target temperatures on the morphology and crystal structure of the deposits were examined. It was found that the morphology of the SALD SiC depends strongly on the target temperature. The contour of the cross section of the SiC deposits changes from a triangle to trapezoid to volcano shape and the surface morphology of the deposited lines changes from smooth to rough to porous as the target temperature increases. A critical temperature was found to be about 700°C to initiate deposition of SiC under the current experimental conditions. X-ray diffraction analyses show that the SALD SiC formed at 1000°C contains both crystalline and amorphous phases. The results are briefly discussed.
"Gas-Phase Selective Area Laser Deposition (SALD) Joining of SiC", S. Harrison and H.L. Marcus, Materials and Design, 20, 147-152 (1999). Abstract: The laser-driven, gas-phase based SFF technique for joining together ceramic components with ceramic filler material, known as Selective Area Laser Deposition (SALD) Joining, was utilized in fabricating joined silicon carbide structures. Specifically, silicon carbide tubes were welded together by depositing silicon carbide from a gas phase reaction. A single laser beam deposition setup and a dual laser beam design were investigated. A gas environment of tetramethylsilane and hydrogen served as the deposition precursors. The quality of the joints were examined by bend tests and hermiticity measurements. In addition, the composition and morphology of the silicon carbide deposit was studied and is discussed here.
"Localized CVD and the Ultrafine Grain Structure", J.E. Crocker, L. Sun, S. Harrison, L.L. Shaw, and H.L. Marcus, Proceedings of TMS Ultrafine Grained Materials Symposium, Nashville, TN, March 2000, pp. 13-21. Abstract: In high rate localized chemical vapor deposition using a laser beam to thermally decompose gas precursors the resulting grain size ranges from the near amorphous to a continuum of ultrafine grain sizes depending on processing parameters. This paper will describe the nature of the grain sizes for various ceramic materials as a function of processing and post-processing conditions. The grain size characterizations were performed using Raman spectroscopy, NMR, TEM, X-ray and other analytic approaches. The results will be described in terms of the various characterization approaches and related to modeling of the processing variables.
"Structural Analysis of
Silicon Carbide Deposited by Gas-Phase Selective Area Laser Deposition
(SALD)", S. Harrison and H.L. Marcus, Proceedings
of the 1999 Solid Freeform Fabrication Symposium, Austin, TX, August,
1999. Abstract:
Silicon carbide deposited by the gas-phase Selective Area Laser
Deposition (SALD) process underwent structural analysis in this
investigation. The silicon carbide
material was locally formed from a gas precursor mixture of tetramethylsilane
and hydrogen, at a deposition temperature of approximately 1100°C and maintained by a closed-loop laser control
system. Ground powder samples of the
SALD silicon carbide material were examined by Magic Angle Spinning-Nuclear
Magnetic Resonance, X-ray Diffraction and Transmission Electron
Microscopy. The results from these
analytical tools show a significant level of twinning in the SALD SiC material
which explains the significant differences between the NMR and X-ray spectra.
"Effect of Hydrogen on Silicon Carbide Deposition from Tetramethylsilane - Raman Scattering Studies", L. Sun, J.E. Crocker, L.L. Shaw, and H.L. Marcus, Proceedings of the 1999 Solid Freeform Fabrication Symposium, Austin, TX, August, 1999. Abstract: Selective area laser deposition (SALD) is a unique technique for fabricating complex ceramic shapes, tailoring functionally graded structures and embedding in-situ sensors into ceramic parts. In general, high deposition rate is desired. For the case of fabricating in-situ sensors, the chemical composition must also be controlled. Proper shapes and deposition rate using tetramethylsilane (TMS) gas precursor to deposit SiC has been demonstrated in previous studies. However, carbon contamination has been found to be a potential obstacle for the further application of this precursor in sensor-related fabrication. It has been suggested using the thermodynamic calculation that hydrogen has significant effect on the composition of SiC deposits. In this study, therefore, the effect of hydrogen on the SALD SiC will be experimentally evaluated.
"Processing and
Characterization of SALDVI Ceramic Structures", J.E. Crocker, L. Sun, H.
Ansquer, L.L. Shaw, and H.L. Marcus, Proceedings
of the 1999 Solid Freeform Fabrication Symposium, Austin, TX, August,
1999. Abstract: Selective
Area Laser Deposition Vapor Infiltration (SALDVI) ceramic structures and
composites are fabricated by the localized chemical vapor infiltration of
powder layers. A matrix of vapor
deposited ceramic material is selectively deposited from gas precursors into a
bed of ceramic powder particles using laser heating. An important aspect of the SALDVI process for building 3-D
structures is the depth of penetration of the infiltration zone into the powder
layer. The infiltration behavior of
vapor deposited silicon carbide from tetramethylsilane gas was investigated for
a range of ceramic powders with different optical, thermal, and physical
properties using image analysis. The
porosity distribution in the silicon carbide matrix SALDVI structure was found
to vary with particle size and particle material. These results will be used to guide experiments on the effect of
layer thickness on the microstructure of multiple layer SALDVI composites.
"A SFF Approach Utilizing Condensed Gas Precursors and Pulsed Laser Deposition", E. Geiss and H.L. Marcus, Proceedings of the 1999 Solid Freeform Fabrication Symposium, Austin, TX, August, 1999. Abstract: Two techniques were studied to direct write diamond-like carbon (DLC) films. The first process employed a pulsed YAG laser to decompose a frozen precursor and deposit thin films directly on SiC and 304 stainless steel. After the initial film is deposited, additional layers may be subsequently condensed and deposited onto the substrate.
"Silicon-29 Solid-State MAS NMR Investigation of Selective Area Laser Deposition Silicon Carbide Material," S. Harrison, X. Xie, K.J. Jakubenas, and H.L. Marcus, Journal of the American Ceramic Society, 1999.
"Gas-Phase Solid Freeform Fabrication of SiC Cermets Using SALDVI", J.E. Crocker, L.L. Shaw, and H.L. Marcus, Proceedings of the 2000 Solid Freeform Fabrication Symposium, Austin, TX, August, 2000. Abstract: Selective Area Laser Deposition Vapor Infiltration (SALDVI) is an experimental solid freeform fabrication (SFF) technique aimed at the direct fabrication of ceramic and ceramic/metal structures and composites. SALDVI uses a layer-by-layer approach in which powders are infiltrated with solid material deposited from gas precursors by chemical vapor deposition (CVD) using laser heating. Experiments have been performed with CO2 and Nd:YAG lasers using the silicon carbide forming gas precursor Si(CH3)4 and Cu, Mo, and Ni metal powders. The microstructure of the resulting SiC/metal cermets was investigated in relation to the processing history. In some cases, the formation of intermetallic silicide phases was observed.
"Gas Phase Solid Freeform Fabrication of SALDVI of SiC
Cermets", J.E. Crocker, L. Shaw, H.L. Marcus, MRS Proceedings, 2000, Abstract: In
this work, the solid freeform fabrication of cermets was explored. Using a laser-based approach, SiC was
deposited by chemical vapor deposition from tetramethylsilane gas into powder
layers of Cu, Mo, or Ni. The resulting
structures were examined to observe the extent of reaction between the metal
powders and the vapor deposited SiC.
Silicide formation was observed, most readily with the Ni powder. The thermal expansion of the metals compared
to that of the vapor deposited SiC affected the interfacial stresses generated
in the cermets during fabrication.
"Finite Element Analysis of the SALDVI Process",
K. Dai, J. Crocker, L. Shaw, and H. Marcus, Proceedings
of the 2000 Solid Freeform Fabrication Symposium, Austin, TX, August, 2000.
Abstract: Selective Area Laser Deposition Vapor
Infiltration (SALDVI) is a developing solid freeform fabrication (SFF)
technique aimed at the direct fabrication of ceramic and ceramic/metal
structures and composites. SALDVI uses
a layer-by-layer approach in which layers of powder are densified with solid
material deposited from gas precursors by chemical vapor deposition (CVD) using
laser heating. In this work, we have
performed numerical simulation using the ANSYS code with 3-dimensional coupled
field elements to calculate the temperature field and the part geometry
resulting from the SALDVI process. The
effects of the powder and vapor deposited material properties on the
temperature distribution and the part geometry have been investigated. The result from the numerical simulation is
found to be consistent with those obtained from experiments performed using the
silicon carbide forming gas precursor Si(CH3)4 and SiC
powder particles.
"SALDVI of SiC Into Metal and Ceramic Powders",
J.E. Crocker, H. Wei, L.L. Shaw, and H.L. Marcus, Proceedings of the 2001 Solid Freeform Fabrication Symposium,
Austin, TX, August, 2001. Abstract: Selective
Area Laser Deposition Vapor Infiltration (SALDVI) is the SFF technique using
gas phase precursors to locally infiltrate a powder bed into a desired
shape. Experiments were performed with
a CO2 laser and the silicon carbide forming gas precursor Si(CH3)4. This paper will report on the
microstructural aspects of SiC into a variety of metal and ceramic powders
including Mo, SiC, ZrO2, and WC.
"Modeling of Selective Area Laser Deposition Vapor Infiltration
(SALDVI) of Silicon Carbide", K. Dai, J. Crocker, L. Shaw and H. Marcus, Proceedings of the 2001 Solid Freeform
Fabrication Symposium, Austin, TX, August, 2001. Abstract:
Selective Area Laser Deposition Vapor Infiltration (SALDVI) is a developing
solid freeform fabrication (SFF) technique in which porous layers of powder are
densified by infiltrating the pore spaces with solid material deposited from a
gas precursor during laser heating. A 3D finite
element model was developed that simulates SALDVI of silicon carbide. The model
predicts the laser input power and the distribution of vapor deposited SiC
within the powder bed as well as on the surface of the powder bed (SALD). The
model includes closed-loop control of the laser power to achieve a desired
target processing temperature on the top surface of the power bed. This model
considers a moving Gaussian distribution laser beam, temperature- and
porous-dependent thermal conductivity, specific heat and temperature-dependent
deposition rate. The simulation results agree fairly well with experimental
data for simple geometries and offer guidelines for further experimental
studies of the SALDVI process.
"Spot Joining of Si3N4 and SiC
Ceramics Using Selective Area Laser Deposition (SALD) Technique", I.M.
Ghayad, E. Geiss , J.E. Crocker, and H.L. Marcus, Proceedings of the 2001 Solid Freeform Fabrication Symposium,
Austin, TX, August, 2001. Abstract: A
new, promising manufacturing path involves a gas-phase decomposition approach,
known as Selective Area Laser Deposition (SALD) Joining. SALD is a gas-phase
Solid Freeform Fabrication (SFF) process in which a specific gas mixture
decomposes either thermally or photolytically from the energy input of a laser
beam to form a solid reaction product. The chemical process is similar to
Chemical Vapor Deposition (CVD) but the product is selectively deposited
locally under the laser spot, which can be scanned, and therefore controlled.
The present paper focuses on deposition of silicon nitride or silicon carbide
filler materials to spot join silicon nitride and silicon carbide ceramic
materials. Chemical and structural characterization of joints were performed.
"Powder Effects in SiC Matrix Layered Structures
Fabricated Using SALDVI", J.E. Crocker, L.L. Shaw, and H.L. Marcus, to appear in Journal of Materials Science,
2002. Abstract: Silicon
carbide has been deposited by laser-induced chemical vapor infiltration from
the gas precursor tetramethylsilane, Si(CH3)4, into
loosely packed powder layers of SiC, ZrO2-Y2O3,
or Mo. The goal is to produce dense
layered structures of arbitrary shape by computer controlled laser scanning
where the pore spaces between the powder particles are filled with solid
material deposited from the gas phase using the Selective Area Laser Deposition
Vapor Infiltration (SALDVI) process.
Layered samples were fabricated for each powder material using both
single line (bar) and multiple line (slab) laser scan patterns and 10 Torr
Si(CH3)4, 2.5 mm/s scan speed, 1000°C
target temperature, and 120 mm layer thickness. Samples of SiC and ZrO2-Y2O3 are
prone to surface cracking in the bar geometry, and cracking and delamination of
layers in the slab geometry. Samples
fabricated with Mo powder have no cracks or delamination defects in either bar
or slab geometry as well as a better surface appearance.