Fiscal Year 2000 Annual Summary Report
Solid
Freeform Fabrication from Gas Precursors Using Laser Processing
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Principal/co-Principal Investigator.
* PI/co-PI Name(s): Harris L. Marcus
* PI Institution: University of Connecticut, Storrs
* PI Phone Number: (860) 486-4410
* PI Fax Number: (860) 486-4745
* PI E-mail Address: hmarcus@mail.ims.uconn.edu
* PI URL Home Page: http://www.ims.uconn.edu/metal/faculty/marcus.htm
* Grant/Contract Number: N00014-95-1-0978
* Period of Performance: 07/01/99 - 06/30/00
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Project Attributes.
* Number of refereed papers/book chapters published: 4
* Number of refereed papers/book chapters to appear: 1
* Number of books published: 0
* Number of unrefereed reports and other articles: 6
* Number of project presentations: 8
* Number of patents granted and software copyrights: 0
* Number of patents filed but not yet granted: 0
* Number of graduate students supported >= 25% of full time: 2
* Number of post-docs supported >= 25% of full time: 0
* Number of minorities supported: 0
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Summary of Objectives and Approach.
SALDVI:
Selective Area Laser
Deposition Vapor Infiltration (SALDVI) is the direct fabrication of ceramics,
metals, and composites from computer representations in which loose powder
layers are densified with solid material deposited from gas precursors into the
pore spaces using chemical vapor deposition and laser heating. SALDVI shapes can be monolithic or multiple
material, and can contain functional embedded devices such as in-situ thermocouples. Our objective is to develop a better
theoretical understanding of the SALDVI process and to assess the ability of
the process to produce functional tailored ceramic and composite structures for
various applications including shapes with embedded devices. Previously we have experimentally
investigated the laser chemical vapor infiltration (LCVI) of silicon carbide
from tetramethylsilane Si(CH3)4 gas using a CO2
laser (10.64 mm wavelength) and Nd:
YAG lasers (1.06 mm wavelength), including the effects of gas pressure, the surface
temperature, the laser scanning speed, and a range of starting powders. The time evolution of the SALDVI workpiece was
experimentally investigated by quantifying the distribution of vapor
infiltrated material as a function of the processing conditions using image analysis. Recently, the feasibility of fabricating cermets
of various metal powders and vapor deposited SiC using SALDVI was investigated. The microstructures of SALDVI cermets
fabricated with Cu, Ni, and Mo powders were investigated with x-ray diffraction
(XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy
(EDS), and optical microscopy at a range of processing histories. In some cases, due to reactions between the
metal powders and the vapor deposited SiC matrix, the formation of
intermetallic silicide phases was observed.
Mechanical properties were also measured by four point bend.
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Summary of Technical Progress.
The
microstructures of the three SALDVI cermets reveal varying degrees of reactions
between the metal powders and the vapor deposited SiC matrix. Both the Cu and Ni powders react with vapor
deposited SiC during the SALDVI process at all of the processing temperatures (1000-1200
C) and heating times (200-800 s) examined here. For the Cu powder, particles at least 20 mm in diameter reach a uniform composition indicative
of a Cu silicide phase even at the shortest heating time of 200 s and lowest
processing temperature of 1000 C.
Further evidence of Cu silicide formation was observed in x-ray
diffraction measurements at 1000 and 1200 C target temperatures. These results indicate that Si is a fast
diffuser in Cu. In the Ni case, the
extent of the reactions progressed more notably with increasing processing
temperature and heating duration. X-ray
diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS) measurements
indicate the formation of the Ni2Si phase, as well as additional
phases not yet identified. For the Mo/SiC cermet, no Mo-Si interdiffusion was
detected by XRD or EDS for the 1000 C target temperature. This is not surprising as the melting
temperature of Mo is 2610 C, so diffusion would be expected to occur slowly at
1000 C. The Mo/SiC cermet shows the
highest bending strength of 50 MPa of the three cermets. This behavior is attributed to the close
thermal expansion match between the two materials resulting in few particle
debonds compared to the Cu and Ni cases.
Figure 1 shows a typical as-fabricated single line, three layer, 20 mm
long SALDVI Mo/SiC cermet (a) and a SEM image of a polished cross-section
through its centerline region (b). The
Mo particles appear well bonded to the SiC matrix and the solid density exceeds
95 % in this region, as measured by quantitative metallography.
Figure 1. As-fabricated three layer, single line macrostructure
(a) and SEM image of the microstructure of Mo/SiC SALDVI cermet.
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Participation on Other Research Projects.
High Temperature X-ray
Diffraction Studies of Palladium Oxide/Palladium Methane Catalyst Materials.
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Transitions and DOD Interactions.
Working with both Bettis
and Knolls on potential applications of the SALD/SALDVI approaches.
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Software and Hardware Prototypes.
1. Prototype Name: SALD and SALDVI System Prototypes.
+ URL:
+ Availability: Available in SFF laboratory, Institute of
Materials Science, UCONN.
+ Description: Hardware and software of performing gas phase
SFF of structures and infiltration of powder layers
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Honors, Prizes, Awards, or Promotions Received.
none
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Current Students and Recent Graduates Supported by ONR.
1. Name: James Crocker
+ US Citizen/Permanent Resident: US Citizen
+ Thesis: Solid Freeform Fabrication Using the SALDVI
Technique
+ Graduated:
+ Home Page:
+ Job: Graduate Assistant
1. Name: Erik Geiss
+ US Citizen/Permanent Resident: US Citizen
+ Thesis: Laser Processing of "Photonic" Single
Crystals for Micro/Macro System Design
+ Graduated:
+ Home Page:
+ Job: Graduate Assistant
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Sabbatical Plans.
none
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Related Research Projects.
Investigation of crack
deflection in layered SiC/C deposited on solid substrates by Selective Area
Laser Deposition (SALD).
Application of laser
processing to create “photonic” single crystals for micro/macro system design.
Multiple material laser
densification applied to dental restorations.
Selective Area Laser
Deposition (SALD) joining of silicon nitride in an international collaboration
with Dr. Ibrahim Ghayad of the Central Metallurgical Research and Development
Institute in Cairo, Egypt. This
research is being performed under the Joint Fund Program between Egypt and the
United States.
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Miscellaneous.
<...any suggestions/research directions/contacts/sbir
topic/muri topics/etc...>
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