1998 MRS Fall Meeting & Exhibit

Chairs

Michael Cima, MIT
Stephen Danforth, Rutgers Univ

Symposium Support 

• Sandia National Laboratories 

* Invited paper

SESSION V1: ORGANICS, COMPOSITES AND LASER CVD 
Chairs: Paul Calvert and Harris L. Marcus 
Monday Morning, November 30, 1998 
Exeter A/B (S)

8:30 AM V1.1 PROCESSING AND PROPERTIES OF HIGH TG LIQUID CRYSTAL RESINS FOR STEREOLITHOGRAPHY. Richard P. Chartoff, John W. Schultz and Jill S. Ullett, University of Dayton, Dayton, OH. This paper describes novel photo-curable liquid crystal (LC) monomers, which represent a new class of stereolithography resins. These LC materials contain stiff, rod-like molecules, that produce high glass transition temperatures. The glass transition [Tg] temperatures that develop depend on the monomer chemical structure and processing conditions. Developing these favorable high temperature properties was achieved using the usual stereolithography configuration. In addition to developing unusually high Tgs, the rod-like molecules can be aligned by an external force. When cured in the aligned state, the aligned structure is ``locked in'' resulting in polymers with anisotropic physical and mechanical properties. By varying the alignment of successive layers, properties such as the thermal expansion coefficient can be optimized. The characteristics model liquid crystal monomers are considered in this paper. Stereolithography processing parameters as well as the physical and mechanical properties of the cured polymers are discussed. 

8:45 AM *V1.2 
EXTRUSION FREEFORM FABRICATION OF ORGANIC-INORGANIC HYBRIDS. Paul Calvert and Chad Souvignier, Arizona Materials Labs., Tucson AZ. 

Layerwise forming methods should provide routes to materials that cannot be formed by conventional molding methods. One example is chemical conversion from liquid to solid where diffusion of reagents and products would be very slow in a large part but can be relatively fast if the reaction takes place one layer at a time. In addition it should be possible to handle the stresses arising from large shrinkages by allowing the contraction to take place one layer at a time. This paper will discuss the application of extrusion freeform fabrication to the direct formation of a shaped polymer from monomer and to the formation of organic-inorganic hybrids and mineralized gels. 
Hydrogels, such as agarose, can be freeformed containing large concentrations of partly-soluble salts. Subsequent treatment with aqueous solutions of the appropriate counter ions can mineralize the gel with calcite or hydroxyapatite. During drying, these materials retain their shape, while undergoing a 50% linear shrinkage, to form dense, strong composite materials. Methacrylate-silica organic-inorganic hybrid materials can be formed from mixtures of silanes and monomers in the same way. However, these parts invariable crack during as silica forms and the part shrinks. This cracking can be avoided by forming open meshes instead of dense parts. The resulting materials show surprisingly good toughness and strength. 
Thus layerwise forming methods do lend themselves to the formation of solid materials by chemical routes but special methods must be used to control shrinkage. 

9:15 AM V1.3 
EFFECTS OF ADDITIVES ON THERMOMECHANICAL PROPERTIES OF COMPOSITES FORMED FROM THERMOSET POLYMERS. Aleksandar Radisic, Vivak M. Malhotra , Dept. of Physics, Southern Illinois University, Carbondale, IL. 

Automotive, aircraft, and heavy-duty friction materials are complex multimaterial composites which contain, besides polymers and fibers, a number of constituents whose exact role is not well delineated. Since the formation of these composites often requires complex shapes, advanced formation techniques are called for. However, for technologies to mature we need to understand the role of various phases in a friction composite and how interaction among the components affect the structural and thermomechanical properties of the material. We probed how epoxy-modified phenolic polymer's structural and thermal behavior was modified by the incorporation of materials such as graphite, coke, and slag fibers, typical friction composites' ingredients. The formed composites, subjected to various degrees of cure, were examined by FTIR, DSC, and DMA measurements at 300 K < T < 600 K. Our results suggest that the incorporation of ingredients, singly and additively, strongly affected the thermomechanical properties of the formed composites. DMA technique provided much more useful information than the DSC method as the storage and loss modulus were much more sensitive to the changes in the structure of the composite. The post curing, i.e., curing above the glass transition temperature, was much more strongly influenced by the temperature than by the length of time (0 < t < 15 hours) at T > Tg. 

9:30 AM V1.4 
RAPID HEATING OF POLYESTER PREFORMS VIA SCATTERING/ABSORBING INORGANIC PARTICULATE ADDITIVES. Lori A. Maiorino , Robert F. Speyer, Georgia Institute of Technology, Dept of Materials Science and Engineering, Atlanta, GA. 

Test-tube-shaped polyester preforms heated with infrared radiation are pressure expanded by high-speed machines to form plastic bottles. In order to improve the rate of heating, graphite and inorganic particulate additives were evaluated. The graphite additions, smaller than the most intense wavelength used (1.17 microns) acted as blackbody absorbers and scatterers of radiant energy. Several different inorganics were incorporated into the polyethylene terephthalate (PET) based polymer. A family of particle sizes and volume percentages of graphite and inorganic particles were mixed into the polymer to form test bars. They were evaluated for infrared absorption using a spectral radiometer and an infrared-heating furnace. 

9:45 AM V1.5 
GRADIENT AND DISCRETE REGION COMPOSITES PRODUCED BY SOLID FREEFORM FABRICATION TECHNIQUES. Robert Crockett and Vito Gervasi, Milwaukee School of Engineering, Rapid Prototyping Center, Milwaukee, WI. 

Stereolithography and Fused Deposition Modeling patterns have been used to create composites with gradient properties. Patterns are produced with an open cellular or columnar structure inside a surface shell. This serves as a host for a filler material, generally epoxy or polyurethane matricies loaded with various fibers or microspheres. Regions within a single object may be separated by thin barriers, allowing filling with different matrix materials to create regions of differing local properties. The internal structure can also be continually gradated in dimension to produce composites with properties ranging from that of the filler material to that of the SFF material, currently epoxy or ABS plastic. This is a general set of processes that can be applied to a variety of existing Solid Freeform Fabrication systems. 

10:30 AM V1.6 
IN SITU FABRICATION OF COMPOSITIONALLY, STRUCTURALLY AND FUNCTIONALLY GRADED CERAMIC MATERIALS BY DIRECT INTEGRATION OF DEPOSITS FROM AQUEOUS SOLUTION: SOFT SOLUTION PROCESSING. M. Yoshimura , W. Suchanek, K.-S. Han, Tomoaki Watanabe, Tokyo Institute of Technology, Materials and Structures Laboratory, Center for Materials Design, Yokohama, JAPAN. 

In contradiction to traditional multistep ceramic processing by (1) powder preparation, (2) shape forming, and (3) firing/sintering, we propose a novel concept, Soft, Solution Processing (SSP) which targets one step fabrication of ceramic materials directly from (aqueous) solutions. This processing route is environmentally friendly (=soft), simple to accomplish, cheap, and does not require high temperatures for firing/sintering. In our approach, the interfacial reactions between a substrate, at the same time the reactant, and species in a solution is accelerated by some heat (= hydrothermal), electrical current (= electrochemical), or their combination (= hydrothermal-electrochemical). We have succeeded to fabricate crystallized films of several double oxides, such as BaTiO3, SrTiO3, BaWO4, SrMoO4, LiNiO2, LiCoO2, etc., and their solid solutions, with controlled compositions, microstructures, and functions, between RT-150 deg C. In addition, by using different solutions, we can integrate such films in order to form graded structures (for example multilayers). The integration issues have been facilitated in a flow-cell type hydrothermal/electrochemical apparatus. Moreover, we can accomplish patterning by local activation of the interfacial reactions using electrode and/or laser radiation. Combination of the patterning of ceramic film(s) and the integration may lead to in situ fabrication of advanced ceramic devices directly from aqueous solutions. 

10:45 AM *V1.7 
MATERIALS FOR TWO-PHOTON INITIATED POLYMERIZATION AND APPLICATION TO THREE-DIMENSIONAL MICROFABRICATION. B. H. Cumpston,¹ S. M. Kuebler,¹ D. McCord-Maughon,¹ M. Lipson,¹ S. R. Marder,^1,2 and J. W. Perry ,^1,2 1 Beckman Institute, California Institute of Technology, Pasadena, CA; ² Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA. 

Two-photon initiated polymerization holds tremendous promise for 3D microfabrication. With this method, one can selectively polymerize very small volumes near the focus of a laser beam, which permits 3D patterning of a photopolymer material system in arbitrary 3D shapes, by scanned laser exposure. We have developed organic chromophores that exhibit large two-photon absorption cross sections, an order of magnitude larger than typical UV photoinitiators used previously. These new molecules are effective in the two-photon initiation of acrylate monomer polymerization, using femtosecond near IR laser pulses. We will discuss our recent work on the design of strongly two-photon absorbing molecules, the development of photopolymer materials systems for two-photon initiated polymerization, and the use of these two-photon photopolymer systems to fabricate a range of 3D micro-optical and micromechanical structures, including photonic band gap structures with micron scale periodicity. 

11:15 AM V1.8 
THREE DIMENSIONAL MICROSTRUCTURES FROM METAL CARBONYLS. Jan-Erik Lind , Olli Nyrhila, Juha Kotila, Tatu Syvanen, Electrolux Rapid Development, Rusko, FINLAND. 

3D-LCVD of nickel and iron carbonyls was studied in order to grow 3-D metal forms under static or scanning Nd:YAG -laser beam. In addition to the growth, emphasis was also based on the prevention of the simultaneous decomposition of carbon monoxide, which interferes with the metal growth process. This was essential, because the quite high precursor gas pressures of the metal carbonyls are very tempting for the 3D-LCVD. Parameters to be optimized included precursor pressure, laser power, laser scan speed and spot size. In order to optimize the growth parameters, the microstructures of the resulted forms were studied with SEM. Comparison between static and scanning growth is presented with the building philosophy in mind, e.g. whether to build structures layer by layer, from modules or in conjunction with another process to compensate for its shortcomings. The used substrates included steel, graphite and porous bronze. 
The results indicated different microstructures between iron and nickel, which also was dependent of the total/precursor pressure. In the scanning experiments, nickel produced very thin films of high reflectivity, whereas iron produced a structure, which could be described as a crystalline spiders web. The static experiments produced solid rods in the case of nickel, whereas with iron, the rods were hollow, even with same spot sizes. Also an evident change in the microstructure of the nickel forms as a function of pressure was observed. The 3-D growth rate of the static experiments seemed very promising for the forthcoming scanning experiments. 

11:30 AM V1.9 
INVESTIGATIONS ON MORPHOLOGY AND MICROSTRUCTURE OF THE SALD AND SALDVI SIC. Lianchao Sun , James E. Crocker, Leon L. Shaw and Harris L. Marcus, Institute of Materials Science, University of Connecticut, Storrs, CT. 

Among the reasons for the actual interest in SiC are its wide band gap, high chemical inertness and thermal stability. Because of these superior properties, SiC is excellent for high temperature device applications. The in-situ SiC/C high temperature thermal sensor embedded within SiC macro-components has been manufactured previously using the Selective Area Laser Deposition (SALD) and the Selective Area Laser Vapor Deposition (SALDVI) techniques at our Laboratory. In this paper, the basic issues associated with manufacturing in-situ thermal sensors and macro-components, including the effects of temperature, tetramethylsilane (TMS) gas pressure, laser scanning speed and scanning pattern on the morphology and microstructure of the SALD and SALDVI SiC have been studied. The instability phenomenon for SiC deposition has been found during SALD process and eliminated through the processing optimization. To explain this phenomenon, a preliminary model based on intrinsic laser beam intensity distribution, thermal conduction behavior of the substrate and mass transport of the gas precursor has been proposed. 

11:45 AM V1.10 
LASER AND FOCUSSED ION BEAM INDUCED DIRECT-WRITE 3D-GROWTH OF METALS AND CERAMICS WITH SUB-100-NM RESOLUTION. Andreas Schertel, Micrion Munich GmbH, Rainer Kassing, University of Kassel and Michael Stuke , Max-Planck-Institut f. biophysikalische Chemie, Goettingen, GERMANY. 

Direct-write growth of 3-dimensional micro- and nanostructures using laser and focussed ion beam induced decomposition of gas phase or/and surface adsorbed precursors will be described. This talk will focus onto the following examples: (1) 3D growth of aluminumoxide by spatially controlled visible laser induced reaction of trialkyl-amine-alane and oxygen [1,2], (2) Focussed ion beam induced growth of tungsten (W) from surface adsorbed tungsten-hexa-carbonyl W(CO)6. In the latter case, sub-100-nm accuracy with excellent reproducability has been achieved and was used to modify the mechanical and optical properties of 3D microstructures. 

SESSION V2: DIRECT METAL FABRICATION 
Chairs: Suman Das and Duane Dimos 
Monday Afternoon, November 30, 1998 
Exeter A/B (S)

1:30 PM V2.1 
FREEFORM FABRICATION OF HIGH PERFORMANCE TITANIUM COMPONENTS VIA SLS/HIP. Suman Das , Joseph J. Beaman, Martin Wohlert, David L. Bourell, University of Texas at Austin, Laboratory for Freeform Fabrication, Austin, TX. 

This paper presents the development of SLS/HIP technology for production of functional high performance components in Ti-6Al-4V alloy. SLS/HIP is a net shape manufacturing technique that combines and exploits the freeform shaping capability of selective laser sintering (SLS) and the full densification capability of hot isostatic pressing (HIP). The advantages of SLS combined with in situ HIP encapsulation include single step net shape canning, full densification by containerless HIP, no container-powder adverse interactions, reduced pre-processing time, and minimal post-process machining compared to conventional HIP of canned powders. Microstructure and mechanical properties of SLS processed and HIP post-processed Ti-6Al-4V are consistent with conventionally processed material. The potential of SLS/HIP technology has been demonstrated by fabricating a component to net shape, namely the Titanium guidance section housing base for the AIM-9 Sidewinder missile. This research is sponsored by DARPA/ONR contract N00014-95-C-0139 titled ``Low Cost Metal Processing Using SLS/HIP''. 

1:45 PM V2.2 
ULTRA HIGH SPEED IMAGING OF THERMAL GRADIENTS DURING LENS^TM PROCESSING. Melissa J. Wert , William H. Hofmeister, Robert J. Bayuzick, Vanderbilt University, Dept of Materials Science and Engineering, Nashville, TN; Michelle L. Griffith, Sandia National Laboratories, Albuquerque, NM; John E. Smugeresky, Sandia National Laboratories, Livermore, CA. 

The Laser Engineered Net Shaping (LENS(tm)) process is a direct fabrication process with the capability to fabricate fully dense components with good dimensional accuracy and unique material properties. Mechanical properties are dependent upon the microstructure of the material, which in turn is a function of the thermal history of solidification. Experiments were conducted recently using ultra high speed imaging techniques to measure melt pool size and determine temperature gradients during LENS(tm) deposition of 316 stainless steel. Concurrent experiments were also carried out using infrared imaging for estimates of thermal gradients and cooling rates in the bulk as it cools below the temperature sensing range of the high speed equipment. The experiments were conducted using two different powder sizes and several laser power settings. 
The intended goal of the experiments is to evaluate the range in molten pool sizes and the temperature gradient during solidification of the molten pool. It is expected that the ultra high speed and infrared imaging techniques will be complementary in providing information for analysis of microstructural development. 

2:00 PM *V2.3 
DIRECT MATERIALS DEPOSITION: DESIGNED MACRO AND MICROSTRUCTURE. J. Mazumder , A. Schiferer and J. Choi, Center for Laser Aided Intelligent Manufacturing University of Michigan, Ann Arbor, MI. 

Rapid Fabrication of three-dimensional shapes of engineering materials such as H13 tool steel and Nickel super alloys are now possible using Direct Materials Deposition (DMD) technique. H13 tool steel is one of the difficult alloys for deposition due to residual stress accumulation from martensitic transformation. However, it is the material of choice for the die and tool industry. DMD offers Copper chill blocks and water cooling channels as the integral part of the tool. On the other hand ZrO2 was co-deposited with nickel superalloys using DMD. This process thus is amenable to produce both macro and microstructure to a designed specification. This paper briefly reviews the state of the art of DMD and describes the microstructure and mechanical properties of selected engineering alloy systems deposited by DMD. 

2:30 PM V2.4 
A NEW SOLID FREEFORM FABRICATION METHOD USING A MICROWELDING TECHNIQUE. Edward L. Dreizin , AeroChem Research Lab., The Titan Corporation, Princeton, NJ; Radovan Kovacevic, Dept of Mechanical Engineering, Southern Methodist University, Dallas, TX. 

A concept of a new Solid Freeform Fabrication technique is discussed in this paper. The technique is based on a patented DROplet Welding (DROW) method developed by AeroChem Research Lab. Uniform, 0.05 1.00 mm diameter, liquid metal droplets are generated remotely and projected to the substrate. The droplets are formed by the rapid melting of the free end of a consumable wire anode in the pulsed micro-arc. The size of the droplets is comparable to those produced in the spray metal transfer mode of conventional arc welding techniques, but DROW uniquely provides precise control of the droplet size, temperature, and the instant of droplet detachment. It is proposed to use the DROW method to build parts by depositing droplets layer by layer. To provide a fast (500-1000 Hz) production rate of metal droplets with precisely controlled properties, the DROW method will be coupled with an active feedback system to control droplet generation. The feedback signal will be formed in real time based on the analysis of the configuration of the DROW electrodes. This analysis will be conducted using a new state-of-the-art high frame rate vision system. The vision/feedback system will monitor and control the size of each droplet and precisely trigger the instant of droplet detachment. This will allow us to increase significantly the present droplet production rate, and to improve the dimensional accuracy, surface quality, and mechanical/metallurgical properties of the metal parts formed. In our preliminary experiments, 0.1 0.2 mm diameter tungsten droplets are deposited onto aluminum substrate in a shielding flow of argon. A three-wavelength optical pyrometer is used to monitor temperature and cooling time. Surface layers consisting of single droplets, one-, and two-dimensional droplet arrays are deposited and analyzed. Attempts to build a multiple layer structure are currently in progress. 

3:15 PM *V2.5 
PART WARPING IN LAYERED MANUFACTURING PROCESSES DUE TO RESIDUAL STRESS. Nathan Klingbeil, Jack Beuth , Carnegie Mellon University, Department of Mechanical Engineering, Pittsburgh, PA. 

Tolerance loss due to residual stress-induced warping is a major concern in solid freeform fabrication processes seeking to build parts directly, without post­processing steps such as sintering or infiltration by a low-melt alloy. An understanding of how residual stresses develop and ultimately how they lead to tolerance loss is a key issue in advancing these processes. In this paper, results are presented from warping experiments on plate-shaped carbon steel/stainless steel specimens created by microcasting and welding processes used in Shape Deposition Manufacturing (SDM). Results from these experiments give insight into differences between the two processes, the role of preheating and insulating conditions during manufacture and the influence of deposition path on magnitudes and distributions of warping displacements. Results are compared to predictions from residual stress models of the tests. These models are able to predict well warping magnitudes and the effects of thermal conditions on them but are not able to capture some subtle trends in the experiments. It is concluded that these trends are sensitive to constraint conditions in the models and in the experiments themselves. Although the work presented in this paper relates to warping of simple plate-shaped geometries, methods have been developed for estimating warping deflections in fully 3-D layered parts. Insights from this work have applications to other direct­build layered manufacturing processes, including those involving non­metallic materials. 

3:45 PM V2.6 
RAPID PROTOTYPING USING VARIABLE DIAMETER JETS. Ampere A. Tseng , Manufacturing Institute, Arizona State University, Tempe, AZ. 

A controllable droplet generator has been developed for manufacturing net shape structures by deposition of semi molten metal drops on a position controlled platform. The semi-molten metal drops are generated using a laminar liquid jet which is excited at a given frequency to break the liquid column into a series of uniform drops. A continuously variable diameter jet is designed and used to enhance the production rate for the creation of the structure. The continuously variable diameter jet can produce a wide range of droplet sizes. Variability in the droplet size allows more efficient and accurate rapid prototyping since the droplet size and mass flux can be changed according to the specific outline geometry and desired internal microstructure of the product. 
The associated spray dynamics and deposition characteristics which are critical to the understanding and successful implementation of these new designs is investigated. Effects of the nozzle geometry on this new jet design is investigated, along with the characteristics of the metal macro- and micro-structures formed using these designs. A predictive model to determine the metal deposit microstructure based on the droplet dynamics and thermal history is also developed. This model will be used to study the relationship between the process parameters and the microstructure or structural integrity of the formed component. Measurement of mechanical properties and microstructures of drops before and after deposition is performed to verify and to further refine the model developed. An aluminum alloy popular in the auto and aerospace industries is selected for both experimental and numerical studies. 

4:00 PM *V2.7 
COLD SPRAY DEPOSITION - HIGH RATE, SOLID STATE, MATERIAL CONSOLIDATION. Mark F. Smith , and Richard A. Neiser Sandia National Laboratories, Albuquerque, NM. 

Cold Spray (also called High Velocity Non-Combustion spraying) is an emerging technology that has been used to deposit a variety of metals and polymers at high rates by accelerating solid (unmelted) powder particles up to high velocities (typically > 500m/s) in a supersonic jet of compressed air or helium. Cold spray offer the possibility of rapidly consolidating metal or polymer powders to build up coatings or free-standing shapes without melting, solidification, pressing, or sintering. Because the impacting particles are not heated, metals have been deposited in an ambient air environment without measurable increases in oxygen as compared to the feedstock powder. The ability to consolidate materials in this manner offers interesting new possibilities in areas such as nanophase materials and direct fabrication from computer models. A discussion of this intriguing new technology and ongoing research at Sandia National Laboratories will be presented. 

SESSION V3: CERAMIC FREEFORM FABRICATION 
Chairs: Stephen C. Danforth and John W. Halloran 
Tuesday Morning, December 1, 1998 
Exeter A/B (S)

8:30 AM V3.1 
SOLID FREEFORM FABRICATION OF SILICON NITRIDE CERAMICS. Charles Gasdaska , Richard Clancy and Vikram Jamalabad, AlliedSignal Research & Technology, Morristown, NJ. 

Silicon nitride ceramics have been prepared using the fused deposition (FD) process in a Stratasys 1650 modeler. The powders are dispersed in a binder, extruded to form a 1.78 mm diameter filament, and deposited in layers by extruding through nozzles as small as 0.25 mm. The additive nature of solid freeform processes also allows multi-material combinations to be deposited which result in enhanced performance. For example, combinations of silicon nitride based materials with different thermal expansion coefficients have been prepared which demonstrate strength increases > 20%. Data will be presented which compares the strength of FD ceramics to conventionally processed ceramics, along with building strategies and software controls for minimizing process-related defects. Process limitations for fabricating various commercial components will be presented, and the possibilities and limitations of this processing technology will be discussed. 

8:45 AM *V3.2 
PROCESSING OF ELECTRONIC AND BIOCERAMIC COMPONENTS BY SFF TECHNIQUES. Ahmad Safari and Stephen C. Danforth, Department of Ceramic and Materials Engineering, Rutgers University, Piscataway, NJ. 

Solid Freeform Fabrication (SFF) is an emerging technology that provides an integrated way of manufacturing 3-D components, from computer aided design (CAD) files. Over the last decade, several SFF methods have been developed as techniques to fabricate polymer, metal or ceramic structures. At Rutgers University, many SFF techniques, including Fused Deposition Modeling (FDM), Fused Deposition of Ceramics (FDC), and Sanders Prototyping (SP) are being utilized to fabricate a variety of ceramic components for different applications. Some of the materials being used include silicon nitride, PZT, calcium phosphate, and alumina. FDC of GS-44 silicon nitride has been successfully accomplished to fabricate parts such as radome, and turbine blades. Novel piezoelectric sensor and actuator structures are being fabricated from PZT-5H ceramics. The designs include the development of tube arrays, dome shaped and concentric ring actuators fabricated by the FDC technique. Piezoelectric ceramic / polymer composites with fine scale features (100 microns) are being studied for ultrasonic medical imaging applications. Bone scaffolds of calcium phosphate ceramics, with a controlled pore channel network, were successfully fabricated using FDC and SP techniques. Work is also underway to evaluate the properties of porous alumina ceramics fabricated by SFF, for use as photonic band gap materials. The design and fabrication of these novel structures will be discussed in this presentation.