Moving Boundary Transport Phenomena in Selective Area Laser Deposition Process

The overall selective area laser deposition process was modeled using the two-layer, three dimensional solid phase heat transfer with the moving boundary condition considered, gas phase mass transfer, and film growth coupled equations. A modified front-tracking finite difference method was used to solve the moving boundary heat conduction in thick deposits. The results correlate with the experimental observations.Mechanical Engineerin

Design of a Solid Freeform Fabrication Diamond Reactor

Solid Freeform Fabrication (SFF) has progressed from the visualization aided stage of computer aided designs (CAD) to rapid prototyping of structural parts. Among the promising techniques for producing structural prototypes is the technology ofchemical vapor deposition (CVD) ofpolycrystalline diamond. This paper discusses the thermodynamic and kinetic theories that suggest that structural diamond may be rapidly deposited at rates approaching 1 mmJhr from the vapor phase at metastable thermodynamic conditions. The design of a reactor that will produce structural diamond prototypes is discussed. This reactor combines downstream microwave plasma enhanced chemical vapor deposition (DMWPECVD) with a scanned CO2 laser that locally heats the substrate to diamond deposition temperatures. The input:Fases are H2, 02' CH4, and Ar. The operating pressure range of the reactor is 1 x 10- to 7 x 102 Torr. The reactor is designed for in situ determination of deposit thickness while deposition occurs as well as having the capacity of fitting on an existing resonance enhanced multiphoton ionization time of flight mass spectroscopy (REMPITOFMS) apparatus that will allow for plasma diagnostics immediately above the heated substrate. Plasma diagnostics will be employed to determine the active metastable species that results in diamond deposition so that optimization can be made ofthe operating parameters to maximize diamond selectivity and deposition rate.Mechanical Engineerin

Preparation and Properties of In-Situ Devices Using the SALD and SALDVI Techniques

One of the many advantages of Selective Area Laser Deposition (SALD) and Selective Area Laser Deposition Vapor Infiltration (SALDVI) is that they can be used to embed in-situ micro-sensors within macro-components. A single-point SiC/C thermocouple sensor embedded within a 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 the temperature gradient and distribution at different positions. In this paper, 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 ofthe embedded thermocouples are compared to reference thermocouples probing the surfaces of the bulk shape.Mechanical Engineerin

Method of producing parts and molds using composite ceramic powders

A method and apparatus for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer controlling a laser to direct the laser energy onto the powder to produce a sintered mass. The computer either determines or is programmed with the boundaries of the desired cross-sectional regions of the part. For each cross-section, the aim of the laser beam is scanned over a layer of powder and the beam is switched on to sinter only the powder within the boundaries of the cross-section. Powder is applied and successive layers sintered until a completed part is formed. Preferably, the powder comprises a plurality of materials having different dissociation or bonding temperatures. The powder preferably comprises blended or coated materials, including precursor materials which are formed into a mass at the irradiated locations, and which either react due to the laser thermal energy or in a later heat treatment to form a compound with properties different than the precursors. Examples are disclosed wherein a compound is formed which has a significantly higher melting point than that of one or more of the precursor powders. A ceramic part, such as a mold for investment casting, may be formed according to the method, where a first material (e.g., ammonium dihydrogen phosphate) has a melting point sufficiently low that it is melted so as to bind the second material (e.g., alumina). Subsequent heat treatment enables chemical reaction of the two materials to form a ceramic (e.g., aluminum phosphate) capable of withstanding high temperatures.Board of Regents, University of Texas Syste

Gas Phase Solid Freeform for Fabrication of Three-dimensional Ceramic Structures

Solid free form of ceramic materials can be achieved by deposition from the gas phase. The Selective Area Laser Deposition, or SALD, technique can be utilized to make ceramic depositions with a uniform chemical composition. In order to make all classes of ceramics, including carbides, nitrides, and oxides, selection of a precursor is an essential step. Often the correct precursor for the deposition requires a special environment, namely, one that can be uniformly heated. System design for a heated deposition chamber is discussed as well as preliminary tests of the system functionality. Silicon Carbide depositions were performed as a means of evaluating system parameters.Mechanical Engineerin

Selective Area Laser Deposition for Silicon Nitride Joining

Ceramic joining is a difficult step in ceramic manufacturing. Joining ceramics, in a chemically homogeneous way, can be performed through the repurposing of an additive manufacturing technique involving local deposition of ceramics from the gas phase. Selective area laser deposition uses a gas phase precursor environment and a laser heat source to form ceramic deposits. These deposits can be positioned with great spatial resolution; as such, it is possible to form the joint with the ceramic material to create a monolithic structure. Silicon nitride is explored as a joining material for silicon nitride work pieces. The experimental conditions are described and the joint formation is characterized.Mechanical Engineerin

Method of producing parts by selective beam interaction of powder with gas phase reactant

A method and apparatus for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer controlling a laser to direct the laser energy onto each layer of the powder to produce a sintered mass corresponding to a cross-section of the part. For each cross-section, the aim of the laser beam is scanned over a layer of powder and the beam is switched on to sinter only the powder within the boundaries of the cross-section. Powder is applied and successive layers sintered until a completed part is formed. Also disclosed is a method of forming a part by interaction of material in the powder layer with reactants in the surrounding atmosphere, at locations of the powder irradiated by the energy, or laser, beam. The reaction may be nitridation, oxidation or carburization of the powder, with the product being a chemical compound of one or more constituents in the powder with one or more gases in the atmosphere. Alternatively, reduction of the powder may be so enabled by the energy beam so that a metallic phase product is formed at the irradiated locations. Particular benefits of the invention include the densification of the material of the part as a result of the reaction, and the ability to form high temperature materials by way of a relatively low temperature process.Board of Regents, University of Texas Syste

Control of the Cross Section Geometry of Extruded Dental Porcelain Slurries for Rapid Prototyping Applications

This study investigates the dependence of the cross section geometry of extruded dental porcelain slurries on the rheological property of the slurry and the extrusion conditions. It is found that a pseudoplastic slurry is a basic requirement for obtaining extruded lines with rectangular cross sections. The cross section geometry of the extrudate is also strongly affected by extrusion parameters including the extrusion nozzle height, nozzle moving speed, and extrusion rate. Proper combinations of these extrusion parameters are necessary in order to obtain extrudates with near rectangular cross sections. The results obtained have been explained in terms of the interactions among the rheological properties of the slurry, the shear rate imposed on the slurry during extrusion, the wettability of the slurry on the substrate, and the forced flow of the slurry during extrusion.The authors gratefully acknowledge financial support provided by the National Science Foundation under Grant Nos: DMI-9908249 and DMI-0218169.Mechanical Engineerin

SALDVI of SiC into Metal and Ceramic Powders

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.The authors acknowledge the support for this research by the Office of Naval Research (grant #N00014-95-1-0978).Mechanical Engineerin

Microstructure Evaluation for Laser Densification of Dental Porcelains

The feasibility of dental restorations has been investigated using a multi-materials laser densification (MMLD) process, where dental alloy and porcelain powders are laser densified layer by layer to form solid bodies. The present study focuses on the densification behavior of dental porcelain powders in response to a moving laser source. Effects of the laser processing temperature and the green density of the powder bed on microstructure, distortion, macro-cracks, porosities and phase contents of the laser densified porcelain have been investigated. The condition to generate continuous porcelain bodies from powder compacts have also be studied. It is found that the geometry, composition and density of densified porcelain bodies are strongly affected by the laser processing temperature and the green density of the powder compact.Mechanical Engineerin