Browsing by Subject "SALD"
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Item Advances in Selective Area Laser Deposition of Silicon Carbide(1994) Tompkins, J.V.; Laabi, R.; Birmingham, B.R.; Marcus, H.L.Selective Area Laser Deposition (SALD) is a Solid Freeform Fabrication (SFF) technique which uses a scanning laser beam to produce solid material by locally decomposing a gas precursor. In this work, a focused C02 laser beam strikes a substrate in the presence oftetramethylsilane (TMS) or diethylsilane (DES), producing silicon carbide objects with high density and no binder phase. Recent investigation has yielded growth rates up to 2.7mlnJmin in the beam area, and has eliminated previously noted contamination ofthe optics by a byproduct which mass spectroscopy identifies as silicon dioxide. This paper reviews a cause of non-uniform growth and delTIOnstrates the addition of hydrogen and reduced scan speeds to lTIake lTIultilayer parts. In addition, it presents a lTIethod for in-situ measurement of height of deposited material.Item Ceramic Joining by Selective Beam Deposition(1995) Tompkins, J.V.; Birmingham, B.R.; Marcus, H.L.Current methods ofjoining of ceramic components may compromise the strength, chemical resistance, or high temperature properties of the resulting ceramic parts. A new method of joining, Ceramic Joining by Selective Beam Deposition, creates an all-ceramic joint between two or more ceramic components through selective decomposition of a gas precursor. An all-ceramic joint not only preserves the valuable properties of the ceramic materials joined, but may be tailored to match the coefficient of thermal expansion ofthe original material(s). The added material may be the same as one or both of the joined Inaterials, or may be a composite material. This preliminary work explores the effect of scanning speed and precursor pressure on Selective Beam Deposition ofsilicon carbide using tetramethylsilane.Item Deposition Rates of Silicon Carbide by Selected Area Laser Deposition(1995) Lee, Y.L.; Tompkins, J.V.; Sanchez, J.M.; Marcus, H.L.The deposition rates using pure tetramethylsilane (TMS) as precursor are calculated numerically for a ~od .grown by th~ .Selected Area Laser Dep?sition J?rocess. In particular, the dependence of the kinettcs of deposItion on pressure of TMS IS examIned. The conditions for which volcano d~pos~tion pr?files occur are also investigated. The results show that deposition rate increases wIth IncreasIng pressure and then becomes saturated. In addition, adsorption-desorption phenomena, rather than effects ofreactants depletion, are responsible for the volcano deposition profile observed experimentallyItem Fractal Growth Modeling of Electrochemical Deposition in Solid Freeform Fabrication(1999) Zhou, Jack G.; He, Zongyan; Guo, JianA new rapid tooling technique ElectroChemical Liquid Deposition Based Solid Freeform Fabrication (ECLD-SFF) was introduced in this paper. In the ECLD-SFF a substrate made of or coated with conductive materials is connected to a DC power supply, and the substrate is put into a plating bath. A very thin metal pin is connected to the DC power as a positive electrode. Between the substrate and the tip of the pin there is a thin layer of metal powder. Under the effects of electric field, metal ions from electrode moving to chemical liquid will deposit onto the powder particle and growing so that the metal particles can be bound by the deposited materials to form freeform solid. By controlling the pin's movement and electrified time, a desired 3-D shape will be built through layer by layer scanning. ELCD-SFF distinguishes itself from other SFF techniques with advantages of products: high build rate, high accuracy, high density, low shrinkage and controllable microstructures. It has been found that the electrochemical deposition among metal particles during ECLD-SFF is a fractal growth process. The fractal dimension and the width of the deposited metal band are all related to electric field density, composition of electroplating liquid and processing time. Several models on the fractal growth between electrodes or metal particles were developed in order to explain these fractal growth phenomena and obtain desired process parameters and conditions for the ECLD-SFF process.Item Gas Phase SFF Control System for Silicon Nitride Deposition by SALD/SALDV(1997) Harrison, Shay; Costa, Chris F.; Jakubenas, Kevin J.; Crocker, James E.; Marcus, Harris L.: 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 ShN4 fabricated shapes are discussed, including composition, morphology, and electrical properties.Item Gas-Phase Laser-Induced Pyrolysis of Tapered Microstructures(1995) Maxwell, James; Pegna, Joseph; Hill, EricGas-phase Selective Area Laser Deposition (SALD) is a useful freeform fabrication tool for the prototyping of simple three-dimensional microstructures. Using this method, slender graphite and nickel rods of various diameters were grown from ethylene and nickel tetracarbonyl, respectively. By varying the laser power during growth, tapered cone-like structures were also generated. Rod diameters and material morphology were correlated with the SALD process parameters to demonstrate the mechanisms through which steady-state rod growth occurs--and through which it can be controlled. Rods, and other similar microstructures, have many useful applications, and are preliminary building blocks for further modelling and development of the SALD process as a micromachining tool. Keywords: Laser chemical vapor deposition, LCVD, SALD, 3-dimensional growth, micro fabrication, rapid prototyping, micro electro mechanical systems, pyroiysis, graphite, nickel, rods, cone.Item Layered Micro-Wall Structures from the Gas Phase(1997) Messia, David; Pegna, Joseph; Lee, Woo HoThe use of3-D LCVD with volumetric rate feedback was investigated in the fabrication ofmicromechanical wall structures. These were constructed by recursive laser scanning and resulted in layered wall composed ofrecursive line deposition. Experiments were designed to uncover the relationship between scan rate, volumetric deposition rate, pressure and laser powerfor pyrolytic graphite from an ethylene precursor. Results point to a conduction dominated heat transfer which greatly limits the volumetric deposition rate at the wall. This also results in a highly unstable deposition process, since volumetric deposition increases by orders ofmagnitude as soon as rod growth is initiated. An unexpected results ofthis work is the ability to grow rods at an angle to the laser axis, with good control ofthe linear growth rate. This is achieved by adaptive laser scanning during rod growth.Item Modeling of Selective Area Laser Deposition for Solid Freeform fabrication(1990) Jacquot, Y.; Zong, S.; Marcus, H.L.The results of a theoretical study of the selective area laser deposition process used for Solid Freeform Fabrication (SFF) from gas phase is presented. We show how the deposition profile of carbon deposited via pyrolytic laser chemical vapor deposition using acetylene as the source gas can be computed by taking into account heat transfer, reaction, and mass transfer processes inside the reactor. The two dimensional representation of the related experimental variables are used to describe the substrate temperature, carbon deposit, and acetylene concentration in the process. The parameters describing these processes are estimated.Item Moving Boundary Transport Phenomena in Selective Area Laser Deposition Process(1991) Zong, Guisheng; Marcus, Harris L.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.Item Optimizing Part Quality with Orientation(1995) Thompson, David C.; Crawford, Richard H.The orientation of SFF-manufactured parts can have a significant effect on the quality of the parts, in both surface effects and strength. Currently, orientation is either ignored or set on the basis of experience. This paper takes some simple experiments and creates quantitative measures relating different aspects of part quality to orientation. This leads to several computational tools for optimizing the orientation of a part for manufacture with SLS or SALD on the basis of part strength, surface "aliasing" error, volumetric supports, and build time as an alternative to human experts.Item Processing Problems Associated with Gas Phase Solid Freeform Fabrication Using Pyrolytic Selective Area Laser Deposition(1991) Zong, G.; Tompkins, J.V.; Thissell, W.R.; Sajot, E.; Marcus, H.L.Concerns critical to selective area laser deposition are discussed. Variables affecting deposition rate, dimensional control, and surface uniformity are analyzed. Localized growth results in undesirable morphology, and contributing factors are cited. Catalytic powders increase nucleation rate and provide superior temperature profiles resulting in good surface uniformity. Specific process control devices are investigated.Item SALD and SALVI Virtual Laboratory(1999) Bzymek, Zbigniew M.; Ferreira, David; Marcus, Harris; Shaw, Leon L.This paper describes efforts to apply virtual manufacturing techniques to produce machine parts using Solid Freeform Fabrication (SFF). In particular, the work was done to develop a Virtual SFF Laboratory for the Selective Area Laser Deposition (S~D) and Selective Area Las~r Deposition Vapor Infl1tration (SALDVI) for the manufacture of machine parts and research on theIr characteristics, as well as for research on development of SAW and SALDVI technologies. It was the goal of the authors to supply the user with a tool to design a part, develop its three dimensional model, render it and observe its shape and dimensions. Except for research, laboratory is intended to be used for teaching principles of design and manufacturing of machine parts, as well as for delnonstrating SAW and SALVI processes to visitors. The Virtual Laboratory was developed on Silicon Graphics workstations. The Virtual Laboratory can create a multi-media, stereoscopic presentations of the SAW and SALVI processes in the Solid Freeform Fabrication Laboratory at the Institute of Material Science (IMS) at the University of Connecticut. The presentations can also be distributed through the Internet.Item Selective Area Laser Deposition - A Method of Solid Freeform Fabrication(1991) Thissell, W.Richards; Zong, Guisheng; Tompkins, James; Birmingham, Britton R.; Marcus, Harris L.Item Selective Area Laser Deposition from Acetylene and Methane to Increase Deposition Control(1991) Birmingham, B.R.; Zong, G.; Tompkins, J.V.; Marcus, H.L.Selective area laser deposition (SALD) has been used to deposit carbon from acetylene. Working at the relatively high pressures required to produce high deposition rates can result in explosive uncontrollable growth. Pr~vious computational modeling indicates that the energy released from the exothermic decomposition of acetylene to carbon may be responsible for this behaviour[l]. Since methane decomposes endothermically to form carbon over certain temperatures, it is possible that methane addition to the process may help control the deposition rate. The purpose of this paper is to describe SALD experiments that were performed using various partial pressures of acetylene and methane as precursor in order to determine if combining an endothermic and an exothermic reaction effects the control of the SALD process.Item Selective Area Laser Deposition from Titanium Tetrachloride(1995) Jakubenas, Kevin; Marcus, H.L.Selective Area Laser Deposition (SALD) has demonstrated the ability to deposit controlled shapes of silicon carbide and silicon nitride by using a laser beam to decompose a precursor gas. The goal of the work here is to include titanium among the list of SALD materials, although this goal has not yet been reached. This paper describes the selection of precursors and the results of some SALD experiments using the first precursor explored, titanium tetrachloride. The results of precursor gas mixture, pressure, and laser power on deposition composition and rates are discussed.Item Selective Area Laser Deposition of Silicon Carbide(1993) Tompkins, James V.Item Solid Freeform Fabrication at The University of Connecticut(1996) Harrison, Shay; Crocker, James E.; Manzur, Tariq; Marcus, Harris L.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 acquisition 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.Item A Theoretical Model for Optimization of SALD Parameters(1998) Bzymek, Zbigniew M.; Shaw, Leon L.; Marks, WojciechThis paper addresses the need to conduct theoretical work concerning an economical way of Solid Freeform Fabrication rendering by using selective Area Laser Deposition (SALD). The part in SALD rendering process is formed layer by layer that, in turn, is composed of stripes of material produced in the path of a laser. There are three situations in which such a stripe can be rendered: a) alone, b) with one neighbor on one side, and c) with neighbors on both sides. Residual thermal stresses in the part are expected to be affected by how a stripe is rendered. Furthermore, the residual thermal stress and the mechanical property of the part are also dictated by other processing variables such as laser scanning patters, laser input power, scanning speed, scanning spacing, deposition temperature, gas precursor pressure, intrinsic thermal conductivity and mechanical properties of the rendered material. A theoretical approach is proposed to address the minimization of residual thermal stresses and rendering times and the maximization of the strength of the part. It is proposed that such multiple optimizations that are dictated by many decision variables can be solved by minimizing and/or maximizing object functions dePending on the design criteria for each attribute of the rendered partItem Thermal Analysis and Modeling of Steady-State Rod Growth During Gas-Phase Solid Freeform Fabrication(1993) Maxwell, James L.; Pegna, JosephAn analysis ofthe steady-state growth ofrods during gas-phase solidfreeform fabrication is presented. It is demonstrated that heat transfer controls the evolution ofshape during laser-induced pyrolysis of slender 3-D structures. Insulating and conductive deposit materials were studied, using both simple analytic and numerical simulations to demonstrate how steady-state rod growth is achieved.