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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
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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