Patent ID: 8865055
Filing Date: 2014-10-21
Classification: B28B,B29B,C04B

Abstract:
1. A freeze-forging method for producing a net-shape transparent sintered three-dimensional magnesium aluminate spinel body of a desired complex geometry, comprising the steps of: (a) providing a ready-to-sinter spinel powder consisting of a nanomixture of magnesium aluminate spinel nanoparticles and a uniformly distributed controlled concentration of nanoparticles of an inorganic sintering aid, wherein said nanomixture has been formed by a process including induced precipitation of said inorganic sintering aid nanoparticles from a dispersion of said spinel nanoparticles in an aqueous solution of said inorganic sintering aid; (b) providing a nonaqueous liquefied vehicle comprising a sublimable organic binding agent and having a solidification temperature of from about room temperature to below about 200° C.; (c) mixing the spinel powder with the liquefied vehicle to form a homogeneous pseudoplastic spinel mix comprising said spinel powder dispersed in said liquefied vehicle; (d) reducing the temperature of said spinel mix to below the solidification temperature of said vehicle to thereby freeze the spinel mix; (e) crushing the frozen spinel mix into powdered form; (f) molding the powdered frozen spinel mix into a net-shaped green body preform of said desired geometry by cold forging the powdered frozen spinel mix in a mold of said desired geometry, said cold forging being carried out at or near room temperature at a pressure of at least about 1 Ksi; (g) densifying said green body preform by hot pressing or pressureless sintering into a sintered spinel body of said desired geometry and substantially free of said vehicle and said sintering aid; and (h) subjecting said sintered spinel body to further densification via hot isostatic pressing to thereby substantially eliminate any residual porosity in said sintered body.