Selective laser sintering of alumina and alumina-zinc borosilicate glass composites using monoclinic hydrogen borate as a binder

Selective Laser Sintering (SLS) is a form of Solid Freeform Fabrication (SFF), which generates three-dimensional parts directly from a computer image. The objective of this dissertation is to develop new inorganic binders for the SLS of alumina ({dollar}rm Alsb2Osb3{dollar}), which is used commercially for various structural and functional applications.; A new low melting inorganic binder, monoclinic HBO{dollar}sb2{dollar}, has been developed for SLS of alumina. It leads to better green SLS parts and higher bend strength for green and fired parts compared to other inorganic binders such as aluminum and ammonium phosphate. This appears to be due to its low viscosity and better wettability of the alumina particle surface. A low density single phase ceramic, aluminum borate ({dollar}rm Alsb{lcub}18{rcub}Bsb4Osb{lcub}33{rcub}{dollar}), and multiphase ceramic composites, {dollar}rm Alsb2Osb3{dollar}-Al{dollar}rmsb4Bsb2Osb9,{dollar} have been successfully developed by laser processing of alumina-monoclinic HBO{dollar}sb2{dollar} powder blends followed by post-thermal processing; both {dollar}rm Alsb{lcub}18{rcub}Bsb4Osb{lcub}33{rcub}{dollar} and {dollar}rm Alsb4Bsb2Osb9{dollar} have whisker-like grains. The physical and mechanical properties of these SLS-processed ceramic parts are correlated to the materials and processing parameters. Further densification of the {dollar}rm Alsb2Osb3{dollar}-Al{dollar}rmsb4Bsb2Osb9{dollar} composites has been carried out by infiltration of alumina sol, colloidal silica, and chromic acid into these porous SLS parts followed by heat-treatment at higher temperature (1600{dollar}spcirc{dollar}C). The densities obtained after infiltration and subsequent firing are between 50 and 80% of the theoretical densities; the bend strengths are between 15 and 30 MPa.; In addition, glass-ceramic composites have been successfully fabricated through a post-processing of green SLS parts obtained with alumina-zinc borosilicate glass composites using monoclinic HBO{dollar}sb2{dollar} as an intermediate binder. Effects of glass content, sintering temperature, and alumina particle size on the densification and strength of alumina-zinc borosilicate glass composite parts have been investigated. Especially, fully dense glass-ceramic parts could be obtained by employing Ceracon forging process. Bend strengths of these Ceracon forged composite parts reach as high as 70 to 110 MPa.; The present investigation demonstrates that monoclinic HBO{dollar}sb2{dollar} is a potentially useful inorganic binder for the SLS of alumina to obtain structurally sound parts. It may prove useful in the future with other ceramic systems as well.