Abstract

A new low melting inorganic binder, monoclinic HBO_2, has been developed for Selective Laser Sintering (SLS) of alumina powder by dehydration process of boron oxide powder in a vacuum oven at 120°C. It led to better green SLS parts and higher bend strength far green and fired parts compared to other inorganic binders such as aluminum and ammmonium phosphate. This appeared to be due to its low viscosity and better wettability of the alumina particle surface. A low density single phase ceramic, aluminum borate (Al_18B_4O_33), and multiphase ceramic composites, A_12O_3-A_14B_2O_9, were successfully developed by laser processing of alumina-monoclinic HBO_2 powder blends followed by post-thermal processing; both Al_18B_4O_33 and A_14B_2O_9 have whisker-like grains. The physical and mechanical properties of these SLS-processed ceramic parts were correlated to the materials and processing parameters. Further densification of the A_12O_3-A_14B_2O_9 ceramic composites was carried out by infiltration of colloidal silica, and chromic acid into these porous SLS parts followed by heat-treatment at high temperature (1600°C). The densities obtained after infiltration and subsequent firing were between 75 and 80% of the theoretical densities. The bend strengths are between 15 and 33 MPa.