Direct Laser Sintering of Bulk Alumina Using 1070 nm Fiber Laser

Abstract

Pellets made of α-alumina were sintered by fiber laser irradiation (1070 nm) for 1 min. The optical measurements showed that the laser selectively applied heat around the voids and gaps between grains in the green pellets. Even though the laser can penetrate deep inside the pellets, the heating efficiency is low because alumina poorly absorbs the laser energy. The graphite layer effectively improved the heating efficiency on the irradiated surface at the low-temperature region to “ignite” laser sintering. The microstructure of the sintered pellets was controlled by the microstructure of the green bodies. Porous pellets were obtained from coarse powders and transparent dense pellets from mixtures of coarse and fine powders. The porous pellets showed excellent bending strength owing to the joining of grains by the selective heating of gaps between them. The transparent pellets comprised large alumina single crystals anisotropically formed by spontaneous melt growth under laser irradiation.