CO2 laser-induced structure changes on an alumina-mullite-zirconia refractory

An Al2O3-ZrO2-SiO2 system refractory with alumina-mullite-zirconia structure (AMZ) has been laser-melted to improve its surface density and to modify its microstructure in this study. Investigations into the laser-melted samples showed that laser scanning velocity had a significant influence on the surface morphology, the microstructure and the phase constituents of the laser-treated zones when other laser parameters were kept constant. Laser overlapping treatment at 8 mm s(-1) produced a crack-free, smooth and dense surface on the refractory but melting treatments at a lower scanning velocity of 4 mm s(-1) and a higher scanning velocity of 12 mm s(-1) generated obvious cracking surface and rough surface respectively. After laser melting treatment, the microstructure was changed into a fine and dense dendrite structure in the central upper region of the laser-molten zone and a planar structure between the dendrite region and the substrate region; the dominant phases were changed from alpha-Al2O3 + Al6Si2O13 + m-ZrO2 to m-ZrO2 + alpha-Al2O3 + Al2.427O3.64 due to the selected evaporation of constituents SiO2 and Al2O3, and the phase m-ZrO2 or c-ZrO2 was uniformly dispersed into the dendrite instead of the nonuniform particle-like shape in the as-received refractory. An increase in scanning velocity resulted in more planar structure region and higher contents of the nonequilibrium phases c-ZrO2 and Al2.427O3.64. (C) 2004 Elsevier B.V. All rights reserved.