CO_2激光诱发锆英石耐火材料结构转变的研究

CO_2 Laser-Induced Structure Changes on a Zircon Refractory

通过对锆英石(ZrSiO_4)耐火材料进行激光表面重熔处理,耐火材料表面的致密度得到提高,组织发生了转变。采用SEM、EDX、XRD研究了激光诱发耐火材料的微观组织和相结构的转变。结果表明:在激光扫描速率为4～16mm/s范围内,均能有效熔化高熔点锆英石:随着扫描速率的增加,熔凝层厚度呈线性下降;扫描速度为4mm/s时,裂纹和孔隙得到消除,但增加到8mm/s、12mm/s、16mm/s时,熔凝区出现了孔隙且在重叠区产生了裂纹。激光熔凝区组织以枝晶结构和枝晶间偏析为主,激光熔凝处理导致相ZrSiO_4分解为ZrO_2和SiO_2,加热过程中SiO_2在一定程度上选择性气化,快速凝固过程中形成m-ZrO_2相取代了平衡条件下的ZrSiO_4相。

A zircon （ZrSiO4） refractory was treated by CO2 laser surface melting in order to improve its surface density and to modify the corresponding microstructure. The laser-induced microstructure and phase structure changes have been investigated by scanning transmission microscopy incorporating energy dispersive X-ray （EDX） technique and X-ray diffraction analysis. Laser surface melting treatment was readily achieved over a wide range of scanning velocities from 4 to 16 mm/s although the melting temperature of the zircon is very high, and the molten depth was almost linearly decreased with increasing scanning velocity. Cracks and pores could be eliminated at the lowest scanning velocity of 4 mm/s whereas some pores in the laser-molten zone and cracks only in the overlapped zone were produced at the higher scanning velocities of 8, 12 and 16 mm/s. The microstructure of the laser-molten zone was characterized by a dendrite structure with interdendritic segregation to some extent. Laser-melting treatment led to the decomposition of ZrSiO4 into ZrO2 and SiO2 and thus the selected evaporation of SiO2 during heating process. The consequent rapid solidification resulted in the formation of the phase m-ZrO2 instead of the phase ZrSiO4 under equilibrium conditions.