Damage mechanism of zirconia metering nozzles modified by Al₂O₃-ZrO₂ composite powder

The modified metering nozzles were fabricated by using sol-gel Al₂O₃-ZrO₂ composite powder as additives in particle and ceramic type zirconia metering nozzles. The physical properties, mineral phase and microstructure of metering nozzles of particle and ceramic types before and after modification were studied and the damage mechanism of nozzles in continuous casting field test was analyzed. The results show that the ceramic type metering nozzle has lower apparent porosity, higher bulk density, higher compression strength and poorer thermal shock stability compared with the particle type metering nozzle. By adding Al₂O₃-ZrO₂ composite powder, the apparent porosity of modified nozzles decreases, the bulk density and compression strength get higher, the thermal shock resistance of the particle type metering nozzle improves markedly, and the count of thermal shocks is about 1.5 times of that before modification. After the analysis of residual samples in continuous casting field test for 35 h, the damage of the ceramic type nozzle is mainly caused by the fracture in the service process for the poor thermal shock stability, cracks generating in the fracture process cause a certain degree of flaking and hole enlargement. Due to low strength and high apparent porosity, flaking and hole enlargement of the unmodified type particle metering nozzle is more serious. The thermal shock, scouring and erosion resistance of the particle type nozzle after being modified by Al₂O₃-ZrO₂ composite powder improve remarkably because of the formation of MgAl₂O₄ spinel enhanced phase, but little hole enlargement occurs after casting test.