激光悬浮区熔定向凝固Al2O3/YAG/ZrO2三元过共晶合金的微观组织

利用自行研制的激光悬浮区熔设备制备了Al₂O₃/YAG/ZrO₂三元过共晶自生复合材料.在过共晶成分下获得了不含初生相的全共晶层片状组织.详细分析了固/液界面形貌形成原因,并由界面形貌出发阐述了Al₂O₃/YAG/ZrO₂三元过共晶组织织构化趋势.结果表明,低凝固速率下,三元过共晶成分下层片间距大于三元共晶成分下层片间距,而在高凝固速率下则相反,这主要是由于ZrO₂的加入影响了体系的传热及传质条件,通过经典非规则共晶模型综合分析了传输条件对层片间距的影响.过共晶平均层片间距(λ_av)与凝固速率（V）满足λ_avV^0.5=14.7μm^1.5·s^-0.5,符合JH模型.对于激光加工中经常出现的带状组织形成机理也进行了讨论.

MICROSTRUCTURE OF Al2O3/YAG/ZrO2 HYPEREUTECTIC ALLOY DIRECTIONALLY SOLIDIFIED BY LASER FLOATING ZONE METHOD

Due to the excellent high temperature mechanical properties,Al203/YAG/Zr02 ternary eutectic in situ composite is considered to be a promising candidate for the material,replace- ment for nickel based superalloy,of new generation aero space engine turbine blade.The directionally solidified A^Os/YAG/ZrO^ hypereutectic ceramics are prepared with recently developed laser float- ing zone melting（LFZM） apparatus.Full eutectic lamellar microstructure,free of primary phase, was obtained with hypereutectic composition.The formation of solid/liquid interface morphology was analyzed in detail.The microstructure texture tendency was explained by combination with interface morphology.The experimental result indicates that,just as the prediction of JH model,av- erage spacing of hypereutectic（Aav） agrees with the inverse-square-root dependence on solidification rate（V） according to Aavl^°’5=14.7 /um1,5-s"0’5.In lower solidification rate,the lamellar spacing of hypereutectic is higher than that of eutectic composition,but the situation reverses in higher rate. The main reason of such phenomenon is that the addition of ZrO₂ effects the thermal and solute transformation in the melt.The influence of transformation condition on lamellar spacing was analyzed synthetically by using classical irregular growth model.The formation mechanism of banded microstructure,often observed in laser zone melted solidification processing,was also discussed.