Abstract
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-s0'5.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 ZrO_2 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.
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