Microstructure Evolution Of Al-12wt%Ni Hypereutectic Alloy With Constant And Changing Growth Rate During Directional Solidification

The hypereutectic Al-12wt.%Ni alloy was directionally solidified by aBridgman directional solidification furnace under different solidification parameters.The growth rate of directional solidification is changed from1m/s to300m/s.The growth rate of coupling eutectic organization formation and the growthmorphologies of the Al3Ni phase and-Al/Al3Ni eutectic colony were alsoresearched.At growth rate of1μm/s, the coupling eutectic organization with planarmorphology can be found when the specimen grew at a certain distance, and theprimary phase disappeared. The Al3Ni phase is facted and the growth morphology isserrated. However, with increasing value of G/V, the morphology of Al3Ni is notchanged from planar to cellular, and then to dendritic. Some facted Al3Ni phaseforms dendritic structure with nearly-facted characterization. During directionalsolidification, the preferred growth direction of Al3Ni phase is disappeared andgrowth with-Al. The interlamellar spacing is decreased with increasing growthrate, but interlamellar spacing is nearly constant when the growth rates are greaterthan20m/s.The origin structure before changing of growth rate determined themicrostructure of the directionally solidified Al-12wt.%Ni alloy. The interlamellarspacing decreased with increasing ratio of higher growth rate and low growth rate.The relationship between interlamellar spacing and growth rate after the changinggrowth rate isλV1/2＝15.The yield strength and elongation rate of Al-12wt.%Ni alloy is heighten bydirectional solidification. The changing growth rate during directional solidificationcan increase the elongation rate of Al-12wt.%Ni alloy greatly.