Al-Y包晶合金非平衡凝固过程及组织特征

包晶凝固过程中小平面-小平面两相复相生长方式是凝固领域研究的一个热点。以初生相和包晶相都是严格计量比金属间化合物的Al-Y包晶合金作为研究对象,利用DSC热分析技术,严格控制冷却速度,获得不同凝固条件的非平衡凝固试样,研究了两相为小平面相的Al-Y包晶合金的凝固行为。发现小平面-小平面包晶系合金包晶凝固过程中,非平衡凝固特性及宏观偏析特点比非小平面包晶系更加明显。凝固特征温度与平衡相图偏差明显,包晶反应温度和包晶相直接凝固温度都远高于平衡相图给定的值,相对于相图是在“过热”条件下发生的,而固溶体型包晶合金一般是在“过冷”条件下发生的。包晶转变过程非常微弱,致使初生相残留量远高于平衡相图。即使对于过包晶成分的合金,其凝固组织中仍存在大量的共晶凝固组织,最终得到的凝固组织与平衡相图存在显著差异。

Investigation of the Non-Equilibrium Solidification and Microstructures of Al-Y Peritectic Alloys

Facted-facted two-phase peritectic solidification behaviors are one of the hotspots of solidification field .In this study, Al-Y peritectic alloys, in which the peritetic phase and primary phase are intermetallic compound with stoichiomet-ric composition, have been chosen for investigation.Using differential scanning calorimetry （ DSC） , the heating and cool-ing curves of Al-Y alloys at different strictly controlled cooling rates were obtained .Concurrently, the non-equilibrium so-lidification microstructures were produced .Based on these experimental results , we found that the non-equilibrium solidifi-cation characteristics and characteristics of macrosegregation of the facted-facted peritectic alloy during solidification process are more obvious than non-faceted peritectic alloys.The solidification characteristic temperature is greatly different from the equilibrium phase diagram.The peritectic reaction temperature and the nucleation temperature of peritectic phase from the melt during cooling are higher than that of the equilibrium phase diagram .This phenomenon can be called as “su-perheating” compared to the “undercooling” needed for solid solution phase peritectic systems.The peritectic transforma-tion is very weak and more primary phase was remained compared to the diagram .Even for the hypo-peritectic alloy, there are a lot of eutectic phases produced from the remaining liquid between the peritectic phase .The resulting solidification microstructures are significantly different with the equilibrium phase diagram .