摘要
本文通过净化法使 Ni-32.5wt-%Sn 共晶合金液获得深过冷,对该合金液在不同过冷条件下的凝固机制和组织进行了研究。结果表明:当过冷度小于约10K 时,该合金液凝固生成 Ni_3Sn相和 Ni(α)相层片共晶。在深过冷条件下,由于 Ni_3Sn 枝晶的自由生长速度远大于 Ni(α)枝晶的自由生长速度,再辉过程中,Ni_3Sn 相和 Ni(α)相不能以匹配方式生长,而由 Ni_3Sn 相作为领先相以枝晶簇方式生长。再辉过程中形成的枝晶簇,其内部 Ni_3Sn 枝晶进一步熔断粗化及 Ni(α)相在Ni_3Sn 枝晶间形成生长,最后形成非规则共晶组织。当过冷度小于130K 时,再辉之后,枝晶簇间存留有较大体积的成分仍为 Ni-32.5wt-%Sn 的合金液,这部分合金液在共晶平台阶段以层片共晶方式凝固,所以试样内部的组织由非规则共晶区和层片共晶区组成。
Bulk undercooled Ni-32.5 wt-%Sn melt was obtained by purifying themelt.The solidification process of the undercooled melt was studied.The formation of thevarious kinds of structures was analyzed.It is found that regular eutectic structure isformed if the melt is undercooled by less than 10K.If the melt is highly undercooled,thefree growth rate of Ni_3Sn dendrites will be greatly larger than that of Ni(α)dendrites,as areasult,the melt does not solidify in regular eutectic morphology but in dendrite clustersmorphology with Ni_3Sn phase acting as the leading phase.The dendrite clusters then devel-op into anomalous eutectic structures through remelting and coarsening of Ni_3Sn dendritesand nucleating and growing of Ni(α)phase within the Ni_3Sn arms.If the undercooling ofthe melt is below 130K,there will still exist bulk melt of the original compositionNi-32.5wt-%Sn between the dendrite clusters after recalescence,which solidifies into regu-lar eutectic structure afterwards.Therefore,the structures of the sample are composed ofregular eutectic zones and anomalous eutectic zones.
