Khan Patan Yousaf, Biswas Krishanu
J Nanosci Nanotechnol. 2015 Jan;15(1):309-16. doi: 10.1166/jnn.2015.9221.
The present investigation reports the result of the investigation on the phase transformation of biphasic Bi-Pb alloy nanoparticles embedded in the aluminum matrix. The samples are prepared by rapid solidification route involving melt spinning of Al-6 wt% (Bi55.9Pb44.1) alloy on a rotating copper wheel in an argon-filled evacuated chamber. The detailed transmission electron microscope (TEM) investigation shows presence of near cuboctahedral shaped biphasic nano-inclusions consisting of the (Bi) solid solution and β, the intermediate phase. β constitutes bulk of the nanoparticle with (Bi) forming the cap. Both the phases bear distinct orientation relationship with the matrix. The compositional analysis indicates substantial increase in solid solubilities of Pb in the (Bi) and Bi in the β-phases as compared to the as-cast sample. Differential scanning calorimetric (DSC) studies indicate substantial superheating (16.4 K) of the embedded nanoparticles with appearance of sharp melting peak. The solidification is observed to be diffused, taking place over a large temperature range (344.5 K to 332 K). The in situ heating stage experiments carried out in TEM indicate formation of core shell morphology during heating with β forming the shell around (Bi). The melting starts from Al/β/(Bi) triple point and then the liquid spreads along matrix-particle interface. The solidification occurs in eutectic manner.
本研究报告了对嵌入铝基体中的双相铋铅合金纳米颗粒相变的研究结果。样品通过快速凝固法制备，该方法包括在充满氩气的真空室中，将Al-6 wt%（Bi55.9Pb44.1）合金在旋转的铜轮上进行熔体纺丝。详细的透射电子显微镜（TEM）研究表明，存在由（Bi）固溶体和中间相β组成的近立方八面体形状的双相纳米夹杂物。β构成纳米颗粒的主体，（Bi）形成帽。这两个相与基体都具有明显的取向关系。成分分析表明，与铸态样品相比，Pb在（Bi）相和Bi在β相中的固溶度大幅增加。差示扫描量热法（DSC）研究表明，嵌入的纳米颗粒有大量过热度（16.4 K），并出现尖锐的熔化峰。观察到凝固是扩散性的，发生在较大的温度范围（344.5 K至332 K）。在TEM中进行的原位加热阶段实验表明，加热过程中形成了核壳形态，β在（Bi）周围形成壳。熔化从Al/β/（Bi）三相点开始，然后液体沿基体-颗粒界面蔓延。凝固以共晶方式发生。
