Waikato Centre for Advanced Materials, School of Engineering, The University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand.
Brunel University London, Institute of Materials and Manufacturing, Kingston Lane, Uxbridge, Middlesex, UB8 3PH, United Kingdom.
Sci Rep. 2016 Dec 23;6:39554. doi: 10.1038/srep39554.
The design of chemical compositions containing potent nuclei for the enhancement of heterogeneous nucleation in aluminium, especially cast alloys such as Al-Si alloys, is a matter of importance in order to achieve homogeneous properties in castings with complex geometries. We identified that AlNb/NbB compounds are effective heterogeneous nuclei and are successfully produced in the form of Al-2Nb-xB (x = 0.5, 1 and 2) master alloys. Our study shows that the inoculation of Al-10Si braze alloy with these compounds effectively promotes the heterogeneous nucleation of primary α-Al crystals and reduces the undercooling needed for solidification to take place. Moreover, we present evidences that these Nb-based compounds prevent the growth of columnar crystals and permit to obtain, for the first time, fine and equiaxed crystals in directionally solidified Al-10Si braze alloy. As a consequence of the potent heterogeneous particles, the size of the α-Al crystals was found to be less dependent on the processing conditions, especially the thermal gradient. Finally, we also demonstrate that the enhanced nucleation leads to the refinement of secondary phases such as eutectic silicon and primary silicon particles.
为了在具有复杂几何形状的铸件中获得均匀的性能，设计含有强核的化学成分以增强铝（尤其是铸造合金如 Al-Si 合金）的异质形核是非常重要的。我们发现 AlNb/NbB 化合物是有效的异质形核剂，并成功地以 Al-2Nb-xB（x=0.5、1 和 2）母合金的形式制备。我们的研究表明，用这些化合物对 Al-10Si 钎料合金进行孕育处理可有效促进初生α-Al 晶体的异质形核，并降低凝固所需的过冷度。此外，我们还提供了证据表明，这些基于 Nb 的化合物可以阻止柱状晶的生长，并首次在定向凝固 Al-10Si 钎料合金中获得细小等轴晶。由于具有强的异质形核剂，α-Al 晶体的尺寸发现不太依赖于工艺条件，特别是热梯度。最后，我们还证明，增强形核导致共晶硅和初生硅颗粒等二次相的细化。
