title: Formation of equiaxed crystal structures in directionally solidified Al-Si alloys using Nb-based heterogeneous nuclei.
abstract: 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 Al3Nb/NbB2compounds 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.
authors.affiliation: 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.
authors.forename: Leandro
authors.initials: L
authors.lastname: Bolzoni
authors.affiliation: Shanghai Jiao Tong University, 800 Dong Chuan Road, Shanghai, 200240, China.|Brunel University London, Institute of Materials and Manufacturing, Kingston Lane, Uxbridge, Middlesex, UB8 3PH, United Kingdom.
authors.forename: Mingxu
authors.initials: M
authors.lastname: Xia
authors.affiliation: Brunel University London, Institute of Materials and Manufacturing, Kingston Lane, Uxbridge, Middlesex, UB8 3PH, United Kingdom.
authors.forename: Nadendla Hari
authors.initials: NH
authors.lastname: Babu