Aluminium phosphide as a eutectic grain nucleus in hypoeutectic Al-Si alloys

Abstract

Aluminium phosphide (AlP) particles are often suggested to be the nucleation site for eutectic silicon in Al-Si alloys, since both the crystal structure and lattice parameter of AlP (crystal structure: cubic F43m; lattice parameter: 5.421 A) are close to that of silicon (cubic Fd3m, 5.431 A), and the melting point is higher than the Al-Si eutectic temperature. However, the crystallographic relationships between AlP particles and the surrounding eutectic silicon are seldom reported due to the difficulty in analysing the AlP particles, which react with water during sample preparation for polishing. In this study, the orientation relationships between AlP and Si are analysed by transmission electron microscopy using focused ion-beam milling for sample preparation to investigate the nucleation mechanism of eutectic silicon on AlP. The results show a clear and direct lattice relationship between centrally located AlP particles and the surrounding silicon in the hypoeutectic Al-Si alloy.

Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

“…[25] Therefore, to achieve a low interfacial energy, it is important to achieve a good lattice match through a small disregistry (d = Da 0 /a o ), where Da 0 is the difference between the lattice parameters of the nucleating and the nucleated metal belonging to the same crystal structure along a specific direction, and having similar crystallography. [33][34][35] At this point, it should be emphasized that the sharp interface between the elongated phase and the matrix grain (or a stray grain) means that there was no specific orientation relationship between them. Therefore, the non-coherent interface was not energetically the starting point of the formation of the intermediate layer, which means that the formation of the layer started from the coherent interface and terminated at the topologically sharp one.…”

Interplay Between Melt Flow and the 3D Distribution and Morphology of Fe-Rich Phases in AlSi Alloys

“…Two mechanisms have been proposed for b-Al 5 FeSi nucleation, on small entrained oxide films [16,40,41] and nucleation on AlP nucleant particles. [42,43] The outer interfaces of oxide films appear to act as preferred substrates for the nucleation and growth of some Ferich phases, especially b phases along oxide films.…”

“…In addition, in the Al-9 wt pct Si-0.2 wt pct Fe alloy, a porosity also occurred but these large intermetallics did not form on the interface melt-pore. The tendency for nucleation on small entrained oxide films [4,16,40,41,44] suggests that b nucleated on the melt-pore interface and grew as large due to a high Fe concentration (near pore in Al-7 wt pct Si-1.0 wt pct Fe alloy), or did not reach large sizes due to low Fe content, or disappeared in the absence of Fe (in Al-9 wt pct Si-0.2 wt pct Fe alloy). The tendency of Fe-rich intermetallics to grow along oxide films [4,44] and the privileged location of the oxides on the melt-surface (high density of oxides as nucleants), together with the high Fe concentration near the porosity surface (segregation in the specimen center [30] ), could explain the location, orientation, and the large sizes of the b-Al 5 FeSi observed in 3D X-ray tomography ( Figure 14).…”

Refinement of Primary Silicon Crystals by Novel Al‐ZnS Master Alloy in Solidification of Hypereutectic Al‐Si Alloys

“…The current commercial practice is to add phosphorous in the form Cu-P, Al-Cu-P and Al-Fe-P master alloys, such that primary Si nucleates heterogeneously on AlP particles. The crystal structure and lattice parameter of AlP are close to that of silicon with the minimal mismatch between them, less than1% [4]. Refining agents like Ga, Ge, Se, Be, Te, Li, Cd, Zn, Mn, V, Cb, Bi, Mo, Hf and S either individually or in combination have also been studied.…”