Which wets TiB2 inoculant particles: Al or Al3Ti?

Abstract

TiB 2 particles are proven effective nucleants of commercial purity aluminium, resulting in smaller grains and hence greater desired mechanical properties; however, there is uncertainty as to the mechanism by which it operates. Here we clarify what happens in the initial stages by computing the total Gibbs energy change associated with four possible nucleation mechanisms, each characterised by the termination of the TiB 2 (0001) substrate (Ti or B) and the solid that forms on it (Al or Al 3 Ti). The appropriate solid//solid interfacial energies are derived from Density Functional Theory (DFT) calculations, while the bulk energies are derived from thermodynamic data, supplemented with strain energies calculated from DFT. Solid//liquid interfacial energies are estimated using simple models with parameters based on the literature and DFT calculations. The results suggest that the Ti termination of TiB 2 is more stable than the B termination in the melt, and that the direct formation of Al off a Ti-terminated TiB 2 substrate is the most favourable mechanism for the nucleation of Al rather than the previously proposed formation of a Al 3 Ti interlayer. On the B termination of TiB 2 , Al formation is more stable for thick solid layers, but this is much more uncertain for thin solid layers where it is possible that Al 3 Ti formation is more stable.

Classical and quantum calculations of the temperature dependence of the free energy of argon

“…Free energy functions can be used for studying important fundamental problems in materials sciences, such as phase and structural transitions [5,6], interfacial energies [7,8], or other critical phenomena [9][10][11]. There are several techniques available for calculating the absolute or relative free energy as a function of temperature of a system, an attractive option when experimental determination is difficult.…”

“…In particular, we may obtain the crystal-melt (or solidliquid) interfacial free energy as a function of temperature for systems in which the liquid and solid are formed from materials with different melting points based on the free energy functions of the solid and liquid phases. The interfacial energy would be the difference between the total free energy for a system with a solid-liquid interface, and the free energies of the bulk solid and liquid components [8]. In this case, the accurate computations of free energies for solid and liquid bulk phases become critical.…”

Effect of Preparation Parameter on Microstructure and Grain Refining Behavior of In Situ AlN-TiN-TiB2/Al Composite Inoculants on Pure Aluminum

“…By adding some special master alloys (intermediate alloys) that contain a lot of particles serving as the substrates for heterogeneous nucleation, the grain size of the inoculated alloys can be obviously reduced and the comprehensive properties are improved [1][2][3][4]. In fact, most of the master alloys belong to Al-based composites, in which the aluminum-based solid solution is the matrix and the refiner particle is the secondary phase.…”

“…Here, the secondary phase is generally a ceramic particle, which plays a role of grain refining. For example, in the conventional Al-5Ti-1B inoculants, TiB 2 and Al 3 Ti particles provide the substrates for the nucleation of Al crystals. However, the activity of Al 3 Ti is strongly affected by the chemical elements contained in an inoculated Al melt.…”

Refining and Reinforcing Effects of In Situ AlN–TiN–TiB2/Al Composite Refiner on Aluminum

“…[1,2] In general, effective refiners should contain certain amount of ceramic or intermetallic particles to serve as the solid substrates for heterogeneous nucleation in aluminum alloy melt. [1,2] In general, effective refiners should contain certain amount of ceramic or intermetallic particles to serve as the solid substrates for heterogeneous nucleation in aluminum alloy melt.…”