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ection III: Supplemental Literature Review

Sc-Ti (Scandium-Titanium) H. Okamoto

The Sc-Ti phase diagram was determined by [1962Bea] by means of thermal analysis, optical pyrometry, metallography, and X-ray diffraction. The result is shown in Fig. 1 with solid lines (invariant reaction lines are not shown for clarity). Based on this result [1987Mur], obtained the phase diagram using a sub-regular solution model, as shown with dashed lines in Fig. 1. [Massalski2] adopted this result. It is clear in Fig. 1 that the calculated result agreed well with the experimental result for the phase relationships among solid phases, but the disagreement was substantial (up to 100 °C) for the solidus. Thermodynamic modeling of the Sc-Ti phase diagram was attempted subsequently by [1999Dan] (sub-regular solution model) and [2009Lel] (cluster variation method). The result of [1999Dan] is shown with dotted lines in Fig. 1. Although this result was claimed to be in fairly good agreement with [1962Bea], the agreement is clearly inferior when compared with the other two results in Fig. 1. The result of [2009Lel] is shown in Fig. 1 with chain lines. In order to show that this result was in excellent agreement with [1962Bea], [2009Lel] plotted several data points along the (aSc) phase boundary as optical pyrometry data taken from [1962Bea]. These points are mysterious because they are not shown in [1962Bea], and the experimental method is not suitable for determining the solubility limit of a phase.

In view of the mismatch between the experimental data and calculated curves along the solidus, further improvement in thermodynamic modeling seems to be needed. Experimental confirmation of the phase diagram may also be needed because a greatly different Sc-Ti phase diagram was reported by [1961Sav], in which the (bSc, bTi) phase was split into (bSc) and (bTi) phases. This phase diagram was not accepted by [1987Mur] because the purity of materials (96%) used in experiments was considered to be the cause of the problem. The same result as [1961Sav] was reported repeatedly by [1962Sav1] and [1962Sav2].

References 1961Sav: E.M. Savitskii and G.S. Burkhanov, Equilibrium Diagram of the Scandium-Titanium System, Zh. Neorg. Khim., 1961, 6(5), p 1253-1255, in Russian, TR: Russ. J. Inorg. Chem., 1961, 6(5), p 642-643 1962Bea: B.J. Beaudry and A.H. Daane, Sc-Ti System and the Allotropy of Sc, Trans. Metal. Soc., AIME, 1962, 224, p 770-775 1962Sav1: E.M. Savitskii and G.S. Burkhanov, Phase Diagrams of Titanium Alloys with Rare Earth Metals, J. Less-Common Met., 1962, 4(4), p 301-314, in German

Fig. 1 Sc-Ti phase diagram

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Journal of Phase Equilibria and Diffusion Vol. 34 No. 2 2013

Supplemental Literature Review: Section III 1962Sav2: E.M. Savitskii and G.S. Burkhanov, Phase Diagrams of Alloys of Titanium with Rare-Earth Metals, Titan Ego Splavy, 1962, p 51-60, in Russian 1987Mur: J.L. Murray, The Sc-Ti (Scandium-Titanium) System, Phase Diagrams of Binary Titanium Alloys, J.L. Murray, ed., ASM International, Metals Park, OH, 1987, p 284-286

1999