The Influence of Scandium on the Composition and Structure of the Ti-Al Alloy Obtained by “Hydride Technology”

Abstract

In this study the influence of scandium on the structural and phase state of the Ti-Al alloy obtained by the method of “Hydride Technology” (HT). The Rietveld method has allowed for determining the content of basic phases of the 49at.%Ti-49at.%Al-2at.%Sc system. By means of the methods of transmission electron microscopy (TEM) and X-ray spectral microanalysis, it has been established that scandium additives into the Ti-Al system result in the change of the quantitative content of phases in local regions of the structure. The Ti2Al5 phase has been found, and Ti2Al has been absent. In the morphology of substructures Ti-Al and Ti-Al-Sc there are lamellar structures or lamellae; the peculiarities of the distribution, fraction and size of which are influenced by scandium additives. The average width of Al-rich lamellae has been 0.85 µm, which is four times greater than that for the Ti-Al system (0.21 µm). For Ti-rich lamellae of the sample of the Ti-Al-Sc alloy, the average width of the lamellae has been 0.54 µm, and for Ti-Al it has been 0.34 µm. Based on the obtained data, a scheme of the distribution of phases in the composition of the Ti-Al-Sc alloy in the lamellar structures has been proposed. It has been established that in the Ti-Al-Sc system there is growth of the near-surface strength relative to Ti-Al. In this way, the microhardness of the Ti-Al-Sc alloy has amounted to 1.7 GPa, that is of the Ti-Al alloy which is 1.2 GPa.

Influence of Dy and Ho on the Phase Composition of the Ti-Al System Obtained by ‘Hydride Technology’

“…In the material, there are unevenly distributed areas with a predominance of Dy (luminous areas in black-white image) up to 300 μm in size. The consequence of the modifying effect of Dy is a relatively larger average grain size (150 µm) of the studied experimental Dy-containing gamma alloys in contrast to alloys with Sc and Y microadditives (100 µm) [ 35 , 36 ]. Grains with an average size of 110–130 µm were formed on the TAH specimen surface.…”

“…It has been established that the microhardness for TAD is 1.61 ± 0.08 GPa, and for TAH is 1.47 ± 0.07 GPa. The microhardness for the Ti-Al system obtained by HT is 1.23 ± 0.06 GPa [ 35 ]. The increased microhardness may be associated with a change in the phase composition [ 41 ].…”