Precipitation of oxide phases in titanium alloys with rare earth metals

M. Popova, N. Rossina, N. Popov, M. Leder

Abstract

The effect of gadolinium microalloying on the formation of oxide and intermetallic phases in heat-resistant pseudo-alpha and two-phase titanium alloys of different chemical compositions during the crystallization and subsequent heat treatment was studied. By means of scanning electron microscopy it was shown that in the alloy containing tin an intermetallic compound of a GdxSny system was formed during crystallization. Gadolinium oxide was subsequently formed on the particles of this intermetallic compound. As a result, these particles have a complex internal structure. The nucleation of these particles occurs primarily in the body of a grain at interfaces. Annealing in beta-phase and two-phase regions with a change in morphology of alpha and beta phases does not lead to a change in the location of such particles. The nature of their distribution allows one to state that they do not significantly affect the properties of the alloy. In the alloys without tin, gadolinium oxide was formed during cooling primarily at the grain and interphase boundaries. The size of such particles is substantially less than that in alloys with tin, while the amount is greater. The heat treatment in the beta-region (homogenization annealing) is accompanied by an increase of the number and size of particles both on grain boundaries and within the grains. Moreover, the gadolinium concentration in solid solution is slightly higher than that in alloys with tin. The particles precipitated at grain boundaries are assumed to decrease the viscous and plastic properties leading to their reduction.

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