Open Access Conference Proceedings

The effect of ageing on microstructure and Vickers microhardness of fully lamellar Ti-45Al-5Nb-0.2B-0.75C (at.%) alloy was studied. The experimental procedure for preparation of the studied alloy included induction melting of pure elements, centrifugal casting of cylindrical bars and hot isostatic pressing of the bars to eliminate porosity. A fully lamellar γ(TiAl)/α2(Ti3Al) microstructure of the samples was achieved by the heat treatment consisting of solid solution annealing in a single α phase field followed by the cooling to room temperature. The ageing experiments were performed at three different temperatures of 750, 850 and 950 °C up to 650 h in protective argon atmosphere. During the ageing the Vickers microhardness first increases with increasing ageing time and after reaching maximum values it decreases. The microstructure analysis by optical microscopy, scanning electron microscopy and X-ray diffraction analysis (XRD) show that the variations of measured microhardness values with the ageing time are connected with precipitation hardening. The peak microhardness values measured in the samples aged at 950 °C for 8 h are connected with the precipitation of carbides mainly of Ti2AlC type. The age softening observed after the ageing at 950 °C for 650 h results from the coarsening of the carbides and partial dissolution of the α2 lamellae.

Keywords: titanium aluminides, microstructure, carbides, precipitation hardening, microhardness

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