Abstract
A β-solidifying Ti–43Al–2Cr–2Mn–0.2Y alloy was directionally solidified by the optical floating zone melting method. The microstructure is mainly characterized by γ/α2 lamellae with specific orientations, which exhibits straight boundaries. The β phase is randomly distributed in the lamellar microstructure, indicating that the β phase cannot be directionally solidified. The directional solidification of γ/α2 lamellae was not affected by the precipitation of the β phase. Hot compression tests show that the deformation behavior of the β-containing lamellar microstructure also exhibits the anisotropic characteristic. The deformation resistance of the lamellae is lowest when the loading axis is aligned 45° to the lamellar interface. Microstructural observation shows that the decomposition of the lamellar microstructure tends to begin around the β phase, which benefits from the promotion of a soft β phase in the deformation. Moreover, the deformation mechanism of the lamellar microstructure was also studied. The bulging of the γ phase boundaries, the decomposition of α2 lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.
Highlights
Introduction γTiAl alloys are known as promising candidates for Ti-based superalloys in aerospace industries because of their low density, high strength and good creep resistance [1,2,3]
Microstructural observation was conducted by scanning electron microscopy (SEM, FEI, Hillsboro, OR, USA) in the back-scattered electron (BSE) mode
It should be noted that the β phase is a disordered phase at high temperatures, but exists as an ordered β0 phase with a B2 structure (CsCl) at room temperature
Summary
A Ti–43Al–2Cr–2Mn–0.2Y ingot (Φ110 × 250 mm) was fabricated by vacuum induction melting. X-ray fluorescence (XRF, PANalytical, Almelo, Overijssel, Netherlands) spectrometry revealed that the actual composition of the ingot was Ti–43.4Al–1.9Cr–2.05Mn–0.18Y. XRF showed that the actual composition of the bar was Ti–43.2Al–1.8Cr–2.1Mn–0.19Y. Isothermal compression tests were conducted using a Gleeble-1500D simulator (DSI, Saint Paul, MN, USA) at different temperatures with a constant strain rate of 0.01 s−1. Microstructural observation was conducted by scanning electron microscopy (SEM, FEI, Hillsboro, OR, USA) in the back-scattered electron (BSE) mode. In order to study the microstructural evolution and deformation behavior of the lamellar microstructure, transmission electron microscopy (TEM, FEI, Hillsboro, OR, USA) was employed. TEM foils were prepared through mechanical polishing and twin-jet electropolishing by using a solution of 6% perchloric acid + 34% butanol + 60% methanol at −20 ◦ C and 25 V
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