Formation of periodic microstructures involving the L1 2 phase in eutectic Al–Ti–Cr alloys

Abstract

The temperature–concentration parameters defining the existence of the eutectic transformation L⇄L1 2+β at the Al-rich corner of the Al–Ti–Cr phase diagram have been studied. The temperature of this transformation decreases from 1275 to 1250 °C with decreasing titanium content in the alloy, and its temperature interval is at most 10 °C. The univariant eutectic transformation line L⇄L1 2+β was constructed, whose coordinates on the concentration triangle are defined by the equation (in at.%): C Al=95.48–3.45 C Ti + 0.068 ( C Ti) 2. As a result of this transformation, periodic microstructures consisting of lamellae and fibres of the cubic L1 2 and β phases are produced. Transformations in the solid state which occur during cooling lead to the precipitation of intermetallic compounds from the β-solid solution: TiAlCr (structural type C14) or AlCr 2 (structural type C11 b). The position of the boundary at which the change of precipitating phases occurs was determined. The analysis of mechanical properties shows that the transition from single-phase L1 2 aloys to eutectic microstructures is accompanied by enhancement of both strength and plasticity, while retaining a high elastic modulus.