Formation of periodic microstructures involving the Ll2 phase in eutectic Al-Ti-Cr alloys

The temperature-concentration parameters defining the existence of the eutectic transformation Lreversible arrowLl(2) + beta at the Al-rich corner of the Al-Ti-Cr phase diagram have been studied. The temperature of this transformation decreases from 1275 to 1250degreesC with decreasing titanium content in the alloy, and its temperature interval is at most 10degreesC. The univariant eutectic transformation line Lreversible arrowLl(2) + beta was constructed, whose coordinates on the concentration triangle are defined by the equation (in at.%): C-A1 = 95.48 3.45C(T1) + 0.068 (C-T1)(2). As a result of this transformation, periodic microstructures consisting of lamellae and fibres of the cubic Ll(2) and beta phases are produced. Transformations in the solid state which occur during cooling lead to the precipitation of intermetallic compounds from the beta-solid solution: TiAlCr (structural type C14) or AlCr2 (structural type Cll(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 Ll(2) aloys to eutectic microstructures is accompanied by enhancement of both strength and plasticity, while retaining a high elastic modulus. (C) 2003 Elsevier Ltd. All rights reserved.