On the Al–Al11Ce3 Eutectic Transformation in Aluminum–Cerium Binary Alloys

Abstract

The L ↔ Al + Al11Ce3 technologically important eutectic transformation in Al–Ce binary alloys, containing from 5 to 20 wt.% Ce and ranging from hypo- to hypereutectic compositions, was examined along with the microstructure and properties of its solidified product. A combination of thermal analysis and metallography determined the coordinates of the eutectic point at 644.5 ± 0.6 °C and 10.6 wt.% Ce, clarifying the existing literature ambiguity. Despite the high entropy of melting of the Al11Ce3 phase, in hypoeutectic alloys the eutectic was dominated by the regular morphology of periodically arranged lamellae, typical for non-faceted systems. In the lamellar eutectic, however, the faceting of Al11Ce3 was identified at the atomic scale. In contrast, for hypereutectic compositions, the Al11Ce3 eutectic phase exhibited complex morphology, influenced by the proeutectic Al11Ce3 phase. The Al11Ce3 eutectic phase lost its coherency with Al; it was deduced that a partial coherency was present only at early stages of lamellae growth. The orientation relationships between the Al11Ce3 and Al in the eutectic structure, leading to partial coherency, were determined to be Al ║ Al11Ce3 with Al ║ Al11Ce3 and Al ║ Al11Ce3 with Al ║ Al11Ce3. The Al11Ce3 phase with a hardness of 350 HV and Al matrix having 35 HV in their eutectic arrangement formed in situ composite, with the former playing a role of reinforcement. However, the coarse and mostly incoherent Al11Ce3 eutectic phase provided limited strengthening and the Al–Ce alloy consisting of 100% eutectic reached at room temperature a yield stress of just about 70 MPa.

High Strength Al–La, Al–Ce, and Al–Ni Eutectic Aluminum Alloys Obtained by High-Pressure Torsion

“…Since the volume fraction of the eutectic particles is close in all alloys-9-11%, the alloys differ mainly in the properties of the eutectic. The hardness of particles increases in the following order: Al 11 Ce 3 , Al 11 La 3 , and Al 3 Ni-3.5, 4.0, and 7.0-7.7 GPa, respectively [5,[36][37][38]. In this case, the particle refinement process can occur simultaneously with the structure formation during SPD.…”

Al–Ca, Al–Ce, and Al–La Eutectic Aluminum Alloys Processed by High‐Pressure Torsion

“…Thus, the presence of ultrafine particles in the structure of all alloys after HPT can only indicate the refinement of the initial large eutectic particles during HPT, and not the precipitation of new particles, due to the absence of solubility of Ca, Ce, and La in the aluminum solid solution. The hardness of the particles decreases in the following order: Al 11 La 3 , Al 11 Ce 3 , and Al 4 Ca -4.0, 3.5, and 1.9 GPa, respectively, [4,6,21] which is apparently one of the reasons for the decrease in the size of these particles in the structure of the HPT-processed alloys in the same order: Al-10% La alloy, Al-10% Ce alloy, and Al-8% Ca alloy.…”

Thermal Stability of Al-Ca and Al-Ce Alloys Obtained by High-Pressure Torsion

“…Consequently, the fraction of dispersionhardening nanosized particles in the Al-8% Ca alloy is more than two times higher than in the Al-10% Ce alloy (since not all particles of the Al 11 Ce 3 phase were refined during HPT). Then, the fact of a similar level of hardening of both alloys can be explained by the different effect of particles on dispersion hardening (the Al 11 Ce 3 particles have a much higher hardness than the Al 4 Ca particles-350-450 and 200-260 HV, respectively) ( Ref 3,22).…”