Effect of the Phase Composition and the Microstructure on the Microhardness of As-Cast Cu-Ce-La Alloys

The Cu-Ce-La system is of interest for the production of both rare-earth-added bronzes and amorphous alloys. In this work, we investigate the phase composition, the microstructure, and the microhardness of 13 as-cast Cu-Ce-La samples corresponding to the copper angle of the Cu-Ce-La phase diagram. The experimental samples are studied by optical microscopy, scanning electron microscopy, electron microprobe analysis, atomic emission analysis with inductively coupled plasma, X-ray diffraction, and differential thermal analysis. The Vickers microhardnesses of the samples are measured. The microstructure of the samples is characterized by the presence of a eutectic, which is observed at Cu-based solid-solution grain boundaries and, according to electron microprobe analysis data, contains copper, lanthanum, and cerium. The X-ray diffraction analysis data also indicate the presence of the Cu6Ce and Cu6La compounds along with the Cu-based solid solution. The volume fraction of the eutectic component is determined (it is equal to the fraction of the area corresponding to the eutectic in the section of a sample). As the Ce and La contents increase, the fraction of the eutectic component increases. According to thermal analysis data, the ternary eutectic equilibrium takes place along with the binary eutectic equilibria. Significant correlation between the fraction of eutectic component in the microstructure and the hardness of the experimental samples is shown to exist. As the fraction of eutectic in the microstructure increases, microhardness HV also increases. The obtained results are of interest for materials scientists for analyzing the effect of rare-earth metal additions on the phase composition, the microstructure, and the mechanical characteristics of copper alloys.