The effect of Nb-addition on the L12 precipitates of rapidly-solidified Al-Cr-Zr alloy

Abstract

A supersaturated Al alloy with 3.14 wt% of Cr, 4.03 wt% of Zr and 1.95 wt% of Nb, which gives rise to about 8 vol% of metastable L1₂-Al₃(Zr_0.67Nb_0.33) precipitates after aging, was prepared by the melt spinning process. Spherical L12-structured precipitates with mean particle radius of 10Å form after aging. Slow volumetric coarsening rates of 5.73 × 10⁻³⁰ (at 375 °C), 2.51x10⁻²⁹ (at 400 °C), and 5.86 × 10⁻²⁸ (at 450 °C) m³/hr are measured for the L12-structured Al₃(Zr_0.67Nb_0.33) precipitates in the melt spun ribbon. From a modified LSW equation for volumetric coarsening, an interfacial energy of 0.013 J/m² is calculated. This value agrees well with the reported values for a coherent interface. Most particle size distributions (PSDs) of precipitates under investigation also fit quite well to that predicted by MLSW theory. The above points, therefore, prove that Nb is really a useful candidate for addition into an Al-Cr-Zr high temperature Al alloy.