Development of Al-Based Metallic Glass Composites Containing Pb-Rich Crystalline 2nd Phase

Abstract

Liquid immiscible alloy systems present a unique opportunity for designing composites with sphere-dispersed and/or interconnected microstructures. Herein, we demonstrate that the addition of Pb in Al₈₄TM₁₀RE₆ (TM=Ni,Co,Fe,Ti, RE=La,Ce,Nd,Gd,Y) metallic glasses can result in liquid-liquid phase separation in a liquid immiscibility gap and substantially solidifies into a Pb-rich crystalline phase and Al-rich amorphous phase. The Pb-rich phase has a spherical shape and is dispersed in the Al-based metallic glass matrix. The average diameter of the Pb-rich spheres changed from 75 ± 10 nm near the wheel side (fastest cooling region) to 138 ± 32 nm near the center of the ribbon (slowest cooling region), which exhibited a melting temperature of about 599 K, close to that of pure Pb (Tm = 600.5 K), due to the low solubility of Pb and other constituent elements. Interestingly, the dispersed Pb-rich 2^nd phase in the Al-based metallic glass matrix causes delayed crack propagation and enhanced fatigue lifetime due to crack blocking and filling by partial liquifaction. These results provide a guideline for how to design promising Al-based metallic glasses containing sphere-dispersed 2^nd phase with low melting temperature, which is a key step in developing damage-tolerant metallic glass composites with a liquid-based healing mechanism.