Microstructure-hardness relationship of Al–(L1₂)Al₃Ti nanocomposites prepared by rapid solidification processing

Abstract

We report here successful synthesis of Al-based nanocomposites with L1₂–Al₃Ti particles in binary Al–Ti (4.1, 5, 8.3, 10, 15 and 20% Ti) and ternary Al-1.6Ti-0.5Cr, Al-3.2Ti-1.0Cr and Al-6.3Ti-2.0Cr alloys, by rapid solidification processing. The microstructure of all the alloys consists of uniform distribution of nanocrystalline L1₂–Al₃Ti intermetallic in ultra-fine α-Al matrix. The volume fraction of L1₂–Al₃Ti phase in the as-spun ribbons was found to increase with the Ti content in the binary alloys with exception of Al-20% Ti alloy, which formed equilibrium DO₂₂–Al₃Ti. The α-Al grains were measured to be in the size range 0.5–1.0 μm embedded with L1₂–Al₃Ti particles of ∼50 nm diameter. Nanoindentation as well as microhardness of nanocomposites in binary Al–Ti alloys measure hardness value of 3.75 GPa (367 VHN). The nanocomposites formed by rapid solidification processing retain about 70–85 % of its room temperature hardness even at 500°C for 100 h, while the hardness of conventional Al alloys such as 2017 is almost lost at 350°C in 30 min.