Structure and mechanical properties of Al₆₅Cu₂₀Ti₁₅-based amorphous/nanocrystalline alloys prepared by high-pressure sintering

Abstract

High strength, amorphous or partly nanocrystalline, multiphase intermetallic alloys with average composition of Al₆₅Cu₂₀Ti₁₅ have been processed by mechanical alloying of the elemental powders followed by consolidation using high-pressure (8 GPa) sintering either at room temperature or at 300-450 °C for 1 min. Examination of the microstructural constituents using X-ray diffraction and transmission electron microscopy shows that the alloy pressed at 400 °C is primarily amorphous, while nanocrystalline intermetallic phases, Al₂Cu, Al₄Cu₉ and Al₅CuTi₂ evolve from the amorphous matrix on pressing at 450 °C. The pressing temperature of 400 °C appears most promising, leading to products with negligible porosity, increment in the Young's modulus by about 85% with respect to that of Al alloys, as well as impressive hardness (7.9 GPa) and compressive strengths (1490 MPa). However, absence of ductility and poor fracture toughness (3.8 ± 0.8 MPa√m) appear as the major challenges to be met for widespread application of these alloys.