Microstructure and mechanical properties of mechanically alloyed and spark plasma sintered amorphous–nanocrystalline Al65Cu20Ti15 intermetallic matrix composite reinforced with TiO2 nanoparticles

Multiphase Al₆₅Cu₂₀Ti₁₅ intermetallic alloy matrix composite, dispersed with 10 wt.% of TiO₂ nanoparticles, has been processed by mechanical alloying, followed by spark plasma sintering under pressure in the temperature range of 623–873 K. Differential scanning calorimetry and X-ray diffraction suggest that equilibrium crystalline phases evolve from the amorphous or intermediate crystalline phases. Transmission electron microscopy shows that the composite sintered at 873 K has partially amorphous microstructure, with dispersion of equilibrium, crystalline, intermetallic precipitates of Al₅CuTi₂, Al₃Ti, and Al₂Cu of 25–50 nm size, besides the TiO₂. The composite sintered at 873 K exhibits little porosity, hardness of 5.6 GPa, indentation fracture toughness in the range of 3.1–4.2 MPa√m, and compressive strength of 1.1 GPa. Indentation crack deflection by TiO₂ particle aggregates causes increase in fracture resistance with crack length, and suggests R-curve type behaviour. The study provides guidelines for processing high strength amorphous–nanocrystalline intermetallic composites based on the Al–Cu–Ti ternary system.