Microstructure and mechanical properties of mechanically alloyed and spark plasma sintered amorphous-nanocrystalline A165CU20Ti15 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 root 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. (c) 2007 Elsevier Ltd. All rights reserved.