A study on the improvement of the fracture toughness of L12-type Cu-added zirconium trialuminide intermetallics synthesized by mechanical alloying

The microstructural evolution and the mechanical properties of L12-type bulk (Al + 12.5 at.% Cu)3Zr intermetallic compounds with a nanocrystalline structure were investigated. The (Al + 12.5 at.% Cu)3Zr powders synthesized by Planetary ball milling (PBM) could be consolidated to full density by spark plasma sintering (SPS) at 580 °C without holding time. This temperature is 300–400 °C lower than the conventional consolidation temperature of zirconium trialuminide. The average grain size of the L12 phase specimens was 8.9 nm which is one of the smallest grain sizes ever reported for the nanocrystalline bulk specimens prepared by various consolidation methods. The micro-hardness was measured to be 975.8 Hv and this value was almost three times higher than that of the micro grain sized specimen. On the other hand, the average fracture toughness (<2 MPam1/2) was lower than that (∼4–5 MPam1/2) of larger-grained bulk specimen (∼100 nm). This result indicates that a grain refinement within 10 nm dose not have an appreciable effect on improving fracture toughness in brittle intermetallics. Thus, it was found that the fracture toughness could be enhanced with proper annealing and boron addition.