Fracture toughness of intermetallic compacts consolidated from nanocrystalline powders

Ball-milled and fully disordered intermetallic powders of Fe–45at.%Al (iron aluminide) and titanium trialuminide (Al3Ti) stabilized to cubic (L12) structure by alloying with 9 at.% Mn, with nanocrystalline (nanophase) grain size in the range of ∼10 and ∼3 nm (from X-ray diffraction, XRD), respectively, were successfully consolidated into nearly pore-free bulk compacts. Fe–45at.%Al powders were consolidated only by explosive shock wave compaction and titanium trialuminide powders were consolidated by hot pressing and explosive shock wave compaction. After shock consolidation a microcrystalline structure appeared in larger powder grains of the Fe–45Al compacts. Compacts were re-ordered after hot or shock consolidation. Vickers indentation fracture toughness of compacts was investigated. Fe–45Al compacts did not develop any corner cracks up to 2000 g indentation load, indicating some intrinsic fracture resistance. Cubic titanium trialuminide compacts developed corner cracks under the indentation load and their average measured fracture toughness was barely ∼2 MPa m0.5, i.e. even lower than the fracture toughness of bulk specimens of coarse-grained cubic titanium trialuminides (∼4–5 MPa m0.5). The results demonstrate that refining the grain size towards the nanolevel is not sufficient to beneficially modify toughness of brittle intermetallics.