Tri-aluminide alloys having the cubic L12 structure were investigated. The alloys fractured in a brittle manner (fracture toughness, 2 to 3MPam½), predominantly by transgranular cleavage. Of nineteen cleavage facets examined in Al3Sc, seventeen were of {110} type and only two were of {100} type. The room-temperature hardness and yield strength (100 to 200DPH, 100 to 270MPa) of all of the alloys were low (comparable to ductile L12 alloys such as Ni3Al); indicating significant dislocation activity. Transmission electron microscopy identified several antiphase boundary coupled dislocations with b = a/2[110], gliding on the {111} planes. The separation between the super-partials was 3.7nm, giving an antiphase boundary energy of 313mJ/m2.

Brittle Cleavage of L12 Trialuminides. E.P.George, J.A.Horton, W.D.Porter, J.H.Schneibel: Journal of Materials Research, 1990, 5[8], 1639-48