Formation of Ni2Al and Ni5Al3 superstructures and reversibility of martensitic transformation in NiAl-based β-alloys

Rapidly crystallized NiAl-based β-alloys - Ni64Al36, Ni65Al35, and Ni56Al34Co10 (at.%) - were studied by methods of resistometry and electron microscopy. The decomposition of the L10-martensite, which was accompanied by formation of Ni5Al3 particles, was observed in alloys whose reverse martensite start temperature was over 250 deg. C. Formation of nanoparticles with the A5B3(Ni5Al3) superstructure in the martensite stabilized it against the reverse shear transformation up to a complete suppression of the thermoelastic β(B2) ↔ L10 transformation. The replacement of nickel by 10 at.% cobalt in the Ni66Al34 alloy decreased the tendency to the formation of Ni5Al3 and Ni2Al particles