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 °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.