The effect of nickel on vacancy hardening in iron-rich FeAl

The hardness and defect morphology of alloys with the composition (Fe-55-x Ni-x)Al-45, where 0.1 less than or equal to x less than or equal to 10 at.% following high-temperature heat treatment and subsequent low temperature annealing was studied. It was found that nickel additions significantly reduced the softening which occurs on low temperature annealing of FeAl and also significantly increased the hardness of this compound. Following low-temperature annealing [001] edge dislocations were observed to form. In addition cuboidal voids were formed in those alloys with less than 10 at.% nickel. It is believed that the hardening which occurs in these alloys is associated with the interaction of the nickel atoms with the thermal vacancies which form on high temperature heat treatment. Possible mechanisms for the hardening which occurs are discussed.