Effect of alloying by titanium on superelasticity in oligocrystals of the FeMnNiAlTi-based alloy

In the present study the superelasticity (SE) under tension/compression was investigated in the oligocrystals of Fe42.5Mn34Al15Ni7.5Ti1 (1% Ti), Fe42Mn34Al15Ni7.5Ti1.5 (1.5% Ti) and Fe41.5Mn34Al15Ni7.5Ti2 (2% Ti) (at %) alloys undergoing α (bcc)–γ′ (fcc) martensitic transformation. It was optically established that, first, with a growth in the Ti concentration from 1 to 2% the average and maximum grain sizes increase. Second, the optimal Ti concentration necessary to suppress the precipitation of the γ-phase particles during quenching is no more than 1.5%. SE strain studied at room temperature depends on the Ti concentration, heat treatment and stress state—tension/compression. In the quenched state the SE with value of 6% was observed only in 1% Ti oligocrystal under compression. Quenched oligocrystals was brittle and broke at the yield stress under tension. Aging at 473 K for 3 h leads to an increase in the SE value to 6.8% in 1% Ti oligo-crystal under compression, observation of the SE of 3.1% in 1.5% Ti oligocrystal and suppression of brittle fracture at the yield stress under tension. The SE strain in aged 1% Ti and 1.5% Ti oligocrystals under tension was εSE(1% Ti)=1.2% and εSE(1.5% Ti)=2%, respectively. SE was not found in a 2% Ti oligocrystal under tension/compression.