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This work investigated the transformation-strain dependence of the stress hysteresis of pseudoelasticity associated with the stress-induced martensitic transformation in binary NiTi alloys. The strain dependence was studied with respect to the deformation mode during the stress-induced martensitic transformation, which was either localized or homogeneous. It was observed that the apparent stress hysteresis of pseudoelasticity was independent of the transformation strain within the macroscopic deformation range, for the specimens deformed in a localized manner. For specimens macroscopically deformed uniformly, the stress hysteresis of pseudoelasticity increased continuously with increasing strain from the beginning of the stress-induced martensitic transformation. The transformation-strain independence of the stress hysteresis for localized deformation is ascribed to be an artificial phenomenon, whereas the transformation-strain dependence of the hysteresis for uniform deformation is believed to be intrinsic to the process of stress-induced martensitic transformation in polycrystalline materials. This intrinsic behavior is attributed to the polycrystallinity of the materials.

With the increasing titanium, the volume fraction of face-centred cubic-structured dendrites decreased, and ordered B2 phase, σ, and Laves phase appeared in CoCrCu0.5FeNiTi x alloy when x > 0.5. With the increase of Ti content, Δ Smix, Δ Hmix, valence electron concentration (VEC), and Λ (=Δ Smix/ δ2) of CoCrCu0.5FeNiTi x alloys decreased, while atomic size difference ( δ) and electronegativity difference (Δ χ) increased. Topologically close-packed (TCP) structures are favoured when Δ Smix > 14.53 J K−1 mol−1. TCP phases can be found when δ > 5.05 and Δ χ ≥ 0.124. Simple solid solution phase is favoured when VEC ≥ 8.26 but multi-phases including TCP phase coexist when VEC < 8.26. Single-disordered solid solution forms only when Λ > 0.637, solid solution and TCP phases coexist when 0.531 < Λ < 0.637, and TCP phases are favoured when Λ < 0.531.

Simple ordered L12 phase and complex ordered µ phase were found in the (FeCoNiMo)90Al10 alloy, while disordered FCC and µ phases were detected in the (FeCoNiMo)90Cr10 alloy. After annealing at 900°C, nano-size precipitates were observed in the L12 phase, and splitting and spheroidisation were occurred in some regions of the eutectic structures in the (FeCoNiMo)90Cr10 alloy. After holding for 100 h at 900°C, (FeCoNiMo)90Al10 alloy showed an excellent hardness resistance. The oxidation kinetics of both (FeCoNiMo)90Al10 and (FeCoNiMo)90Cr10 alloys followed a parabolic rate law at 900°C. An external layer of Al2O3 and an underlying MoO2 subscale were found in the (FeCoNiMo)90Al10 alloy. A semi-continuous oxide layer of MoO2 and Cr2O3 was observed in the (FeCoNiMo)90Cr10 alloy.

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