Multiple see more thermocycling (>30 cycles) forced the check details formation of reversed austenitic twins. The volume content of twins increased with the increasing number of γ-α-γ transformations owing to the accumulation of internal stresses in the γ phase. Thus, the multiple thermocycling of alloy 1 with ongoing direct γ-α and reverse α-γ martensite transformations led to fragmentation of the initial austenite up to a nanoscale level (nanofragmentation). γ-ϵ-γ transformations The X-ray investigations

of the iron-manganese single-crystalline samples of alloy 2 have shown that the initial orientation is nonideally restored as in the case of the iron-nickel alloys (alloy 1). However, it is considerably better recovered after γ-ϵ-γ transformations in Fe-Mn alloys than after γ-α-γ transformations in Fe-Ni alloys. The X-ray rotational and rocking patterns of the thermally cycled austenite of alloy 2 show the tailing of all diffraction reflections of the γ and ϵ phases (Figure  1B). The misorientation angle increases much less than that for γ-α-γ transformations. Thus, after the first γ-ϵ-γ cycle, ψ = 4°, but after 150 cycles, ψ = 10° is reached, a magnitude which is almost achieved after the first

γ-α-γ transformation in alloy 1. However, full recrystallization of the austenite of alloy 2 was not achieved by repeated γ-ϵ-γ transformations, and even after 1,000 cycles, only ψ ≤ 17° was realized and the Debye lines on the X-ray SB273005 chemical structure patterns were not really continuous. It is important to

note that the initial orientation of the austenite single-crystalline sample was restored and no new orientations appeared in this case. Misorientation as a result of precipitation hardening in the α-martensite of alloy 1 is much higher than that in the many ϵ-martensite of alloy 2, although for both cases, it is smaller than that for the corresponding austenite phases. γ-ϵ′-γ transformations The initial orientation of the austenite of alloy 3 was completely restored during these transformations. Azimuthal tailing of the diffraction reflections of austenite increased only slightly with the number of cycles (Figure  3, curve 1), and even after 1,000 cycles, only ψ ≤ 3.5° was reached. Figure 3 Misorientation angle ψ of the austenite of alloys 3 (1) and 4 (2). N, number of thermocycles. In alloy 4, where the γ-ϵ transformation was observed during quenching, the quantity of ϵ-martensite is diminished during -196°C ↔ 300°C cycles, and only γ-ϵ′-γ transformations are taking place after 20 to 30 cycles. Azimuthal tailing of the γ-phase reflections was observed mainly within the first 10 cycles, during which γ-ϵ-γ transformations proceed (Figure  3). The misorientation of austenite did not change during the subsequent γ-ϵ′-γ transformations. Thus, misorientation is constrained to ψ ≤ 7° if the number of γ-ϵ′-γ transformations increased from 20 to 1,000, whereas ψ = 6° is already achieved after the first 10 cycles.