Effect of deformation on damping capacity and microstructure of Fe-22%Mn-8%Co alloy has been investigated. The ! " stressinduced martensitic transformation occurs during deformation in the alloy. The amount of " martensite increases rapidly up to 5% deformation, and gradually increases with further deformation. The damping capacity of the alloy exhibits a maximum at around 5% deformation, and decreases with further deformation in spite of the increase in " martensite content. The deterioration of damping capacity beyond 5% is ascribed to the dislocations introduced during deformation, which obstruct the movement of damping sources of the alloy.

The damping capacity of Co-Mn system which undergoes fcc ! hcp martensitic transformation has been studied as a function of " volume fraction using an inverted torsional pendulum. The damping capacity increases linearly with increasing " volume fraction regardless of manganese content, and is represented by ¼ 0:05 þ 0:27f " where is the damping capacity in logarithmic decrement of Co-Mn system and f " is the " volume fraction. The main damping mechanism of Co-Mn system containing " martensite is the movement of stacking fault boundaries in " martensite plates.

Effect of thermal cycling(γ↔ε) on γ→ε martensitic transformation kinetics and damping capacity of Fe-17mass%Mn alloy has been studied. The amount of ε martensite increases with thermal cycling in spite of decrease in Ms temperature. The increase in ε martensite content with thermal cycling is attributable to an increase in the density of martensite nucleation sites by introduction of dislocations during thermal cycling. The γ→ε martensitic transformation kinetics shows a burst mode in the non-cycled specimen, while the kinetics exhibits a sigmoidal mode in the cycled specimens. The damping capacity of the alloy increases with increasing the ε martensite content in the non-cycled specimen. On the contrary, the damping capacity of the alloy decreases with increasing the ε martensite content in the cycled specimens. The reason is that the dislocations introduced during thermal cycling, which obstruct the movement of the damping sources, become more with thermal cycling.

Recrystallization behaviors have been investigated with respect to two different kinds of the initial structures, original austenite and martensite, in an Fe-32%Ni alloy. The recrystallized austenite grain size from the martensite is much smaller than that from the original austenite, and decreases linearly with increasing the initial hardness, independent of the initial structure. The recrystallization sequences are different between the two structures: only one step due to recrystallization appears in hardness-temperature curve of the original austenite, whereas two steps corresponding to reverse transformation of α’ to r’ and recrystallization are shown in that of the martensite.

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