Epsilon martensite to austenite reversion and related phenomena in Fe-24Mn and Fe-24Mn-6Si alloys
- Ibaraki Univ., Hitachi, Ibaraki (Japan). Dept. of Materials Science
Fe-24Mn and Fe-24Mn-6Si alloys whose Ms temperatures are higher than room temperature have been found to show markedly different martensite ({epsilon}) {r_arrow} austenite ({gamma}) reverse transformation behavior in spite of exhibiting a similar {gamma} {r_arrow} {epsilon} forward transformation behavior. Hereafter, they are referred to as 24Mn and 24Mn-6Si, respectively. Closely connected with the one-way and two-way shape memories and microstructure memory, the {gamma} {Leftrightarrow} {epsilon} transformations were studied by in-situ transmission electron microscopy (TEM) observations and tension tests. The {epsilon} {r_arrow} {gamma} reversion was found to occur not only from the outside but also from the inside of {var_epsilon} plates in both alloys. The dislocations yielded by the reverse transformation can move easily showing cross slip in 24Mn while small segments of stacking faults remain even at 873 K in 24Mn-6Si. This difference in the dislocation substructure in the reversed {gamma} at elevated temperatures leads to cause the reversible {gamma} {Leftrightarrow} {epsilon} cyclic transformations in 24Mn-6Si and less reversible ones in 24Mn. In-situ TEM observations of {gamma} {r_arrow} {epsilon} transformation after annealing at 873 K in 24Mn-6Si reveal that stacking faults are piled up to form nano-scale {epsilon}/{gamma} lamellar plates. On the other hand, {gamma} is stabilized with cyclic {gamma} {Leftrightarrow} {epsilon} transformations in 24Mn. Since the dislocation density in the reversed {gamma} differs in the two alloys distinguishably, the strengths of {gamma} at various situations were measured, and the characteristic features are confirmed macroscopically: the recovery of these transformation induced dislocations was studied as a function of annealing temperature. The suitable upper annealing temperature is imperative for obtaining an excellent reversibility in the cyclic {gamma} {leftrightarrow} {epsilon} transformations in 24Mn-6Si.
- OSTI ID:
- 605859
- Journal Information:
- Acta Materialia, Vol. 46, Issue 4; Other Information: PBD: 13 Feb 1998
- Country of Publication:
- United States
- Language:
- English
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