Fe-Mn-Si계 합금의 마르텐사이트 변태 특성에 미치는 결정립 크기의 영향

Abstract

Effects of thermomechanical treatment and colling rate on the microstructure and grain size has been investigated in bulk- and ribbon-type Fe-Mn-Si based shape memory alloy, and the correlationship between those intrinsic factors and martensitic transformation characteristics has been discussed. The results obtained are summarized as follows. (1) In F5 plate which revealed γ→ε→α' martensitic transformation behavior by cold rolling, α' martensite were reversed to austenite while deformed grains were recrystallized by annealing at 700℃×1hr. The reversed austenite grains were grown and the volume fraction of thermal ε martensite was increased. (2) In F3 plate which revealed γ→ε martensitic transformation behavior by cold rolling, deformed grains were recrystallized by annealing above 800℃×1hr and the volume fraction of thermal ε martensite was about 10%. (3) When Fe-Mn-Si based SMA ribbons were fabricated by RSP, grain size of the ribbon was refined up to 4 ㎛ and the uniformity of grains were improved by increasing wheel speed i.e cooling rate. The volume fraction of thermal ε martensite was increased by increasing colling rate. (4) M (s) and A_(s) temperatures of the melt-spun ribbon were decreased while transformation temperature hysteresis(A_(f)-M_(s)) was increased by increasing wheel speed. (5) Refined grains of the melt-spin ribbon were partially grown by annealing above 300℃×3min. By increasing annealing temperature, the volume fraction of thermal ε martensite was increased and that of α′martensite were also highly increased in the resultant ribbons. (6) M_(s) temperature of annealed ribbon was higher than that of as-spun ribbon and transformation temperature hysteresis(A_(f)-M_(s)) was decreased by increasing annealing temperature.