Shape memory effect in Fe–Mn–Ni–Si–C alloys with low Mn contents

An attempt was made to develop a new Fe–Mn–Si–based shape memory alloy from a Fe–17Mn–6Si–0.3C (mass%) shape memory alloy, which was previously reported to show a superior shape memory effect without any costly training treatment, by lowering its Mn content. The shape memory effect and the phase transformation behavior were investigated for the as-solution treated Fe–(17–2x)Mn–6Si–0.3C–xNi (x = 0, 1, 2, 3, 4) polycrystalline alloys. The shape recovery strain exceeded 2% in the alloys with x = 0–2, which is sufficient for an industrially applicable shape memory effect; however, it suddenly decreased in the alloys between x = 2 and 3 although the significant shape recovery strain still exceeded 1%. In the alloys with x = 3 and 4, X-ray diffraction analysis and transmission electron microscope observation revealed the existence of α′ martensite, which forms at the intersection of the ɛ martensite plates and suppresses the crystallographic reversibility of the γ austenite to ɛ martensitic transformation.

► A class of new Fe–Mn–Ni–Si–C shape memory alloys with low Mn contents has been designed.
► A Mn content for the onset of the α′ martensite is less than 13 mass%, and the ɛ martensite still exists in the alloy with a 9 mass% Mn.
► The shape recovery strain decreases considerably when the Mn content is reduced from 13 to 11 mass%.
► The sudden decrease in the shape recovery strain is mainly caused by the formation of α′ martensite.