Martensitic transformation behavior of FeMnGe alloys
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Martensitic transformation behavior of FeMnGe alloys Xing Lu Department of Materials Science and Engineering, Dalian Railway Institute, Dalian 116028, and State Key Laboratory for RSA, Institute of Metal Research, Chinese Academy of Sciences, Shengyang 110015, People’s Republic of China
Zuoxiang Qin and Yansheng Zhang Department of Materials Science and Engineering, Dalian Railway Institute, Dalian 116028, People’s Republic of China
Bingzhe Ding and Zhuangqi Hu State Key Laboratory for Rapidly Solidified Nonequilibrium Alloys, Institute of Metal Research, Chinese Academy of Sciences, Shengyang 110015, People’s Republic of China (Received 22 January 1999; accepted 8 November 1999)
The martensitic transformation behavior of FeMnGe alloy (0–6 wt% Ge) was investigated by resistivity and dilation methods. Ge depresses the martensitic transformation of FeMn alloy. The effect of Ge on starting temperature of martensitic transformation (Ms) temperature of FeMn alloy is −12 K/wt% Ge. Comparing Ge (4s24p2) with Si (3s23p2) and Al (3S23P1), which have similar outer shells of electrons, we found that their effects on the Ms of FeMn alloy are completely different. The result suggests that the outer shell of electron is not the main factor governing the Ms temperature of FeMn alloy, although it is essential in the alloy’s antiferromagnetic transition. I. INTRODUCTION
The shape-memory behavior in FeMnSi-based alloy is associated with ␥ → ⑀ martensitic transformation. The complete shape-memory effect (SME) of ⑀ martensite is attributed to preferential multiplication of a single type of Shockley partial dislocations upon transformation; these accumulate a stress field which assists the partial dislocations when moving backward to restore the original oritentation of parent phase upon reverse transformation.1 There are four roles for Si in FeMn alloys2–4: (i) increasing the strength of matrix; (ii) reducing the Ne´el temperature of FeMn alloy; (iii) reducing the stacking fault energy, and thus increasing starting temperature of martensitic transformation (Ms) of FeMn alloy slightly; (iv) increasing the c/a ratio of ⑀ martensite. For these roles, Si is an indispensable element to obtain the SME in FeMnSi-based shape-memory alloy. Si (3s23p2), Al (3S23P1), and Ge (4s24p2) have similar outer shells of electrons. Zhang et al.5–8 have suggested that the influences of Al, Ge, and Si on the antiferromagnetic transition of FeMn alloy are quite similar. They showed that all three elements increase the susceptibility, reduce the Ne´el temperature (TN), and change the Pauli paramagnetism above TN to paramagnetism state obeying the Curie–Weiss law. But the effect of Si and Al on the martensitic transformation of FeMn alloy is completely different. Si promotes the martensitic transformation, while Al strongly depresses the martensitic transformation of FeMn alloy.9 Then, an interesting J. Mater. Res., Vol. 15, No. 2, Feb 2000
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