Journal of
MATERIALS RESEARCH
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.
question arises: Namely, does Ge (4s24p2) have the same
I. INTRODUCTION
role in the martensitic transformation of FeMn alloy as Si
(3s23p2)? In the present paper, we will report our experi-
mental results on the martensitic transformation behavior
of FeMnGe alloy by resistivity and dilation methods.
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 dislo-
cations when moving backward to restore the original
oritentation of parent phase upon reverse transforma-
tion.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.
II. EXPERIMENTAL PROCEDURES
The FeMnGe alloys were melted in a VSG10 vacuum
induction furnace, and then cast into 3.5-kg ingots. Be-
fore melting, the furnace was evacuated to 13 Pa first,
then filled with an argon atmosphere of 8.8 × 104 Pa to
decrease Mn evaporation. The ingots were forged into
20 × 20 mm2 rod. The rods with a length of about 70 mm
were solid-solution treated at 1273 K for 1 h followed by
water quenching to obtain homogeneous structure. The
resistance (3 × 70 mm2) and dilation samples (3.5 ×
50 mm2) were obtained by electric spark maching.
Table I presents the analyzed chemical compositions of
tested alloys. The resistivities were measured by four-
terminal method, a Solartron 7081 precision voltmeter
reading the voltage drop. The thermal-expansion curve
was measured by a DP-49 dilatometer equipped with a
cryostat, and an electrolyzed copper rod was used as a
temperature calibrator.
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 antiferromag-
netic 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 obey-
ing the Curie–Weiss law. But the effect of Si and Al on
the martensitic transformation of FeMn alloy is com-
pletely different. Si promotes the martensitic transforma-
tion, while Al strongly depresses the martensitic
transformation of FeMn alloy.9 Then, an interesting
III. RESULTS AND DISCUSSION
The thermal-expansion curves of tested alloys are
presented in Figs. 1–4. The thermal route is
500 K → 100 K → 500 K. The alloy contracts when the
J. Mater. Res., Vol. 15, No. 2, Feb 2000
© 2000 Materials Research Society
329
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