Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

10A/2001G237

Precursor Phenomenon of Martensitic Transformation in FePd Alloy Observed
by Various Wavelengths
T. Ohba1, M. Mitsuka1, T. Fukuda2, T. Kakeshita2, M. Tanaka3
1
Shimane University, Depart. of Materials Science, Matsue 690-8504, Japan.
2
Osaka University, Materials Science and Engineering, Suita 565-0971, Osaka, Japan.
3
KEK-PF, Tsukuba, 305-0801, Japan
Introduction
Martensitic transformation is typical first-order anddisplacive transformation. The transformation has beenutilized for steel-hardening. Shape memory effect andsuper-elasticity are also caused by the transformation.
However, the mechanism of the transformation has notbeen solved completely. In this experiments, FePd wasused for understanding the transformation.
FePd is one of typical alloys showing martensitic
transformation, whose behavior is closer to second-ordertransformation. Studies of precursor phenomenon on
FePd alloys were performed by several researchers.
Sugiyama et al.1 reported tweed patterns along [110]observed by electron microscopy. Muto et al.2-3 observedhigh-resolutin-electron-microscopy and reported resultsof simulations under the assumption of irregularly
distributed modulated cubic. Seto et al.4 carried out Xray and neutron experiments and reported two-phases
mixtures with tetragonal lattices prior to the martensitic
transformation. Phonon behavior was also studied by
Sato5.
In this experimental research, synchrotron radiation
experiments were performed. Several wavelengths werechosen to see a depth effect on the precursor phenomenon.
Experimental
Single crystal of Fe-31.2at%Pd with 6 mm diameterand 2 mm thickness is prepared with mechanical polished(100) plane after heat treatment to exclude stress. The Xray diffraction experiments were carried out by vertical
type 4-circle diffractometer, BL-10A, at Photon Factoryin KEK. Wavelengths λ = 0.55 Å, 0.70 Å, 0.85 Å, 1.00 Å,
1.50 Å and 1.70 Å were monochromatized by Si(111)(a)(b)
Figure 1 Enlarged 400 reflection with wavelength
λ=0.85Å. (a) shows photograph exposed at 190 K. (b)shows photograph at 193 K.

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single crystal monochromator. Oscillation photographs
were taken on IP (Imaging Plate) to observe thediffraction patterns. Temperature was controlled by
Oxford Cryostream system.
Results and discussions
Figure 1 shows enlarged oscillation photographs around
400 Bragg reflection observed with wavelength λ=0.85Å.
Splitting of Bragg reflection was caused by mosaic of thecrystal. Although the mosaic structure of the sample
made the situation difficult, essential feature can be seen.
Comparing (a) and (b) made us notice that decreasing
temperature weakened diffuse streak.
Figure 2 shows 400 Bragg reflection and diffuse streaks
observed with wavelength λ=1.0Å. Appearance of Braggreflections and diffuse streaks looks different from Fig. 1.
Those observations with several wavelengths revealed thecharacteristics of transformation phenomena.

(a)(b)
Figure 2 Enlarged 400 reflection with wavelength
λ=1Å at (a) 190 K and (b) 193 K.
References[1] M. Sugiyama, R. Oshima, E. F. Fujita, Trans. JIM, 27,(1986), 719-730.
[2] S. Muto, S. Takeda, R. Oshima and F. E. Fujita, J. J.
Appl. Phys., 27, (1988), L1387-L1389.
[3] S. Muto, S. Takeda, R. Oshima and F. E. Fujita, J.
Phys. Condens, Matter 1, (1989), 9971-9983.
[4] H. Seto, Y. Noda and Y. Yamada, J. Phys. Soc. Jpn,59, (1990), 956-977.
[5] M. Sato, B. H. Grier, S. M. Shapiro and H. Miyajima,J. Phys. F: Metal Phys., 12, (1982), 2117-2129.