ᐇ㦂ሗ࿌᭩ᵝᘧ䠄୍⯡฼⏝ㄢ㢟䞉ᡂᯝබ㛤฼⏝䠅㻌

MLFExperimental Report㻌ᥦฟ᪥ Date of Report㻌
December 14, 2014ㄢ㢟␒ྕ㻌 Project No. 2014A0025㻌⿦⨨㈐௵⪅ Name of responsible person㻌㻌

Kazuya Aizawa㻌ᐇ㦂ㄢ㢟ྡ㻌 Title of experiment㻌⿦⨨ྡ Name of Instrument/䠄BL No.䠅㻌

Detection of critical point in martensitic transformation of an Fe-Pd

㻌 TAKUMI/ BL19alloyᐇ᪋᪥ Date of Experiment㻌
November 4 - November 8㻌ᐇ㦂㈐௵⪅ྡ㻌 Name of principal investigator㻌
Takashi Fukuda
ᡤᒓ㻌 Affiliation㻌㻌 Osaka University㻌ヨᩱ䚸ᐇ㦂᪉ἲ䚸฼⏝䛾⤖ᯝᚓ䜙䜜䛯୺䛺䝕䞊䝍䚸⪃ᐹ䚸⤖ㄽ➼䜢䚸グ㏙䛧䛶ୗ䛥䛔䚹䠄㐺ᐅ䚸ᅗ⾲ῧ௜䛾䛣䛸䠅㻌Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
㻝㻚㻌 ヨᩱ Name of sample(s) and chemical formula, or compositions including physical form.㻌
The specimen used in this experiment was a single crystal of A1-type Fe-30.7at.%Pd alloy, which was analyzedby ICP. A single crystal of the alloy was grown by a floating zone method. A parallelepiped single crystal withdimensions of 26.8 mm x 2.7mm x 2.7 mm was used for the present experiment. The single crystal washeat-treated for homogenization at 1373 K for 24 hours followed quenching into ice water. The martensitic
transformation temperature of this specimen was approximately T0 = 270 K, which was measured by a SQUID
magnetometer beforehand. The edges of the specimen was parallel to [001], [100] and [010] directions.
㻌㻌㻞㻚㻌 ᐇ㦂᪉ἲཬ䜃⤖ᯝ㻌 䠄ᐇ㦂䛜䛖䜎䛟䛔䛛䛺䛛䛳䛯ሙྜ䚸䛭䛾⌮⏤䜢グ㏙䛧䛶䛟䛰䛥䛔䚹䠅㻌
Experimental method and results. If you failed to conduct experiment as planned, please describe reasons.
The specimen was inserted between two pistons, which were made of an aluminum alloy. Then the specimen
with pistons were set into a compressing stage attached to a cold stage. The specimen was compressed in the[001] direction in TAKUMI (BL19). We needed to apply the minimum stress of -4 MPa to hold the specimen forthe measurements. Here the minus sign on stress means compressive stress is applied on the specimen. The
diffraction patterns with the scattering vector parallel to the [001] direction (load direction) were detected by theSOUTH BANK and those with scattering vector parallel to the [100] direction (perpendicular to the loaddirection) were detected by the NORTH BANK. We measured the position and peak separation of (002) peak in
the SOUTH BANK and (200) peak in the NORTH BANK. The slit condition used in TAKUMI was 3 mm inheight and 3 mm in width.
(1) Change in peak profile by the application of stress
Figure 1 shows stress dependence of the peak profile of the 002 reflection (load direction). At 370 K (= T0 + 100K), which is by 100 K above the transformation temperature T0, the peak gradually shift to left. There is no peakseparation and broadening of the peak by the application of the stress. The result implies that the specimen1㻞㻚㻌 ᐇ㦂᪉ἲཬ䜃⤖ᯝ䠄䛴䛵䛝䠅㻌 Experimental method and results (continued)
deforms elastically at this temperature. At 330 K (T0 + 60 K), we notice a broadening of peak between 74 MPaand 114 MPa. The broadening suggests the onset of phase transformation. At 280 K (T0+10 K), we notice thebroadening of the peak even at 35 MPa, and the peak width is almost constant up to 154 MPa. This implies thatphase transformation occurs between 4 MPa and 35 MPa at 280 K. At 240 K (= T0 - 30 K), the peak becomessharp with increasing stress. Presumably, the broad peak at 240 K is due to the coexistence of several variants.
With increasing stress, selection of variants occurs, and results in the sharping of the peak. Similar results wereobtained for the 200 reflection (perpendicular to the load direction) although the peak shifted to right side withincreasing stress.

Figure 1 Peak profile from the SOUTH BANK.
Compressive stress indicated in each panel is applied inthe [001] direction. Measurements were made in thestress applying process.

Figure 2 Stress dependence of lattice parameter c.
Evaluation of c was made by fitting the 002 reflection
using Gaussian function.

(2) Stress dependence of lattice parameter
Figure 2 shows stress dependence of lattice parameter c evaluated by fitting peaks shown in Figure 1 byGaussian function. At 380 K and 240 K, the lattice parameter c decreases nearly linearly as stress increases. Thisis characteristic feature of elastic strain. The average Young’s modulus is about 16 GPa at 380 K, and 6 GPa at240 K. At intermediate temperatures, the temperature dependence of the lattice parameter c is not linear. Inparticular, at temperatures of 280 K, 290 K, 300 K, and 310 K, which are above T0 = 270 K, we notice aninflection point. The inflection point also suggests that phase transformation occurs near the point. On one hand,when the stress is below the inflection point, the lattice softening occurs as stress increases. On the other hand,when the stress is above the inflection point, the lattice hardening occurs as stress increases. At temperatures
below T0, there is no softening of lattice. Similar results were obtained for lattice parameter a, which wereevaluated by the peak profile of the 200 reflection (perpendicular to the load direction) although a increased withincreasing stress.
Summary
In the present experiments, clear peak separation was not observed for the stress-induced martensitic
transformation. It seems that the first order nature weakens or disappears by the application of compressivestress. This will be one aspect of the critical phenomena of martensitic transformation in Fe-Pd system.
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