実験報告書様式（一般利用課題・成果公開利用）

MLF	 Experimental Report

提出日 Date of Report
May 7, 2011

課題番号 Project No.

装置責任者 Name of responsible person

2011B0053

Stefanus HARJO

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Deformation structure and fatigue damage in Ti alloys by in-situ

Engineering Diffractometer (BL-19)

neutron diffraction during cyclic tensile test

実施日 Date of Experiment

実験責任者名 Name of principal investigator

February 11, 2011 – February 14, 2011

Satoshi MOROOKA所属 Affiliation
Yokohama National University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.

A Ti-Fe-O-(N) based alloy was used in this investigation. The Ti-Fe-O alloy, which is a near a-type
titanium alloy, has been proposed for a new high-strength titanium alloy. The alloy derives its strength fromsolid solution hardening by interstitial elements such as oxygen and nitrogen. The supersaturation of ironleads to retention of b phase, which is effective to refine a matrix structure. The chemical compositions ofan alloy used in this studied were 0.994Fe, 0.386O, 0.003N, 0.003C, 0.013Si, 0.014Ni, 0.002Sn, 0.006Al,0.01Cr, 0.0005H in mass%. And the scattering length density is 5.4x1010 cm-2. The Ti-Fe-O alloy wereprepared by hot-rolling at 1123 K to plates with 30mm in thickness after annealing at 1023K for 3.6ks. And
then, the Ti-Fe-O alloy was prepared by groove-rolling at 973K for 1h. After that, the specimen was
prepared by aging at 1173K and 1223K for 3.6ks to obtain equal and needle-shape duplex grain structureand full needle-shaped grain structure, which were named as 900-HGR and 950-HGR alloy.

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Experimental method: Cylindrical tensile specimens with 5mm in diameter and 4mm in gauge length
were machined. The time-of-flight (TOF) in-situ neutron diffraction measurements were performed using
TAKUMI at J-PARC. A tensile-compressive tester was made in such a way that the central position of aspecimen does not move when a specimen is elongated. The geometrical arrangement for diffraction
measurement in the axial and the transverse directions of the specimen is illustrated in Figure 1. The
sampling volume for neutron diffraction is wide range at the parallel position of the tensile specimen, sothat bulky averaged information is obtained. The TOF diffraction was acquired with a count time of about
10min for sufficient scattering intensity to analyze the diffraction-profiles. The uncertainties in elastic
lattice strain and the change in dislocation density measurements represent the statistical uncertainty in the
single peak fitting, based upon the estimated standard deviations of the peak positions.
12. 実験方法及び結果（つづき） Experimental method and results (continued)

Figure 2 is schematic illustration to explain the experimental condition. At room temperature, cyclic
testing was performed using a tensile-compressive tester under tensile-tensile cyclic-loading conditions atconstant maximum and minimum load amplitudes of 0MPa and about 600MPa. The stress ratio is about
0.01. The cyclic frequency was 0.1Hz. Fatigue data were collected at N=0, 10, 20, 30 ~ 300 cycles. The
plastic stain was evaluated by strain gauge method.
Experimental result: Examples of diffraction profiles obtained for 900-HGR and 950-HGR alloys arepresented in Figure 3. The hk.l peak intensities in the axial and transverse directions are different,indicating recrystallized texture and, the background in the transverse direction was not linear due to theincoherent scattering. As seen in the axial direction, {10.1} peak was split off two peaks. These peaks wereα- titanium phase and oxygen concentrated α-titanium phase (TixO). Table 1 shows change in intensity on
the heat-treatment at 1173K and 1223K for 1hour. This indicates recrystallized texture generation.
Table 1 Change in crystal orientation on the heat-treatment.
Sample10.000.2

10.1

As-HGR

72030

900-HGR

39.8

35.6

114

950-HGR

22.4

207.9

386.5

Figure 4 shows the residual plastic strain as a function of the fatigue cycle using of strain gauge method.
In case of 900-HGR, the residual plastic strain increases with increasing of the number of cycles. Thismeans increasing of the dislocation density during cyclic deformation. However, in case of 950-HGR, inthe beginning, the residual plastic strain rapid increases with increasing of the number of cycles. And then,the residual plastic strain decreases with increasing of the number of cycles. This means dislocations
induced by martensitic transformation (form equal structure toward needle structure) must be rearranged
and some are annihilated during cyclic deformation.
Figure 5 shows the elastic lattice strain determined from peak shifts of {10.0}, {00.2} and {10.1}
reflection peaks ε10.0, ε00.2 and ε10.1, as a function of the number of cyclic deformation for 900-HGR (a) and950-HGR (b) alloys. As is observed in (a), ε10.0, ε00.2 and ε10.1 in the axial direction increase linearly tillapproximately 50 cycles. After 50 cycles, {10.0} and {00.2} elastic lattice strain increases slightly or notchanges while {10.1} decreases with increasing of the number of cycles. This implies that the {10.1}
family grains are plastically softer than {10.0} and {00.2} grains, resulting in stress partitioning that iscalled intergranular stresses. As is observed in (b), change in elastic lattice strain of 950-HGR much smaller
than that of 900-HGR. This indicates that 950-HGR alloy is occurred the plastic strain relaxation. Needlessto say, this means dislocations induced by martensitic transformation must be rearranged and some areannihilated during cyclic deformation.

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Figure 1 Schematic illustration of the diffraction geometry adopted on TAKUMI and the principle of collecting
the in-situ neutron diffraction.

Figure 2 (a) The experimental schedules and (b) tensile-tensile cyclic loading condition.

4Figure 3 Diffraction profiles obtained during cyclic loading in the both directions for 900-HGR and 950-HGRalloys.

Figure 4 The residual plastic strain as a function of the number of cyclic deformation using of strain gauge
method for 900-HGR and 950-HGR alloys. In case of 900-HGR, the residual plastic strain increases withincreasing of fatigue cycles. However, in case of 950-HGR, in the beginning, the residual plastic strain rapid
increases with increasing of fatigue cycles. And then, the residual plastic strain decreases with increasing offatigue cycles.

5Figure 5 shows the elastic lattice strain determined from peak shifts of {10.0}, {00.2} and {10.1} reflection peaks

ε10.0, ε00.2 and ε10.1, as a function of the number of cyclic deformation for 900-HGR (a) and 950-HGR (b) alloys inthe axial direction. The stress partitioning of 900-HGR is larger than that of 950-HGR.

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