富山大学研究推進機構水素同位体科学研究センター研究報告 39：37－45，2019.

技術報告

水素イオン照射装置の構築と Ti 板へのイオン照射試験
赤丸1

悟士 1,*，西村克彦 2

富山大学研究推進機構水素同位体科学研究センター
2
富山大学理工学研究部〒930-8555 富山市五福 3190

Construction of hydrogen ion irradiation apparatus
and preliminary experiment for hydrogen ion irradiation using Ti sheet
Satoshi Akamaru1,*, Katsuhiko Nishimura2

1

Hydrogen Isotope Research Center, Organization for Promotion of Research,
University of Toyama, Gofuku 3190, Toyama 930-8555, Japan2
Graduated School of Science and Engineering, University of Toyama,
Gofuku 3190, Toyama 930-8555, Japan*Corresponding author.

(Received May 7, 2020; accepted August 7, 2020)
Abstract
A hydrogen ion irradiation apparatus was constructed, and the amount of implanted hydrogen in a Ti sheet
was evaluated. A focused hydrogen ion beam having a spot area of approximately 3×3 mm2 was used toirradiate a Ti sheet. After hydrogen irradiation for 12 h, the Ti sheet surface showed an irradiated mark. The
thermal desorption spectrum indicated that hydrogen was possibly soluble in the Ti metal without Ti hydride
formation. As the irradiation time was extended to 36 h, the amount of implanted hydrogen increased. Theseresults proved that the Ti sheet captured the irradiated hydrogen.

37

赤丸 悟士・西村 克彦

1. Introduction
Hydrogen atoms in a steel and aluminum alloys cause the hydrogen embrittlement. To study
the mechanism of hydrogen embrittlement, the amount of hydrogen in a metal should becontrolled. A simple method to charge hydrogen is to immerse a metal in hydrogen gas underhigh pressure and temperature, thus controlling the amount of charged hydrogen in a metal.
However, this method is rarely applied to aluminum alloys because their surface is, in mostcases, covered with a native oxide layer, which prevents dissociation of hydrogen molecules.
So, aluminum alloys hardly absorb hydrogen atoms under moderate hydrogen-gas conditions.
Hydrogen ion irradiation with accelerating voltage of several kilovolts allows theintroduction of hydrogen to overcome the native oxide layer and to easily control the amountof hydrogen in the materials. Therefore, this technique can contribute to the study of thehydrogen embrittlement mechanism.
In this study, a hydrogen ion irradiation apparatus was constructed and the amount ofimplanted hydrogen in a titanium sheet was evaluated. Since titanium is a hydrogen absorbingmaterial, it can capture irradiated hydrogen. And there are few reports about the introductionof hydrogen into Ti by the method of low-energy (several kV) hydrogen ion irradiation [6]. A
vacuum system for thermal desorption spectrometry (TDS) measurement was also constructed
to evaluate the hydrogen retention in the titanium sheet.

2. Constructed systems
2.1. Hydrogen ion irradiation apparatus
We constructed an ion irradiation apparatus equipped with a sample heating stage. Theapparatus consisted of an ion gun (ACIG-3P-2, AVC Co., Ltd.), a gas supply system, vacuum
pumps, and sample heating stage. A schematic of the apparatus is shown in Fig.1. The sample38

水素イオン照射装置の構築と Ti 板へのイオン照射試験

HH
gas
gas
22

Ion
Iongungun

Ionization
Ionizationgauge
gauge1 1
Evacuation
systemVacuum pump
1 1

Ion
Iongungunchamberchamber

SampleSampleSampleSamplechamberchamber

HeatingHeatingstage
stage
Ionization
Ionization
gauge
gauge2 2

Thermocouple
Thermocouple

Evacuation
system2
Vacuum pump2Fig. 1

Schematic of ion implantation apparatus.

stage made of Cu can be heated up to 573 K using an inserted sheath heater during ion
irradiation. The temperature of the sample stage was measured by a thermocouple attached toit. The sample was placed on the Cu stage and its temperature was represented by the stagetemperature. The apparatus was evacuated by two set of vacuum pumps (evacuation system 1and 2 in Fig. 1). The pressure in a sample and ion gun chambers could be as low as 1×10-5 and1×10-4 Pa, respectively. B-A type ionization gauge (MG-2F and MG-2, ANELVA Co., Ltd.)
were used for pressure measurements. Hydrogen gas (Taiyo Nippon Sanso Co., Ltd., purity
99.9999%) was introduced to the ion gun chamber through a needle valve. The pressure of theion gun chamber was adjusted to approximately 5×10-2 Pa during hydrogen ion beamirradiation. At that time the sample chamber was maintained at approximately 5×10-4 Pa. The
acceleration voltage was fixed at 3 kV and the ion current at the sample surface wasapproximately 3 μA. In this system, the irradiated hydrogen ions were assumed as H2+ and H+(the ratio of the ions was not examined). After hydrogen ion irradiation, the sample was kept
in vacuum for 12 h for ion gun cooling before introducing air.

39

赤丸 悟士・西村 克彦

Quadrupole mass spectrometer

Muffle furnace

Ionization gauge
Quartztube
Vacuumpump

Fig. 2Sample

Pt wireThermocouple

Schematic of thermal desorption spectrometry system.

2.2. Thermal desorption spectrometry
Figure 2 shows the thermal desorption spectrometry (TDS) system used in this study. Thesample was bound to the contact point of the sheathed thermocouple using a φ0.45 mm Pt wire.
The thermocouple was introduced into a quartz tube evacuated to 2×10-5 Pa. The sample washeated at a constant rate of 3 K/min up to 873 K using a tubular furnace. The amount ofdesorbed gas species was analyzed using a quadrupole mass analyzer (QMA-200, Balzers).
The peak intensities of mass numbers 2, 17, 18, and 28 corresponding to H2+, OH+, H2O+, and
CO+/N2+, respectively, were monitored during sample heating.

3. Experimental
A Ti sheet sized 12×25 mm2 with 0.3 mm thickness (JIS H 4600 1st grade, TP-270) wasused as the sample. Only one Ti sheet was repeatably used for hydrogen irradiation anddesorption in this study. Exceptionally, a Ti sheet sized 25×25 mm2 was used for adjusting theposition of the focused ion beam. Experimental scheme of hydrogen implantation and TDS
measurements is as follows.
(1) The as-received Ti sheet (Ti sheet cut to a certain size was cleaned with acetone) was40水素イオン照射装置の構築と Ti 板へのイオン照射試験

set to the TDS system. The first TDS measurement was performed to examine thecontent of impurity hydrogen.
(2) The Ti sheet was annealed at 873 K in vacuum for completely release of impurityhydrogen.
(3) The sample was then set to the hydrogen ion irradiation system and was irradiated withhydrogen ions for 12 h at room temperature (about 290 K). The second TDS
measurement was carried out to evaluate the amount of implanted hydrogen.
(4) The hydrogen ion irradiation for 36 h was performed at room temperature (hydrogenirradiation for 12 h and then keeping in vacuum for 12 h were repeated 3 times). It wasfollowed by the third TDS measurement.

4. Results
Figure 3 shows the Ti sheet surface
after hydrogen ion irradiation. A triangle
mark (3 mm in height, 3 mm in base) of
the irradiation center indicated by the redcircle can be observed in this figure,suggesting that the ion beam was focusedon the area indicated by the mark. The
mark disappeared after annealing in
vacuum at 873 K.

Fig. 3

Ti sheet after hydrogen ion irradiation.

Figure 4 shows the spectrum of TDS measurements for the as-received Ti sheet. Since thechange in peak intensity of mass numbers 17, 18, and 28 was negligibly small during theheating process, the ion current of only mass number 2 corresponding to H2+ was plotted in thisfigure. The mass current showed a small shoulder at approximately 670 K (⁓160 min in Fig. 4)

41

赤丸 悟士・西村 克彦

QMC

mass current, I

900-11

Ti sheet 0.3 mm
as-received

800

5 10-11

4 10-11700

3 10-11600

temperature

first run

2 10-11500

1 10-11400
annealing at 873 Kin vacuum

00Fig. 450

100
150time, t / min.

temperature, T / K/A6 10300200250

Thermal desorption spectrums of as-received Ti sheet.

and a large peak at 840 K (210 min in Fig. 4). A x-ray diffraction analysis of the as-received Ti
sheet indicated that the Ti sheet consisted of almost all α phase and trace of impurity phase (itwas possible to titanium carbide). The large peak was caused by the hydrogen desorption from
α-titanium phase. The small shoulder indicated by the blue arrow was possible to desorb
hydrogen from impurity, or to decompose a little amount of δ phase because the hydrogenconcentration in α and (α+δ) phase boundary at 300 K was considerably low [3-5]. Above 840
K, the rate of hydrogen release decreased smoothly and the mass current decreased to 1/10 at250 min. After TDS measurement, the Ti sheet was annealed at 873 K in vacuum. The TDS
spectrum of the annealed Ti sheet is also shown in Fig. 4. There was no noticeable hydrogen
release up to 850 K, suggesting that almost all hydrogen was desorbed from the Ti sheet. The
slightly released hydrogen above 850 K can be attributed to the residual hydrogen in the Ti42水素イオン照射装置の構築と Ti 板へのイオン照射試験

sheet.
Figure 5 shows the TDS results after the hydrogen ion irradiation of the Ti sheet. For thefirst run, the TDS spectra sharply increased above 850 K. The mass current at 873 K was larger
than that after annealing (before irradiation, gray color in Fig. 4). The mass current afterirradiation at 36 h was larger than that after irradiated 12 h. The value of integrated spectrum
after irradiated 36 h at 873 K was also two times larger than that after irradiated 12 h. Theseresults indicated that hydrogen was implanted by ion gun apparatus, and the amount ofimplanted hydrogen increased with the irradiation time. A sharp increase of ion current around873 K was probably related to the desorption from α phase. The desorption temperature forirradiated Ti sheets slightly higher than that for as-received one. It could be due to the differenceof hydrogen distribution in Ti sheet; Since irradiated hydrogen was accumulated near thesurface at a small area, hydrogen in Ti sheet easily diffuse into bulk at low temperature. For the900
Ti sheet 0.3 mmirradiated by hydrogen ion at RT

800-11mass current, IQMC

700
first runtemperature

1 10-11500
second run

00Fig. 5600

temperature, T / K

blue: 36 hours (12 x 3 times)
red : 12 hours/A

2 10400
300

50

100
150time, t / min.

200

250

Thermal desorption spectrum of Ti sheet after hydrogen ion irradiation.

43

赤丸 悟士・西村 克彦

TDS results after the hydrogen ion irradiation for 36 h (blue color in Fig. 5), a small shoulder
was observed at approximately 800 K (200 min). Ma et al. reported that peaks in the TDS
measurement of titanium hydride corresponded to the phase boundary [1,2]. It seemed that thesmall shoulder is caused by the formation of a β phase [1,2]. More experimental will be required
to determine the relationship between TDS peaks and the phase boundary in consideration ofhydrogen distribution in Ti sheet.

5. Conclusions
A hydrogen ion irradiation system was constructed to implant hydrogen atoms in metalsheets. The proposed system confirmed that hydrogen atoms could be implanted into Ti sheet
using an ion irradiation apparatus. Moreover, from TDS measurements, we note that theamount of implanted hydrogen increased with the irradiation time. The ion irradiation system
could be useful for charging hydrogen to aluminum alloys and for further research on hydrogen
embrittlement of aluminum alloys.

Acknowledgement
This study was supported by KAKENHI grant number 18H01747. The authors thank AVC
Co., Ltd. and R-DEC Co., Ltd. for the planning and development of the main structure of theion gun apparatus.

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水素イオン照射装置の構築と Ti 板へのイオン照射試験

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