1. Highly Sensitive Detection of Hydrogen in Metallic Materials with Secondary Ion Mass Spectrometry
–Interstitial Hydrogen and Hydrogen Trapped by Trap Sites –
Tohru Awane, and Junichiro Yamabe
Thank you very much for your kind introduction. I deeply appreciate for giving me this great opportunity to speak about our research.
The theme of my presentation is our unique methodology for local analysis of hydrogen in metals with secondary ion mass spectrometry, SIMS. I start my presentation from talking about the background of this research.
SISS-19 in Kyoto, Japan on May11 and 12, 2017

2. New stage where hydrogen energy is used by millions of people.
Fuel Cell Vehicle: MIRAI
(TOYOTA)
Fuel Cell Vehicle: CLARITY
(HONDA)
Fuel Cell Forklift Truck
(TOYOTA INDUSTRIES CORP.)
Hydrogen station (hydrogen supplying system ) in a gas station near my apartment
Now we are rushing into a new stage where hydrogen energy is used by millions of people. Recently, fuel cell vehicles of mass production type are launched on the market. Hydrogen station for supplying high pressure hydrogen gas into fuel cell vehicles are built in gas stations in towns.
With this background, we increasingly need to investigate the health of metallic components exposed to high pressure hydrogen gas in the hydrogen facilities.

3. Hydrogen embrittlement Hydrogen-charged sample
Small amount of hydrogen in metals degrades their mechanical properties.
f =1.2 Hz
Hydrogen-charged sample
CH= 3.7 mass ppm
Acceleration by
hydrogen
Non-charged sample
CH= 2.7 mass ppm
Crack length 2a [mm]
CH: Hydrogen content
The acceleration of the crack growth rate is caused by hydrogen of mere 1mass ppm.
When the metallic components such as pipes or tanks are exposed to high pressure hydrogen gas, hydrogen invades the inside of the metals. The hydrogen in the material degrades the mechanical properties of the material. This figure shows fatigue crack growth rate of Hydrogen-charged and non-charged type 304 stainless steel. In this case, the hydrogen of mere 1 mass ppm accelerates the fatigue crack growth rate. We need to analyze such a small amount of hydrogen less than several mass ppm.
Number of cycles, N
Fatigue crack growth rate of hydrogen-charged and non-charged type 304 stainless steel
Y. Murakami et al., Met. Mat. Trans. A, Vol. 39A, 2008, pp

4. The range of hydrogen invasion into metals
The invasion of hydrogen can range over several millimeters or more from the surface in contact with the hydrogen gas. Therefore it is necessary to prepare a cross-section sample for investigating the hydrogen distribution. A dynamic SIMS has been greatly expected for the investigation.

5. Local area analysis of hydrogen in the metallic cross-section sample with the SIMS has been extremely difficult.
However, it is well-known that local area analysis of hydrogen in the metallic cross-section sample with the SIMS has been extremely difficult due to various interfering factors.

6. Background hydrogen (HBG)
Emission source of HBG
(H2O, CXHY, or CXHYOZ) H H
Sputtered area H H H
Sample for
measurement
The most influential interfering factor in hydrogen measurements with SIMS is background hydrogen, HBG, that is originate from water, hydrocarbon, or organic material molecules existing in a chamber vacuum, on a sample surface, or a chamber surface. The background hydrogen is never distinguishable from hydrogen contained in the sample that is the target hydrogen on SIMS data.
SIMS Chamber
C. W. Magee, et al, J. Vac. Sci. Technol. Vol.19, 1981,

7. Problems in the metallic cross-section sample
● Metal hydroxide layer: M(OH)n
● Escape of hydrogen from the near-surface region H
Cross-section surface H H H H H H H H H H H H
There are some interfering factors arising from particular natures of metals. Metal hydroxide layer occurs on the metallic surface. Background hydrogen of high intensity is emitted from this layer in a SIMS measurement. Hydrogen escapes from the near-surface region due to frictional heat when cutting or polishing the sample. Therefore we need to measure hydrogen in the deeper region that is not affected by the surface effects.
Hydrogen in the deeper region needs to be measured

8. Hydrogen entering into metal at the time of manufacture (HM)
Molten type
316L stainless
steel
Metals contain more or less hydrogen entering into the material at the time of manufacture. It disturbs accurate SIMS analysis of net amount of hydrogen that invades the material from hydrogen environments.
We need to break through the interfering factors for accurate analysis of hydrogen in metals.
Hydrogen thermal desorption spectrum of type 316L stainless steel
Y. Murakami et al., Metall. Mater. Trans., Vol.39A (2008), pp – 1339.

9. Aim of this research Net hydrogen ⇒ HN
Accurate SIMS analysis of net amount of hydrogen (1H) that invades metals by hydrogen gas exposures
Net hydrogen ⇒ HN
Interstitial hydrogen
in type 316L stainless steel
(Austenitic Fe based alloy)
Hydrogen trapped by intermetallic particles
in 6061-T6 aluminum alloy
Matrix of 6061-T6
The aim of this research is accurate SIMS analysis of net amount of hydrogen, 1H that invades metals by exposures of the metals to hydrogen gas. We call it net hydrogen, HN.
The first target is interstitial hydrogen in type 316L stainless steel. The interstitial hydrogen means that hydrogen existing inside the crystal lattices. We investigate distribution of the interstitial hydrogen in a Hydrogen-charged 316L cross-section sample.
The second target is hydrogen trapped by intermetallic particles in 6061-T6 aluminum alloy. Countless researchers in the fields of material science, hydrogen embrittlement, or analytical chemistry eagerly pursued the detection or observation of hydrogen trapped by trap sites in metals because hydrogen trapping is the most important phenomenon on researches for hydrogen embrittlement or hydrogen diffusion in metals. It is just a long-cherished desire.
In order to succeed in these analyses, we will break through the interfering factors with our unique methodology.
Intermetallic particles
Austenitic (FCC) crystal lattice

10. interstitial hydrogen in type 316L stainless steel
SIMS analysis of
interstitial hydrogen
in type 316L stainless steel
Now I talk about the first target, the interstitial hydrogen in 316L stainless steel.

11. SIMS：IMS-7f
The SIMS is used for this research is IMS-7f made by Cameca, Ametek, France. The IMS-7f is a dynamic SIMS equipped with a cesium ion source and a double-focus sector-type mass analyzer.

12. Preparation of 316L samples
40 mm in length
5 mm in diameter
Taken from the same lot
H-charged 316L sample
Non-charged 316L sample
HBG + HM
HN + HBG + HM
Cutting
and
polishing
Depth direction
Depth direction
This side shows how to prepare the 316L samples. Two round bar are prepared from this materials. They are taken from the same lot. One of the round bars is exposed to hydrogen gas of 10MPa, 250 degrees in Celsius for 192 hours. A cross-section sample is prepared from this hydrogen-charged round bar. Another round bar is prepared to estimate background in measurements for the Hydrogen-charged 316L sample. This round bar is not exposed to hydrogen gas. A cross-section is also prepared from this non-charged round bar. The two cross-section samples contain the same amount of hydrogen entering at the time of manufacture.
10Ma
Temperature (℃）
250
Bulk hydrogen content with TDS
H-charged 316L sample　 ⇒　22.4 mass ppm
Non-charged 316L sample ⇒　1.7 mass ppm
192 hr
Time (hr)

13. SIMS measurement conditions for the 316L samples
Depth profiles (relationship between secondary ion and depth) are acquired.
Impact energy: 15kV (Cs source HV; 10 kV, Sample HV; -5 kV)
Primary ion: Cs+
Intensity of primary ion beam (Ip): 60 nA
Detector for secondary ion: Electron multiplier (EM)
Measured ion：1H-, 16O-, 56Fe-　
Lower sputtering rate
Higher sputtering rate
Large raster or low-intensity beam
Small raster or high-intensity beam
Analyzed area
This slide shows SIMS measurement conditions for 316L samples. We acquire depth profiles for the measurements of this material.
5.6 mm f
Raster size: 50 mm square
High HBG amount
Low HBG amount
Y. Homma, et al, . J Vac. Sci. Technol. A3, 356 (1985), pp

14. The highly sensitive analytical method for hydrogen in metallic materials with SIMS
Silicon sputtering for reduction of HBG
(2) Extraction of 1H- data without surface effects
(3) Estimation of HBG and HN in the measurements for
H-charged 316L sample
In order to realize the accurate analyses of net hydrogen in metals, we developed our unique methodology called The highly sensitive analytical method for hydrogen in metallic materials with SIMS. This methodology consists of these three steps. I will explain the essences of them.
Tohru Awane et al., ANALYTICAL CHEMISTRY, Vol. 83 (2011), pp

15. (1) Silicon sputtering for reduction of HBG
The first step is silicon sputtering for reduction of background hydrogen. In this method, a pure silicon placed closed to a sample for measurement is sputtered by a primary ion beam of SIMS. The sputtered silicon covers the emission source of background hydrogen, so that the emission is effectively inhibited.

16. (1) Silicon sputtering for reduction of HBG
Depth profiles of 1H- acquired from a hydrogen-implanted silicon
Implanted
hydrogen
layer
HBG
Secondary ion intensity (cps)
The HBG intensity linearly decreases with sputtering time on the double logarithmic plot.
Primary beam: 60 nA
Raster size　150 mm
Depth direction
For the silicon sputtering, we used a hydrogen-implanted silicon wafer. By the silicon sputtering for 11 hours, background hydrogen decreased to one-tenth.
Sputtering time (sec)
HBG decreases to 1 / 10 after 11 hours.

17. (2) Extraction of 1H- data without surface effects
Schematic of typical depth profile of 1H- of a H-charged metallic sample with SIMS
The second step is extraction of 1H- data without surface effects.
This slide shows a schematic of typical depth profile of 1H- of a Hydrogen-charged metallic sample with SIMS. The variation characteristic can be classified into the three stage. Background hydrogen emitted from metal hydroxide layer or water molecules on the surface is detected in the region I. Hydrogen atoms partially escape from the region II. Of course, we cannot do accurate analyses of the net hydrogen. Therefore, we extract the 1H- data from the region III for the accurate analyses.

18. (2) Extraction of 1H- data without surface effects
Depth profiles of 1H- of 316L samples
Gross intensity of 1H-
= Intensity of
(HN + HBG)
H-charged
462~1140cps
Secondary ion intensity (cps)
Non-charged
HBG
Intensity
Now I show you the actual depth profiles of 1H- of 316L samples. The region from 10 to 16 micrometers deep in the Hydrogen-charged sample corresponds to the region III of the previous slide. We define the mean intensities in this depth region as the gross intensity that is the sum of background hydrogen intensity and net hydrogen intensity. We also defined the mean intensities of the region from 3 to 6 micrometers deep in the Non-charged sample as background hydrogen intensity.
26.8
~74.5cps
Depth (mm)

19. (3) Estimation of HBG and HN
in the measurements for H-charged 316L sample
HBG intensity in measurements of the H-charged 316L sample cannot be directly measured, and it varies with sputtering time.
HBG
HN + HBG
HBG H I II H
III H
Non-charged
H-charged
Non-charged
Non-charged
(II)
Estimated intensity of HBG in II
The third step is estimation of background hydrogen and net hydrogen in the measurements of H-charged 316L sample. Background hydrogen intensities in measurements of the Hydrogen-charged sample cannot be directly measured. Therefore we use the method shown in this slide for estimating the background hydrogen intensity. We measure 1H- intensities of the same Non-charged sample before and after the measurements of the Hydrogen-charged sample. And then the target background hydrogen intensities are estimated from the relationship between the 1H- intensities and the sputtering time in the measurements of the Non-charged 316L sample.
1H- intensity (Log)
Non-charged
(III)
Sputtering time (Log)

20. (3) Estimation of HBG and HN
in the measurements of H-charged 316L sample
Calculation of HN intensities _ =
Gross intensity of 1H-
HBG intensity
HN intensity
= Intensity of
(HN + HBG)
Each net hydrogen intensity at each measurement point of the hydrogen-charged sample is determined by subtracting the background hydrogen intensity from the gross hydrogen intensity.

21. Distance from the cross-section edge(mm)
Relationship between HN intensity and the distance from the edge of the H-charged 316L sample
HA4
HA6
HA3
HN intensity (cps)
HA5
HA1
HA2
This slide shows the relationship between net hydrogen intensity and distance from the edge of H-charged 316L sample. Before the hydrogen gas exposure, we predict hydrogen can diffuse all over the range of this round bar. It is clear that the prediction is exact.
Distance from the cross-section edge(mm)

22. The quantitative capability Mean HN intensity by SIMS (cps)
Relationship between mean HN intensities by SIMS and hydrogen contents quantified by TDA
[×105]
Hydrogen intensity
by SIMS 1
0.8
Mean HN intensity by SIMS (cps)
0.6
Hydrogen content
by TDA
0.4
0.2
The quantitative capability of our methodology is verified by comparison between mean net intensities by SIMS and hydrogen contents quantified by TDA. They show a linear relationship. 40 80
120
Hydrogen content quantified by TDA (mass ppm)
J. Yamabe et al, International Journal of Hydrogen Energy, Vol. 38 (2013),

23. The minimum detectable hydrogen content
Non-charged S10C (ferritic steel)
Bulk hydrogen content
= 0.02 mass ppm
H-charged S10C
Bulk hydrogen content
= 0.14 mass ppm
200~500 cps
100 cps
Its minimum detectable hydrogen content is 0.12 mass ppm for ferric steel, S10C.
The small difference of the hydrogen content,
0.12 (= 0.14 – 0.02) mass ppm can be clearly detected.
A. Nishimoto, and T. Awane et al., ISIJ International, Vol. 55, No. 1, pp

24. Hydrogen trapped by intermetallic particles
in 6061-T6 aluminum alloy
Thus we have successfully gained the powerful methodology to break through the various interfering factors and to realize accurate analysis of hydrogen. Next we challenge the second target, hydrogen trapped by intermetallic particles in 6061-T6 aluminum alloy with the methodology.
"Hydrogen trapped at intermetallic particles in aluminum alloy 6061-T6 exposed to high-pressure hydrogen gas and the reason for high resistance against hydrogen embrittlement"
Junichiro Yamabe, Tohru Awane, Yukitaka Murakami,
International Journal of Hydrogen Energy,
Volume 42, Issue 38, 21 September 2017, Pages

25. Preparation of 6061-T6 samples
Samples for TDA measurement
Samples for SIMS and
SEM-EDX measurement
This slide shows how to prepare the aluminum alloy samples. All the samples are taken from the core of one round bar. Cross-section samples are prepared from a Hydrogen-charged sample, a Non-charged sample, and a Hydrogen charged sample with heating of TDA measurement. The hydrogen-charged sample is exposed to hydrogen gas of 100 MPa, 200oC for 300 h.

26. Measurement of hydrogen desorption properties
TDA spectra of non-charged and H-charged samples
Determination of
desorption energy
The left figure shows hydrogen desorption properties acquired of the Hydrogen-charged and the Non-charged sample. In the measurement of the H-charged sample, a peak was observed at a temperature of 350oC. No peak is observed in the measurement of the Non-charged sample. It is confirmed that hydrogen uptake actually occurred by the hydrogen exposure. . The desorption energy of the hydrogen trapping site associated with this peak is determined by the Choo-Lee method. It is 200 kJ/mol or higher. This desorption energy is much higher than those reported previously. This high desorption energy can cause a surprising effect on hydrogen uptake into the sample. I would like to talk about this in another chance.
W.Y. Choo et al., Metall. Trans., Vol.12A (1982), pp.135–140.

27. Typical BSE images and EDX spectra of matrix and intermetallic particles
Before heating of TDA
After heating up to 520oC by TDA
This slide shows that typical BSE image and EDX spectra of matrix and intermetallic particles before heating of TDA and after heating up to 520oC by TDA. The intermetallic particles are observed as bright spots in the BSE images. They contains more Si, Cr, Fe, Mn, Cu as compared to the matrix. The shape, the size, and the compositions of the intermetallic particles by the heating.

28. SIMS measurement conditions for 6061-T6 samples
Impact energy: 15kV (Cs source HV; 10 kV, Sample HV; -5 kV)
Primary ion: Cs+
Detector for secondary ion: Electron multiplier (EM)
Measured ion：1H-, 30Si-, 52Cr- , 56Fe-, etc.
Ip= 60 nA
Ip= 200 ~ 380 nA
This slide shows the SIMS measurement condition for the aluminum alloy samples. We acquire depth profiles and ion maps for the measurements of this material,. Such a high-intensity beam is used for the ion map measurements to reduce the influence of background hydrogen. However the high-intensity beam having a larger diameter makes image resolution worse. Therefore small analytical area less than 14 um in diameter is made by the field aperture of 100 um in diameter. And then the small analytical areas is scanned in the range of the raster by dynamic transfer optical system.

29. 2D ion maps of H-charged 6061-T6 sample
Locally-concentrated hydrogen is detected at the intermetallic particles.
This slide shows 2D ion maps of H-charged sample. Si, Cr, and Fe are the main components of the intermetallic materials. The locally-concentrated of 1H- was detected at the same positions as the intermetallic particles. What is the locally-concentrated hydrogen? Is it the real trap hydrogen or not?
What is the locally-concentrated hydrogen?

30. False detection of trapped hydrogen
2D maps of 1H- and 12C8- acquired from a H-charged spherical graphite cast iron
Spherical graphite
We concern about false detection of trapped hydrogen. I would like to show the example of false detection. These are 2D maps of 1H-, and 12C8- acquired from a H-charged spherical graphite cast iron.
Locally-concentrated is detected at the graphite. It looks like hydrogen trapped by the graphite.
12C8-
1H-

31. Verification of the authenticity of the trapped hydrogen
The locally-concentrated hydrogen is apparently detected at the graphite because of higher HBG intensity caused by its lower sputtering rate
The authenticity is verify by a sample that is heated by TDA measurement and perfectly desorbs hydrogen. The locally-concentrated is detected even in the heated sample. It is apparently detected at the graphite because of higher HBG intensity caused by its sputtering rate lower than that of the matrix. We conclude that the 1H- signal is not the trapped hydrogen.
Sputtering rates in case of irradiation of Ar+ with an acceleration voltage of 5kV,
C → 2.4 atoms / ion, Fe → 4.1 atoms / ion
We conclude that the locally-concentrated hydrogen is
not the real trapped hydrogen but the false detection.

32. Verification of the locally-concentrated hydrogen
in H-charged 6061-T6 sample
Is it REAL trapped hydrogen or not?
H-charged sample
Non-charged sample
(Before measurements of the H-charged one)
H-charged sample after TDA measurement
Non-charged sample
(After measurements of the H-charged one)
Analytical area: circular area of 5.6 mm in diameter.
After heating up to 520oC by TDA
Depth direction
Secondary ion intensity (cps)
Now I get back on the track for the aluminum alloy sample. In order to verify whether the locally-concentrated hydrogen in the Hydrogen-charged sample is the trapped hydrogen or not, we prepared the Non-charged sample and the Hydrogen-charged sample after TDA measurement. The left figure shows the depth profile of 1H- for the Hydrogen charged sample and the Non-charged sample. The blue lines show profiles for the Hydrogen-charged sample. The peaks of the locally concentrated hydrogen ranging from 1,000 to 10,000 cps are clearly observed.
On the other hand, the green and the red line show profiles for the Non-charged sample. They were acquired before and after the measurements for the Hydrogen-charged sample. No peak is observed in the profiles of the Non-charged sample. Moreover, the variation of the intensities between the green and red lines are very small. This fact reveal that the variation of background hydrogen does not affect the detection of the peaks.
The right figure with purple lines show profiles for the Hydrogen-charged sample after TDA measurement. This sample perfectly desorbed hydrogen. No peak is observed in the profiles. This fact strongly support that the detection of the peaks is not affected by the difference of background hydrogen amount between the intermetallic particle and the matrix. We conclude that the locally-concentrated hydrogen is the real hydrogen trapped by the intermetallic particles.
Depth direction
Depth direction
Sputtering time (s)

33. 3D imaging of 1H- in 6061-T6 samples
H-charged sample
after TDA measurement
H-charged sample
Now you can see the three dimensional image of the real trapped hydrogen in the Hydrogen-charged sample in the left figure. Thus we succeeded for the first time in visualizing hydrogen trapped in metals. On the hand, no hydrogen signal is observed in the Hydrogen-charged sample after TDA measurement.
The 3D images were constructed with (FIJI IS JUST) IMAGE J:

34. 3D animations of 1H- in 6061-T6 samples
H-charged sample
after TDA measurement
H-charged sample
300 mm
300 mm
Now you are watching the actual SIMS measurement of the aluminum alloy sample. The animations are going along the depth direction. In the animation of the Hydrogen-charged sample, the trapped hydrogen appears from the inside and fades away.
The 3D animations were constructed with (FIJI IS JUST) IMAGE J:

35. Summary Interstitial hydrogen in type 316L stainless steel
The highly sensitive analytical method for hydrogen in metallic materials with SIMS
Hydrogen trapped by intermetallic particles
in 6061-T6 aluminum alloy
In this presentation, we demonstrated our unique methodology for the local analysis of hydrogen in metallic materials and the effectivity. We have thoroughly excluded the false signals cause by background hydrogen and gained the real hydrogen signal in SIMS measurements. We believe that the research achievements will dramatically advance the field of local analysis of hydrogen in metals, which has stagnated for a long time. I would be happy if my presentation in this conference could be the start point of the dramatic advance.

36. We are grateful to Mr. Shiro Miwa (CAMECA, AMETEK) for the helpful technical supports on SIMS analyses.
At the end of my presentation, I would like to mention one acknowledgement. We are grateful to Mr. Shiro Miwa (CAMECA, AMETEK) for the helpful technical supports on SIMS analyses.
Thank you very much for your attentions.

37. The speaking words for the slides
P1, The theme of my presentation is our unique methodology for local analysis of hydrogen in metals with secondary ion mass spectrometry, SIMS. I start my presentation from talking about the background of this research.
P2, Now we are rushing into a new stage where hydrogen energy is used by millions of people. Recently, fuel cell vehicles of mass production type are launched on the market. Hydrogen station for supplying high pressure hydrogen gas into fuel cell vehicles are built in gas stations in towns.
With this background, we increasingly need to investigate the health of metallic components exposed to high pressure hydrogen gas in the hydrogen facilities.
P3, When the metallic components such as pipes or tanks are exposed to high pressure hydrogen gas, hydrogen invades the inside of the metals. The hydrogen in the material degrades the mechanical properties of the material. This figure shows fatigue crack growth rate of Hydrogen-charged and non-charged type 304 stainless steel. In this case, the hydrogen of mere 1 mass ppm accelerates the fatigue crack growth rate. We need to analyze such a small amount of hydrogen less than several mass ppm.
P4, The invasion of hydrogen can range over several millimeters or more from the surface in contact with the hydrogen gas. Therefore it is necessary to prepare a cross-section sample for investigating the hydrogen distribution. A dynamic SIMS has been greatly expected for the investigation.
P5, However, it is well-known that local area analysis of hydrogen in the metallic cross-section sample with the SIMS has been extremely difficult due to various interfering factors.
P6, The most influential interfering factor in hydrogen measurements with SIMS is background hydrogen, HBG, that is originate from water, hydrocarbon, or organic material molecules existing in a chamber vacuum, on a sample surface, or a chamber surface. The background hydrogen is never distinguishable from hydrogen contained in the sample that is the target hydrogen on SIMS data.
P7, There are some interfering factors arising from particular natures of metals. Metal hydroxide layer occurs on the metallic surface. Background hydrogen of high intensity is emitted from this layer in a SIMS measurement. Hydrogen escapes from the near-surface region due to frictional heat when cutting or polishing the sample. Therefore we need to measure hydrogen in the deeper region that is not affected by the surface effects.

38. P8, Metals contain more or less hydrogen entering into the material at the time of manufacture. It disturbs accurate SIMS analysis of net amount of hydrogen that invades the material from hydrogen environments.
We need to break through the interfering factors for accurate analysis of hydrogen in metals.
P9, The aim of this research is accurate SIMS analysis of net amount of hydrogen, 1H that invades metals by exposures of the metals to hydrogen gas. We call it net hydrogen, HN.
The first target is interstitial hydrogen in type 316L stainless steel. The interstitial hydrogen means that hydrogen existing inside the crystal lattices. We investigate distribution of the interstitial hydrogen in a Hydrogen-charged 316L cross-section sample.
The second target is hydrogen trapped by intermetallic particles in 6061-T6 aluminum alloy. Countless researchers in the fields of material science, hydrogen embrittlement, or analytical chemistry eagerly pursued the detection or observation of hydrogen trapped by trap sites in metals because hydrogen trapping is the most important phenomenon on researches for hydrogen embrittlement or hydrogen diffusion in metals. It is just a long-cherished desire.
In order to succeed in these analyses, we will break through the interfering factors with our unique methodology.
P10, Now I talk about the first target, the interstitial hydrogen in 316L stainless steel.
P11, The SIMS is used for this research is IMS-7f made by Cameca, Ametek, France. The IMS-7f is a dynamic SIMS equipped with a cesium ion source and a double-focus sector-type mass analyzer.
P12, This side shows how to prepare the 316L samples. Two round bar are prepared from this materials. They are taken from the same lot. One of the round bars is exposed to hydrogen gas of 10MPa, 250 degrees in Celsius for 192 hours. A cross-section sample is prepared from this hydrogen-charged round bar. Another round bar is prepared to estimate background in measurements for the Hydrogen-charged 316L sample. This round bar is not exposed to hydrogen gas. A cross-section is also prepared from this non-charged round bar. The two cross-section samples contain the same amount of hydrogen entering at the time of manufacture.
P13, This slide shows SIMS measurement conditions for 316L samples. We acquire depth profiles for the measurements of this material.
P14, In order to realize the accurate analyses of net hydrogen in metals, we developed our unique methodology called The highly sensitive analytical method for hydrogen in metallic materials with SIMS. This methodology consists of these three steps. I will explain the essences of them.

39. P15, The first step is silicon sputtering for reduction of background hydrogen. In this method, a pure silicon placed closed to a sample for measurement is sputtered by a primary ion beam of SIMS. The sputtered silicon covers the emission source of background hydrogen, so that the emission is effectively inhibited.
P16, For the silicon sputtering, we used a hydrogen-implanted silicon wafer. By the silicon sputtering for 11 hours, background hydrogen decreased to one-tenth.
P17, The second step is extraction of 1H- data without surface effects.
This slide shows a schematic of typical depth profile of 1H- of a Hydrogen-charged metallic sample with SIMS. The variation characteristic can be classified into the three stage. Background hydrogen emitted from metal hydroxide layer or water molecules on the surface is detected in the region I. Hydrogen atoms partially escape from the region II. Of course, we cannot do accurate analyses of the net hydrogen. Therefore, we extract the 1H- data from the region III for the accurate analyses.
P18, Now I show you the actual depth profiles of 1H- of 316L samples. The region from 10 to 16 micrometers deep in the Hydrogen-charged sample corresponds to the region III of the previous slide. We define the mean intensities in this depth region as the gross intensity that is the sum of background hydrogen intensity and net hydrogen intensity. We also defined the mean intensities of the region from 3 to 6 micrometers deep in the Non-charged sample as background hydrogen intensity.
P19, The third step is estimation of background hydrogen and net hydrogen in the measurements of H-charged 316L sample. Background hydrogen intensities in measurements of the Hydrogen-charged sample cannot be directly measured. Therefore we use the method shown in this slide for estimating the background hydrogen intensity. We measure 1H- intensities of the same Non-charged sample before and after the measurements of the Hydrogen-charged sample. And then the target background hydrogen intensities are estimated from the relationship between the 1H- intensities and the sputtering time in the measurements of the Non-charged 316L sample.
P20, Each net hydrogen intensity at each measurement point of the hydrogen-charged sample is determined by subtracting the background hydrogen intensity from the gross hydrogen intensity.
P21, This slide shows the relationship between net hydrogen intensity and distance from the edge of H-charged 316L sample. Before the hydrogen gas exposure, we predict hydrogen can diffuse all over the range of this round bar. It is clear that the prediction is exact.
P22, The quantitative capability of our methodology is verified by comparison between mean net intensities by SIMS and hydrogen contents quantified by TDA. They show a linear relationship.
P23, Its minimum detectable hydrogen content is 0.12 mass ppm for ferric steel, S10C.

40. P24, Thus we have successfully gained the powerful methodology to break through the various interfering factors and to realize accurate analysis of hydrogen. Next we challenge the second target, hydrogen trapped by intermetallic particles in 6061-T6 aluminum alloy with the methodology.
P25, This slide shows how to prepare the aluminum alloy samples. All the samples are taken from the core of one round bar. Cross-section samples are prepared from a Hydrogen-charged sample, a Non-charged sample, and a Hydrogen charged sample with heating of TDA measurement. The hydrogen-charged sample is exposed to hydrogen gas of 100 MPa, 200oC for 300 h.
P26, The left figure shows hydrogen desorption properties acquired of the Hydrogen-charged and the Non-charged sample. In the measurement of the H-charged sample, a peak was observed at a temperature of 350oC. No peak is observed in the measurement of the Non-charged sample. It is confirmed that hydrogen uptake actually occurred by the hydrogen exposure. The right figure shows the determination of the desorption energy of the trapping site associated with the peak-1 by the Choo-Lee method. It was 200 kJ/mol or higher. This desorption energy is much higher than those of trap sites in aluminum alloys that has been previously reported.
P27, This slide shows that typical BSE image and EDX spectra of matrix and intermetallic particles before heating of TDA and after heating up to 520oC by TDA. The intermetallic particles are observed as bright spots in the BSE images. They contains more Si, Cr, Fe, Mn, Cu as compared to the matrix. The shape, the size, and the compositions of the intermetallic particles by the heating.
P28, This slide shows the SIMS measurement condition for the aluminum alloy samples. We acquire depth profiles and ion maps for the measurements of this material,. Such a high-intensity beam is used for the ion map measurements to reduce the influence of background hydrogen. However the high-intensity beam having a larger diameter makes image resolution worse. Therefore small analytical area less than 14 m in diameter is made by the field aperture of 100 m in diameter. And then the small analytical areas is scanned in the range of the raster by dynamic transfer optical system.
P29, This slide shows 2D ion maps of H-charged sample. Si, Cr, and Fe are the main components of the intermetallic materials. The locally-concentrated of 1H- was detected at the same positions as the intermetallic particles. What is the locally-concentrated hydrogen? Is it the real trap hydrogen or not?

41. P30, We concern about false detection of trapped hydrogen
P30, We concern about false detection of trapped hydrogen. I would like to show the example of false detection. These are 2D maps of 1H-, and 12C8- acquired from a H-charged spherical graphite cast iron.
Locally-concentrated is detected at the graphite. It looks like hydrogen trapped by the graphite.
P31,The authenticity is verify by a sample that is heated by TDA measurement and perfectly desorbs hydrogen. The locally-concentrated is detected even in the heated sample. It is apparently detected at the graphite because of higher HBG intensity caused by its sputtering rate lower than that of the matrix. We conclude that the 1H- signal is not the trapped hydrogen.
P32, Now I get back on the track for the aluminum alloy sample. In order to verify whether the locally-concentrated hydrogen in the Hydrogen-charged sample is the trapped hydrogen or not, we prepared the Non-charged sample and the Hydrogen-charged sample after TDA measurement. The left figure shows the depth profile of 1H- for the Hydrogen charged sample and the Non-charged sample. The blue lines show profiles for the Hydrogen-charged sample. The peaks of the locally concentrated hydrogen ranging from 1,000 to 10,000 cps are clearly observed.
On the other hand, the green and the red line show profiles for the Non-charged sample. They were acquired before and after the measurements for the Hydrogen-charged sample. No peak is observed in the profiles of the Non-charged sample. Moreover, the variation of the intensities between the green and red lines are very small. This fact reveal that the variation of background hydrogen does not affect the detection of the peaks.
The right figure with purple lines show profiles for the Hydrogen-charged sample after TDA measurement. This sample perfectly desorbed hydrogen. No peak is observed in the profiles. This fact strongly support that the detection of the peaks is not affected by the difference of background hydrogen amount between the intermetallic particle and the matrix. We conclude that the locally-concentrated hydrogen is the real hydrogen trapped by the intermetallic particles.
P33, Now you can see the three dimensional image of the real trapped hydrogen in the Hydrogen-charged sample in the left figure. Thus we succeeded for the first time in visualizing hydrogen trapped in metals. On the hand, no hydrogen signal is observed in the Hydrogen-charged sample after TDA measurement.
P34, Now you are watching the actual SIMS measurement of the aluminum alloy sample. The animations are going along the depth direction. In the animation of the Hydrogen-charged sample, the trapped hydrogen appears from the inside and fades away.

42. P35, In this presentation, we demonstrated our unique methodology for the local analysis of hydrogen in metallic materials and the effectivity. We have thoroughly excluded the false signals cause by background hydrogen and gained the real hydrogen signal in SIMS measurements. We believe that the research achievements will dramatically advance the field of local analysis of hydrogen in metals, which has stagnated for a long time. I would be happy if my presentation in this conference could be the start point of the dramatic advance.
P36, At the end of my presentation, I would like to mention one acknowledgement. We are grateful to Mr. Shiro Miwa (CAMECA, AMETEK) for the helpful technical supports on SIMS analyses.