Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold
The damage of deformed double forged pure tungsten (W) and tungsten alloyed with 5 wt.% tantalum (WTa5) have been studied in experimental simulations of ITER-like transient events (surface heat load of 0.45 MJ/m² and the pulse duration of 0.25 ms) with quasi-stationary plasma accelerator QSPA...
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| Zitieren: | Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold / V.A. Makhlai, S.S. Herashchenko, N.N. Aksenov, O.V. Byrka, I.E. Garkusha, S.V. Malykhin, S.V. Surovitskiy, N.V. Kulik, V.V. Staltsov, S.I. Lebedev, P.B. Shevchuk,M. Wirtz, M.J. Sadowski // Вопросы атомной науки и техники. — 2018. — № 6. — С. 59-62. — Бібліогр.: 15 назв. — англ. |
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irk-123456789-1488192019-02-19T01:23:54Z Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold Makhlai, V.A. Herashchenko, S.S. Aksenov, N.N. Byrka, O.V. Garkusha, I.E. Malykhin, S.V. Surovitskiy, S.V. Kulik, N.V. Staltsov, V.V. Lebedev, S.I. Shevchuk, P.B. Wirtz, M. Sadowski, M.J. ИТЭР и приложения для термоядерного реактора The damage of deformed double forged pure tungsten (W) and tungsten alloyed with 5 wt.% tantalum (WTa5) have been studied in experimental simulations of ITER-like transient events (surface heat load of 0.45 MJ/m² and the pulse duration of 0.25 ms) with quasi-stationary plasma accelerator QSPA Kh-50. The plasma exposures were performed for targets maintained at room temperature and preheated at 200 or 300°C. The large and fine cracks appeared in result of plasma impacts. The high number of repetitive plasma loads below the melting threshold led to the clear degradation of thermo-mechanical properties of the affected surface layers on tungsten. Comparative analysis of the cracks propagation to the bulk is presented for both W and WTa5 samples. Вивчено пошкодження деформованого подвійною ковкою чистого вольфраму (W) та з легуючою 5 об.% домішкою танталу (WTa5) при експериментальному моделюванні умов перехідних процесів в ІТЕР (теплове навантаження на поверхню 0,45 МДж/м² , тривалість імпульсу 0,25 мс) у квазістаціонарному плазмовому прискорювачі КСПП Х-50. Опромінення мішеней плазмою проводили при кімнатній початковій температурі та з підігрівом до 200 та 300°C. В результаті плазмового впливу з’являлися великі й маленькі тріщини. Велика кількість повторюваних плазмових навантажень нижча порога плавлення привела до явної деградації термомеханічних властивостей пошкоджених приповерхневих шарів вольфраму. Представлено порівняльний аналіз розповсюдження тріщин в об'єм для W- і WTa5-зразків. Изучены повреждения деформированного двойной ковкой чистого вольфрама (W) и с легирующей 5 об.% добавкой тантала (WTa5) при экспериментальном моделировании условий переходных процессов в ИТЭР (тепловая нагрузка на поверхность 0,45 МДж/м² , длительность импульса 0,25 мс) в квазистационарном плазменном ускорителе КСПУ Х-50. Облучение мишеней плазмой проводили при комнатной начальной температуре и с подогревом до 200 и 300°C. В результате плазменного воздействия появлялись большие и мелкие трещины. Большое количество повторяющихся плазменных нагрузок ниже порога плавления привело к явной деградации термомеханических свойств поврежденных приповерхностных слоев вольфрама. Представлен сравнительный анализ распространения трещин в объем для W- и WTa5-образцов. 2018 Article Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold / V.A. Makhlai, S.S. Herashchenko, N.N. Aksenov, O.V. Byrka, I.E. Garkusha, S.V. Malykhin, S.V. Surovitskiy, N.V. Kulik, V.V. Staltsov, S.I. Lebedev, P.B. Shevchuk,M. Wirtz, M.J. Sadowski // Вопросы атомной науки и техники. — 2018. — № 6. — С. 59-62. — Бібліогр.: 15 назв. — англ. 1562-6016 PACS: 52.40.HF http://dspace.nbuv.gov.ua/handle/123456789/148819 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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ИТЭР и приложения для термоядерного реактора ИТЭР и приложения для термоядерного реактора |
| spellingShingle |
ИТЭР и приложения для термоядерного реактора ИТЭР и приложения для термоядерного реактора Makhlai, V.A. Herashchenko, S.S. Aksenov, N.N. Byrka, O.V. Garkusha, I.E. Malykhin, S.V. Surovitskiy, S.V. Kulik, N.V. Staltsov, V.V. Lebedev, S.I. Shevchuk, P.B. Wirtz, M. Sadowski, M.J. Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold Вопросы атомной науки и техники |
| description |
The damage of deformed double forged pure tungsten (W) and tungsten alloyed with 5 wt.% tantalum (WTa5)
have been studied in experimental simulations of ITER-like transient events (surface heat load of 0.45 MJ/m²
and
the pulse duration of 0.25 ms) with quasi-stationary plasma accelerator QSPA Kh-50. The plasma exposures were
performed for targets maintained at room temperature and preheated at 200 or 300°C. The large and fine cracks
appeared in result of plasma impacts. The high number of repetitive plasma loads below the melting threshold led to
the clear degradation of thermo-mechanical properties of the affected surface layers on tungsten. Comparative
analysis of the cracks propagation to the bulk is presented for both W and WTa5 samples. |
| format |
Article |
| author |
Makhlai, V.A. Herashchenko, S.S. Aksenov, N.N. Byrka, O.V. Garkusha, I.E. Malykhin, S.V. Surovitskiy, S.V. Kulik, N.V. Staltsov, V.V. Lebedev, S.I. Shevchuk, P.B. Wirtz, M. Sadowski, M.J. |
| author_facet |
Makhlai, V.A. Herashchenko, S.S. Aksenov, N.N. Byrka, O.V. Garkusha, I.E. Malykhin, S.V. Surovitskiy, S.V. Kulik, N.V. Staltsov, V.V. Lebedev, S.I. Shevchuk, P.B. Wirtz, M. Sadowski, M.J. |
| author_sort |
Makhlai, V.A. |
| title |
Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold |
| title_short |
Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold |
| title_full |
Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold |
| title_fullStr |
Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold |
| title_full_unstemmed |
Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold |
| title_sort |
erosion properties of tungsten and wta5 alloy exposed to repetitive qspa plasma loads below melting threshold |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2018 |
| topic_facet |
ИТЭР и приложения для термоядерного реактора |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/148819 |
| citation_txt |
Erosion properties of tungsten and WTa5 alloy exposed to repetitive QSPA plasma loads below melting threshold / V.A. Makhlai, S.S. Herashchenko, N.N. Aksenov, O.V. Byrka, I.E. Garkusha, S.V. Malykhin, S.V. Surovitskiy, N.V. Kulik, V.V. Staltsov, S.I. Lebedev, P.B. Shevchuk,M. Wirtz, M.J. Sadowski // Вопросы атомной науки и техники. — 2018. — № 6. — С. 59-62. — Бібліогр.: 15 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2018. №6(118)
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2018, № 6. Series: Plasma Physics (118), p. 59-62. 59
EROSION PROPERTIES OF TUNGSTEN AND WTa5 ALLOY EXPOSED
TO REPETITIVE QSPA PLASMA LOADS BELOW MELTING
THRESHOLD
V.A. Makhlai1,2, S.S. Herashchenko1, N.N. Aksenov1, O.V. Byrka1, I.E. Garkusha1,
S.V. Malykhin2, S.V. Surovitskiy2, N.V. Kulik1, V.V. Staltsov1, S.I. Lebedev1, P.B. Shevchuk1,
M. Wirtz3, M.J. Sadowski4
1National Science Center “Kharkov Institute of Physics and Technology”,
Institute of Plasma Physics, Kharkiv, Ukraine;
2National Technical University “Kharkiv Polytechnical Institute”, Kharkiv, Ukraine;
3Forschungszentrum Julich, EURATOM Association, Julich, Germany;
4National Centre for Nuclear Research (NCBJ), Otwock-Świerk, Poland
E-mail: gerashchenko@kipt.kharkov.ua
The damage of deformed double forged pure tungsten (W) and tungsten alloyed with 5 wt.% tantalum (WTa5)
have been studied in experimental simulations of ITER-like transient events (surface heat load of 0.45 MJ/m2 and
the pulse duration of 0.25 ms) with quasi-stationary plasma accelerator QSPA Kh-50. The plasma exposures were
performed for targets maintained at room temperature and preheated at 200 or 300°C. The large and fine cracks
appeared in result of plasma impacts. The high number of repetitive plasma loads below the melting threshold led to
the clear degradation of thermo-mechanical properties of the affected surface layers on tungsten. Comparative
analysis of the cracks propagation to the bulk is presented for both W and WTa5 samples.
PACS: 52.40.HF
INTRODUCTION
Lifetime of Plasma Facing Materials (PFM) is a
critical issue for successful implementation of fusion
reactor project [1-3]. Tungsten is chosen as the main
plasma facing material for ITER and DEMO divertor
design due to its advantageous properties: high thermal
conductivity, high temperature strength and stability,
high recrystallization temperature and high spattering
threshold for hydrogen [2, 3]. Analysis of tungsten
lifetime of PFM has been performed with number of
simulation facilities (e-beams, lasers, linear devices,
plasma gun and QSPA) [4-14]. In spite of extensive
R&D efforts, the macroscopic erosion of tungsten due
to the brittle destruction (cracks, debris and dust
particles), as well as material modifications and
properties changes after repetitive plasma pulses
required addition studies. Possible synergetic effects,
induced by the combined heat and particle loads, remain
also key issues which have to be comprehensively
studied at the fusion-reactor relevant conditions [4, 7].
The most important issues for simulation experiments
with plasma accelerators are studies of properties of
different tungsten grades [8, 10-15]. Issues related to
tungsten damage in the course of a large number of
plasma exposures should also be studied. In this paper,
some evaluations of the mechanisms of damage of pure
tungsten and tungsten-tantalum alloy under ELM
conditions are presented. The important issue the
damage of tungsten under a large number of plasma
exposures with heat load below the melting threshold is
also discussed.
1. EXPERIMENTAL DEVICE AND
DIAGNOSTICS
Heat load tests of tungsten with energy density,
pulse duration and particle loads relevant to ITER
transient events have been carried out in a QSPA Kh-50
quasi-stationary plasma accelerator [10-13]. The main
parameters of the hydrogen plasma streams are as
follows: ion impact energy about 0.4 keV, maximum
plasma pressure 0.32 MPa, and the stream diameter
18 cm. The plasma pulse shape is triangular, pulse
duration 0.25 ms [13]. The surface energy loads
measured with a calorimeter were 0.45 MJ/m2 (below
tungsten melting threshold (0.6 MJ/m2)) [10-14].
Surface analysis of exposed samples was carried out
with an optical microscope MMR-4 equipped with a
CCD camera and Scanning Electron Microscope (SEM)
of the JEOL JSM-6390 type. Precise measurements of
the surface roughness with a T500 Hommelwerke tester
T500 were also performed.
X-ray diffraction (XRD) has been used to study
structure, sub-structure and stress state of targets. -2
scans were performed using a monochromatic Cu-Kα
radiation [10]. Computer processing of the experimental
diffraction patterns was performed using the New
Profile 3.5 software package. The analysis of diffraction
peaks intensity, profiles, width (В), angular positions
were applied to evaluate texture, coherent scattering
region size. Changes of phase state on the surface were
obtained from XRD spectrum analysis. The asymmetry
parameter (δВ) of a diffraction profile was also
estimated. The asymmetry (δВ0) is attributed by the
presence of complexes of point defects [10]. The sign of
δВ is caused by the type of defects: vacancies (δВ>0)
(in other words, the diffusion maximum appear on left
from the main peak) or interstitial atoms (δВ<0) (when
the diffusion maximum on right from main peak).
Residual macro-stresses (σ) and the lattice parameter in
the stress free state (a0) were determined using а-sin2ψ –
plots by the peaks (400) located in the precision area of
angles [10]. It should be mentioned, if lattice parameter in
60 ISSN 1562-6016. ВАНТ. 2018. №6(118)
the stress free state (a0) is less than the corresponding
reference value (aref = 0.3165 nm) then a lot of vacancies
are present the structure. If a0>aref the surplus interstitial
atoms are observed the structure. It can be also
attributed to some penetration of heavy impurities into
the materials.
Surface analysis of exposed sample was carried out
with MMR-4 optical microscope, equipped with a CCD
camera. Weight loss measurements were also performed.
2. EXPERIMENTAL RESULTS AND
DISCUSSION
Double forged samples of pure tungsten (W) and
tungsten alloyed with 5 wt.% tantalum (WTa5) were
used for the plasma loads tests. Samples have sizes of
12×12×5 mm. All samples were supplied by Plansee
AG (Austria), prepared and delivered from
Forschungszentrum Julich (Germany) [6]. Before each
plasma pulse, the surface temperature of one part of
pure W targets had been near a room temperature (RT).
Other part of samples had been preheated to 200 or
300°C with special heater [11]. Surface pattern, damage
and structure of tungsten samples have been analyzed
after plasma irradiation.
2.1. FEATURES OF PURE W UNDER HIGH
NUMBER OF REPETITIVE PLASMA
EXPOSURES
Samples of pure W were used for the high number
(up to 400 pulses) plasma loads tests. Before each
plasma pulse, the surface temperature of all targets had
been near room temperature (RT). Samples had very
small initial surface roughness (Ra 0.1 m, Rz 0.4 m,
Rmax 0.5 m) (Fig. 1). The compressive residual macro
stresses of -200 MPa was registered in surface layers
of targets in initial state. The microhardness is
Hv = 650 kg/mm2. Lattice parameter a0 0.31641 nm<aref
i.e. excess vacancies presents in structure. It agrees with
sign of asymmetry parameter (δВ 5%) associated with
excess number of vacancies complex [10].
The high number of plasma pulses result in surface
modification. The melting onset of edge of cracks was
observed whereas other surface remained non-melted
(see Fig. 1,b). Melted edges ejected some nm-particles.
Such small particles are able to be melted even for
rather small heat loads below the surface melting
threshold [14]. Thus, surface modification may cause
changes of physical properties of the surface layer and
thus influences the material behavior under the high
plasma heat loads [9, 10, 14]. Plasma irradiation results
in a symmetrical tensile stress in a thin sub-surface
layer. Measurements demonstrated that the maximal
value 350 MPa of residual stress in the thin sub-
surface layer appeared as result of the first plasma
pulses. Increasing the number of plasma pulses led to
some relaxation of residual stress (up to 250 MPa). At
the same time the microhardness of the exposed surface
was also slightly decreased (up to Hv = 450 kg/mm2)
with a further increase of the exposition dose. This
could be caused by annealing of vacancies in the
irradiated structure. It agrees with slightly increases of a
lattice parameter up to 0.31647 nm. The asymmetry
became negative and rose with an increase in the
number of pulses. Width of diffraction profiles (i.e. an
average dislocation density) weakly changed in the
surface layer.
Near linear rise of roughness is observed under
plasma irradiation with heat load below melting
threshold. The maximal values of roughness parameters
(Ra 0.2 m, Rz 1.2 m, Rmax 1.7 m) were
received after 400 plasma pulses. A network of macro-
cracks developed on the tungsten irradiated with 10
pulses of 0.45 MJ/m2 [10]. A rise of the irradiation
pulses number led to some growth of cracks width and
splitting of crack mesh (see Fig. 1). Both width and
depth of cracks were somewhat increased. The cracks
and growth of some edges of grains caused the
development of a surface profile.
a
b
Fig. 1. SEM images of the pure tungsten surface after 400
plasma pulses with different magnification
2.2. COMPARISON OF PURE W AND WTa5
EXPOSED TO PLASMA STREAMS
As it was shown earlier [10], the network of macro
cracks is formed on a pure W surface exposed to 100
plasma pulses below melting threshold at the initial base
temperatures of RT. Nevertheless, only separate major
cracks appear on WTa5 surfaces but the network of
cracks does not develop at the same conditions.
Therefore, the studies of the surface and sub-surface
layers pattern of pure W and WTa5 samples have been
carried out to reveal the damage of samples preheated to
different initial temperatures (Tin) and irradiated by 100
plasma pulses with heat loads below the melting
threshold (Figs. 2, 5).
The irradiation of pure W preheated to 200°C result
in an appearance of only small isolated cracks on
exposed surfaces. (see Fig. 2,a). A corrugated structure
of hills and cracks appeared on the surfaces of WTa5 at
the same base temperature (Fig. 3,a). High exfoliation
of the surface layer of WTa5 sample was also observed.
ISSN 1562-6016. ВАНТ. 2018. №6(118) 61
The cross-sections showed the crack appearance along
the surface. The maximum depth of cracks occurrence
was almost 300 µm for pure W (Fig. 4,a) and 200 µm
for WTa5 (Fig. 5,a).
a
b
Fig. 2. SEM images of W surfaces exposed at
Tin = 200°C (a) and Tin = 300°C (b).The length of the
marker line is 100 μm
a
b
Fig. 3. SEM images of WTa5 alloy surfaces exposed at
Tin = 200°C (a) and Tin = 300°C (b). The length of the
marker line is 100 μm
The SEM images demonstrated only small isolated
cracks on the exposed surfaces of pure W preheated to
300°C. Whereas large isolated cracks were observed on
the exposed WTa5 surface (see Figs. 2,b and 3,b). The
plasma irradiation at the initial temperature of 300°C
caused a decrease in the depth of cracks occurrence up
to 200 µm for pure W (see Fig. 4,b). However, the
cross-section of WTa5 sample showed that some cracks
penetrated from surface to a depth of 2 mm (see
Fig. 5,b).
a
b
Fig. 4. Cross-section of W targets exposed at
Tin = 200°C (a) and Tin = 300°C (b). The length of the
marker line is 100 μm
a
b
Fig. 5. Cross-section of the WTa5 alloy targets exposed
at Tin = 200°C (a) and Tin = 300°C (b). The length of
the marker line is 200 μm
CONCLUSIONS
Experimental studies of the macroscopic erosion of
double forging pure tungsten and tungsten-tantalum
62 ISSN 1562-6016. ВАНТ. 2018. №6(118)
alloy have been performed with a QSPA Kh-50 quasi-
stationary plasma accelerator. The heat loads on the
surface were 0.45 MJ/m2 (i.e., below the melting
threshold). The plasma pulse duration amounted to
about 0.25 ms.
The high number of repetitive plasma loads below
the melting threshold led to the clear degradation of
thermo-mechanical properties of the affected surface
layers of tungsten. A network of cracks appeared on the
exposed surfaces. The melting onset of edge of cracks
was observed whereas other surface remained non-
melted. The melted edges ejected the nm-particles. Such
small particles are able to be melted even for rather
small heat loads below the surface melting threshold.
Surface modification and development of cracks led to
an increases in roughness of the exposed surfaces. For
both double forging pure tungsten and tungsten-
tantalum alloy the cracks propagated to the bulk mainly
transversely and parallel to the irradiated surface.
ACKNOWLEDGEMENTS
This work has been carried out within the
framework of the EUROfusion Consortium and has
received funding from the Euratom research and
training programme 2014-2018 under grant agreement
No 633053. The views and opinions expressed herein
do not necessarily reflect those of the European
Commission. This work has been performed under
EUROfusion WP PFC. This work has been also
supported by the National Academy Science of Ukraine,
under project X-4-3/2018 and NMRT-2/2018.
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Article received 15.10.2018
ОСОБЕННОСТИ ЭРОЗИИ ВОЛЬФРАМА И СПЛАВА WTa5, ОБЛУЧЕННЫХ
ПОВТОРЯЮЩИМИСЯ ПЛАЗМЕННЫМИ НАГРУЗКАМИ КСПУ НИЖЕ ПОРОГА ПЛАВЛЕНИЯ
В.А. Махлай, С.С. Геращенко, Н.Н. Аксенов, О.В. Бырка, И.Е. Гаркуша, С.В. Малыхин, С.В. Суровицкий,
Н.В. Кулик, В.В. Стальцов, С.И. Лебедев, П.Б. Шевчук, M. Wirtz, М.Я. Садовский
Изучены повреждения деформированного двойной ковкой чистого вольфрама (W) и с легирующей
5 об.% добавкой тантала (WTa5) при экспериментальном моделировании условий переходных процессов в
ИТЭР (тепловая нагрузка на поверхность 0,45 МДж/м2, длительность импульса 0,25 мс) в
квазистационарном плазменном ускорителе КСПУ Х-50. Облучение мишеней плазмой проводили при
комнатной начальной температуре и с подогревом до 200 и 300°C. В результате плазменного воздействия
появлялись большие и мелкие трещины. Большое количество повторяющихся плазменных нагрузок ниже
порога плавления привело к явной деградации термомеханических свойств поврежденных
приповерхностных слоев вольфрама. Представлен сравнительный анализ распространения трещин в объем
для W- и WTa5-образцов.
ОСОБЛИВОСТІ ЕРОЗІЇ ВОЛЬФРАМУ ТА СПЛАВУ WTa5, ОПРОМІНЕНИХ
ПОВТОРЮВАЛЬНИМИ ПЛАЗМОВИМИ НАВАНТАЖЕННЯМИ КСПП НИЖЧЕ ПОРОГА
ПЛАВЛЕННЯ
В.О. Махлай, С.С. Геращенко, М.М. Аксьонов, О.В. Бирка, І.Є. Гаркуша, С.В. Малихін, С.В. Суровицький,
М.В. Кулик, В.В. Стальцов, С.І. Лебедєв, П.Б. Шевчук, M. Wirtz, М.Я. Садовський
Вивчено пошкодження деформованого подвійною ковкою чистого вольфраму (W) та з легуючою 5 об.%
домішкою танталу (WTa5) при експериментальному моделюванні умов перехідних процесів в ІТЕР (теплове
навантаження на поверхню 0,45 МДж/м2, тривалість імпульсу 0,25 мс) у квазістаціонарному плазмовому
прискорювачі КСПП Х-50. Опромінення мішеней плазмою проводили при кімнатній початковій температурі
та з підігрівом до 200 та 300°C. В результаті плазмового впливу з’являлися великі й маленькі тріщини.
Велика кількість повторюваних плазмових навантажень нижча порога плавлення привела до явної
деградації термомеханічних властивостей пошкоджених приповерхневих шарів вольфраму. Представлено
порівняльний аналіз розповсюдження тріщин в об'єм для W- і WTa5-зразків.
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