Blister Skin Thickness Research Articles

Grazing-incidence electron microscopy of surface blisters in single- and polycrystalline tungsten formed by H +, D + and He + irradiation

Blisters on single- and polycrystalline tungsten surfaces formed by hydrogen and helium ion irradiation were investigated by grazing-incidence electron microscopy (GIEM) with an ultra-high-voltage transmission electron microscope. It was found that the blister skin thickness formed by D + irradiation of polycrystalline tungsten (PCW) was considerably larger than the calculated ion range of the implants; however, this skin thickness (or blister depth) is not related to the pre-existing grain boundaries in the PCW. Blister formation was also observed with GIEM for single crystal tungsten (SCW) irradiated with H +, D +, and He +. The critical ion fluence for blister formation in SCW is estimated to be ∼10 23 H +(D +)/m 2 for H(D) and ∼10 21 He +/m 2 for He. The size of the blisters and their skin structure depends on the irradiating conditions. Typical skin thickness was about 50–150 nm. Based on the assumption that gas particles (H 2, D 2, and He) accumulate within the blisters during H +, D +, and He + irradiation, the GIEM measurements provide a means to derive an estimate of the amount of gas so accumulated, by reproducing the observed blister shapes with finite element method (FEM) calculations. From the GIEM images and FEM calculations we have estimated the number of implanted ions being retained in the blisters, and compared these amounts with published retention measurements. A mechanism for the blister formation is proposed based on the present results.

Substructures of Gas-Ion-Irradiation-Induced Surface Blisters in Silicon Studied by Cross-Sectional Transmission Electron Microscopy

Internal structures of surface blisters and their precursors in Si formed by H + , D + and He + irradiation were examined by cross-sectional transmission electron microscopy (XTEM). The skin structures of H + -D + - and He + -blisters reflected the difference in the damage accumulation, and chemical interaction between the implant ion and silicon. These differences had a direct influence on the defect structures of the damaged layer, which played essential roles in the blistering mechanisms. It was found that blister skin thickness derived by grazing incidence electron microscopy (GIEM) and electron energy-loss spectroscopy, (EELS) was underestimated compared to direct measurement by XTEM. The origin of this discrepancy is discussed.

Studies on modification of some first wall materials using 3–6.8 MeV He ions

Because very few results are reported in the MeV region, we have started a systematic investigation concerning the fluence and energy dependence of blistering induced in some useful materials for the first wall (stainless steels, Ni, Cu, Mo). They have been irradiated with 3.0, 4.7 and 6.8 MeV He ions. The irradiation effects have been investigated by means of a TEMSCAN-200-CX electron microscope and two metallographic microscopes. Irradiation phenomena as sponge- and wave-like structures, submicronic cracks, multilayer flaking, micro-conglomerates, secondary blisters, microcraters were observed. An interesting effect is the amorphous phase in the Ti-modified austenitic steel 12KH18N10T, phase formatted during irradiation with 6.8 MeV He + ions up to a dose of crater occurrence (7×10 18 ions per cm 2), the temperature of specimens (100 μm thick) being maintained during irradiation in the range 30–60°C. The X-ray microanalysis shows the presence of the major alloy elements in the amorphous area, whereas in that embedding a microcrystallite it is to be noticed the Ni depletion and the presence of Si and Mo. A potential explanation of the energy dependence of average blisters diameter d and blister critical dose could be stressed-induced model, because, in our cases (medium energy He ions), d– t m , where t is the blister skin thickness. For our high energy data, an m=1.8 value is relatively convenient, except Mo, where m=1.5 is more suitable.

Surface Microstructure of High Temperature Beryllium Implanted with Deuterium

ABSTRACTWe have investigated implantation temperature effects on the formation of blisters on the surface of Be foils implanted with low energy, 1.5 keV, deuterium ions to doses ranging from 3×1016 to 1.2×1018 ions cm-2, a dose exceeding by far the saturation (≈1.8×1017 ions cm-2: 30% at.). The implantation temperature was varied from 293 K (RT) to 983 K. The samples have been characterized by scanning electron microscopy (SEM). For saturated samples, blisters were present even at high temperatures, viz 983 K, and no blisters were found for samples implanted below 20% at.. However, on samples in which a dramatic grain growth has been observed, blisters were found to decorate the grain boundaries and to interconnect with each other. The average blister diameter increases with increasing temperature, thus indicating the thermodynamical aspect of blister formation and coalescence. On the other hand, for low temperature (473 K), the surface structure that has developed is similar to that at RT, except for an increased most probable blister diameter and blister density, and there was no indication that the blisters ruptured. The blister skin thickness agrees well with the projected range of the implanted ions. Over-saturated samples at RT retained only ≈30% at., corroborating the observations that some blisters formed on already ruptured ones.

Radiation blistering in inconel-625 due to 100 keV helium ion irradiation

The objective of this study was to determine whether the change of angle of incidence of an ion beam impinging on surface blisters during their growth phase (before exfoliation) could influence the blister skin thickness and the blister crater depth. Polished, polycrystalline Inconel-625 samples were irradiated at room temperature and at normal incidence to the major sample surface with 100 keV helium ions to a total dose of 6.24 × 10 18 ions/cm 2 . The results revealed that many exfoliated blisters leave craters which have two or three concentric pits. The blister skin thickness near the center of the blister was found to agree well with the calculated projected range of 100 keV He ions in nickel. However, the blister skin thickness of some exfoliated blisters along the edge of the fracture surface showed different thicknesses. A model is proposed to explain the observed blister crater/blister skin fracture features in terms of a change of angle of incidence of the incident ions to the surface during the growth phase of surface blisters.

SAXS study of molybdenum irradiated with helium ions

Defects produced by helium ion irradiation have been investigated by means of small-angle X-ray scattering (SAXS) measurements, transmission electron microscope (TEM) and scanning electron microscope (SEM) observations. He + ions with projectile energy of 2 MeV were implanted in thin high-purity molybdenum foils with dose rates of 7–56 μA cm −2 up to total doses of 0.43–3.46 × 10 18 ions cm −2. The critical fluence producing blisters and the blister skin thickness were measured to be about 0.5 × 10 18 ions cm t-2 and 2.8 ± 0.4 μm, respectively, from SEM observations. Two types of bubbles were observed by TEM. The angular dependence of SAXS intensity was explained by the superposition of three Gaussian-shaped scattering curves, suggesting three different types of irradiation defects. Type II, which had a dimension of 4–7 nm, was identified with polygonal bubbles observed by TEM. This type appeared beyond the critical dose of 0.6 × 10 18 ions cm −2 . Type III, which had a dimension of 0.6–2.7 nm, was identified with finer bubbles observed by TEM and distinguishable from type II. The SAXS results have been applied to evaluate quantitatively the kinetics of formation of these bubbles.

On the correlation of blister diameter and blister skin thickness in helium-ion-irradiated Nb

On the correlation of blister diameter and blister skin thickness in helium-ion-irradiated Nb

On the correlation of blister diameter and blister skin thickness in helium-ion-irradiated Nb

A systematic study of the correlation between blister diameter and blister skin thickness has been performed for helium-ion irradiation of monocrystalline and polycrystalline Nb for ion energies ranging from 20 to 500 keV. The results indicate that a relationship Dmp∝t1.50 between the most probable blister diameter, Dmp, and blister skin thickness, t, which has been suggested by other authors, does not exist for the various types of Nb targets studied. For example, for room-temperature irradiation of annealed polycrystalline Nb the experimentally determined relationship is Dmp=10.3t1.22. Furthermore, the D-t relationship was found to depend on the irradiation temperature in contrast to theoretical predictions by the lateral stress model of blister formation. These results do not appear to support the lateral stress model which predicts the relationship D∝t1.5. However, the experimentally determined relationships can be explained in part by the gas pressure model of blister formation.

Correlation of blister diameter and blister skin thickness for helium-bombarded V

A correlation of the most probable blister diameter Dmp and mean blister skin thickness t for helium-ion-irradiated annealed polycrystalline and monocrystalline V (100) surfaces yields a relationship Dmp∝t0.89. This relationship is different from the relationship Dmp∝t1.5 suggested by other authors for vanadium. The relationship observed in the present studies does not support the lateral stress model for blister formation, which predicts Dmp∝t1.5. Evidence is presented for blister formation by internal gas pressure, as suggested earlier by the present authors.

Helium Blistering in Metals

In a fusion reactor, various parts will be exposed to an important flux of helium atoms. Under certain conditions this will cause blistering resulting in surface erosion and plasma contamination. We discuss measurements of the following blister parameters: blister skin structure and thickness, helium depth distribution, and swelling. These data refer mainly to 10-20 ke V He blistering of Nb and Cu where the blister skin is apparently two times thicker than in the “gas pressure” model. However, the observation of a depletion at the center of the helium distribution, of bubbles in the skin, and of ∼ 40 percent swelling allow us to conclude that this model is still valid.

The significance of a correlation of blister diameter with skin thickness for Ni and Be for blistering models

It has been sugguested that large lateral stresses introduced in an ion implanted surface layer may cause elastic instability and buckling of the implant layer (blister formation), and result in a relationship D mp ∝ t 3 2 between the most probable blister diameter D mp and the blister skin thickness, t, for metals such as Be, V, stainless steel, Nb and Mo. To test this relationship a systematic study of the correlation between blister diameter and skin thickness for helium blistering of annealed polycrystalline Ni and Be ahs been conducted for helium ion energies in the range of 15–300 keV. For beryllium the relationship between D mp (μm) and t(μm) can be fitted by the expression D mp = 24.6 t 1.25 whereas for nickel a best fit is obtained for the expression D mp = 1.24 t 1.15. These results, together with our earlier results for Nb and V show that the relationship between D mp and t is strongly dependent on the type of metal studied and do not support the lateral stress model for blister formation.

Correlation between blister skin thickness, the maximum in the damage-energy distribution, and projected ranges of helium ions in Nb for the energy range 10–1500 keV

The skin thickness of blisters formed on polycrystalline niobium under irradiation at room temperature by 4He + at energies of 15 to 80 keV have been measured. Similar measurements were conducted for 10-keV 4He + irradiation at 500°C to increase blister exfoliation, and thereby allow examination of a larger number of blister skins. For energies less than 100 keV the skin thicknesses are compared with both the projected range and the damage-energy distributions constructed from moments interpolated from Winterbon's tabulated values. The projected ranges and damage-energy distributions have also been computed with a Monte-Carlo program. For energies greater than 100 keV the projected ranges of 4He +in Nb were calculated using either Brice's formalism or the one given by Schiøtt. The thicknesses of blister skins for 60 and 80-keV irradiations, and those reported earlier for 100 to 1500-keV irradiations correlate well with calculated projected ranges. For irradiation energies less than 60 keV the measured thicknesses are greater than the calculated ranges.

Correlation between blister skin thickness, the maximum in the damage-energy distribution, and projected ranges of helium ions in Nb for the energy range 10–1500 keV

The skin thickness of blisters formed on polycrystalline niobium under irradiation at room temperature by 4 He + at energies of 15 to 80 keV have been measured. Similar measurements were conducted for 10-keV 4 He + irradiation at 500°C to increase blister exfoliation, and thereby allow examination of a larger number of blister skins. For energies less than 100 keV the skin thicknesses are compared with both the projected range and the damage-energy distributions constructed from moments interpolated from Winterbon's tabulated values. The projected ranges and damage-energy distributions have also been computed with a Monte-Carlo program. For energies greater than 100 keV the projected ranges of 4 He + in Nb were calculated using either Brice's formalism or the one given by Schiøtt. The thicknesses of blister skins for 60 and 80-keV irradiations, and those reported earlier for 100 to 1500-keV irradiations correlate well with calculated projected ranges. For irradiation energies less than 60 keV the measured thicknesses are greater than the calculated ranges. L'épaisseur des parois de cloques formées sur du niobium polycristallin sous irradiation à la température ambiante par des ions He + d'énergies comprises entre 15 et 80 keV a été mesurée. Des mesures similaires ont été conduites pour des ions 4 He + de 10 keV irradiant du niobium à 500°C afin d'accroître l'exfoliation des cloques et par suite de permettre l'examen d'un grand nombre de parois de cloques. Pour des énergies inférieures à 100 keV les épaisseurs des parois de cloques sont comparées à la fois au parcours projeté et aux distributions dommage-énergie construites à partir des moments interpolés à partir des valeurs de Winterbon. Les parcours projetés et les distributions dommage-éinergie ont été calculés également avec un programme Monte-Carlo. Pour des énergies supérieures à 100 keV les parcours projetés de 4 He + dans Nb ont été calculés en utilisant soit le formalisme de Brice, soit celui proposé par Schiøtt. L'épaisseur des parois de cloques pour des irradiations de 60 et 80 keV et celles rapportées antérieurement pour des irradiations de 100 à 1500 keV sont en bonne corrélation avec les parcours projetés calculés. Pour des irradiations d'énergie inférieure à 60 keV les épaisseurs mesurées sont supérieures à celles des parcours calculés. An polykristallinem Niob wurde die Schichtdicke von Oberflächenblasen gemessen, die während der Bestrahlung mit 4 He + einer Energie zwischen 15 und 80 keV bei Raumtemperatur gebildet wurden. Ähnliche Messungen wurden nach einer 10 keV - 4 He + -Bestrahlung bei 500°C durchgeführt, bei der die Abblätterung der Oberflächenblasen zunimmt und dadurch eine Untersuchung vieler Schichten von Oberflächenblasen ermöglicht wird. Bei Energien unterhalb 100 keV wird die Schichtdicke mit der Projektion der Weglänge und der Verteilungskurve für die Strahlungsschadenenergie verglichen, die beide aus Momenten konstruiert wurden, welche aus tabellierten Winterbon sehen Werten interpoliert worden waren. Die Projektion der Weglänge und die Verteilungskurve für die Schadensenergie wurden ferner mit einem Monte-Carlo-Programm berechnet. Bei Energien oberhalb 100 keV wurde die Projektion der Weglänge von 4 He + in Niob entweder mit dem Briceschen oder dem Schiøttschen Formalismus berechnet. Die Schichtdicke der Oberflächenblasen bei einer 60 keV- und 80 keV-Bestrahlung und die Werte, die früher für eine 100 keV– bis 1500 keV-Bestrahlung mitgeteilt wurden, stimmen mit der Projektion der berechneten Weglänge gut überein. Bei Bestrahlung mit einer Energie unterhalb 60 keV ist die gemessene Dicke grösser als die berechnete Weglänge.

Correlation between blister skin thickness, the maximum in the damage-energy distribution, and projected ranges of He+ ions in metals: V

Correlation between blister skin thickness, the maximum in the damage-energy distribution, and projected ranges of He+ ions in metals: V

Correlation between blister skin thickness, the maximum in the damage-energy distribution, and projected ranges of He+ ions in metals: Nb

The skin thicknesses of blisters formed on niobium by helium-ion irradiation at room temperature for energies from 100 to 1500 keV have been measured. The projected ranges of helium ions in Nb for this energy range were calculated using either Brice’s formalism or the one given by Schiott. For the damage-energy distribution Brice’s formalism was used. The measured skin-thickness values corrleate more closely with the maxima in the projected-range probability distributions than with the maxima in the damage-energy distributions. The results are consistent with our model for blister formation and rupture proposed earlier.