Radiation Blistering Research Articles

The role of inert gases in first wall phenomena in fusion devices

Abstract The first wall surfaces of fusion devices will be exposed to bombardment by inert gaseous projectiles such as helium. The flux, energy, and angular distribution of the helium radiation will depend not only on the type of device but also on its design parameters. For near term tokamak devices, the first wall surface phenomena caused by helium bombardment that appear to be quite important are physical sputtering and radiation blistering. Examples of these processes for a number of first wall candidate materials are discussed. While the physical sputtering phenomenon is understood, the mechanism of blister formation is not yet fully comprehensible. The various models proposed for radiation blistering of metal during helium bombardment is critically reviewed in the light of most recent experimental results.

Observations of a fcc helium gas-bubble superlattice in copper, nickel, and stainless steel

Abstract Transmission electron microscopy is used to investigate the spatial arrangement of the small gas bubbles produced in several fcc metals by 30 keV helium ion irradiation to high dose at 300 K. In what is a new result for this important class of metals it is found that the helium gas bubbles lie on a superlattice having an fcc structure with principal axes aligned with those of the metal matrix. The bubble lattice constant al , is measured for a helium fluence just below the critical dose for radiation blistering of the metal surface (∼4 ± 1017 He/cm2). Implantation rates are typically ∼ 1014 He ions cm−2 sec−1. The values of al obtained for copper, nickel and stainless steel are (7.6 ± 0.3) nm, (6.6 ± 0.5) nm and (6.4 ± 0.5) nm respectively. Above the critical dose the bubble lattice is seen to survive in some blister caps as well as in the region between blisters. Bubble alignment is also observed in the case of hydrogen bubbles produced in copper by low energy proton irradiation to high fluence ...

A fracture model of radiation blistering

The formation process of blisters is interpreted by a fracture model on the basis of the stress fields around a lenticular bubble calculated in a previous paper. This model implicitly presumes a microcrack nucleated at a depth near the projected range of the ions. Two factors are separated theoretically to explain the blister formation: One is a geometrical factor which depends only on the ratio of size to depth, from a free surface, and the other factor is proportional to the square of the ratio between the internal gas pressure of the bubble to plastic yield stress of the target materials, depending entirely on the physical and chemical properties of the materials and gas atoms. The relation between the blister diameter and the cover thickness must be basically linear as expected from the first factor, but is modulated by the second factor, giving a slight departure from linearity as observed by experiment. The ratio of the gas pressure to the yield stress must be 0.02–0.2 in magnitude and depends on the ion energy and the target materials. This value leads to an estimation that the amount of gas atoms contained in the blister is about 10% of the injected ions. Griffith’s criterion for the crack propagation in the subsurface layer with taking into account of ductility of the materials near the crack tip was derived, and showed that the estimated internal pressure of the blister is far smaller than the necessary pressure to satisfy the criterion. The objections against the gas-pressure model were criticized on the basis of the present model.

Helium gas bubble lattices in face-centred-cubic metals

ION irradiation of metals with helium or hydrogen isotopes commonly results in the formation of microscopic gas bubbles. At very high doses, radiation blistering and related phenomena can cause severe damage to surfaces1. Much research has been stimulated by the need to find materials with acceptable erosion and gas loading properties for use in future controlled thermonuclear reactors. Bubble formation is also important in fission-reactor fuel technology and other applications2,3. The underlying bubble structure of face-centred-cubic (f.c.c.) metals has remained largely unknown, although much has been done on depth profiling light gases implanted to high doses (see, for example, refs 3–5). Inert-gas bubbles lying on a space lattice have been reported previously only for the body-centred-cubic (b.c.c.) metal molybdenum6,7. There have been many observations, mainly for b.c.c. metals, of the similar ordering of voids produced by particle irradiation8,9. The void lattice spacing is typically 5–10 times that found for bubbles (∼5 nm). We report here on the bubbles produced in several f.c.c. metals by 30 keV helium-ion irradiation to a level just below the critical dose for blistering. A new result for this important class of metals is that the helium gas bubbles lie on a superlattice having an f.c.c. structure with principal axes aligned with those of the matrix.

Depth distribution of cavities in 20- and 500-KeV4 He+-irradiated nickel

Studies on depth distribution of damage and of cavities (voids and bubbles) in ion irradiated metals are of importance for an understanding of the mechanisms of radiation blistering and are of general interest to the field of radiation damage.The present paper describes transmission electron microscopy results on depth distribution of cavities and of dislocation damage in nickel irradiated at 500°C with 20- and 500-keV 4He+ ions. The results are compared with calculated projected range and damage energy distributions.High purity (99.995%) annealed polycrystalline nickel foils were irradiated at 500°C with either 20- or 500-keV 4He+ ions to total doses of 2.9 x 1016 and 1 x 1017 ions/cm2, respectively. Thin foils suitable for transmission electron microscopy were prepared from the irradiated samples by a transverse sectioning technique described elsewhere, which allows one to obtain depth distribution of damage and of bubbles from a single specimen.Figure 1 shows typical bright field transmission electron micrographs of the plated and irradiated regions of annealed polycrystalline nickel irradiated at 500°C with 500-keV 4He+ ions to a dose of 1 x 1017 ions/cm2.

In-situ detection of radiation blistering and dynamic deuterium depth profiling during D + bombardment of solids

An in-situ method, based on the scattering of laser light at a non-specularangle from the irradiated surface, is used to detect the onset of radiation blistering of metal surfaces under deuteron bombardment. At the same time the dynamic depth profile of deuterium in the near surface region of the target is followed without interruption over the course of implantation by observing the energy spectra of tritons and protons from the D-D reaction initiated by the primary deuteron beam. The use of a beam having a gradation in current density across the target area allows a variety of effects to be studied in a single irradiation of the particular sample. The use of these techniques is illustrated with reference to an investigation of radiation blistering in microcrystallite copper at 350 K.

Radiation Blistering of Vanadium Irradiated with 40keV4He Ions

(1977). Radiation Blistering of Vanadium Irradiated with 40keV 4He Ions. Journal of Nuclear Science and Technology: Vol. 14, No. 10, pp. 765-767.

The dynamics of radiation blistering and near-surface deuterium retention in deuteron-irradiated copper

The effect of radiation blistering on the retention of deuterium in the near-surface region of 200-keV d+ irradiated Cu at 350 K has been studied. Blistering is detected using an in situ method based on the scattering of laser light. The incident deuteron beam is used both for implantation and to obtain the dynamic deuterium depth profile. Discrete blisters of approximately 4-μm average diameter are found to form rapidly at a well-defined fluence of (7±1) ×1018d+/cm2. The rate deuterium accumulates in the first 0.4 μm is found to fall dramatically at the onset of blistering from a steady value, of ∼2% of the implantation rate, to nearly zero. Typical D : Cu loadings at the critical dose for blistering are ∼1 at.%.

Radiation Blistering of Vanadium Irradiated with 40 keV 4He Ions

Radiation Blistering of Vanadium Irradiated with 40 keV 4He Ions

Facies of ion bombarded surfaces

Observations made in the optical examination of a variety of brittle materials subjected to bombardment by 140 keV protons, deuterons, and helium ions are summarized. Among the materials studied were commercial glasses, carbides, oxides, silicon nitride, titanium boride, and carbon. In most cases, when swelling occurred, it was by the introduction of porosity. The radiation blistering appeared to take place by fracturing in the porous layer under surface stress rather than by plastic deformation under the gas pressure of segregated implanted gas.

Radiation blistering of Nb Implanted sequentially with helium ions of different energies (3–500 keV)

Radiation blistering of Nb Implanted sequentially with helium ions of different energies (3–500 keV)

Radiation blistering of Nb Implanted sequentially with helium ions of different energies (3–500 keV)

Cold rolled, polycrystalline niobium samples were irradiated at room temperature with 4He + ions sequentially at 14 different energies over an energy range from 3–500 keV. The dose for each energy was chosen to give an approximately uniform concentration of helium between the implant depths corresponding to 3 keV and 500 keV. In one set of experiments the irradiations were started at the Kurchatov Institute with 3-keV 4He + ions and extended up to 80 keV in several steps. Subsequently, the same target area was irradiated with 4 He + ions at Argonne National Laboratory (ANL) starting at 100 keV and increased to 500 keV in steps of 50 keV. Another set of irradiations was started at ANL with 500-keV 4 He + ions and continued with ion energies decreasing to 100 keV. Subsequently, the same area was irradiated at the Kurchatov Institut starting at 80 keV and continued with ion energies decreasing to 3 keV. Both sets of irradiations were completed for two different total doses, 0.5 C cm −2 and 1.0 C cm −2.

Dose dependence of the photon emission from sputtered aluminum atoms during helium irradiation

Polycrystalline aluminum samples are irradiated with 40-keV He+. At moderate target temperatures (∼0.3Tm) a prominent and distinct enhancement of the light intensity from sputtered excited aluminum atoms is observed after implantation to a critical dose of 4×1017 He+/cm2. It is shown that this effect is associated with a sudden increase in the erosion rate of Al and in the surface exfoliation due to radiation blistering. At higher target temperatures (∼0.7Tm) a less pronounced increase in the photon intensity and a different surface structure is observed.

Proton-bombardment–induced blistering of vanadium

Samples of annealed and severely cold-rolled vanadium were bombarded at room temperature with 150-keV H+ ions at fluxes from 1.2×1015 to 1.2×1016 H+/cm2 sec to doses of from 3.6×1017 to 3.2×1019 H+/cm2. All samples irradiated to doses greater than 1.1×1019 H+/cm2 exhibited blistering in spite of the fact that temperatures never exceeded the peak miscibility gap temperatures below which vanadium hydride is stable with respect to gaseous hydrogen even at low hydrogen partial pressures. Niobium also blistered under similar conditions. This unexpected observation must be reconciled by any acceptable theory of radiation blistering.

Crazing of graphite and lithium niobate on ion bombardment

Crazing patterns extending beyond the areas of natural graphite crystals bombarded with 140-keV H+, D+, or He+ ions were examined under the interference microscope and identified as elongated narrow protuberances. They are attributed to radiation blistering and gas migration along dislocations. Similar patterns were found on ion-bombarded lithium niobate plates.

Blisters and deckeldicke

A relatively new area in the application of ion beams to materials is the investigation of the phenomenon of radiation blistering which occurs when light gaseous ions, usually helium, are implanted in surfaces to high doses. This results in surface blistering and exfoliation.

Radiation blistering of structural materials for fusion devices and reactors

Radiation blistering can be an important erosion process when the structural components of controlled thermonuclear fusion devices or reactors are exposed to the impact of energetic particles leaving the plasma region. A brief review of some of the important parameters governing the radiation blistering process is given. Erosion rates associated with helium blistering in V, Nb and Type 304 stainless steel are reported for different irradiation temperatures and different projectile energies.

Effect of Temperature on First-Wall Erosion by Radiation Blistering

The effect of target temperature on blister formation and the erosion rates associated with helium blistering has been investigated for vanadium and Type 304 stainless steel. The irradiation temper...

Interaction of Light Ions with Surfaces

The interaction of the light ions hydrogen and helium with surfaces have a number of special features. Their low mass results in low sputtering coefficients, and long range in the solid. In addition both atoms have high diffusion coefficients in most metals leading to high release rates of implanted atoms at high doses. Despite the high diffusion coefficient both types of atom can be readily trapped at damage sites in the lattice, resulting in large concentrations of gas accumulating in the metal. This causes the now familiar phenomenon of radiation blistering. This review attempts to outline the importance of these different factors, to correlate the observed topographical changes due to radiation blistering with gas release, and to compare and contrast the behaviour of hydrogen and helium ions incident on surfaces.

Radiation Blistering in Niobium

Radiation Blistering in Niobium