Blistering,flaking and bubble formation in metal-metalloid metallic glasses bombarded with helium ions

The blistering and flaking behaviour of metallic glasses Fe₈₀B₂₀, Fe₄₀Ni₄₀B₂₀, Fe₄₀Ni₄₀P₁₄B₆ and Fe₄₀Ni₃₈Mo₄B₁₈ under helium ion bombardment at room temperature has been investigated. A trend of continuous layer-by-layer surface erosion of metallic glasses due to repetitive exfoliation was observed. Results as a function of projectile energy (50 keV ? E ? 150 keV) and helium current density (10–100 μ/cm₂) showed that the critical dose and the blister size dependence on these parameters is similar to crystalline solids. However, unlike in crystalline materials, cold work of Fe₄₀Ni₄₀P₁₄B₆ to 30% thickness reduction did not seem to affect the surface erosion behaviour. A comparative study of the same alloy Fe₄₀Ni₄₀P₁₄B₆ in amorphous and thermally crystallized forms showed about 50% higher resistance against blistering for the former. Microstructural investigations revealed helium bubble formation as a precursor stage to blistering but irradiation-induced partial crystallization was not observed for these metallic glasses.     

Helium irradiation of Ni-(Zr or Nb) metallic glasses: Blistering,flaking and bubble formation

NiZr and NiNb are potential metallic glasses for nuclear applications. We have studied blistering, flaking and bubble formation in Ni₆₄Zr₃₆, Ni₃₃Zr₆₇ and Ni₆₀Nb₄₀ glasses under helium ion bombardment at room temperature. The effect of projectile energy (50–150 keV), total dose (0.01–10 × 10¹⁸ ions/cm²), dose rate (10–100 μA/cm²) and thermal crystallization on critical dose for blistering and/or flaking, average blister diameter and development of surface topography was examined. The surface damage effects in metallic glasses were in general similar to those for crystalline materials with the notable exception that the critical dose values are higher by about 50–100% for metallic glasses. TEM investigations revealed irradiation induced partial crystallization of Ni₃₃Zr₆₇ glass. Metallic glasses Ni₆₄Zr₃₆ and Ni₆₀Nb₄₀ were stable under helium irradiation and have also shown very high resistance against blistering and/or flaking. The possible mechanisms of helium trapping in metallic glasses are also discussed.     

Graphite surface erosion by 100 keV helium and hydrogen bombardment

Surface erosion in pyrolytic graphite by 100 keV ⁴He⁺ and 200 keV H⁺₂ ion bombardment has been observed by scanning electron microscopy. The particle fluence ranged from 1 × 10¹⁷ to 5 × 10¹⁸ particles/cm². Although the surface is eroded at 1 × 10¹⁷ particles/cm² in helium bombardment, it is not eroded so heavily even at 5 × 10¹⁷ particles/cm² in hydrogen bombardment. In helium bombardment flaking is significantly observed at 1 × 10¹⁸ particles/cm², and a cone structure appears at 5 × 10¹⁸ particles/cm², which is produced after the first cover flakes off completely. In hydrogen bombardment at 1 × 10¹⁸ particles/cm², many circular blisters are formed which are sputtered off at 5 × 10¹⁸ particles/cm². The surface roughness of the target also affects the erosion.     

Tungsten Blister Formation Kinetic as a Function of Fluence,Ion Energy and Grain Orientation Dependence Under Hydrogen Plasma Environment

This work deals with the formation kinetic of tungsten (W) blisters under smooth plasma conditions, i.e. low hydrogen flux and energy in order to analyze the first stages of their formation. In addition, we focus on determining the W grain orientation where blisters grow preferentially. For this purpose, mirror-polished polycrystalline tungsten samples were exposed to hydrogen plasma under fixed hydrogen flux of 2.2 × 10²⁰ m^?2 s^?1, with a fluence in the range of?~?10²⁴ m^?2, ion energy of?~?20, 120 and 220 eV, and sample surface temperature of?~?500 K. The formation of blisters at the surface was investigated using SEM, AFM and EBSD to determine the size, the distribution and the orientation of grain where blisters are formed, respectively. The critical fluence for initiating blisters was established around 2.3 × 10²⁴ m^?2. The evolution of blister size distribution and density is discussed as function of fluence and ion energy. At lower ion energy, i.e. 20 eV, only nanoblisters (less than 150 nm) are observed whatever the fluence value (1.5 and 2.3 × 10²⁴ m^?2). At higher ion energy i.e. 120 and 220 eV, micrometric (~ few to tens of µm) blisters are observed and their density highly depends on fluence. We show that blisters can also be formed on (001) oriented grains contrarily to previous results from the literature where the (111) orientation seemed more favorable. Such information is of importance for tungsten based fusion tokamak operation and design.     

Preliminary observations of blistering of niobium by 1–15 keV helium ions

We have bombarded at room temperature polycrystalline targets of cold-rolled Marz grade niobium with beams of helium ions of 1, 5, 10 and 15 keV at doses varying from 0.1 to 10.0 C/cm². We have chosen the doses so as to obtain surfaces where the thickness removed by sputtering is respectively less than, comparable to, and greater than the implantation depths. The targets were not further treated beyond mechanical polishing. The vacuum during bombardment was 2 × 10^?8 torr. Blisters of 0.1 to 3.0 μm size have been observed. The blister covered area increases with dose up to a point, but at the higher doses the blisters, if any, are masked by a micro-relief of wide valleys, presumably sputtering-induced, and tiny pock-marks which could be small ruptured helium blisters.     

Blistering of niobium due to 0.5 to 9 keV helium and hydrogen bombardment

Blistering of well-annealed niobium single crystals due to 0.5 to 9 keV helium and hydrogen ion bombardment at temperatures between ?110°C and 1000°C has been investigated by Rutherford backscattering (RIBS) in double alignment and with a scanning electron microscope (SEM). For He bombardment blistering was observed by RIBS in the temperature range investigated for all energies above 1 keV. The critical dose at which blisters first appear is about 1 to 2 × 10¹⁷ incident He ions per cm². It increases slightly with increasing ion energy and with decreasing target temperature. Blisters of 500 to 5000 Å in diameter were found. The depth at which the blisters develop increases from ≈ 180 Å for 1 keV to 1100 Å for 9 keV He ions. It is a factor of ≈ 3 larger than the theoretical mean range of the ions in amorphous material. Above ≈ 600°C grain boundaries develop extending also into the unbombarded region. For hydrogen bombardment no blistering could be observed at room temperature up to doses of 2 × 10¹⁹ ions per cm².     

Room temperature aging effects of blistering and surface roughening after Ar+ ion bombardment on Mo single crystals

300 keV Ar⁺ ions are bombarded on the surface of Mo single crystals to doses of $\text{1 × 10}{}^{17}$, $\text{6.2 × 10}{}^{17}$, $\text{1 × 10}{}^{18}$ and $\text{2.8 × 10}{}^{18}$ ions/cm². After bombardment with $\text{6.2 × 10}{}^{17}$ ions/cm², blistering is observed after room-temperature aging of less than 100 days, in spite of the large sputtering yield. Disappearance of the formed blisters and concurrent surface roughening are observed with further aging. For higher dose bombardments, only surface roughening is observed without prior formation of blisters. Distribution of the injected ions associated with large sputtering yield is derived. From this distribution, the critical amount of injected ions required for blistering to occur is estimated to be equal to or less than $\text{3.4 × 10}{}^{17}$ ions/cm².     

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 ∼10²³ H⁺(D⁺)/m² for H(D) and ∼10²¹ He⁺/m² 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 (H₂, D₂, 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.     

Argon ion impact desorption cross sections of chlorine and carbon from molybdenum

Total desorption cross sections have been measured for Cl (σ_Cl) and C(σ_C) on molybdenum by argon ion bombardment for an incidence angle of 60° from the surface normal. For the bombardment an ion gun with low current density (i₀ ~ 1 × 10 ^?7 A cm^?2) at low system pressure (~10^?9 Torr) was used. The detection was performed by AES and the data were sensitivity factor corrected. The AES analysis of the surface after adsorption showed that Mo, C and Cl contributed to more than 94% of the atomic composition. With known i₀, it is possible to obtain σ from the adsorbate signal vs ion bombardment time curve. For ion energies between 0.2 keV to 1.0 keV the measured value for σ_Cl and σ_C are 0.5?3 × 10^?15 cm² and 0.2?4 × 10^?15 cm², respectively. The possible effects of the surface roughness due to prebombardment are discussed.     

The structure of graphite bombarded with light,gaseous ions

Natural and highly-oriented pyrolytic graphite crystals have been injected with helium, deuterium and carbon ions at energies up to 100 keV and doses up to 10¹⁸ ions/cm². This results in twinning in thick samples, the density of twinning increasing with energy and dose, and varying with target temperature. Twinning is shown to provide an important plastic deformation mode and a model of twinning related to the depth variation of atomic displacements is presented: a method of calculating the strains involved is discussed. It is suggested that surface distortions observed in other graphites originate in the same way. Measurements show that some gas is retained in the samples, but its direct role is uncertain. Very thin (thickness ? 0.1 μm) crystals blister under gas-ion bombardment and are demonstrated to retain sufficient gas to produce the blisters observed. It is shown that the blisters can grow laterally by cleavage in graphite, rather than by increasing their curvature and bursting as in metals. The origin of these blisters is obscure.     

Thermal annealing behavior of hydrogen and surface topography of H2+ ion implanted tungsten

Tungsten (W) has been proposed as a plasma-facing material in fusion reactors due to its outstanding properties. Degradation of the material properties is expected to occur as a result of hydrogen (H) isotope permeation and trapping in W. In this study, two polycrystalline W plates were implanted with 80 keV H₂⁺ ions to a fluence of 2 × 10²¹ H⁺/m² at room temperature (RT). Time-of-flight secondary ion mass spectrometry (ToF-SIMS), focused ion beam (FIB), and scanning electron microscopy (SEM) were used for sample characterization. The SIMS data shows that H atoms are distributed well beyond the ion projected range. Isochronal annealing appears to suggest two H release stages that might be associated with the reported activation energies. H release at RT was observed between days 10 and 70 following ion implantation, and the level was maintained over the next 60 days. In addition, FIB/SEM results exhibit H₂ blister formation near the surface of the as-implanted W. The blister distribution remains unchanged after thermal annealing up to 600 ?C.     

Corrosion Resistance Modification of AISI 304 Stainless Steel Using Argon Ion Bombardment

Ion implantation has been widely used as a surface modification technique to improve surface properties. In this work, argon ions of 30 keV energy have been implanted into AISI 304 stainless steel at different fluences ranging from 3 × 10¹⁷ to 1 × 10¹⁸ Ar⁺/cm². The surface bombardment with inert gases mainly produces structural changes and modify topography and morphology of the surface. The AFM analysis of implanted samples clearly shows significant change in surface. In order to evaluate the effect of the ion bombardment on the corrosion behavior, potentiodynamic tests were performed. The results show that the corrosion resistance of the samples strongly depends on the implantation fluences.     

Recovery of Technetium with Active Carbon Column in Partitioning Process of High-Level Liquid Waste

Blistering and exfoliation of several tungsten alloys, which cause surface damage, were investigated using 3-MeV He-ion bombardment at room temperature (RT), 400, and 550°C. The alloy W-0.3TiC, which was fabricated by the mechanical alloying method and had an ultrafine grain structure, a K-doped W alloy, and pure W metal were examined to explore a way of suppressing the surface damage. In RT irradiation, surface exfoliation occurred at a fluence of (1–2) × 10²² He/m² in all the tested specimens. In the case of 550°C irradiation, surface exfoliation was observed above 2 × 10²² He/m² irradiation in pure W and K-doped W, but no surface exfoliation was observed in W-0.3TiC up to a fluence of 2 × 10²³ He/m². The results showed that W-0.3TiC showed a higher resistance to surface exfoliation by He-ion bombardment and the level of resistance was temperature-dependent. The surface morphology, cross-sectional morphology, and microstructure were characterized by transmission electron microscopy. Helium thermal desorption spectrometry was carried out to determine the mechanism whereby the surface attained resistance to the damage through He-ion bombardment. The improvement in the resistance to the surface exfoliation could be attributed to the ultrafine grain structure and the intergranular enhanced He diffusion behavior of the MA-processed material.     

Ar离子辐照的非晶态合金表面发泡扫描电镜观测

１５０、１９５和３００ｋｅＶＡｒ离子在室温下辐照非晶态合金Ｃｏ７０．２Ｆｅ３． ９Ｎｄ３．９Ｓｉ１４Ｂ８和Ｃｏ６６Ｆｅ４．５Ｖ２．２５Ｎｉ２．２５Ｓｉ１０Ｂ１５，扫描电镜在一定的辐照剂量范围观测到了表面发泡形成，发泡形成的临界剂量和直径随离能量增加而增加。Ａｒ离子能量高于１９５ｋｅＶ时，发泡和发泡破裂是主要的表面损伤现象，而在１５０ｋｅＶＡｒ离子辐照下，未观测到发泡破裂。     

D2 gas-filled blisters on deuterium-bombarded tungsten

Most of spherical blisters formed by deuterium (D) bombardment (38 eV/D) up to 3 × 10²⁴ D/m² at 300 K on polycrystalline tungsten are fully elastic deformations. This has been proven by opening individual blisters with a focused ion beam and in situ observation of their complete relaxation by scanning electron microscopy. The D₂ gas filling is confirmed by observing simultaneously the D₂ puff. The gas pressure is causal for the stability of such spherical blisters after implantation and the gas release leads to sudden relaxation. The dilatation of the blister cap by trapped D can be excluded as cause for the blisters.     

Deuteron and helium ion irradiation of ceramic coatings on Nb-1% Zr

The surface damage to insulating barium alumino-silicate glass coatings due to irradiation by 100- and 250-keV deuterons and helium ions at room temperature and at 300° C has been studied. Blisters are observed after irradiation at room temperature with both deuterons and helium ions with energies of 100 keV and 250 keV. For deuteron irradiation a large fraction of the blisters have diameters which are approximately 3 to 5 times larger than the diameter observed with helium ions for identical irradiation conditions, but the density of blisters is nearly an order of magnitude lower. For irradiation at 300° C, no blisters are observed with either type of particle. The sharp rise in permeation rate with temperature is thought to be responsible for this behavior. The blister skin thicknesses have been measured and correlated with calculated projected-range values.     

Ion bombardment of insulators

Some of the effects which were observed when some stable inorganic insulators were subjected to ion bombardment are described. Most of the results were for bombardment at room temperature with the light ions H⁺, D⁺, He⁺, having energies in the neighborhood of 100 keV. Phenomena associated with destruction of the surface: stress, deformation, fracture, and blistering, are emphasized.     

Measurement of the depth distribution of light impurities in first-wall materials: He in Nb

We have measured the concentrations and depth profiles of implanted helium in niobium by a method demonstrated previously with hydrogen and lithium in copper. The three targets, bombarded at room temperature with 10 keV He⁺ at doses of 0.01, 0.16 and 0.98 C/cm⁺, were respectively: unblistered; covered with circular blisters; and marked with “microrelief”, without blisters. The corresponding doses retained in the metal were 0.0076, 0.039 and 0.052 C/cm² (i.e.≈3 × 10²² He atoms/cm³) with a 10% normalization uncertainty. The profile shapes did not change much: in particular we did not observe, as the dose increased, an accumulation near the surface, which is receding by erosion (sputtering, blistering). These results show that a mechanism of helium loss starts operating at a dose ?0.16 C/cm², i.e. before the bursting of blisters (if they burst at all), and it is most effective near the surface.     

Erosion yield of Ti from TiC-deposited graphite by hydrogen ion bombardment at high temperatures

Erosion yields of Ti atoms from a TiC-deposited graphite by bombardment with 1 keV hydrogen ion beam of various current densities at 900°C have been investigated by means of the Rutherford backscattering (RBS) technique. It has been observed that the sputtering yields for Ti atoms at 900°C are almost zero below a critical ion flux of 1 × 10¹⁵/cm²·s, compared with the sputtering yield of Ti atoms at room temperature which has been measured to be 1 × 10⁻²atoms/ion. No sputtering of Ti atoms observed at 900°C is explained in terms of self-sustaining coating of the TiC surface with segregated carbon layer. The condition for the self-sustaining coating is discussed.     

Ion mass effects on bombardment-induced disordering of γ'-Ni3Si

The kinetics of disordering of the ordered compound γ'-Ni₃Si during ion bombardment were investigated at a temperature of 270°C. The disordering followed first order kinetics and the rate constant was measured as a function of incident ion flux, ion energy, and ion mass. The rate constant varied approximately in direct proportion with the ion flux during bombardment with 1 MeV ⁸⁴Kr⁺-ions: from ~ 0.28 min ^?1 at ~ 70 nA/cm² to ~ 50 min ^?1 at ~ 4.4 μA/cm ². During bombardment with a flux of $\text{~ 1 μA}\text{cm}{}^2$ of ¹³²Xe⁺-ions, the rate constant was directly proportional to the calculated near-surface damage ra te. It varied from ~ 50 min ^?1 for 200 KeV ions with calculated damage rates of ~ 2.3 × 10^?1 dpa to ~ 1.8 min ^?1 for 3 MeV ions with damage rates of 2 × 10^?3dpa/s. The disordering rate was also observed to be directly proportional to the near surface damage rate for heavier mass ions (⁴⁰Ar⁺, ⁸⁴Kr⁺ and ¹³²Xe⁺); the ratio of disordering rate to damage rate was ~ 17. This ratio dropped to ~ 3 for ²⁰Ne⁺-ion bombardment, and to ~ 0.4 for bombardment with ⁴He⁺-ions. The decrease in the ratio with decreasing mass is discussed in terms of cascade size, replacement-to-displacement ratio, and random recombination.