Growth Of Blisters Research Articles

Evolution of colloidal coatings due to a wetting and drying process

Paints and coatings are usually made by depositing a volatile liquid containing dispersed colloidal particles. The dry film is obtained through the evaporation of the volatile liquid. Depending on the ability of the particles to deform under capillary effect, we show that the drying can yield continuous coatings with no porosity, uniform porous coatings, or the formation of singularities, such as cracks causing the final film to be non-uniform. The evolution of the resulting coatings is then subjected to a wetting and drying process. Wetting leads to an increase in the water content of the unsaturated porous coating while drying results in water reduction. The response of the coatings to such a process can exhibit slight or significant changes in the morphology of the coatings that are related to their rheological properties. In particular, the growth of blisters is reported during the wetting and drying process.

Phase-Field Model of Hydride Blister Growth Kinetics on Zirconium Surface

The precipitation of zirconium hydride blisters on the surface of zirconium alloy cladding destroys the integrity of the material and leads to material failure, which has serious potential safety hazards. To study the corrosion kinetics of zirconium hydride blisters, we established a phase-field model coupled with anisotropic elastic, which can reflect the microstructure evolution process of zirconium hydride blisters. The model studies the natural growth of hydride blister and the structural evolution process after applying radial stress and discusses the corrosion characteristics, stress distribution, and displacement changes. Zirconium hydride blisters tend to be semi-ellipsoidal in natural growth. Applying radial outward stress will promote the growth of blisters and aggravate the harm of corrosion. The stress state changes with applying stress, which affects the elastic driving force, resulting in the change of blister morphology. This work is helpful to understand the corrosion kinetic mechanism of hydride blisters.

Investigation of Oxidation Behaviors of Al-Mg Alloys with a Grain Refiner at High Temperature

Studies to investigate the oxidation behavior of Al–Mg alloys with Al-5 mass%Ti-1 mass%B master alloy as a grain refiner at high temperature were conducted. The Scheil-Gulliver cooling calculation showed that, in 0.2 mass%Ti-inoculated alloy, TiAl3 was formed before the primary Al formation, which may act as a grain refiner. The optical microstructures showed a significant grain refinement after the addition of 0.2 mass%Ti using Al-5 mass%Ti-1 mass%B master alloy. Moreover, the oxidized cross-sections, throughout the oxidation time, show coarse and dark areas (regarded as oxide clusters), which were nonuniformly distributed in the matrix after oxidation at 500 °C under an ambient atmosphere. In addition, an accumulation of oxygen by diffusion for a long duration led to the growth of blisters after 50 h. At the oxidation temperature, Mg3Ti2Al18 was found to be only stable Ti-containing phase and possibly formed MgO by the interaction with the diffused oxygen.

Effect of Techniques for Polishing Molybdenum Mirrors on their Optical Stability under Cleaning D2–N2 Plasma

The effect of cleaning with D2–(2–4) mol % N2 glow discharge plasma on the reflectivity of Mo(111) single-crystal mirrors is studied. The surface of each mirror is prepared by mechanical polishing with diamond pastes or diamond powder. Polishing of the mirrors is accompanied by the formation of a layer of material up to 3 microns thick, different in structure from the bulk metal. The peculiarity of this layer is a gradual improvement in its structure further away from the surface of the mirror and transition from an amorphous layer to a layer with nanoscale crystallites, and then a gradual transformation into the structure of an unbroken single crystal. When polishing, the diamond abrasive is pressed into the surface layer of the mirror. During the plasma-cleaning process, carbon particles pressed into the surface layer of the mirror initiate the development of negative roughness (pits or depressions). At the same time, a 5–10-nm layer of molybdenum nitride is formed. In disordered layers of the mirrors, the probability of the origination and growth of blisters is reduced. Aluminum is chosen as the metal that changes the total reflection coefficient of Mo. The use of a D2–N2 mixture to increase the rate of Al sputtering in the last stage of cleaning is replaced by plasma exposure in deuterium with $${\text{D}}_{3}^{ + }$$ ions, which initiates the dissociation of molybdenum nitride and the removal of nitrogen from the surface layer of the mirror. As a result of prolonged plasma exposure, the reflectivity of the mirrors polished with diamond paste increases to a steady-state value close to the reflection of the reference mirror.

Decrease of blistering on Helium irradiated tungsten surface via transversal release of helium from the grooved surfaces

• A new way to reduce blistering that the nano-channels were fabricated on the tungsten surface by FIB • The presence of " grooved surfaces " contributes to reduce blisters and inhibit the rapid growth of He blisters. • He-induced blistering shows a clear crystal orientation dependence. Although tungsten is considered as one of the primary candidates for plasma-facing material (PFM) in future fusion reactors, blistering induced by plasma irradiation adversely affects fusion reactors. To overcome blistering, in this study, we proposed an approach to reduce the blistering by releasing hydrogen or helium (H/He) through the grooved surfaces of PFM. In order to verify the feasibility of this approach and the effectiveness of the transverse release of H/He, the deep grooves as the channel simulants on the tungsten surface were fabricated with different spacing using focused ion beam (FIB). The result of helium irradiation shows that the presence of grooved surfaces can reduce blisters and inhibit the rapid growth of He blisters. In addition, the blistering reduced significantly with decreasing groove spacing, especially when the groove spacing is less than 2 µm. In addition, He-induced blistering shows obvious crystal orientation dependence, and the (001) surface shows the most serious radiation damage.

Thermal Annealing Effect on Structure and Properties of Tungsten Surface Irradiated with High Fluence and Low Energy Alpha-Particles

The paper presents research into the surface morphology, helium cluster formation and mechanical properties of high-purity tungsten after the high fluence and low-energy helium ion implantation and subsequent annealing. Investigations are based on scanning electron and atomic force microscopy observations and thermal desorption measurements. Because of the local stresses appearing within the energy loss straggling of helium ions, atoms migrate at distances significantly increasing the ion projective range, and create mobile coalescence of helium atoms and immobile helium-vacancy clusters. The latter form helium bubbles in the energy loss straggling which cause the surface blistering. Local stresses induced by helium coalescence and helium-vacancy clusters beyond the energy loss straggling result in the material strengthening or hardness increase. Subsequent 600°С annealing provides the size growth of blisters on the metal surface irradiated with helium ions and high helium desorption due to the migration of mobile coalescence of helium atoms. With the increasing annealing temperature from 600 to 1000°С, the layer corresponding to the projective range of helium ions fully fractures due to the interstitial helium atoms releasing from immobile helium-vacancy clusters. After 1000°С annealing, the tungsten hardness returns to its initial value.

Effect of notches on creep–fatigue behavior of a P/M nickel-based superalloy

A study was performed to determine and model the effect of high temperature dwells on notch low cycle fatigue (NLCF) and notch stress rupture behavior of a fine grain LSHR powder metallurgy (P/M) nickel-based superalloy. It was shown that a 90second (s) dwell applied at the minimum stress (“min dwell”) was considerably more detrimental to the NLCF lives than similar dwell applied at the maximum stress (“max dwell”). The short min dwell NLCF lives were shown to be caused by growth of small oxide blisters which caused preferential cracking when coupled with high concentrated notch root stresses. The cyclic max dwell notch tests failed mostly by creep accumulation, not by fatigue, with the crack origin shifting internally to a substantial distance away from the notch root. The classical von Mises plastic flow model was unable to match the experimental results while the hydrostatic stress profile generated using the Drucker–Prager plasticity flow model was consistent with the experimental findings. The max dwell NLCF and notch stress rupture tests exhibited substantial creep notch strengthening. The triaxial Bridgman effective stress parameter was able to account, with some limitations, for the notch strengthening by collapsing the notch and uniform gage geometry test data into a singular grouping.

Blistering on tungsten surface exposed to high flux deuterium plasma

The blistering behaviour of tungsten surfaces exposed to very high fluxes (1–2 × 1024/m2/s) of low energy (38 eV) deuterium plasmas was investigated as a function of ion fluence (0.2–7 × 1026 D/m2) and surface temperature (423–873 K). Blisters were observed under all conditions, especially up to temperatures of 873 K. The blister parameters are evaluated with blister size, blister density and surface coverage. The blister size always peaked at less than 0.5 μm and no blister larger than 10 μm is observed even at high fluence. The blister densities are found in high magnitude of 106 blisters/m2, with the surface coverages lower than 2%. The formation of cracks in the sub-surface region was observed by cross-section imaging. Changes in blister size and shape with fluence and temperature suggest processes of predominantly nucleation and subsequent growth of blisters. The smaller blister size is considered to be caused by a combination of flux-related effects such as enhanced defect formation in the near surface region, reduced deuterium diffusivity and relatively short exposure times.

Thermal shock behaviour of blisters on W surface during combined steady-state/pulsed plasma loading

The thermal shock behaviour of blister-covered W surfaces during combined steady-state/pulsed plasma loading was studied by scanning electron microscopy and electron backscatter diffraction. The W samples were first exposed to steady-state D plasma to induce blisters on the surface, and then the blistered surfaces were exposed to steady-state/pulsed plasma. Growth and cracking of blisters were observed after the exposure to the steady-state/pulsed plasma, while no obvious damage occurred on the surface area not covered with blisters. The results confirm that blisters induced by D plasma might represent weak spots on the W surface when exposed to transient heat load of ELMs. The cracks on blisters were different from the cracks due to the transient heat loads reported before, and they were assumed to be caused by stress and strain due to the gas expansion inside the blisters during the plasma pulses. Moreover, most of cracks were found to appear on the blisters formed on grains with surface orientation near [1 1 1].

Water-induced blister formation in a thin film polymer.

A failure mechanism of thin film polymers immersed in water is presented: the formation of blisters. The growth of blisters is counterintuitive as the substrates were noncorroding and the polymer does not swell in water. We identify osmosis as the driving force behind the blister formation. The dynamics of the blister formation is studied experimentally as well as theoretically, and a quantitative model describing the blister growth is developed, which accurately describes the temporal evolution of the blisters.

Self-sealing shells: blowouts and blisters on the surfaces of leaky wind-blown bubbles and supernova remnants

Blowouts can occur when a dense shell confining hot, high pressure, gas ruptures. The venting gas inflates a blister on the surface of the shell. Here we examine the growth of such blisters on the surfaces of wind-blown-bubbles (WBBs) and supernova remnants (SNRs) due to shell rupture caused by the Vishniac instability. On WBBs the maximum relative size of the blister (R_bstall/R) is found to grow linearly with time, but in many cases the blister radius will not exceed 20 per cent of the bubble radius. Thus blowouts initiated by the Vishniac instability are unlikely to have a major effect on the global dynamics and properties of the bubble. The relative size of blisters on SNRs is even smaller than on WBBs, with blisters only growing to a radius comparable to the thickness of the cold shell of SNRs. The small size of the SNR blowouts is, however, in good agreement with observations of blisters in the Vela SNR. The difference in relative size between WBB and SNR blisters is due to the much higher speed at which gas vents out of WBBs, which translates into a greater energy flux through a rupture of a given size from interior gas of a given pressure. Larger blisters are possible if shell ruptures are bigger than expected. We expect the observed velocity structure of SNR shells to be affected by the presence of blisters until the shell is no longer susceptible to ruptures, since the initial expansion of blisters is faster than the ongoing expansion of the shell.

Failure Investigation of Hydrogen Blistering on Low-strength Carbon Steel

The current study assesses the root causes of hydrogen blisters on low strength carbon steel equipment. For this purpose, some experiments including hardness test, non-destructive test (NDT), metallography, and fractograpghy are conducted. The microstructure of two blisters is assessed by means of optical microscopy and scanning electron microscopy (SEM). The microstructural studies show that the steel plate has some inclusions and banded ferrite/pearlite structure. The energy dispersive x-ray spectroscopy (EDS) results indicate that these inclusions mainly contain Mn, S, Al, Ca, and Si. The results show that the inclusions and planar imperfections found in the NDT have been the nucleation locations for blisters in the plate. Remediation action plans are recommended to prevent further occurrence and growth of hydrogen blisters.

Cathodic disbonding of an unpigmented epoxy coating on mild steel under semi- and full-immersion conditions

Cathodic disbonding of an unpigmented epoxy coating around a defect was studied with samples fully- and semi-immersed in 3.5 wt.% NaCl solution. Disbonding and the growth of blisters were monitored by scanning acoustic microscopy, which showed growth of blisters within the disbond for both type of samples. Scanning Kelvin probe potential maps suggest that blisters first form at local anodes. For semi-immersed samples, disbonding of the immersed part and the non-immersed part propagate with parabolic kinetics at identical rates, similar to fully-immersed samples. This implies that ion transport is along the coating–metal interface in both cases.

Imaging the Origins of Coating Degradation and Blistering Caused by Electrolyte Immersion Assisted by SECM

AbstractA new method to image the origins of coating degradation and the nucleation and subsequent growth of blisters by using SECM in the feedback mode is proposed. The unique role of chloride ions towards coating performance has been established at a very early stage following immersion of the sample. We believe this to show the earlier stages of blistering in a coated metal system ever recorded. The method allowed for the first time to detect the nucleation and to monitor quantitatively the growth process of an individual blister, because it effectively advanced towards the microelectrode when scanned at constant height over the sample.

Numerical analysis of the kinetics of propagation of hydrogen blisters in the oil-and-gas equipment

We consider a problem of cracking of metals (formation of blisters) in the oil-and-gas equipment. The causes of initiation of the nuclei of hydrogen blisters are investigated and, on this basis, a mathematical model of their growth is developed with regard for the electrolytic hydrogenation of the metal surface, hydrogen diffusion into the metal, and its accumulation in the internal microdefects. We also present an example of analysis of the kinetics of growth of circular blisters in low-carbon and low-alloy steels under the action of hydrogen penetrating into the metal in the process of corrosion in wet hydrogen-sulfide media.

Characterization of coating systems by scanning electrochemical microscopy: Surface topology and blistering

Operation of the scanning electrochemical microscope used in feedback mode over a coated metal allows changes in the state of the coating surface to be monitored during immersion in aqueous electrolytes. This paper reports changes in the coating induced by specific anions in the electrolyte in situ during immersion. Significant surface roughening is observed for immersion times shorter than 1 day when the electrolyte contains chloride ions. This effect is also observed when the oxygen dissolved in the electrolytic phase is employed as redox mediator for SECM imaging. The coated system exposed to chloride-free electrolytes containing sulphate or nitrate maintains a featureless topography within the same time scale. The observed features are due to the nucleation and growth of blisters at the metal/coating interface induced by chloride ions in the environment. The implication is that ionic migration occurs simultaneously with the absorption of water by the coating already from the beginning of exposure to the aqueous environment. The unique role of chloride ions compared with sulphate or nitrate ions towards coating performance has been established at a very early stage following immersion of the sample.

UV aging characterization of epoxy varnish coated steel upon exposure to artificial weathering environment

Abstract Epoxy varnish coating was exposed to artificial weathering environment produced by fluorescent UV/condensation weathering equipment for different time periods. The degradation process of epoxy varnish coating was studied by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and adhesion test. The results showed that the electrochemical behavior of aged coating was closely related to the formation and development of blisters on the surface due to coating degradation. The coating resistance, Rp, decreased to a lower value after 28 days of exposure, which indicated significant deterioration of barrier properties. Small blisters were observed on coating surface after 21 days of exposure. With increasing aging time, blisters grow up and subsequently broke. The mechanism of blisters formation and subsequent breakage were suggested. The soluble degradation products penetrate into the coating along with water to form osmotic cells leading to the form of blisters on the coating surface under the alternating wet and UV irradiation condition. The spread of degradation areas caused the growth and development of blisters. With the loss of coating material and embrittlement, cracks appear on the surface and the blisters break, which may result in the significant deterioration of bulk properties of the coatings.

A new hypothesis for the development of blisters in asphalt pavements

Asphalt layers used to provide smooth, compliant, surfaces on pavements often experience the growth of small uplift blisters. Conventional wisdom has it that these blisters are the result of a build-up of either volatile gases or water vapour beneath the asphalt that accompanies a significant increase in surface temperature. This paper argues that in many cases such a cause is unlikely. It suggests an alternative explanation based upon a gradual growth of upward thermal buckles, induced by the cyclical changes of membrane stresses that accompany the constrained in-plane expansion and contraction, resulting from fluctuations in surface temperature. With asphalt displaying reduced elastic-visco-plastic stiffness at high temperatures a proportion of the growth in an upward buckle, occurring at elevated temperatures, will not be recovered when temperatures again drop. Over time a form of thermo-mechanical ratchet process appears to be set in motion, resulting in the gradual upward growth of these blisters. Recognizing the correct physical causes of these blisters is suggested to be the important first step in evolving appropriate practical measures to prevent their increasingly prevalent and damaging future development.

Influence of post-annealing time on blistering evolution in Si 〈1 0 0〉 implanted with high-fluence H ions

The influence of post-annealing time on blistering characteristics induced by 5×1016cm−2 ion-implanted H in Si <100> was studied in terms of the formation and growth of blisters. Ion energies consisted of 40 and 100keV. Post-annealing treatments were carried out using furnace annealing (FA) at 400 and 500°C for a duration of 0.25–3h in a nitrogen ambient. Raman scattering spectroscopy (RSS), optical microscopy (OM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) were utilized to analyze the defect complex phases, the appearance of optically-detectable blisters and craters, the average depth of craters, and the hydrogen and oxygen depth profiles in the implanted layer, respectively. Furthermore, a characteristic time for the growth of optically-detectable blisters which was determined from the blister-covered fractions for various post-annealing times is proposed and used as a criterion to identify the effectiveness in the formation and growth of optically-detectable blisters. The results revealed that the characteristic time for the 400°C-annealed specimens in the 40keV implant is much shorter than it is in the 100keV one. However, the characteristic time for the 500°C-annealed specimens in the 40keV implant is slightly longer than it is in the 100keV implant. In addition, both the characteristic times for the 500°C-annealed specimens are much shorter than those for the 400°C ones. The above-mentioned phenomena hold true for craters.

Morphological change of polycrystalline copper after ion irradiation followed by annealing

For etchings of LSI and MEMS, a dry etching makes the process simple. In the present study, helium ion etching for polycrystalline copper was conducted, and after that the surface uniformity was examined. The irradiated surface showed unevenness with a roughness of sub-micron size, caused by growth of blisters. When the ion was injected obliquely to the surface, the roughness was reduced owing to the selective etching for the protuberance parts. However, the blisters still existed and the roughness was not significantly reduced. For the irradiated surface, annealing with temperature of 1000K was conducted for the blisters to be ruptured. After the annealing, the blisters disappeared and the surface significantly became smooth. Thus, the ion irradiation followed by annealing can be recognized as a useful etching method.