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Spent nuclear fuel is planned to be deposited in the 50 mm thick copper canisters at about 500 m depth in the bedrock. Hydrogen uptake may occur in the disposal conditions in copper due to corrosion reactions and effects of irradiation. Therefore, it is important to know in which conditions the hydrogen uptake results in the formation of pressurized hydrogen bubbles near the copper surface. During the thermal desorption spectroscopy (TDS) measurements the existing hydrogen bubbles grow due to accumulation of dissolved hydrogen and build-up of hydrogen gas pressure inside the voids. The further growth of the voids occurs by plastic deformation and results opening of the voids near the copper surface due to increasing temperature. The friction-stir weld metal samples of phosphorous-doped oxygen-free copper were cathodically charged with hydrogen in a 1.0 N H2SO4 solution with added 10 mg/L thiourea at various electrochemical potentials, -0.95…-1.3 VSCE. A threshold potential of -1.10 VSCE was found for the marked increase of hydrogen uptake and hydrogen-induced void formation near the copper surface.

Ferritic nodular cast iron, intended for use as the material for inserts of canisters for long-term geological disposal of spent nuclear fuel, was studied for hydrogen sensitivity. In the canisters, the insert provides the mechanical strength against external loads. Hydrogen was charged from 0.1 N H(2)SO(4)solution in free-corrosion tests and under controlled cathodic potential. Hydrogen uptake and trapping were then measured using thermal desorption spectroscopy. The hydrogen desorption rate after hydrogen charging manifests two distinct peaks. Plastic deformation during hydrogen charging increases the hydrogen uptake considerably. Hydrogen reduces the elongation to fracture and time to fracture in slow strain rate testing and constant load testing (CLT), respectively. Especially, the strain rate in CLT is dramatically increased. The appearance of hydrogen-induced cracking in the ferrite phase changes from ductile dimple fracture to brittle cleavage fracture due to hydrogen charging, which initiates from theinterphases of the graphite nodules. The results are discussed in terms of the role of hydrogen and the graphite nodules in hydrogen embrittlement of ductile cast iron.

The KBS-3 method for long-term disposal of spent nuclear fuel is designed with an external self-standing copper shell, which provides the most important barrier against corrosion and escape of radionuclides, and an internal nodular cast iron insert, which provides the load-bearing structure against external loads. The material intended for the load-bearing insert is ferritic nodular cast iron EN 1563 grade EN-GJS-400-15U. In this paper, hydrogen uptake and sensitivity to hydrogen-induced cracking of the cast iron were studied using tensile testing under continuous electrochemical charging in 1 N H2SO4 solution. Hydrogen uptake was measured by using the thermal desorption method. It was found that the hydrogen desorption profile manifests three distinct peaks at initial locations of 400, 500, and 700 K with a heating rate of 6 K/min. Plastic deformation results in a remarkable increase of the 400 K peak, which indicates hydrogen uptake during deformation. In the constant extension rate tests (CERT) and the constant load tests (CLT), electrochemical hydrogen charging reduced markedly the elongation to fracture and time to fracture, respectively. In CLT, hydrogen charging increased dramatically the creep rate at the applied load of about 0.7 yield stress. Ligaments between the graphite nodules exhibit brittle cleavage facets in the presence of hydrogen, while the ligaments show a characteristic ductile appearance of shear and small dimples when testing in air or distilled water. The obtained results are discussed in terms of the known mechanisms of hydrogen-induced cracking and the role of the graphite nodules in the embrittlement of ductile cast iron.

Stress corrosion cracking (SCC) of oxygen-free phosphorous-alloyed copper was investigated in sulphide- and chloride-containing deoxygenated water at 90 degrees C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low sulphide environment, where only slight corrosion on grain boundaries and slip lines occurred. Hydrogen content measurements show an increase in hydrogen uptake of the plastically deformed specimens, which is dependent on the sulphide concentration and on plastic deformation of copper. However, the highest hydrogen content was measured in friction stir welds, welded in air without shielding gas, and tested in the high sulphide environment. The embedded oxide particles in the weld metal act as local hydrogen trapping sites and selectively react with the sulphide solution. A relatively thick air-formed oxide film covers the copper canisters when deposited, which transforms into a sulphide film in the repository conditions. Thus, some of the coupon specimens were pre-oxidised. The conversion of the pre-existing Cu2O film into Cu2S film occurs quickly and the transformation is almost 100% efficient. The structure and properties of the Cu2S films, susceptibility of copper to sulphide-induced SCC and hydrogen uptake of copper in reducing, anoxic repository conditions are discussed.

A historical overview of copper behavior in geological spent nuclear fuel disposal is presented. The KBS-3 method was approved as the reference method by the Swedish government in 1984. The KBS-3 copper canister has an external, self-standing copper shell and an internal structural nodular cast iron insert. Degradation mechanisms of copper are associated with sulfide present in groundwater, in buffer and locally produced by microbiological activity. General corrosion, radiation-induced corrosion, localized corrosion, stress corrosion cracking, and hydrogen-induced cracking of copper are considered. Creep ductility of pure oxygen-free Cu-OF was low, and therefore the choice at present is oxygen-free copper with phosphorous alloying (Cu-OFP, 30…100 ppm P).

Single crystals of oxygen-free copper oriented to easy glide of dislocations were tensile tested in order to study the hydrogen effects on the strain localisation in the form of slip bands appearin...

Positron annihilation spectroscopy and thermal desorption spectroscopy experiments were combined to ascertain the role of hydrogen on generation of vacancies and vacancy clusters in Ni alloys. The effects of grain size and deformation temperature are emphasized for pure Ni single crystals and polycrystalline Ni-201 alloy samples with two grain sizes that were thermally pre-charged with 3000 appm hydrogen. Variation in positron lifetime and intensity suggests that hydrogen enhances and stabilizes vacancies and vacancy clusters. Additionally, grain boundaries and the regions adjacent to them are preferential sites for vacancy and cluster formation. Hydrogen-altered vacancies and vacancy clusters are manifest in yield behavior differences: uniform vacancy distributions augment strength increases after hydrogen charging; enhanced yield strength during cryogenic deformation is ascribed to an ‘Orowan type’ strengthening mechanism while cross-slip restriction dominates hardening behavior at room temperature.

Role of microstructure in susceptibility of 18Cr ferritic stainless steel to hydrogen embrittlement was studied. Specimens of the studied steel were charged with hydrogen electrochemically from 0.1 N H 2 SO 4 solution under controlled cathodic potential providing a homogeneous hydrogen distribution over the specimen cross-sections. Thermal desorption spectroscopy analyses were carried out investigating the uptake, trapping and diffusion of hydrogen in the ferritic stainless steel. Microstructural change caused by heat-treatment at 1050 °C and 1200 °C associated preferably with grain size growth from 18 µm to 65 µm and 349 µm, respectively, resulting in significant degradation of the mechanical properties of the studied steel. The effect of the grain size growth on hydrogen susceptibility was studied with constant extension rate test (CERT) performed under continuous hydrogen charging. It is found that hydrogen has a remarkable effect on the elongation to fracture of the Fe-Cr ferrite: in the presence of H elongation to fracture of the steel reduces up to 75% compared to the H-free counterpart. In general, the hydrogen sensitivity of the mechanical properties increases with increase of the mean grain size of the studied ferritic stainless steel. However, the detailed analysis reveals a complicated, non-linear behavior of the hydrogen sensitivity. Scanning electron microscopy (SEM) of the fracture surfaces of the tensile specimens tested during continuous hydrogen charging reveals a quasi-cleavage fracture surface morphology. Hydrogen-induced cracking in the studied 18Cr ferritic steel was studied using electron backscatter diffraction (EBSD) analysis from the side surfaces of the tensile tested specimens.

The effect of continuous hydrogen charging on tensile properties of EUROFER 97 and ODS-EUROFER steels was studied at room and elevated temperatures of 100 °C and 300 °C. The hydrogen effect decreases with increase of the temperature for ODS-EUROFER steel, while susceptibility to hydrogen of EUROFER 97 steel remains approximately the same at all testing temperatures. Continuous hydrogen charging results in a reduction of the grain boundary cohesion of the EUROFER 97 and ODS-EUROFER steels tested at RT. With increase of the testing temperature up to 300 °C EUROFER 97 steel exhibits relatively high amount of micro-cracks which agglomerate in sub-micrometer size cracks, while the hydrogen-induced intergranular crack nucleation in ODS-EUROFER steel is effectively suppressed. Possible mechanism of the hydrogen-induced crack nucleation and propagation under applied external stress is discussed.

Economically attractive and safe process instrument for hydrogen charging from glow discharge plasma was developed. The unique shape of the ionizer allows to restrict the plasma dispersion and focus it on the sample. The instrument can be combined with a loading device for in-situ hydrogen charging during tensile testing and heating to an elevated temperature. Successful results of hydrogen charging were obtained for ODS-EUROFER steel, which is one of the most promising structural materials for fusion reactors and Gen-IV nuclear reactors. The suitable parameters of hydrogen charging were found experimentally. The plasma exposure time for homogenization of hydrogen concentration in the certain shape of the specimen of the ODS-EUROFER steel was determined to be more than 30 min. Comparative study of the surface morphology of the specimens before and after hydrogen plasma charging was performed by means of scanning electron microscopy (SEM).

Hydrogen effects on the mechanical properties of the ferrite-martensite EUROFER 97 and oxide dispersion strengthened ODS-EUROFER steels were studied under continuous hydrogen charging from hydrogen-enriched plasma at temperatures up to 300 °C. Hydrogen uptake measured using thermal desorption spectroscopy was found to be markedly higher in ODS-EUROFER steel in comparison to that in EUROFER 97 steel evidencing on high hydrogen trapping ability of the oxide-dispersion strengthening yttria nanoparticles. It is found that EUROFER 97 and ODS-EUROFER steels manifest rather different sensitivity to hydrogen embrittlement with increase of temperature. It is shown that increase of the temperature up to 300 °C decreases the hydrogen effects on the mechanical properties of ODS-EUROFER steel, while sensitivity to hydrogen of EUROFER 97 steel remains the same as at room temperature. FEG-SEM fractography was performed to investigate of the hydrogen-induced fracture mode at elevated testing temperatures. Possible role of the interface between yttria nanoparticles and steel matrix and the distribution of yttria nanoparticles in the hydrogen embrittlement mechanism are discussed.

Strain accumulation was studied by digital image correlation technique (DIC) during microstructurally small fatigue crack propagation in polycrystalline 18%Cr ferritic stainless steel. Load-controlled fatigue testing was performed with R-ratio of 0.1 and frequency 10 Hz. The maximum applied stress was well below the yield stress of the studied material. The effect of the observed strain field on crack growth rate variation is discussed. Fracture surfaces were studied by scanning electron microscopy (SEM) evidencing the connection between the mechanism of the fatigue crack growth, accumulated strain and crack growth rate. Detailed study of fracture surface morphology was carried out by atomic force microscopy (AFM). Results indicate two processes of material damage accumulation and failure during cyclic loading: 1) local shear strain zones form successively ahead of the crack tip, and 2) fatigue crack growth occurs by both single- and multiple-slip mechanisms. The place and intensity of shear strain localization zones vary during the crack growth that is related closely to the local variation of crack growth rate.

The role of the excessive metal vacancy generation in transgranular stress corrosion cracking (TGSCC) of pure copper was studied in relation to crack initiation and growth mechanisms. Electrochemically polarized specimens were strained at room temperature in 0.3 m NaNO2 solution. Cation vacancy redistribution under applied anodic polarization took place at the p-n junction of the duplex Cu2O oxide film, resulting in cation vacancy transport in the p-type layer of the oxide to the metal substrate interface and in excessive metal vacancy accumulation in the metal substrate. The rapid initiation of TGSCC at room temperature in the cold-worked oxygen-free high-conductivity copper samples occurred during slow strain rate tests under anodic polarization in 0.3 m NaNO2 solution. The duplex Cu2O oxide film structure formed by cathodic deposition, before applying the anodic polarization, was characterized with X-ray diffraction and field emission scanning electron microscopy/electron backscatter diffraction/energy-dispersive spectroscopy. The redistribution of cation vacancies in the p-type oxide phase due to the anodic polarization and the metal vacancy accumulation in the copper substrate interface was studied by using positron annihilation spectroscopy.

Constant load tests of high-strength carbon steels with different micro-alloying using strengths in the range of 1000–1400 MPa were performed at ambient temperature under continuous electrochemical hydrogen charging. Hydrogen markedly affects delayed fracture of all the studied steels. Fractography of the studied steels shows that fracture mechanism depends on the chemical composition of the studied steels and hydrogen-induced cracking exhibits intergranular or transgranular character occurring often in the form of hydrogen flakes. The size and chemical composition of non-metallic inclusions are analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Hydrogen-induced cracking initiates at TiN/TiC particles in steels with Ti alloying. Crack paths are studied with electron backscatter diffraction mapping to analyze crack initiation and growth. The thermal desorption spectroscopy method is used to analyze the distribution of hydrogen in the trapping sites. The mechanisms of hydrogen effects on fracture of high-strength steels are discussed.

The mechanisms of hydrogen influence on vacancy cluster formation in copper are studied using numerical simulations. Vacancy agglomeration in clusters larger than divacancies is found to be energetically favourable, but in pure copper the cluster creation is prevented by the lack of binding between single vacancies. Hydrogen dissolved in the lattice readily accumulates in vacancy-type defects, changing their properties. A single vacancy can accommodate up to six hydrogen atoms. Hydrogen stabilizes divacancies and promotes vacancy cluster nucleation. In larger vacancy clusters, accumulated hydrogen prevents cluster collapse into stacking fault tetrahedra. In small voids, hydrogen prefers to remain in atomic form at the void surface, but when voids become sufficiently large, hydrogen molecules in the void interior can also be formed. Some common impurities in copper (O, S, P and Ag) contribute to void formation by capturing vacancies in their vicinity. In contrast, substitutional Ni has little effect on vac...

High-strength carbon steels of 1200 MPa strength level with different microalloying were tensile tested at constant extension rate and constant load under continuous electrochemical hydrogen charging. The results show that hydrogen markedly reduces elongation and time to fracture of all the studied steels. Fractography of the steels shows that nonmetallic inclusions (NMIs) play the major role in crack initiation in hydrogen-charged specimens. The role of NMIs in the hydrogen-induced fracture of steels is discussed.

Hydrogen effects on the mechanical tensile properties of the ferrite–martensite EUROFER 97 and ODS-EUROFER steels were studied after electrochemical hydrogen charging at room temperature. Hydrogen was introduced into the steels from 0.1 N NaOH solution under controlled cathodic potential. Hydrogen TDS measurements show that yttria nanoparticles increase considerably the hydrogen uptake in ODS-EUROFER steel in comparison to that in EUROFER 97 steel. Hydrogen has only a minor effect on the yield stress and tensile strength of the studied steels. EUROFER 97 and ODS-EUROFER steels manifest rather different sensitivity to hydrogen embrittlement. It is shown that hydrogen reduces markedly elongation to fracture of ODS-EUROFER steel, if hydrogen concentration exceeds a certain critical value. FEG-SEM fractography observations evidence the intergranular fracture mode of ODS-EUROFER steel. The possible role of yttria nanoparticles in the hydrogen embrittlement mechanism is discussed.

Hydrogen diffusion and trapping in AISI 316L stainless steel and pure nickel are studied with thermal desorption spectroscopy method. Specific features of hydrogen uptake and desorption for a multi-component alloy in comparison with that for pure metal and the effects of hydrogen concentration profile after electrochemical charging on the hydrogen desorption are discussed. It is shown that hydrogen diffusion and trapping in multi-component alloy are caused by the specific atomic distribution of hydrogen in the crystal lattice of alloy.

One of the most intricate issues of nuclear power is the long-term safety of repositories for radioactive waste. These repositories can have an impact on future generations for a period of time orders of magnitude longer than any known civilization. Several countries have considered copper as an outer corrosion barrier for canisters containing spent nuclear fuel. Among the many processes that must be considered in the safety assessments, radiation induced processes constitute a key-component. Here we show that copper metal immersed in water uptakes considerable amounts of hydrogen when exposed to γ-radiation. Additionally we show that the amount of hydrogen absorbed by copper depends on the total dose of radiation. At a dose of 69 kGy the uptake of hydrogen by metallic copper is 7 orders of magnitude higher than when the absorption is driven by H2(g) at a pressure of 1 atm in a non-irradiated dry system. Moreover, irradiation of copper in water causes corrosion of the metal and the formation of a variety of surface cavities, nanoparticle deposits, and islands of needle-shaped crystals. Hence, radiation enhanced uptake of hydrogen by spent nuclear fuel encapsulating materials should be taken into account in the safety assessments of nuclear waste repositories.

The effect of hydrogen on the microstructure of mechanically tested ODS-EUROFER steel was investigated by means of transmission electron microscopy, thermal desorption spectroscopy, and atomistic simulations. The presence of yttrium oxide particles notably increases hydrogen uptake in ODS-EUROFER steel as compared to ODS-free EUROFER 97. Under tensile loading, hydrogen accumulation promotes the loss of cohesion at the oxide particle interfaces. First-principles molecular dynamics simulations indicate that hydrogen can be trapped at nanoparticle/matrix interface, creating OH-groups. The accumulation of hydrogen atoms at the oxide particle surface can be the reason for the observed hydrogen-induced oxide/matrix interface weakening and de-cohesion under the action of external tensile stress.

Two oxygen-free copper grades with purity of 99.99 % were studied by means of free decay inverted torsion pendulum at the temperature range of 90 – 300 K and frequencies of 0.5 – 2 Hz. One copper grade was oxygen free electrolytically refined copper with oxygen content of 1.2 wt. ppm. The other one was oxygen-free phosphorous-alloyed grade with oxygen content less than 5 wt. ppm and phosphorous content of 30 – 70 wt. ppm. Electrochemical hydrogen charging induces a complex internal friction peak in the studied copper grades. The observed internal friction peak has a relaxation origin with apparent activation enthalpy and pre-exponential factor for the oxygen-free grade of 0.276 ± 0.002 eV and 10-11.59 ± 0.08 s, respectively. The internal friction peak can be fitted by three broadened Debye peaks (P1, P2 and P3) with activation enthalpies and pre-exponential factors of 0.248 ± 0.003 eV and 10-11.4 ± 0.4 s; 0.297 ± 0.004 eV and 10-11.8 ± 0.2 s; 0.36 ± 0.04 eV and 10-12.7 ± 1.4 s, respectively. Phosphorous doping markedly reduces the height of the observed peak. It was also shown that prior deformation by tension suppresses high-temperature components of the complex internal friction peak. Mechanism of relaxation is presumably caused by interaction of H – H pairs (low-temperature component, peak P1), interaction of hydrogen atoms with dislocations (P2) and interaction of hydrogen with impurities (high-temperature component, peak P3). Absorption of hydrogen in the studied copper grades during electrochemical hydrogen charging was confirmed by the thermal desorption method.

Mechanical loss of pre-strained and hydrogen-charged specimens of 316L austenitic stainless steel has been measured by the free-decay method using an inverted torsion pendulum at frequencies around 1 Hz. It is found that in addition to known hydrogen Snoek-like relaxation process observed at about 240 K a new peak of mechanical loss appears around 270 K. The peak has a relaxation origin with enthalpy close to 0.78 eV and pre-exponential factor of relaxation time is found to be about 10-12.5s. Effects of the pre-strain and parameters of electrochemical hydrogen charging on the hydrogen peak in deformed austenitic stainless steels are measured. The obtained results are discussed in terms of the Snoek-Köster mechanism and specifics of hydrogen atomic distribution in a multi-component substitutional alloy of austenitic stainless steel. Based on the analysis the binding energy of hydrogen to dislocation in 316L steel is evaluated to be about 0.16 eV.

Hydrogen solubility and diffusion in austenitic stainless steels, namely AISI 310, AISI 301LN and AISI 201, are studied with thermal desorption spectroscopy (TDS) after electrochemical potentiostatic hydrogen pre-charging. Temperature dependencies of hydrogen desorption for all studied steels manifest a complex main peak caused by hydrogen releasing from the steel lattice by diffusion. Depending on the steel and heating rate the peak is situated from 350 to 500 K and its shape reflects a specific of hydrogen diffusion in stainless steels, which are multicomponent alloys. Analysis of the TDS curves is based on the hydrogen diffusion model taking into account trapping of hydrogen atoms in the energetically deep interstitial positions in the steel crystal lattice. Diffusion coefficient of hydrogen and its total content after the same charging procedure are obtained from the TDS curves and compared for the studied steels.

Tensile tests accompanied with on-line in situ field emission gun-scanning electron microscopy observations were performed to study hydrogen effects on plastic strain localization in the form of slip lines in single crystals of austenitic stainless steel. It was found that the slip lines on the hydrogen-charged specimens were markedly shorter and more grouped together than the straight slip lines on the hydrogen-free specimens. Hydrogen thermal desorption and positron annihilation spectroscopy were applied to study the combined effect of hydrogen and plastic deformation on excessive generation of vacancies.

Dynamic strain aging (DSA) affects a material’s mechanical behaviour. In the current study, the deformation microstructures of AISI 316 stainless steel specimens were examined after tensile testing at several temperatures both in and out of the DSA-regime (200, 288 and 400 °C), and the effect of straining on free nitrogen evolution at those temperatures was studied by Anelastic Mechanical Loss Spectrometry (Internal Friction). Analysis of the nitrogen-induced Snoek-like peak after straining indicated that DSA behaviour is associated with the formation of sub-micron scale, nitrogen-enriched zones in the austenitic matrix. Long-range planarity was observed in the dislocation structures at 400 °C and short-range planarity at 288 °C, but at 200 °C the microstructure exhibited cellular dislocation structure. Diffusion re-distribution of nitrogen in the DSA-regime affected the deformation behaviour of the material by restricting cross-slip, which in turn promotes strain localization, degrading the mechanical performance of the material.

Atomic distribution of hydrogen, its elemental diffusion jumps and its interaction with dislocations in a number of austenitic stainless steels are studied with anelastic mechanical loss (AML) spectrometry in combination with the hydrogen thermal desorption method. Austenitic stainless steels of different chemical composition, namely, AISI 310, AISI 201, and AISI 301LN, as well as LDX 2101 duplex stainless steel are studied to clarify the role of different alloying elements on the hydrogen behavior. Activation analyses of the hydrogen Snoek-like peaks are performed with their decomposition to sets of Gaussian components. Fine structure of the composite hydrogen peaks is analyzed under the assumption that each component corresponds to diffusion transfer of hydrogen between octahedral positions with certain atomic compositions of the nearest neighbouring lattice sites. An additional component originating from hydrogen-dislocation interaction is considered. Binding energies for hydrogen-dislocation interaction are also estimated for the studied austenitic stainless steels.

An experimental method is presented for the determination of the extent of damage of photoactive titanium dioxide (TiO 2 ) coatings on stainless steel substrate by measurement of open-circuit potential (OCP) during the deformation of a coated specimen under UV illumination. 50 and 100 nm anatase and 100 nm rutile TiO 2 coatings were produced on AISI 304 stainless steel substrate using atomic layer deposition. The photoactivity of the coatings was confirmed by the measurement of OCP under periodic UV illumination. The changes in the OCP of 50 nm thick anatase coating observed during the tensile tests with UV illumination indicated that the onset of cracking of the coating occurred at 1.1% engineering strain and that about 70% of the coating was detached at 16% strain. 100 nm anatase coating exhibited similar behavior. Small changes in the OCP of 100 nm rutile coating up to 30% strain indicated considerably smaller detachment of the coating.

Nonlinear elastic wave modulation spectroscopy (NEWMS) experiments were performed on aluminum alloy grade 6082 after various number of fatigue cycles up to 50 000 cycles. Two continuous longitudinal elastic waves (low frequency f 1 in the range between 20 and 40 kHz and high frequency f 2 = 4.8 MHz ) were introduced into specimens by two piezoelectric transducers, and the elastic response of the specimens was monitored by a third piezoelectric transducer. The second-order ( f 2 ± f 1 ) and the third-order ( f 2 ± 2 f 1 ) intermodulation products were determined from the measured signal by Fourier transform. The dependences of the amplitudes of the intermodulation products on the number of fatigue cycles and dependences of the intermodulation products on driving frequency f 1 and driving amplitude A 1 were investigated for various number of fatigue cycles. The second-order intermodulation products increased steadily with increasing number of fatigue cycles (total change about 30 dB). The third-order intermodulation products increased markedly up to 30 000 cycles, and saturated afterwards (total change about 50 dB). These increases of intermodulation products are ascribed to formation and gradual growth of cracks in specimens with increasing number of fatigue cycles. The cracks were confirmed by electron microscopy. The obtained results are discussed in terms of nonlinear acoustic models.

A forced torsion pendulum for measurement of friction forces between solid surfaces and flowing liquid environments was designed and assembled. The apparatus utilizes the axial Couette flow generated in removable cylinder specimen cell filled with a liquid. The cell is co-axial with the pendulum shaft and the liquid flow is excited within a thin layer adjacent to the inner wall of the cell, which is covered by the studied metal foil. The damping and the resonant frequency of the pendulum are calculated online. The construction allows control of the electrochemical potential of the studied metal foil immersed in an electrolytic environment. The high sensitivity of the apparatus was confirmed in measurements of the resonance parameters of the pendulum. The surface morphology of the metal wall exposed to distilled water has a measurable effect on damping and resonant frequency of the pendulum. A 3% reduction of damping was observed during illumination of a photoactive surface by an ultraviolet light.

Elongation to fracture values higher than 300% were obtained for cold rolled AISI 304 type steel grades in hot tensile tests. The effects of heating rate and carbon content on the elongation of the steels studied are discussed based on internal friction measurements and TEM observations. A slow heating rate to the test temperature and high carbon content of the steel led to a fine and equiaxial grain structure of the steels.

The effects of the temperature of preliminary thermomechanical treatment (TMT) on the superplastic forming parameters of commercial grade aluminium base alloy AA5083 have been studied. The TMT performed included multiple-pass warm rolling followed by cold rolling with a reduction ratio per pass approximately equal to two. The temperature of the warm rolling, T WR , was varied between 250 and 500 °C. The dependence of superplastic elongation on the temperature of warm rolling during TMT was investigated by tensile testing dog-bone samples at 350 and 500 °C. The research shows that material warm rolled at temperatures close to 350 °C yields maximum values of elongation to fracture. Refinement and change of distribution of intermetallic particles occur in the process of warm rolling AA5083. Pycnometric measurements show that the porosity of the material after a full cycle of TMT, encompassing warm and cold rolling, increases monotonically with the rolling temperature. SEM/EDS observations additionally show that warm rolling at lower temperatures is accompanied by the formation of Si- and Mg-rich segregations at the interfaces between the intermetallic particles and matrix. Both these phenomena lead to a significant decrease in the SPF properties of AA5083.

Complex two-component peak of anelastic mechanical losses was observed in multicomponent substitutional austenitic alloys after prior plastic deformation. In AISI 316L, AISI 316LN, AISI 310 and AISI 304 austenitic stainless steels, this peak is situated in the wide range of temperature from 200 to 400 K. Characteristics of the observed peak for different thermo-mechanical treatments were studied employing low-carbon AISI 316L austenitic stainless steel. It is shown that the low-temperature component (peak P1 with maximum at 250 K) has a relaxation origin, while the high-temperature component (peak P2 located at 340–360 K) represents a transitional process developing in a deformed austenitic stainless steel during linear heating. The activation enthalpy and the pre-exponential factor of the relaxation time of peak P1 are 0.48 ± 0.06 eV and 10 −11±1 s, respectively. Effects of prior cold deformation and heating rate on the observed anelastic mechanical losses are also described. The origins of the peaks are discussed in terms of interactions of dislocations with point defects generated by plastic deformation.

Auto-oscillations of the electrochemical potential around its average value close to +100 mVSCE under galvanostatic polarization of pure copper in 0.3M NaNO2 solution were studied in annealed state of copper and during slow strain rate tensile tests of cold-deformed copper. The oscillations occur in the potential range where the passivation current increases dramaticaly due to Cu++ cation generation in the semi-coherent oxide film on the copper substrate. Parameters of the oscillations were measured depending on the polarization conditions. It was supposed that the observed oscillations represent a nonlinear relaxation process in the passive oxide film interacting with the metal substrate at the semi-coherent oxide/metal interface. Based on the idea that cation vacancy balance at the Cu2O/Cu interface depends on the stresses induced in the metal substrate by the interface conditions, a model of the observed nonlinear phenomena was formulated.

The effects of strain rate on interactions between copper and its oxide films have been studied. The electrochemical oxidation process of copper is accompanied by the generation of vacancies in the copper substrate. Diffusion of vacancies from the oxide/metal interface or annihilation of vacancies by dislocation reactions is essential for oxidation to continue. Sufficiently slow straining without breaking the passive film on copper leads to a re-arrangement of the dislocation sub-structure at the interface, which helps to consume the oxidation-generated vacancies. The balance of slow straining and oxidation/dissolution produces environmentally-enhanced plasticity in the copper substrate, and simultaneously, accelerated corrosion. These conditions occur as long as the strain rate is low, i.e., on order of less than 10−8 s−1. The effects of slow straining on oxidation/dissolution of high purity copper were studied at various strain rates, even as low as 10−10 s−1. The electrochemical oxidation behaviour of cold-deformed copper was recorded by dynamic polarization scans. The synergistic effects of oxidation/dissolution process and straining on the mechanical properties of metal, i.e., dislocation sub-structure of copper were studied by TEM. The results are discussed in conjunction with a TGSCC model (SDVC, Selective Dissolution – Vacancy Creep). Central to the TGSCC model is the concept of vacancies generated in the process of oxidation/dissolution taking part in substrate recovery and playing a key role in the stress corrosion crack growth behaviour.

Maraging steels show an excellent combination of high strength and ductility, which makes them very attractive in a large variety of potential applications. The present work is concerned with the main factors influencing the stability of metastable austenite in such a steel. At subzero temperatures a large variation in the isothermal transformation behaviour of austenite to martensite has been observed. Factors such as the austenite grain size and the interstitial content in solid solution are known to influence austenite stability and, therefore, the martensitic transformation. In this steel, the addition of titanium results in carbonitride precipitation. These precipitates play an indirect but important role in the stability of austenite by means of removing interstitials from the solid solution and by inhibiting an austenite grain growth. The combination of techniques such as X-ray diffraction, magnetisation measurements, three-dimensional neutron depolarisation, and internal friction measurements enables a complete characterisation of the transformation. A step towards understanding the factors responsible for the variation in the behaviour observed is the main contribution of this work.