R. Zabels

Shear banding mechanism of plastic deformation in LiF irradiated with swift heavy ions

The effect of ion irradiation on the behavior of plastic deformation at micro- and nanoindentation on (001) face of LiF has been investigated. The irradiation was performed using heavy ions (U, Au, Ti and S) with energy in the range from 3 MeV to 2 GeV at fluences up to 5x1013 ions/cm2. In non-irradiated LiF, the indentation produces dislocation gliding on the {110} planes along the and directions. At high fluence irradiation, the resource of the dislocation slip along the preferable directions becomes exhausted due to immobilization of dislocations by radiation defects and their aggregates. The present study demonstrates the change of the mechanism of plastic deformation from homogenous dislocation slip to localized shear banding in samples irradiated to high fluences. The factors facilitating of the localization of deformation have been analyzed.

Nanoindentation and Raman Spectroscopic Study of Graphite Irradiated with Swift 238U Ions

Modifications of the structure and mechanical properties of the isotropic fine-grained graphite R6650 irradiated with 2.6 GeV 238U ions at fluences up to 1013 ions/cm2 at room temperature are studied. A strong ion-induced increase of Youngs modulus and hardness is observed that points to the formation of a hard form of carbon. Raman spectra ascertain the disordering of graphite and its transformation to glassy carbon.

Modification of LiF structure by irradiation with swift heavy ions under oblique incidence

The structural modifications of LiF irradiated with swift heavy ions under oblique angles have been investigated using AFM, SEM, chemical etching, nanoindentation and optical absorption spectroscopy. LiF crystals were irradiated under incidence angles of 30 and 70 degrees with 2.2 GeV Au (fluence 57?l011 ions-cm2) and 150 MeV Kr ions (fluence 1012?1014 ions?cm?2). Structural study on sample cross-sections shows that two damage regions ? (1) nanostructured zone and (2) dislocation ? rich zone, which are typical for irradiations at normal incidence, appear also in samples irradiated under oblique angles. However in the latter case a more complex structure is formed that leads to stronger ion-induced hardening.

The Role of Diffusion Accommodation and Phase Boundary Wetting in the Deformation Behaviour of Ultrafine Grained Sn-Pb Eutectic

Mechanical properties, microstructure of the Sn–38wt. %Pb eutectic and the development of deformation - induced diffusion processes on interphase boundaries (IB) were investigated. Experiments were carried out both in deformed and annealed states of eutectic using micro- and nanoindentation, SEM, AFM and optical microscopy techniques. It was found that the deformation of the annealed alloy is localized at the Pb/Sn interphase boundaries and occurs by grain boundary sliding (GBS) accompanied by sintering micropore processes under the action of the capillary forces on the Pb/Sn IB. During severe plastic deformation of Sn-Pb eutectic phase transition in the Sn grain boundary occurs. This deformation-induced process takes place due to the wetting of tin with Pb. These diffusion accommodation processes (sintering and wetting) are facilitated by the low values of the Pb/Sn interphase energy (0.07 J/m2). Wetting is thermodynamically favourable because the condition γgb > 2 γib is satisfied and it is also kinetically allowed due to the relatively high homologous temperature (> 0.5•Tm). The obtained values of the nanohardness and elastic modulus evidence that the IBs in the Sn–Pb eutectic have to be considered as a separate quasi-phase with its own properties.

The Role of Interphase Boundaries in the Deformation Behaviour of Fine-Grained Sn-38wt.%Pb Eutectics

The Role of Interphase Boundaries in the Deformation Behaviour of Fine-Grained Sn-38wt.%Pb Eutectics The mechanical properties of binary Sn-38wt.%Pb eutectic alloys in the deformed and annealed states were investigated at room temperature using tensile, micro- and nano-indentation tests. The softening and high plasticity of a deformed Sn-Pb eutectic are explained as a result of grain boundary sliding (GBS) and fast diffusion-driven processes developing along the Sn-Pb interphase boundaries (IBs). From the results of micro- and nano-hardness measurements it follows that the Sn and Pb phases in the annealed eutectic are strengthened, and the relaxation processes occur mainly at the IB. Such IBs in the annealed Sn-Pb eutectic act as barriers to the motion of a dislocation ensemble when the size of the plastic zone is comparable with the grain size, lowering the hardness values due to the development of GBS when more grains are involved in the process of deformation. The nanohardness and elastic modulus values obtained evidence that an IB in the Sn-Pb eutectic is to be considered as a separate phase with its own mechanical properties. Starpfāžu Robežu Loma Smalkgraudainās Sn-38at.%Pb Eitektikas Plastiskā Deformācijā Sn-Pb eitektiskais sakausējums tiek plaši pielietots gan elektrotehnikā, gan arī aparātbūvē. Darbā veikti deformētas un atkvēlinātas binērās Sn-38wt.%Pb eitektikas mehānisko īpašību un struktūras pētījumi, izmantojot stiepes, mikro- un nanocietības metodes. Deformētas eitektikas augstais plastiskums un mīkstināšanās deformācijas procesā izskaidroti ar slīdēšanu un difūzijas kontrolētu relaksācijas procesu norisi pa starpfāžu robežām. Atkvēlinātā eitektikā Pb un Sn fāzes uzrāda relatīvi augstu stiprību, bet deformācijas procesi ir lokalizēti starpfāžu robežās. Nanocietības un Junga modula dati liecina par to, ka starpfāžu robežas var uzskatīt par trešo fāzi, kurai ir savas īpašibas, kas nosaka eitektikas plastiskumu.