I. Manika

Effect of substrate hardness and film structure on indentation depth criteria for film hardness testing

The indentation depth limits for the Vickers microhardness testing of amorphous, polycrystalline, multilayer and single crystal coatings were investigated. The coating/substrate hardness ratio was varied in the range from 0.01 to 20. The critical indentation depth hc, below which the substrate has a negligible effect on the hardness, was estimated from the experimentally obtained hardness versus indentation depth curves. The results show a marked effect of the coating structure on the size of the influence zone beneath the indenter. The indentation depth limits were found to increase in the row of single crystal → polycrystalline → amorphous coatings. The obtained indentation depth criteria are compared with the reference data obtained by using finite element and kinematic calculations.

Hardening and long-range stress formation in lithium fluoride induced by energetic ions

Abstract LiF crystals were irradiated with Au, Pb, Bi and S ions in the energy range 400–2300 MeV and studied by means of Vickers microindentation. Remarkable hardening effects are observed which depend on the applied fluence and ion species, and correlate with the ion energy loss along the ion path. Structural investigations reveal irradiation-induced stress extending deep into the adjacent non-irradiated crystal and leading to the formation of dislocations. X-ray diffraction measurements of the irradiated crystals show a decrease of the lattice constant indicating the presence of internal stress.

Hardening and formation of dislocation structures in LiF crystals irradiated with MeV–GeV ions

Abstract Material modifications of LiF crystals irradiated with Au, Pb and Bi ions of MeV to GeV energy are studied by means of microindentation measurements and dislocation etching. Above a critical irradiation fluence of 10 9 ions/cm 2 , the microhardness can improve by a factor of 2 in the bulk and by more than 3 on the surface. Radiation-induced hardening follows the evolution of the energy loss along the ion path. Annealing experiments indicate that complex defect aggregates created in the tracks play a major role for the hardness change. Evidence for severe structural modifications is found when etching indentation impressions in highly irradiated crystals leading to similar pattern as in amorphous or micro-grained materials. Dislocation etching also reveals long-range stress fields extending far beyond the implantation zone deep into the nonirradiated crystal.

Swift-ion-induced hardening and reduction of dislocation mobility in LiF crystals

Ion-induced change in Vickers hardness and arm length of dislocation rosettes created by indentation on the (1 0 0) face of LiF crystals was studied. The irradiations were performed using swift U, Bi and Ni ions with a specific energy of 11 MeV per nucleon at fluences between 106 and 1013 ions cm−2. Remarkable effects of the ion-induced hardening and reduction of dislocation arm length were observed above the threshold fluences of about 109–1010 ions cm−2 and 106–107 ions cm−2, respectively. The products of track core damage and aggregates of single defects in the halo of overlapping tracks are responsible for the effects. The results are analysed using the Orowans model of dislocation impeding by strong obstacles. The advantages of the dislocation mobility method for the diagnostics of track damage at low-fluence irradiations are demonstrated.

Atmosphere-Induced Effect in Microhardness, Dislocation Mobility and Plasticity of C60 and Graphite Crystals

Abstract Formation of hard, brittle and toluene-insoluble near-surface layer (∼0.3 μm) of C60 crystals under atmospheric exposure was observed. Similar atmosphere-induced effect was found for graphite crystals and might also be expected for other molecular solids. Data on ageing kinetics of C60 and graphite crystals are presented. Variation of hardness with indentation depth can be described by the microhardness model for bilayer medium with different mechanical properties. Specific feature of C60 and graphite crystals is that no size effect appears in the intrinsic microhardness and dislocation mobility characteristics in the indentation depth range of 0.6–4μm.

Atmosphere-induced change of microhardness and plasticity of C60 single crystals and polycrystalline films

Abstract The effect of air exposure and visible light illumination on the microhardness, plasticity and dislocation mobility in the C60 single crystals was investigated. Microhardness values for defined structural states of the fullerene (pristine, oxygen-intercalated, photo-oxidized) are reported. It has been shown that oxygen intercalation in the fullerene lattice during air-aging in the dark results in the suppression of dislocation mobility. However, only a slight increase in the hardness of oxygenated samples was observed. A remarkable increase in the hardness and decrease in the plasticity of the C60 crystals under illumination-assisted air exposure was noted. Photochemical transformation was found to be localized in the nearsurface layer of 1–5 μm. The data on the recovery of the micromechanical properties of the photo-oxidized surface layer under heating in air are presented.

STRUCTURE AND MECHANICAL PROPERTIES OF AL-B COMPOSITE POWDER

Abstract Al-B composite powder has been obtained by crushing pieces of composite material presenting industrial waste. Structural peculiarities and microhardness of separate powder particles (d∼1 mm) have been investigated. Original design of high precision microhardness tester made it possible to detect the properties of powder both in near-surface layer and below it. The powder represents a new structurally non-homogenous material with the increased microhardness (1.5 GPa) which grows up to 4 GPa in near-surface layers. Stable oxide compounds are formed on internal surfaces and defects of the aluminium alloy. Powder compacts were obtained. Adhesion on Al–B and Al–Al interfaces at various temperatures and pressures were investigated. The applications of the powder compacts were considered.

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.

Temperature Dependence of the Microhardness and Dislocation Mobility in the Near-Surface Layer of C60 Crystals

Abstract Temperature dependence of the Vickers microhardness and dislocation mobility of as grown and aged in air C60 single crystals in the range of 300-550K has been investigated. An anomalous change of the hardness in the near-surface layer of C60crystals around 470K is observed which is explained by the phase transition from an oxygen-intercalated to an oxidised structure. the growth of the oxide film on heating the crystals in air at temperatures higher than 470K is detected, and hardness of 280 MPa of the oxide film is measured. the stress-promoted oxidation of fullerite in the local zones of indentation at 390-470K is discovered. It has been found that ageing of the crystals in air reduce the temperature of the stress-promoted oxidation.

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.