K. Sülleiová’s research while affiliated with Slovak Academy of Sciences and other places

The present paper is devoted to the possibilities to classify the spatial arrangement of the elements (features) of a stochastic process with geometrical objects. The fundamental quantities describing point processes were introduced. Experimental possibilities of structural objects determination, possibilities of evaluation of the size distribution of the secondary phases, testing of planar point structures (estimation of the process intensity, square method and characteristics of the second order) were estimated. Interparticle distances, namely mean interparticle distance, mean minimum distance, mean visibility and mean path of spherical contact were defined. Selected processes were described and demonstrated from simulated realizations on Al-Al4C3 dispersion strengthened material, prepared by a powder metallurgy method of reaction milling. Interparticle distances of Al4C3 particles were evaluated. Polygonal methods and quadrant counts method were used for characterization of the particle arrangement.

The tribological behavior of AZ31 Mg alloy reinforced with multiwall carbon nanotubes (MWCNTs) was studied through experiments on a ring-on-block wear testing apparatus against 45C steel. The composites were successfully fabricated using stir-casting processing with different percentages of MWCNTs and then age hardened for 10 h. The effect of the various concentrations of MWCNTs on the microstructures, tribological properties, and wear mechanisms of the composites were systematically examined by scanning electron microscopy (SEM). With increasing percentage content of MWCNTs, the wear rate and the coefficient of friction decreased, which is attributed to the microhardness and self-lubricating properties of the MWCNTs. The microstructure characterization results established different mechanisms—specifically, abrasion, oxidation, and delamination—and very small plastic deformation.

p>The present paper is devoted to the possibilities to classify the spatial arrangement of the elements (features) of a stochastic process with geometrical objects. The fundamental quantities describing point processes were introduced. Experimental possibilities of structural objects determination, possibilities of evaluation of the size distribution of the secondary phases, testing of planar point structures (estimation of the process intensity, square method and characteristics of the second order) were estimated. Interparticle distances, namely mean interparticle distance, mean minimum distance, mean visibility and mean path of spherical contact were defined. Selected processes were described and demonstrated from simulated realizations on Al-Al₄C₃ dispersion strengthened material, prepared by a powder metallurgy method of reaction milling. Interparticle distances of Al₄C₃ particles were evaluated. Polygonal methods and quadrant counts method were used for characterization of the particle arrangement.</p

Micromechanisms of fracture of AZ61-F composites in the zone of quasi-superplastic deformation were analyzed and quantified in this work. Deformation of AZ61-F magnesium alloys with 1 wt.% of Al₂O₃ phase was tested at a temperature of 473 K and different strain rates. It was shown that at the temperature of 473 K and the highest strain rate applied from 1 × 10 ^{− 2} to 1 × 10 ^{− 4} s ^{− 1}, a significant growth of ductility was observed. The mean dimples diameter of the ductile fracture decreased with the decreasing strain rate. The grain size of 0.7 μm was reached by severe plastic deformation using equal channel angular pressing (ECAP). Secondary Mg₁₇Al₁₂ and Al₂O₃ phases were identified. The maximum strain was reached at the temperature of 473 K and strain rate of 1 × 10 ^{− 4} s ^{− 1}.

The development of the nanostructure in commercial pure copper and the strength and ductility after severe plastic deformation (SPD) with the technology of equal channel angular pressing (ECAP) are analysed. Experimental results and analyses showed that both strength and ductility can be increased simultaneously by SPD. The final grain size decreased from the initial 50μm by SPD to 100-300 nm after 10 passes. An increase of the ductility together with an increase of strength caused by SPD are explained by a strong grain refinement and by a dynamic equilibrium of weakening and strengthening, and it is visible on the final static tensile test stress-strain charts.

Micromechanisms of fracture of AZ61-F composites in the zone of quasi-superplastic deformation were analysed and quantified in this work. Deformation of AZ61-F magnesium alloys with 1 wt.% of Al2O3 phase was tested at a temperature of 473 K and different strain rates. It was shown that at the temperature of 473 K and the highest strain rate applied from 1 × 10⁻² to 1 × 10⁻⁴ s⁻¹, a significant growth of ductility was observed. The mean dimples diameter of the ductile fracture decreased with decreasing strain rate. The grain size of 0.7 μm was reached by severe plastic deformation using equal channel angular pressing (ECAP). Secondary Mg17Al12 and Al2O3 phases were identified. The maximum strain was obtained at the temperature of 473 K and strain rate of 1 × 10⁻⁴ s⁻¹.

The micromechanisms of fracture of AZ61 + 1 wt. % Al2O3 composite in the zone of superplastic deformation was analysed and quantified in this work. The specimens were tested at temperature of 200°C at different strain rates. Changing the strain rate, from 1x10⁻² s⁻¹ to 1x10⁻⁴ s⁻¹, a significant growth of ductility was observed. At maximum value of superplasticity the fracture was transcrystalline ductile with dimples of two size categories. Based on the statistical analysis of fracture micromechanisms at the elevated temperature and strain rates of 10⁻⁰- 1x10⁻⁴ s⁻¹ hyperbolic dependency was depicted according to Gurland - Plateau theory.

Deformation of AZ61-F magnesium alloys with 1 wt % of Al2O3 phase was tested at different temperatures and different strain rates. It was shown that at temperatures 473–523 K and the highest strain rate applied from 1×10–2 s–1 to 1×10–4 s–1, a significant ductility growth was observed. The grain size of 0.6–0.8 μm was reached by severe plastic deformations by means of equal channel angular pressing (ECAP). Secondary Mg17Al12 and Al2O3 phases were identified. Maximum strain was gained at temperature of 473 K and strain rate of 1×10–4 s–1.