Viktor Puchý

Wear Behavior of ZrO2-CNF and Si3N4-CNT Nanocomposites

Tribological behavior of ZrO2 and Si3N4 based nanocomposites with addition of carbon nanofibres and nanotubes has been studied by the pin-on-disc technique. Friction coefficients were measured and recorded, wear rates were calculated in terms of material volume loss per load and sliding distance. The wear damage was studied using optical and electron microscopy and its mechanisms were identified. In monolithic materials the dominant wear mechanism was abrasion, in composites with CNF and with higher volume fraction of CNTs (5 and 10%) fiber pull-out and lubricating by the carbon phases occurred.

Effect of Microsecond Pulse Laser Modification on Electromagnetic Properties of Grain Oriented Silicon Steel

A microsecond pulsed laser beam was used to local magnetic domain modification of electrical grain oriented silicon steel. It was carried out using three different laser pulse regimes: a single pulse laser regime, a multipulse laser regime and a multipulse laser regime with modulation of laser pulses. The laser processing variables were pulse energy and and number of pulses. The samples were tested for nanohardness and coercivity before and after laser treatment. Light optical microscopy, scanning electron microscopy and magnetic force microscopy were used to observe the cross-sectional profile, surface of the samples, and magnetic domain visualization, respectively. The local laser treatment of grain oriented silicon steel surface has been studied in terms of its influence on the magnetic domains and coercivity. It was found that laser-modified samples showed coercivity improvement in comparison to the non-treated samples. The most significant improvement in coercivity was obtained in the modulated multipulse regime and negligible improvement in the single pulse laser regime. Three main effects responsible for the observed improvement were identified, namely: magnetic domain refinement, influence of number of laser pulses and shape of laser HAZ profile. The present work highlights on differences in the magnetic domain structure, microstructure of the laser modified material and basic electromagnetic and mechanical properties. In present study, the pulse laser surface processing was presented as a useful energy efficient alternative to other techniques e.g. mechanical scribing, electrical discharge scribing, plasma jet scribing, etc. The refined magnetic domains in electrosteels are responsible for the observed low coercivity, which indicates perspective application of the investigated laser modified steels in the power transformer cores with lower core losses.

Mechanical and Tribological Properties of Al2O3-ZrO2 Based Composites Prepared by EPD

Alumina and both tetragonal and cubic zirconia based composites with various volume fractions of constituents as well as with addition of carbon nanofibers were prepared by EPD. Mechanical properties (hardness, Youngs modulus) were measured by depth sensing indentation methods and related to chemical composition. Tribological behavior was studied using pin-on-disc technique at room temperatures in air at dry sliding. Coefficient of friction and wear rates were measured, the types of wear regimes were observed and damage micromechanisms identified.

Microstructure, Properties and Damage Mechanisms by Water Jet Cutting of TiB2-Ti Cermets Prepared by SPS

Process parameters of abrasive water jet (AWJ) machining of TiB2+Ti ceramic matrix composites with 10%, 15% and 20% of Ti reinforcement were investigated. The article focuses on microstructure damage processes and kerf geometry in AWJ machining of TiB2+Ti composites. Two different abrasive water jet cutting speeds and three sorts of composite materials, together with a reference monolithic one, are considered. Microstructure in machined samples was observed using scanning electron microscope. The characteristics of the cuts such as kerf top width, kerf angle and surface roughness were studied. The influence of cutting speed on abrasive process in composites with various amounts of Ti was investigated. It was found that roughness decreases and kerf taper ratio increases with increase in amount of Ti.

Magnetic losses reduction in grain oriented silicon steel by pulse and continuous fiber laser processing

The present paper shows the impact of different laser scribing conditions on possible reduction of magnetic losses in grain oriented electrical steel sheets. The experimental Fe-3%Si steel was taken from industrial line after final box annealing. The surface of investigated steel was subjected to fiber laser processing using both pulse and continuous scribing regimes in order to generate residual thermal stresses inducing the magnetic domains structure refinement. The magnetic losses of experimental samples before and after individual laser scribing regimes were tested in AC magnetic field with 50Hz frequency and induction of 1.5T. The most significant magnetic losses reduction of 38% was obtained at optimized conditions of continuous laser scribing regime. A semi quantitative relationship has been found between the domain patterns and the used fiber laser processing.