Materials Engineering - Materiálové inžinierstvo (MEMI)
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Examination and Polishing of Surface Scratches on Handheld Devices
Get PDFPollution is a current environmental problem. Personal used mobile phones and devices with LCD displays are often thrown away only the optical matter. The renewal of these device surfaces is at the focus of common interest. Our examination was a well-defined micro-scratch test using a special microhardness and scratch tester equipment (MCT). This equipment provides four different means of analyzing the scratch: acoustic emission detection, tangential force measurement, scratch depth measurement, optical observation through a digital microscope. The scratches were made with normal force from 0.5 to 15 N, the same length (20 mm) with the same diamond indenter. The scratches were analyzed with contact and non-contact methods, laser surface topographical analysis, optical microscopic examination, and surface roughness testing. On the LCD display we created specified scratches with the MCT scratch tester and after these scratches had to be repaired by polishing. Three different polishing speeds and loads were used. The measured wear rates show that higher polishing loads result increased wear rates but this trend does not true for the polishing speed
Surface property control by electron beam deflection during hardening
Get PDFThe usage of the high-energy electron beam source enables repeated surface quenching of chosen locations of an engineering part surface. Different techniques of electron beam deflection allow creating hardened layers of different shapes, hardness levels and thicknesses. Experiments were carried out with 42CrMo4 (1.7225) steel. The deflection modes tested were one-point, 6-point, line, field, and meander. The influence of process speed and defocusing of the electron beam was also taken into account. The electron beam surface quenching resulted in a very fine martensitic microstructure with a hardness of over 700 HV0.5. The thickness of the hardened layers depends on the deflection mode and is affected directly (except field deflection) by process speed. The maximum hardened depth (NCHD) was 1.49 mm. Electron beam defocusing affects the width of the hardened track and can cause extension of the trace up to 40%. The hardness values continuously decrease from the surface to the material core
Fracture toughness transition of ferritic-pearlitic steel at static and dynamic loading evaluated by Master curve concept
Get PDFThe paper focuses on assessing the usability of fatigue pre-cracked Charpy type specimens when evaluating the resistance of steel with ferritic-pearlitic structure to the initiation of unstable fractures. The suitability of using the specimens is evaluated on the basis of comparing experimentally established values of fracture toughness on pre-cracked Charpy type specimens and the values of this characteristics determined using Compact Tension (CT) specimens. For the evaluation and comparison of the fracture toughness temperature dependences determined on individual specimen types the master curve concept quantifying fracture toughness transition was applied. In the case of the steel employed, very good agreement was found to exist between the characteristics determined on individual types of specimen. It was shown that fracture toughness determined on pre-cracked Charpy type specimens can be regarded as a representative measure of resistance of the material employed to the brittle fracture occurrence
Mechanical properties of AlSi10Mg alloy processed by SLM
Get PDFThe paper deals with mechanical properties of AlSi10Mg aluminium alloy processed by the selective laser melting (SLM) technique. The influence of surface quality and building orientation of the samples on mechanical properties was evaluated. It was found that orientation of the samples had no effect on tensile properties (UTS, 0.2% proof stress) whereas surface quality had a significant effect. An 11% increase in ultimate tensile strength was found in the case of samples of lower surface roughness, and an increase of almost factor two in elongation at break was found for machined samples in comparison to as-built samples
Residual life of external steel constructions
Get PDFThe contribution is focused to the aspects of prevention untimely damage of exterior steel constructions at variable climatic conditions. The aspects for assurance of continual service of strategic steel constructions (bridges, pipelines, pylons, pressure vessels, containers, frameworks, cranes, chimneys, towers, etc.) is by action of severe climatic conditions in our climatic zones deteriorative. The service safety of construction mentioned is decreasing and could cause preterm damages. To avoid preterm damage there are two ways. First is to create conditions excluding the damage and second is proposal of construction safety also after expected limit state. During the lifetime is needed to assure failure free service of external steel constructions stressed by variable loading. At the same time is needed to calculate with action of aggressiveness of external environment as well as worsen atmospheric conditions. From load and conditions analysis could be calculated the residual life of external steel constructions
Production of hydroxyapatite-titanium composite powders by high-energy ball milling suitable for spark plasma sintering processes
Get PDFHydroxyapatite-titanium (HA-Ti) composite powders were prepared by high-energy ball milling for subsequent production of samples by spark plasma sintering (SPS). Different milling times for the preparation of HA-Ti composite powders were used. The microstructural properties and phase composition of the composite powders were studied by scanning electron microscopy and X-ray analysis. The results showed no formations of new phases in the structure during high-energy ball milling and a gradual reduction of the particles size with increasing milling time. Sintered samples from HA-Ti composite powder were prepared. A cross section analyzed by SEM and phase composition obtained by X-ray diffraction was studied. The results showed changes of phase compositions in the structure.
Examination of metal side heating of LAMP joint by CO2 laser beam
Get PDFNowadays the vehicle industry is focusing on making materials and technologies for automotive parts that satisfy the newest requirements. Reduction of the manufactured vehicle’s weight is such a requirement. There exist many solutions to satisfy this requirement. One of them is when hybrid materials is combined and fixed together. In this research some aspects of the hybrid joining process of steel and PMMA sheet were investigated. Due to the non-transparent type joining CO2 laser were applied from the metal parts and the laser power and the speed of spot movement were changed in order to roughly determine the process window. In case of adhesive based joining the surface conditions have high importance on the bond strength, therefore the effect of cleaning and blasting of the metal surface was also examined. To determine the role of the value of clamping force it was also changed in some cases. Tensile tests were carried out and the tearing force and the bonded area were measured. In this way the joint strength was determined in case of different setting. New bubble formation was also detected during the process
Corrosion resistance of AZ31 magnesium alloy influenced by conventional cutting fluid
Get PDFThis paper deals with the evaluation of cutting fluid impact on corrosion resistance of AZ31 magnesium alloy in aggressive environment containing chloride ions supported by photo documentation. Ground samples were immersed in the standard commercial cutting fluid for 5 minutes to simulate conditions during machining process at the temperature of 22 ± 2 °C and subsequently cleaned and immersed in 0.1M NaCl solution at the temperature of 22 ± 2°C in order to measure electrochemical corrosion characteristics. Cyclic potentiodynamic polarization (CPP) tests were chosen as a testing method. The measured CPP curves of immersed samples and ground samples were analysed by Tafel extrapolation method. The values of obtained electrochemical characteristics show that the chosen cutting fluid has negative effect on corrosion resistance of AZ31 magnesium alloy in sodium chloride solution.
The effect of high temperature annealing in different atmospheres on microstructure of ODS materials
No full textMechanically alloyed oxide dispersion strengthened materials MA 6000 and MA 956 have been annealed at 1100ºC for 24 and 240 hours in air, vacuum of 10 -3 Pa and hydrogen atmosphere.. Mass changes due to oxidation and evaporation were measured. Fracture surfaces, microstructure of the materials and changes in chemical composition were examined along with surface layers evolution and pores formation. On fracture surfaces and polished sections, formation of voids and altered microstructure sub-surface zones in both materials has been studied. Different mechanisms causing void formation are discussed and proposed in discussion. Also the mechanisms and reaction sequences of surface oxidation reactions are examined
On the recrystallization and texture of Fe-36%Ni alloy after accumulative roll bonding and annealing at 600 °C
Get PDFMicrostructure and texture evolution of Fe-36%Ni (wt.%) alloy after 1, 5 and 10 accumulative roll-bonding (ARB) cycles and annealing at 600 °C up to 3600 seconds were studied using electron backscatter diffraction. Microstructural and textural changes after ARB and annealing were compared to those existing in the literature after conventional rolling. The microstructure was not stable at 600 °C for all ARB samples even after 3600 seconds of annealing. The recrystallization texture was dominated by the Cube {001} texture component. Recrystallization kinetics were determined using microhardness measurement and were close to those after cold rolling with Avrami time exponent around unity. The texture evolution at high strain was discussed in terms of grain boundary migration obstruction by the formation of layer interfaces and small recrystallized grains near the bonded interfaces