Materials Engineering - Materiálové inžinierstvo (MEMI - E-Journal)
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High Nitrogen Austenitic Stainless Steel Precipitation During Isothermal Annealing
Get PDFThe time-temperature-precipitation in high-nitrogen austenitic stainless steel was investigated using light optical microscopy, transmission electron microscopy, selected area diffraction and energy-dispersive X-ray spectroscopy. The isothermal precipitation kinetics curves and the corresponding precipitation activation energy were obtained. The diffusion activation energy of M2N precipitation is 129 kJ/mol. The results show that critical temperature for M2N precipitation is about 825°C with the corresponding incubation period 2.5 min
Fracture behaviour of weld joints made of pearlitic and bainitic steel
Get PDFThe paper is concerned with microstructure evaluations and the hardness and fracture behaviour of welded joints made from cast bainitic Lo8CrNiMo steel and pearlitic rail steel of the type UIC 900A. The materials mentioned are predetermined for frogs of switches. The study is based mainly on microstructural observations and hardness measurements of the base materials, weld, and heat affected zone (HAZ). Dynamic fracture toughness was evaluated based on data from pre-cracked Charpy type specimens. The pearlitic UIC 900A steel and its HAZ had the lowest dynamic fracture toughness values and therefore the highest risk of brittle fracture. At application temperature range, this steel is on the lower shelf of the ductile-to-brittle transition, and the tempering in the HAZ did not affect the toughness substantially. The cast bainitic steel in the weld joint is characterized by higher toughness values compared to the pearlitic one, and a further increase in toughness may be expected in the HAZ. The weld zone itself is characterized by high scatter of toughness data; nevertheless, all the values are above the scatter band characterizing the pearlitic steel
The variable contact pressure influence on the tensile force in the process of strip sliding in the flat die in ironing
Get PDFPossibilities to influence the deep drawing process during its duration are limited and generally consist of influences at the flange of the thin sheet, mainly by the contact pressure (the blank holding force). The common characteristics of previous investigations were setting of the fixed values of the blank holding force or the holder's pressure within the ironing tool. The objective of this investigation was the continuous setting of the variable pressure during the sliding process, via the preset functions, in order to analyze the variable pressure influence on the ironing process. This is why an experimental computerized device was designed and constructed for analyzing the influence of the variable contact pressure on the sliding process of the model strip during the flat-die test. The multi-parameter experiment was conducted; various materials of the tested pieces were applied (primarily thin sheet made of Al alloys and low-carbon steels sheet, with and without coating); different versions of the tool's contact elements were used, with various friction regimes and influential parameters (variable contact pressure during the sliding process, etc.). This experimental device practically represents a simulator for realization and studying of the physical model of an important segment of the ironing process in the completely realistic conditions (materials, tools, etc.). The aim was to find the optimal combination of the variable contact pressure and the tribological parameters, so that the punch force, as one of the process output parameters, would have the minimal value, as well as to avoid the undesired effects during the forming (difficult sliding of the flange, appearance of thin sheet's wrinkling, structural destruction, etc.). Understanding the mutual dependence of the holder's variable pressure and other influences should enable improvement of the ironing process control and should contribute to better understanding of the phenomena occurring at the thin sheet's flange.
Influence of processing on microstructure and mechanical properties of magnesium alloy AZ91
Get PDFThis paper deals with differences of mechanical characteristics and fracture surface morphology of AZ91 magnesium alloy in extruded state and after subsequent equal channel angular pressing (ECAP). According to the results, the tensile properties were not controlled by grain size only as values of the tensile strength and 0.2 proof stress were similar for both alloys despite having average grain size 15.9 μm for the extruded alloy and 1.2 μm for the ECAPed alloy. In contrast, microhardness seemed to be dependnt solely on the grain size. Fractographic analysis has shown changes in the damage mode from quasi-cleavage fracture in extruded state to rather ductile fracture with dimple morphology in exECAPed state during tensile loading.
Zirconia / Alumina Composite Foams with Calcium Phosphate Coating
Get PDFIn this study, mechanical properties of calcium phosphate foams were enhanced by zirconia/alumina porous cores prepared by polymer replica technique. This technique was chosen to ensure interconnected pores of optimal size for cell migration and attachment. The porosity of ZA cores (50 – 99%) was controlled by multistep impregnation process, the size of pore windows was 300 – 500 μm. Sintered ZA cores were impregnated by hydroxyapatite or β-tricalcium phosphate slurry to improve bioactivity. The bone like apatite layer was formed on coatings when immersed in a simulated body fluid. Neither of tested materials was cytotoxic. Thus, the composite foam can be potentially used as a permanent substitute of cancellous bone
Characteristics of diamond – like carbon(DLC) film deposited by PACVD process
Get PDFDiamond – like carbon (DLC) film is promising materials for many technical and engineering applications. DLC films are used in many different industries for example: in medicine, in electronics, in optics and the automotive industry. They have excellent tribological properties (low friction coefficient), chemical inertness and high mechanical hardness. This paper provides an analysis of the microstructure, mechanical and tribological properties of DLC films. In the study of the coating used several surface sensitive techniques and methods, i.e. High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM), Raman spectroscopy and tribological tests like ball-on-disc. HRTEM investigation shows an amorphous character of DLC layer. In sliding dry friction conditions the friction coefficient for the investigated elements is set in the range between 0.02-0.03. The investigated coating reveals high wear resistance. The coating demonstrated a good adhesion to the substrate.
Use of Cold Gas Dynamic Spraying of bi-metallic powder mixtures as alternative to classic powder metallurgy route for producing intermetallic materials
Get PDFThe paper presents cold gas dynamic spraying (or Cold Spray) as a novel surface treatment technology capable not only of surface modifications but also being used as bulk creating technology. This is demonstrated on numerous samples where bi-metallic powder feedstock is deposited into bulk, self-standing pieces of material that does not need the support of substrate. Mixtures from the group of Fe, Al, Ti, Ni, Cu were used for the initial bi-metallic mixtures. The deposited samples were then subjected to annealing at temperatures ranging from 300 to 1100°C in protective atmosphere and resulting morphologies and microstructures were analysed. Generally materials with high proportion of intermetallic phase content were obtained. These are discussed as potential scaffolds for metal or polymer matrix composites or as hi temperature resistive supports for catalysts with filter functions.
Magnetic nanostructures formation via local anodic oxidation and magnetron sputtering through lithographic mask
Get PDFChanges of magnetic properties of thin metallic films caused by the magnetron sputtering technique and by oxidation lithography were studied. The magnetic nanostructure formation was done via a lithography by sputtering the material through a mask. The anodic oxidation lithography (LAO) via scanning probe microscopy (SPM) device Ntegra Aura was used to attempt to create the magnetic nanostructures. At the beginning, the work has been scoped to the preparation and testing multilayered magnetic nanostructures based on different combinations in material composition of layers. The magnetic properties of these samples were examined by Kerr phenomenon. We observed increasing of the magnetic hardness of the magnetic nanostructure when the copper layer in the composition of ferromagnetic and antiferromagnetic multilayers has been replaced by an aluminium layer. Adding the aluminium layer onto the copper layer resulted in a decrease of magnetic hardness. This work was followed by creating of horizontal nanostructures by LAO. Changes induced by the LAO observed in the magnetic properties of the samples correspond mainly to topographical changes of the surface. Changes in the magnetic properties induced by LAO or by a variability of sputtered layers could lead to the further production of magnetic printed circuit or photonic nanostructures
Experimental and numerical investigation of a simplified exhaust model
Get PDFA simplified experimental equipment was built to investigate heat radiation and free convection around hot exhaust pipe. Temperatures were measured on the surface of the pipe as like as on heat insulating and -reflecting aluminum shield. Special care was taken to the temperature measuring method: result proved that inappropriate fixing of measuring thermocouples lead to an error of up to 30 % in the temperature-increase values. A detailed 1D numerical model was set up and parametrized so as to the calculation results can be fitted to measured temperature values. In this way thermal properties of the surfaces – as emissivities, absorption coefficients and convective heat transfer coefficients – were determined for temperature sweeps and stationary state cases. The used methods are to be further improved for real automotive parts and higher temperatures
Changes in mechanical properties of as-cast magnesium alloy AZ91 after equal channel angular pressing
Get PDFThis paper deals with differences in mechanical characteristics of AZ91 magnesium alloy in the as-cast state and after the subsequent equal channel angular pressing (ECAP) and with measurement of local microhardness. According to the obtained results, the tensile properties increased by a factor of two due to the ECAP procedure. The proof stress, σ0.2, increased to 160 MPa and the ultimate tensile strength, σUTS, to 321 MPa. The local microhardness of ECAPed alloy varied between 70 and 91 HV 0.025 due to microstructural bimodality.