Papers by Author: Leszek Adam Dobrzański

Abstract: The purpose of this work is the development of the aluminium alloy matrix composite materials using powder metallurgy technologies, including mechanical alloying and hot extrusion with the required properties and structure of the designed material. In this work halloysite nanotubes, was used as alternative reinforcement of metal matrix composites. Halloysite is a clayey mineral of volcanic origin, characterised by high porosity, high ion exchange, large specific surface and easy chemical, as well as mechanical treatment. High energy ball milling leads to uniform distribution of the halloysite reinforcing particles throughout the AlMg1SiCu matrix and simultaneously reduces the particle size. Proved microstructural changes influence the mechanical properties, especially microhardness, and compression yield, as well as wear resistant. The tribological analysis reveals that composite materials – irrespective of the measuring cycles number and load – are characterised by much smaller wear volume in comparison to the matrix material. The MMCs obtained as a result of mechanical alloying, cold compacting and hot extrusion are characterised with the microstructure of homogeneous distribution of halloysite particles in fine-grain matrix of AlMg1SiCu alloy, facilitate the obtainment of higher values of mechanical properties, compared to the base alloy. The composite materials reinforced with nanoparticles with 15% mass share are characterised by more than 180% higher yield strength and almost twice as higher microhardness compared to the matrix material. The analysis of the investigation results has confirmed that halloysite nanotubes can be applied as effective reinforcement in the MMCs.

Abstract: The article presents the strategic positions of 140 critical materials surface engineering technologies. Critical technologies are such having the best development prospects and/or key significance in industry for the assumed time horizon. For the purpose of preparing forecasts and analyses, expert studies were carried out comprised of three stages with the e-Delphix method. The strategic positions of the technologies were expressed with numbers and entered into the matrix of strategies for technologies consisting of 16 fields.

Abstract: The investigations results concern the influence of laser heat treatment on the structure and mechanical properties of aluminium alloy, where the mutual relationships were tested and presented in this paper. The aim of this investigations was to improve the mechanical and wear resistance properties of the top surface layers of the aluminium alloy AlSi12CuNiMg by remelting and feeding the tungsten carbide powder in to the molten material and next quick solidification. The powder of tungsten carbide has been introduced in the liquid metal using gravity feeder at a constant rate of 3 g/min. In order to remelting the aluminium alloy surface, there has been used the high power diode laser HPDL, with an applied power of the laser beam in the range between 1.6 kW and 2.0 kW. The linear laser scan rate of the beam was set as much as 0.4 m/min. As a result of laser treatment of aluminium alloy a composite layer with higher hardness and enhanced wear resistance compared to the base material has been obtained.

Abstract: The investigations are focused on high-manganese austenitic steels used for reinforcing elements of car body. The purpose of this work was to examine the influence of thermo-mechanical treatment workout using Gleeble simulator and LPS module for semi-industrial hot-rolling on the structure and transformations occurring during cold deformations. Thermo-mechanical treatment consists of four passovers with a planned strain rate of about 20%. There were three variants of cooling after thermo-mechanical treatment: cooling in water, natural air-cooling and cooling in water after isothermal holding in the temperature of last deformation 850°C for 30 s. Structural observation were carried on LEICA MEF4A light microscope, analysis of the chemical composition were made with XPert PRO diffractometer, and the results were analyzed with OriginLab. It was found that the high-manganese austenitic X11MnSiAl7-1-3 steel after thermo-mechanical treatment on Gleeble simulator is characterized by dynamically recrystallized structure. In intervals time between each compression metadynamic and static recrystallization take place. After hot-rolling these steels has austenitic structure with dynamically recovered grains and with small metadynamically and statically recrystallized grains that are located on a border of elongated grains of austenite.

Abstract: In the present work selected results of TEM and XRD investigations of the new AA-6061 matrix composite materials reinforced with halloysite nanoparticles manufactured by mechanical alloying and hot extrusion are present. Halloysite nanotubes, being a clayey mineral of volcanic origin which is characterized by high porosity, large specific surface, high ion exchange and easy chemical and mechanical treatment, can be used as alternative reinforcement of metal matrix composite materials. The composite materials obtained as a result of mechanical alloying and hot extrusion are characterized with the structure of evenly distributed, disperse mineral phase particles in fine-grain matrix of AA-6061 alloy, facilitate the obtainment of higher values of strength properties, compared to the initial alloy. Thanks to HRTEM analysis, the occurrence of grains sized ca. 20÷30nm in the composite materials reinforced with halloysite nanotubes with 15% mass share has been confirmed. The crystallite size and lattice strain of the obtained composites were calculated from X-ray line broadening, applying different profiles of diffraction lines. The achieved values of crystallite size for composites powders after 6 hours of milling were in the range 65-150nm, depending on the calculation method.

Abstract: Taking into consideration increased quantity of accessories used in modern cars, decreasing car’s weight can be achieved solely by optimization of sections of sheets used for bearing and reinforcing elements as well as for body panelling parts of a car. Application of sheets with lower thickness requires using sheets with higher mechanical properties, however keeping adequate formability. The goal of structural elements such as frontal frame side members, bumpers and the others is to take over the energy of an impact. Therefore, steels that are used for these parts should be characterized by high value of UTS and UEl, proving the ability of energy absorption. Among the wide variety of recently developed steels, high-manganese austenitic steels with low stacking faulty energy are particularly promising, especially when mechanical twinning occurs. Beneficial combination of high strength and ductile properties of these steels depends on structural processes taking place during cold plastic deformation, which are a derivative of SFE of austenite, dependent, in turn on the chemical composition of steel and deformation temperature. High-manganese austenitic steels in effect of application of proper heat treatment or thermo-mechanical treatment can be characterized by different structure assuring the advantageous connection of strength and plasticity properties. Proper determinant of these properties can be plastic deformation energy supply determined by integral over surface of cold plastic deformation curve. Obtaining of high strength properties with retaining the high plasticity has significant influence for the development of high-manganese steel groups and their significance for the development of materials engineering.

Abstract: The aim of this work is to determine the effect of a reinforcing phase and manufacturing conditions on the structure and properties of newly developed nanostructural powders of composite materials with the aluminium alloy matrix reinforced with natural halloysite nanotubes. Composite materials were manufactured employing as a matrix the air atomized powders of AA 6061 aluminium alloy and as a reinforcement the halloysite nanotubes. Composite powders of aluminium alloy matrix reinforced with 5, 10 and 15 wt.% of halloysite nanotubes were fabricated by high-energy mechanical alloying using a planetary mill. Elaborated composite powders were characterized for their apparent density, microhardness, particle size distribution and microstructure. A structure of newly developed nanostructured composite materials reinforced with halloysite nanotubes prove that a mechanical alloying process allow to improve the arrangement of reinforcing particles in the matrix material. A homogenous structure with uniformly arranged reinforcing particles can be achieved by employing reinforcement with halloysite nanotubes if short time of mechanical alloying is maintained thus eliminating an issue of their agglomeration.

Abstract: The high-manganese austenitic steels are an answer for new demands of automotive industry concerning the safety of passengers by the use of materials absorbing high values of energy during collisions. The chemical compositions of two high-manganese austenitic steels containing various Al and Si concentrations were developed. Additionally, the steels were microalloyed by Nb and Ti in order to control the grain growth under hot-working conditions. The influence of hot-working conditions on a recrystallization behaviour was investigated. Flow stresses during the multistage compression test were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steel was compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light microscopy. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25) Mn alloys. Making use of dynamic and metadynamic recrystallization, it is possible to refine the microstructure and to decrease the flow stress during the last deformation at 850°C. Applying the true strains of 0.23 and 0.19 requires the microstructure refinement by static recrystallization. The obtained microstructure – hot-working relationships can be useful in the determination of powerful parameters of hot-rolling and to design a rolling schedule for high-manganese steel sheets with fine-grained austenitic structures.

Abstract: This paper presents technology of multicrystalline silicon solar cells with laser texturisation step. The texturing of polycrystalline silicon surface using Nd:YAG laser makes it possible to increase absorption of the incident solar radiation. Moreover, the additional technological operation consisting in etching in 20 % KOH solution at temperature of 80°C was introduced into technology of the photovoltaic cells manufactured from laser textured wafers allows to remove laser induced defects but cause the texture to flatten out reducing it optical effectiveness. This paper demonstrates, that laser processing is very promising technique for texturing multicrystaline silicon independent on grains crystallographic orientation compared to conventional texturing methods in technology of solar cells.

Abstract: The purpose of this research paper is focused on the high speed steel surface layers improvement properties using HPDL laser. The paper present laser surface technologies, investigation of structure and properties of the high speed steel alloying with carbides using high power diode laser HPDL. Investigation indicate the influence of the alloying carbides on the structure and properties of the surface layer of investigated steel depending on the kind of alloying carbides and power implemented laser (HPDL). In the effect of laser alloying with powder of carbides occurs size reduction of microstructure as well as dispersion hardening through fused in but partially dissolved carbides and consolidation through enrichment of surface layer in alloying additions coming from dissolving carbides. Introduced particles of carbides and in part remain undissolved, creating conglomerates being a result of fusion of undissolved powder grains into molten metal base. The structural mechanism was determined of surface layers development, effect was studied of alloying parameters, gas protection method, and thickness of paste layer applied onto the steel surface on structure refinement and influence of these factors on the mechanical properties of surface layer, and especially on its hardness, abrasive wear resistance, and roughness. It has the important cognitive significance and gives grounds to the practical employment of these technologies for forming the surfaces of new tools and regeneration of the used ones.