Papers by Author: Leszek Adam Dobrzański

Abstract: In this paper there is presented the structure and proprieties of the modeling cast magnesium alloys as cast state and after heat treatment, depending on the cooling medium (furnace, water, air), with different chemical composition. The improvement of the manufacturing technique and chemical composition as well as of heat treatment and cooling methods leads to the development of a material designing process for the optimal physical and mechanical properties of a new developed alloy. In the analysed alloys a structure of solid solution and fragile phase  (Mg17Al12) occurred mainly on grain borders as well as eutectic and AlMnFe, Mg2Si phase. The investigation is carried out to testy the influence of the chemical composition and precipitation processes on the structure and mechanical properties of the magnesium cast alloys with different chemical composition in its as cast alloys and after heat treatment.

Abstract: The properties of thin hard coatings and consequently their functionality are influenced by microstructural characteristics such as mechanical properties. A variety of interlayers has been used in hybrid coatings for various purposes. The paper presents investigation results of the structure, erosion and corrosion resistance, and mechanical properties of the galvanic Ni/Cr, hybrid Ni/Cr + Zr/ZrN (galvanic + PVD) and monolithic nitride coatings deposited by PVD technique (dc magnetron sputtering) onto brass (CuZn40Pb2) substrates. The ceramic PVD coatings or layers are the Cr-, Ti-, TiAl-, Zr-nitrides. The investigation covered the metallographic analysis on the scanning electron microscope, mechanical properties and erosion test. The corrosion tests were made in a 1 M NaOH solution. It was found out that PVD coatings display high corrosion resistance.

Abstract: The work presents the research results of modern composite materials. The matrix material was EN AC AlSi12 alloy while the reinforcement ceramic preforms, obtained through sintering process of Al2O3 Alcoa CL 2500 powder with addition of carbon fibers as pore forming agent burned out during sintering. The composites were produced with use of porous material pressure infiltration method. The main limitation of base technology is a difficulty in obtaining composite materials with volumetric participation of ceramic phase in amount not less than 20%. Obtained on the base of ceramic preforms composite materials were tested with scanning electron microscopy. Additionally, hardness and tensile test was performed for acquired materials. Achieved results indicate the possibility of producing, with use of pressure infiltration method, porous preforms composed of Al2O3 particles, new composite material with desired microstructure and properties, being a cheaper alternative for materials with base of ceramic fibers.

Abstract: This investigation aims at establishing the relationships between the thermomechanical conditions and the mechanical properties of a direct injection moulded polypropylene/polycarbonate blend (70/30wt composition). Rectangular plates (2 mm thick) were injection moulded by systematic variations of the processing conditions. The moulding programme was based on a design of experiments (DOE) approach, being considered variations in two levels of the melt (240 and 280°C) and the mould (5 and 80°C) temperatures and the injection flow rate (3.8 and 38 cm3/s). For comparison purposes, neat polypropylene was also moulded under the same set of processing conditions. In both cases the thermomechanical environment was characterised by computer simulations of the mould filling phase using commercially available codes (Moldflow). Tensile specimens were cut from the injected plates. The microstructure of the mouldings was characterized by polarized light microscopy, PLM. The mechanical characterization encompass the assessment of the tensile (at 5 mm/min at 23 °C) and impact toughness (unnotched Charpy test). The results are analysed by ANOVA. The presence of PC particles affects the crystallization of PP, this being revealed on the mouldings microstructures observed by PLM that are distinct for the neat and PP/PC blends. The mechanical properties are determined differently by the processing variables.

Abstract: Basing on the experimental results of the hardenability investigations, which employed Jominy method, the model of the neural networks was developed and fully verified experimentally. The model makes it possible to obtain Jominy hardenability curves basing on the steel chemical composition. The modified hardenability curves calculation method is presented in the paper, initially developed by Tartaglia, Eldis, and Geissler, later extended by T. Inoue. The method makes use of the similarity of the Jominy curve to the hyperbolic secant function. The empirical formulae proposed by the authors make calculation of the hardenability curve possible basing on the chemical composition of the steel. However, regression coefficients characteristic for the particular steel grade must be known. Replacing some formulae by the neural network models is proposed in the paper.

Abstract: Investigations carried out referred to obtaining material based on the high-speed steel and non-alloy steel. The conventional powder metallurgy method was used for manufacturing these materials, consisting in compacting the powder in the closed die and sintering it next, the isostatic pressing method, and the modern pressureless forming powder metallurgy. Forming methods were developed during the investigations for high-speed and non-alloy steel powders, making it possible to obtain materials with three layers in their structure. Investigations included determining the sintering conditions, and especially the temperature and treatment cycle, as well as examining the selected mechanical properties. It was found out, basing on the comparison of structures and properties of test pieces made with the pressureless forming method, as well as with the isostatic pressing and pressing in the closed die, with further sintering, that in structures of all examined test pieces in the sintered state fine carbides occurred distributed homogeneously in the high-speed steel layer. It was noticed, that increase of the sintering temperature, regardless of the manufacturing method, results in the uncontrolled growth and coagulation of the primary carbides and melting up to forming of eutectics in layers consisting of the high-speed steel. It was found out basing on the microhardness tests that hardness of test pieces both those pressureless formed, compacted in the closed die, and isostatically cold pressed and sintered grows along with the sintering temperature. It was also noted that the sintering temperature range is bigger in case of the pressureless formed materials.

Abstract: Investigations of composite materials based on EN AW-Al Cu4Mg1(A) aluminum alloy reinforced with the Ti(C,N) particles with various weight ratios of 5, 10 and 15% are presented. The metallographic examinations of composite materials show banding of the reinforcing particles in aluminum matrix after extrusion process. Structure oriented in parallel with extrusion direction is observed in composites materials. Portion of reinforcement particles Ti(C,N) has influence on the mechanical properties of composite materials. The increase of hardness, abrasive wear and decrease of compression strength, tensile strength is observed with the portion growth of reinforcement particles.

Abstract: The paper presents investigation results of tribological and cutting properties of the coatings deposited with the PVD and CVD techniques on cutting inserts made from the Al2O3 + TiC tool ceramics. Tests were carried out on the inserts made from ceramics, uncoated and PVD or CVD-coated with gradient, mono-, multilayer and multicomponent hard wear resistant coatings composed of TiN, TiCN, TiAlN, TiAlSiN and Al2O3 layers. Substrate hardness tests and micro hardness tests of the deposited coatings were made on the ultra-micro-hardness tester. It was demonstrated, basing on the technological cutting tests of grey cast iron (260 HB), that putting down onto the tool ceramics the thin anti-wear PVD and CVD coatings increases their abrasion wear resistance, which has a direct effect on extending tool life of the cutting edge.

Abstract: Computer based classification methodology is presented in the paper for defects being developed in the Al alloys as the car engine elements are made from them produced with the vacuum casting method. Identification of defects was carried out using data acquired from digital images obtained using the X-ray defect detection methods. The developed methodology as well as the related X-ray image analysis and quality control neural networks based software were carried out to solve this problem.

Abstract: This work presents mechanical properties and corrosion resistance of duplex stainless steels obtained through powder metallurgy starting from austenitic X2CrNiMo17-12-2 (AISI 316L), martensitic X6Cr13 (AISI 410L) powders by controlled addition of alloying elements in the proper quantity to obtain the chemical composition of the structure similar to biphasic one. In the mixes preparations the Schaffler’s diagram was taken into consideration. Prepared mixes of powders have been sintered in a vacuum furnace with argon backfilling. After sintering rapid cooling was applied using nitrogen. Produced duplex stainless steels have been studied by SEM with EDS and light optical microscopy (LOM) and X-rays analysis to determine obtained structures. Corrosion properties have been studied through electrochemical methods in 1M NaCl.