Materials Engineering - Materiálové inžinierstvo (MEMI - E-Journal)
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The influence of heat treatment on properties of lead-free solders
Get PDFThe article is focused on the analysis of degradation of properties of two eutectic lead-free solders SnCu0.7 and SnAg3.5Cu0.7. The microstructures of the intermetallic compound (IMC) layers at the copper substrate - solder interface were examined before and after heat treatment at 150°C for 50, 200, 500 and 1000 hours. The thickness of IMC layers of the Cu6Sn5 phase was growing with the increasing time of annealing and shown the typical scallops. For the heat treatment times of 200 hours and longer, the Cu3Sn IMC layers located near the Cu substrate were also observed. The experiments showed there is a link between the thickness of IMC layers and decrease of the shear strength of solder joints. In general, the joints made of the ternary solder showed higher shear strength before and after heat treatment in comparison to joints from solder SnCu0.7
Influence of the surface finishing on the corrosion behaviour of AISI 316L stainless steel
Get PDFThe influence of the surface preparation of AISI 316L stainless steel by mechanical grinding, polishing and following passivation was examined by immersion corrosion tests in solution simulating body fluids. Decreasing of the surface roughness by finer preparation resulted in decrease of corrosion rates of AISI 316L stainless steel. Passivation of specimens resulted in decreasing of the corrosion rates and in decreasing of the corrosion process speed independently on the roughness of specimens before passivations. Lowest corrosion rates were observed in the case of polished and passivated specimens. However no significant difference in corrosion rates between polished and ground specimens with following passivation was observed
Optimal welding technology of high strength steel S690QL
Get PDFIn this paper is presented the detailed procedure for defining the optimal technology for welding the structures made of the high strength steel S690QL. That steel belongs into a group of steels with exceptional mechanical properties. The most prominent properties are the high tensile strength and impact toughness, at room and at elevated temperatures, as well. However, this steel has a negative characteristic - proneness to appearance of cold cracks. That impedes welding and makes as an imperative to study different aspects of this steel's properties as well as those of eventual filler metal. Selection and defining of the optimal welding technology of this high strength steel is done for the purpose of preserving the favorable mechanical properties once the welded joint is realized; properties of the welded metal and the melting zone, as well as in the heat affected zone, which is the most critical zone of the welded joint
CHARACTERIZATION AND PERFORMANCE OF DUPLEX-COATINGS ON Cr-V COLD WORK TOOL STEEL
Get PDFSpecimens made of Vanadis 6 steel were heat treated, plasma nitrided and coated with Cr2N. The microstructure, phase constitution and mechanical properties of plasma nitrided areas and duplex-coatings have been investigated using the light microscopy, scanning electron microscopy, X-ray diffraction and microhardness measurements. The adhesion of the coatings and the wear performance were studied using the scratch test and ring-on-plate tribological testing. Worn surfaces were examined by scanning electron microscopy. Nitrided areas formed at lower temperature were free of compound “white” layer while hose developed at higher temperatures contained as the white layer so the nitrided network. Significant increase in substrate hardness was detected due to the nitriding. Beneficial effect of the nitriding on the adhesion of Cr2N coatings was clearly determined whereas the extent in improvement of the adhesion depends on the presence/no presence of “white” layer on the surface. The extent of beneficial effect of plasma nitriding on the wear performance follows the impact of the constitution of nitrided areas on the adhesion. The amelioration of wear performance of Cr2N coatings can be attributed to the supporting effect of hard nitrided intermediate region, which provides excellent resistance of the substrate against plastic deformation, under heavy loading in particular. Practical testing demonstrated many times prolonged service-time of duplex-treated tools for sheet metal working.
The Investigation of the Corrosion Resistance of the Tension Clamps Skl14
Get PDFAt the level crossings it is possible to find the problems with the corrosion of the parts of the fastening system. These problems are especially at the rubber level crossings and in the tunnels. As a part of the thesis the problem of the corrosion of the tension clamp Skl14 of the producer Vossloh at the rubber level crossings is examined. For the purposes of the comparison the tension clamps without the corrosion protection and the tension clamps with the corrosion protection KTL were examined. As a first step the corrosion features of the tension clamps Skl14 were solved. The examination was divided into two parts. First part it was the examination according to ČSN EN ISO 9227. The samples of the tension clamps were putted into the corrosion chamber. After 1728 h the results of the corrosion impacts were not satisfied. It was decided for the second step of the examination. It was the immersion in an electrolyte solution. As a result of the paper the corrosion features of the tension clamps without the corrosion protection and with the corrosion protection are compared
Study of the influence of agricultural waste on the porosity of clay brick
Get PDFThis paper deals with the influence of two organic residues on the porosity of clay bricks. The insulation capacity of the brick increases with increasing the porosity. Combustible organic additions are often used to form pores. The formation of the more homogenous porous structure is favourably impacted by using the crushed rough olive stones containing oil. Plasticity, bulk density and mechanical properties were studied. The additions of organic residues have proved successful to form pores while maintaining the mechanical properties in the limits of the Algerian norms
EVALUATION OF FIBRE LENGTH DISTRIBUTION IN A SHORT GLASS FIBRE REINFORCED PA-6
Get PDFThe aim of this work is to evaluate the fibre length distribution in a polyamide reinforced by short glass fibre. The fibre length and the fibre orientation distributions strongly influence the mechanical properties of short fibre reinforced composites. The sample investigated is a 30GFPA6 (polyamide-6 reinforced by 30 % by weight glass fibre), extracted from an injection-moulded plate. The digital reconstruction of the three-dimensional structure of the sample was obtained by synchrotron radiation micro-computed tomography (micro-CT), a high spatial resolution non-destructive technique. One global and one local method have been tested for the automatic evaluation of the fibre length distribution in our sample. The global method is based on the mean fibre length distribution computed from the Star Length Distribution (SLD), a morphological parameter. The local method is based on a 3D skeletonize function. The results are discussed in the light of the experimental data available in literature
Prediction of maximum casting defect size in MAR-M-247 alloy processed by hot isostatic pressing
Get PDFNickel based MAR-M-247 superalloy treated by hot isostatic pressing was investigated with the aim to identify the influence of casting defect size on fatigue life. Two testing temperatures of 650 and 800°C and one stress amplitude were chosen for fatigue tests. The Murakami approach and the largest extreme value distribution theory were applied. It has been found that the maximum size of casting defects in a specimen can be satisfactorily predicted. Fatigue life of specimens was in the good agreement with assumptions based on the evaluation and prediction of the casting defect size
ELECTROCHEMICAL METHODS TO IMPROVE THE WEAR RESISTANCE OF COATING DEPOSITED ON THE METAL SURFACE
Get PDFIt was established that existing methods show low accuracy when assessing the durability of coatings. Furthermore, they don’t allow assessment of the contribution into durability of structural components and fillers for thermodiffusion and polymer-composite coatings, respectively. A method to evaluate durability of thermal diffusion chrome coatings on carbon steel and gray cast irons has been developed - the speed υp of destruction of the structural components of the coating. In addition, the destruction of each structural component is characterized by a constant value of destruction speed υp and potential φ, and their sharp vibrations are in complete destruction of the coating and the beginning of the destruction of the base metal. From the start of the test until the abrupt change in the rate of destruction υp, which is found on the curve υp - τ is the assessment of durability coating t¶ hat is specified with the curve φ - τ. Accuracy of the durability decreases from ± 30 min to ± 2 min. Developed as a way to assess the durability fillers polymer composite coatings, along with the finding that the rate of destruction υp of the time includes total disability coverage t3aƧ and time breakdown cover τn which are fixed on the curve φ - τ.
Influence of the surface finishing on electrochemical corrosion characteristics of AISI 316L stainless steel
Get PDFStainless steels from 316 group are very often and successfully uses for medical applications where the good mechanical and chemical properties in combination with non-toxicity of the material assure its safe and long term usage. Corrosion properties of AISI 361L stainless steel are strongly influenced by surface roughness and treatment of the engineering parts (specimens) and testing temperature. Electrochemical characteristics of ground, mechanically polished and passivated AISI 316L stainless steel specimens were examined with the aim to identify the polarization resistance evolution due to the surface roughness decrease. Results obtained on mechanically prepared specimens where only natural oxide layer created due to the exposure of the material to the corrosion environment was protecting the materials were compared to the passivated specimens with artificial oxide layer. Also the influence of temperature and stabilization time before measurement were taken into account when discussing the obtained results. Positive influence of decreasing surface roughness was obtained as well as increase of polarization resistance due to the chemical passivation of the surface. Increase of the testing temperature and short stabilization time of the specimen in the corrosion environment were observed negatively influencing corrosion resistance of AISI 316L stainless steel