Key Engineering Materials Vol. 586

Abstract: Mechanical properties and surface morphology of metallized and grafted PE samples were studied upon their surface modification (plasma exposure and grafting) and subsequent metallization (Au sputtering).

Abstract: This contribution deals with the analysis of the renovation layer quality of continuous casting steel rollers, developed through the submerged arc surfacing method (SAW). The continuous casting roller was analysed through the degradation phenomena which act during the operation. Four kinds of filler materials were used for the renovation of the worn roller. Surfacing was carried out as a three-layer in order to eliminate the need for intermediate layer formation. The quality of weld deposits was evaluated in terms of the structure and microhardness after thermal cyclic loading. The best properties showed newly developed filler material W8-WLDC8 from point of view of the microhardness.

Abstract: Modern materials fabrication methods which utilize severe plastic deformation (SPD) do not often allow to obtain enough volume of material to prepare standardized samples for mechanical tests. Therefore, there is a need for mini-samples testing. Mini-samples tests require special approach in terms of precise strain measurements. Accurate strain measurements may be achieved by means of non-contact optical method, namely Digital Image Correlation (DIC). The aim of this work is to present the methodology and results of mini-samples tests in which displacement fields measurements performed by means of DIC and inverse method were utilized for calculation of stress intensity factors and crack tip position tracking. The influence of the subarea of optical measurements for which calculation were performed on the calculations results has been investigated during tests in SPD processed Al alloys and brittle WC-Co sinters produced by means of impact sintering method.

Abstract: Microstructure of Cu-2wt.%Co alloy after various heat treatment (and hence with various phase constitution) was studied after equal-channel angular pressing (ECAP) using transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) technique in a scanning electron microscope (SEM). We also focused on local mechanical properties measured across the section perpendicular to the ECAP extrusion direction. Starting from the grain size well above 1mm in the Cu-2wt.%Co solid solution, ECAP subsequently reduces grain size down to the submicron level. A comparison with pure Cu shows that the grain size homogenization is shifted towards higher number of ECAP passes. Fine dispersion of precipitates further slows down the grain refinement and grain size homogenization during ECAP processing. Local mechanical properties measured across the section perpendicular to the ECAP extrusion direction reveal systematic inhomogeneities of deformed microstructure caused by local gradients of temperature and pressure and by the processing geometry itself. This should be considered while characterizing the microstructure by a single EBSD measurement on a small selected area.

Abstract: At present, there are no generally accepted and widely recognized procedures to determine condition of material of devices subject to complex long-term thermo-mechanical loads. Condition of pipeline material usually changes when subjected to the conditions of long-term operation. Its structure changes and, consequently, so do its mechanical properties, including fatigue characteristics and crack resistance. Therefore, the durability of a component operating under thermal and mechanical loads cannot be discussed separately from its current material properties. This applies in particular to changes that take place in the material micro-structure and to their connection with mechanical properties. This paper covers analyses of stress in the material of a selected pipeline component – pipe tee that is used in chemical plants. Thermo-mechanical interactions determining stress distribution in the component have been taken into account in the calculations. Morphology and location of the cracks indicated that a fatigue-like nature of impacts was the cause of material destruction. Loads of this type occur mainly in conditions of start-up and shut-down. For these reasons, condition of the material in the above-mentioned unstable conditions was subjected to numerical stress analysis. Due to geometric complexity of the pipeline, the distribution of stress in the T-pipe was calculated in two stages: the object was modeled from a global and local perspective. The resulting stress distributions helped to determine factors affecting durability of the tested object. Metallurgy tests were also conducted in order to ascertain factors determining the degradation of material structure and processes of crack formation and development. As a result of research one ascertained that the process of T-pipe cracking under operating conditions was a combined effect of thermo-mechanical and chemical actions determined by the course of intercrystalline corrosion. Synergic interaction of corrosion processes and variable thermal and mechanical loads caused nucleation and propagation of cracks. The crack systems in T-pipe areas subject to the highest stress showed courses characteristic for thermal fatigue of material. The results obtained will identify degradation mechanism of materials used in chemical installations.

Abstract: Ultrahigh strength amorphous alloys Fe65.9Cr11.6Si7.5B15 and Co43Ta5.5Fe20B31.5 prepared by rapid quenching have the form of ribbons with thickness of about 40 micrometers with some imperfections in the sample width and the cross section. Fractographic analysis of Co- and Fe-based high strength soft magnetic materials showed the high localization of the plastic deformation and the ductility in narrow shear bands. To estimate the fracture stress, the Vickers microhardness and the average width of dimples (or the wavelength of the vein features) on the fracture surface were used. Based on the microhardness, the tensile yield strength was calculated as 4 and 5 GPa for Fe-based and Co-based glass, respectively. We estimated the fracture toughness from the measured mean value of the dimple size.

Abstract: Nanoindentation-induced phase transformation of amorphous, annealed amorphous and microcrystalline hydrogen-free silicon thin films were studied. Series of nanoindentation experiments were performed with a sharp Berkovich indenter at various unloading rates. The structural changes in indentation deformed regions were examined using Raman spectroscopy. Analyses of indentation curves and Raman spectra suggest that high pressure phases appear more easily in annealed amorphous Si thin films than in microcrystalline ones.

Abstract: The die radius represents the important local part of drawing die due to transferring contact loading under deep drawing. Within the experiments local contact pressure on die radius was researched using numerical simulation of strip drawn test and micro deep-drawing. Experimental research of strip drawn test was done using coatings with different alloying – under alloyed, optimal and slightly pre alloyed. Alloying level was evaluated by phase composition and % Fe in coating. Presented coatings were created on IF steel sheet DX54D. Experimental results of strip drawn test were used to verify strip-drawn test numerical simulation. Based on numerical simulation results, contact pressure on drawing die radius at deep drawing of cups Ø 50 mm and Ø 15 mm were observed.

Abstract: This paper is focused on determination of micro-mechanical material properties of aluminium metal foam at level of single cell wall. For the purpose of homogenization, complex and heterogenous inner structure of metal foams requires deep understanding of its deformation mechanisms and local mechanical properties. Therefore, a series of micro-scale bending tests of specimens prepared from foam's cells wall were performed. Initially, a technique of specimen preparation was developed. Dimensions and geometry of the specimens were inspected using scanning electron microscopy (SEM). Custom-designed three-point bending device suitable for testing at micro-scale was used for loading. Thin pure aluminium metal sheets were used for calibration of the described method. Six single cell wall specimens were tested. It can be concluded that the developed specimen preparation technique and loading method are suitable to determine local mechanical properties of thin walled metal foams.

Abstract: The effect of solution annealing temperature (550 and 570°C) on the Vickers microhardness of the quenched and naturally aged states of EN AW 6082 and lead free aluminium alloy was investigated. The different chemical composition of analysed alloys did not affect the alloys microhardness after quenching. The total strengthening of both alloys was similar due to the same conjunction of the individual strengthening mechanism of alloys matrix after quenching. The microhardness of EN AW 6082 increased with ageing time increasing according to logarithmic dependence because the increment in alloy microhardness decreased with the increase in ageing time. On the contrary, microhardness of lead-free EN AW 6023 did not increase markedly either after 500 hours natural ageing. This alloy have very slow rate of natural ageing, probably due to suppressed diffusion of alloying elements and clusters and/or GP-zone formation in supersaturated solid solution.