Papers by Keyword: Electron Microscopy

Abstract: In this research, the possibility of applying multilayer multielement super hard coatings by Cathodic Arc is investigated. More precisely the structure of the coating consisting of quaternary CrAlSiN and ternary AlSiN layers is examined by electron microscopy, X-ray diffraction and X-ray photoelectron microscopy analytical methods. The as-deposited samples were found to have distinguishable layers. The CrAlSiN layer is characterized by an extra sequence of repeated nanolayers. The AlSiN layer consisted of nanosized grains having a preferential orientation. Finally the surface layer was found to contain a solid solution of CrxAl1-xN, while Si3N4was identified only by XPS most probably due to its amorphous structure.

Abstract: The article shows the analysis of castings parts produced by rheocasting method SEED. Structures of as cast and heat treated castings samples were observed by light microscopy and electron microscopy. Scanning electron microscope was also used for studying of fracture surfaces after destruction of the samples during testing of mechanical properties. Also analysis of chemical composition of specific phenomena found within the structure is described. Findings resulting from those analyses are related with the technological settings and other process conditions.

Abstract: Microstructural and mechanical development of the various heat-treated 935 Ag-Cu alloys were explored. The heat-treatment processes were applied viz. holding before quenching for 2 and 15 min, homogenization at 750 °C for 60 min followed by water quenching, and aging at 350 °C for 15 to 60 min followed by water quench. It was found that the specimens with copper addition gave a high resiliency in all heat treatment conditions however the effect of homogenization with aging treatment fostered deep blemish or fire scale on its surface. The amplifications of resiliency of 935 heat-treated AgCuSn and AgCuBe alloy were increased but elongation values were slightly reduced. The 935 AgCuBeSn specimens produced adequate resiliency and elongation after aging at 350 °C for 15 to 60 min followed by water quenching. Partial dissolution and spheroidization of eutectic phase were occurred by homogenization treatment at 750 °C. Aging treatment promoted precipitation of 3-20 nm fcc (Cu,Sn)–rich precipitates and engendered an improvement of hardness, yield strength and the modulus of resilience or resiliency.

Abstract: The microstructure of the Ni₅₀Mn₂₅Ga₂₅ Heusler alloy (HA) rod cast to a copper mould and melt-spun ribbon was studied. According to X-ray diffraction analyses in both cases, the solidified alloy is a single-phase. In suction casting, the radial columnar crystals grow by cellular or dendritic growth, which leads to chemical inhomogeneity of the whole cast rod on the microscopic scale. The melt-spun ribbon exhibits a homogeneous alloy at the wheel side and an inhomogeneous alloy on the free surface side of the ribbon formed by cellular and dendritic growth. At both types of casting, the columnar crystals growth along the <100> crystal direction. According to texture analyses by EBSD, the fine grain structure at the wheel side of the ribbon exhibits no texture, while the columnar grain structure on the free surface side exhibits the <100> fibre texture with a declination by about 10 degrees in the spinning direction. Melt-spinning leads to significant refinement of the HA microstructure.

Abstract: Two repair weld metals Inconel 52 and its newer version Inconel 52M were used as materials for development of repair welding method of a VVER 1000 pressure vessel. The properties and microstructure of the trial welds were investigated using light, scanning and transmission electron microscopy. Both modifications of Inconel revealed a structure of elongated grains with clear evidence of dendritic segregation. Fine chromium carbides occurred at wavy grain boundaries and fine cuboidal titanium carbides pinned dislocations within grains. Coarser skeletal titanium carbides and globular oxides were sparsely precipitated in interdendritic spaces. Some small common defects were observed in the weldments. No cracks were detected which could be classified as ductile dip cracking. It was concluded that both Inconel 52 and Inconel 52M are acceptable for repair welding.

Abstract: The article deals with the shrinkage of a cement composite with various contents of waste micronized limestone powder with a fraction size of 0-63 μm and crushed limestone with a fraction size of 0-2 mm. Waste micronized powder is produced by high-speed grinding of marble sludge. The difference in shrinkage of various mixtures has been described by means of structural analysis. Electron microscopy has been used for this analysis. Mixtures with 10 wt. % of cement and various ratios of micronized marble powder to crushed limestone (1: 1; 1: 2; 2: 1; 1: 0) were investigated. The increasing amount of waste micronized powder adversely affects the shrinkage of the cement composite. This effect is caused by the increasing water–cement ratio for the purpose of achieving the same workability of the mixture.

Abstract: It is well known that the introduction of sustained tensile loads during high-temperature fatigue (dwell-fatigue) significantly increases the crack propagation rates in many superalloys. One such superalloy is the Ni-Fe based Alloy 718, which is a high-strength corrosion resistant alloy used in gas turbines and jet engines. As the problem is typically more pronounced in fine-grained materials, the main body of existing literature is devoted to the characterization of sheets or forgings of Alloy 718. However, as welded components are being used in increasingly demanding applications, there is a need to understand the behavior. The present study is focused on the interaction of the propagating crack with the complex microstructure in Alloy 718 weld metal during cyclic and dwell-fatigue loading at 550 °C and 650 °C.

Abstract: Several W-B-C layers were prepared by magnetron sputtering. The microstructure of thin layers was observed by means of scanning and transmission electron microscopy on cross sections prepared using a focused ion beam. Both undisturbed layers and the volume under indentation prints were inspected. The W-B-C layers are fine nanostructured materials about 2 μm thick and indents with loads up to 1 N do not cause any visible defects (cracks, delamination etc). The results were correlated with mechanical properties characterized by means of nanoindentation experiments in both the static and the dynamic loading regime using a Berkovich indenter. Elastic modulus, indentation hardness and fracture resistance of prepared nanostructured coatings were evaluated and discussed.

Abstract: The microstructure and creep properties of a P911-type steel normalized at 1060°C and then subjected to one-step tempering at 760°C for 3 h or two-step tempering at 300°C for 3 h + 760°C for 3 h were examined. The transmission electron microscope (TEM) observations showed that the tempered martensite lath structure (TMLS) with a lath thickness of 340 nm evolved after both tempering regimes. High dislocation densities of 3×10¹⁴ or 5×10¹⁴ m^-2 retained after one-and two-step tempering respectively. M₂₃C₆ carbides with a mean size of 120 nm and V-rich MX carbonitrides having a “wing” shape with an average length of about 40 nm precipitated on high-and low-angle boundaries and within ferritic matrix, respectively. A number of Nb-rich M(C,N) carbonitrides with a mean size of 20 nm precipitated on dislocations during low temperature tempering. The creep tests were carried out under constant load condition at 650°С at applied stresses of 100 and 118 MPa. Analysis of creep rate versus time curves showed that the use of two-step tempering decreases the minimum creep rate providing an increase in the creep strength in long-term conditions.

Abstract: Typical microstructures of dual-phase (DP) steels consist of hard martensite particles dispersed within a ductile ferritic matrix. These microstructures possess a complex network of grain and interphase boundaries, which, together with the mechanical contrast of their phase composition, control micro-damage initiation mechanisms, induced by deformation. Accordingly, in this study we analyze the influence of individual microstructural features and interfaces on damage nucleation and progression in DP steels with respect to applied tensile strain. Prominent micro-damage mechanisms include cracking of martensite and damage initiation at interphase boundaries. Influence of martensite morphology is discussed based on a statistical analysis of the damage features as observed by electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) maps. Prior austenite grain boundaries (PAGbs) in martensite show a brittle behavior and are highly susceptible to crack propagation.