Papers by Keyword: Electron Microscopy

Abstract: In the paper, the atomic structure of amorphous and nanocrystalline alloys of the electrolytically obtained CoP, NiP, CoNiP, CoW, and CoNiW systems has been studied. The structure was investigated by electron microscopy and diffraction using a Libra 200 HR FE transmission electron microscope at an accelerating voltage of 200 kV within a temperature range of 50-35 °C. The obtained radial atom distribution function and the coordination sphere radii are in good agreement with the data for the cobalt structure in the cubic and hexagonal modifications. The high coordination numbers of the third and fourth coordination spheres allow suggesting a predominantly cubic structure of the local atom environment in CoP samples but somewhat lower, which is explained by the presence of free volume and phosphorus atoms distorting the local structure. When heating, the near atomic order also corresponds to the cubic phase of cobalt, and the ordering occurs in the second, third, and fourth coordination spheres. The data obtained for CoNiP alloys indicate that by configuration, the local atomic environment is closer to the hexagonal structure of nickel. In general, the structure of the CoP-CoNiP system alloy films obtained by electrolytic deposition is already in one of the local minima of the total system energy, which is confirmed by the near atomic order similar to the cubic phase of cobalt or hexagonal phase of nickel. This determines the good stability of the structure and properties during thermal exposure.

Abstract: The reduction of harmful greenhouse gas (GHG) emissions can be realized by utilizing lightweight structural metals, such as magnesium. Magnesium alloys have the potential to replace higher-density aluminum and ferrous components in automotive and aerospace industries, thereby decreasing vehicle weight and the associated fuel requirements. However, their strength and ductility must be improved to ensure widespread application. This goal can be achieved through ultrasonic processing in the molten state, a technique that is gaining popularity in the manufacturing of light alloys. In this study, the effects of high-intensity ultrasonic vibration on the microstructure and hardness of AZ91E Mg alloy was investigated. The molten alloys were subjected to sonication of varying durations, and the resulting castings were characterized using optical microscopy, scanning electron microscopy and hardness testing. Sonication was found to successfully increase the hardness of the alloy relative to the base condition. This improvement was attributed to the refinement of the magnesium grain structure as well as the Mg₁₇Al₁₂ and Mn-Al secondary phases in the sonicated alloys. The competitiveness of magnesium alloys can be significantly enhanced via ultrasonic processing, offering important opportunities for the production of greener, light metal components.

Abstract: The development of novel light metal alloys represents an important task in the further optimization of technical materials. Multi-component systems with more than 4 metals are very promising to outperform currently existing alloys, but lack significant research in systems not dominated by transition metals to date. In this work, alloys containing the elements Al, Cu, Mg and Zn were produced using magnetron sputter deposition. A detailed structural investigation using electron microscopy provided valuable insights into the influences of different metals and their relative proportions in the alloy on material properties.

Abstract: Conventional long-term creep test (CCT) to the rupture and so called accelerated creep test (ACT) of the dissimilar weld joint made of FB2 and F martensitic steels and of the base materials were carried out at temperatures ranging from 550 °C to 650 °C in the stress range from 70 to 220 MPa. Assessment of microstructure development and changes of hardness was correlated with the creep strength. During creep at temperatures above 575 °C Laves phase precipitated in all parts of the weld joint and especially in the heat affected zones. Coarse Laves phase particles and their clusters with chromium carbides served as nucleation centers for cavities. As the fine grained heat affected zone of F steel was the softest part of the weld joint, many cavities originated and cause failure of samples. The aim of this paper is to compare results and possibilities of the “standard” methods and advanced scanning electron microscopy performed by instrument equipped with a concentric backscatter electron detector (CBS). Filtering of the signal enables improving and/or diminishing of selected type of contrast caused by various types of particles of secondary phases. The images were used as an input data for image analysis and developments of microstructures during CCT and ACT were compared. Results have shown that specimens after ACT contains significantly lower content of the Laves phase.

Abstract: In the present study, bulk 10 % cerium stabilized zirconia was prepared by spark plasma sintering technique. Various time temperatures regimes were used and prepared sample were subjected to microstructure observation by electron microscopy and X-ray diffraction and mechanical testing by nanoindentations. It was shown, that conditions of spark plasma sintering process can strongly influence properties of resultant sample, mainly grain size which warried from some tens or hundreds of nanometre to approximately 100 micrometres. Also some structure changes in the sintering process were observed resulted to phase changes and decomposition.

Abstract: This study investigated the prospective application of the advantageous intensive plastic deformation method of rotary swaging for production of Al-Cu composite wires. Such materials are perspective to be used within a wide range of commercial and industrial branches, from transportation to electrotechnics. Cu-Al laminated wires with two unique different stacking sequences were rotary swaged down to 5 mm diameter at room temperature to minimize the development of brittle intermetallics at the interfaces. The analyses primarily focused on the mutual comparison of both the stacking sequences (Al sheath reinforced with Cu wires vs. Al sheath and Al core reinforced with Cu inter-layer) from the viewpoints of mechanical properties, sub-structure development, and occurrence of residual stress. While the individual Cu wires exhibited bimodal structure and the presence of residual stress within the growing grains, the Cu inter-layer featured recrystallized grains and homogeneous stress distribution. The mechanical properties for both the composites were enhanced by the swaging technology; the composite reinforced with Cu wires exhibited slightly higher ultimate tensile strength than the one with Cu inter-layer (258 MPa vs. 276 MPa). However, the latter featured significantly higher plasticity.

Abstract: The effect of beryllium hardening has been studied. Beryllium is sintered by method of hot isostatic pressing (HIP), depending on the temperature of powders pressing. The research results of electron microscopic studies were the base for demonstrating formation of the hydraulic phase at the grain boundary of sintered beryllium and influence of the reinforcing phase on the mechanical properties of the HIP blank. The dependence of beryllium precision elastic limit and conventional yield strength from the size of the reinforcing particles of beryllium oxide has been found. The obtained equation provides a description of the “dispersion-grain-boundary" mechanism of isostatic pressed Beryllium hardening.

Abstract: In order to study the distribution of carbonaceous rocks in Guangxi, and reveal the microstructure of carbonaceous rocks, and explore the laws of physical and mechanical properties of carbonaceous rocks, and study the characteristics of carbonaceous rocks, the Regional division of the typical carbonaceous rocks in Guangxi was carried out. Subsequently, an electron microscopy scan test was conducted to analyze the microstructure characteristics of carbonaceous mudstone, shale and limestone. At the same time, the mineral composition of the carbonaceous rock, the chemical composition test was analyzed, and the physical and mechanical parameters test was conducted. Finally, the microscopic classification of carbonaceous rocks was linked to the physical and mechanical parameters. The results show that: (1) Guangxi carbonaceous rocks can be divided into three typical areas: Hechi District, Baise District and Liuzhou District. (2) The microstructure of carbonaceous limestone in Guangxi was mostly scaly, the mineral crystals of carbonaceous mudstone microstructure were mainly petal-like, and the clay minerals of carbonaceous shale microstructure was striped. (3) The microscopic chemical elements of Guangxi carbonaceous rocks were mainly carbon, silicon, and mineral components were mainly illite, and the illite content was linear with density.

Abstract: The present study includes a detailed analysis of titanium based composite foam developed by powder metallurgy route and to understand the role of process parameters and the particle size of the space holder (cenosphere) on the kinetics and mechanism of wear. Cenosphere of varying particle size (<150 μm; 150-212 μm; > 212 μm) were mixed with titanium in a ratio of 1:3, compacted at 100 MPa and sintered at 1000°C and 1200°C for a period of 2,4 & 6 hrs in each temperature. The kinetics of wear and frictional coefficient of sintered composites were evaluated by reciprocating wear testing machine against diamond indenter at applied load of 10 N. The mechanism of wear was studied by a detailed analysis of the post wear microstructure. The composite foam with cenosphere particle size in the range of 150-212 μm showed minimum wear rate. The mechanism of wear was found to be a combination of adhesive and abrasive.

Abstract: Ti6Al4V coatings were cold sprayed onto the same bulk alloy using standard conditions and a set of parameters developed to improve the coating’s performance. In addition, the enhanced coating was heat treated to improve coating adhesion and reduce porosity. Wear tests were performed, onto the coatings and the substrate, in oscillating conditions, which simulate wear induced by the contact with bearing parts during vibration. Wear behaviour at room temperature is dominated by a mixed mechanism, which involves plastic deformation and transference from the counterbody forming mechanically mixed layers. As temperature is increased, the formation of mechanically mixed layers dominates wear. The wear resistance of the enhanced coatings is similar to the bulk alloy, or even better in some conditions. Consequently, cold sprayed improved coatings could be used for repairing titanium components from the contact wear point of view.