Application of the electron backscateered diffraction method in microstructure research for determining of causes of metal structures destruction

The application of the diffraction method for backscattered electrons allows us to take a fresh look at the structural changes in the material as a whole and on the processes of destruction of metal structures in particular. The aim of this work was to apply the method of diffraction of backscattered electrons to reveal the characteristic distinctive features of the structure of the material in areas under the fracture and away from it.The diffraction of backscattered electrons is a method that allows one to determine the orientation of individual grains, the local texture, and also to identify the phases in the sample under research. This method can determine local and general deformations, the number of recrystallized and deformed grains, the size and misorientation of grains, etc.The results of a study of the mast fragment of the unit for drilling and repairing wells with a carrying capacity of 200 tons (APC-200) are presented with the establishment of characteristic structural differences between the sites under the fracture and away from it.The appearance and development of a subgrain structure at the site under the slope is established. It is shown that the material of the mast was made of rolled metal, for which no additional heat treatment was carried out, and destruction could occur at almost any point.

Effect of Layer-by-Layer Texture Inhomogeneity on the Stress Corrosion of Gas Steel Tubes

Based on the data of X-ray texture and structure analysis of the material of main gas pipelines it was shown that the layerwise inhomogeneity of tubes is formed during their manufacturing. The layerwise texture inhomogeneity of steel tubes, obtained by hot rolling at the air, differs depending on variation of technological parameters of their processing in inner and outer layers, i.e. the temperature and deformation gradients, penetration of interstitial impurities into the surface layer from surrounding atmosphere etc. The thickness of the surface layer with modified texture parameters depends on the temperature of rolling and its regime. Under exploitation when stress-corrosion cracks grows and reach the layer with a modified texture, their opening is slowing down or stops because of the high mutual misorientation of grains of different layers and the necessity of changing the plane of moving cracks, what requires additional tensile stresses. Layered textures of different gas tubes were compared. It was shown that character and degree of arising inhomogeneity correlates with the tubes resistance to stress-corrosion cracking.

Identification of Electrical Fire Melted Marks of Copper Wires by Electron Backscattered Diffraction (EBSD)

A variety of electrical apparatus used in daily life can cause fires because of internal or external factors. During cause identification of an electrical fire, the first short circuit melted marks of copper wire have been considered highly important because they are direct proofs. Additionally, overloaded short circuit caused by the overload of current due to excessive electrical usage can give rise to an electrical fire. Despite extensive research on the first short circuit in fire scenes, the overloaded short circuit remains difficult to be distinguished because of the limitation of commonly used testing methods. Conventional metallographic method is intuitionistic and simple, but may not provide detailed data of crystals such as misorientation of grains. Here a new method (electron backscattered diffraction, EBSD) is applied for identification of the first and overloaded short-circuited melted marks of copper wires in electrical fire scenes. Results show obvious morphological distinctions in melted marks of copper wires between the first and overloaded short circuits. Qualitative and Quantitative differences obtained from the contrast of the above two short circuit situations may assist for cause identification of electrical fires in the future.

Phase Field Crystal Modeling for Nanocrystalline Growth

The two-mode phase field-crystal (PFC) method is used to simulate the nanograin growth, including the grain growth in different sets of crystal planes, the grain boundary structure with mismatch, the grain orientation and also the incoherent grain boundary in two dimensional plane. It is obviously observed that there are dislocation structures in nanograin boundary due to mismatch and misorientation of grains. These simulation results can not only be used in artificial controlling the grain boundary of nanograin, but also is of significant for designing new nanograin with a good grain boundary for structure materials.

On the Influence of the Misorientation of Grains, Grain Size and Boundary Volume on the Strength and Ductility of Ultrafine Grained Cu

The influence of the microstructure and the misorientation relationship of grains on mechanical properties is investigated in specimens of ultrafine-grained copper processed by equal channel angular extrusion (ECAE) route Bc for 1, 4 and 12 passes. XRD texture analyses have shown that the major texture component is developed during the first pass of ECAE, and remains approximately constant with greater number of passes. EBSD measurements indicate that the majority of grain boundaries are still of low angle (>15°), while after four and twelve passes more than 50 % of all boundaries are high angle ones. TEM analyses have shown that the microstructure evolves from microbands and elongated cells towards a more equiaxed homogenous microstructure. On the microscale observed by TEM the degree of misorientation among subgrains/cells increases and the width of boundaries decreases while the cell/subgrain size remains approximately constant as the number of passes increases. The mechanical properties show a saturation level with a maximum in the yield stress and UTS after 4 passes. The strength of the material decreases between the fourth and the twelfth passes and the uniform elongation increases. It is suggested that the increase in ductility (and decrease in strength) is associated with the decrease in width of boundaries leading to an increase in the mean free path of dislocations.

Preferred inclinations of grain boundaries in epitaxially grown bicrystalline thin films of gold

Energy and concomitant structure of grain boundaries are related to inclination of the boundary plane as well as misorientation of grains defining the boundary. Although increasing information is becoming available on variation of grain boundary energy with misorientation, still relatively little is known about variation of grain boundary energy with inclination. The purpose of this research is to examine preferred inclinations of preselected grain boundaries in gold by transmission electron microscopy (TEM) in order to identify principal structural elements and to relate these elements to the energy of special grain boundary configurations.Grain boundaries examined in this research are produced by a new technique involving vapor deposition of gold on common (001) surfaces of bicrystalline substrates of NaCl, characterized by preselected rotation about a common [001] axis, and subsequent epitaxial growth to form a bicrystalline thin film. These films are then removed from their substrates and examined by TEM. The principal advantage of this technique is that the grain boundary is formed during the deposition and growth process, thus resulting in a more perfect boundary structure while eliminating necessity of a separate bonding operation.