MICROSTRUCTURAL PHASE ANALYSIS OF COPPER WIRE SAMPLES HEATED BY DIRECT CURRENT

Abstract

According to statistics, one of the most common causes of vehicle fires is the fire hazard of operating onboard electrical networks - 35%. The most common causes of vehicle fires, during their operation, are malfunctions of electrical equipment (short circuit and overload of on-board electrical wiring) and fuel systems. In this regard, the problem arose to identify the cause and establish the involvement of the ignition of the on-board electrical system and the electrical equipment of the vehicle by studying the microstructures of the conductive elements of the power grid. Microstructures were studied using a method of metallographic and X-ray spectral analysis, using a scanning electron microscope with an X-ray microanalysis system. The microstructure of the reference model of the wire is a copper polycrystal, which is elongated in the direction of deformation. It should be noted that after etching the microstructural heterogeneity is detected, it is observed on both longitudinal and transverse slices. The passage of a direct current through a wire significantly changes its microstructure: in it there are local areas of the globular shape, indicating the melting and subsequent rapid crystallization, resulting in the formation of separate sections in the form of round inclusions. It should be noted that under the influence of short-circuit currents, the gullet form is formed on the surface of the wires, and the dimensional characteristics of the melting regions become larger. In the complex action of the short-circuit of the direct current and the open flame of the model focus on the regions of the melting it becomes noticeable that from the action of the current, due to the sharp heating of the metal formed fine-grained structure, and with the subsequent action of the open flame in the wires formed a large-grained structure, and the action of the flame It is manifested in the fact that the oxidation of the grain boundaries occurs, which results in the destruction of the material of the wire along the grain boundaries. Performing research using the method of local X-ray spectral analysis enables us to determine the oxygen content of copper conductors by the principle of individuality of the spectra and provides sufficiently accurate data on its content in the structure of the conductor, depending on the heating conditions, which confirms the expediency of its use to detect the involvement of the conductors of the onboard electrical grids prior to the occurrence of fires.