Mass transfer, morphology and phase composition of steel surface after electrospark deposition of tin bronze

The surface of SCMnCr 3 steel after electrospark deposition of a coating of ERCuSn-C (Sn ≈7.9 wt.%) tin bronze was studied using scanning electron microscopy and X-ray diffractometry. The following structural morphological elements were found on it: craters, influxes, pores, structures characteristic of viscous media rupture, spherical and irregular inclusions, etc. Their appearance is associated with the thermomechanical effect of the electric discharge on the surface of electrode materials due to the high plasma temperature in the interelectrode gap. The presence of a system of microcracks in the coatings is explained by the formation of high thermomechanical stresses that arise from the difference in thermal expansion coefficients of the liquid and solid phases, their temperature dependence at a large temperature gradient in the applied coating. The behavior of the mass transfer coefficient, specific mass changes (related to the processed surface area of the cathode-substrate) of the cathode and anode from the energy of the electric spark discharge pulse and the relative amplitude of electrode-anode oscillations is due to the change in the volume of the electrode substance (primarily the anode), passing into the liquid state and the size of the interelectrode gap. X-ray examination of the phase composition of steel surface after deposition of a tin bronze coating on it revealed the presence of the following crystallographic phases: a solid solution of tin in copper α-(Cu, Sn), α-phase of iron (α-Fe) and α-Cu(Sn, Fe). The last phase is not typical for initial materials of the electrodes used. The diffraction lines from α-Cu(Sn, Fe) are shifted towards small Bragg angles relative to the reflections of α-(Cu, Sn). The appearance of α-Cu(Sn, Fe) is associated, first of all, with the introduction of iron atoms and atmospheric elements into the crystal lattice of α-(Cu, Sn).