STRESS-STRAIN STATE OF THE SURFACE OF A HIGH-SPEED MOLYBDENUM STEEL COATING OBTAINED BY PLASMA SURFACING

The evolution of the stress-strain state of a molybdenum high-speed steel coating during electron beam processing has been studied. The model was based on the equations of thermoelasticity and thermal conductivity. The model of linear isotropic hardening was used as the main model of the plasticity of the material. At the upper boundary of the calculated area, the heat flow was set taking into account the evaporation losses of the substance, and it was considered stress-free. At the lower boundary, the heat flow and displacement were considered to be zero. Periodic boundary conditions for temperature and displacement were set at the lateral boundaries of the computational domain. The distributions of temperature and components of the stress tensor over the distance from the irradiation surface at various time points are established. It is shown that the action of an electron beam leads to the formation of a bipolar thermoelastic wave with stable poles in the region of tensile and compressive stresses, which are located at distances of 4.2754 and 12.826 μm from the irradiation surface. The appearance of a maximum of tensile stresses is caused by both the formation of a stretching wave and quenching effects, as well as the presence of carbide phases. The maximum of compressive stresses is caused by the superposition of incident and reflected thermoelastic waves. The distribution of equivalent plastic deformations over the distance from the irradiation surface is obtained. His analysis showed that, regardless of time, a layer up to 20 μm thick is affected by plastic deformation. The highest values (approximately 1.97) are observed near the surface of the material. The areas of greatest plastic deformations are arranged in a pattern. This is a consequence of the appearance of maxima of the positive and negative components of the stress tensor in the range from 4 to 15 μm. This distribution of equivalent plastic deformations explains the appearance of the microcrack network observed on electron microscopic images.