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 machining was studied. The model was based on the equations of thermoelasticity and thermal conductivity. A linear isotropic hardening model was used as the primary model of material plasticity. A heat flux accounting for evaporation losses was specified at the upper boundary of the computational domain; the domain was assumed to be stress-free. At the lower boundary, the heat flux and displacements were assumed to be zero. Periodic boundary conditions for temperature and displacement were specified at the lateral boundaries of the computational domain. The distributions of temperature and stress tensor components were determined over distances from the irradiated surface at various points in time. It was shown that exposure to the 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 irradiated surface. The peak tensile stress is due to both the formation of a tensile wave and quenching effects, as well as the presence of carbide phases. The peak compressive stress is caused by the superposition of incident and reflected thermoelastic waves. The distribution of equivalent plastic strains by distance from the irradiated surface was obtained. Analysis revealed that, regardless of time, plastic strain affects a layer up to 20 μm thick. The highest values ​​of equivalent plastic strain (approximately 1.97 – the exact definition needs to be clarified) are observed near the material surface. The areas of greatest plastic strain are arranged in a pattern.

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