Physical nature of hardening of heat-resistant metal of high hardness formed by plasma in nitrogen medium

The structure, phase and chemical composition of a heat­resistant alloy formed by plasma in a nitrogen medium with subsequent high­ temperature tempering have been studied by scanning electron microscopy and microrentgenospectral analysis. It was found that in the deposited alloy, the main phases are a solid solution of α­iron and carbonitrides based on iron, tungsten, chromium, molybdenum, and aluminum (Fe6W6NC and AlN). High­temperature treatment (four­fold high­temperature tempering at a temperature of 580 °C for 1 h) of the deposited coating leads to an increase in the crystal lattice parameters (from 2.866 to 2.89 Å) and in the sizes of coherent scattering regions (from 25 to 100 nm), and to a decrease in internal elastic stresses (from 1000 to 600 MPa). A pronounced oriented dendritic structure is observed on the deposited surface. After surfacing and high­temperature tempering, the oriented dendritic structure is practically not visible. The distribution of microhardness over the depth of the deposited layer in the state after surfacing is characterized by a significant spread at its high average value on the surface of 4.142 GPa (dispersion 1.0956) and the middle part of the surfacing – 5.153 GPa (dispersion 1.5697). The spread of microhardness values is associated with the complex thermal effect of multilayer plasma surfacing along a helical line and mixing of the substrate material with the surfacing coating. High-temperature tempering leads to an equalization of the microhardness values and an increase in its average value to 5.7 – 6.5 GPa. The nature of hardening of the deposited heat­ resistant metal of high hardness, additionally alloyed with nitrogen and aluminum, was clarified. The main hardening of the deposited metal occurs at high temperature tempering due to an increase in the carbide and carbonitride phases and the formation of fine aluminum nitride.

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