PROPERTIES OF MULTILAYER PLASMA COATINGS FROM MATERIALS BASED ON M-CROLL

Abstract

The article describes the structures and properties of m-croll plasma powder coatings deposited under optimal conditions. Most of the modern nickel-based alloys used in technology used to form plasma coatings contain 6-12% aluminum, 20-30% chromium, and 0.15-1.0% reactive element (yttrium, tantalum, etc.). With an increase in the concentration of the reactive element, the production of new oxide grains during deposition inside the film itself is inhibited and, in the presence of more than 0.82% yttrium, it completely stops, and the rate increases with oxygen diffusion. This is caused by a significant refinement of the oxide film and alloy grains and the formation of yttrium-rich phases - Ni5Y, Ni9Y, Ni3Al2Y, (NiCo)4.25Al0.15Y, which have low resistance to high-temperature oxidation. All this should be taken into account during the formation of the coating when optimizing the content of rare earth (REM) metals in the alloy. Consequently, the introduction of reactive elements into the plasma coating contributes to the absence of stresses in the film caused by internal oxidation. However, an increase in the concentration of the reactive element is limited by an increase in the oxygen diffusion rate and the processes of alloy embrittlement. Therefore, most NiCrAlYТа alloys for sputtering are limited in oxygen content to 0.05%. The mechanical properties of alloys are significantly improved when they are alloyed with tantalum, niobium, and titanium, since in their presence a superlattice of the β-phase (Ni2AlTa, Ni2AlNb) is formed due to the ordering of elements in the aluminum sublattice. However, the formation of such a superlattice requires a concentration of elements that exceeds a certain limit. Niobium has a positive effect on the heat resistance of the NiCrAlI alloy, but reduces its corrosion resistance. Tantalum has the most favorable effect on both the mechanical and protective properties of MCrAlI alloys. In addition to participating in the formation of the β-phase superlattice, tantalum increases heat resistance and resistance to high-temperature salt corrosion of grain boundaries, segregating primarily in the alloy regions, and also binds free carbon into carbides. All refractory elements form inclusions, which in most cases reduce the diffusion mobility of atoms in the coating. High-quality wear-resistant coatings based on titanium dioxide - aluminum oxide and nickel-chromium-aluminum-yttrium-tantalum alloy must be formed from materials with strictly defined sizes and morphology of the particles of the initial powder, with a chemical and phase composition uniform over the cross section of the initial powders and a minimum grain size of phase inclusions.