Рhysico-mechanical properties and structuralphase state of individual coatings based on nitrides W and Сr

Abstract

Abstract. Problem. Ti, Zr, Mo, W and Cr nitride coatings are promising materials because they have high hardness and excellent tribological characteristics and are therefore widely used as a quick-wear protective cutter. At the same time, the structure and tribological properties of W-N coatings are poorly understood. All of the above coatings based on Ti-N, Zr-N, Mo-N, Cr-N and W-N phases are sensitive to the partial pressure of N2 used during deposition. Coatings with nanolayer configurations of pure metal and metal nitride have higher mechanical properties than single-layer ones. Therefore, the topic of the work and the problems considered are relevant. Goal. The aim of this work is to study the physicomechanical properties and structural-phase state of CrWN nanolayer coatings deposited on a steel substrate with different surface roughness. Such nanostructured CrWN coatings have different component concentrations. Methodology. In the work, samples of fixed-speed P6M5 steel of fixed size 15 mm × 15 mm × 5 mm were used as substrates, which were polished by a mechanical method combined with a diamond grinding wheel. Different surface roughness was achieved by grinding paper with different grain sizes by wet grinding, with preliminary grinding on the previous grain size. A target consisting of Cr and W with different area ratios was used: 95: 5, 75:25, 50:50. For the qualitative and quantitative analysis of the composition and structure of coatings, radiographic analysis was used, studies of the surface structure of coatings and obtaining energy dispersion spectra were performed on a scanning electron microscope. Results. Radiographic studies show that the obtained coating includes such phases as WN, W2N, CrN with a cubic (NaCl-type structure) crystalline lattice without a pronounced axis of grain orientation. Studies carried out on a scanning electron microscope of the obtained Cr-W-N coatings showed a nanocrystalline structure with a grain size of up to 50 nm. According to the analysis of the elemental composition of coatings, a clear correlation between the composition of the target and the composition of the obtained coating is observed. The main factors affecting the hardness and wear resistance of Cr, W and N coatings are the condensation parameters such as the stress applied to the substrate, the substrate temperature, the concentration of the gases in which the deposition occurs, their pressure and the composition of the target. Originality. It has been found that the main factors that influence the hardness and wear resistance of Cr, W and N coatings are the condensation parameters such as the stress applied to the substrate, the substrate temperature, the concentration of the gases in which the deposition occurs, their pressure and the composition of the target. The microhardness of the nanolayers was about 3 GPa for Cr39W11N50 coating and 5 GPa for Cr75W1N24 and was significantly dependent on the coating roughness and had a maximum value on the 1200 grit abrasive samples. Practical value. The investigated results of the dependence of the microhardness on the roughness show a decreasing nature with a decrease in surface roughness, that is, an increase in surface smoothness leads to a slight decrease in the hardness of the coating. The obtained values of microhardness of P6M5 steel with wear resistant coatings based on W and Cr nitrides allow to apply such coatings for surface hardening of machine tools and cutting tools.