Study of the influence of alphanizing on the structure and properties of the alloy BT6

The paper considers the influence of two technologies of alphanizing (oxidation) on the structure and properties of the deformable titanium alloy BT6, which is used, in particular, in the aviation and space industries. The application of oxide coating by methods of chemical-thermal treatment (CTO) allows to compensate for the main drawback of the alloy – low wear resistance of the surface. The initial set of properties increases. The objects of research are titanium alloy BT6 and its oxide coatings. Two samples of the part with oxide coatings obtained by different technologies were compared. The first technology is alphanizing in finegrained graphite, the second one is alphanizing in a vacuum. The aim of the work is to find out the influence of two technologies of alphanizing on the structure and properties of the BT6 alloy. Alphanizing was carried out: 1) in fine-grained graphite at a temperature of 800 ± 10 ° C with exposure for 8 hours; 2) in an electric furnace at a temperature of 760–780 ° C in a vacuum of 10-1 – 10-3 mm Hg. for 1.5–2 hours. A study of the microstructure (light and electron microscopy) was performed. We used a microscope type Carl Zeiss Axio Observer A1m using a digital camera, adapter devices for converting an optical signal, a computer. Statistical processing was carried out according to the SIAMS700 program. Electron microscopic studies were performed using a scanning electron microscope (SEM) EVO 50 with an energy-dispersive microanalyzer INCA Energ 350. X-ray phase analysis was carried out using an X-ray diffractometer Shimadzu XRD7000, Japan (CuKa radiation, monochromator), in the following mode: range from 5 to 70 ° on a scale of 2θ, increments of 0.03°, scanning speed of 1.5 ° / min. Powders obtained from two types of coatings were investigated. The microhardness of the samples was measured on the DM8 microhardometer according to GOST 9450–76. The wear resistance of the alloy was assessed at a special laboratory installation. The phase composition and structure of the BT6 alloy after alphanizing were clarified. In the diffusion layer, the following points were detected: after alphanizing in graphite – TiO2 phases; Ti3O; TiN. After carbonation in vacuum – TiO2; Ti6O11. In the alphad layer, after processing in graphite, grains of α – solid solution, intermetallics Ti–Al-V, Ti–V and Ti–Al were detected; the alphanized layer contains more titanium after treatment in vacuum, and areas with 100% (at.) titanium have also been identified; the region of solid solution (α) and the intermetallics Ti–Al-V, Ti–V and Ti–Al are visible. The thickness of the oxidized layer is on average 103.6 μm (graphite), and in a vacuum – 66.8 μm. The average grain size in the layer is 17.2 μm (graphite); 6.0 μm (vacuum). It has been established that chemical-thermal treatment (alphanizing) contributes to a significant increase in microhardness in the diffusion layer. The hardness of HV580 (vacuum) and HV724 (graphite) was obtained on the surface. Alphanizing in graphite and in vacuum ensures the wear resistance of the product, but the best result is obtained after alphanizing in a vacuum. Both technologies improve the properties, but it is more profitable to carry out alphanizing in a vacuum, since in this case the process is carried out within 2 hours instead of 8 hours in graphite. Alphanizing (oxidation) provides wear resistance of the BT6 alloy, which contributes to the reliable operation of the product during operation.