Исследование влияния высокотемпературной термической обработки на фазовый и химический состав сплава ВКНА-1В

The paper dwells on the features of the chemical composition and structure of alloys based on Ni3Al. It examines the effect of heat treatment on the structure and phase parameters and on the short-term strength of the intermetallic VKNA-1B alloy.Smelting bar stock was made by technique of vacuum induction. A directional solidification method was used to provide heat treatment of samples on the UVNS-4 installation.The heat treatment was performed in the following modes: heating to a temperature of 1200, 1290, 1300 ° C, holding for 100, 4, 4 hours, respectively, furnace cooling to 800 ° C, then air-cooling. For heating was used the batch furnace VEBK S 400/100 with a maximum operating temperature of 1350 ° C. Samples were loaded in the furnace at 800 0C.The phase composition of the VKNA-1B alloy was examined through physicochemical analysis based on electrochemical insulating phases in different electrolytes. The composition and quantity of the isolated phases were determined by the results of X-ray and chemical analysis methods.To analyse the microstructure was used a scanning electron microscope JSM-840. In original cast state the VKNA-1B alloy has a cellular-dendritic structure. In the axes of the dendrites there is a γ'-phase (~ 75-80% vol.) surrounded by a viscous γ-phase in the form of thin layers; in the inter-dendritic regions there are large particles of γ'-phase. The increasing temperature of heat treatment comes with coarsening γ'-phase particles in inter-dendritic regions and, essentially, has no effect on the phase composition of the alloy. Results of mechanical tensile tests have shown that the alloy retains high strength values after long-term exposure and the increasing cell size of γ'-phase in the axes of the dendrites when raising the temperature leads to an increase in short-term strength of the alloy.Проведено исследование фазового и химического состава интерметаллидного сплава ВКНА-1В в исходном литом состоянии (вакуумная индукционная выплавка и вакуумный индукционный переплав) и после различных режимов высокотемпературной термической обработки. Определены пределы кратковременной прочности и текучести на образцах сплава ВКНА-1В и проведена корреляция значений механических свойств с фазово-химическим составом. Установлено, что высокотемпературная термообработка, изменяя соотношение γʹ/γ-фаз, практически не влияет на стабильность карбидной фазы, что и отражается на стабильности кратковременных свойств интерметаллидного сплава на основе соединения Ni3Al при комнатной температуре. DOI: 10.7463/aplts.0615.082965

The maraging steel corrosion properties with hardening of different kinds after double aging

The paper proposes to use high-strength corrosion-resistant maraging steels, which were developed for aircraft industry instead of carbon steel with coating to improve operation properties of the forcemeasuring resilient member in electronic strain-gauge balance.It examines the possibility to apply the martensitic-aging steels of Fe-Cr-Ni-Mo-Ti (ЭП678) and Fe-Cr-Ni-Mo-Cu-Nb (ЭП817) alloying systems. It was shown, that a traditional heat strain-hardening treatment including hardening and overageing of this steels provides combination of durability viscosity and corrosion- resistance, but at the same time it increases nonelastic effects and lowers the limit of elasticity because of reversing austenite formation. In this connection, it was proposed to use hardening with double aging i.e. main and low-temperature aging with no austenite formation as heat strainhardening treatment of steels for force-measuring resilient member. The goal of this work was to study the influence of double aging on the structure and properties of ЭП678 (06Х14Н6Д2МБТ) and ЭП817 (03Х111Н10М2Т) steels.The modes of double aging for ЭП817 steel were conformed to 4500С + 400 0С and 475 0С+ 400 0С, for ЭП678 steel – 530 0С + 500 0С. The structure and properties of hardened steels after main and double aging were compared.Metallographic analysis of samples after electrolytic etching was conducted with Leitz Metallovert microscope while the CamScan 4DV raster electronic microscope was used for Microroentgen-spectral analysis. The quantity of austenite was controlled with computerized setting DRON-4, the hardness was measured with ТК-2М instrument, corrosion-resistance was estimated with polarized curves, which were taken using a П-5848 potentiostat.The conducted research has shown, that double aging causes the additional hardening of steels due to disintegration of martensite and formation of dispersed Cu – corpuscles in ЭП817 steel and of Ni3Ti in ЭП678 steel. At the same time, it was established that additional disintegration of martensite influences on the corrosive properties of steels in a variety of ways. The experiments have proved that double aging deteriorates the corrosion-resistance of ЭП678 steel, leads to the sharp increase of corrosion current on cathode and anode polarization curves due to formation of nonuniform structure.According to experimentally obtained data, the corrosion-resistance of ЭП817 steel after double aging, on the contrary, was improved i.e. the corrosion current was essentially reduced and there was no phase of disastrous dissolution on polarization curves.It was proved that there are two reasons for enhancement of corrosion-resistance, namely a surface "refinement" owing to a cathode formation of Cu – corpuscles with respect to the chrome-nickel matrix and their more uniform allocation, thus facilitating to formation of uniform protective passive skin on the surface.Thus, the results of conducted research have shown that the double aging due to additional disintegration of martensite is an effective way to hardening of maraging steels, which are used for making the force-measuring resilient member.It was established, that the effect of double aging on corrosion properties is determined with the nature of strain-hardening stages: the corrosion-resistance is improved if the formation stage is the cathode in respect to matrix. Conversively, the corrosion-resistance is worsened because of increased extent of structure heterogeneity.Obtained data can be used with a complex approach to the choice of the material and modes of heat strain-hardening treatment of maraging steels for force-measuring resilient member to provide the required values of elasticity and corrosion-resistance limit. It was proved, that maraging ЭП817steel has an advantage over ЭП678 steel in corrosion-resistance and may be recommended for making a forcemeasuring resilient member.</p

Research of High-Heat Treatment Effect on Phase and Chemical Composition of the VKNA-1V Alloy

The paper dwells on the features of the chemical composition and structure of alloys based on Ni3Al. It examines the effect of heat treatment on the structure and phase parameters and on the short-term strength of the intermetallic VKNA-1B alloy.Smelting bar stock was made by technique of vacuum induction. A directional solidification method was used to provide heat treatment of samples on the UVNS-4 installation.The heat treatment was performed in the following modes: heating to a temperature of 1200, 1290, 1300 ° C, holding for 100, 4, 4 hours, respectively, furnace cooling to 800 ° C, then air-cooling. For heating was used the batch furnace VEBK S 400/100 with a maximum operating temperature of 1350 ° C. Samples were loaded in the furnace at 800 0C.The phase composition of the VKNA-1B alloy was examined through physicochemical analysis based on electrochemical insulating phases in different electrolytes. The composition and quantity of the isolated phases were determined by the results of X-ray and chemical analysis methods.To analyse the microstructure was used a scanning electron microscope JSM-840. In original cast state the VKNA-1B alloy has a cellular-dendritic structure. In the axes of the dendrites there is a γ'-phase (~ 75-80% vol.) surrounded by a viscous γ-phase in the form of thin layers; in the inter-dendritic regions there are large particles of γ'-phase. The increasing temperature of heat treatment comes with coarsening γ'-phase particles in inter-dendritic regions and, essentially, has no effect on the phase composition of the alloy. Results of mechanical tensile tests have shown that the alloy retains high strength values after long-term exposure and the increasing cell size of γ'-phase in the axes of the dendrites when raising the temperature leads to an increase in short-term strength of the alloy