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.

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