Variable Controled Temperature Gradient Effect on the Features of Structure, Phase Composition, Properties of High-Temperature Superalloys in Their Directional Solidification

The paper presents the research into the conditions of directional solidification with a variable controlled gradient. In our work first, we determined the factors influencing the temperature gradient at the growth front . We found that the most significant method is to remove the crystallization heat by radiation or convection cooling when the mould is immersed into the liquid metal coolant. When examining this process, we discovered important factors: temperature in the heating furnace, the liquid metal coolant temperature, heat shields, separating the heating zone from the cooling zone, the thermal conductivity of the ceramic mould. The study offers the method for the experimental evaluation of the temperature gradient values at the growth front by thermocouples. Findings of experimental studies conducted on the single-crystal samples with crystallographic orientation CLC of Recontaining VZHM3 alloy, show that by controlling the temperature gradient values (G = 20, 50, 100, 150 and 200°C/cm) we can significantly influence the size of the structural superalloy components. Metallurgical studies carried out by optical and electron microscopy showed that with the increase in the temperature gradient with 20°C/cm to 200°C/cm, the interdendritic distance halves from 310 microns to 130 microns, the size of the reinforcing particles γ'-phase in axes and mezhosnom space is reduced by 3 times, the particle size of the eutectic γ-γ' is reduced by more than 2 times, the volume fraction of microporosity is reduced by more than 10 times. By the method of least squares we obtained the regularities of changes of structural components VZHM3 alloy, which are presented in the form of equations. With increasing temperature gradient alloy, single crystal casting properties of cast samples VZHM3 values of tensile strength at 20°C increase in ~1.5 times, while 980°C - by 10-20%, the time to failure at 1100°C and σ=120 MPa increases more than 2 times. This work is within the framework of an integrated research area 9.5: Directional crystallization (with variable controlled gradient) of high-temperature superalloys ("Strategic trends in development of materials and technologies for their processing for the period up to 2030") and is aimed at creating the concept of "The advanced engine".

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