The electrical resistivity of IN 718 alloy was studied in a liquid state with contactless induction method of rotating magnetic field. Solidification process was studied by differential thermal analysis. It was founded that electrical resistivity varies in a complicated way with increasing temperature. It is shown that heating of the liquid metal above certain temperatures causes of hysteresis, i.e. discrepancy between the temperature dependences of heating and cooling. It was revealed, that the changes of niobium contents within alloy composition do not lead to a qualitative change of temperature dependence type, but accompanied by some peculiarities. Effect of titanium content on electrical resistivity changes within the alloy composition does not clearly detect. The temperature of maximal melt heating determines the degree of supercooling of liquid alloy.
Keywords: Electrical resistivity, differential thermal analysis, nickel based alloy IN 718, liquidstate, temperature dependence, niobium and titanium influence
IntroductionThe precipitation-hardening iron-nickel based alloy IN 718 is widely used in manufacture of hightemperature components in the gas turbine industry, power plant and petrochemical plants [1,2]. It is a superalloy, having a compensation of high strength at moderate temperatures, corrosion and oxidation resistance. Because of its excellent balance of properties and reasonable cost, IN718 is accounting for more than 50% of commercial superalloy productions in the world [1]. With the development of land-based power generation and aircraft propulsion, scaling-up of components has become the necessity. The size of IN 718 ingot produced by VIM-ESR-VAR triple melting has increased dramatically over the past 10 years in response to market demands [2][3][4]. However, the solute segregation problem, mainly niobium segregation, is a big obstacle for producing large size IN 718 ingots. Particularly, some macro-segregations defects such as freckles and white spots formed during the solidification process will lead to entire failure for the whole ingot. It has been founded for a lot of steels and alloys that the melting temperature represents melt superheat, which has a great effect on liquid structure, as-cast microstructure and combination of properties of the alloy [5][6][7][8][9][10][11][12]. So, the information about structural transformation in a liquid state during heating has a great importance for the elaboration of melting processes [13]. One of the methods of study of structural transformation in the liquid metal is measuring of temperature dependences of structure-sensitive properties of melt, such as electrical resistivity, kinematic viscosity, density, surface tension and others. Previously it has been founded by the [13] that the