## 1 Introduction  
Inconel 718 belongs to the category of nickel-based superalloys and is known for its tensile, fatigue, creep, and fracture characteristics, as well as its excellent corrosion resistance at temperatures above 650 \({}^{\circ}\)C--properties superior to stainless steels. These characteristics, combined with good welding properties, resistance to post-weld cracking, and good processing properties, justify its use in difficult operating conditions: sheet metal parts for aircraft and gas turbine engines, components in oil refineries, cooling equipment for seawater, cryogenic tanks, and other uses where heat transfer processes are important [1, 2, 3, 4]. Inconel 718 exhibits excellent corrosion resistance at high temperatures due to its high contents of nickel and chromium. This alloy falls under the category of precipitation-hardened nickel-based superalloys, and its good mechanical properties result from both solid solution hardening and precipitation hardening processes. To enhance its mechanical characteristics, this alloy includes elements such as aluminum, titanium, niobium, molybdenum, and tungsten [5; 6; 7; 8]. Solid solution hardening occurs when alloying elements dissolve into the base metal matrix, forming a solid solution with improved strength. The most critical hardening mechanism is the precipitation of intermetallic phases from the solid solution [9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. The chemical composition of the alloy and the applied heat treatment determine the nature, distribution, and morphology of the formed precipitates. The elements that contribute to precipitation hardening are primarily Nb, Al, and Ti. Heat treatment involves solution quenching at temperatures between 970 \({}^{\circ}\)C and 1175 \({}^{\circ}\)C, followed by one or more tempering steps at temperatures between 600 \({}^{\circ}\)C and 815 \({}^{\circ}\)C. During cooling, aluminum and titanium, which are supersaturated in the \(\gamma\) solid solution at the treatment temperature, precipitate to form the \(\gamma^{\prime}\) phase with the stoichiometric formula Ni\({}_{3}\)(Al, Ti). Niobium is the primary hardening element in the alloy, forming the \(\gamma^{\prime\prime}\) compound (Ni\({}_{3}\)Nb) by precipitation. Grain boundary hardening occurs through the precipitation of carbides. The formation of discrete globular carbides along the grain boundaries prevents their migration, thereby enhancing creep resistance and maintaining sufficient ductility in the surrounding matrix. This ductility allows the matrix to absorb the resulting stresses, preventing premature fracture. However, if carbides precipitate as a continuous film along the grain boundaries, the properties of the alloy decrease significantly. The grain size, as well as the size, morphology, and distribution of the precipitates, plays a crucial role in determining the alloy's behavior in various applications [5; 23; 24; 25]. Thermal diffusivity plays a crucial role in determining the performance of Inconel 718 under high-temperature operating conditions. It influences the cooling rate during heat treatments, as well as the size and distribution of precipitated particles. Depending on the cooling rate, either fine microstructures with good mechanical properties or brittle phases with low material durability can be obtained. High thermal diffusivity enhances the material's ability to dissipate heat, which is vital in high-temperature applications, preventing overheating and material degradation. Thermal diffusivity also impacts oxidation at elevated temperatures. An alloy with adequate thermal diffusivity can form a uniform protective oxide layer, improving corrosion resistance in oxidizing environments. Uniform heat distribution helps prevent the formation of cracks and other surface defects, thereby maintaining the structural integrity of the material under severe operating conditions.