Fine Grains Forming Process, Mechanism of Fine Grain Formation and Properties of Superalloy 718

Abstract

The mechanical properties of Inconel 718 superalloy are determined primarily by its microstructure and grain size. The grain structure of Inconel 718 is traditionally refined by aging treatment, and a high volume fraction of acicular ¤ phase precipitates before the structure forms. During the following static or dynamic recrystallization process, the existing ¤ phase inhibits recrystallized grain growth and acquires a fine grain structure. In the proposed approach, the Inconel 718 specimens are re-solution heat treated at a temperature higher than the ¤ solvus temperature to ensure thorough dissolution of the precipitated ¤ phase into the austenite matrix and produce a niobium oversaturated matrix. The specimens are then cold compressed to produce a dislocation saturated matrix and are finally recrystallized at 950°C to induce the precipitation of fine ¤ phase. The ¤ phase precipitates exert a strong grain-boundary pinning effect, and thus a fine grain structure is obtained despite the high recrystallization temperature. The average grain size in the refined microstructure is found to be 23 µm, which is around half that of the grain size in the specimens prepared using the conventional process. Hardness testing and tensile testing at 25 and 650°C revealed its superior mechanical properties.

Grain Refinement of Inconel 718 Superalloy—The Effect of Rotating Magnetic Field

“…Inconel (Nickel-based) superalloys are currently used in the aircraft/aerospace industry, mostly due to their excellent creep properties, hot corrosion resistance and oxidation resistance. These superalloys can withstand intense mechanical stresses and pressures, when submitted at high working temperatures (heat resistant alloys), while retaining reliable creep and corrosion-resistance properties [ 1 , 2 , 3 , 4 ].…”

“…Therefore, Inconel 718, a Ni-Cr-Fe austenite (γ) superalloy [ 1 , 2 , 5 ] has been mostly employed in turbojet engines in the form of major parts of turbines wheel, discs and blades. It is also used in rocket engines, combustion chambers and nuclear reactors as it offers robustness and prevents the occurrence of brittle transformation in the components at high temperatures [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ].…”

Image Processing of Mg-Al-Sn Alloy Microstructures for Determining Phase Ratios and Grain Size and Correction with Manual Measurement

“…Examining the grain sizes in microstructures is of primary importance. Compared to coarse grain structures, the number of grains per unit area in a fine-grained microstructures is greater [49]. According to the Hall-Petch effect, the increased length of grain boundaries creates difficulty in dislocation movements, thereby improving the mechanical properties of the material [49][50][51].…”

“…Compared to coarse grain structures, the number of grains per unit area in a fine-grained microstructures is greater [49]. According to the Hall-Petch effect, the increased length of grain boundaries creates difficulty in dislocation movements, thereby improving the mechanical properties of the material [49][50][51]. Scanning electron micrographs are taken and analysed manually to assess the total number of grains and length of grain boundaries present in microstructures [9,52].…”

Surface modification of structural material for nuclear applications by electron beam melting: enhancement of microstructural and corrosion properties of Inconel 617

“…Excellent high temperature oxidation resistance, corrosion resistance, and high temperature phase stability make solid solution strengthened nickel-base superalloy more popular as a next generation candidate structural material in nuclear reactors such as Pressurized Water Reactors (PWR) and Very High Temperature Reactor (VHTR) [1][2][3][4][5]. Inconel 617 is a class of Ni based superalloy with the following major alloying elements: Chromium, Molybdenum, Titanium, Cobalt, Aluminum, Iron, Cooper etc.…”