Comprehensive performance and application of high temperature alloy Alloy 718
Alloy 718 (UNS N07718, 2.4668 NiCr19Fe19Nb5Mo3, Inconel 718) is a precipitation-strengthened nickel-based high-temperature alloy with excellent comprehensive performance in the temperature range of -253 ℃ to 700 ℃ . Especially below 650 ℃ , its yield strength ranks first among deformed high-temperature alloys. In addition, Alloy 718 also has good fatigue resistance, radiation resistance, oxidation resistance and corrosion resistance. At the same time, the alloy’s processing performance, welding performance and long-term organizational stability are also quite outstanding. It can manufacture various complex-shaped parts and is widely used in aerospace, nuclear energy and petroleum industries.
Chemical composition and structure of Alloy 718
The chemical composition of Alloy 718 mainly includes nickel (Ni), chromium (Cr), iron (Fe), niobium (Nb) and molybdenum (Mo), among which nickel and chromium give it excellent anti-oxidation and corrosion resistance. The addition of niobium and molybdenum significantly improves its high temperature strength and creep resistance. The specific ingredients are shown in Table 1:
| element | content(%) |
| nickel | 50-55 |
| chromium | 17-21 |
| iron | margin |
| niobium | 4.75-5.5 |
| molybdenum | 2.8-3.3 |
This chemical composition design makes Alloy 718 have excellent mechanical properties and corrosion resistance at high temperatures. Its microstructure is mainly composed of γ matrix phase, γ” and γ’ precipitation phases and a small amount of δ phase. Among them, the precipitation of γ” and γ’ phases is the main reason for improving the strength of the alloy, while the δ phase can stabilize the grains during appropriate heat treatment.
Mechanical properties of Alloy 718
Alloy 718 are particularly outstanding under high temperature conditions. Its yield strength and tensile strength are both extremely high below 650 ℃ , and the alloy also has good creep resistance and fatigue resistance. Table 2 lists the typical mechanical properties data of Alloy 718 at different temperatures.
| Temperature ( ℃ ) | Yield strength (MPa) | Tensile strength (MPa) | Elongation (%) |
| room temperature | 1034 | 1241 | 16 |
| 650 | 725 | 965 | 12 |
| 700 | 510 | 725 | 10 |
This excellent mechanical property makes Alloy 718 widely used in key components such as aeroengine turbine disks, turbine blades, combustion chambers and fasteners.
Processing and welding properties of Alloy 718
Alloy 718 has good processing properties and can be made into products of various shapes through forging, rolling, drawing and extrusion processes. In addition, the welding performance of Alloy 718 is also quite excellent. Commonly used welding methods include TIG, MIG, laser welding and electron beam welding. During the welding process, the alloy does not have a significant tendency to crack, which is mainly attributed to its good high-temperature plasticity and appropriate precipitation strengthening mechanism.
Heat Treatment Process of Alloy 718
The microstructure and properties of Alloy 718 are extremely sensitive to heat treatment processes. Common heat treatment processes include solution treatment, aging treatment and double aging treatment. Through reasonable heat treatment, the precipitation of γ”, γ’ and δ phases can be controlled, thereby adjusting the mechanical properties and microstructure stability of the alloy.
For example, a typical heat treatment process is as follows:
- Solution treatment: heat to 980-1010 ℃ , keep warm for 1 hour, then cool rapidly.
- Aging treatment: It is carried out in two steps, first at 720-740 ℃ for 8 hours, and then at 620-650 ℃ for 8 hours.
This double aging treatment gives the alloy optimal strength and toughness at high temperatures.
Application of Alloy 718 in the aerospace industry
Alloy 718 has been widely used in the aerospace field, mainly for manufacturing key components such as turbine disks, turbine blades, combustion chambers and fasteners that work under high temperature conditions. For example, the turbine disk of an aircraft engine needs to operate for a long time under high temperature and high pressure environments, which places extremely high demands on the material’s high temperature strength and fatigue resistance. Alloy 718 has become the preferred material for manufacturing these key components due to its excellent comprehensive performance.
Application of Alloy 718 in Nuclear Energy and Petroleum Industry
In the nuclear energy industry, Alloy 718 is often used to manufacture reactor internal structural parts and nuclear fuel element clamping devices. These parts need to work stably for a long time in a high temperature and high radiation environment. Alloy 718’s radiation resistance and structural stability ensure the reliable operation of these parts in harsh environments.
In the oil industry, Alloy 718 is widely used to manufacture high-pressure wellhead equipment and deep-sea drilling equipment, which need to work in corrosive media and high-pressure and high-temperature environments. Alloy 718’s corrosion resistance and high-temperature strength make it an ideal material for these applications.
in conclusion
Alloy 718 is a precipitation-strengthened nickel-based high-temperature alloy with excellent comprehensive properties. Its mechanical properties, fatigue resistance, radiation resistance, corrosion resistance, and good processing and welding properties at high temperatures have made it widely used in the aerospace, nuclear energy, and petroleum industries. Through reasonable heat treatment processes, its organizational structure and mechanical properties can be further optimized to meet the requirements under different use conditions. In the future, with the in-depth study of high-temperature alloy properties and the advancement of process technology, Alloy 718 will continue to play an important role in more fields.