Super high temperature guard in the aerospace field
Inconel 718 is a nickel-chromium-iron-based high temperature alloy, which was successfully developed by the International Nickel Company (INCO) in the late 1950s and is now produced by the Specialty Metals Company (SMC) of the United States. As an important member of the nickel-based alloy family, this material has become one of the core materials in high-end manufacturing fields such as aerospace, energy and chemical industry due to its excellent high temperature strength, oxidation resistance and corrosion resistance.
The chemical composition of Inconel 718 is based on nickel (50-55%), with chromium (17-21%) and iron (remainder) added to form solid solution strengthening, and precipitation strengthening is achieved through elements such as niobium (4.75-5.5%) and molybdenum (2.8-3.3%). Among them, the γ” phase (Ni₃Nb) formed by niobium and nickel is the key to the material maintaining ultra-high strength below 650℃, while the chromium element gives it excellent oxidation resistance. Aluminum (0.65-1.15%) and titanium (0.65-1.15%) together form γ’ phase (Ni₃(Al,Ti)), further strengthening the matrix. This multiphase strengthening mechanism enables it to maintain structural stability in high temperature environments.
The physical properties of the material are outstanding: density 8.19 g/cm³, melting point range 1260-1336℃, thermal expansion coefficient 13.0 μm/m·℃ (20-100℃). Its mechanical properties change significantly with the heat treatment process. After standard aging treatment (720℃×8h+620℃×8h), the room temperature tensile strength can reach 1430 MPa, the yield strength is 1240 MPa, and the elongation is 12%. It can still maintain a tensile strength of about 1000 MPa at a high temperature of 650℃, which is more than 3 times that of ordinary stainless steel.
Processing technology and technical difficulties
The processing of Inconel 718 needs to overcome three core challenges:
1. Hot working control: Forging needs to be carried out in the range of 1120-1140℃, and the final forging temperature must not be lower than 930℃, otherwise it is easy to cause excessive precipitation of δ phase and cracking. During the rolling process, a multi-pass small deformation process is required, and the cumulative deformation is usually controlled between 60-80%.
2. Cold working difficulties: The material work hardening index is as high as 0.45. The deformation of each pass during cold rolling should not exceed 15%. A solid solution treatment of 1065℃×30min is required in the middle to eliminate stress. Precision stamping requires the use of carbide dies, and the blanking gap is controlled at 8-12% of the plate thickness.
3. Welding technology: Pulse TIG welding is recommended, and the shielding gas is Ar+He mixed gas (ratio 7:3), which needs to be preheated to 260-320℃ before welding. Direct aging treatment (720℃×8h) must be carried out after welding, otherwise liquefaction cracks are prone to occur in the heat-affected zone. The joint strength of electron beam welding and laser welding can reach more than 90% of the parent material.
Heat treatment process
The heat treatment of materials is divided into three stages:
1. Solution treatment: 980℃±10℃ for 1h/25mm thickness, and rapid cooling to room temperature. In this stage, γ” and γ’ phases are dissolved to obtain a supersaturated solid solution.
2. Intermediate aging: 720℃±10℃ for 8h, and cooled to 620℃ at 50℃/h. At this time, the γ” phase begins to precipitate evenly, forming reinforced particles with a diameter of about 20nm.
3. Final aging: 620℃±10℃ for 8h, air cooling. The γ” phase further grows to 40-60nm, and the volume fraction can reach more than 15%.
In special application scenarios, double aging process (650℃×24h+760℃×10h) can be used to increase the durability by more than 30%, but it will sacrifice some room temperature strength.
Typical application areas of Inconel718
Aerospace:
Engine turbine disc (accounting for 35% of modern aircraft engines)
Rocket engine thrust chamber
Energy equipment:
Nuclear power reactor pressure vessel bolts
Gas turbine blades
Petrochemical:
Deep-sea Christmas tree components
Acidic environment valves
Of course, as the largest aviation high-temperature alloy, Inconel 718 occupies an irreplaceable position in the field of high-end equipment with its excellent comprehensive performance and mature process system. With the development of additive manufacturing technology, its application boundaries are expanding from traditional forgings to complex topological structure components.
If you have large-scale forging processing needs, you can choose to cooperate with Mulan Metal. Mulan Metal has 12 years of metal forging processing experience, helping customers in more than 30 countries to complete various forging processing businesses and gain unanimous recognition. We look forward to your cooperation consultation.
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