As a key metallic material in high-end manufacturing, high-temperature alloys play an irreplaceable role in aerospace, energy, and other fields, thanks to their excellent high-temperature resistance and corrosion resistance. The following provides a comprehensive introduction to high-temperature alloys from five dimensions: definition and classification, performance characteristics, production processes, application fields, and typical grades.
I. Definition and classification
High-temperature alloys are metal materials based on iron, nickel, and cobalt, capable of long-term stable operation at temperatures above 600°C and under certain stress conditions. Due to their high degree of alloying (often with the addition of elements such as Cr, Mo, and W), they are also known in the industry as “superalloys”. Their core advantages lie in their combination of high-temperature strength, oxidation resistance, fatigue toughness, and fracture toughness, making them core materials for extreme operating conditions.
Based on different matrix elements, high-temperature alloys are primarily categorized into three major groups, each exhibiting significant differences in application scenarios and performance:
Iron-based high-temperature alloy
Also known as heat-resistant alloy steel, its matrix is primarily composed of iron with a small amount of nickel and cobalt. Its upper limit of use temperature is relatively low, generally ranging from 750 to 780℃. It is only suitable for medium and low temperature heat-resistant components (such as boiler heating surfaces and industrial furnace supports), and cannot meet the extreme operating conditions above 1000℃. Currently, its application proportion in high-end fields is gradually declining.
Nickel-based superalloy
With a nickel content of ≥50%, it is currently the most widely used category – China’s production and usage account for more than 70% of the total high-temperature alloy. Its high temperature resistance is outstanding, allowing it to work for long periods at 1000~1200℃, and it has excellent creep resistance and thermal corrosion resistance. Its core applications include key components such as aeroengine turbine blades and nuclear power evaporators, making it the “lifeline material” for high-end equipment.
Cobalt-based superalloy
With a cobalt content of approximately 60%, it requires the combination of elements such as Cr, Ni, and W to enhance its heat resistance. Its operating temperature can reach above 1100℃, and its resistance to high-temperature wear and thermal fatigue is superior to that of nickel-based alloys. However, due to the scarcity of cobalt resources globally (with reserves only being 1/10 of nickel), the difficulty and high cost of processing, it is currently only used in small quantities in special applications such as aeroengine combustion chamber liners and medical implant devices.
II. Core Performance Features
The “irreplaceability” of high-temperature alloys stems from three key properties, which are also their core advantages over ordinary metal materials:
Excellent high-temperature strength
At high temperatures ranging from 600 to 1200℃, it can still maintain high tensile strength and yield strength, making it less prone to plastic deformation or fracture. For example, the tensile strength of nickel-based alloy GH4169 can reach over 1000MPa at 700℃, which is 3 to 4 times that of ordinary stainless steel at the same temperature.
Strong antioxidant and thermal corrosion resistance
Under high-temperature conditions, a dense layer of Cr₂O₃ and Al₂O₃ oxide films quickly forms on the surface of alloys, effectively isolating them from corrosive media such as oxygen, sulfides, and chlorides, thus preventing the internal erosion of the alloy. For instance, in petrochemical cracking furnaces, the nickel-based alloy GH3044 can resist high-temperature sulfide corrosion for extended periods at 1100℃.
Excellent organizational stability and reliability
High-temperature alloys have a single austenite structure (without phase transformation), and during long-term high-temperature service, they will not experience performance degradation due to structural precipitation (such as sigma phase and carbides). For most grades, after 10,000 hours of service at 1000℃, the strength degradation rate is ≤10%, meeting the requirements of “long lifespan and high reliability” for critical equipment.
III. Production Process
The performance of high-temperature alloys relies on precise preparation processes, with core procedures encompassing three major steps: melting, casting, and heat treatment. Each step requires strict control of parameters:
Smelting: ensuring uniform composition and purity
The mainstream adopts the “multi-furnace combined melting” process, which specifically includes:
Vacuum induction melting (VIM): Initially, metal raw materials are melted in a vacuum environment to eliminate gases (H, O, N) and impurities (S, P), ensuring precise control over alloy composition;
Vacuum arc remelting (VAR)/electroslag remelting (ESR): Secondary remelting of VIM ingots to refine grain size, eliminate shrinkage cavities, enhance ingot density (up to over 99.95%), and prevent cracking during subsequent processing.
Casting: adapting to different component shapes
With investment casting as the core technology, it is divided into three forms according to the performance requirements of components:
Equiaxed grain casting: grains are randomly distributed, suitable for components with lower strength requirements (such as engine casings);
Directional columnar crystal casting: grains are aligned along the direction of stress, improving creep resistance by 30%, and is used for turbine guide vanes;
Single crystal casting: The entire component is composed of a single grain, free from grain boundary interference, and exhibits optimal high-temperature fatigue resistance. It is the sole choice for aeroengine turbine blades.
Heat treatment: customized performance regulation
Exclusive processes need to be designed according to the brand and application scenario. Common types include:
Solution treatment: Heat the alloy to 1050~1200℃, maintain the temperature, and then rapidly cool it down to eliminate internal stress and obtain a uniform microstructure;
Aging treatment: Low-temperature heat preservation at 650~750℃ leads to the precipitation of γ′ phase (such as Ni₃Al), significantly enhancing the strength of the alloy;
Homogenization treatment: For large forgings, long-term high-temperature heat preservation (1200℃×24 hours) is used to eliminate composition segregation and ensure consistent overall performance.
IV. Main application areas
The application scenarios of high-temperature alloys are highly concentrated in extreme operating conditions characterized by “high temperature, high pressure, and high corrosion”, covering four core areas:
Aerospace industry (accounting for about 40%)
Nickel-based superalloys are the “sole materials” for hot-end components of aero-engines, such as turbine blades, combustion chambers, turbine disks, and other key components (e.g., GH4169, GH3039). For example, the high-pressure turbine blades of a certain type of passenger aircraft engine need to operate under 1100°C and 300MPa stress for extended periods, and only single-crystal nickel-based alloys can meet these requirements. Additionally, cobalt-based superalloys are relied upon for their high-temperature erosion resistance in missile engine nozzles and spacecraft thermal protection panels.
Energy sector (accounting for approximately 30%)
Gas turbine: The combustion chamber and turbine blades are made of nickel-based alloy GH3536, which can withstand high-temperature gas scouring at 1200℃;
Nuclear power: The heat transfer tubes of nuclear island evaporators are made of nickel-based alloy Inconel 690, which exhibits excellent corrosion resistance against high-temperature and high-pressure water, ensuring the safe operation of nuclear power plants;
Coal-fired power: The main steam pipeline of ultra-supercritical units utilizes iron-based alloy GH2132, which enhances power generation efficiency to over 45% at 650℃.
Automotive industry (accounting for about 15%)
With the popularization of turbocharging technology, the application of high-temperature alloys in the automotive industry has seen rapid growth: the turbine wheel of a turbocharger utilizes the nickel-based alloy K418, capable of withstanding exhaust gas temperatures of 900°C; the bipolar plate of fuel cells in new energy vehicles employs the corrosion-resistant nickel-based alloy Inconel 625, extending battery life to over 10 years.
Other industrial sectors (accounting for about 15%)
Petrochemical: The cracking furnace tube is made of nickel-based alloy GH3044, which cracks petroleum into ethylene at 1100℃;
Metallurgy: The copper plate coating of the continuous casting machine’s crystallizer adopts cobalt-based alloy, which enhances the high-temperature wear resistance by 5 times;
Glass manufacturing: The flame nozzle of the glass kiln utilizes high-temperature alloys to resist erosion from glass melt at 1600℃.
