High-temperature alloys are classified into three categories: 760°C high-temperature materials, 1200°C high-temperature materials, and 1500°C high-temperature materials, with a tensile strength of 800 MPa. In other words, these are high-temperature metallic materials designed for long-term operation at temperatures ranging from 760 to 1,500°C or higher under specific stress conditions. They possess excellent high-temperature strength, good resistance to oxidation and thermal corrosion, as well as favorable fatigue properties and fracture toughness, among other comprehensive characteristics. As such, they have become indispensable key materials for hot-end components in both military and civilian gas turbine engines.
According to current theory, high-temperature materials for 760°C can be primarily classified by matrix element into iron-based high-temperature alloys, nickel-based high-temperature alloys, and cobalt-based high-temperature alloys. By fabrication process, they can be classified into wrought high-temperature alloys, cast high-temperature alloys, and powder metallurgy high-temperature alloys. By strengthening mechanism, they include solution-strengthened, precipitation-strengthened, oxide-dispersion-strengthened, and fiber-reinforced types. High-temperature alloys are primarily used to manufacture high-temperature components such as turbine blades, guide vanes, turbine discs, high-pressure compressor discs, and combustion chambers for gas turbines in aviation, naval vessels, and industrial applications. They are also used in the manufacture of aerospace vehicles, rocket engines, nuclear reactors, petrochemical equipment, and energy conversion devices such as coal conversion systems.
Category
760°C High-Temperature Materials: Deformable High-Temperature Alloys
Deformable high-temperature alloys refer to a class of alloys that can undergo hot and cold deformation, operate within a temperature range of -253 to 1,320°C, possess good mechanical properties and comprehensive strength and toughness indices, and exhibit high resistance to oxidation and corrosion. Based on their heat treatment processes, they can be classified into solution-strengthened alloys and age-hardening alloys. The first digit following “GH” indicates the classification code: 1. Solution-hardened iron-based alloys; 2. Age-hardening iron-based alloys; 3. Solution-hardened nickel-based alloys; 4. Cobalt-based alloys. The second, third, and fourth digits following “GH” indicate the sequential number.
1. Solution-Strengthened Alloys
The operating temperature range is 900–1300°C, with a maximum oxidation resistance temperature of 1320°C. For example, the GH128 alloy has a tensile strength of 850 MPa and a yield strength of 350 MPa at room temperature; at 1,000°C, the tensile strength is 140 MPa and the elongation is 85%; at 1,000°C under a stress of 30 MPa, the creep life is 200 hours with an elongation of 40%. Solution-hardened alloys are generally used to manufacture components such as combustion chambers and engine casings for aviation and aerospace engines.
2. Age-Hardening Alloys
Operating temperatures range from –253 to 950°C. These alloys are generally used to manufacture structural components such as turbine discs and blades for aviation and aerospace engines. Alloys used for turbine discs operate at temperatures ranging from –253 to 700°C and must possess good strength at both high and low temperatures, as well as fatigue resistance. For example, the GH4169 alloy has a maximum yield strength of 1,000 MPa at 650°C; alloys used for blades can operate at temperatures up to 950°C. For instance, the GH220 alloy has a tensile strength of 490 MPa at 950°C, and a fatigue life exceeding 40 hours at 940°C with a stress of 200 MPa.
Worked high-temperature alloys primarily supply structural forgings, discs, rings, bars, plates, tubes, strips, and wires to the aerospace, aviation, nuclear energy, petroleum, and civilian industries.
760°C 800 MPa-Class High-Temperature Casting Alloys
Casting high-temperature alloys refer to a class of high-temperature alloys from which parts can be—or must be—formed exclusively by casting. Their main characteristics are:
1. A wider composition range. Since there is no need to balance deformation processing properties, alloy design can focus on optimizing service performance. For example, in nickel-based high-temperature alloys, adjusting the composition can increase the γ' content to 60% or higher, enabling the alloy to maintain excellent performance at temperatures as high as 85% of its melting point.
2. A broader range of applications. Due to the unique advantages of the casting process, high-temperature alloy castings with arbitrary complex structures and shapes—whether near-net-shape or without excess material—can be designed and manufactured according to the specific requirements of the component.
Based on the operating temperature of the cast alloys, they can be classified into the following three categories:
Category 1: Equiaxed-grain cast high-temperature alloys used at temperatures ranging from –253 to 650°C. These alloys exhibit good overall performance over a wide temperature range, particularly maintaining both strength and ductility without significant decline at low temperatures. For example, the K4169 alloy, which is widely used in aviation and aerospace engines, has a tensile strength of 1,000 MPa, a yield strength of 850 MPa, and a tensile ductility of 15% at 650°C; its endurance life under a stress of 620 MPa at 650°C is 200 hours. It has been used to manufacture diffuser casings in aircraft engines and various complex structural components for pumps in aerospace engines.
Category 2: Equiaxial-grain cast high-temperature alloys used at 650–950°C. These alloys exhibit high mechanical properties and resistance to thermal corrosion at high temperatures. For example, the K419 alloy has a tensile strength greater than 700 MPa and tensile ductility greater than 6% at 950°C; and at 950°C for 200 hours, the creep strength limit exceeds 230 MPa. These alloys are suitable for use as turbine blades, guide vanes, and monoblock turbines in aircraft engines.
Category 3: Directionally solidified columnar-grain and single-crystal high-temperature alloys used at 950–1100°C. These alloys exhibit excellent comprehensive properties, as well as resistance to oxidation and thermal corrosion, within this temperature range. For example, the DD402 single-crystal alloy has a creep life exceeding 100 hours at 1,100°C under a stress of 130 MPa. This is the turbine blade material with the highest operating temperature in China and is suitable for manufacturing first-stage turbine blades for new high-performance engines.
As precision casting technology continues to advance, new specialized processes are constantly emerging. Fine-grain casting technology, directional solidification technology, and CA technology for complex thin-walled structural components have all significantly improved the quality of cast high-temperature alloys and expanded their range of applications.
760°C, 800 MPa-class high-temperature materials: Powder metallurgical high-temperature alloys
These high-temperature alloy products are manufactured using atomized high-temperature alloy powders through a production process involving hot isostatic pressing (HIP) or HIP followed by forging. The powder metallurgy process, characterized by fine powder particles and rapid cooling rates, ensures uniform composition without macroscopic segregation. Additionally, the fine grain structure results in excellent hot working properties, high metal utilization, and low cost, while significantly improving the alloy’s yield strength and fatigue performance.
FGH95 powder metallurgy high-temperature alloy has a tensile strength of 1500 MPa at 650°C and a creep life exceeding 50 hours under a stress of 1034 MPa; it is currently the powder metallurgy high-temperature alloy with the highest strength level for disc components operating at 650°C. Powder metallurgy high-temperature alloys can meet the operational requirements of engines operating under high stress levels and are the material of choice for high-temperature components such as turbine discs, compressor discs, and turbine vanes in high thrust-to-weight ratio engines.
1200°C, 100 MPa-class high-temperature oxide dispersion-strengthened (ODS) alloys
These special high-temperature alloys are produced using a unique mechanical alloying (MA) process, in which ultrafine (less than 50 nm) oxide dispersion-strengthening phases—which are highly stable at high temperatures—are uniformly dispersed throughout the alloy matrix. The alloy’s strength is maintained even at temperatures approaching its melting point, and it exhibits excellent high-temperature creep resistance, superior high-temperature oxidation resistance, and resistance to carbon and sulfur corrosion.
Currently, three main ODS alloys have been commercialized:
MA956 alloy can operate at temperatures up to 1,350°C in an oxidizing atmosphere and ranks first among high-temperature alloys in terms of resistance to oxidation, carbon, and sulfur corrosion. It can be used for combustion chamber liners in aircraft engines.
MA754 alloy can operate at temperatures up to 1,250°C in an oxidizing atmosphere while maintaining relatively high high-temperature strength and resistance to corrosion by medium-alkali glass. It is currently used to manufacture guide vane rings and guide vanes for aircraft engines.
MA6000 alloy has a tensile strength of 222 MPa and a yield strength of 192 MPa at 1,100°C; its creep strength at 1,100°C for 1,000 hours is 127 MPa, ranking first among high-temperature alloys, and it can be used for aircraft engine blades.
Intermetallic Compound High-Temperature Materials
Intermetallic compound high-temperature materials are a class of lightweight high-temperature materials with significant application potential that have been recently researched and developed. Over the past decade, fundamental research on intermetallic compounds, alloy design, process development, and applied research have matured. Notable achievements have been made, particularly in the preparation and processing technologies, toughening and strengthening, mechanical properties, and applied research of Ti-Al, Ni-Al, and Fe-Al-based materials.
Ti₃Al-based alloys (TAC-1), TiAl-based alloys (TAC-2), and Ti₂AlNb-based alloys offer advantages such as low density (3.8–5.8 g/cm³), high strength and stiffness at elevated temperatures, as well as excellent resistance to oxidation and creep, enabling a 35–50% reduction in the weight of structural components. The Ni₃Al-based alloy MX-246 possesses excellent corrosion resistance, wear resistance, and cavitation resistance, demonstrating outstanding application potential. Fe₃Al-based alloys exhibit good oxidation and erosion resistance, high strength at moderate temperatures (below 600°C), and low cost, making them a new material capable of partially replacing stainless steel.
Environmental High-Temperature Alloys
In many sectors of the civilian industrial sector, components in service are exposed to high-temperature corrosive environments. To meet market demands, a series of high-temperature alloys has been categorized based on their intended operating environments.
1. High-temperature alloy master alloy series
2. Corrosion-resistant high-temperature alloy plates, bars, wires, strips, tubes, and forgings
3. High-strength, corrosion-resistant high-temperature alloy bars, spring wires, welding wires, plates, strips, and forgings
4. Glass-Corrosion-Resistant Product Series
5. Environmentally Corrosion-Resistant and Hard-Surface Wear-Resistant High-Temperature Alloy Series
6. Special Precision Casting Parts (Blades, Turbochargers, Turbine Rotors, Guide Vanes, Instrument Fittings)
7. Centrifuges, High-Temperature Shafts, and Accessories for Glass Wool Production
8. Cobalt-Based Alloy Heat-Resistant Pads and Slide Rails for Steel Billet Heating Furnaces
9. Valve seat rings
10. Cast “U”-shaped resistance bands
11. Centrifugal cast pipe series
12. Nanomaterial product series
13. Low-density high-temperature structural materials
14. Functional materials (expansion alloys, high-temperature high-elasticity alloys, constant-elasticity alloy series)
15. Biomedical material product series
16. Target material series for electronic engineering
17. Power Plant Nozzle Series Products
18. Stellite Alloy Wear-Resistant Plates
19. Ultra-High-Temperature Oxidation- and Corrosion-Resistant Furnace Rolls and Radiation Tubes.
Development Trends
The trend in high-temperature alloy development is to further increase the operating temperature of the alloys and improve their ability to withstand various loads at medium or high temperatures, thereby extending the service life of the alloys. Regarding turbine blade materials, single-crystal blades will enter the practical application stage, and the comprehensive performance of directionally solidified blades will be improved.
In addition, it will be possible to manufacture multi-layered, diffusion-bonded hollow blades using quenched alloy powders, thereby meeting the need for higher combustion gas temperatures. For guide vane and combustion chamber materials, it will be possible to use oxide-dispersion-strengthened alloys to significantly increase operating temperatures. To improve corrosion and erosion resistance, protective coating materials and processes for these alloys will also see further development.