Temperature Management: Metal Solutions for High-Performance Engines

With the ability to spin up to 125,000 rpm at exhaust gas temperatures higher than 1000°C, it is crucial to understand which superalloy is fit for your application. Some metals will work flawlessly for an entire race season, while others will fail instantly. Knowing how to choose the alloy for the right temperature range is crucial.

At Dynamic Metals, we are pleased to offer a wide array of metals for various aerospace, motorsport, and power generation applications: Inconel 625 and 718, Nimonic 75, 80A, and 90, Waspaloy, and Rene 41.

The Mechanisms of High-Temperature Failure

High-temperature failure of metal materials is possible in several ways:

Creep is a process by which metals change shape over time when subjected to prolonged stresses. Even if stresses are lower than those leading to yield strength, creep can happen – that means that a turbine blade operating at 900°C will stretch through creep, regardless of its initial thickness.

Oxidation is a mechanism through which oxygen interacts with the surface of the metal, destroying its integrity. However, nickel-chromium-based alloys create a protective oxide layer of Cr2O3, provided that chromium content in the alloy is higher than 15%. Also, remember that the rate of oxidation doubles each 25-30°C rise.

Thermal fatigue is caused by the expansion and shrinking of metal due to thermal cycling.

Hot corrosion is the process of forming aggressive molten salts by the reaction of sulfur with the surface contaminants.

Inconel 625: Weldable Nickel Alloy with Outstanding Temperature Capability

This material achieves its strength through solid solution strengthening, not precipitation. That means Inconel 625 can be welded and fabricated in its strengthened state; no heat treatment after fabrication is required.

Temperature capability: Inconel 625 withstands temperatures up to 980°C. It is resistant to oxidation up to 1095°C. At 650°C, tensile strength is about 760 MPa. At 870°C – 380 MPa.

Applications: Exhaust headers, turbine ducts, and afterburners. At Dynamic Metals, Inconel 625 is primarily available in a wide range of thickness.

Inconel 718: Extraordinary High-Strength Metal Suitable for Temperatures Under 650°C

This alloy's outstanding characteristics are attributed to precipitation hardening – a formation of Ni3Nb particles providing extra strength.

Limitation: Precipitates disappear above 650°C, which leads to considerable weakening of the metal. At 540°C, tensile strength reaches 1240 MPa in precipitation-hardened metal. That is the highest tensile strength at that temperature of any wrought alloy.

Applications: Used in turbocharger compressor housings, bearing housings, and turbine discs. Because of its high strength and low weight, it cannot withstand temperatures above 700°C.

Nimonic 75: Strong Resistance to High Temperatures

Unlike Inconel 718, Nimonic 75 relies on solid solution strengthening for achieving its high temperatures.

Temperature capability: Nimonic 75 exhibits excellent high-temperature behavior up to 1000°C. At 815°C, tensile strength is equal to 455 MPa. That is less than precipitation hardening superalloys, but enough to be used widely.

Applications: Heat shields, thermal barriers, and exhaust hangers in racing cars. It is very easy to form into shapes, so we supply Nimonic 75 mainly in sheets.

Nimonic 80A: Maximum High-Temperature Properties Among Super Alloys

As with the previous alloys, Nimonic 80A uses solid solution strengthening as the base of its extraordinary strength, supplemented by precipitation strengthening using gamma-prime, Ni3(Al,Ti). Unlike Inconel 718, gamma-prime precipitates do not vanish at temperatures above 650°C and remain active until 900°C.

Temperature capability: Tensile strength at 815°C is 760 MPa. Yield strength is 520 MPa. At 900°C, it still offers 550 MPa. Stress-rupture properties at 345 MPa of tensile stress is 1000+ hours at 815°C.

Applications: Gas turbine blades, turbocharger turbine wheels, and exhaust valves.

Nimonic 80A is relatively easy to mill in the solution-treated state and then age hardened.

Nimonic 90: Improved Creep Properties in Extremely High Temperatures

Nimonic 90 was developed based on Nimonic 80A with the addition of Cobalt and aluminum/titanium ratio to enhance creep properties.

Temperature capability: Nimonic 90 can be operated at maximum temperatures reaching 950°C. At 815°C, its rupture life under 380 MPa stress is 1000+ hours (Nimonic 80A lasts 100-200 hours).

Applications: Used in turbine blades in aerospace industry, extremely high-speed turbocharger wheels (200,000+ rpm) and other critical parts of jet engines. More expensive (by 30-40%) than Nimonic 80A, used only where necessary.

Waspaloy: One of the Best Wrought Superalloys for High Temperatures

Waspaloy is considered to be one of the best wrought superalloys for high-temperature applications. It is designed for turbine blades and related parts.

Temperature capability: Can operate continuously up to 900°C, resistant to oxidation up to 1050°C. Its tensile strength at 815°C is 860 MPa. Stress-rupture life of Waspaloy is over 200 hours at 870°C under 240 MPa stress.

Applications: Used in first-stage turbine blades of jets engines, industrial gas turbines operating continuously at 870-900°C and other extreme racing turbocharger applications.

René 41: Outstanding High-Temperature Performance

René 41 is the best of readily available wrought nickel superalloys in terms of temperature capability.

Temperature capability: Can withstand continuous operation up to 980°C, and is resistant to oxidation to 1090°C. Tensile strength at 870°C is 965 MPa, and at 980°C – 690 MPa (other alloys have zero tensile strength at this point).

Applications: Applications include high-pressure turbine blades in advanced jet engines, afterburners, extreme racing turbochargers and the turbine wheels of the land speed record vehicle, as well as first-stage industrial gas turbine blades at temperatures close to 1000°C. It is the most expensive alloy, 40-60% more than Inconel 718.

Choosing the Correct Superalloy

Under 650°C: Inconel 718 (maximum strength) and Inconel 625 (better fabricability)

Between 650-850°C: Inconel 625 (for moderate stress levels) or Nimonic 80A (higher loads)

Between 850-950°C: Nimonic 90, Waspaloy or René 41 (depending on stress level)

Over 950°C: René 41

Low stress, oxidation resistant: Nimonic 75 (excellent up to 1000°C)

Conclusion

Since 2010, we've been supplying superalloys to various aerospace, motorsport, and power generation industries. At Dynamic Metals, you can order the following superalloys certified according to AS9100 standard: Inconel 625 and 718, Nimonic 75, 80A, and 90, Waspaloy, and René 41.