Introduction and Application of High-temperature Alloys
High-temperature alloys, also known as superalloys, are a class of metal materials that can maintain their strength and corrosion resistance in high-temperature environments.
Introduction and Application of High-temperature Alloys
High-temperature alloys are iron-based, nickel-based, and cobalt-based alloys that are usually used at temperatures above 540°C. These alloys are widely used in various industrial fields due to their excellent properties at high temperatures, such as creep resistance, oxidation resistance, and corrosion resistance.
Metallurgical Principles of High-temperature Alloys
High-temperature alloys usually have a face-centered cubic (FCC) crystal structure. Iron and cobalt are not FCC structures at room temperature, but they will transform into FCC structures after high temperatures or alloying. Nickel maintains FCC structure at all temperatures. The properties of high-temperature alloys are not only determined by their chemical composition, but also affected by heat treatment, forging, and casting processes.
Characteristics and Properties of High-temperature Alloys
Ordinary steel and titanium alloys are not strong enough at temperatures above 540°C and may be damaged by corrosion.
If strength needs to be maintained at higher temperatures (melting point of most alloys is about 1371-1204°C), nickel-based superalloys are usually selected.
Nickel-based superalloys can be used at higher temperature ratios than commercial materials.
Cobalt-based superalloys can be used as a substitute for nickel-based superalloys, depending on the required strength and corrosion type.
At lower temperatures, iron-nickel-based superalloys have a wider range of applications than nickel-based and cobalt-based superalloys.
The strength of superalloys depends not only on chemical composition, but also on heat treatment, forging, casting processes, especially the process after heat treatment, forging or casting.
Iron-nickel-based superalloys are cheaper than nickel-based and cobalt-based superalloys.
In order to improve corrosion resistance at high temperatures, most processed superalloys contain a certain amount of chromium.
Superalloys have high oxidation resistance, but in some cases, corrosion resistance is insufficient. For example, at aircraft engine turbine temperatures above 760°C, superalloys require coatings.
Superalloy coating technology is an important part of its application and development. Uncoated superalloys are inefficient for long term use at high temperatures.
In superalloys, especially nickel-based superalloys, a variety of elements are added, with some alloys containing up to 14 or more controlled elements.
The elements used in superalloys, such as nickel, cobalt, chromium, tungsten, molybdenum, rhenium, and hafnium, are generally expensive and vary over time.
Applications of Superalloys
Superalloys have a wide range of uses in high temperature applications, including aircraft components, chemical and petrochemical equipment.
It is important to note that not all applications require strength at high temperatures. The composition and corrosion resistance of superalloys make them a standard material for manufacturing medical devices. Superalloys have also found applications at very low temperatures.
Superalloys play an important role in modern industry due to their unique combination of properties, especially in the aerospace, energy, and chemical industries.
