What materials are used to make high-temperature alloys?

The core secret behind the stable performance of high-temperature alloys in extreme environments ranging from hundreds to over a thousand degrees Celsius lies in the carefully designed material composition. This special alloy, known as “industrial vitamin”, is not a simple combination of individual elements, but a “material composite” formed by scientifically proportioning the base metal with multiple alloying elements and forging through complex processes. Each component plays a unique role in its performance system.

The base metal is the “skeleton” of high-temperature alloys, determining the basic properties of the material. Nickel based high-temperature alloys are mainly based on nickel, accounting for more than 50% of the total. The face centered cubic crystal structure of nickel endows the alloy with excellent high-temperature stability, making it less prone to crystal structure collapse even at temperatures close to the melting point. This is also the core reason why nickel based alloys are capable of handling ultra-high temperature components such as aircraft engine turbine blades. Iron based high-temperature alloys are based on iron and often contain a high proportion of chromium, resulting in relatively low costs. They are suitable for use in medium temperature environments ranging from 600 to 800 ℃, such as low-pressure turbine components in gas turbines. Cobalt based high-temperature alloys are based on cobalt and are commonly used in applications that require frequent temperature fluctuations, such as the nozzle lining of rocket engines, due to their excellent thermal shock resistance and wear resistance.

The precise ratio of alloy elements is the “seasoning” for the performance of high-temperature alloys, which enhances the comprehensive ability of materials through synergistic effects. Chromium is an essential element in almost all high-temperature alloys. By forming a dense chromium oxide film, it provides a layer of “protective clothing” for the material, effectively resisting high-temperature oxidation and gas corrosion, with a content usually between 10% and 20%. Tungsten, molybdenum, and other refractory metals are like “steel bars” that are integrated into the matrix through a solid solution strengthening mechanism to improve the high-temperature strength and creep resistance of the alloy. In single crystal high-temperature alloys, the total content of these elements can reach more than 20%, enabling them to maintain sufficient bearing capacity above 1100 ℃. Elements such as niobium and tantalum act like “rivets”, forming intermetallic compound strengthening phases with nickel, evenly distributed in the matrix, further locking in crystal slip and improving the stability of the material at high temperatures. For example, in GH4169 alloy, the addition of niobium increases the proportion of strengthening phases to about 30%, significantly enhancing the mechanical properties of the alloy.

The “finishing touch” of trace alloying elements often brings about a leap in performance. Although the addition of rhenium element usually does not exceed 5%, it can significantly improve the high-temperature strength and creep resistance of nickel based single crystal alloys, and is known as the “key driver to improve the temperature resistance limit”. It is commonly used in the turbine blades of the new generation of aircraft engines. Elements such as boron and zirconium act as “grain boundary adhesives”, enriched at the boundaries of crystals, strengthening grain boundary bonding and reducing grain boundary slip at high temperatures, thereby reducing the risk of material brittle fracture. Carbon element plays a diffusion strengthening role at grain boundaries and within crystals by forming carbide phases, balancing the strength and toughness of materials and avoiding the increase in brittleness caused by excessive strengthening.

In addition to metallic elements, the performance of high-temperature alloys is closely related to their microstructure, which is jointly shaped by material composition and process. By controlling the size, distribution, and morphology of strengthening phases, such as the γ ‘phase (Ni3Al) in nickel based alloys, the strength can be significantly improved without reducing plasticity; Oxide dispersion strengthened alloys introduce nanoscale oxide particles to pin dislocation motion at high temperatures, allowing the material to remain stable in ultra-high temperature environments. The formation of these microstructures depends on the precise ratio of matrix metal and alloy elements, as well as the synergistic effect of subsequent heat treatment processes.

The material composition of high-temperature alloys is an art of balance, from the selection of base metals to the ratio of alloying elements – it requires maintaining strength at high temperatures while also possessing sufficient plasticity; It is necessary to resist oxidation corrosion while avoiding brittleness caused by excessive strengthening. It is precisely this complex and exquisite composition design that enables high-temperature alloys to stand out in extreme environments in aerospace, energy and power fields, becoming the “material cornerstone” that supports high-end equipment to break through performance limits. With the development of materials science, the understanding of the composition of high-temperature alloys continues to deepen, and new element combinations and strengthening mechanisms are continuously driving these special materials towards higher temperature resistance limits and better comprehensive performance.