The core value of high-temperature alloys lies in their comprehensive performance stability under extreme environments. Key indicators such as high-temperature strength, oxidation resistance, creep resistance, and corrosion resistance are influenced by multiple factors in a synergistic manner. From component design to forming processes, and from microstructure to post-treatment, subtle adjustments in each link can significantly alter alloy properties. Precisely controlling these factors is the core prerequisite for achieving adaptability of high-temperature alloys to different working conditions.
Composition is the foundation that determines the performance of high-temperature alloys, with the ratio of matrix elements to alloy elements directly setting the performance tone. Matrix elements such as nickel and cobalt ensure the basic high-temperature stability of the alloy. Nickel-based alloys, with their excellent solid solution strengthening capabilities, have become the mainstream choice for high-temperature applications; cobalt-based alloys, on the other hand, excel in terms of resistance to hot corrosion. The addition of alloy elements serves a clear functional purpose: chromium forms a dense oxide film to enhance oxidation resistance, molybdenum and tungsten improve high-temperature strength through solid solution strengthening, niobium and titanium precipitate strengthening phases to optimize creep resistance, while trace elements such as carbon and boron refine grain size, improving the weldability and toughness of the alloy.
The forming and heat treatment processes are key means to regulate the microstructure and unleash the performance potential of high-temperature alloys. Advanced processes such as directional solidification and single crystal casting can eliminate grain boundary defects and significantly enhance the creep resistance of alloys. For example, by eliminating transverse grain boundaries, the high-temperature fracture life of single crystal nickel-based alloys is several times longer than that of conventionally cast alloys. The parameter control of heat treatment processes is particularly important. Solution treatment can dissolve excess phases and homogenize the composition, while aging treatment can promote the uniform precipitation of strengthening phases. Improper control of temperature or holding time can lead to coarse or uneven distribution of strengthening phases, directly reducing the high-temperature strength of the alloy.
Microstructure serves as the core bridge connecting components and properties, with grain size, phase composition, and defect state all exerting significant impacts on performance. Grain size must be tailored to meet operational requirements. Coarse grains can enhance creep resistance, but toughness may decrease. Conversely, fine-grained alloys exhibit superior low-temperature toughness and fatigue resistance. A balance of properties can be achieved through grain refinement techniques. The type and content of strengthening phases are crucial. The quantity, morphology, and distribution of precipitated phases such as γ’ and γ” directly determine the high-temperature strengthening effect of the alloy. The emergence of harmful phases can lead to intergranular embrittlement, compromising the stability of the alloy.
Environmental media and post-coating technologies can also indirectly affect the service performance and lifespan of high-temperature alloys. In corrosive media containing sulfur, chlorine, and other elements, alloys are prone to hot corrosion and pitting corrosion, necessitating the enhancement of corrosion resistance through component optimization or coating protection. Aluminum- and chromium-based coatings can form stable oxide films, effectively blocking the reaction between high-temperature combustion gases and the alloy substrate, thereby extending service life. However, if the adhesion and compactness of the coating are not up to standard, it can lead to spalling failure, which in turn exacerbates alloy corrosion. In the future, through multi-factor collaborative regulation, we can further overcome the performance bottlenecks of high-temperature alloys and adapt them to more demanding service environments.
