High-temperature alloys are metallic materials that retain superb mechanical qualities in extremely hot environments. There is no single metric that defines how well an alloy will perform in high-temperature applications which may include many thermal cycles with sharp thermal gradients.
Mechanical Performance
Resistance to deformation at high temperatures is the first critical characteristic to consider. The mechanical strength of these alloys is defined by tensile yield (YTS), ultimate tensile (UTS), creep strength, and Young’s modulus. These are temperature-dependent properties that may not exhibit a linear relationship between temperature and strength and may also microstructurally degrade due to high-temperature exposure. Furthermore, very slow deformations at high temperature – known as creep – begin occurring at just under one half of the absolute melting point, shortening the life of components.
Corrosion Resistance
High-temperature alloys must also exhibit good resistance to application-specific conditions. Corrosion resistance includes low susceptibility to oxidation, hydrogen embrittlement, and other chemical reactions in the environment.
Properties describing adhesion and diffusion control the protective performance of the alloy against deterioration of strength in specific atmospheres. Most high-temperature alloys are built from several alloying elements at concentrations that provide the optimal combination of thermodynamic and chemical corrosion resistance. In refractory alloys, for example, zirconium, yttrium, and aluminium are stabilizers of the protective surface layers that can form.
High-Temperature Alloys: Refractory Metals
Using refractory metals as both base materials and additives for high-temperature alloys yields products with practically unmatched thermodynamic properties in extremely hot environments. Molybdenum, tungsten, and their alloys function very well in vacuum, hydrogen, and inert atmospheres, but will embrittle when returned to room temperature because of recrystallization.
High-temperature applications with severe thermal cycling require refractories with greater ductility. Molybdenum has been alloyed with various elements for this purpose. Additionally, lanthanum has been used to maintain ductility through the largest gamut of processing temperatures, but it requires thermomechanical working to achieve the full effects of ductility enhancement. Molybdenum is also alloyed with titanium and zirconium (TZM) for increasing recrystallization temperature, higher strength, and higher hardness over pure molybdenum and lanthanum-based alloys.
At H.C. Starck Solutions, we generate finely-tuned molybdenum alloys for service as heating elements or furnace fixtures that maintain shape and functionality after many processing cycles. These are suitable for tough applications such as nuclear fuel and magnetic material processing applications, as well as vacuum processes.
High-Temperature Alloys from H.C. Starck Solutions
H.C. Starck Solutions is one of the world-leading suppliers of high-temperature alloys and refractory metals for demanding applications. If you would like to learn more about the range of alloys that we provide for heat treatment, gas turbines, nuclear reactors, and more, simply contact a member of the team today.
