text: Nickel-based superalloys are used in load-bearing structures requiring the highest homologous temperature of any common alloy system (Tm = 0.9, or 90% of their melting point). Among the most demanding applications for a structural material are those in the hot sections of turbine engines (e.g. turbine blade). They comprise over 50% of the weight of advanced aircraft engines. The widespread use of superalloys in turbine engines coupled with the fact that the thermodynamic efficiency of turbine engines is a function of increasing turbine inlet temperatures has provided part of the motivation for increasing the maximum-use temperature of superalloys. From 1990-2020,  turbine airfoil temperature capability increased on average by about 2.2 °C/year. Two major factors have made this increase possible:
  * Processing techniques that improved alloy cleanliness (thus improving reliability) and/or enabled the production of tailored microstructures such as directionally solidified or single-crystal material.
  * Alloy development resulting in higher temperature materials primarily through the additions of refractory elements such as Re, W, Ta, and Mo.
  About 60% of the temperature increases related to advanced cooling, while 40% have resulted from material improvements. State-of-the-art turbine blade surface temperatures approach 1,150 C. The most severe stress and temperature combinations correspond to an average bulk metal temperature approaching 1,000 C..
  Although Ni-based superalloys retain significant strength to 980 C, they tend to be susceptible to environmental attack because of the presence of reactive alloying elements. Surface attack includes oxidation, hot corrosion, and thermal fatigue.