How many defects may occur to an overheated turbine blade?

• A. Three
• B. Four
• C. Five
• D. Six

Answer: (B)

Overheating a turbine blade accelerates several damage mechanisms, so four distinct defect types are typically observed. Prolonged high temperature and stress cause creep, leading to deformation and possible microcracking. Oxidation and, in some environments, hot corrosion form oxide scales that thicken or spall, eroding material and protection. Thermal gradients from heating and cooling drive thermal-fatigue cracking, especially in stressed areas like roots or airfoil leading/trailing edges. Additionally, the high heat alters the metal’s microstructure, weakening it through grain growth or carbide changes. Because these four damage modes can all occur together, four defects are commonly cited for an overheated blade.