Investigating the failure of bevel gears in an aircraft engine

► Retained austenite was transformed to un-tempered martensite by higher internal shear stress.
► Internal stresses were validated by the DEA in the case.
► Fatigue crack originated from existing cracks in tempered martensite.
► The mode of bevel gears failure was contact fatigue.
► Variation in hardness at the case/core resulted in complete detachment of case.