Improved Damage Tolerance in Titanium Alloy Fan Blades With Low Plasticity Burnishing

摘要

Low Plasticity Burnishing (LPB) has been applied to produce a layer of deep high magnitude compressive residual stress in the leading edge of Ti- 6Al-4V first stage fan blades. The goal was to improve damage tolerance from 0.13 to 0.5 mm (0.005 to 0.02 in.). LPB processing of the airfoil surface was performed on a conventional four-axis CNC mill. The LPB control system, tooling, and process are described. A zone of through-thickness compression on the order of 690 MPa (-100 ksi) was achieved extending 2.5 mm (0.10 in.) cord-wise from the leading edge and along the lower half of the blade from the platform to mid- span damper. Cantilever fatigue testing was performed at R=0.1 using FOD simulated by a 60 degree V notch. The processing provided complete tolerance of FOD up to nominally 1.3 mm (0.05 in.) in depth, an order of magnitude improvement in damage tolerance. The benefits of the deep layer of surface compression were confirmed through fatigue performance modeling.