Foreign Object Damage and Laser Peening

Forged titanium gas turbine engine blades are expensive and have long lead times.  Vacuum die casting (VDC) advancements resulted in improvements to the quality of titanium alloy castings for static and rotating engine components.  Although cast components are considerably less expensive than their forged counterparts, they must (and can) have equivalent fatigue life and resistance to foreign object damage (FOD) induced crack growth to be considered for engine applications.

Laser peening has been demonstrated to be an effective technique for increasing the fatigue life of engine components and increasing their resistance to crack growth after foreign object damage (FOD).

Thermal relaxation tests, cyclic stress relaxation tests, and component fatigue test results demonstrate the benefit of laser peening vacuum die cast titanium alloy blades.  VDC produced blades have equivalent fatigue life and foreign object damage resistance as compared to similarly laser peened forged (wrought) blades.

Both cast and wrought Ti-6Al-2Sn-4Zr-2Mo samples were resistant to the thermal relaxation of compressive residual stresses at 400ºF and 900ºF.  Cast and wrought Ti-6Al-2Sn-4Zr-2Mo  and Ti-6Al-4V samples were also resistant to the relaxation of compressive residual stresses from laser peening under cyclic loading conditions.  Laser peened cast blades could cost 20-25% less than laser peened forged blades. Laser peening resulted in a 15x increase in FOD tolerance for the F101 and F110 engines, calling for a major reduction in inspection man-hour costs and increased flight safety.

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