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Low plasticity burnishing (LPB) has been investigated as a surface enhancement process and corrosion mitigation method for aging aircraft structural applications. Compressive residual stresses reaching the alloy yield strength and extending to a depth of 1.25 mm (0.050 in.), deeper than typical corrosion damage, is achievable. Excellent surface finish can be achieved with no detectable metallurgical damage to surface and subsurface material.Salt fog exposures of 100 and 500 hrs. reduced the fatigue strength at 2x10 6 cycles by fiftypercent. LPB of the corroded surface, without removal of the corrosion product or pitted material, restored the 2x10 6 fatigue strength to greater than that of the original machined surface. The fatigue strength of the corroded material in the finite life regime (10 4 to 10 6 cycles) after LPB was 140 MPa (20 ksi) higher than the original uncorroded alloy, and increased the life by an order of magnitude.Ease of adaptation to CNC machine tools allows LPB processing at costs and speeds comparable to machining operations. LPB offers a promising new technology for mitigation of corrosion damage and improved fatigue life of aircraft structural components with significant cost and time savings over current practices.

Low plasticity burnishing (LPB) has been demonstrated to increase the damage tolerance of Ti6Al-4V fan blades by an order of magnitude. First stage Ti-6Al-4V fan blades were LPB processed using a conventional 4 -axis CNC machine tool. LPB dramatically improved surface finish with negligible blade distortion and produced compressive residual stresses of -690 MPa (-100 ksi) through the entire thickness of the blade leading edge. Fatigue testing demonstrated that the deep compression of LPB provided a 3X improvement in HCF endurance limit, complete tolerance of FOD up to 1.3 mm (0.050 in.) deep, and an order of magnitude improvement in fatigue life. Damage tolerance for the TI-6AL-4V fan blade was improved by an order of magnitude.The benefit of the LPB generated compressive layer in improving damage tolerance was confirmed using the fatigue crack growth code AFGROW. Crack growth modeling indicates tolerance of deeper FOD is achievable with optimization of the depth and magnitude of the residual stress field. LPB has been demonstrated to be an effective and affordable means of improving the damage tolerance of Titanium alloy fan and compressor blades. Application of LPB during manufacturing and overhaul operations could significantly reduce the cost of engine inspection and maintenance while improving fleet readiness.