Low Plasticity Burnishing (LPB) Treatment to Mitigate FOD and Corrosion Fatigue Damage in 17-4 PH Stainless Steel

Abstract

The benefits of applying low plasticity burnishing (LPB) to 17 -4PH Stainless Steel (H1100) on both the fatigue and corrosion fatigue performance were compared with the shot peened (SP) and low stress ground (LSG) conditions. LPB treatment dramatically improved both the high cycle fatigue (HCF) performance and fatigue strength. The baseline LSG and SP treatments showed similar fatigue strengths of about 150 ksi (~1035 MPa), while LPB treatment improved the fatigue strength by about 30%. Introduction of an EDM notch of ao = 0.010 in. (0.25 mm) and co = 0.030 in. (0.75 mm) simulating a semi-elliptical surface foreign object damage (FOD), decreased the fatigue strength of both SP and LSG by nearly 80%, while LPB helped retain much of the fatigue strength at the levels comparable to baseline material without FOD. Corrosion fatigue strength (in the presence of active corrosion medium of 3.5% NaCl solution) of the LSG material showed a drop of nearly 33% from the baseline material without corrosion; LPB material showed corrosion fatigue strength nearly the same as the baseline material without corrosion. While the introduction of a simulated FOD on the LSG dramatically decreased the fatigue strength to less than 15 ksi (~100 MPa), LPB retained nearly 90% of the fatigue strength of the baseline material without corrosion. Mechanistically, the effect of corrosion and FOD resulted in early crack initiation and growth, thus resulting in a dramatic decrease in fatigue performance. Despite the existence of s imilar corrosion conditions, the deep compressive surface residual stresses from LPB treatment helped to mitigate the individual and synergistic effects of corrosion fatigue and FOD.