N. Jayaraman, P. S. Prevey, Lambda Technologies, Cincinnati, OH

Summary:

The benefits of applying Low plasticity burnishing (LPB) to 17-4PH and Custom450 Stainless Steels on both the fatigue and corrosion fatigue performance was compared with the shot peened (SP) and low stress ground (LSG) conditions. LPB treatment dramatically improved both the HCF performance and fatigue strength. Introduction of an EDM notch of a_o = 0.25 mm (0.01 in.) and c_o = 0.75 mm (0.03 in.) (to simulate 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 a corrosion fatigue strength nearly the same as the baseline material without corrosion. While the introduction of a simulated FOD on the LSG was to dramatically decrease the fatigue strength to less than 100 MPa (~15 ksi), LPB helped retain 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 dramatic decrease in fatigue performance. Despite the existence of similar corrosion conditions, the deep compressive surface residual stresses from LPB treatment, helped to mitigate the individual and synergistic effects of corrosion fatigue and FOD.