Mitigation of FOD and Corrosion Fatigue Damage in 17-4 PH Stainless Steel Compressor Blades with Surface Treatment

Compressor blades of a military aircraft turbine
engine made of 17-4 PH stainless steel have
been reported to have blade edge foreign object
damage (FOD), corrosion pitting, and erosion
damage that reduce fatigue life. This paper
reports the findings of a comprehensive
investigation of the effect of residual
compressive stresses, imparted by various
surface treatments, to improve leading edge
damage tolerance and active corrosion fatigue
performance in a salt water environment. Initial
fatigue and corrosion fatigue tests were
conducted in feature specimens designed to
simulate the geometrical conditions of thick
section and blade leading edges of compressor
blades. The FOD tolerance and corrosion
fatigue performance of 17-4PH prepared by low
plasticity burnishing (LPB), shot peening (SP),
and low stress grinding (LSG) were compared.
LPB dramatically improved both high cycle
fatigue (HCF) and corrosion fatigue
performance, providing tolerance of 0.040 in.
deep FOD in thick section and 0.050 in. deep
leading edge FOD. Shot peening afforded little
benefit in the presence of FOD 0.010 in. deep.
Fatigue initiation at relatively low applied stress
levels originating from existing corrosion pits
outside of the LPB treated zone limited the
ability to test the surface treatments on actual
fielded T56 blades retired from service. In the
absence of prior pitting, LPB provided 0.020 in.
deep FOD tolerance on new T56 blades. Both
the damage tolerance and active corrosion
fatigue performance of 17-4PH in salt water
increased with the depth of the compressive
zone produced.