Fatigue crack growth rate and fracture toughness evaluation of 15-5 precipitation hardening stainless steel fabricated by laser powder bed fusion process

Abstract

The present article reports the fatigue crack growth (FCG) rate and fracture toughness of 15-5 Precipitation Hardening (PH) Stainless Steel (SS) specimens fabricated by Laser powder bed fusion (L-PBF) additive manufacturing (AM) technique. The effect of notch orientation (parallel and orthogonal in reference to build direction) on FCG and fracture toughness is investigated. The FCG and fracture toughness data of L-PBF specimens in the solution annealed (SA) and SA + aged condition were compared to that of wrought 15-5 PH SS. It was found that dependence of FCG on the build orientation was insignificant up to the stress intensity factor range (ΔK) of 30 MPa√m, and beyond that, a higher FCG rate is recorded for L-PBF specimens. The SA specimens were found to have a slightly lower FCG rate at Paris region as compared to SA + aged specimens. The fractography showed predominantly transgranular mode of crack growth, with presence of fine pores and signature of plastic deformation at higher stress intensity. The crack branching and zig-zag path was observed for the L-PBF specimens with notch orientation orthogonal to build direction (horizontal notch). The fracture toughness (K1C) of horizontally notched L-PBF fabricated 15-5 PH SS specimens in aged condition showed higher values (51–62 MPa√m) as compared to vertical (parallel) notched specimens (40–46 MPa√m). The observed fracture toughness values of L-PBF 15-5 PH SS specimens appear to be significantly lower than the reported fracture toughness values of wrought 15-5 PH SS material.