Structural integrity of additively manufactured stainless steel with cold sprayed barrier coating under combined cyclic loading

Abstract Integration of metal additive manufacturing (AM) and cold spray (CS) technologies provide an unprecedented opportunity to manufacture coated material systems with complex geometrical features. The application of these material systems in functionally critical components requires adequate structural integrity, particularly in the presence of cyclic loading. This work aims to study the multiaxial fatigue (axial-torsional cyclic loading) behavior of a coated material system consists of 15Cr-5Ni PH stainless steel (15-5 PH SS) substrate additively manufactured by direct metal laser sintering with a layer of newly commercialized chromium carbide nickel (CrC-Ni) barrier coating deposited by CS coating. The influence of AM and CS-induced residual stresses on fatigue performance of test specimens was thoroughly studied. Additionally, the effect of surface roughness and processes induced defects were considered to explain the crack growth mechanism. Stresses assessed by synchrotron X-ray diffraction indicated a substantial accumulation of the residual stresses, particularly in the outer surface of the as fabricated 15-5 PH SS specimens. The state of residual stress was changed notably following the deposition of CrC-Ni coating in the axial, hoop, and radial directions of the fatigue test specimen. Also, CS deposition of CrC-Ni coating caused significant improvement in the surface quality of the additively manufactured components. Fatigue test results indicated that the CS deposition of CrC-Ni substantially enhances the fatigue life of the AM-produced 15-5 PH SS substrate in all loading conditions, particularly in the high cycle fatigue regime. The improvement in the fatigue life of the specimens with coating was associated with the reduced surface equivalent residual stress and improvement in the specimens' surface condition (i.e., reduced surface roughness). In addition, the fractographic analysis of the specimen indicated although the crack tends to initiate in the surface of both as fabricated and cold sprayed specimens, the mechanism of crack growth differs notably following the CS coating. While the cracks tend to propagate in the planes parallel or with a small deviation from the build layers of the AM produced specimens, deposition of CrC-Ni coating increased the deviation of crack growth plane from the build layers of the substrate.