Application of hybrid additive manufacturing technology for performance improvement of martensitic stainless steel

Abstract

Additive manufacturing (AM) is considered to be an attractive technology that offers tremendous advantages in rapidly producing complex-shaped components close to their final/net shape. However, uncontrolled metallurgical defects (pores, cracks, and inclusions), deleterious tensile residual stresses (RS), as well as scattered and unsatisfactory material performance have hindered its applications. In this study, layer-by-layer ultrasonic micro-forging treatment (UMT) was combined with directed energy deposition (DED) to substantially improve the mechanical performance (e.g., strength-ductility synergy, and fatigue behavior) and corrosion resistance of as-built 15–5PH stainless steel (SS). The surface RS distribution, mechanical properties, corrosion resistance, and microstructural properties of the non-UMT and UMT specimens were analyzed. In particular, focused ion beam (FIB) was employed to prepare the specimen for transmission electron microscopy (TEM) observations of the surface severe plastic deformation (SSPD) zone after UMT. The results indicated that the process with UMT resulted in higher surface compressive stress (~−750 MPa), reduced oxide inclusions, and refined martensite blocks (23.8% finer than that of the non-UMT specimen). The improvement of these characteristics induced by UMT further led to a comprehensive increase in the strength, elongation, fatigue resistance, corrosion resistance, and surface hardness of the DED fabricated parts. This work demonstrated the tremendous potential of integrated DED technology for tailoring the microstructure, controlling the quality, and producing martensitic SS with excellent mechanical performance and corrosion resistance.