Additively Manufactured (AM) components' surface nishing is crucial in adopting them for intended applications in challenging environments involving fatigue, corrosion, high temperature, and nuclear radiation. In our prior research, chempolishing(C) was utilized as an electroless etching process that uniformly smoothens complex AM components' accessible interior and exterior surfaces (Tyagi et al., Additive Manufacturing, Vol.25 pp.32). A wide range of electropolishing(E) has been demonstrated for AM surface nishing. However, electropolishing can impact a surface that can be juxtaposed to counter electrode and can a very smooth surface to sub-micrometer level roughness. However, a knowledge gap exists about the impact of applying both approaches on the same surface one after another and what new advantages may arise because of combining two methods. This paper uses dual-stage liquid-based surface nishing strategies produced by alternating the chempolishing(C) and electropolishing(E) steps.Two dual-stage surface nishing approaches, i.e., chempolishing followed by electropolishing(CE) and electropolishing followed by chempolishing (EC), were performed on the 316 stainless AM steel component. Impacts of EC and CE approaches were compared with single-stage C and E surface nishing approaches. An optical microscope and mechanical pro lometer were utilized to investigate the wide range of surface roughness parameters. CE and EC produced Ra ~ 1.4 µm and ~ 1.6 µm, respectively. Surface roughness on CE and EC treated AM samples was lower than those individually treated by C and E approaches. Scanning electron microscopy provided further insights into the microstructural difference between CE and EC treated AM samples. This paper reports a liquid contact angle study on CE and EC treated AM samples to provide insights into the relative difference in surface energy that is crucial for making coatings on AM parts. A spectroscopic re ectance study was also employed to register the difference in physical properties of AM components treated with CE, and EC approaches. This study reveals industrially practicable interior and exterior surface nishing approaches for complex AM metal components that require minimum tooling and real-time process monitoring.
This study investigates the application of electroless nickel deposition on additively manufactured stainless steel samples. Current additive manufacturing (AM) technologies produce metal components with a rough surface. Rough surfaces generally exhibit fatigue characteristics, increasing the probability of initiating a crack or fracture to the printed part. For this reason, the direct use of as-produced parts in a finished product cannot be actualized, which presents a challenge. Post-processing of the AM parts is therefore required to smoothen the surface. This study analyzes chempolish (CP) and electropolish (EP) surface finishing techniques for post-processing AM stainless steel components CP has a great advantage in creating uniform, smooth surfaces regardless of size or part geometry EP creates an extremely smooth surface, which reduces the surface roughness to the sub-micrometer level. In this study, we also investigate nickel deposition on EP, CP, and as-built AM components using electroless nickel solutions. Electroless nickel plating is a method of alloy treatment designed to increase manufactured component’s hardness and surface resistance to the unrelenting environment. The electroless nickel plating process is more straightforward than its counterpart electroplating. We use low-phosphorus (2–5% P), medium-phosphorus (6–9% P), and high-phosphorus (10–13% P). These Ni deposition experiments were optimized using the L9 Taguchi design of experiments (TDOE), which compromises the prosperous content in the solution, surface finish, plane of the geometry, and bath temperature. The pre- and post-processed surface of the AM parts was characterized by KEYENCE Digital MicroscopeVHX-7000 and Phenom XL Desktop SEM. The experimental results show that electroless nickel deposition produces uniform Ni coating on the additively manufactured components up to 20 μm per hour. Mechanical properties of as-built and Ni coated AM samples were analyzed by applying a standard 10 N scratch test. Nickel coated AM samples were up to two times scratch resistant compared to the as-built samples. This study suggests electroless nickel plating is a robust viable option for surface hardening and finishing AM components for various applications and operating conditions.
The surface roughness of as produced additively manufactured (AM) components is very high and may lead to component failure and undesirable coefficients of friction. In rough surfaces, small cracks form at regions of high surface roughness acting as a stress raiser or crack nucleation sites. Likewise, rough surfaces impact both static and kinetic friction that can impede desired motion and oppose desired mechanical forces. For using these components in many applications, it is necessary to reduce surface deviations drastically during postprocessing. For parts with complex geometries and enormous internal surface areas, this reduction presents a complex engineering problem. We have explored chempolishing (C) and electropolishing (E) to reduce the external and internal surface roughness of stainless-steel components in our previous studies. Chempolishing is an electroless etching process that can uniformly smoothen the accessible surfaces of complex AM components. Electropolishing can produce an extremely smooth surface to sub-micrometer level roughness. Our prior work showed that chempolishing and electropolishing produced very distinct surface microstructures. It is quite possible that in future surface finishing, chempolishing and electropolishing may be applied on the same AM component to reduce the surface roughness of complex AM components. The resulting microstructure after the sequential application of chempolishing and electropolishing may be quite different as compared to that of after chempolishing or electropolishing alone. Here, we report the application of altering the sequence of chempolishing and electropolishing to reduce the external and internal surface roughness of 316 steel components. It is unknown what will be the impact of manipulating the sequence of electropolishing and chemical polishing on surface roughness and microstructure of AM materials. This paper focuses on the post-process sequencing of chempolishing, followed by electropolishing (CE) and vice versa (EC). We found chempolishing followed by electropolishing reduced internal surface roughness by as much as 12 micrometers. Whereas the electropolishing followed by chempolishing reduced external surface roughness by an average of ∼15 micrometers. The structure and properties of the surface finished pieces were examined using: Scanning Electron Microscopy (SEM), Surface Profilometry, and Water Contact Angle Measurement. SEM provided direct insight that CE and EC process produced significantly different microstructures from each other and also from chempolished and electropolished processes. Water contact angle measurements performed on CE, and EC treated AM samples showed that surface energy was quite different. Hence, CE and EC are expected to perform quite differently under a corrosive environment and also yield various adhesion quality for the protective coatings. Confirmation of structural changes provided in this experiment shed light on the capabilities of postprocessing improvements we can make to materials performance.
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