Tahsin Tecelli Öpöz

Additive manufacturing (AM) enables the fabrication of complex, customisable components from metals, composites and polymers such as polylactic acid (PLA); however, the process commonly produces poor surface finishes and inherent defects. Centrifugal disc finishing (CDF) is an established mass finishing technique in conventional manufacturing but remains insufficiently characterised for additively manufactured polymers. This exploratory study investigates the influence of CDF on fused deposition modelling (FDM)-fabricated PLA components with varying geometrical features, focusing on three-dimensional surface parameters including average areal surface roughness, skewness and kurtosis. Samples were processed up to 720 min with analysis at predetermined intervals to capture transient and steady-state-like behaviour. Surface characterisation was conducted using non-contact optical interferometry to obtain quantitative roughness data and three-dimensional topographical maps, supported by digital optical microscopy and gravimetric analysis to quantify material removal rates. Analysis of the experimental data indicated apparent relationships between processing time, geometry and surface response. Results indicate that material removal behaviour and roughness evolution may be geometry-dependent. Flat and convex surfaces appeared to follow expected transient-like and steady-state-like behaviour, whereas restricted geometries and intricate features exhibited distinct responses with characteristic transition times. Surface roughness reductions ranged from 36% to 89% depending on geometry. These findings provide preliminary quantitative insight into geometry-specific mass finishing behaviour, supporting improved process understanding and informing future optimisation of post-processing strategies for additively manufactured polymer components.

Additive manufacturing (AM) enables the fabrication of complex geometries and high-performance alloys such as 17-4PH stainless steel. However, the surface defects inherent to AM components compromise corrosion resistance. The post surface treatment can reduce and eliminate these defects. This study examines the effect of centrifugal mass finishing on the corrosion behaviour of 17-4PH stainless steel produced by AM. Corrosion behaviour of the samples in a 0.6 M NaCl solution is assessed using electrochemical technique testing, including asymmetry electrochemical nose, potentiodynamic polarisation curves, electrochemical impedance spectroscopy, and Mott-Schottky. All electrochemical testing were conducted in concordance with the specifications of ASTM standards. The electrochemical impedance spectroscopy were performed over period ranging from 2 h to 96 h with intervals of approximately one day. Finished specimens exhibit significantly improved corrosion resistance compared with as-built counterparts. Notably, the polished surfaces demonstrate spontaneous oxidised layer recovery between −0.297 V and 0 V, indicative of the enhancement of the protection during early immersion stages. This behaviour is attributed to surface modifications induced by the finishing process, including reduced roughness in 78% and imperfections. These findings highlight the importance of optimising post-processing protocols to improve the durability of AM stainless steels in aggressive environments.

Commercially available 316L (1.4404) stainless steel is commonly used for industrial filtration due to its combination of good material properties, particularly its corrosion resistance, which is a critical factor for filters in corrosive (e.g., saltwater) environments. Recently, laser powder bed fusion (LPBF) has enabled new more complex and efficient filtration pieces to be manufactured from this material. However, it is critical to know how the corrosion resistance is affected by this manufacturing strategy. Here, the corrosion resistance of LPBF manufactured 316L stainless steel is compared with wrought 316L sheet. The corrosion of the samples in saltwater was assessed with asymmetric electrochemical noise, potentiodynamic polarisation curve, and electrochemical impedance spectroscopy. The samples before and after corrosion were examined with scanning electron microscopy and energy-dispersive spectroscopy. The LPBF samples had higher corrosion resistance than the sheet samples and were more noble. The corrosion resistance of the LPBF sample increased with time, while the wrought sample corrosion resistance reduced over time. The corrosion mechanism of both samples was stable with time, formed of a passive film process and a bared material process. This paper presents the first study about the temporal evolution of the LPBF 316L stainless steel corrosion mechanism.

This study investigates the influence of surface finish and post-processing conditions on the mechanical properties of 17-4 PH stainless steel (SS) produced using the atomic diffusion additive manufacturing process (ADAM). Diverse sample orientations, including horizontal (0°), 30°, 60°, and vertical (90°), were examined, with selected samples undergoing post-processing through machining, polishing, and heat treatment. Tensile strength testing, surface roughness measurement, and hardness measurement were conducted to assess the effect of surface finish conditions and post-processing on mechanical properties. The results reveal significant variations in the tensile strength of the samples based on the build orientation (183.5 to 1034.5 MPa), and subsequent machining. Notably, post-built machining is found to enhance both the absolute ultimate tensile strength (UTS) and the isotropy of the material. Further improvements are attainable through heat treatment. A microstructure analysis, in conjunction with tensile testing outcomes, demonstrates the potential for refining the properties of ADAM-printed samples through suitable machining, heat treatment, and geometry modifications. This study identifies avenues for ongoing process development and outlines possibilities for enhancing mechanical properties of additive manufactured parts, particularly through ADAM process.

Commercially pure aluminium is employed in several industrial applications. On some applications, the surface of this material needs to be functionalised. Laser surface texturing is a powerful tool to functionalise aluminium and aluminium alloy surfaces. However, the corrosion resistance of the laser textured aluminium alloy can be modified, and this has rarely been investigated in the literature. Consequently, the corrosion resistance of the laser textured commercially pure aluminium in saltwater was evaluated using several electrochemical techniques: asymmetric electrochemical noise, potentiodynamic polarisation curve and electrochemical impedance spectroscopy. Although the non-laser surface textured samples possessed higher kinetic corrosion resistance in the first hours of immersion, the corrosion mechanism (process group of the corrosion) was found to be more unstable than the laser textured specimens. The oxidised layer of the textured samples was also nobler than the native passive film.

Titanium surface modification by the Hydroxyapatite (HA) mixed Electrical Discharge Machining (EDM) is an alternative and promising technique to enhance the biocompatibility and to promote the biological performance in bone, which is dependent on surface properties, such as surface roughness, chemistry, and wettability. HA powder is used for the first time with electrical discharge machining to improve osteoblastic cell activity on the developed surfaces for Ti6Al4V. Different HA concentrations in deionized water were tested as an experimental variable during EDM. Abrasive polishing and electrical discharge machined control surfaces without powder addition also analyzed to compare the results. The surface characteristics of analyzed samples were evaluated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffractometry (XRD), white light interferometry, and contact angle measurements. The wettability tests suggest that the hydroxyapatite powder mixed EDM’ed surfaces shows highly hydrophilic characteristics compared the other surfaces, abrasive polished and EDM’ed without powder addition in the dielectric. The results from the MTT assay revealed that those surfaces modified using HA powder addition in distilled water dielectric liquid promoted the most significant cell attachment/growth. The results indicate that HA powder mixed EDM offers a promising method for the surface modification of biomaterials such as titanium alloys

This article presents an important investigation of material removal mechanism in grinding utilizing single grit scratch tests. The investigation helps people to understand the abrasive cutting behaviour when the abrasive cutting edge shape alters during single grit grinding. The results provide fundamental knowledge of the grinding material removal process, which helps to improve grinding performance and quality. Cubic boron nitride grits of 40/50 mesh size were used to perform scratch tests on the alloy Inconel 718. The concepts of material pile-up ratio and actual material removal area were introduced to measure the material removal efficiency during grinding. It is found that pile-up ratio decreases and actual material removal area increases when the depth of cut increases, albeit the material removal mechanism is highly dependent on the abrasive grit cutting edge shape. The material removal mechanism along the scratch length shows different behaviours at the entrance and exit sides of the scratching passes. When a grit was moving along its scratch path, it pushed material forward resulting in high material accumulation at the exit side of the scratches. Consequently, cutting is more prominent at the entrance side of the scratch, whereas ploughing or pile-up is extremely high at the exit side of the scratches. The research finding provides crucial information for grinding process optimization.