Papers by Keyword: Stainless Steel

Abstract: The study investigates the impact of printing resolution on the dimensional change and microstructure of additive-manufactured parts, specifically dental crowns produced through binder jetting and sintering. Dental crowns are crucial for dental restoration, providing strength and support to damaged teeth. The additive manufacturing process involves digital scanning, 3D metal printing, sintering, and post-processing. The focus here is on the dimensional accuracy and microstructure of the sintered parts made from 17-4PH stainless steel powder. Two printing resolutions, 250 μm and 400 μm, are evaluated to observe their effects on the final properties. Results reveal that printed parts exhibit a significant enlargement (17-19%) due to allowances for binder removal during sintering. Sintered parts, while smaller than printed parts, still exhibit a 4-7% enlargement compared to the original CAD model. Microstructural analysis indicates the presence of ferrite and austenite matrix structures, with particles identified as silicon dioxide residue from the binder. The finer resolution (250 μm) shows greater particle area and count, leading to higher microhardness. These findings provide insights into the dimensional changes and microstructural features crucial for precision in dental applications utilizing additive manufacturing technology.

Abstract: Ni-YSZ cermet remains to be the most used anode material for solid oxide fuel cells (SOFCs), and metal-supported solid oxide fuel cells are considered as the third generation SOFCs which can possibly address the overpotential and ohmic losses due to thicker components of electrolyte-and anode-supported cells. This study investigates the low-temperature deposition of crystalline NiO-YSZ thin film anodic layers on stainless steel (SS316L) substrates via screen-printing and hot pressing. Results revealed that screen-printing and hot pressing of NiO-YSZ on SS316L substrates at only 700°C (100 MPa) successfully deposited a ~40-μm thin film with a cubic crystalline structure. The thin film can also be fully reduced to Ni-YSZ with a cubic crystalline structure for both Ni and YSZ. In addition, EDS mapping revealed a relatively homogenous distribution of the Ni-YSZ components.

Abstract: Austenitic stainless steels tend to form chromium depletion zones during welding. The chromium combines with available carbon around the grain boundaries to produce chromium-deficient areas, thus becoming susceptible to intergranular corrosion. The sensitization phenomenon of 304 stainless steel during gas tungsten arc welding (GTAW) process has been investigated. In this experiment, there were four welded samples observed. Two welded samples were cooled in air and cooled in oil immediately after welding, respectively. Meanwhile, another two welded samples were normalized by heated to 800 and 900 °C and held for 0.5 h before cooled in air. The welded samples were analyzed using optical microscopy, scanning electron microscopy and energy dispersive microscopy (SEM-EDS), and a Vickers hardness testing machine. The results show that normalizing affects significant changes in the microstructure due to the sensitization phenomenon. It can be seen that there is more carbide deposition in the welded sample with cooled in air and welded samples which normalized by heated to 800 °C and 900 °C and held for 0.5 h before being cooled in air. Meanwhile, the sample that was cooled in oil immediately after welding showed fewer chromium carbides. Normalizing the welded samples to 800 and 900 °C and holding it for 0.5 h before cooling in air triggers the sensitization process. Sensitization looks less occur in 304 stainless steel welds which were rapidly cooled in oil.

Abstract: This research aims to study the electropolishing conducted under vacuum status. The electropolishing can be used to finishing high purity components of SUS 316L to make them shine and without leaving residual stress, micro-cracks, etc. In the research, the electropolishing process parameters are selected, such as current density, degree of vacuum and polishing time to conduct the electropolishing experiment. The experimental results show that the bubbles attached to the surface of the work-piece in the vacuum state are reduced, thereby improving the surface roughness and surface pitting. The vacuum status in the process can improve the electropolishing process.

Abstract: This research investigated metal injection moulding of dental pins for orthodontics application. 316L stainless steel powder was selected as an alternative low-cost material in comparison to the more expensive titanium alloy counterpart. The feedstock was prepared at 60% solid loading using an environmentally friendly multi-component binder. Injection moulding was operated using a four-cavity mould. The effects of moulding temperature of 250-280 °C measured at the barrel on mouldability, and specimen properties were studied. After debinding, specimens were sintered at 1250 °C for 2 hours in a hydrogen atmosphere. Experimental results indicated that injection at moulding lower temperature of 250-260 °C gave better mouldability, providing less specimen distortion and demoulding difficulty. The green density was 5.49 g/cm³, giving 93.41% theoretical density. Injection at lower temperature of 250-260 °C also provided higher sintered density and slightly lower volume shrinkage. Sintered microstructure experienced densification with small degree of isolated porosity in specimen center, however with interconnected porosity along specimen edges, responsible for 6.87 g/cm³ sintered density (86.01% theoretical density).

Abstract: Ceramic/ metal functionally graded materials (FGMs) have been promising to sustain coating structures working under super high temperature as well as high temperature gradient conditions. Compositional gradients in the FGMs can be engineered according to functional performance requirements. This study aims to fabricate Al₂O₃/ZrO₂/SUS304 hybrid FGMs with continuous compositional gradient manners using a combination of centrifugal slurry methods and spark plasma sintering (SPS). The compositional gradients in the FGMs were investigated on microstructures with elemental distributions and hardness on the cross sections of the FGMs. It was demonstrated that the compositions of ZrO₂ and SUS304 continuously varied in the FGMs, while Al₂O₃ resided only on ZrO₂-rich sides, which can effectively enhance the fracture toughness of the ZrO₂-rich layer. Ball milling treatments can make the Al₂O₃ layer more formed in the ZrO₂-rich layer. With increasing the amount of Al₂O₃, the Al₂O₃ layer resided closer to the top of the ZrO₂ surfaces in the FGMs subject to ball milling treatments, which can prevent the crack propagation from the ZrO₂ top surfaces.

Abstract: This work examines the feasibility of joining two dissimilar metals, vanadium (V) and wrought Nitronic 40 stainless steel, through electron beam additive manufacturing (EBAM). Depositing V on Nitronic 40 led to mixed results with some builds exhibiting microcracking and other builds exhibiting severe cracking resulting in delamination. These build failures are thought to be caused by a large coefficient of thermal expansion (CTE) mismatch and solubility issues, demonstrating the challenges associated with this material combination. The large melting temperature discrepancy between Nitronic 40 and V was thought to exacerbate the issues with CTE mismatch and solubility. Four strategies could be employed by EBAM to mitigate the observed issues to successfully deposit V on Nitronic 40: (1) adjust wire feed speed, (2) use dual wire feeders, (3) use different wire feedstocks to control composition, and (4) create a transition layer known as buttering to accommodate CTE mismatch.

Abstract: To investigate the behaviour of oxidation and chromium volatilisation, AISI 430 stainless steel was oxidised in O₂-H₂O and Ar-CO₂-H₂O atmospheres for 96 h at 800°C with varying water vapour content. In the O₂-H₂O environment, the volatilisation rate of Cr and Mn increased as the water vapour content increased from 5% to 20%. In the case of Ar-CO₂-H₂O conditions, the presence of water vapour in the Ar-20%CO₂ environment reduced the oxidation rates of the steel. However, increasing the H₂O content in Ar-20%CO₂ had an insignificant effect on the oxidation rate. Water vapour was found to accelerate the volatilisation rate of Cr and Mn. Breakaway oxidation occurred in Ar-20%CO₂-40%H₂O, resulting in the highest volatilisation rates of Cr and Mn.

Abstract: Microstructure fabrication and chemical surface functionalization with low-surface-energy materials are the key steps to achieve hydrophobic surfaces with high water droplet contact angles (CA). In this work we employed wire Electric Discharge Machining (EDM) as a way to induce microstructure topography on stainless steel 304 coupons. The resulting topography was rendered hydrophobic using trichloro-1H,1H,2H,2H-perfluorooctyl silane (PFOTS) via gas phase deposition. The channels created by machining and PFOTS functionalization facilitate water condensation by increasing nucleation sites and enhancing droplet coalescence. The resulting surface is hydrophobic (CA~140^o) in contrast to the bare stainless steel 304, which is hydrophilic (CA~76^o).

Abstract: Laser metal deposition (LMD) industrial use demands research about the influence of the parameters in the built parts density, accuracy and mechanical properties. Especially for the thin-wall parts, knowledge about the correlations between processing parameters and the final result is indispensable. This study explores the relationship between process parameters and the quality of AISI316L stainless steel thin-walled parts produced by LMD. A six-axis robot equipped with a deposition head allowed relative spatial movement between the powder nozzle and laser beam and substrate with high accuracy. Controlled energy input provided by continuous wave Ytterbium fibre laser allows using less material flow rate and the production of thin layers in test samples. Three processing parameters were selected to investigate the effects on part characteristics using a Box-Behnken experimental design. Through this method, each parameter was evaluated between 600 W to 800 W laser power, 6 mm/s to 14 mm/s feedrate and 0.2 mm to 0.4 mm layer thickness. All remaining parameters were fixed using argon to provide an inert atmosphere, 8.8 g/min powder feeding rate and 1.5 mm spot diameter. The method was used to test the manufacture of thin-wall cylindrical specimens with 10 mm in height and 75 mm in diameter. Fabricated AISI316L samples were evaluated regarding the dimensional and geometrical characteristics. It was observed that higher energy input density during the laser additive manufacturing implies lower geometric precision. Feedrate and layer thickness has the highest impact on both the wall thickness and vertical accuracy. Given the inability to produce parts with an acceptable final surface, the process finds great applicability when complemented with additional finishing technologies.