Search Results (155)

It has been demonstrated that a monomolecular surface film with semiconducting characteristics forms on an austenitic, corrosion- and heat-resistant chromium–nickel steel with 0.10 wt.% C, 20 wt.% Cr, 9 wt.% Ni, and 6 wt.% Mn (10Kh20N9G6), microalloyed with yttrium, in aqueous 1 M H₂SO₄. This passive layer exhibits semiconducting behavior, as confirmed by electrochemical impedance and capacitance measurements. For the first time, key electronic parameters, including the flat-band potential, the thickness of the semiconductor layer, and the Fermi energy, have been determined from experimental Mott–Schottky plots obtained for the interphase boundary between the yttrium-microalloyed austenitic Cr–Ni steel (10Kh20N9G6) and aqueous 1 M H₂SO₄. The results reveal a systematic shift in the flat-band potential toward more negative values with increasing yttrium content in the alloy, indicating a modification of the electronic structure of the passive film. Simultaneously, a decrease in the Fermi energy is observed, suggesting an increase in the work function of the metal surface due to the presence of yttrium. These findings contribute to a deeper understanding of passivation mechanisms in yttrium-containing stainless steels. The formation of a semiconducting passive film is essential for enhancing the electrochemical stability of stainless steels, and the role of rare-earth microalloying elements, such as yttrium, in this process is of both fundamental and practical interest. Full article

The presence and development of pathogens in the human body remains a serious problem. The existence of microorganisms is primarily related to their ability to adhere to various surfaces. The aim of this study was to evaluate the ability of Si(C,N) coatings on a nickel-chromium alloy surface to reduce bacterial and fungal adhesion and to provide antimicrobial activity. This publication also focused on determining which coating variant is most effective in reducing microbial adhesion. Si(C,N) coatings were sputtered onto the surface of the prosthetic alloy using the magnetron sputtering method. Observation was performed using a fluorescence microscope and a flow cytometer. The number of adhered bacterial cells decreased compared to the samples without coating (sample series A) by approximately 84% in sample series B and by 29% in sample series F. In the case of adhesion of fungal cells, their number decreased compared to the samples without coating (sample series A) by approximately 76% in sample series B and by 47% in sample series F. The applied one-way analysis of variance test indicated a statistically significant effect of the tested factor at a level below 0.001. Based on the conducted research, it was noticed that the use of Si(C,N) layers on the surface of the prosthetic alloy limits the adhesion of bacteria and fungi. Full article

This study examines the high-temperature degradation of Hastelloy C276, a corrosion-resistant nickel-based alloy, during exposure to combustion products generated by methane and 99% cracked ammonia. Using a high-pressure optical combustor (HPOC) at 4 bar and exhaust temperatures of 815–860 °C, standard tensile specimens were exposed for five hours to fully developed post-flame exhaust gases, simulating real industrial turbine or burner conditions. The surfaces and subsurface regions of the samples were analysed using scanning electron microscopy (SEM; Zeiss Sigma HD FEG-SEM, Carl Zeiss, Oberkochen, Germany) and energy-dispersive X-ray spectroscopy (EDX; Oxford Instruments X-MaxN detectors, Oxford Instruments, Abingdon, United Kingdom), while mechanical properties were evaluated by tensile testing, and the gas-phase compositions were tracked in detail for each fuel blend. Results show that exposure to methane causes moderate oxidation and some grain boundary carburisation, with localised carbon enrichment detected by high-resolution EDX mapping. In contrast, 99% cracked ammonia resulted in much more aggressive selective oxidation, as evidenced by extensive surface roughening, significant chromium depletion, and higher oxygen incorporation, correlating with increased NO_x in the exhaust gas. Tensile testing reveals that methane exposure causes severe embrittlement (yield strength +41%, elongation −53%) through grain boundary carbide precipitation, while cracked ammonia exposure results in moderate degradation (yield strength +4%, elongation −24%) with fully preserved ultimate tensile strength (870 MPa), despite more aggressive surface oxidation. These counterintuitive findings demonstrate that grain boundary integrity is more critical than surface condition for mechanical reliability. These findings underscore the importance of evaluating material compatibility in low-carbon and hydrogen/ammonia-fuelled combustion systems and establish critical microstructural benchmarks for the anticipated mechanical testing in future work. Full article

The shift toward digital and smart manufacturing requires an accurate prediction of cutting behavior, such as cutting forces. Controlling cutting forces in machining is important for maintaining product quality, particularly in steels such as X5CrNi18-10. This steel has high toughness, which resists cutting, thereby increasing overall cutting forces. Proper selection of machining parameters and conditions can help reduce cutting forces during machining. Several studies have been dedicated to understanding the influence of cutting parameters on cutting forces. However, limited attention is given to the influence of the cutting conditions on cutting forces. The primary objective of this study is to understand the behavior of cutting forces in chromium-nickel alloy steel by varying machining parameters, specifically cutting conditions (dry and wet), using a full factorial (3¹ × 2²) design of experiments (DoE). The secondary objective is to develop a multilinear regression model to predict cutting forces. The root mean square (RMS) values of the cutting force components were calculated from the acquired data and analyzed using OriginPro 2025b. In addition, this study analyzes the effects of cutting parameters and cutting forces on root mean square (RMS) surface roughness (R_q) to understand their impact on quality using the AltiSurf 520 profilometer. The results suggest a significant effect of the selected machining parameters and conditions on cutting force reduction and on improved surface quality when cutting forces are low. This research provides a valuable insight into optimizing the machining process for hard steels. Full article

Background/Objectives: Dental malocclusions are often treated with appliances made of metal alloys. These alloys biodegrade in oral cavity and release toxic metals such as nickel and chromium. This study aimed to assess nickel and chromium content in the saliva of patients with and without fixed metallic orthodontic appliances. Methods: This was a descriptive cross-sectional study aiming to assess nickel and chromium content in saliva. A survey was conducted to record socio-demographic characteristics and clinical signs due to the wearing of fixed metallic orthodontic appliances. A 10 mL saliva sample was used to measure salivary pH and assess nickel and chromium concentrations using atomic emission spectrophotometry. A Student’s t-test compared saliva metal levels in non-wearers and wearers of metal orthodontic appliances. A Chi-square test was used to assess the influence of pH on metal release in patients. Results: A total of 92 participants, divided in two groups; 46 without appliance and 46 wearing appliance were received during the study period. Their mean age was 17.05 ± 6.46 years. Patients’ mean saliva pH was 6.97 ± 0.44. The mean nickel concentration was 4.39 ± 4.01 µg/L in the saliva of non-appliance wearers and 20.41 ± 18.56 µg/L in the saliva of appliance wearers, respectively. The chromium mean concentration was 1.3 ± 1.33 µg/L for non-appliance wearers and 9.38 ± 19.49 µg/L and for appliance wearers. Metal release is influenced by the pH of foods. Conclusions: Metal orthodontic appliances increase the release of nickel and chromium in saliva. It is necessary to monitor the risk of intolerance and optimize treatment duration. Full article

This study investigates hydrogen embrittlement mechanisms at the interfaces of explosively welded joints between 304L austenitic stainless steel and carbon/low-alloy steels (St41k, 15HM), focusing on the unique properties of local melting zones (LMZs) formed during joining. Advanced microstructural characterization, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and microhardness testing, was combined with controlled electrochemical hydrogen charging. Results demonstrate that while base materials suffered substantial hydrogen-induced degradation—blistering in carbon steels and microcracking in stainless steel—the LMZ exhibited exceptional resistance to hydrogen damage. Compositional analyses revealed that the LMZ possessed intermediate chromium (4.8–8.8 wt.%) and nickel (1.7–3.6 wt.%) contents, reflecting mixing from both plates, and significantly higher microhardness compared to adjacent zones. The superior hydrogen resistance of the LMZ is attributed to their refined microstructure, increased density of hydrogen trapping sites, and non-equilibrium phase composition resulting from rapid solidification. These findings indicate that tailoring the process of the LMZ in clad steel joints can be an effective strategy to mitigate hydrogen embrittlement risks in critical hydrogen infrastructure. Full article

Background/Objectives: Achieving durable intraoral repairs of fractured metal and zirconia restorations requires optimal adhesion. This in vitro study evaluated the effects of mechanical surface treatments and commercial repair systems on the shear bond strength (SBS) of composite resin to nickel–chromium (Ni-Cr) alloy and zirconia, including the influence of thermocycling aging. Methods: In this study, 144 Ni-Cr and zirconia discs (12 × 12 × 2 mm) were randomly assigned to three surface treatments: untreated control, airborne particle abrasion (50 µm Al₂O₃), and medium grit diamond bur grinding. Each group was further subdivided to assess two intraoral repair kits (GC Corp (Tokyo, Japan). and Bisco Inc. (Schaumburg, IL, USA)). Composite resin cylinders were bonded following the manufacturer’s instructions. Half of the specimens (n = 12/subgroup) underwent 5000 thermocycles (5–55 °C). Micro-shear bond strength testing was performed, and failure modes were analyzed. Data were analyzed using three-way ANOVA and post hoc tests (p < 0.05). Results: Air abrasion significantly increased SBS compared to control and bur grinding for metal (p < 0.001). For zirconia, both air abrasion and bur grinding yielded similarly improved SBS over the control (p < 0.001). The GC repair kit demonstrated significantly superior bond stability after thermocycling across both substrates. Aging significantly reduced SBS in all groups (p < 0.001), with the most substantial reductions observed in untreated controls and groups repaired with the Bisco system. Conclusions: Airborne particle abrasion combined with a HEMA-free, 10-MDP-containing universal adhesive achieved the strongest and most durable resin bonds to both metal and zirconia, supporting its clinical use for the intraoral repair of ceramic and metal restorations. Full article

In the nuclear industry, the decontamination of nuclear metallic structures is an essential process to reduce radiation exposure during maintenance or dismantling. The oxide layer, such as chromium (III) oxide (Cr₂O₃), formed on stainless steel and nickel-based alloys, contributes significantly to surface radioactivity by trapping radioactive contaminants. To address this, permanganic acid (HMnO₄) has proven to be a promising oxidizing agent for dissolving these oxide layers—particularly chromium oxide—on stainless steel and nickel-based alloys. In this study, HMnO₄ was synthesized via ion exchange using AmberLite IRN97 H resin and potassium permanganate (KMnO₄). The optimized process yielded a highly acidic solution (pH~1.6) with potassium concentrations below 0.1 ppm, indicating near-complete exchange efficiency. Dissolution kinetics were investigated at HMnO₄ concentrations ranging from 240 to 1920 ppm and temperatures from 30 °C to 80 °C. At a constant temperature, increasing HMnO₄ concentration significantly improved Cr dissolution, with up to 31% of total chromium solubilized after 33 h. Lower temperatures favored higher dissolution efficiency, likely due to improved thermal stability of HMnO₄. For durations shorter than 4 h, the influence of temperature was limited compared to the effect of acid concentration. To assess post-treatment options, HMnO₄ decomposition was studied using oxalic acid (H₂C₂O₄) at 80 °C. Results showed that a minimum H₂C₂O₄/HMnO₄ molar ratio above 2.75 was necessary to achieve effective reduction while preventing MnO₂ precipitation. However, even under strongly acidic conditions and with a large excess of reductant, Mn²⁺ yields remained below 55%, suggesting that thermal degradation of oxalic acid and possible formation of undetected manganese species limited the reduction process. Full article

The Ni-Resist ductile iron, with a nickel content ranging from 18% to 36%, is a material designed for service under extreme conditions. One of the main objectives of this study was to determine the minimum nickel content required to stabilize the austenitic structure at cryogenic temperatures. Additional aims included investigating structural features related to the solidification of austenite dendrites, graphite nodules, and eutectic carbides. Moreover, the electrical conductivity, which is critical for certain applications of Ni-Resist ductile irons, was also examined. To this end, castings with varying nickel content (21%, 25%, 28%, and 35%) and with or without chromium additions were prepared. Microstructural characterization was performed using optical, scanning, and transmission electron microscopy, X-ray diffraction (XRD), and electrical conductivity measurements. The results showed that a highly branched dendritic microstructure predominates, with graphite nodules located in interdendritic regions and along austenite grain boundaries. In chromium-alloyed ductile irons, the austenitic matrix contains Cr = 1.7 ± 0.3 wt.% in the vicinity of M₇C₃-type eutectic carbides. Furthermore, thermal stability analysis indicated that a minimum nickel content of 25 wt.% is sufficient to ensure structural stability at cryogenic temperatures down to 25 K. Finally, complementing the above-mentioned investigations, the electrical conductivity characteristics of the studied high-nickel austenitic cast irons were determined. Full article

Background/Objectives: Metal–ceramic crowns may be constructed using different techniques and coping materials. A systematic review analysing the coping material, method of construction, and instruments used for measuring the metal–ceramic crown marginal gap has not been completed. The aim of this systematic review was to appraise the literature relating to the instruments used for the in vitro marginal gap measurement of single pre-cemented metal–ceramic crowns and assess whether the crown coping material and method of coping construction influence the marginal gap. Methods: A systematic search was performed in November 2024 across the EBSCO Host, Scopus, PubMed, and Web of Science databases, adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and specific eligibility criteria. The Joanna Briggs Critical Appraisal Checklist was used to assess article quality. Results: Fourteen studies evaluated marginal gaps in 402 crowns using the following techniques: direct view microscopy (eight studies), replica techniques (three studies), scanning electron microscopy (two studies), and profilometry (one study). The mean marginal gap for all the metal–ceramic crowns across all the studies was 65.97 ± 32.58 µm. The pre-cementation mean marginal gaps showed no significant difference between Computer-Aided Design–Computer-Aided Manufacturing (CAD-CAM) milled copings (87.95 ± 26.35 µm) and conventionally cast copings (90.45 ± 24.37 µm) (t = −0.197, p = 0.847). The mean marginal gaps varied significantly (F = 11.34, p < 0.001) by coping material: cobalt–chromium (Co-Cr) led to 84.28 µm, nickel–chromium (Ni-Cr) led to 70.98 µm, titanium led to 50.18 µm, and noble metal alloys led to 27.90 µm. Six studies addressed confounding factors and followed a standardised approach for measuring marginal gaps. Conclusions: Direct view microscopy was the most commonly used instrument for measuring the marginal gaps of single pre-cemented metal–ceramic crowns, yielding the smallest reported mean marginal gap of 75.00 ± 26.87 µm. Metal–ceramic crowns constructed with noble metal alloys exhibited the lowest mean marginal gaps. Metal–ceramic crowns constructed using conventional casting techniques presented similar marginal gaps to CAD-CAM crowns. Full article

The determination of uncertainty in porosity analysis based on X-ray computed tomography (XCT) images is currently the focus of research. This study aims to contribute to that by investigating the variation in porosity analysis resulting only from the segmentation and data analysis and by focusing on metal parts produced by different additive manufacturing processes, partially fabricated with intended porosity. Samples manufactured from aluminum, titanium alloy and nickel-chromium-based feedstock by liquid metal jetting (LMJ), laser-based powder bed fusion (PBF-LB) and directed energy deposition (DED) were scanned by XCT. The reconstructed volumes were distributed to four operators with different experience levels using Avizo, Dragonfly, Image J/Fiji, IPSDK Explorer, and VG Studio Max for porosity analysis. It was found that for all parts, the majority of operators chose a global manual threshold for image segmentation. Depending on the characteristics of the pores in the investigated samples, relative standard uncertainties up to 12% and 38% were observed for the LMJ and PBF-LB parts. For the part produced by DED, which showed the lowest overall porosity, relative standard uncertainties between 70% and 89% were observed for different image qualities; all were affected by the presence of artefacts investigated on purpose. Full article

Although dental implants appear to be an alternative for treatment of tooth loss, fixed prosthetic restorations are an irreplaceable part of oral rehabilitation. Regarding the EU directives concerning cobalt health risks, titanium alloys may be an alternative to cobalt–chromium and nickel–chromium for metal–ceramic dental restorations. The presented review briefly describes the specific properties of titanium, and the challenges met during production and use of titanium–ceramic fixed prosthetic restorations. Full article

The objective of this study was to characterize austenitic stainless steel 310 produced by Wire and Arc Additive Manufacturing (WAAM), addressing a gap in the literature regarding this alloy. Microstructural, chemical, and mechanical analyses were performed. Optical and electron microscopy revealed a predominantly columnar grain structure with characteristic tracks along the deposition direction. Point and mapping EDS analyses indicated a homogeneous distribution of iron, chromium, and nickel; however, point measurements suggested a possible underestimation of nickel, likely due to high relative error. Tensile tests demonstrated anisotropic mechanical behavior, with yield strength meeting standards at 45° and 90°, but lower at 0°. Ultimate tensile strength and elongation were below conventional requirements, with a maximum elongation of 15% at 90°. Additionally, the sample exhibited a total porosity of approximately 0.89%, which contributes to the reduction in mechanical properties, especially in the direction parallel to the deposition tracks. Overall, the WAAM-produced 310 stainless steel presented a microstructure similar to hot-rolled and annealed AISI 310 steel, but with distinctive features related to the additive process, such as mechanical anisotropy and microstructural directionality. These limitations highlight the need for process optimization to improve mechanical performance but reinforce the alloy’s structural potential in additive manufacturing. Full article

Interest in surface integrity has grown in the manufacturing industry; indeed, it has become an integral part of the industry. It can be studied by examining surface roughness parameters, hardness variations, and microstructure. However, evaluating all these parameters together can be a challenging task. To address this multi-criteria decision-making model (MCDM), techniques such as Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and Grey Relational Analysis (GRA) provide a suitable solution for optimizing the machining parameters that lead to improved product quality. This work investigated surface roughness parameters, including arithmetic average surface roughness (2D) (Ra), mean surface roughness depth (2D) (Rz), area arithmetic mean height (3D) (Sa), and maximum surface height (3D) (Sz), in conjunction with Vickers macrohardness (HV) and optical micrographs, to analyze machined surfaces during the turning of X5CrNi18-10 steel. The results suggest that machining with a spindle speed (N) of 2000 rpm or v_c of 282.7 m/min, a feed rate (f) of 0.1 mm/rev, and a depth of cut of 0.5 mm yields the best surface, achieving an “A” class surface finish. These parameters can be applied in manufacturing industries that utilize chromium–nickel alloys. Additionally, the method used can be applied to rank the quality of the product. Full article

Machining chromium–nickel alloy steel is challenging due to its material properties, such as high strength and toughness. These properties often lead to tool damage and degradation of tool life, which overall impacts the production time, cost, and quality of the product. Therefore, it is essential to investigate early signs of tool damage to determine the effective machining conditions for chromium–nickel alloy steel, thereby increasing tool life and improving product quality. In this study, the early signs of tool wear were observed in a physical vapor deposition (PVD) carbide-coated tool (Seco Tools, Björnbacksvägen, Sweden) during the machining of X5CrNi18-10 steel under both dry and wet conditions. A finish turning operation was performed on the outer diameter (OD) of the workpiece with a 0.4 mm nose radius tool. At the early stage, the tool was examined from the functional side (f–side) and the passive side (p–side). The results indicate that dry machining leads to increased coating removal, more heat generation, and visible damage, such as pits and surface scratches. By comparison, wet machining helps reduce heat and wear, thereby improving tool life and machining quality. These findings suggest that a coolant must be used when machining chromium–nickel alloy steel with a PVD carbide-coated tool. Full article