Metallurgical and Materials Data

Fabrication and Characterization of Tungsten-Based Hard Materials by Novel Mechanical Alloying and Spark Plasma Sintering Methods

2025-05-04T14:39:05+00:00

The influence of Ir and Y₂O₃ on the densification, microstructure, and wear characteristics of pure W-based alloy/composite was examined. The precursor powders, including W, Ir, and Y₂O₃, underwent mechanical alloying for 30 hours, resulting in two compositions: W–1.5 wt.% Ir and W–1.5 wt.% Ir–2 wt.% Y₂O₃. Subsequently, the prepared mixtures were subjected to spark plasma sintering at a temperature of 1650 °C for 5 minutes, with a simultaneous application of 50 MPa pressure. X-ray diffraction, scanning electron microscopy combined with energy dispersive spectroscopy, a micro-Vickers hardness tester, and two-dimensional optical profilometry were employed to analyze the synthesized powders, along with the consolidated and worn samples. Results indicated that the W–1.5 wt. % Ir-2 wt. % Y₂O₃ composite produced a highly dense sample characterized by the smallest grain size, superior micro-hardness, and enhanced wear resistance. The composite achieved values of up to 98% density, 3.6 µm grain size, 4.9 GPa HV₀.₅ hardness, and 2.5 × 10⁻⁵ mm³/Nm wear resistance, in contrast to pure tungsten, which exhibited 83.1% density, 6.6 µm grain size, 1.9 GPa HV₀.₅ hardness, and 6.2 × 10⁻⁵ mm³/Nm wear resistance. Thus, both Ir and Y₂O₃ have been recognized as effective additives that can enhance the consolidation and refinement of tungsten's microstructure under current mild processing conditions. This advancement not only makes these materials commercially viable but also enhances their performance in a range of demanding applications, such as fusion, military, tooling, electrode manufacturing, and coatings.

Biofunctional Properties of Multilayer Zirconia in Dentistry: Influence of Sintering and Surface Treatments

2025-06-30T19:35:22+00:00

The objective of this study was to analyze the differences in biofunctional properties between conventionally and speed-sintered multilayer monolithic zirconia with different surface finishing properties. Zirconia discs (Katana STML; SagemaxNexxZr T Multi), shade A2, were cut by the dry milling method, according to the fraction of each layer (Katana n=4, Sagemax n=3). The final dimensions were 10 × 13 × 1mm. Milling was followed by two sintering protocols, conventional (i.e. long), and speed ones. After sintering, the samples underwent a surface treatment according to which they were divided into two subgroups: glazed and polished. A digital spectrophotometer, Datacolor SF300, was used for sample color measurements. The structural analysis was performed for the Katana STML samples that, after sintering, exhibited total color change greater than AT values. The refinement of the collected x-ray diffraction data was done based on the Rietveld method. Biocompatibility of the materials was evaluated by direct MTT assay for 72 h on human gingival fibroblasts (hGFs). The polished Katana specimens exhibited the highest color change, with DE* ranging from 1.514 to 3.013 between layers. DE* values for all layers were above the perceptibility threshold (PT) (DE*>1.2), and the enamel layer (EL) exceeded clinically acceptable limits (DE*>2.7). Additionally, lightness difference (DL*=2.453), contributed the most to the color change of this sample. For glazed samples, DE* values ranged from 1.528 to 2.580. The structural and microstructural analysis revealed the nanoparticulate nature of the CS- and SS-Katana. The increasing of microstrain was observed in the SS-Katana, while the quantitative analysis revealed the appearance of an additional tetragonal phase (S.G. P4₂/nmc) in this sample, which coexists with one cubic (S.G. Fm-3m) and one tetragonal phase. On the contrary, DE values for polished and glazed Sagemax samples, obtained from all layers, were clinically acceptable (DE*<2.23). After 24h of direct contact of the hGFs with the polished and glazed surfaces, similar (P>0.05) mitochondrial activity, LDH realize, and cell adhesion were recorded. Increased lightness of speed sintered Katana STML can be due to the presence of the yttria-lean T1 phase with higher tetragonality, whose presence can be caused by the speed sintering protocol.

Electrochemical Evaluation of 304 Stainless-Steel in Aqueous Curry-Leaf Extract: Effect of NaCl on Passivity and Food-Contact Safety

2025-06-30T18:43:05+00:00

Stainless-steel drinkware and food containers must withstand complex, plant-based beverages that may include dissolved salts. This study quantifies the corrosion behaviour of 304 stainless steel (commercially “Ever Silver”) in three media at 25 °C: de-ionised water, an aqueous extract of shade-dried curry leaves (CLE), and CLE containing 5 000 ppm NaCl. Potentiodynamic polarisation was carried out in a three-electrode cell (Ever Silver working electrode, SCE reference, Pt counter). Key parameters—including corrosion potential (E_corr), Tafel slopes, linear polarisation resistance (LPR), and corrosion current density (i_corr)—were extracted from the Tafel plots.

Relative to water (LPR ≈ 6.2 × 10⁴ Ω cm²; i_corr ≈ 0.86 µA cm⁻²), exposure to CLE alone reduced passivity markedly (LPR ≈ 4.0 × 10⁴ Ω cm²; i_corr ≈ 1.11 µA cm⁻²), indicating enhanced anodic dissolution driven by phytochemicals that adsorb on the surface. Incorporating 5 000 ppm NaCl partially restored passivity (LPR ≈ 4.4 × 10⁴ Ω cm²; i_corr ≈ 1.05 µA cm⁻²): chloride ions appear to promote a more compact, adsorbate-assisted film, offsetting some of the extract’s aggressiveness, though the alloy remains less resistant than in pure water.

The hierarchy of corrosion resistance derived from LPR and i_corr is: water > CLE + NaCl > CLE. Practically, 304 stainless vessels can safely accommodate curry-leaf infusions, and moderate chloride contents (typical of culinary use) mitigate rather than exacerbate deterioration compared with salt-free extracts. These findings support the suitability of “Ever Silver” containers for flavoured beverages while providing quantitative guidance for food-contact applications involving herbal ingredients.

Influence of Colgate mouthwash on corrosion resistance of orthodontic wire made of Ni-Ti alloy immersed in artificial saliva

2025-05-04T16:19:40+00:00

This study investigates the corrosion resistance of orthodontic wire made of Ni-Ti alloy when immersed in artificial saliva, both in the absence and presence of Colgate mouthwash. The evaluation was carried out using potentiodynamic polarization techniques and electrochemical impedance spectroscopy (EIS). Polarization results show that the presence of Colgate mouthwash reduces the corrosion resistance of the Ni-Ti alloy, as indicated by a decrease in linear polarization resistance and an increase in corrosion current. EIS analysis confirms this trend, revealing reductions in charge transfer resistance, impedance magnitude, and phase angle, along with an increase in double-layer capacitance. These findings suggest that the aggressive components in Colgate mouthwash accelerate corrosion processes. Therefore, individuals wearing orthodontic appliances composed of Ni-Ti alloy are advised to avoid using Colgate mouthwash to prevent potential degradation of their dental wires.

An Examination of the Effect of Listerine Mouthwash on the Corrosion Characteristics of Orthodontic Wire Composed of Ss316l Alloy in Simulated Saliva by Electrochemical Impedance Spectra

2025-05-07T15:49:19+00:00

Orthodontic appliances are frequently fabricated from corrosion-resistant alloys such as stainless steel. However, the complex oral environment, which includes exposure to various mouthwashes, can influence the electrochemical stability of these materials. This study investigates the corrosion behavior of orthodontic wire composed of SS 316L alloy in artificial saliva, both in the absence and presence of Listerine mouthwash, using Electrochemical Impedance Spectroscopy (EIS). The electrochemical parameters—including charge transfer resistance (Rt), impedance, phase angle, and double layer capacitance (Cdl)—were systematically analyzed. The results indicate that Listerine mouthwash enhances the corrosion resistance of SS 316L alloy, as evidenced by increased Rt, impedance, and phase angle, along with reduced Cdl. These findings support the safe use of Listerine mouthwash by individuals with orthodontic wires made of SS 316L alloy.