Search Results (4)

This work shows an approach on the role of the gas mixture used in the pulsed DC plasma nitriding aiming to enhance the niobium cavitation erosion resistance through the formation of niobium nitride on the treated surfaces. For this purpose, nitriding was carried out at 1353 K (1080 °C) for 2 h, under a pressure of 1.2 kPa (9 Torr), and a 5 × 10⁻⁶ Nm³s⁻¹ (300 sccm) flow rate for three distinct gas mixtures, namely 30% N₂ + 50% H₂ + 20% Ar, 50% N₂ + 30% H₂ + 20% Ar, and 70% N₂ + 10% H₂ + 20% Ar. Surfaces were comparatively characterized before and after nitriding through scanning electron microscopy (SEM), X-ray diffractometry, 3D roughness, and nanoindentation hardness measurements. The cavitation erosion test was carried out in accordance with ASTM G32-09, obtaining the cumulative mass loss (CML) curve and the average (AER) and maximum (MER) erosion rate of the tested surfaces. Surfaces showed multiphase layers mainly constituted of ε-NbN and β-Nb₂N nitride phases, for the three distinct gas mixture conditions investigated. A CML of 25.0, 20.2, and 34.6 mg, and an AER of 1.56, 1.27, and 2.16 mg h⁻¹ was determined to the 960 min (16 h) cavitation erosion testing time, for NbN surfaces obtained at the 30% N₂, 50% N₂, and 70% N₂ gas mixture, respectively. In this case, the nominal incubation period (NIP) was 600, 650, 550 min, and the maximum erosion rate (MER) was 4.2, 3.4, and 5.1 mg h⁻¹, respectively. Finally, the enhancement of the cavitation erosion resistance, based on the NIP of the NbN surfaces, regarding the Nb substrates (with NIP of ≈100 min), was up ≈6 times, on average, thus significantly improving the cavitation erosion resistance of the niobium. Full article

The working conditions of tools during plastic working operations are determined by, among other things, temperature, loads, loading method, and processing speed. In sheet metal forming processes, additionally, lubricant and tool surface roughness play a key role in changing the surface topography of the drawpieces. This article presents the results of friction analysis on the edge of the punch in a deep drawing process using the bending under tension test. A DC04 steel sheet was used as the test material. The influence of various types of titanium nitride and titanium coatings applied on the surface of countersamples made of 145Cr6 cold-work tool steel was tested by means of high-intensity plasma pulses, magnetron sputtering, and electron pulse irradiation. The influence of the type of tool coating on the evolution of the coefficient of friction, the change in the sheet surface topography, and the temperature in the contact zone is presented in this paper. An increase in the coefficient of friction with sample elongation was observed. Countersamples modified with protective coatings provided a more stable coefficient value during the entire friction test compared to dry friction conditions. The electron pulse irradiated countersample provided the highest stability of the coefficient of friction in the entire range of sample elongation until fracture. The skewness Ssk of the sheet metal tested against the coated countersamples was characterized by negative value, which indicates a plateau-like shape of their surface. The highest temperature in the contact zone during friction with all types of countersamples was observed for the uncoated countersample. Full article

In the present study, the sputtered aluminum nitride (AlN) films were processed in a reactive pulsed DC magnetron system. We applied a total of 15 different design of experiments (DOEs) on DC pulsed parameters (reverse voltage, pulse frequency, and duty cycle) with Box–Behnken experimental method and response surface method (RSM) to establish a mathematical model by experimental data for interpreting the relationship between independent and response variables. For the characterization of AlN films on the crystal quality, microstructure, thickness, and surface roughness, X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission-scanning electron microscopy (FE-SEM) were utilized. AlN films have different microstructures and surface roughness under different pulse parameters. In addition, in-situ optical emission spectroscopy (OES) was employed to monitor the plasma in real-time, and its data were analyzed by principal component analysis (PCA) for dimensionality reduction and data preprocessing. Through the CatBoost modeling and analysis, we predicted results from XRD in full width at half maximum (FWHM) and SEM in grain size. This investigation identified the optimal pulse parameters for producing high-quality AlN films as a reverse voltage of 50 V, a pulse frequency of 250 kHz, and a duty cycle of 80.6061%. Additionally, a predictive CatBoost model for obtaining film FWHM and grain size was successfully trained. Full article

Polyetheretherketone (PEEK) has become an alternative material for orthopaedics and dental implants. However, bio-inertness is an important limitation in this material. In the present study, a hydroxyapatite (HA)–titanium nitride (TiN) coating was fabricated via pulsed DC magnetron sputtering and treated with hydrothermal treatment to improve the bioactive property of PEEK. The dissolution behavior of the coating was studied in simulated body fluid solution (SBF) at 1, 3, 5, 7, 14, 21, 28, and 56 days. The coating surface was analyzed before and after the immersion process by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and scanning electron microscope (SEM). The calcium and phosphorus concentration alteration in SBF was quantified by an inductively coupled plasma-optical emission spectrometer (ICP-OES). Coating dissolution and the precipitation of calcium phosphate complex from SBF were observed as occurring suddenly and continuously throughout the immersion times. These processes resulted in an alteration in both physical and chemical coating properties. After 56 days, the coating remained on PEEK surfaces and the Ca/P ratio was 1.16. These results indicate that HA-TiN coating via pulsed DC magnetron sputtering followed by hydrothermal treatment improved the bioactivity of materials and provided a potential benefit to orthopedics and dental applications. Full article