TY - JOUR A1 - Brand, Marco A1 - Goßling, Mareen A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela T1 - Comparative Performance of Ni- and Fe-Based Mixed Alloy Brazed Coatings via Laser Remelting JF - Lubricants (Special Issue Analysis, Evaluation and Diagnosis of Tribological Phenomena in Machining Processes) N2 - Traditionally, repairing coated substrates requires completely removing damaged, wear-resistant layers before recoating. This process leads to high costs, extended downtime, and material waste. Flexible brazing tapes, which are composed of alloy powder and an organic binder, offer an alternative to full coating removal for targeted repairs. Despite this, the process of vacuum brazing these tapes may lead to the formation of defects, including pores caused by trapped gases or residual binder, which compromise coating durability and corrosion resistance. This study focuses on the utilization of laser remelting as a method for post-processing nickel- and iron-based mixed alloy brazing tapes, with the aim of improving the integrity of the coating. Surface quality was assessed via microscopy and microhardness testing by systematically varying laser power, scanning speed, and hatch distance. Among the parameters studied, the most suitable laser parameter combination was found to be 350 W laser power, 250 mm/s scanning speed, and a hatch distance of 0.02 mm. These parameters yielded crack- and pore-free coatings with a remelting depth of 160.3 ± 17.2 µm and a microhardness of 701 ± 23 HV1, which is an 85% increase over as-brazed samples. Wear testing revealed a reduced coefficient of friction, and electrochemical corrosion tests showed lower corrosion current density and enhanced repassivation behavior in remelted coatings. These improvements demonstrate that laser remelting significantly enhances the microstructure, hardness, wear resistance, and corrosion performance of brazed coatings, providing an effective method for localized repair while minimizing material consumption and processing duration. KW - brazing tapes KW - sliding wear resistance KW - reuse KW - repair KW - laser surface refining KW - remelting KW - corrosion protection Y1 - 2026 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:1010-opus4-49343 VL - 2026 IS - 14 (4) PB - MDPI ER - TY - JOUR A1 - Brand, Marco A1 - Utu, Ion-Dragos A1 - Sirbu, Nicusor-Alin A1 - Perianu, Ion-Aurel A1 - Predu, Denis Andrei A1 - Marginean, Gabriela T1 - Microstructural Characteristics of Graded Ni-Fe Coatings Fabricated Through DED-L JF - Materials (Special Issue Advanced Coating Research for Metal Surface Protection) N2 - Directed Energy Deposition-Laser (DED-L) enables high-performance coatings through melting and successive powder deposition. Its compositional flexibility suits functionally graded layers that enhance corrosion and wear resistance. This study aimed to improve parameters for producing dense, defect-free, graded Ni- and Fe-based coatings by varying the scanning speed and deposition strategy (monodirectional versus bidirectional, with/without layer rotation), while keeping the power and hatch distance constant. Laser and electron microscopy were used to link parameters to porosity and uniformity. Optimal settings minimized pores, improved interlayer bonding and preserved geometry; inadequate parameters yielded porous, irregular deposits. A bidirectional path with 90° rotation appeared best. Ongoing research activities are needed to assess its properties. Highlights What are the main findings? - Bidirectional samples show fewer pores than samples with monodirectional movement. - Increasing the scanning speed leads to lower porosity (bidirectional scanning mode with 90° layer rotation). - Bidirectional deposition with 90° layer rotation exhibits best quality What are the implications of the main findings? - Systematic study of scanning speed and deposition strategy. - Practical guidance for process improvement of graded metal coatings; properties under evaluation. - Functionally graded Ni-Fe coatings fabricated by DED-L with tailored microstructures. KW - parameter study KW - directed energy deposition-laser KW - functionally graded materials KW - deposition strategy KW - powder processing KW - surface protection Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:1010-opus4-49138 SN - 1996-1944 VL - 2026 IS - 19 (2) PB - MDPI ER - TY - JOUR A1 - Anghel, Iasmina-Mădălina A1 - Pascu, Alexandru A1 - Hulka, Iosif A1 - Woelk, Dino Horst A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela T1 - Characterization of Cobalt-Based Composite Multilayer Laser-Cladded Coatings JF - Crystals (Special Issue Crystallization of High Performance Metallic Materials (2nd Edition)) N2 - Laser cladding is an essential method for strengthening and restoring component surfaces. To increase its efficacy and provide a reliable surface treatment technique, it is necessary to optimize process parameters, enhance material adhesion, and guarantee high-quality, reliable coatings. These measures help to extend the lifespan of components. In this study, the surfaces of AISI 904L stainless steel samples were cladded to prepare various Co-based composite coatings with single and multiple layers reinforced with WC–CoCr–Ni powder. The phases within the newly developed layers were investigated using X-ray Diffraction (XRD), while the microstructure was examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). Further tests were performed to assess the hardness, wear resistance and corrosion performance of the deposited coatings. Analyzing and comparing the coatings, it was observed that the coating performance increased with increasing thickness and generally due to a lower amount of Fe present within the microstructure. KW - laser cladding KW - CoCr-based coatings KW - wear KW - corrosion KW - hardness Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:1010-opus4-48757 SN - 2073-4352 VL - 2025 IS - 15 (11) PB - MDPI ER - TY - JOUR A1 - Woelk, Dino Horst A1 - Eßler, Julian A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela T1 - Comparative Corrosion and Wear Behaviors of Cermet Coatings Obtained from Conventional and Recycled Powders JF - Applied Sciences N2 - Many components in industry are subjected to high loads during operation and therefore often do not reach their intended service life. Conventional steels frequently do not provide sufficient protection against wear and corrosion. One solution is to coat these components using methods like thermal spraying to apply cermet coatings such as Cr3C2-NiCr or WC-Co-Cr. In light of increasingly strict environmental regulations, more eco-friendly alternatives are needed, especially ones that use little or no Cr, Ni, Co, or W. Another alternative is the recycling of powder materials, which is the focus of this research project. This study investigated whether filter dust from an HVOF system could be used to develop a new coating suitable for use in applications requiring resistance to wear and corrosion. This is challenging as the filter dusts have heterogeneous compositions and irregular particle sizes. Nevertheless, this recycled material, referred to as “Green Cermets” (GCs), offers previously untapped potential that may also be of ecological interest. An established WC-Co-Cr coating served as a reference. In addition to friction wear and corrosion resistance, the study also examined particle size distribution, hardness, microstructure, and susceptibility to crack formation at the interface and inside the coating. Even though the results revealed a diminished performance of the GC coatings relative to the conventional WC-CoCr, they may still be applicable in various industrial applications. KW - recycling KW - HVOF KW - WC-Co-Cr KW - thermal spraying KW - filter dust KW - corrosion KW - wear Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:1010-opus4-48157 VL - 2025 IS - 15(14), Special Issue Composites from Sustainable Resources: Properties, Manufacturing, and Applications SP - 1 EP - 16 PB - MDPI ER - TY - JOUR A1 - Eßler, Julian A1 - Woelk, Dino Horst A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela T1 - Impact of hBN Content on the Tribological Behavior and Thermal Diffusivity of HVOF-Sprayed Cr3C2-NiCr Coatings JF - Materials (Special Issue Advances in Tribological and Other Functional Properties of Materials) N2 - Considering the significant health risks posed by hard chrome plating during its application, thermally sprayed Cr3C2-NiCr cermet coatings represent a suitable alternative. Incorporating hexagonal boron nitride (hBN) as a dry lubricant into the feedstock powder can further enhance wear resistance and thermal conductivity, crucial for preventing premature failure caused by inadequate lubrication. In this study, the mass fraction of hBN was varied between 0 and 15 wt.% to assess its influence on the tribological performance of the coatings using pin-on-disk tests. The coating’s hardness was measured via the Vickers method, and its cracking tendency at the coating/substrate interface was evaluated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to analyze the microstructure and phase composition, while thermal diffusivity was determined using the laser flash method. The findings revealed that the inclusion of hBN, at concentrations of up to 10 wt.%, leads to an improvement in thermal diffusivity and a reduction in the coefficient of friction. However, exceeding this threshold leads to a decrease in hardness and increased crack formation tendency, highlighting the trade-off between frictional and mechanical properties. KW - boron nitride composite coatings KW - HVOF KW - Cr3C2-NiCr KW - sliding wear KW - thermal diffusivity Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:1010-opus4-47295 VL - 2024 IS - 17 (22) SP - 1 EP - 14 PB - MDPI ER - TY - JOUR A1 - Utu, Ion-Dragos A1 - Anghel (Petculescu), Iasmina-Madalina A1 - Hulka, Iosif A1 - Marginean, Gabriela T1 - Design, Manufacturing, Microstructure, and Surface Properties of Brazed Co-Based Composite Coatings Reinforced with Tungsten Carbide Particles JF - Crystals MDPI N2 - Brazing is a joining process that involves melting a filler metal and flowing it into the joint between two closely fitting parts. While brazing is primarily used for joining metals, it can also be adapted for certain coating deposition applications. The present study investigates the microstructure and corrosion behavior and sliding wear resistance of WC (Tungsten Carbide)-CoCr-Ni reinforced Co-based composite coatings deposited onto the surface of AISI 904L stainless steel using a vacuum brazing method. The primary objective of this experimental work was to evaluate the influence of WC-based particles added to the microstructure and the properties of the brazed Co composite coating. The focus was on enhancing the sliding wear resistance of the coatings while ensuring that their corrosion resistance in chloride media was not adversely affected. The morphology and microstructure of the composite coatings were investigated using scanning electron microscopy (SEM) and phase identification by X-ray diffraction (XRD). The SEM analysis revealed in the coating the presence of intermetallic compounds and carbides, which increase the hardness of the material. The sliding wear resistance was assessed using the pin-on-disk method, and the corrosion properties were determined using electrochemical measurements. The results obtained showed that as the WC particle ratio in the Co-based composite coating increased, the mechanical properties improved, the alloy became harder, and the tribological properties were improved. The evaluation of the electrochemical tests revealed no significant alterations of the manufactured composite in comparison with the Co-based alloys. In all cases, the corrosion behavior was better compared with that of the stainless-steel substrate. KW - co-based coatings KW - brazing KW - wear resistance KW - corrosion behavior Y1 - 2024 U6 - https://doi.org/10.3390/cryst14060576 VL - 14 (2024) IS - 6, Aufsatz 576 ER - TY - JOUR A1 - Muntean, Roxana A1 - Valean, Petru-Cristian A1 - Kazamer, Norbert A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela A1 - Şerban, Viorel-Aurel T1 - Effect of Feedstock Powder Intrinsic Characteristics on the Tribological Behavior of Inductively Remelted NiCrBSi Flame-Sprayed Coatings JF - Lubricants N2 - Ni-based alloys are among the materials of choice in developing high-quality coatings for ambient and high temperature applications that require protection against intense wear and corrosion. The current study aims to develop and characterize NiCrBSi coatings with high wear resistance and improved adhesion to the substrate. Starting with nickel-based feedstock powders, thermally sprayed coatings were initially fabricated. Prior to deposition, the powders were characterized in terms of microstructure, particle size, chemical composition, flowability, and density. For comparison, three types of powders with different chemical compositions and characteristics were deposited onto a 1.7227 tempered steel substrate using oxyacetylene flame spraying, and subsequently, the coatings were inductively remelted. Ball-on-disc sliding wear testing was chosen to investigate the tribological properties of both the as-sprayed and induction-remelted coatings. The results reveal that, in the case of as-sprayed coatings, the main wear mechanisms were abrasive, independent of powder chemical composition, and correlated with intense wear losses due to the poor intersplat cohesion typical of flame-sprayed coatings. The remelting treatment improved the performance of the coatings in terms of wear compared to that of the as-sprayed ones, and the density and lower porosity achieved during the induction post-treatment had a significant positive role in this behavior. KW - NiCrBSi coatings KW - flame spraying; induction remelting KW - wear resistance Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:1010-opus4-45869 VL - 2023 (Special Issue Advances in Surface Engineering and Tribology) IS - 11 (9) PB - MDPI ER - TY - JOUR A1 - Kazamer, Norbert A1 - Muntean, Roxana A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela T1 - Considerations on the Wear Behavior of Vacuum-Remelted ZrO2-Reinforced Self-Fluxing Ni-Based Thermally Sprayed Alloys JF - Materials MDPI N2 - Without proper post-processing (often using flame, furnace, laser remelting, and induction) or reinforcements’ addition, Ni-based flame-sprayed coatings generally manifest moderate adhesion to the substrate, high porosity, unmelted particles, undesirable oxides, or weak wear resistance and mechanical properties. The current research aimed to investigate the addition of ZrO2 as reinforcement to the self-fluxing alloy coatings. Mechanically mixed NiCrBSi-ZrO2 powders were thermally sprayed onto an industrially relevant high-grade steel. After thermal spraying, the samples were differently post-processed with a flame gun and with a vacuum furnace, respectively. Scanning electron microscopy showed a porosity reduction for the vacuum-heat-treated samples compared to that of the flame-post-processed ones. X-ray diffraction measurements showed differences in the main peaks of the patterns for the thermal processed samples compared to the as-sprayed ones, these having a direct influence on the mechanical behavior of the coatings. Although a slight microhardness decrease was observed in the case of vacuum-remelted samples, the overall low porosity and the phase differences helped the coating to perform better during wear-resistance testing, realized using a ball-on-disk arrangement, compared to the as-sprayed reference samples. KW - self-fluxing; ZrO2; NiCrBSi; vacuum post-treatment; thermal spraying Y1 - 2023 U6 - https://doi.org/10.3390/ma16145183 VL - 2023 IS - 16 / 14 SP - 5183 ER - TY - JOUR A1 - Eßler, Julian A1 - Woelk, Dino Horst A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela T1 - Influence of the powder feed rate on the properties of HVOF sprayed WC-based cermet coatings JF - Materials Today: Proceedings N2 - In this study, the characteristics of HVOF sprayed WC/Co-Cr and WC/Cr3C2/Ni coatings were investigated in correlation with the variation of the powder feed rate. For this purpose, the mass flow was adjusted to four different levels. The other process parameters were all kept constant. The morphological and mechanical properties as well as the electrochemical corrosion behaviour were investigated and associated with the achieved microstructure. Both scanning electron microscopy and confocal laser scanning microscopical images of the cross sections demonstrated a good correlation between the selected powder feed rate and the degree of internal porosity produced, which can be attributed to the deposition process. The coatings which fulfilled the requirements of the pre-qualification step were selected for further hardness measurements, tribological tests and electrochemical corrosion measurements in a 3.5 wt% NaCl aqueous solution. It was found that the powder feed rate strongly influenced the characteristics of the HVOF-sprayed cermet coatings. The tendency to crack formation, especially at the interface coating/substrate, was lower for the samples coated with a lower mass flow rate. These studies have shown that the applied powder feed rates had an important influence on the coatings microstructure and implicitly on the sliding wear behavior respectively on the electrochemical corrosion resistance of the investigated cermet coatings. KW - Powder feed rate HVOF Cermet Wear Corrosion Y1 - 2022 U6 - https://doi.org/10.1016/j.matpr.2022.11.120 VL - 2023 IS - 78 SP - 227 EP - 234 ER - TY - JOUR A1 - Utu, Ion-Dragos A1 - Hulka, Iosif A1 - Kazamer, Norbert A1 - Constantin, Albert Titus A1 - Marginean, Gabriela T1 - Hot-Corrosion and Particle Erosion Resistance of Co-Based Brazed Alloy Coatings JF - Crystals N2 - Tape brazing constitutes a cost-effective alternative surface protection technology for complex-shaped surfaces. The study explores the characteristics of high-temperature brazed coatings using a cobalt-based powder deposited on a stainless-steel substrate in order to protect parts subjected to hot temperatures in a wear-exposed environment. Microstructural imaging corroborated with x-ray diffraction analysis showed a complex phased structure consisting of intermetallic Cr-Ni, C-Co-W Laves type, and chromium carbide phases. The surface properties of the coatings, targeting hot corrosion behavior, erosion, wear resistance, and microhardness, were evaluated. The high-temperature corrosion test was performed for 100 h at 750 � C in a salt mixture consisting of 25 wt.% NaCl + 75 wt.% Na2SO4. The degree of corrosion attack was closely connected with the exposure temperature, and the degradation of the material corresponding to the mechanisms of low-temperature hot corrosion. The erosion tests were carried out using alumina particles at a 90� impingement angle. The results, correlated with the microhardness measurements, have shown that Co-based coatings exhibited approximately 40% lower material loss compared to that of the steel substrate. KW - co-based alloys KW - hot corrosion KW - solid particle erosion KW - microstructure KW - brazing Y1 - 2022 U6 - https://doi.org/10.3390/cryst12060762 VL - 2022 IS - 12 SP - 762 PB - MDPI ER - TY - JOUR A1 - Utu, Ion-Dragos A1 - Marginean, Gabriela A1 - Hulka, Iosif A1 - Şerban, Viorel-Aurel A1 - Cristea, Dan T1 - Properties of the thermally sprayed Al2O3–TiO2 coatings deposited on titanium substrate JF - International Journal of Refractory Metals and Hard Materials N2 - Based on the fact that titanium and titanium alloys have poor fretting fatigue resistance and poor tribological properties, it is necessary to apply some surface engineering methods in order to increase the exploitation characteristics of these materials. One may either implement some surface treatment technologies or even deposit overlay coatings by thermal spraying. The present study is focused on the achieved properties of the ceramic coatings (Al2O3 + 13 wt.% TiO2) deposited onto a titanium substrate using high velocity oxygen fuel (HVOF) and plasma spraying (APS) respectively. The effect of the deposition method on the microstructure, phase constituents, and mechanical properties of the ceramic coatings was investigated by means of scanning electron microscopy (SEM), X-ray diffraction technique (XRD) and nanoindentation tests. The sliding wear performances of the Al2O3–TiO2 coatings were tested using a pin on disk wear tester. KW - Titanium KW - Al2O3–TiO2 coatings KW - Nanoindentation Y1 - 2015 VL - 51 SP - 118 EP - 123 ER -