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A comparative study of bronze coatings on steel produced by plasma and cold metal transfer wire-arc depositing was carried out. The microstructure, interface characteristics, hardness, and shear bond strength of bronze deposits were investigated. Cold metal transition (CMT) deposition presented lesser penetration cracks and lower dilution than that of plasma arc deposition (PAD). The interfacial bonding of CMT deposits appeared as diffusion bonding characteristics, whereas PAD achieved a good metallurgical bond. Plasma arc deposited specimens showed more severe penetrating cracks and less CMT due to the difference of dilution rate. As heat input increased, microstructure of CMT and PAD deposited layer transformed from α-Cu + spherical or dendritic Fe-rich phase to massive Fe-rich phase + ε-Cu. The volume percentage of α-Cu +γ 1 in CMT deposits was observed higher than that of PAD, and Fe-rich phase in the PAD was significantly higher than that of CMT, leading in a significant increase of microhardness of PAD. Interfacial bonding strength of PAD under high heat input was much higher than that of CMT. Graphical abstract

In this study, as-cast ductile iron was austempered to produce austempered ductile iron (ADI). A CrAlSiN film was then deposited on the surface of ADI specimens using the cathodic arc deposition (CAD) method. The gas flow ratio of Ar/N2 varied (2, 2.5, and 3) under different processing parameters, designated as S1, S2, and S3, respectively. The composition, structure, hardness, adhesion, and wear resistance of the coated specimens were analyzed to evaluate the effect of the gas flow ratio on surface hardness and abrasion resistance. The experimental results indicated that CrN/Al(Si)N nano-multilayered films were successfully synthesized using oppositely positioned dual targets (Cr and AlSi) reacting with N2 gas during the CAD process. The coatings significantly enhanced the surface hardness and wear resistance of ADI. A comparison of the three coating conditions with varying gas flow ratios revealed that as the Ar/N2 gas flow ratio decreased (i.e., N2 gas flow increased), the surface hardness of the coated ADI specimens increased while the abrasion rate decreased. Among the tested conditions, S1 exhibited the highest hardness (1479 HV0.1) and the lowest wear rate (1.6 × 10−⁶ g/m).

The thin-walled aerobat shell has the common characteristic structures of staggered internal ribs and curved overhanging gaps, which are prone to the unstable flow of the molten pool during directed energy deposition-arc (DED-Arc), causing a significant decline in the forming accuracy of the components. To avoid this, DED-Arc strategies and process technologies for the characteristic structures were investigated. For the internal circumferential transverse ribs, the deflection deposition process was adopted to transform the molten pool from an overhanging state to a horizontal state to avoid the unstable flow, and a model of the depositional path point set was established based on aerobat shell feature points to ensure the forming accuracy. For internal longitudinal ribs extending in the direction of the inner-wall generatrix, a new hybrid path planning method was proposed, in which the rib contour was deposited first, followed by continuous filling via chamfering scanning or a single pass. This approach avoids the generation of protrusions and depressions when filling longitudinal ribs with irregular cross-section and improves the depositional flatness. For curved overhanging gaps, a novel process method of deflection deposition with a separation path was established. The partial separation path was deposited point by point at the boundary of gaps by adjusting the component deflection angle, which effectively inhibited the molten pool’s unstable flow and avoided deposition collapse. Ultimately, an aluminum-alloy aerobat shell was manufactured through DED-Arc using the established process technologies. The average overall size deviation was about ± 0.8 mm, and the average horizontal and vertical ultimate tensile strengths were 323.9 and 309.3 MPa, respectively, which met the component delivery requirements.

The creation of coatings by the cathodic arc evaporation method has outstanding advantages: these coatings are highly durable and wear-resistant, especially since the method has an intense ionization process and the atoms can penetrate deep into the surface substrates, resulting in excellent adhesion. Furthermore, this approach provides precise control over the chemical composition and thickness of the coating, ensuring consistent quality across the entire surface. However, uneven evaporation and ejection of molten metal droplets from the cathode during cathode arc deposition produce particles and droplets, resulting in an uneven coating surface. This study presents a new design for a magnetically controlled cathode arc source to effectively reduce particles and droplets during the cathodic arc deposition of multi-component alloy targets for nitride-based hard coatings. The study compares the performance of a new source with a conventional magnetic-controlled arc source for depositing TiAlNbSiN and AlCrSiN films. In the conventional source, the magnetic field is generated by a permanent magnet (PM), whereas in the new source, it is generated and controlled using an electromagnet (EM). Both films are produced using multi-component alloy targets (TiAlNbSi and AlCrSi) with identical composition ratios. The plasma characteristics of the two different arc sources are investigated using an optical emission spectrometer (OES), and the surface morphology, structural characteristics, deposition rate, uniformity, and surface roughness (Sa) are examined using scanning electron microscopy (SEM). When the EM was applied to have high plasma density, the hardness of the TiAlNbSiN film deposited with the novel arc source measured 31.2 ± 1.9 GPa, which is higher than that of the PM arc source (28.3 ± 1.4 GPa). In contrast, the AlCrSiN film created using a typical arc source exhibited a hardness of only 25.5 ± 0.6 GPa. This lower hardness may be due to insufficient ion kinetic energy to enhance stress blocking and increase hardness, or the presence of the h-AlN phase in the film, which was not detected by XRD. The electromagnet arc source, with its adequate ion bombardment velocity, facilitated a complementary effect between grain growth and stress blocking, leading to a remarkable hardness of 32.6 ± 0.5 GPa.

To improve the low deposition rate of atomic layer deposition (ALD), we introduced filtered cathodic vacuum arc (FCVA) technology for the high-rate deposition of Al2O3 films. The FCVA-Al2O3 process achieved a deposition rate of 15 nm/min, which is approximately an order of magnitude higher than that of conventional ALD. This process does not involve hydrogen, preventing hydrogen ion penetration and thereby ensuring the high stability of the oxide TFT backplane. FCVA-Al2O3 films were integrated with inkjet-printed (IJP) organic layers to form a hybrid thin-film encapsulation (TFE) structure for OLEDs. The resulting laminated encapsulation exhibited excellent water vapor barrier properties (WVTR, Water Vapor Transmission Rate of 1.2 × 10−4 g/m2/day), demonstrating the great potential of FCVA for packaging high-throughput and high-performance flexible electronics. In addition to evaluating barrier properties (surface roughness, residual stress, and WVTR) to assess the suitability of TFE, the impact of FCVA technology was assessed via oxide thin-film transistor (TFT) electrical performance and OLED device reliability tests. The electrical properties of oxide TFTs show no significant degradation post-encapsulation, while OLED performance, despite a slight increase in current efficiency, remains effectively unchanged. Additionally, the lifetime of OLED devices reached 300 h under accelerated aging conditions (85 °C, 85% relative humidity), which is nearly twice that of devices without FCVA-Al2O3 encapsulation.

Wire Arc Additive Manufacturing (WAAM), also known as Wire Arc Directed Energy Deposition, is used for fabricating large metallic components with high deposition rates. However, the process often leads to residual stress, distortion, defects, undesirable microstructure, and inconsistent bead geometry. These challenges necessitate reliable in-situ monitoring for process understanding, quality assurance, and control. While several reviews exist on in-situ monitoring in other additive manufacturing processes, systematic coverage of sensing methods specifically tailored for WAAM remains limited. This review fills that gap by providing a comprehensive analysis of existing in-situ monitoring approaches in WAAM, including thermal, optical, acoustic, electrical, force, and geometric sensing. It compares the relative maturity and applicability of each technique, highlights the challenges posed by arc light, spatter, and large melt pool dynamics, and discusses recent advances in real-time defect detection and control, process monitoring, microstructure and property prediction, and minimization of residual stress and distortion. Apart from providing a synthesis of the existing literature, the review also provides research needs, including the standardization of monitoring methodologies, the development of scalable sensing systems, integration of advanced AI-driven data analytics, coupling of real-time monitoring with multi-physics modeling, exploration of quantum sensing, and the transition of current research from laboratory demonstrations to industrial-scale WAAM implementation.

In this paper, we present a comparative study of tribological properties of TiN coatings deposited by low-voltage electron beam evaporation, magnetron sputtering and cathodic arc deposition. The correlation of tribological behavior of these coatings with their intrinsic properties and friction condition was studied. The influence of surface topography and the surrounding atmosphere was analyzed in more detail. We limited ourselves to the investigation of tribological processes that take place in the initial phase of the sliding test (the first 1000 cycles). A significant difference in the initial phase of the sliding test of three types of TiN coatings was observed. We found that nodular defects on the coating surface have an important role in this stage of the sliding test. The tribological response of TiN coatings, prepared by cathodic arc deposition, is also affected by the metal droplets on the coating surface, as well as those incorporated in the coating itself. Namely, the soft metal droplets increase the adhesion component of friction. The wear rates increased with the surface roughness of TiN coatings, the most for coatings prepared by cathodic arc deposition. The influences of post-polishing of the coating and the surrounding atmosphere were also investigated. The sliding tests on different types of TiN coatings were conducted in ambient air, oxygen and nitrogen. While oxygen promotes tribo-chemical reactions at the contact surface of the coating, nitrogen suppresses them. We found that the wear rate measured in ambient air, compared with that in an oxygen atmosphere, was lower. The difference is probably due to the influence of humidity in the ambient air. On the other hand, wear rates measured in a nitrogen atmosphere were much lower in comparison with those measured in an oxygen or ambient air atmosphere.

This paper investigates the feasibility of producing hard structures capable of wear resistance by depositing a hardfacing flux-cored wire while using arc directed energy deposition (DED-Arc) as process. The present paper discloses the compatibility of a metal hardfacing flux-cored wire with this technology by deposition of single walls and block fabrication. The deposition of walls and blocks was made using different parameters and deposition strategies, in order to avoid solidification cracking associated with the precipitation of chromium carbides. Macro and microstructural analyses, as well as hardness tests, were carried out to validate the use of this wire with DED-Arc. The use of a grinder for slag removal was also investigated. Withal, the deposition of a 40-layer wall and blocks indicated that a hardfacing flux-cored wire can be used to produce a near net shape part by additive manufacturing. Additionally, gradient properties of additively manufactured metal parts can be achieved by depositing layers of materials with different characteristics and, with DED-Arc, this can be done through the use of different types of metal wire. Thus, studies on the possibility of constructing a bi-metallic part, by DED-Arc, using a low carbon steel (ER70S-6) and the same hardfacing-cored wire were developed, focusing on crack minimization procedures, such as the application of pre-heating. Assessment of metallurgical transformations and mechanical properties were investigated to assure that the material properties were kept. A final multi-metal part was produced with DED-Arc.

This study aims at evaluating the effect of microstructure imperfections on the corrosion fatigue performance of an ER70S-6 alloy produced by wire arc additive manufacturing (WAAM) process, in a 3.5% NaCl solution. For reference, a regular ST-37 alloy with relatively similar chemical composition was considered as a counterpart alloy. This was justified by the fact that the ER70S-6 alloy is usually used for conventional welding of ST-37 steel. The results obtained indicated that while the ST-37 alloy exhibited fatigue strength of 240 MPa in the corrosive solution, the additively manufactured ER70S-6 alloy showed fatigue strength of only 140 MPa. These differences were related to microstructural imperfections that are inherently produced during the WAAM process.

Directed Energy Deposition-Arc (DED-Arc) method is popularly being used to produce the near-net-shape products having large structure and complex geometrical features. The repeated heating of previously fabricated layers, during the layer-by-layer deposition of metal in DED-Arc, may result into anisotropy in the mechanical properties and microstructure at different locations. In the present work, the microscopic and mechanical properties of gas metal arc welding-based DED-Arc of material 5356 aluminum alloy thin plate and block are investigated. Microstructural examinations are conducted by optical microscope, energy-dispersive x-ray analysis, scanning electron microscope, and x-ray diffraction analysis. Microscopic examination illustrated that the microstructure has inter-layer and inner layer regions in vertical direction and homogeneous microstructure in horizontal direction of plate and block. Inner and inter-layer regions are also found in the width direction of the block. Macro- and micro-pore are observed in both plate and block samples, and air gaps are present in block samples due to improper penetration between two adjacent layers. α-Al and β-Al 3 Mg 2 second-phase particles are found near the boundary and within the matrix. Mechanical properties are examined by tensile tests and microhardness tests. The average hardness value is found to increase from the bottom region to top the region in both the plate and block. As compared with the casted 5356 Al alloy, the DED-Arc fabricated 5356 Al alloy plate sample has better tensile properties. Block samples showed poor tensile properties due to the presence of more pores and air gaps. The fractures of all the samples collected from both thin plate and block are ductile in nature.