Experimental Characterization of Additively Manufactured Metallic Alloys for Electric Propulsion Applications

Surface and Interface Characteristics of an Electrodeposited Ni-Layer on Additively Manufactured Inconel-718 Alloy

The present study explores the effect of an electrodeposited nickel layer on Inconel-718 alloy produced using different additive manufacturing (AM) routes, like Laser Powder Bed Fusion (L-PBF), Electron Beam Powder Bed Fusion (EB-PBF), and Laser-Directed Energy Deposition (L-DED). Comparative analyses were conducted by characterizing the physical, mechanical, and surface properties of Ni-coated AM-built Inconel-718 alloy surfaces. Different microstructures of Ni coatings were observed for different AM-built surfaces of Inconel-718 alloy. Influence on the Ni-layer hardness was also noted, plausibly as a consequence of variations in the residual stress of coated specimens. The hardness of Ni-coated specimens was not correlated well with the scratch resistance due to the unique natures of the Ni layer interface with the substrate surface, depending upon the AM route adopted to produce the Inconel-718 alloy builds. A comprehensive analysis of the scratch failure in identically coated specimens built using different AM routes has also been discussed.

The Effect of TVAC Cycles on Physical Properties and Morphology of Alumina Coated AA7075 via Hard Anodization and Pulsed Laser Deposition: A Comparative Study for Space Applications

Abstract. Aluminium alloys used in space structural applications are exposed to extreme environmental conditions. To preserve the integrity of structural materials in such environments, various surface treatments have been developed with the goal of forming thin films of hard oxides. Traditionally, the standard surface treatment for space applications has been hard anodization, which produces aluminium oxide layers through an electrochemical reaction between the substrate and an electrolyte. As an alternative to this well-established technique, thin film deposition via Pulsed Laser Deposition (PLD) has been explored. This study compares the traditional hard anodization method with PLD to evaluate their respective strengths and weaknesses and assess the potential of PLD as a viable alternative to coat AA7075-T6, a widely used alloy in the space industry. This work examines the effects of Low Earth Orbit (LEO) conditions on the morphology and on the interface between the aluminum substrate and the deposited alumina. The LEO environment experienced by the “6S CubeSat” of the PoliSpace project [1] is simulated through thermal cycling in a Thermal Vacuum Chamber (TVAC), in accordance with the “ECSS-E-ST-10-03C” standard. The samples underwent a tailored thermal cycle, in which the maximum and minimum temperatures represent limiting conditions selected to prevent damage to sensitive components, such as the structural batteries. A high vacuum level was ensured during each test to fully simulate the space environment. The physical and elastic properties of both coatings were evaluated employing Brillouin spectroscopy, offering insights into how the fabrication method influences the final characteristics of the deposited films. Visual tests confirmed the different nature of the two interfaces and the expected higher compactness of the PLD-deposited alumina with respect to the anodic one.

Experimental Investigation of Electrical Parameter Effects in Wire Arc Atomization of 316L Stainless Steel Powders for Additive Manufacturing

Conventional industrial‐scale production of metal powders generally occurs in large plants, where each batch sizes several hundred kilograms of powder. However, these production methods are economically impractical for manufacturers with lower demands, such as those involved in prototyping and developing new alloys for additive manufacturing. This study investigates wire arc atomizing as a viable alternative for producing metal powders that are specifically tailored to precise requirements and manufactured in a batch size of one. The wire melting process is controlled by modulating the electrical current, using pulsed and unpulsed DC. Arc power varies across a wide range to assess its impact on particle size distribution. Furthermore, the produced metal powders undergo comprehensive characterization and evaluation to determine their suitability for additive manufacturing, ensuring they meet specific application requirements.

Analysis of Thermally Oxidized Surfaces of Additive Manufacturing Metal Powders Using Triboelectric Charging

In powder-based additive manufacturing (AM), thermal exposure during processing can modify powder surface chemistry and promote oxide growth, even under inert atmospheres from residual oxygen contamination. This study investigates the effect of thermal oxidation on the surface chemistry and triboelectric charging behavior of three AM metal alloy powders: AlSi10Mg, 316L stainless steel (SS 316L), and Ti6Al4V. The work examines the evolution of the oxide layer during baking at 100 and 300 °C using triboelectric charging corroborated by X-ray photoelectron spectroscopy (XPS), diffuse-reflectance spectroscopy, and work-function measurements. The results show that heating modifies the surface oxide state of all powders, with changes dependent on the alloy composition and baking temperature. For AlSi10Mg, heating modified the Al2O3-rich surface oxide, with changes consistent with increased oxide ordering and γ-Al2O3-like characteristics, with the work function increasing from 4.34 ± 0.01 eV in the as-received (AR) condition to 4.92 ± 0.03 eV after baking at 300 °C. The corresponding triboelectric n-exponent increased from 0.91 to 1.38. For SS 316L, transformation of Cr(OH)3 to Cr2O3 reduced triboelectric charge accumulation, while the oxygen concentration increased from 49.92 to 54.87 at.% and the work function decreased from 5.74 ± 0.02 to 5.28 ± 0.04 eV after baking at 300 °C. This reflected a drop in the n-exponent from 0.82 for AR to 0.73 at 300 °C. For Ti6Al4V, charging variations were associated with titanium oxide evolution and surface modifications consistent with rutile-related titanium oxide characteristics, with the work function increasing from 5.33 ± 0.01 to 5.44 ± 0.03 eV after baking at 300 °C. The corresponding triboelectric n-exponent increased from 0.49 to 0.52. Overall, triboelectric charging is a sensitive approach for detecting thermally driven surface oxide modifications in additive manufacturing powders.

PhD Thesis

Preliminary Experiment of EDM Wire Cut on AZ31 Magnesium Alloy

The AZ31 magnesium alloy has become quite popular in the aerospace industry as well as in the automotive sector because of its high strength‐to‐weight ratio and corrosion resistance properties. However, the magnesium alloy's tendency for being highly reactive, having low thermal stability, and ignitability causes conventional machining processes to be quite challenging. Wire electrical discharge machining (WEDM) is a non‐contact machining technique that can serve this purpose by using sparks of electricity to remove material from the workpiece. Nonetheless, very few studies have focused on understanding the effects of the WEDM process parameters on the machinability of AZ31 magnesium alloys. This study examines the preliminary effects of three key WEDM parameters, T on , T off , and SV, on the machining of AZ31 magnesium alloys. The experiments were performed on the FANUC series of wire EDM machines using a 0.25 mm wire electrode made of brass under two parameter conditions, one representing low discharge energy and the other representing high discharge energy. The surface roughness was evaluated by utilizing a Mitutoyo SJ‐310 surface roughness tester, and the machining time was determined by obtaining the value directly from the machine interface. The experimental result shows that lower energy ( T on  = 10 µs, T off  = 12 µs, SV = 15 V) led to a smoother surface finish, that is, a surface roughness of 4.012 µm and lower machining time, 91 s, as compared to higher energy, which gave a surface roughness value of 4.605 µm with machining time of 201 s. From these experimental results, it can be observed that the AZ31 magnesium alloy is extremely susceptible to excess discharge energy during WEDM, resulting in increased thermal erosion and poor surface finish. The initial results obtained from this experiment will prove valuable in future studies for optimizing the machining process statistically by employing the Taguchi method.