Upcycling of Copper Scrap into High-Quality Powder for Additive Manufacturing: Processing, Characterization, and Sustainability Assessment

Abstract

Copper is a critical material for energy transition and green technologies, making its sustainable use increasingly important. Its superior thermal and electrical conductivity make it highly well-suited for additive manufacturing (AM). In this study, copper sourced from offshore electrical cables was upcycled to produce high-quality metal powder for AM. The scrap was processed to separate the metal from plastic and rubber, then refined through ultrasonic atomization, achieving a purity of ~99.5% wt.% with minimal impurities. Characterization demonstrated good flowability, apparent and tap densities, and a well-distributed particle size. To assess its performance in AM, the powder was printed using Directed Energy Deposition (DED) with a laser beam, confirming its high printability and compatibility with the base material. Finally, a comparative Life Cycle Assessment (LCA) revealed a significant environmental advantage of the recycling-based process over conventional mining, reducing global warming potential by more than 70%. These findings highlight the importance of feedstock origin in AM sustainability and support the adoption of circular economy strategies to lower the environmental footprint of advanced manufacturing.

1. Introduction

Copper (Cu) plays an important role in modern infrastructure and the clean energy transition due to its superior electrical and thermal conductivity. It is a key material in technologies such as electric vehicles, wind turbines, solar panels, and power grids [1,2]. The critical role of copper in the energy sector, and more specifically for the green transition, is confirmed by recent studies [3,4]. Additionally, the academic effort has been focused on methodologies to increase the utilization efficiency of copper-based feedstock by optimization of the manufacturing processes or of surface modifications [5,6,7].

As such, copper has become one of the most critical minerals supporting the development of a circular economy. According to the International Energy Agency, nearly 50% of total copper demand by 2040 will be driven by clean energy technologies, with overall global demand expected to increase by at least 50% by 2050 [1]. However, this rapidly growing demand presents major challenges for sustainable resource management. Traditional copper mining is both environmentally damaging and increasingly inadequate to meet future consumption levels. In response, recycling and upcycling have emerged as vital strategies to close the supply–demand gap. These practices significantly reduce environmental impacts by lowering energy use by up to 15%, while also decreasing greenhouse gas emissions, solid waste generation, and reliance on primary copper extraction [8,9]. This pressing need for sustainable copper sourcing underscores the importance of innovative recycling methods, particularly in advanced manufacturing sectors.

Metal powder recycling for additive manufacturing (AM) is becoming an essential area of research, as it supports both environmental sustainability and economic efficiency. In this context, it is important to distinguish between “recycled” and “reused” powders. Recycled powders are produced by converting post-industrial or post-consumer metal scrap into new, high-quality feedstock, while reused powders are those recovered from previous AM build cycles—typically sieved and requalified for continued use. Both strategies contribute to a more circular and resource-efficient manufacturing model. The use of recycled or reused metal powders can notably reduce the cost of raw materials and enhance feedstock availability, making AM more accessible and sustainable for a wide range of applications [10,11]. Despite these advantages, reusing metal powders presents certain technical challenges. Reused powders often undergo changes in particle morphology, size distribution, microstructure, and chemical properties due to repeated thermal cycling during the AM process. These variations can influence powder flowability and packing density, ultimately affecting the repeatability and quality of printed components [12]. For instance, studies on stainless steel and cobalt–chrome powders subjected to Direct Metal Laser Sintering (DMLS) have employed methods like laser diffraction, X-ray tomography, and microscopy to assess the evolution of powder properties in virgin versus reused conditions [13]. In parallel with studies on powder reuse, research on producing AM powders directly from secondary metal sources has also gained momentum. Several promising approaches have demonstrated the feasibility of converting metallic scrap into high-quality feedstock. One such study showed that atomizing Inconel 718 scrap metal significantly reduces energy consumption and CO₂ emissions—by more than 90%—compared to conventional powder production, while maintaining comparable mechanical and fatigue performance. Importantly, this was achieved without requiring any adjustments to the standard AM process parameters [14]. Building on this concept, Vanazzi et al. introduced a method to produce Inconel 718 powder using a mixture of machining waste, failed AM builds, and disqualified powder. Their work confirmed that the resulting powder complied with industrial quality standards and successfully produced dense, mechanically robust parts via Directed Energy Deposition (DED) with a laser beam [15]. These advancements in recycling high-performance alloys set the stage for exploring similar upcycling strategies for pure copper, a material with unique processing challenges in AM.

Additive manufacturing of copper has gained increasing attention due to its potential to produce complex, near-net-shape components with excellent thermal and electrical properties. Various AM techniques have been explored for this purpose, including laser powder bed fusion (LPBF), electron beam melting, binder jetting, ultrasonic AM, and DED [16,17]. However, copper’s high thermal conductivity and peculiar wavelength-dependent reflectivity continue to pose significant challenges, particularly in laser-based processes where efficient energy absorption is critical [18]. More specifically, copper is characterized by reflectivity values greater than 95% at a wavelength of 1064 nm, which is common to many industrial machines equipped with near-infrared lasers [19]. However, light absorption from copper is enhanced when decreasing the wavelength to values typical of green (500–550 nm) and blue lasers (400–500 nm), thus broadening the margins of improvement for AM of pure copper and copper-based alloys [18,19]. Among the different AM technologies, DED with a suitable wavelength of the laser beam has shown promising results in overcoming copper’s processing difficulties. Liu et al. (2023) demonstrated the first successful fabrication of bulk pure copper parts with well-defined geometries using a blue laser-based DED system, achieving densities as high as 99.6%—a major milestone in addressing copper’s reflectivity and heat dissipation issues [20]. The use of blue lasers significantly enhances energy absorption, enabling stable melt pool formation and improved layer adhesion. These advantages have made DED with a blue laser a particularly attractive technique for applications requiring high part density and structural integrity. When considering a green laser, high power would still be needed for the DED process to overcome the fast cooling due to the high thermal conductivity of copper and maintain a suitable size of the melt pool to increase density in the printed parts [21]. Complementing these findings, Aghayar et al. (2024) applied LPBF with a near-infrared laser to produce pure copper electrodes and reported not only high density but also improved mechanical performance and corrosion resistance compared to conventionally cast parts [22]. Nevertheless, the following challenges remain: from the process point of view, it would be beneficial to switch to shorter wavelengths to improve part quality also for LPBF processes [18]. Achieving fully dense copper parts consistently, managing residual stresses, and ensuring uniform microstructure across complex geometries are still active areas of investigation [20,22]. Despite these hurdles, the growing body of research clearly illustrates the potential of AM to advance the use of pure copper in demanding sectors such as aerospace, electronics, and energy.

In addition to material innovations, assessing the environmental and economic impacts of using recycled powders is gaining importance in AM research. Moghimian et al. developed a life-cycle-based framework to evaluate the sustainability of recycled and reused metal powders, examining key parameters such as CO₂ emissions, energy consumption, feedstock quality, and production costs. Their work also emphasized the need for clear terminology to distinguish between “recycled” and “reused” powders, supporting more consistent and reliable sustainability assessments [23].

This study aims to explore the viability of producing high-quality copper powder for AM through the upcycling of offshore electrical cable scrap. By employing ultrasonic atomization, we seek to refine recycled copper into powder suitable for DED processing with an infrared laser beam. Our objectives include assessing the material properties of the resultant powder, evaluating its performance in AM applications, and conducting a comprehensive Life Cycle Assessment (LCA) to quantify the environmental benefits of this recycling approach.

Our findings demonstrate that the proposed approach is indeed capable of producing copper powders with reduced content of contaminants such as tin (Sn) and iron (Fe) with respect to the raw material, and copper content increased up to ~99.5% wt.%. Moreover, the production and analysis of multi-layer specimens proved that the recycled powders possess characteristics compatible with DED machine setup and process. These favorable characteristics combine with a substantial reduction of environmental impact, given the reduction of over 70% of global warming potential of the upcycling process compared to conventional manufacturing of copper powders from raw materials.

2. Materials and Methods

2.1. Raw Material Preparation

Disqualified offshore electrical cables were retrieved and processed to separate the metallic and non-metallic components constituting the scrapped cables. A shredder (Copper-rec, Grand-Couronne, France) was used to cut the parts and separate the polyethylene-based external sheathing from the metallic core. The insulation part was automatically kept apart from the metal. At the end of the process, copper-based chips with approximate widths and lengths of 1 mm and 4 mm, respectively, were obtained and prepared for the following step of the process, namely the ultrasonic atomization.

An analysis of the chemical composition of copper-based chips was conducted to identify the presence of potential impurities. The analysis was conducted by means of X-Ray Fluorescence (XRF) (Thermo Fisher Scientific, Waltham, MA, USA) measurements on a small sample of shredded chips. Three measurements taken at different random locations on the sample were then averaged, and the built-in evaluation software was exploited to identify the concentration of Cu and other contaminants present in the reclaimed metal.

2.2. Ultrasonic Atomization

The ultrasonic atomization process was carried out using a laboratory-scale rePowder atomizer (AMAZEMET, Warsaw, Poland). Initially, the pre-processed metal feedstock was placed into a graphite crucible within an induction furnace and heated to temperatures between 1100 °C and 1300 °C, under an inert atmosphere of nitrogen gas at a controlled pressure of 0.6 bar, allowing the metal scrap to fully melt and reach the necessary temperature for the atomization process. Subsequently, the molten material was cast onto a sonotrode plate oscillating at a frequency of 40 kHz, spreading across its surface and forming a thin metallic film. The ultrasonic motion of the plate disrupts the surface tension of the molten metal, inducing the formation of droplets that detach from the liquid phase and solidify into micrometer-sized spherical powder. The atomization process was also conducted under an inert nitrogen atmosphere and a constant ultrasonic wave amplitude (50%).

The resulting powder was subjected to a multi-stage dry sieving procedure to achieve particle size classification suitable for AM, with particular focus on DED applications. Sieving was performed using a laboratory-scale ultrasonic sieving system (Assonic, Dorsten, Germany) equipped with a stack of precision-woven stainless steel meshes with nominal aperture sizes of 150 µm and 53 µm, arranged in descending order. Each sieving cycle processed approximately 200 g of copper powder, with vibration amplitude progressively increased in three stages: 50% for the initial 3 min, 80% for the following 3 min, and 100% during the final 10 min, to optimize separation efficiency across the particle size spectrum.

2.3. Characterization of Atomized Powders

Comprehensive characterization of the atomized metal powder was conducted to evaluate its suitability for DED applications. Chemical composition of the metal powders was analyzed by Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES) (Thermo Fisher Scientific, Waltham, MA, USA). Morphological analysis was performed using scanning electron microscopy (SEM) (Philips, Amsterdam, The Netherlands), according to the ASTM F1877 standard [24].

Particle size distribution (PSD) was determined using a multidimensional vibratory sieving system (Giuliani, Turin, Italy) in accordance with ISO 3310-1 and ISO 2591-1 standards [25,26]. The analysis was carried out using a stack of eight precision stainless steel sieves with nominal aperture sizes ranging from 32 µm to 150 µm. Following sieving, the material retained on each sieve was collected and weighed. The PSD was calculated based on the mass fraction retained on each mesh, providing a distribution of particle sizes within the analyzed range.

Apparent density and tap density were measured according to ASTM B212 and ASTM B527, respectively, using a Hall funnel (Bettersize, Dandong, China) and an automatic tap density device (Bettersize, Dandong, China). Flowability was further evaluated through Hall flow rate testing according to ASTM B213.

2.4. Deposition of Atomized Powder

To obtain a suitable combination of printing parameters for the deposition, a design of experiment (DOE) was devised using the Box–Behnken Design (BBD), considering three main parameters: laser power (W), powder feed rate (g/min), and laser scanning speed (mm/min) to model the single tracks. The track width, height, and size of the heat-affected zone (HAZ) were selected as the responses for the model. The Box–Behnken Design is highly efficient, as it requires fewer experimental runs compared to full factorial designs while still allowing for the estimation of quadratic effects and interactions among factors, making it particularly suitable for resource-constrained optimization studies. By incorporating strategically placed midlevel and center runs, this structured design accounts for two-factor interactions and squared terms, thereby improving the detection of synergistic interactions among process variables and reducing the need for costly sequential experiments [27]. Design Expert 12.0.3.0 software was employed to generate the BBD for the three parameters at three levels, with three repetitions of the center point. For each condition, single tracks of 40 mm length were deposited on a stainless steel base plate. The specimens were sectioned at mid-length by electro-discharge machining (EDM), embedded, and polished following standard metallographic procedures. Cross-sectional images were acquired by optical microscopy, and the track geometry was quantified through image analysis using ImageJ 1.54p software. For each response variable in the DOE, the average of three independent measurements was considered. The summary of the BBD is presented in

Table 1. Design factors and their values.

Factors	Name	Units	Type	Factors Levels
				−1	0	+1
A	Powder feed rate	g/min	Numeric	6	8	10
B	Laser power	W	Numeric	1800	2000	2200
C	Scanning speed	mm/min	Numeric	600	700	800

.

Depositions were made using a LASERTEC 65 3D (DMG MORI, Bielefeld, Germany) equipped with a coaxial nozzle and a 2400 W infrared (IR) fiber laser (λ = 1020 nm) with a top-hat profile and a spot size of 3 mm at the stand-off distance (13 mm). Specimens were built on a 316 stainless steel plate. Argon Grade 5 (99.999% purity) was employed as both the shielding and carrier gas, with flow rates of 5 L/min and 4.5 L/min, respectively. Subsequently, the samples were sectioned using electrical discharge machining (EDM) and prepared for light optical microscopy (LOM) following standard metallographic procedures. LOM images were captured by an S8APO stereomicroscope (Leica, Wetzlar, Germany), and track dimensions were measured using ImageJ (Fiji) software. Finally, microhardness measurements were conducted on the polished surface using a Vickers indenter HM-200 (Mitutoyo, Kawasaki City, Japan) with a test load of 200 g (HV0.2) and a dwell time of 10 s.

2.5. Life Cycle Assessment (LCA)

To assess the environmental performance of copper powder production for AM, a cradle-to-gate LCA was conducted following the ISO 14040 and 14044 standards [28,29]. The functional unit is defined as 10 kg of packed copper powder, suitable for AM applications. The cradle-to-gate system boundaries included all upstream activities: raw material acquisition, pre-treatment, atomization, sieving, and packaging, while excluding downstream use and end-of-life phases. This study compares two fundamentally different production routes:

The conventional process, based on primary copper production, includes ore mining, refining, and transformation into powder.

The f3nice process, which is a recycling-based pathway, utilizes copper recovered from discarded offshore electrical cables.

The assessment was conducted using the Environmental Product Declaration (EPD) 2018 method in the SimaPro software (v9.4), with Ecoinvent v3.8 as the primary database. The EPD method provides a standardized framework for quantifying environmental impacts across the life cycle of products. It covers multiple impact categories such as global warming potential, eutrophication, acidification, ozone depletion, and resource use, ensuring transparency and comparability across product systems.

The life cycle inventory combined primary and secondary data. For the conventional route, data were mainly sourced from the Ecoinvent database. For the f3nice process, site-specific data were used for key stages such as pre-treatment, atomization, and sieving, while background processes (e.g., energy, auxiliary materials, transport) were modeled with Ecoinvent datasets or literature values. This ensured both representativeness of the recycling process and consistency across system boundaries.

3. Results

3.1. Reclaimed Copper Scrap and Atomized Powders

Figure 1 shows the different steps involved in the upcycling process from the raw material preparation to the sieved powder ready for 3D printing processes. Starting with the feedstock material preparation, a dismantled subsea power cable is displayed in panel (a), with its components progressively separated until exposing the internal copper conductors. These conductors were subsequently shredded into chips to serve as feedstock material, as shown in panel (b), where the shredded copper is loaded into a graphite crucible prior to melting. In panel (c), the molten copper is directed onto a sonotrode plate oscillating at 40 kHz, where atomization of the liquid copper is occurring. Finally, panel (d) displays the atomized copper powder collected from the atomization chamber and sieved to a 53–150 µm size range.

3.2. Chemical Characterization

The chemical composition of the raw feedstock material, analyzed by means of XRF measurements, was compared to that of the final copper powder, characterized by ICP-OES and Inert Gas Fusion (only for quantification of oxygen concentration in the atomized powders). While this comparison provides useful insights, it is important to note that the XRF and ICP-OES techniques differ in analytical sensitivity and detection limits concerning specific elements. In particular, light elements such as Al and Si were not detected by the detector of the available XRF analyzer and were consequently observed only by the ICP-OES analysis of atomized powders.

Despite these methodological differences, the results reveal a notable enhancement in purity following the ultrasonic atomization process. Specifically, elements such as Fe and Sn were found significantly reduced in concentration in the final copper powder, as reported below in

Table 2. Measured chemical composition for the scrap metal before atomization and atomized copper powders.

Element	Raw Material Before Atomization [wt. %]	Atomized Copper Powder [wt. %]
Cu	99.21 ± 0.088	Balance
O	N/A	0.039 ± 0.008
Al	N/D	0.01
Cr	N/D	0.28
Fe	0.043 ± 0.008	0.01
P	N/D	<0.01
Mg	N/D	<0.01
Mn	N/D	<0.01
Mo	N/D	<0.01
Ni	N/D	0.01
Pb	N/D	0.03
Si	N/D	0.01
Sn	0.69 ± 0.063	0.12
Zn	N/D	<0.01
Zr	N/D	<0.01

N/D (not detected); N/A (not assessed).

:

3.3. Particle Size Distribution

Figure 2 shows the PSD of a sample of copper powder with a mass of 100 g and nominal size in the 53–150 µm range, collected after the sieving process on the ultrasonic sieving machine. The resulting PSD exhibits a unimodal profile, with the majority of the mass concentrated within the 53–90 µm range and the highest mass fraction retained above the 75 µm sieve. No powder fraction was observed above 150 µm, confirming a clean upper cut-off. However, a small but non-negligible quantity of particles was detected below 53 µm, despite the intended lower cutoff, which may be attributed to the agglomeration of fine particles. These particles may adhere to one another or to larger particles through van der Waals forces and electrostatic interactions, thus forming soft agglomerates that only partially disintegrate during sieving. This phenomenon can result in the presence of fine particles in larger size fractions, as they were originally part of larger structures.

From the cumulative distribution, the key percentile values were determined as D10 = 49.9 µm, D50 = 64.5 µm, and D90 = 86.1 µm, confirming a relatively narrow and well-centered distribution, indicating suitability for DED processes.

3.4. Morphology and Physical Properties

The physical properties of the copper powder were evaluated to determine its suitability for DED processes. The apparent density was measured at 5.13 g/cm³, indicating a moderate packing efficiency of the freely settled powder. Following 3000 tapping cycles, in accordance with standardized protocols, the tap density increased to 5.70 g/cm³, yielding a Hausner ratio of approximately 1.11, which suggests good flowability and low interparticle friction. This is consistent with the Hall flow rate, recorded at 13.4 s/50 g. All measurements were conducted at ambient temperature (21 °C).

Concerning the morphology of the particles, SEM images reported in Figure 3 showed that the powders presented high sphericity due to the characteristics of the ultrasonic atomization process. The presence of elongated particles and agglomerates was limited, reflecting the findings of the PSD analysis and suggesting an optimal processability. Moreover, the absence of satellites was in accordance with the measured flowability, conferring the powders a suitable behavior in terms of powder transport within the DED setup during deposition.

3.5. DOE on Single Tracks

Figure 4 presents cross-sectional images of the 15 single tracks produced under varying parameters. A summary of the deposition setup based on the Box–Behnken Design (BBD) and the corresponding measurement results is provided in

Table 3. BBD setup for the relevant factors comprised in the DOE and results for the measured response.

Sample	A Powder Feed Rate (g/min)	B Laser Power (W)	C Laser Scan Speed (mm/min)	R1 Width (mm)	R Height (mm)	R3 HAZ (mm)
1	10	2000	600	3.20	0.80	0.50
2	10	1800	700	2.79	0.63	0.36
3	6	2200	700	3.09	0.46	0.55
4	10	2200	700	3.29	0.73	0.54
5	6	2000	600	2.99	0.52	0.62
6	6	1800	700	2.76	0.47	0.49
7	6	2000	800	2.81	0.45	0.51
8	10	2000	800	2.97	0.58	0.39
9	8	1800	600	3.09	0.70	0.52
10	8	2200	600	3.19	0.69	0.57
11	8	1800	800	2.83	0.53	0.45
12	8	2200	800	2.99	0.54	0.49
13	8	2000	700	3.07	0.61	0.54
14	8	2000	700	2.98	0.62	0.55
15	8	2000	700	3.03	0.61	0.51

.

It can be noted that no cracks were detected either at the interface between the base plate and the deposited material or in the Cu single track. Nevertheless, it was possible to appreciate the influence of printing parameters on the shape of the welding track and the depth of the heat-affected zone. In addition, spattering was observed, which is a common phenomenon in laser powder DED processes arising from unstable melt-pool dynamics driven by vapor recoil pressure, strong Marangoni flows, and powder–melt interactions. Although suitable parameter combinations helped to reduce its occurrence, it could not be entirely avoided, and some porosity and oxide inclusions were still present in the final microstructure, as later confirmed in Figure 5a. Moreover, the impact of parameters on the internal porosity was carefully evaluated, since this would result in degradation of the structural integrity of complex parts and of the achievable mechanical, electrical, and thermal performances. Overall, the parameters set number2 and number 8 appeared to produce a shallow HAZ and lower porosity content. These two features are favorable since they ensure optimal welding of the deposited material and base plate with limited interdiffusion and grant sufficient density to allow for building of subsequent layers, avoiding cracking and delamination phenomena.

3.6. Multi-Layer 3D Deposition of Recycled Copper Powders

After obtaining the geometric models for the dimensions of the single tracks, the next step was to realize a multi-layer sample with a minimum amount of porosity. In this regard and based on the observations from micrographs of the cross-sections, parameters of sample 8 were selected as the starting point for fine-tuning, given the minimum amount of porosity and suitable profile of the transition layers between the base plate and printed track. At this stage, the parameter window that yielded the most stable tracks with reduced internal porosity was first identified. In addition, the aspect ratio of the deposited tracks, defined as the width-to-height ratio, was taken into account, since values above 5 are generally recommended in the literature [30]. On this basis, a number of single-layer specimens were produced to refine the process window before proceeding to multi-layer deposition. A multi-layer cuboid of 30 × 20 × 3 mm³ was deposited using the parameters presented in

Table 4. Printing parameters for the deposition of the multi-layer cuboid.

Powder Flow Rate (g/min)	Laser Power (W)	Laser Scanning Speed (mm/min)	Hatch Distance (mm)	Layer Thickness (mm)	Carrier Gas Flow (L/min)
10	2000	750	1.65	0.7	4.5

and a zig-zag scanning strategy with 90-degree rotation between consecutive layers. The height of the specimen was limited to 3 layers for the purposes of this investigation. The deposition was carried out with a diode laser system rated at 2500 W (λ = 1020 nm), delivering a 3 mm spot diameter at the working distance of 13 mm.

In this case, laser scanning speed and hatch distance were optimized to avoid delamination of the deposited multi-layer material. The quality of the process was assessed by analyzing the cross-section of the specimen by LOM and the hardness profile across the steel–copper interface by indentation. As shown in Figure 5a, interdiffusion between the base plate and first layer was detected, whereas the second and third layers (delimited by the yellow dashed line) were unaffected by diffusion phenomena. Accordingly, the hardness profile presented in Figure 5b, alongside an optical image of the scanned area, decreased from ~170 HV for bulk 316 L to ~100 HV for deposited copper. This reduction in hardness with increasing distance from the substrate can be attributed to dilution effects at the interface, where considerable amounts of Fe, Ni, and Cr enter the melt pool. Due to the limited mutual solubility of Cu with these elements, there is a tendency for phase segregation and the formation of intermetallic or Ni/Cr-rich hard particles [31,32]. In addition, the layers adjacent to the base plate experience higher cooling rates than subsequent layers, resulting in a finer microstructure and increased hardness in those regions [33]. An abrupt change in the hardness curve was localized above the upper boundary of the base plate, confirming that the interdiffusion proceeded faster in the upper Cu phase.

3.7. Key Environmental Impact Results

The results of the LCA highlight notable contrasts in the environmental performance of the conventional mining-based process versus the f3nice recycling-based approach. The f3nice process reflects core principles of the circular economy, illustrating how the use of waste-derived feedstock can substantially mitigate environmental impacts while delivering high-quality metal powders for advanced manufacturing applications. The following sections present a detailed breakdown of the key environmental impacts for each process, along with a comparative analysis highlighting their relative performance.

3.7.1. Environmental Hotspots

In the conventional mining-based process, the copper production phase is by far the most environmentally impactful, dominating nearly all assessed categories. It accounts for approximately 98% of eutrophication, 90% of acidification, and around 83% of the global warming potential. By comparison, downstream processes such as rolling and atomization contribute significantly less—an order of magnitude lower—highlighting the disproportionate burden posed by copper extraction and primary refining.

In the f3nice recycling-based process, the primary environmental hotspot shifts to the atomization step, which is responsible for over 80% of the impact in categories like global warming, acidification, and fossil fuel depletion. This is largely due to the high energy demand and the use of nitrogen gas. Another critical contributor is the shredding step, which is necessary to separate copper from cable insulation. This phase significantly affects eutrophication and global warming due to the generation of polyethylene waste. While packaging has a relatively minor overall impact, its influence becomes more noticeable in categories related to renewable biomass use, driven by the inclusion of wooden pallets and HDPE bottles.

3.7.2. Comparative Interpretation

The LCA reveals a marked environmental advantage of the recycling-based f3nice process over the conventional mining-based alternative across all assessed impact categories.

As illustrated in Figure 6 and detailed in

Table 5. Summary of environmental impacts per functional unit (EPD 2018 method).

Impact Category	UoM	Conventional	f3nice	% Reduction vs. Conventional
Acidification	kg SO2-eq	2.74 × 100	4.43 × 10−2	98.4%
Eutrophication	kg PO43−-eq	4.58 × 100	1.98 × 10−2	99.6%
Global warming (GWP100a)	kg CO2-eq	9.41 × 101	2.52 × 101	73.2%
Photochemical oxidation	kg NMVOC-eq	1.73 × 100	3.54 × 10−2	98.0%
Abiotic depletion, elements	kg Sb-eq	2.88 × 10−2	5.71 × 10−5	99.8%
Abiotic depletion, fossil fuels	MJ	9.78 × 102	1.17 × 102	88.0%
Water scarcity	m3-eq	4.82 × 101	1.15 × 101	76.1%
Ozone layer depletion (ODP)	kg CFC-11-eq	1.02 × 10−6	2.26 × 10−7	77.8%

, the f3nice process demonstrates significantly lower environmental impacts compared to the conventional route in every evaluated category, including global warming potential, acidification, and resource depletion. Notably, the recycling-based approach results in only 26.8% of the global warming impact and 22.2% of ozone layer depletion relative to the conventional process. The most substantial reductions are observed in acidification and eutrophication, where f3nice contributes to just 1.6% and 0.4%, respectively. These findings highlight the remarkable environmental benefits of adopting recycled feedstocks in place of primary raw materials for metal powder production.

4. Discussion

4.1. Refining of Copper from Scrap Metal

Based on data present on the Ecoinvent database, the initial amount of copper metal inside the scrapped cables was estimated to be around 66% of the total initial weight, whereas the remaining 34% was attributed to polymeric-based and non-copper metallic claddings. Above 90% of the copper content was effectively turned into powders, achieving a high efficiency for the overall upcycling process targeted to the production of AM feedstock.

Additionally, based on the measured chemical compositions reported in Table 2, it was possible to observe a refining effect of the melting and atomization process on the quality of copper powders. In fact, the concentration of volatile elements such as Sn was decreased most probably due to evaporation from the liquid metal in the heating crucible before the atomization process. Other elements, such as Fe, on the other hand, may have been oxidized preferentially due to residual oxygen at low partial pressures that was inevitably present in the atmosphere of the melting furnace. Indeed, after the liquid metal was poured into the atomization chamber, a thin layer of slag constituted by lighter unmelted solid or oxides was found at the bottom of the crucible. The final concentration of Cu was in the 99.3–99.5% wt.% range, and the oxygen content was limited to 390 ppm, which constitutes a substantial improvement in the copper grade. Further measurements of electrical conductivity and mechanical properties derived from the AM processing of the powders, which would provide a quantitative assessment of the impact of Cu and O concentrations, were not included in this phase of the investigation. Nevertheless, the findings described in this study yield a successful outcome for the proposed upcycling process and provide a promising basis for further implementation of the atomized powders in view of application as AM feedstock. It must be underlined that the atomization process employed for upcycling did not require special processing techniques or additional steps for functionalization of the copper particles to target a decrease in reflectance, as proposed by recent studies [34,35]. Moreover, the possibility of adding disqualified powders to the secondary sourced metal would contribute to the regeneration of those powders by means of an alternative methodology with respect to currently employed techniques [36].

4.2. Compatibility of Recycled Powders with DED Process

Physical properties of the powders presented the typical characteristics of the particles obtained by ultrasonic atomization processes. The narrow PSD observed after the sieving procedure is strictly related to the interaction between the liquid metal and the oscillating sonotrode, resulting in a lower fraction of coarse particles when the frequency is increased. Therefore, it was easier to cut the distribution of the collected powders sharply at 150 µm so as to avoid clogging of the deposition nozzle of the DED machine. Additionally, the almost perfectly spherical shape with no satellites ensured a suitable flowability and packing behavior of the powders, which is a fundamental requirement for seamless powder delivery to the laser spot and affects the full densification of printed parts. Specifically, the high sphericity is again a direct consequence of the atomization process employed for the powder production phase, since the micrometric displacements of the sonotrode combined with the static inert gas atmosphere avoided the deformation of particles induced by the supersonic gas jets employed in gas atomization technology. Nevertheless, the presence of finer powders should always be controlled to avoid degradation of flowability or formation of dust clouds during deposition. In this case, as demonstrated by the PSD analysis reported in Figure 2, the content of fines was below 1%, still matching the conventional recommendations for powder use in DED machines.

4.3. Analysis of Material Response to DED Parameters and Discussion of the Obtained Structures

To analyze the response of the deposited material to the variation of printing parameters, a quadratic regression model was used for modeling the responses, and the generalized equation is defined as follows [37]:

$$\mathrm{ }Y=b_0+{\sum }_{i=1}^n{b}_i{x}_i+{\sum }_{i=1}^n{b}_{ii}{x}_i^2+{\sum }_{i<j}^n{b}_{ij}{x}_i{x}_j+e$$

(1)

where Y is the predicted response; $x_i$ and $x_j$ are the input factors; $b_0$ is the intercept term; $b_i$ is the linear term coefficient; $b_j$ is the squared term coefficient; $b_{ij}$ is the interaction term coefficient; and e is the observed experimental error. The polynomial quadratic regression model is widely adopted, as it considers non-linear effects and investigates the influence of reciprocal interactions among factors on the predicted response.

$$\begin{array}{c}Width=3.017+0.1025A+0.1025B-0.105C-0.015AC+0.025BC-0.008A^2+0.0117B^2-0.0183C^2\\ \begin{array}{cc}\hfill Heigth=0.61 +& 0.10625A+0.0137B-0.077C+0.025AB-0.0375AC+0.0075BC-0.0375A^2\hfill \\ & - 0.0025B^2+0.005C^{2}HAZ\hfill \\ & =0.52-0.0525A+0.0387B-0.04625C-0.0025BC-0.01625A^2-0.0087B^2\hfill \\ & - 0.00375C^2\hfill \end{array}\\ HAZ=0.52-0.0525A+0.0387B-0.04625C-0.0025BC-0.01625A^2-0.0087B^2-0.00375C^2\end{array}$$

The predicted versus actual values for three different response variables derived from the model are presented in Figure 7. Based on the alignment of the data points along the diagonal reference line, each subplot demonstrates a strong linear correlation, suggesting that the model’s predictions and experimental measurements are in good agreement. Moreover, the coefficients of determination (R-squared) for the models were 0.93, 0.99, and 0.97 for the width, height, and HAZ, respectively, thus indicating a good fit for the models.

It is well established in the literature that the deposition of pure copper using infrared (IR) lasers presents significant challenges [13]. This is primarily due to the high reflectivity of copper in the IR wavelength range, which leads to poor energy absorption and consequently results in melt pool instability. Such instability often manifests as defects, including balling and excessive spattering. Additionally, high thermal conductivity of copper can hinder complete melting of the powders, contributing to lack-of-fusion defects and porosity within the deposited material. The large mismatch in the coefficient of thermal expansion between the copper deposit and the substrate further exacerbates the issue, potentially inducing high tensile stresses and cracking in the HAZ.

Therefore, in the present study, the DOE approach was employed to systematically explore and identify a narrow process window capable of producing a stable melt pool and mitigating these challenges. Furthermore, to diminish the heat sink effect of the baseplate and minimize cracking, the baseplate was preheated to 200 °C before deposition. As shown in Figure 5a, no cracks were observed at the Cu-baseplate interface, and the deposition exhibited minimal porosity, indicating robust bonding and defect control. The hardness profile revealed a smooth transition from ~170 HV in the 316 L baseplate to ~100 HV in the deposited Cu, aligning with the upper range expected for pure Cu (50–100 HV, depending on microstructure and processing). The elevated hardness is a consequence of the very high cooling rates at the melt-pool boundary during DED, typically on the order of 3 × 10³–5 × 10⁴ K·s⁻¹, which promote rapid solidification [38,39]. The accelerated solidification refines the cellular/dendritic structure and reduces grain/feature size, which in turn increases hardness through the Hall–Petch effect (${\sigma }_y\propto d^{-1/2}$) [40]. Moreover, the hardness values for the recycled Cu deposition were in good agreement with those deposited with virgin powder reported in the literature [33]. These results demonstrate the efficacy of our approach in overcoming the inherent challenges of Cu deposition via DED. Similarly, fine-tuning of process parameters has been applied to also improve LPBF processing of copper with IR laser [41], although current trends are evolving towards the use of laser sources with different wavelengths [42]. As a matter of fact, beyond assessing the compatibility of recycled powders with the DED process, another beneficial outcome was identified. Indeed, by exploiting IR lasers, it would be possible to leverage commercially available machines with well-established process setups, paving the way for reliable production of multi-material components.

4.4. Environmental Assessment

Based on the LCA comparison of conventional versus recycled copper powder production for AM, the f3nice recycling-based process significantly reduces environmental impacts, cutting global warming potential by over 70% and acidification by 98%. Besides shedding light on the environmental assessment of copper feedstock production for AM from waste metal, which, to the best of the authors’ knowledge, has not been explored so far by the research community, these results underline the importance of feedstock origin and support the adoption of circular economy strategies in AM. As material sourcing is a major contributor to the environmental burden of advanced manufacturing technologies, prioritizing secondary raw materials is essential. Future research should explore other recycled copper sources, include end-of-life scenarios for a full cradle-to-grave perspective, and benchmark copper against other AM-relevant metals like aluminum and titanium to better guide sustainable material selection.

5. Conclusions

A novel approach to the production of AM-grade copper powders from scrap metal was presented. The analysis of the results of this study led to the following conclusions:

• The methodology described in this study ensured an efficient way to upcycle copper metal from waste through transformation into powders by ultrasonic atomization. The final copper concentration was increased up to ~99.5% wt.% with minimal content of impurities.
• Printability tests demonstrated the compatibility of the atomized powders with DED manufacturing technology, overcoming the major challenges related to the unfavorable interactions between copper and IR laser.
• Recycled copper powders effectively reduced the environmental impact of feedstock manufacturing, resulting in a considerable reduction of global warming potential by over 70% as the key impact factor.

Overall, the feasibility of the approach for the recovery of such an important critical raw material as copper was assessed. Moreover, the applicability of the transformed scrap as feedstock to be used in advanced processes such as AM was proven, despite current technological limitations of conventional DED processes. Consequently, this study represents the basis for the identification and implementation of a short supply chain model, where scrap metal could be upcycled directly into AM feedstock, further increasing the value of previously wasted raw materials.

Additional studies will be needed to evaluate the printability of recycled copper powders with laser sources more suitable for processing copper-based materials, such as green and blue lasers. In addition, the impact of feedstock on achievable thermal and electrical properties of AM components should be assessed to certify the high quality of powder feedstock for the manufacturing of relevant industrial components such as, for example, windings for electric motors, induction coils, tools for injection molding, heat exchangers, and heat sinks. Future research could also include a Life Cycle Costing (LCC) analysis to complement the LCA and provide economic insights alongside environmental performance.

In conclusion, this study highlights the environmental benefits of using recycled copper powder in additive manufacturing, demonstrating its potential to support more sustainable and circular production models. As AM continues to grow, integrating secondary raw materials will be key to reducing its environmental footprint.