Additive Manufacturing, AM, is considered to be environmentally friendly when compared to conventional manufacturing processes. Most researchers focus on resource consumption when performing the corresponding Life Cycle Analysis, LCA, of AM. To that end, the sustainability of AM is compared to processes like milling. Nevertheless, factors such as resource use, pollution, and the effects of AM on human health and society should be also taken into account before determining its environmental impact. In addition, in powder-based AM, handling the powder becomes an issue to be addressed, considering both the operator´s health and the subsequent management of the powder used. In view of these requirements, the fundamentals of the different powder-based AM processes were studied and special attention paid to the health risks derived from the high concentrations of certain chemical compounds existing in the typically employed materials. A review of previous work related to the environmental impact of AM is presented, highlighting the gaps found and the areas where deeper research is required. Finally, the implications of the reuse of metallic powder and the procedures to be followed for the disposal of waste are studied.2 of 25 sold in 2016 was 983, whereas, in the year 2017 this value rose to 1768 units, which implies an 80% increase [1].As far as economy and sustainability are concerned, AM offers several advantages over conventional manufacturing techniques, which confers many potential applications to AM in diverse industrial sectors, such as automotive, aerospace, biomedical, energy, and consumer goods [4]. In the aerospace industry, for example, AM enables aerospace motorists to create blades with much more complex internal cooling channels, allowing engines to run at higher temperatures and thus increase their performance [5]. In the report presented by the National Institute of Standards and Technology (NIST) of the U.S. Department of Commerce, it is stated that in aerospace engines titanium parts are machined down to size from large initial blocks, which leads to more than 90% waste material, material waste that could be reduced by using AM [6]. The European Commission in the Digital Transformation Monitor of 2017 presented similar numbers, where the disruptive nature of 3D printing was studied. It was estimated that by 2050, AM could save up to 90% of the raw material needed for manufacturing [3].Nonetheless, the possibilities of AM are not only limited to a reduction of raw material usage. The possibility of manufacturing lighter components could lead to energy savings, estimated between 5% and 25% by 2050, as well as a reduction in manufacturing costs of around 4-21% for the same period [7]. This trend is applicable to different industrial sectors. For example, SmarTech expects the overall market for AM in automotive to reach 5.3 billion USD in revenues by 2023 and to achieve 12.4 billion USD by 2028 [8].The lack of European and international standardization related to AM is proving to be an impediment to the...

Tooling in the die and mould industry is subjected to high-wear and high-temperature environments, which often leads to the premature failure of this high-added-value tooling. When severe damage occurs, an alternative to replacing the whole component consists of the repair by laser-directed energy deposition (L-DED). For that end, intermediate layers are commonly employed as buffer material, where introducing a functionally graded material (FGM) might be beneficial to avoid material incompatibilities and improve the overall performance of the tooling. In the present work, an FGM composed of gradient AISI 316L to AISI H13 has been manufactured, and its microstructure and hardness analysed. Firstly, cracking owing to the formation of brittle intermediate phases has been detected. Secondly, an increase of the hardness and a decrease of the corrosion resistance has been observed when transitioning from AISI 316L to AISI H13. Thirdly, despite the FGM composition evolving linearly, nonlinear material properties such as hardness and corrosion have been observed, which are conditioned by the microstructure formed during the L‑DED process and the nonlinear influence of the composition of steel on such properties. Consequently, nonlinear compositional gradients are recommended if linear mechanical properties are to be obtained in the case of steel FGMs.

Multi-material structure fabrication has the potential to address some critical challenges in today’s industrial paradigm. While conventional manufacturing processes cannot deliver multi-material structures in a single operation, additive manufacturing (AM) has come up as an appealing alternative. In particular, laser-directed energy deposition (L-DED) is preferred for multi-material AM. The most relevant applications envisioned for multi-material LDED are alloy design, metal matrix composites (MMC), and functionally graded materials (FGM). Nonetheless, there are still some issues that need to be faced before multi-material L-DED is ready for industrial use. Driven by this need, in this literature review, the suitability of L-DED for multi-material component fabrication is first demonstrated. Then, the main defects associated with multi-material LDED and current opportunities and challenges in the field are reported. In view of the industrial relevance of high-performance coatings as tools to mitigate wear, emphasis is placed on the development of MMCs and FGMs. The identified challenges include—but are not limited to—tightly controlling the composition of the multi-material powder mixture injected into the melt pool; understanding the influence of the thermal history of the process on microstructural aspects, including the interactions between constituents; and studying the in-service behaviours of MMCs and FGMs with regard to their durability and failure modes.

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