New Trends in Powder Engineering and Additive Manufacturing (Editorial Board Members’ Collection Series)

1. Introduction and Scope

The production of metal alloys and compounds in powder form has traditionally been linked to techniques such as gas atomization or mechanical alloying. For the manufacture of bulk pieces and components, powder metallurgy routes based on the pressing and sintering of powders have been used. In recent decades, additive manufacturing techniques have appeared as an alternative to produce parts with complex geometry and reduce the loss of material. The integration of powder engineering and additive manufacturing has driven the development of advanced materials and more efficient processes. Designing powders with controlled characteristics allows for improved repeatability, reduced defects, and expanded additive manufacturing applications (in demanding industries such as aerospace, automotive, and biomedical). Together, both disciplines allow optimization from the raw material to the final product, enhancing manufacturing innovation.

This Special Issue “New Trends in Powder Engineering and Additive Manufacturing” focuses on powder metallurgy, which is a set of fabrication techniques related to three major processing steps. First, the precursor material is physically powdered (micro- or nanometric particles). Second, the powder is consolidated to obtain bulk specimens (traditionally by injection into a mold or passed through a dye). Third, pressure and/or temperature is applied. Powder metallurgy is now also applied in the production of composites. Furthermore, new topics have emerged, such as additive manufacturing, MA, the circular economy or raw materials.

2. Overview of the Contributions

A total of eight peer-reviewed articles were published as part of this Special Issue. They cover several of the key aspects of the powder engineering and additive manufacturing process, ranging from powders to AM bulk parts. Although an incomplete overview (only eight manuscripts), it provides information on some of the most interesting aspects and materials.

The articles cover several topics, such as the correlations between processing and the microstructure or between the microstructure and the mechanical properties, as well as the corrosion resistance.

Four articles analyze stainless steel, focusing on the mechanical response, corrosion, and wear resistance. Steels are a traditional topic in metal science and engineering, due to their use in many fields such as biomedical, construction, automotive, chemical, aerospace, marine, nuclear, and petrochemical.

One article analyzes the corrosion resistance of 316L stainless steel [1]. One pathway to improve the corrosion resistance of stainless steels is the addition of chromium (<12 weight %). Its corrosion resistance in aggressive conditions favors its applicability in the nuclear, biomedical, marine, and petrochemical industries. The 316L stainless steel was produced via ball milling followed by spark plasma sintering, an additive manufacturing technique. This study shows that the reduction in the grain size negatively affects the electrochemical passivation behavior. However, the passivation in HNO₃ before consolidation may mitigate this effect. The corrosion resistance was improved by the prior passivation of the powder (especially in small particle sizes). On the other hand, the decrease in grain size provoked the reduction in the length of the passive domain.

In another work, additive manufacturing extrusion was applied to produce 316L stainless steel [2]. Different amounts of copper (Cu) powder were added to the paste composition to reduce the sintering temperature (by promoting persistent liquid phase sintering). The authors recognized that no adequate densification was achieved, which would be necessary to yield competitive properties. One feature of this study was the use of methylcellulose as an alternative binder to wax-based binders. The relative density and Vickers hardness increased with the Cu content.

Another work focused on 316 austenitic steels and nickel-based superalloys produced using laser powder bed fusion [3] to fabricate multi-material components. AM technology is a pathway for the development of Functionally Graded Materials (FGMs). One of the principal interests of additive manufacturing is the customization of components and parts according to the required geometry and properties. In this case, the authors discussed its applicability to the aerospace, energy, biomechanical, automotive, and marine fields. The analysis of the results confirmed the feasibility of producing FGM components at the layer level. The interface of the samples produced appeared to be free of defects such as lack of fusion and delamination, which is a signal of a good metallurgical bond.

The final work related to steels explored the technical feasibility of the isostatic hot pressing (HIP) fabrication of integral bimetallic components using supercritical carbon dioxide, turbomachinery steel powder, and nickel alloy [4]. There was a dense distribution of Ti-rich carbonitrides, and alumina particles were found to decorate prior particle boundaries near the interface on the 282 side, affecting both the tensile strength across the interface and the tensile failure location. A pilot-scale bimetallic SS415/282 pipe was developed to show the viability of the scale-up. In addition, the simulations performed with DICTRA software helped to explain the interdiffusion and phase evolution at the interface between steel and alloy 282 during the HIP cycle.

Three articles focused on Al-based alloys (Al-Mg-based, Al-Fe-based, Al-Zn-based). These alloys are used in the automotive, aerospace, and transport industries. They commonly have high strength, good plasticity, and high performance in corrosion resistance. Thus, it is expected that aluminum alloys will effectively reduce the self-weight of components, while maintaining sufficient strength and toughness.

In one of the articles, two Al-based alloys (Al-Fe-Si-Cr-Ni) were produced via gas atomization. This technique favors the formation of spherical particles that can be sieved and used in additive manufacturing processes. The authors recommend minimizing the internal porosity of the powders and discuss the influence of the alloying element content on the solidification processes [5]. Gas atomization has made it possible to increase the solid solubility of elements with a low diffusion coefficient (Fe, Ni, Mn, Zr, Cr) in the α-Al matrix. As a result, it has led to (a) the formation of metastable phases and (b) a higher performance of aluminum alloys at high temperatures.

Another work analyzed the high-temperature microstructural and mechanical properties of the Al-Mg-Sc-Zr alloy processed by the additive manufacturing technique of laser powder bed fusion (LPBF), highlighting its potential for aerospace applications [6]. The researchers also studied the microstructural evolution by highlighting the formation of nano-Al₃(Sc, Zr) particles that reinforce the alloy. The reinforcement mechanisms were heterogeneous nucleation and grain refinement. Complementary fracture tests revealed ductile behavior, with abundant dimples on the fracture surfaces, which was attributed to the second-phase particles.

In a third Al-based article, the Al-rich Al-Zn-Mg-Si alloy was produced via laser-directed energy deposition, DED [7]. In train railways, it is good to repair aluminum alloy through directional energy deposition in order to (a) reduce the cost and (b) improve the performance of the aluminum alloy. The analysis of the results showed low porosity and a correct bonding interface. The grains in the repaired area were columnar crystals growing vertically along the boundary of the melt pool. A sharp decline in tensile strength and hardness from the heat-affected zone to the matrix was detected, which was attributed to the large temperature gradient in the deposition process, consequently provoking the softening of the substrate. Due to the softening, an additional heat treatment was recommended to improve the mechanical response.

In the final study, zinc dendritic particles were produced via electrolysis from an alkaline electrolyte [8]. The formed dendrites showed a (002) preferred orientation, which was strong, as the precursors of the dendrites had a (101) (002) preferred orientation. This (002 plane) orientation was explained by the low surface energy. Likewise, zinc dendrites formed under diffusion control during electrolysis. At low overpotentials (−100 mV), irregular particles called dendrite precursors are generated. At higher overpotentials (−160 mV and above), dendrites of different shapes form, from compact and massive to branched in 2D and 3D. These could be applied in rechargeable batteries and catalysts.

3. Conclusions and Outlook

The research compiled in this Special Issue effectively demonstrates the dynamic and multifaceted nature of current advancements in powder engineering and additive manufacturing. The collected contributions underscore the increased technological and scientific relevance of steels, Al alloys, and Zn in terms of applications in different fields such as batteries, catalysis, aerospace, nuclear, biomedical, marine, petrochemical, and so on. These applications focus on the mechanical and functional properties as well as the corrosion and wear resistance.

The findings demonstrate that careful control of processing conditions and optimized microstructure favor significant property improvements. Together, the contributions gathered in this Special Issue offer valuable insight and experimental support for the design of robust, cost-effective, and high-performance pieces and components. This Special Issue can serve a reference for further academic and technological research on powder technology and additive manufacturing.