This work aims at investigating the causes affecting the dimensional and geometrical accuracy of holes in metal binder jetting stainless steel parts. Parallelepiped samples with a through hole were produced using AISI 316L and 17-4PH powders, differing for diameter (3, 4, 5 mm), and position of the axes with respect to the building plane (6, 9, 12 mm distance). Dimensions and geometrical characteristics were measured at green and sintered state by a coordinate measuring machine, determining the dimensional change and the geometrical characteristics. As expected, the shrinkage of linear dimensions is anisotropic; moreover, change in volume and sintered density are significantly affected by the position in the printing chamber. Higher shrinkage was measured along building direction (Z) – 18.5 ÷ 19.5%, than in the building plane – 16.5 ÷ 17.5%, and slightly higher shrinkage – 0.5 ÷ 0.8% was measured along powder spreading direction (X) than binder injection direction (Y). A variation up to 3% in relative density of sintered parts depending on the position in the building plane was observed in 316L. The dimensional change of diameters generally confirmed the shrinkage predicted by the model previously developed—difference between real and expected dimensional changes lower than 3%, except for three geometries (4 ÷ 6%). The cylindricity form error of sintered parts was strongly underestimated by the prediction model (up to 0.15 mm), but underestimation was considerably reduced (generally lower than 0.05 mm) adding the cylindricity form error due to printing. Dimensional and geometrical accuracy of holes are strongly affected by shape distortion of the parallelepiped geometry, in turn due to layer shifting and inhomogeneous green density during printing, and to the effect of frictional forces with trays during sintering. Gravity load effect was also observed on the holes closest to the building plane. Future work will improve the reliability of the prediction model implementing the results of the present work.

As the hydrogen market is projected to grow in the next decades, the development of more efficient and better-performing polymer electrolyte membrane fuel cells (PEMFCs) is certainly needed. Water management is one of the main issues faced by these devices and is strictly related to the employment of fluorinated materials in the gas diffusion medium (GDM). Fluorine-based polymers are added as hydrophobic agents for gas diffusion layers (GDL) or in the ink composition of microporous layers (MPL), with the goal of reducing the risk of membrane dehydration and cell flooding. In this review, the state of the art of fluorinated polymers for fuel cells is presented. The most common ones are polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP), however, other compounds such as PFA, PVDF, PFPE, and CF₄ have been studied and reported. The effects of these materials on device performances are analyzed and described. Particular attention is dedicated to the influence of polymer content on the variation of the fuel cell component properties, namely conductivity, durability, hydrophobicity, and porosity, and on the PEMFC behavior at different current densities and under multiple operating conditions.

Friction and wear are responsible for around 23% of the energy consumption in transportation, manufacturing, power generation, and residential sectors. Employed components are exposed to a wide range of operational conditions, therefore a suitable material design is fundamental to decreasing tribological issues, energy consumption, costs, and environmental impact. This study aims to analyze the effect of different solid lubricants on the suitability of copper matrix composites (CuMCs) as a potential solution to reduce the depletion of sliding electrical contacts working under extreme conditions. CuMCs samples are produced by cold-pressing and sintering to merge a high electrical conductivity with the lubricant effect supplied by different species, namely tungsten disulfide micro-powder (WS₂), inorganic fullerene-like (IF) tungsten disulfide nanoparticles, and graphene nanoplatelets (GNP). The crystalline structure of the pristine and composite materials is characterized via XRD. The electrical tests show a small decrease of conductivity compared to pure copper, due to the insulating effect of WS₂; however, the measured values are still adequate for conduction purposes. Micro-scratch and wear tests highlight the positive effect of the combination of WS₂ structures and GNP. The friction coefficient reduction leads to the possibility of extending the lifetime of the components.