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Binder jetting of 17-4PH martensitic stainless steel is of great interest to several industries that could exploit the higher degree of geometrical complexity granted by 3D printing, thus this paper aims at providing a comprehensive description of the material development throughout the multiple manufacturing stages and treatments.

In this work, insight into the as-sintered 17-4PH microstructure and the manufacturing process effects on the copper precipitation is provided. Furthermore, conventional ageing treatments were applied to the specimens starting from either the as-sintered or the solution-annealed state and studied with particular attention to the microstructure and the resulting mechanical properties.

The analysis of the as-sintered microstructure revealed a continuous δ ferrite network along martensitic grains, with Cu-rich phases within the ferritic phase. Solution annealing was able to redistribute the alloying elements within the matrix and limit the continuity of the ferritic network leading to an enhancement in ductility. On the contrary, the direct ageing treatments performed on the as-sintered microstructure lead to overageing of the Cu-precipitates and impairing of the tensile properties compared to those starting from solution annealed condition. Nonetheless, hardness remains comparable independently from the ageing temperature and the ferritic network retains its morphology and distribution.

A stepwise description of the microstructural development throughout thermal treatments is provided granting the chance to design the most convenient post-processing route to achieve the required mechanical properties with a minimisation of energy and cost consumption.

Binder jetting is a promising route to produce complex copper components for electronic/thermal applications. This paper aims to lay a framework for determining the effects of sintering parameters on the final microstructure of copper parts fabricated through binder jetting.

The knowledge gained from well-established powder metallurgy processes was leveraged to study the densification behaviour of a fine high-purity copper powder (D₅₀ of 3.4 µm) processed via binder jetting, by performing dilatometry and microstructural characterization. The effects of sintering parameters on densification of samples obtained with a commercial water-based binder were also explored.

Sintering started at lower temperature in cold-pressed (∼680 °C) than in binder jetted parts (∼900 °C), because the strain energy introduced by powder compression reduces the sintering activation energy. Vacuum sintering promoted pore closure, resulting in greater and more uniform densification than sintering in argon, as argon pressure stabilizes the residual porosity. About 6.9% residual porosity was obtained with air sintering in the presence of graphite, promoting solid-state diffusion by copper oxide reduction.

This paper reports the first systematic characterization of the thermal events occurring during solid-state sintering of high-purity copper under different atmospheres. The results can be used to optimize the sintering parameters for the manufacturing of complex copper components through binder jetting.

This paper aims to investigate the structure and scratch resistance properties of gas nitrided pure iron samples.

The effects of material strain hardening and amount of grain boundaries exposed on nitriding surface were evaluated by cold rolling the starting samples to different reduction levels before gas nitriding.

The study finds that nitriding without any prior cold rolling produced a comparatively wide compound layer with a large fraction of porous zone featuring low scratch hardness values but no evidence of damage. On the contrary, cold rolling before nitriding led to a more irregular and thinner compound layer with reduced amount of porous zone and much finer nitrides in the diffusion zone. Scratch hardness was increased but failure mechanism changed by generation of conformal cracks within the track groove and the appearance of discontinuous spallation at high loads.

One of the issues of great industrial importance concerning nitriding of steels is the need to predict the extent of the nitrided layer in products showing small variations in microstructure or in extent of cold working due to complex manufacturing cycles. Despite the practical importance, relatively little information is available in literature about these issues. The present paper is therefore aimed at investigating the structure and mechanical properties of pure iron samples, gas nitrided with different amounts of cold working and microstructural conditions.