The current paper is devoted to classification of powder-bed additive manufacturing (PB-AM) techniques and description of specific features, advantages and limitation of different PB-AM techniques in aerospace applications. The common principle of “powder-bed” means that the used feedstock material is a powder, which forms “bed-like” platform of homogeneous layer that is fused according to cross-section of the manufactured object. After that, a new powder layer is distributed with the same thickness and the “printing” process continues. This approach is used in selective laser sintering/melting process, electron beam melting, and binder jetting printing. Additionally, relevant issues related to powder raw materials (metals, ceramics, multi-material composites, etc.) and their impact on the properties of as-manufactured components are discussed. Special attention is paid to discussion on additive manufacturing (AM) of aerospace critical parts made of Titanium alloys, Nickel-based superalloys, metal matrix composites (MMCs), ceramic matrix composites (CMCs) and high entropy alloys. Additional discussion is related to the quality control of the PB-AM materials, and to the prospects of new approaches in material development for PB-AM aiming at aerospace applications.
The design of aluminium–graphite metal matrix composites (MMCs) with advanced mechanical properties and high corrosion resistance is in demand for aerospace, transportation, and industrial applications. Breakthroughs in this field are limited due to the tendency of aluminium–graphite MMCs to corrode. In the present research, aluminium-based MMCs were produced by a relatively novel combined two-staged method. Multiwall carbon nanotubes (MWCNTs) were added into molten Al1070 and processed by high-pressure die casting followed by cyclic extrusion. For the composites produced by this method, it was previously demonstrated that mechanical properties are improved in comparison with pure aluminium alloys. In the current study, the manufactured Al–MWCNT composites were investigated by electrochemical tests (such as open circuit potential), potentiodynamic tests, linear polarization tests, and electrochemical impedance spectra to understand the corrosion resistance of the obtained composite material. The experimental testing of the corrosion resistance of Al–MWCNT MMCs showed that due to the advantages of the fabrication method, the addition of CNTs to aluminium does not cause a radical decrease of corrosion resistance.
Additive manufacturing of Nitinol is a promising field, as it can circumvent the challenges associated with its conventional production processes and unlock unique advantages. However, the accompanying surface features such as powder adhesions, spatters, ballings, or oxide discolorations are undesirable in engineering applications and therefore must be removed. Plasma electrolytic polishing (PeP) might prove to be a suitable finishing process for this purpose, but the effects of post-processing on the mechanical and functional material properties of additively manufactured Nitinol are still largely unresearched. This study seeks to address this issue. The changes on and in the part caused by PeP with processing times between 2 and 20 min are investigated using Nitinol compression springs manufactured by Laser Beam Melting. As a benchmark for the scanning electron microscope images, the differential scanning calorimetry (DSC) measurements, and the mechanical load test cycles, conventionally fabricated Nitinol springs of identical geometry with a medical grade polished surface are used. After 5 min of PeP, a glossy surface free of powder adhesion is achieved, which is increasingly levelled by further polishing. The shape memory properties of the material are retained without a shift in the transformation temperatures being detectable. The decreasing spring rate is primarily attributable to a reduction in the effective wire diameter. Consequently, PeP has proven to be an applicable and effective post-processing method for additively manufactured Nitinol.
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