Soundness of additively manufactured parts depends on a lot of process and geometrical parameters. A wrong process design leads to defects such as lack of fusion or keyhole porosity that have a detrimental effect on the mechanical properties of the printed parts. Process parameter optimization is thus a formidable challenge that requires in general a huge amount of experimental data. Among the others, heat source power and scan speed are the most defects-affecting parameters to be optimized. The energy density is used in literature to quantify their combination. Unfortunately, in different works it was demonstrated that it fails if used as design parameter mainly because it does not take into account the material properties and the interaction between heat source and the powder bed. In this contribution, a modified volumetric energy density equation that takes into account the powder-heat source interaction to optimize the combination of power-scan speed values for porosity assessment in powder bed fusion process design is proposed and verified on both AlSi10Mg alloy and Maraging steel 300.

Additive manufacturing (AM) offers the potential to economically produce customized components with complex geometries in a shorter design-to-manufacture cycle. However, the basic understanding of the fatigue behavior of these materials must be substantially improved at all scale levels before the unique features of this rapidly developing technology can be used in critical load bearing applications. This work aims to assess the fatigue strength of Ti–6Al–4V smooth and circular notched samples produced by selective laser melting (SLM). Scanning Electron Microscopy (SEM) was used to investigate the fracture surface of the broken samples in order to identify crack initiation points and fracture mechanisms. Despite the observed fatigue strength reduction induced by circular notched specimens compared to smooth specimens, notched samples showed a very low notch sensitivity attributed both to hexagonal crystal lattice characteristics of tempered alpha prime grains and to surface defects induced by the SLM process itself.

Despite the great potential of Mg and its alloys as material for biodegradable implants, their low resistance to the simultaneous action of corrosion and mechanical stresses in the human body have hampered their use. Stress Corrosion Cracking has been reported as one of the most critical failure modes to overcome to allow such materials to be clinically applied. Thus, in this paper we investigate the effect of Equal Channel Angular Pressing (ECAP) on the Stress Corrosion Cracking (SCC) susceptibility of the AZ31 Mg alloy. To do so, AZ31 alloy has been subjected to 1, 2 and 4 passes of ECAP, and the samples so obtained have then been tested by means Slow Strain Rate Tests (SSRTs) in Simulated Body Fluid (SBF) at 37 °C. Samples subjected to one pass of ECAP are shown to be less susceptible to SCC compared to the material in the as-received condition, while further ECAP processing (2 and 4 passes) are found to worsen the SCC susceptibility. To understand the different SCC susceptibilities shown by the differently ECAPed samples, microstructural analyses, potentiodynamic polarization curves, hydrogen evolution experiments and Scanning Electron Microscopy (SEM) analyses of the fracture surfaces were carried out. The improved corrosion resistance of the samples subjected to 1 pass of ECAP compared to the samples in the as received condition (due to a finer grain size) and to the samples subjected to 2 and 4 passes (due to a more favourable texture evolution) represents the reason of their reduced SCC susceptibility.

The fatigue behavior and fracture mechanisms of additively manufactured Ti-6Al-4V specimens are investigated in this study. Three sets of testing samples were fabricated for the assessment of fatigue life. The first batch of samples was built by using Laser-Engineered Net Shaping (LENS) technology, a Direct Energy Deposition (DED) method. Internal voids and defects were induced in a second batch of samples by changing LENS machine processing parameters. Fatigue performance of these samples is compared to the wrought Ti-6Al-4V samples. The effects of machine-induced porosity are assessed on mechanical properties and results are presented in the form of SN curves for the three sets of samples. Fracture mechanisms are examined by using Scanning Electron Microscopy (SEM) to characterize the morphological characteristics of the failure surface. Different fracture surface morphologies are observed for porous and non-porous specimens due to the combination of head write speed and laser power. Formation of defects such as pores, unmelted regions, and gas entrapments affect the failure mechanisms in porous specimens. Non-porous specimens exhibit fatigue properties comparable with that of the wrought specimens, but porous specimens are found to show a tremendous reduced fatigue strength.