Abstract In powder bed fusion of metal with laser beam (PBF-LB/M), repetitive melting and solidification of newly added layers lead to thermal stresses and distortions during part build-up. Particularly at critical component features such as unsupported overhangs, super-elevated edges pose a risk in terms of crashes with the recoating system during powder spreading. Damaged recoater lips lead to irregularities in the form of stripes in the powder bed. These local inhomogeneities cause lack-of-fusion porosity and geometric defects on the part surface. However, quantitative information on important quality aspects, such as tensile properties, dimensional accuracy, roughness, and hardness of parts printed under irregular powder bed conditions is scarce. Here, we show that samples from build jobs with recoater crashes maintain their elastic tensile properties and hardness, but lose elongation at break. Finite-element simulations of in-process distortions are used to design an artifact that intentionally damages the silicone rubber lip of the recoater but does not cause machine breakdown. The lowest mean yield strength of the damage-affected samples is 243 MPa, which is still within the material data sheet limits for AlSi10Mg. Therefore, recoater crashes do not necessarily result in rejects, but users must consider the likely presence of porosity.
Abstract Laser-based powder bed fusion of metals exhibit process-induced anisotropy and residual stresses, making post-manufacturing heat treatment occasionally beneficial. For AlSi10Mg, a T6 heat treatment (solution annealing, quenching, artificial aging) is recommended. Nevertheless, mechanical strength decreases as (1) the eutectic Si network dissolves, (2) the amount of dissolved Si in the Al grains decreases, and (3) the size of the silicon particles and aluminum crystals increases during solution annealing. This changes the mechanical characteristics directly or by influencing the formation of precipitation during the aging process. The success of solution annealing is affected by the annealing duration and the part’s temperature at the moment of quenching. Short annealing durations dissolve a sufficient amount of Si and Mg in the Al matrix. Therefore, both the annealing temperature’s holding duration and the heating process significantly impact the resulting microstructure. In this study, samples of different shape and size where subjected to a T6 heat treatment with different solution annealing temperatures and durations. The influence on mechanical properties after quenching and aging was investigated by hardness and tensile tests. Maximum strength is achieved by quenching promptly upon reaching the solution annealing temperature, while longer durations reduce strength as explained by the Larson-Miller parameter.
Abstract Laser‐based powder bed fusion (PBF‐LB) has gained prominence in the realm of additive manufacturing of metals. This technique utilizes a laser beam to consolidate powder layers, which inherently introduces high thermal gradients and rapid cooling rates. This results in characteristic process effects, including inhomogeneities, surface roughness, anisotropy, and residual stress, which play a pivotal role in altering the fatigue properties of the manufactured components. This paper presents fatigue tests involving samples of AlSi10Mg manufactured using PBF‐LB with varying surface roughness and residual stress. An approach to predict fatigue life based on stress amplitude, residual stress, and crack size is presented, using a smooth sample as a reference. An empirical model for fatigue life prediction is developed from experimentally measured values of fatigue life, peak surface roughness, and residual stress.
Abstract The adoption of Design for Additive Manufacturing (DfAM) practices brought new industrial components embedding unconventional shapes such as lattice structures or freeform surfaces resulting from topological optimisations. As a drawback of design freedom, designers need to use thermal post-processing to achieve homogeneous properties in metal 3D printing. This contribution analyses the effect of T6-like heat treatment on the hardness of a complex component. Hardness values are reported along with good design practices for effective thermal post-processing to complement the DfAM knowledge base.
Abstract Fatigue tests were performed with samples of AlSi10Mg produced by PBF-LB/M. The failure is caused by inhomogeneities nearby or at the surface of the samples. Therefore, the fatigue strength depends on the crack growth behavior at inhomogeneities under the local stress state at the surface, including residual stresses. For a given size of the failure-causing inhomogeneity, the fatigue lifetime can be described using a crack growth law proposed by Murakami et al. The fatigue limit is given by the threshold value of fatigue crack growth according to the approach of El Haddad. Knowing the distribution of the maximum value of inhomogeneity size in a specimen, it is possible to estimate the S–N curve for 10%, 50%, and 90% crack probability.
Abstract Due to various causes, process interruptions during powder bed fusion of metal with laser beam (PBF-LB/M) can occur. This can be performed deliberately, e.g. as part of sensor integration or hybrid manufacturing. However, unplanned interruptions are also possible, for example, due to a power outage. In particular, long-term interruptions may result in significant quality losses, making it necessary to cancel the build job. Depending on the extent of the print job and the location of the interruption, this can mean a major economic loss. Most of the previous studies have found only minor reduction of the mechanical properties. However, these studies often dealt with the effect of planned interruptions and relatively short interruptions of about 1 h. Significantly longer interruption times are also realistic, especially when they occur overnight or during weekends. The aim of this study is to investigate the effects on the component quality of a process interruption when the manufacturing process is continued several hours after the interruption. For this purpose, the effects of different interruption durations (1, 4, 10 and 16 h) on the microstructure, hardness, tensile strength and fatigue properties of the PBF-LB/M-fabricated components made of AlSi10Mg were investigated. In addition, the layer shift resulting from the interruption is measured and described geometrically. The results show that for AlSi10Mg specimens in which the layer shift was removed and which are not highly loaded, an unplanned long-term process interruption up to 10 h does not result in a significant loss of quality under the considered conditions. Furthermore, it is apparent that the procedure for restarting the process is very important for the resulting component quality.
Abstract Osseointegration is highly desirable for implants used for bone replacement. Polyetheretherketone (PEEK) is an attractive material due to its characteristics such as high biocompatibility and Young's modulus similar to human bones. However, PEEK is bioinert, meaning cells do not adhere and proliferate on its surface. This problem is addressed in this study, with the goal of enhancing osseointegration of additively manufactured PEEK. The influences of surface modifications and porous structures on cellular behavior were assessed by wettability and in vitro tests with subclone of the human osteosarcoma cell line‐2 osteoblasts. Overall, the combination of surface modification, type of plasma process used, atmospheric pressure versus vacuum‐based, and surface structuring, especially gyroid structures, improve the cellular proliferation on PEEK. Therefore, its ability to enhance osseointegration is highly promising.
