The advancement in additive manufacturing encourages the development of simplified tools for deep and swift research of the technology. Several approaches were developed to reduce the complexity of multi-track modeling for additive manufacturing. In the present work, a simple heat source model called concentrated heat source was evaluated for single- and multi-track deposition for directed energy deposition. The concentrated heat source model was compared with the widely accepted Goldak heat source model. The concentrated heat source does not require melt pool dimension measurement for thermal model simulation. Thus, it reduces the considerable time for preprocessing. The shape of the melt pool and temperature contour around the heat source was analyzed for single-track deposition. A good agreement was noticed for the concentrated heat source model melt pool, with an experimentally determined melt pool, using an optical microscope. Two heat source models were applied to multi-track 3D solid structure thermo-mechanical simulation. The results of the two models, for thermal history and residual stress, were compared with experimentally determined data. A good agreement was found for both models. The concentrated heat source model reported less than the half the computational time required for the Goldak model. The validated model, for 3D solid structure thermo-mechanical simulation, was used to analyze thermal stress evolution during the deposition process. The material deposition on the base plate at room temperature results in lower peak temperatures in the layers near the base plate. Consequently, the higher thermal stress in the layers near the base plate was found, compared to the upper layers during the deposition process.

This work is focused on the influence of heat treatment on the mechanical properties of duplex steel SAF 2507 produced by direct laser deposition (DLD). Duplex steels combine the advantages of ferritic and austenitic steels and reach excellent combination of mechanical and corrosion properties. The best properties are achieved by approximately equal phase ration of ferrite and austenite. Therefore, the proportion of austenite and ferrite before and after heat treatment was investigated within the study. Direct laser deposition technology was used for sample production. The DLD works on the principle of laser melting of the feedstock material (powder), which is carried by a protective gas into the nozzle. The material is successively deposited on the build platform. This technology can be used as an additive manufacturing process for surface repairs and component modifications. In this experimental study, the samples were deposited and subsequently subjected to the heat treatment. Solution annealing was chosen as the heat treatment method. The microstructure was characterized by LM, SEM and EBSD analyses. The mechanical tests were performed by a tensile testing on miniaturized specimens extracted from the experimental material in three orientations. The heat treatment had a fundamental effect on the proportion of austenite and ferrite, but also on the resulting mechanical properties. From the mechanical properties the maximum values of YS/UTS ∼ 680/830 MPa were reached and after heat treatment ∼ 540/760 MPa were reached.

Additive manufacturing (AM) becomes a more and more standard process in different fields of industry. There is still only limited knowledge of the relationship between measured material data and the overall behaviour of directed energy deposition (DED)-processed complex structures. The understanding of the structural performance, including flow curves and local damage properties of additively manufactured parts by DED, becomes increasingly important. DED can be used for creating functional surfaces, component repairing using multiple powder feeders, and creating a heterogeneous structure with defined chemical composition. For thin parts that are used with the as-deposited surface, this evaluation is even highly crucial. The main goal of the study was to predict the behaviour of thin-walled structures manufactured by the DED process under static loading by finite element analysis (FEA). Moreover, in this study, the mechanical performance of partly machined and fully machined miniaturized samples produced from the structure was compared. The structure studied in this research resembles a honeycomb shape made of austenitic stainless steel AISI 316L, which is characterized by high strength and ductility. The uncoupled damage models based on a hybrid experimental-numerical approach were used. The microstructure and hardness were examined to comprehend the structural behaviour.

In the present study, the effect of material deposition at the elevated temperature baseplate on the microstructure and mechanical properties was investigated and correlated to the unique thermal history by using numerical simulation. Numerical results agreed well with the experimental results of microstructure and mechanical properties. Numerical results revealed a significant decrease in temperature gradient and a 40% decrease in thermal stress due to material deposition on the elevated temperature baseplate. The reduced thermal stress and temperature gradient resulted in coarser grain features, which in turn led to a decrease in hardness and tensile strength, especially for the bottom region near the baseplate. Meanwhile, no significant effect could be found for ductility. In addition, an elevated temperature baseplate promoted less heterogeneity in hardness and tensile properties along the building direction. The current work demonstrates a collective and direct understanding of the baseplate preheating effect on thermal stress, microstructure and mechanical properties and their correlations, which is believed beneficial for the better utilization of baseplate preheating positive effects.

The super duplex stainless steel (SDSS) powder SAF2507 was deposited using directed energy deposition. In the as-built state, the microstructure consists of a nearly balanced ferrite–austenite ratio, with an austenite content of 47 vol.%, in contrast to the SDSS processed by the powder bed method, which produces a very low austenite content. This work investigated the differences in the microstructure, mechanical and corrosion properties of the “high-austenite” as-built state and the solution-annealed (SA) state (at 1100 °C for 60 min, followed by quenching in water). In the SA state, an increase in austenite content to 55 vol.% was observed. In addition, the partitioning of alloying elements into austenite and ferrite also occurred, the austenite grains coarsened and a ferrite grain size reduction was found. Microstructural changes were evident in the development of the mechanical properties. The increase in austenite content was accompanied by an increase in the elongation, and conversely, both the yield strength and ultimate tensile strength decreased. No secondary phases, such as carbides or sigma phase, were observed in either state. Both the as-built and solution-annealed samples exhibited a passivation zone in model seawater at 70 °C, but at the same time, the corrosion current density (i_corr) of the as-built state was five times higher.