ÚK-odbor reverzního inženýrství a aditivních technologií

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Influence of Laser Strategies on Performance of Lattice Structures from Magnesium Alloy WE43 Produced by Laser Beam Powder Bed Fusion
(WILEY-V C H VERLAG GMBH, 2025-03-05) Jaroš, Jan; Ožvoldík, Daniel; Vaverka, Ondřej; Nopová, Klára; Hurník, Jakub; Zikmund, Tomáš; Kaiser, Jozef; Koutný, Daniel
Lattice structures made of magnesium alloys are perspective for lightweight and biomedical applications. The processing of magnesium alloys and the production of complex geometries is possible with laser beam powder bed fusion. However, the small material volume of the lattice structures and the magnesium alloy require specific process parameters in order to achieve a high quality of the material. Therefore, the influence of two perspective laser strategies (contour strategy and hatch strategy), their combination, and skywriting is investigated. The geometry of the body-centered-cubic (BCC) lattice structure is used, representing the most difficult lattice structure to produce due to the struts inclination. A relative material density of over 99% is achieved with three laser strategies. The laser strategies have a direct influence on the pore distribution, pore shape, and microstructure. All these parameters can influence the mechanical performance of the BCC structures. The best performance is achieved with the hatch strategy with skywriting, which results in a low number of dangerous pores and a fine microstructure. The Young's modulus of material of 40 GPa and the effective elastic modulus of BCC structure of 136 MPa are achieved.
Pad Alignment Methods and Their Impact on Large Hydrostatic Bearing Precision
(MDPI, 2024-08-13) Foltýn, Jan; Hurník, Jakub; Michalec, Michal; Svoboda, Petr; Křupka, Ivan; Hartl, Martin
Hydrostatic bearings are frequently used for moving large structures smoothly and precisely. In such applications, difficulties with manufacturing, transportation, and assembly arise. The safety and precision of the entire supported structure depend on the accuracy of the hydrostatic bearing alignment. There are several suitable methods for its alignment, yet it is not clear which method can achieve the highest bearing precision. This study provides a comparative experimental assessment of the three methods. The measurements were performed on a hydrostatic bearing test rig with independent positioning of the pads. Conventional measuring devices, a pressure distribution alignment method, and an optical method, OCMM (optical coordinate measuring machine), were compared. The accuracy of the selected methods and the difficulty of the aligning process were included in the comparison. The OCMM method was able to achieve an accuracy 1.6 times higher relative to the pressure method and 6 times higher compared to conventional measuring devices. This method is versatile and can be applied for a wide range of bearing sizes.
Comparative analysis of microstructure, mechanical, and corrosion properties of biodegradable Mg-3Y alloy prepared by selective laser melting and spark plasma sintering
(KeAi Communications, 2024-04-27) Minárik, Peter; Zemková, Mária; Šašek, Stanislav; Dittrich, Jan; Knapek, Michal; Lukáč, František; Koutný, Daniel; Jaroš, Jan; Král, Robert
This work explored possibilities of biodegradable magnesium alloy Mg-3Y preparation by two modern powder metallurgy techniques - spark plasma sintering (SPS) and selective laser melting (SLM). The powder material was consolidated by both methods utilising optimised parameters, which led to very low porosity ( -0.3%) in the SLM material and unmeasurably low porosity in the SPS material. The main aim of the study was the thorough microstructure characterisation and interrelation between the microstructure and the functional properties, such as mechanical strength, deformability, and corrosion resistance. Both materials showed comparable strength of -110 MPa in tension and compression and relatively good deformability of -9% and -21% for the SLM and SPS materials, respectively. The corrosion resistance of the SPS material in 0.1 M NaCl solution was superior to the SLM one and comparable to the conventional extruded material. The digital image correlation during loading and the cross-section analysis of the corrosion layers revealed that the residual porosity and large strained grains have the dominant negative effect on the functional properties of the SLM material. On the other hand, one of the primary outcomes of this study is that the SPS consolidation method is very effective in the preparation of the W3 biodegradable alloy, resulting in material with convenient mechanical and degradation properties that might find practical applications. (c) 2024 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University
Different Response of Cast and 3D-Printed Co-Cr-Mo Alloy to Heat Treatment: A Thorough Microstructure Characterization
(MDPI, 2021-04-22) Roudnická, Michaela; Bigas, Jiří; Molnárová, Orsolya; Paloušek, David; Vojtěch, Dalibor
The Co-Cr-Mo alloy is a biomaterial with very good corrosion resistance and wear resistance; thus, it is widely applied for knee replacements. The wear resistance is influenced by the amount of hcp phase and morphology of carbidic precipitates, which can both be altered by heat treatment. This study compares a conventional knee replacement manufactured by investment casting with a material prepared by the progressive technology of 3D printing. The first set of results shows a different response of both materials in increasing hardness with annealing at increasing temperatures up to the transformation temperature. Based on these results, solution treatment and subsequent aging at conditions to reach the maximum hardness was applied. Microstructural changes were studied thoroughly by means of optical, scanning electron and transmission electron microscopy. While increased hardness in the conventional material is caused by the precipitation of fine hard carbides combined with an increase in the hcp phase by isothermal transformation, a massive fcc -> hcp transformation is the main cause for the hardness increase in the 3D-printed material.
Cyclic behaviour and microstructural evolution of metastable austenitic stainless steel 304L produced by laser powder bed fusion
(Elsevier, 2023-04-25) Šmíd, Miroslav; Koutný, Daniel; Neumannová, Kateřina; Chlup, Zdeněk; Náhlík, Luboš; Jambor, Michal
It has been documented that the hierarchical character of microstructure produced by laser powder bed fusion (L-PBF) is the key to superior mechanical properties. Especially important is a fine cell microstructure possessing heterogeneous distribution of dislocation density and alloying elements. Despite multiple studies that have investigated the effect of such L-PBF structure on the stress-strain response during monotonic loading, just a few investigations were devoted to cyclic behaviour. The present study delivers an insight into the cyclic behaviour of L-PBF processed metastable austenitic stainless steel 304L and its relation to the observed microstructure evo-lution and strain-induced martensitic transformation (SIMT). The combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations, and feritscope measurements enabled to follow the onset of strain-induced martensite (SIM) nucleation and underlying dislocation microstructure evolution. The cyclic behaviour consisted of initial cyclic softening regardless of subjected strain amplitude. Afterwards, milder cyclic softening or saturation stage followed until a final failure was characteristic for the tests held at low strain amplitudes (e(a) = 0.5%). The third fatigue life stage, cyclic hardening, was recorded during fatigue tests held at e(a) > 0.5%. The excellent cyclic strength of stainless steel 304L is a direct consequence of cell microstructure containing high dislocation density walls and elemental microsegregation, which effectively inhibit dislocation motion. Cyclic softening was linked with cyclic strain localization into slip bands of decreased dislocation density and heavily altered dislocation cell walls. These bands have been observed for the first time in L-PBF-processed metals. This microstructural feature seems to be a variant of persistent slip bands (PSBs), a typical dislocation arrangement observed in conventionally produced materials subjected to cyclic loading. PSBs present the areas of intensive cyclic plasticity where the SIMT preferentially occurs upon further cycling. The increasing a'-martensite volume fraction, accompanied by a formation of intermediate e-martensite and deformation twinning, resulted in recorded cyclic hardening. The martensite nucleation sites are strongly determined by the underlying cell microstructure, in terms of cell walls dislocation density and chemical segregation, which is tightly related to utilized L-PBF process parameters. The present findings indicate a possible opportunity to control the magnitude of the SIMT susceptibility by fine-tuning of the L-PBF process parameters and conse-quently tailoring the cyclic behaviour.

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