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The Corrosion Resistance of Hard Anodised EN AW 7075 T6 Alloy
(Electrochemical Society, 2021-08-22) Kusmič, David; Klakurková, Lenka; Juliš, Martin; Gejdoš, Pavel; Čech, Ondřej
In this paper, commercially cold-rolled and artificial aged EN AW 7075 T6 alloy has been used. To ensure increased corrosion resistance, surface hardness, scratching resistance, and aesthetic features, this aluminium alloy was subsequently hard anodised and hot-water sealed (AC-A). The hard anodizing and sealing process increased surface hardness up to 304 13 HV 1 from an initial surface hardness of 194 3 HV 1. Also, the microhardness of the anodised layer and bulk material has been documented. Scanning electron microscopy (SEM) was used for microstructure and trapped precipitates investigation in the 42.9 1.4 thick formed anodised layer investigation. The T6 treated (AC) and hard anodised together with sealed (AC-A) EN AW 7075 alloy corrosion properties were evaluated using the anodic potentiodynamic polarisation tests (PPT) in a neutral 2.5% NaCl deaerated solution. The corrosion rate CR (mm/y) decreased approx. 39-times for the hard anodised and sealed EN AW 7075 alloy (AC-A), associated with the shift of the E corr (mV) to more positive values, degreased Icorr (µA) and increased Rp (Ohm) values compared to the artificial aged (AC) alloy. Additionally, the pitting was evaluated using laser confocal microscopy, and the pitting coefficient was also calculated.
Fabrication of customized open-cell titanium foams by direct foaming for biomedical applications
(ELSEVIER, 2024-11-01) Oliver Urrutia, Carolina; Casas Luna, Mariano; Koledová, Zuzana; Slámečka, Karel; Zikmund, Tomáš; Kaiser, Jozef; Čelko, Ladislav; Montufar Jimenez, Edgar Benjamin
Titanium (Ti) foams offer a promising alternative for bone reconstruction and repair due to their high porosity and lower stiffness compared to solid metals, which improves in vivo osseointegration by reducing the stress shielding effect and allowing bone ingrowth. In this work, customized Ti foams were successfully fabricated for the first time at room temperature using a direct foaming method. Ti powder suspension with a water-soluble surfactant and environmentally friendly thickener was foamed by mechanical stirring. Then, 3D-printed moulds were utilized to achieve near-net shape foams, which were subsequently consolidated by sintering, thus avoiding the need for complex processing of molten Ti. The resulting Ti foams exhibited a cancellous-like open-cell structure, high porosity (> 80%), and a five times higher effective surface area than a 3D Ti mesh with a primitive cubic-based cell fabricated by additive manufacturing. In addition, the Ti foams exhibited similar mechanical properties to cancellous bone and facilitated the adhesion, proliferation, and maturation of human osteoblasts in vitro.
Effect of Preheating on the Residual Stress and Material Properties of Inconel 939 Processed by Laser Powder Bed Fusion
(MDPI, 2022-09-13) Malý, Martin; Nopová, Klára; Klakurková, Lenka; Adam, Ondřej; Pantělejev, Libor; Koutný, Daniel
One of the main limitations of laser powder bed fusion technology is the residual stress (RS) introduced into the material by the local heating of the laser beam. RS restricts the processability of some materials and causes shape distortions in the process. Powder bed preheating is a commonly used technique for RS mitigation. Therefore, the objective of this study was to investigate the effect of powder bed preheating in the range of room temperature to 400 °C on RS, macrostructure, microstructure, mechanical properties, and properties of the unfused powder of the nickel-based superalloy Inconel 939. The effect of base plate preheating on RS was determined by an indirect method using deformation of the bridge-shaped specimens. Inconel 939 behaved differently than titanium and aluminum alloys when preheated at high temperatures. Preheating at high temperatures resulted in higher RS, higher 0.2% proof stress and ultimate strength, lower elongation at brake, and higher material hardness. The increased RSs and the change in mechanical properties are attributed to changes in the microstructure. Preheating resulted in a larger melt pool, increased the width of columnar grains, and led to evolution of the carbide phase. The most significant microstructure change was in the increase of the size and occurrence of the carbide phase when higher preheating was applied. Furthermore, it was detected that the evolution of the carbide phase strongly corresponds to the build time when high-temperature preheating is applied. Rapid oxidation of the unfused powder was not detected by EDX or XRD analyses.
Pressure-less spark plasma sintering of 3D-plotted titanium porous structures
(Elsevier, 2022-12-14) Kashimbetova, Adelia; Slámečka, Karel; Díaz de la Torre, Sebastian; Hernández-Morales, Bernardo; Mendez-Garcia, Jose C.; Pina-Barba, Maria Cristina; Hui, David; Čelko, Ladislav; Montufar Jimenez, Edgar Benjamin
Additive manufacturing of titanium porous structures by direct ink writing involves the removal of the binder needed for powder extrusion and subsequent sintering to consolidate the 3D-plotted body. In this work, pressure-less spark plasma sintering (PL-SPS) was systematically studied for fast consolidation of titanium porous structures. Furthermore, poloxamer 407 was used as the binder and the lowest temperature possible was identified for its thermal elimination. The results show for the first time that PL-SPS generated sintering conditions similar to those generated by conventional pressure-less sintering, producing hierarchical titanium porous structures with equivalent densification, shrinkage, and surface roughness, but with minimal grain growth. The thermal responses of the die and material showed efficient radiation heat transfer, allowing fast heating (100 °C/min) of one sample per run, promoting the formation of sintering necks and powder densification in 10 min, which is much faster than conventional sintering that requires at least 2 h of dwell time. However, the process operates at a sintering temperature 200-300 °C above the conventional sintering temperature, and at the expense of high consumption of electrical energy to achieve such a high heating rate. The mechanical strength of the resulting titanium structures increases with increasing strand densification at nearly constant strand separation, resulting in strong and plastic porous structures.
Aerogel-Based Materials in Bone and Cartilage Tissue Engineering-A Review with Future Implications
(MDPI, 2023-09-13) Lázár, István; Čelko, Ladislav; Menelaou, Melita
Aerogels are fascinating solid materials known for their highly porous nanostructure and exceptional physical, chemical, and mechanical properties. They show great promise in various technological and biomedical applications, including tissue engineering, and bone and cartilage substitution. To evaluate the bioactivity of bone substitutes, researchers typically conduct in vitro tests using simulated body fluids and specific cell lines, while in vivo testing involves the study of materials in different animal species. In this context, our primary focus is to investigate the applications of different types of aerogels, considering their specific materials, microstructure, and porosity in the field of bone and cartilage tissue engineering. From clinically approved materials to experimental aerogels, we present a comprehensive list and summary of various aerogel building blocks and their biological activities. Additionally, we explore how the complexity of aerogel scaffolds influences their in vivo performance, ranging from simple single-component or hybrid aerogels to more intricate and organized structures. We also discuss commonly used formulation and drying methods in aerogel chemistry, including molding, freeze casting, supercritical foaming, freeze drying, subcritical, and supercritical drying techniques. These techniques play a crucial role in shaping aerogels for specific applications. Alongside the progress made, we acknowledge the challenges ahead and assess the near and far future of aerogel-based hard tissue engineering materials, as well as their potential connection with emerging healing techniques.

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