| 1. |
- Khrapov, D., et al.
(författare)
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Different approaches for manufacturing ti-6al-4v alloy with triply periodic minimal surface sheet-based structures by electron beam melting
- 2021
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:17
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Tidskriftsartikel (refereegranskat)abstract
- Targeting biomedical applications, Triply Periodic Minimal Surface (TPMS) gyroid sheet-based structures were successfully manufactured for the first time by Electron Beam Melting in two different production Themes, i.e., inputting a zero (Wafer Theme) and a 200 µm (Melt Theme) wall thickness. Initial assumption was that in both cases, EBM manufacturing should yield the structures with similar mechanical properties as in a Wafer-mode, as wall thickness is determined by the minimal beam spot size of ca 200 µm. Their surface morphology, geometry, and mechanical properties were investigated by means of electron microscopy (SEM), X-ray Computed Tomography (XCT), and uniaxial tests (both compression and tension). Application of different manufacturing Themes resulted in specimens with different wall thicknesses while quasi-elastic gradients for different Themes was found to be of 1.5 GPa, similar to the elastic modulus of human cortical bone tissue. The specific energy absorption at 50% strain was also similar for the two types of structures. Finite element simulations were also conducted to qualitatively analyze the deformation process and the stress distribution under mechanical load. Simulations demonstrated that in the elastic regime wall, regions oriented parallel to the load are primarily affected by deformation. We could conclude that gyroids manufactured in Wafer and Melt Themes are equally effective in mimicking mechanical properties of the bones.
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| 2. |
- Khrapov, D., et al.
(författare)
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Geometrical features and mechanical properties of the sheet-based gyroid scaffolds with functionally graded porosity manufactured by electron beam melting
- 2023
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Ingår i: Materials Today Communications. - : Elsevier. - 2352-4928. ; 35
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Tidskriftsartikel (refereegranskat)abstract
- Functionally graded porous scaffolds (FGPS) constructed with pores of different size arranged as spatially continuous structure based on sheet-based gyroid with three different scaling factors of 0.05, 0.1 and 0.2 were produced by electron beam powder bed fusion. The pore dimensions of the obtained scaffolds satisfy the values required for optimal bone tissue ingrowth. Agglomerates of residual powder were found inside all structures, which required post-manufacturing treatment. Using X-ray Computed Tomography powder agglomerations were visualized and average wall thickness, wall-to-wall distances, micro- and macro-porosities were evaluated. The initial cleaning by powder recovery system (PRS) was insufficient for complete powder removal. Additional treatment by dry ultrasonic vibration (USV) was applied and was found successful for gyroids with the scaling factors of 0.05 and 0.1. Mechanical properties of the samples, including quasi-elastic gradients and first maximum compressive strengths of the structures before and after USV were evaluated to prove that additional treatment does not produce structural damage. The estimated quasi-elastic gradients for gyroids with different scaling factors lie in a range between 2.5 and 2.9 GPa, while the first maximum compressive strength vary from 52.5 for to 59.8 MPa, compressive offset stress vary from 46.2 for to 53.2 MPa.
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| 3. |
- Khrapov, D., et al.
(författare)
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Trapped powder removal from sheet-based porous structures based on triply periodic minimal surfaces fabricated by electron beam powder bed fusion
- 2023
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 862
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Tidskriftsartikel (refereegranskat)abstract
- Electron Beam Powder Bed Fusion-manufactured (E-PBF) porous components with narrow pores or channels and rough walls or struts can be filled with trapped powder after the manufacturing process. Adequate powder removal procedures are required, especially for high-density porous structures. In the present research, sheet-based porous structures with different thicknesses based on triply periodic minimal surfaces fabricated by E-PBF were subjected to different post-processing methods, including a traditional powder recovery system for E-PBF, chemical etching and ultrasound vibration-assisted powder removal. Wall thickness, internal defects, microstructure and morphology features, powder distribution inside the specimens, mechanical properties and deformation modes were investigated. A powder recovery system could not remove all residual powder from dense structures. In turn, chemical etching was effective for surface morphology changes and subsurface layers elimination but not for powder removal, as it affected the wall thickness, considerably influencing the mechanical properties of the whole structure. The ultrasound vibration method was quite effective for the removal of residual powder from sheet-based TMPS structures and without a severe degradation of mechanical properties. Ultrasound vibration also caused grain refinement.
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| 4. |
- Surmeneva, M. A., et al.
(författare)
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The influence of chemical etching on porous structure and mechanical properties of the Ti6AL4V Functionally Graded Porous Scaffolds fabricated by EBM
- 2022
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 275
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Tidskriftsartikel (refereegranskat)abstract
- Functionally Graded Porous Scaffolds (FGPS) manufactured from Ti and Ti alloys such as Ti6Al4V is an attractive candidate for mimicking host bone tissue. Porous specimens manufactured by powder-bed fusion additive manufacturing (PBF-AM) methods always contain some amount of powder attached to the surfaces of the outer or the inner parts. Powder removal is an important issue for the porous structures with high relative density designed for biomedical applications. In some cases, traditional powder removal methods such as standard powder recovery systems (PRS) become ineffective. Chemical and electrochemical etching is one of the possible solutions for effective residual powder removal from PBF-AM structures. Traditional single-stage HF/HNO3 chemical etching protocols of the Ti6Al4V often leads to the overetching of the periphery of the porous samples leaving inner parts untouched. The aim of present research was to determine if fractionated chemical etching of porous Ti6Al4V Functionally Graded Porous Scaffolds (FGPS) with multiple immersions could facilitate trapped powder removal and reduction the surface roughness without critical degradation of the mechanical properties. Protocols with different number and time of immersions were studied. Mechanical properties and fracture modes of as manufactured and chemically etched Ti6Al4V FGPS were investigated. Results clearly illustrate that fractionating of the etching times have positive effect. It is possible to achieve more uniform etching of the thin structures at the periphery and inside porous structures, facilitate removal of the powder particles attached to the surfaces, and removal of the powder trapped inside the structures without serious degradation of the mechanical properties.
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