| 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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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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| 3. |
- Khrapov, D., et al.
(författare)
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X-ray computed tomography of multiple-layered scaffolds with controlled gradient cell lattice structures fabricated via additive manufacturing
- 2019
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Konferensbidrag (refereegranskat)abstract
- In this paper we report on the characterization by X-ray computed tomography of calcium phosphate (CaP) and polycaprolactone (PCL) coatings on Ti-6Al-4V alloy scaffolds used as a material for medical implants. The cylindrical scaffold has greater porosity of the inner part than the external part, thus, mimicking trabecular and cortical bone, respectively. The prismatic scaffolds have uniform porosity. Surface of the scaffolds was modified with calcium phosphate (CaP) and polycaprolactone (PCL) by dip-coating to improve biocompatibility and mechanical properties. Computed tomography performed with X-ray and synchrotron radiation revealed the defects of structure and morphology of CaP and PCL coatings showing small platelet-like and spider-web-like structures, respectively.
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| 4. |
- Mehta, Bharat, 1993, et al.
(författare)
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Microstructure, mechanical properties and fracture mechanisms in a 7017 aluminium alloy tailored for powder bed fusion – laser beam
- 2023
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 226
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Tidskriftsartikel (refereegranskat)abstract
- This study addressed a 7017 Al-alloy tailored for powder bed fusion – laser beam (PBF-LB) process. The alloy was prepared by mixing 3 wt% Zr and 0.5 wt% TiC powder to standard pre-alloyed 7017 grade aluminium powder. This made printing of the alloys possible avoiding solidification cracking in the bulk and achieving high relative density (99.8 %). Such advanced alloys have significantly higher Young's modulus (>80 GPa) than conventional Al-alloys (70–75 GPa), thus making them attractive for applications requiring high stiffness. The resulting microstructure in as-printed condition was rich in particles originating from admixed powders and primary precipitates/inclusions originating from the PBF-LB process. After performing a T6-like heat treatment designed for the PBF-LB process, the microstructure changed: Zr-nanoparticles and Fe- or Mg/Zn- containing precipitates formed thus providing 75 % increase in yield strength (from 254 MPa to 444 MPa) at the cost of decreasing ductility (∼20 % to ∼9 %). In-situ tensile testing combined with SXCT, and ex-situ tensile testing combined with fracture analysis confirmed that the fracture initiation in both conditions is highly dependent on defects originated during printing. However, cracks are deflected from decohesion around Zr-containing inclusions/precipitates embedded in the Al-matrix. This deflection is seen to improve the ductility of the material.
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