| 1. |
- Shah, Furqan A., et al.
(författare)
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Osseointegration of 3D printed microalloyed CoCr implants—Addition of 0.04% Zr to CoCr does not alter bone material properties
- 2018
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Ingår i: Journal of Biomedical Materials Research - Part A. - : Wiley. - 1549-3296 .- 1552-4965. ; 106:6, s. 1655-1663
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 Wiley Periodicals, Inc. Electron beam melting (EBM) is a three-dimensional (3D) printing technique for the production of metal structures where complex geometries with interconnected porosities can be built. Incorporation of as little as 0.04% Zr into the CoCr alloy can significantly improve the biomechanical anchorage of constructs fabricated by EBM. Here we investigate bone material properties, including microstructure and composition, adjacent to 3D printed CoCr implants with and without addition of 0.04% Zr, after 8 weeks of healing in the rabbit femur. In low amounts, zirconium addition does not alter the microstructure and extracellular matrix composition of bone formed adjacent to the surface of EBM manufactured implants. Bone ingrowth into surface irregularities of 3D printed CoCr and CoCr + Zr implants is seen. Extensive remodeling is also evident. Osteocytes attach directly on to the implant surface. The interfacial tissue at CoCr and CoCr + Zr has similar mineral crystallinity, apatite-to-collagen ratio, carbonate-to-phosphate ratio, Ca/P ratio, bone-implant contact, percentage porosity, and osteocyte density (N.Ot/B.Ar). Compared to the native bone, the mineral crystallinity of the interfacial tissue was lower while N.Ot/B.Ar was higher for both CoCr and CoCr + Zr. Overall, the results indicate that bone tissue adjacent to CoCr and CoCr + Zr implants is highly mature and exhibits comparable healing kinetics. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1655–1663, 2018.
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| 2. |
- Stenlund, Patrik, et al.
(författare)
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Osseointegration Enhancement by Zr doping of Co-Cr-Mo Implants Fabricated by Electron Beam Melting
- 2015
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 6, s. 6-15
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Tidskriftsartikel (refereegranskat)abstract
- Direct osseous healing to prosthetic components is a prerequisite for the clinical success of uncemented treatment in total hip replacements (THR). The demands imposed on the material properties are constantly being stepped up to withstand the impact of an active lifestyle and ensure lifelong integration. Cobalt–chromium–molybdenum (Co-Cr-Mo) materials are interesting for their excellent mechanical stability, corrosion resistance and possibility to be produced by additive manufacturing into complex designs with modifiable stiffness. The bone response to Co-Cr-Mo is regarded as inferior to that of titanium and are usually cemented in THR. The hypothesis in the present study was that a low amount of Zr in the Co-Cr-Mo alloy would improve the bone response and biomechanical anchorage. The results showed significantly higher implant stability for the Co-Cr-Mo alloy with an addition of 0.04% Zr after eight weeks of healing in rabbits, while no major differences were observed in the amount of bone formed around the implants. Further, bone tissue grew into surface irregularities and in direct contact with the implant surfaces. It is concluded that additively manufactured Co-Cr-Mo alloy implants osseointegrate and that the addition of a low amount of Zr to the bulk Co-Cr-Mo further improves the bone anchorage.
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| 3. |
- Wei, Daixiu, et al.
(författare)
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Development of strong and ductile metastable face-centered cubic single-phase high-entropy alloys
- 2019
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 181, s. 318-330
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Tidskriftsartikel (refereegranskat)abstract
- Face-centered cubic (fcc)-phase high-entropy alloys (HEAs) have attracted much academic interest, with the stacking fault energy (SFE) playing an important role in regulating their mechanical behaviors. Here, we revealed the principles for regulating both the elastic and plastic behaviors by composition modification and Mo addition in an fcc-phase quaternary CoCrFeNi system with the assistance of ab initio and thermodynamics calculations. An increase in Co content and a decrease in Fe and Ni contents reduced the fcc phase stability and SFE, but enhanced the elastic modulus, anisotropy, and lattice friction stress. A minor substitution of Co by Mo increased the lattice constant, but decreased the SFE and elastic modulus. Based on these findings, we developed a series of strong and ductile metastable fcc-phase CoxCr25(FeNi)(70-x)Mo-5 (x = 30, 40, 50) HEAs with mechanical properties superior to those of the CoCrFeNi HEM. The careful investigation revealed that the enhanced mechanical properties are due to the Mo-addition-induced strengthening accompanied with a low-SFE-induced restriction of planar behavior of dislocations, mechanical twinning, and strain-induced martensitic transformation. The findings shed light on the development of high-performance HEAs.
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| 4. |
- Wei, Daixiu, et al.
(författare)
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Novel Co-rich high entropy alloys with superior tensile properties
- 2019
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 7:2, s. 82-88
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Tidskriftsartikel (refereegranskat)abstract
- We developed a series of Co-rich CoxCr25(FeNi)(75-x) (x = 35, 45, 55, 65) high entropy alloys with improved strength and/or ductility, derived from lowering the stacking fault energy (SFE) and reducing the fcc phase stability of the equiatomic CoCrFeNi alloy. Thermodynamics and ab initio calculations demonstrated that increasing Co while decreasing Fe and Ni concentrations lower the SFE and reduce the fcc phase stability. The Co35Cr25Fe20Ni20 and Co45Cr25Fe15Ni15 alloys with single fcc phase, exhibit superior tensile properties, contributing to the twinning and fcc -> hcp martensitic transformation. The present study offers a guideline for designing high-performance high entropy alloys. [GRAPHICS] IMPACT STATEMENT A series of novel Co-rich non-equiatomic high entropy alloys with enhanced tensile properties were developed by lowering the stacking fault energy and reducing the phase stability of equiatomic CoCrFeNi alloy.
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| 5. |
- Wei, Daixiu, et al.
(författare)
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Si-addition contributes to overcoming the strength-ductility trade-off in high-entropy alloys
- 2022
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions.
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