| 1. |
- Zhang, Ranran, et al.
(författare)
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Effects of the hierarchical macro/mesoporous structure on the osteoblast-like cell response
- 2018
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Ingår i: Journal of Biomedical Materials Research. Part A. - : Wiley. - 1549-3296 .- 1552-4965. ; 106:7, s. 1896-1902
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Tidskriftsartikel (refereegranskat)abstract
- To improve the success of medical devices, implants with strong surface bioactivity are urgently required. Coatings with a macroporous structure produced by micro-arc oxidation possess advantages, such as strong adhesion to substrate and excellent resistance to wear and corrosion. Mesoporous structures contain pores with sizes of 2-50 nm, which can endow the biomaterials with the ability to enhance osteogenesis and to be loaded with diverse drugs. Thus, in this study, we aimed to evaluate the effects of both macroporous and mesoporous structures using a hierarchical macro/mesoporous structure to modify the titanium implant surface. The behaviors of SaOS-2 human osteosarcoma cells on the macro/mesoporous structure, including initial adhesion, proliferation, alkaline phosphatase (ALP) activity, and collagen secretion, were investigated. Cells that attached on the macro/mesoporous surface showed the highest cell numbers and greatest spreading area after incubation for 1, 2, and 4 h compared with the polished smooth substrate and macroporous surface in the presence of fetal bovine serum (FBS). However, in the absence of FBS, cell adhesion on the polished substrate, macroporous structure, and macro/mesoporous structure did not differ significantly. Cell proliferation on the macroporous and macro/mesoporous surfaces increased compared with that on the smooth substrate surface. Furthermore, ALP activity and collagen secretion were enhanced on the macro/mesoporous structure. Our findings provided important insights into the cellular responses to macro/mesoporous structures in the field of implant surface modification.
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| 2. |
- Ma, Jing, et al.
(författare)
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Suppressing pore-boundary separation during spark plasma sintering of tungsten
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 438:1-3, s. 199-203
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Tidskriftsartikel (refereegranskat)abstract
- A tungsten powder with bimodal particle size distribution is consolidated by spark plasma sintering (SPS). Effects are made for understanding the densification and grain growth mechanisms and their relations to the SPS processing parameters. By holding the sample at an intermediate temperature, i.e., 1200 degrees C for 5 min, where the densification is enhanced by particle close packing, the pore-boundary separation that yields the formation of entrapped pores inside individual grains at final stage of sintering is suppressed. This optimization of the SPS process is beneficial for preparing fine grained bulk tungsten with homogeneous microstructure from the powders produced in industrial-scale. The prepared tungsten with minimized porosity appears a potential candidate for plasma-facing materials in the divertor region in the International Thermonuclear Experimental Reactor (ITER).
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| 3. |
- Ma, Shengyuan, et al.
(författare)
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Indoor thermal environment in a rural dwelling heated by air-source heat pump air-conditioner
- 2022
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Ingår i: Sustainable Energy Technologies and Assessments. - : Elsevier BV. - 2213-1388 .- 2213-1396. ; 51
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Tidskriftsartikel (refereegranskat)abstract
- Air-source heat pumps (ASHP) are increasingly used to improve space heating. However, few relevant studies have focused on the rural residential buildings that use ASHP air-conditioners for heating conditions. Therefore, this paper presents experiments and numerical simulations to analyse the impact of ASHP air-conditioners on the indoor thermal environment of a rural dwelling during heating seasons. In this study, the influences of different air-supply parameters (temperature, angle and velocity of air supply) and the position of the ASHP airconditioner on the local thermal comfort were evaluated. The influence weights of both the above factors and their interaction were obtained. The simulation results showed that the temperature differences between the head and foot region (Delta Th-f) in most cases exceeded 3.0celcius, demonstrating the thermal comfort in the rural dwelling was more unacceptable than the urban buildings. Moreover, the results of orthogonal design indicated that air-supply velocity had the most significant impact on the Delta Th-f values, followed by the air-supply temperature, air-supply angle and installation height. Reducing any air-supply parameter or enhancing the installation height might improve the thermal comfort performance. This research can provide practical strategies for improving the indoor thermal environment of rural dwellings, and guide the design of ASHP air-conditioning systems.
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| 4. |
- An, Di, et al.
(författare)
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Additive manufacturing and characterization of complex Al2O3 parts based on a novel stereolithography method
- 2017
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Ingår i: International Journal of Applied Ceramic Technology. - : Wiley. - 1546-542X .- 1744-7402. ; 14:5, s. 836-844
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we prepared Al2O3 ceramic green parts with complex geometry and architecture using an additive manufacturing process based on stereolithography. The rheological and thermal behavior of Al2O3 slurry was firstly examined and used to establish the conditions for molding and debinding. As opposed to previous researches that only focused on manufacture techniques, the sintering behavior and densification process were systematically investigated. In addition, special attentions were paid to the evolution of microstructure between green bodies and sintered parts. The results showed that debound parts were equipped with uniform particle packing and narrow pore size distribution. The dimensions of the Al2O3 parts changed anisotropically with the different processing steps. The densification process was greatly accelerated by the decrease in pore size and annihilating of interconnected pores in which significant grain growth was observed above 1450 degrees C. The sintered part also had a homogeneous microstructure and no interface between adjacent layers. High densification (relative density of 99.1%) and much desirable Vickers hardness (17.9 GPa) of Al2O3 parts were achieved at the sintering temperature of 1650 degrees C.
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| 5. |
- Chen, Jinhan, et al.
(författare)
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The effect of hot isostatic pressing on thermal conductivity of additively manufactured pure tungsten
- 2020
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Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 87
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Tidskriftsartikel (refereegranskat)abstract
- The crack-healing behaviors and microstructure evolution of pure tungsten produced by laser powder bed fusion (LPBF) were studied and compared before and after post hot isostatic pressing (post-HIP) treatment. An average thermal conductivity of 133 W.m(-1).K-1 at room temperature (RT) was obtained after HIP, which was 16% higher than that of as-built sample (115 W.m(-1).K-1). Although the HIP process had little effect on density, it resulted in a large grain size of > 300 mu m accompanied by a decrease in dislocation density and crack healing, which led to a substantial improvement of thermal conductivity of pure tungsten. The positive correlation between relative density and thermal conductivity of as-built tungsten was reported.
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| 6. |
- Li, Hezhen, et al.
(författare)
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Asynchronous densification of zirconia ceramics formed by stereolithographic additive manufacturing
- 2021
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 41:8, s. 4666-4670
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Tidskriftsartikel (refereegranskat)abstract
- Stereolithography has been proven as a feasible approach to make crack-free ceramic macrostructure with customized designs, but the microstructure, especially pore structure remains to be tailored more precisely for better performance, where the sintering protocol and related densification characteristics could play a vital role as the slurry preparation and debinding protocol do. Herein we report a phenomenon named “asynchronous densification”, that is, the surface region of zirconia ceramics formed by stereolithographic additive manufacturing would be densified prior to the bulk at 1200°C during the conventional pressureless sintering in air. The cause of this asynchronism is unclear but supposed to be correlated with low packing density, high sintering activity, poor thermal conduction of ceramics and impurities. Early densification of the surface may have negative effects towards ceramic components with more homogeneous microstructure, suppressed pore coalescence and limited grain growth, and therefore needs to be better controlled through optimization in sintering protocol.
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| 7. |
- Li, Hezhen, et al.
(författare)
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Dental ceramic prostheses by stereolithography-based additive manufacturing : potentials and challenges
- 2019
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Ingår i: Advances in Applied Ceramics. - : Informa UK Limited. - 1743-6753 .- 1743-6761. ; 118:1-2, s. 30-36
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Tidskriftsartikel (refereegranskat)abstract
- The current method for making dental ceramic prostheses in a subtractive manner causes a severe waste of materials while requires excessive manual works that bring in the uncertainty for control of quality. The rapid development and commercialisation of additive manufacturing (AM) has aroused interest and wonders both in material and dental communities about their potentials and challenges in fabricating of ceramic prostheses in a materials-saving manner. In this work, AM approach was applied to fabricate the dental bridges and implants made of zirconia. The achieved geometries and dimensional accuracy are used to demonstrate the potential of this technique in fabricating of dental ceramic prostheses, whereas the observed macro and micro defects formed during the treatment process is used to reveal the challenges facing in order to adapt this technology into real dental practice. Suggestions are provided for future development of the technology, particularly on minimising the processing defects.
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| 8. |
- Li, Hezhen, et al.
(författare)
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Stereolithography-fabricated zirconia dental prostheses : concerns based on clinical requirements
- 2020
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Ingår i: Advances in Applied Ceramics. - : Informa UK Limited. - 1743-6753 .- 1743-6761. ; 119:5-6, s. 236-243
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Tidskriftsartikel (refereegranskat)abstract
- With the recent rapid development of the additive manufacturing family of technologies, the interest in application potential of stereolithography on producing ceramic dental prostheses has aroused and been widely discussed. While someone claimed the birth of 'stereolithography-fabricated ceramic dental prostheses', an overall evaluation based on the clinical requirements is lacking, making the optimism a kind of unrealistic. In this article, the prototypes of ceramic dental prostheses and standard specimens produced by the ceramic stereolithography approach are compared with those made by the classic subtractive manufacturing method by following the critical clinical requirements. Concerns on the upcoming challenges and future improvement towards clinical applications are presented that include productivity, delivery time, dimensional tolerance, mechanical and aesthetic properties. It is concluded that it is far too early to call 'stereolithography-fabricated ceramic dental prostheses' as a success as usable and competitive products for clinical applications.
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| 9. |
- Li, Kailun, et al.
(författare)
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Crack suppression in additively manufactured tungsten by introducing secondary-phase nanoparticles into the matrix
- 2019
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Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 79, s. 158-163
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Tidskriftsartikel (refereegranskat)abstract
- In this study, an effective strategy was developed to suppress cracking by introducing secondary-phase ZrC nanoparticles into a tungsten (W) matrix. Pure W and W-0.5wt%ZrC bulks were additively manufactured via the laser powder bed fusion (LPBF) technique, and their cracking behaviour was compared. It was observed that the crack density of W-ZrC was reduced by 88.7% compared with that of pure W. The grains in W-ZrC were obviously refined compared with the grains in pure W, which significantly increased the cracking resistance. In addition, ZrC diminished the oxygen impurities, further increasing the cracking resistance. This study provides a promising strategy for the additive manufacturing of high-quality W by introducing secondary-phase nanoparticles into the metal matrix.
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| 10. |
- Liu, Xihe, et al.
(författare)
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Morphological Development of Sub-Grain Cellular/Bands Microstructures in Selective Laser Melting
- 2019
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Ingår i: Materials. - : MDPI AG. - 1996-1944 .- 1996-1944. ; 12:8
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, single-layer and bulk 316 L selective laser melting (SLM) experiments were conducted, fine submicron-scale geometric symmetrical cellular (hexagonal, pentagonal and square), elongated cellular and bands solidification morphologies were found in the laser-melt top surface. Meanwhile, morphological developed sub-grain patterns with quasi-hexagonal cellular, elongated cellular and bands structures (size similar to 1 m) coexisting inside one single macro-solidified grain were also identified. This demonstrated the transitions from quasi-hexagonal-cells to elongated cells/bands, and transitions reverse, occurred in the whole bulk under some circumstances during SLM. Based on the experimental realities, these morphologies are formed by the local convection and Benard instabilities in front of the solid/liquid interface (so-called mushy zones) affected by intricate temperature and surface tension gradients. Quasi-hexagonal cellular convective fields are then superimposed on macro-grain solidification to form the sub-grain patterns and micro-segregations. This explanation seems reasonable and is unifying as it can be expanded to other eutectic alloys with face center cubic (FCC) prevenient phase prepared by SLM, e.g., the Al-Si and Co-Cr-Mo systems.
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