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- Fowler, Lee
(författare)
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Development of titanium-copper alloys for dental applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Titanium alloys find wide application in the medical implants industry, which includes areas of orthopaedic and dental implants. The reason for the popularity of the material is high mechanical strength, low density, and reported growth of bone onto the material, as well as corrosion resistance. Despite the general success of titanium materials, a drawback is that it is vulnerable to bacterial colonization, which can cause implant failure through inflammatory diseases. Peri-implantitis is one such disease, which can lead to irreversible bone loss and subsequently implant instability.This thesis focuses on the use of copper (Cu) as an antibacterial element in titanium alloys, where the purpose is designing inherently antibacterial materials.With an understanding that copper can reduce bacterial populations by ion release of Cu into solutions, as well as by direct contact of bacteria with Cu surfaces: studies on the effect of Cu ions on bacteria and cells were conducted, in addition to studies on Ti-Cux alloys.Varying Cu concentrations in solution were introduced to bacteria (Staphylococcus epidermidis) and cells (MC3T3 murine calvarial osteoblasts), and it was found that the lethal dosage for Cu ions was in the range from 9x10-5 to 9x10-6 g/ml, for bacteria and cells. The Cu ions were also found to cause a stress response for this bacteria at concentrations between 9x10-6 to 9x10-7 g/ml, and recommended to be avoided for implant materials.For Ti-Cux binary alloys, studies established that a 10wt%Cu alloy, which released 9x10-8 g/ml, reduced the bacterial population by 27 % in 6 hours in a direct contact test. This alloy was found to be composed of intermetallic (Ti2Cu) and hexagonal closed packed titanium (HCP-Ti) crystals. A separate study on aged heat treated Ti-Cux alloys, showed that an additional phase of Ti3Cu was present in lower volume fraction. The aged alloys of Ti-Cux showed higher volume fraction of Ti2Cu but only a slightly higher antibacterial ability, compared to those without ageing. The hardness of the Ti-Cux alloys was however detrimentally affected by ageing, especially for the 10wt%Cu alloy.Investigations on the alloying of Cu with an existing implant alloy, Ti-10wt%Ta-1.6wt%Nb-1.7wt%Zr (TNTZ), was also performed and at higher wt%Cu alloys with three-phased microstructures were present. Alloying of Cu in the TNTZ material increased hardness and with further development of this novel alloy, a potential biomaterial for clinical applications could be designed.In conclusion, the results of this thesis demonstrate that the use of Cu in proximity to cells and bacteria requires dose dependent consideration for material design, so that antibacterial materials can be developed that do not harm tissue. The appropriate design of alloys can also be performed so as to allow antibacterial ability to be achieved, along with ensuring appropriate mechanical and corrosion properties. Furthermore, Cu as an antibacterial element can be alloyed into various titanium alloy systems and with further development in this area; antibacterial alloys could benefit the implant industry and patients alike.
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| 2. |
- Karlsson, Dennis, 1991-
(författare)
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Additive Manufacturing of Ferritic Materials : A Journey from Stainless Steels to High-Entropy Alloys
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Design of new materials with complex geometries is an important part of new innovative solutions for technical applications. With the use of additive manufacturing (AM), the design possibilities are endless and geometries that are impossible to manufacture by conventional techniques are available. However, the number of alloys commercially available is limited and extensive research is needed to establish new materials with unique properties. An important group of materials is ferritic stainless steels which have a body centered cubic crystal structure. They are often used for their high strength, corrosion resistance or electrical properties at high temperatures. However, they are often less ductile than austenitic stainless steels and issues with cracking may arise during thermal cycling in the L-PBF process. In this thesis, two AM techniques, laser powder bed fusion (L-PBF) and binder jetting were used to produce components of two different ferritic stainless steels and of the AlCoCrFeNi high-entropy alloy (HEA). The main objective was to investigate the microstructural development, phase stabilities and mechanical properties in relation to conventional manufacturing routes. Furthermore, thermodynamic calculations were used to explain the phase stabilities and solidification. L-PBF enables manufacturing of the ferritic stainless steels SS441 and SS446 with excellent mechanical properties. It was shown that solid particles may form in the melt and act as heterogeneous nucleation points, resulting in effective grain refinement for SS441. Other secondary phases can form during the thermal cycling in the L-PBF process, enhancing the mechanical properties. An example is the formation of austenite in SS446. Furthermore, the formation of solid particles and segregated microstructure during solidification was predicted by thermodynamic calculations.The AlCoCrFeNi alloy could be produced with an intriguing hierarchical microstructure and excellent mechanical properties using binder jetting and post-treatments. The microstructure of the final component can also be controlled by pre-annealing of the feedstock powder. Thermodynamic calculations were used to design the phase composition of the alloy. A characteristic single-phase solid solution is only observed at very high temperatures close to the melting point. Hence, the AlCoCrFeNi alloy is not a thermodynamically true HEA, but is stabilized due to kinetic effects during manufacturing.
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| 3. |
- Nilsson Åhman, Hanna
(författare)
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Powder Bed Fusion – Laser Beam of Mg alloy WE43 : Establishing the process – structure – properties relationship
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Powder bed fusion - laser beam (PBF-LB) of Mg alloy WE43 (Mg-4wt%Y-3wt%RE-Zr) has great potential for the development of future biodegradable metal implants, as well as aerospace lightweight materials. However, the work published thus far has mainly focused on obtaining a fully dense material, and the understanding of the relationship among the PBF-LB process parameters, structure and the resulting material properties remains limited. Thus, the aim of the thesis was to relate the main PBF-LB processing parameters to the formation of key microstructural features in WE43, and their effect on corrosion and tensile test properties. The work was carried out on PBF-LB processing units EOS M100 and EOS M290, and the investigated process parameters included laser power, laser scanning speed, hatch distance and sample wall thickness. Depending on the resulting thermal conditions, two main microstructural regions were observed. For process parameters resulting in warmer processes, such as higher laser powers and shorter scan lengths, mainly equiaxed dendritic grains were observed. The grains measured up to 10 µm in maximum diameter and exhibited a weak texture, with the inter-dendritic regions rich in Mg-RE intermetallic compunds. For process parameters resulting in conductive mode melting, mainly a lamellar structure was observed. The lamellar structure consisted in large grains with basal texture, and an intragranular structure where lines of Mg-RE intermetallic compunds precipitated parallel to the melt pool boundary. The larger grains had a maximum diameter of around 60 µm to 100 µm in the build direction, and up to 250 µm in the transverse direction, with a preferential growth along the melt pool.A larger number of dendritic grains was detrimental to the corrosion properties but resulted in higher tensile strength. The result was ascribed to the higher amount of Mg-RE intermetallics and the smaller grains, strengthening the material, but also causing microgalvanic corrosion. Hot isostatic pressing also resulted in growth of the secondary phases and was thus also detrimental to corrosion properties. While a change in hatch distance (40-60 mm) did not cause any dendritic structure to form, a higher hatch distance resulted in improved corrosion properties, but had minor effect on tensile properties, showing the possibilities of applying hatch distance variations to balance corrosion and tensile properties.In conclusion, the findings presented here show the possibilities of controlling the microstructure and thus the material properties by changing some of the key PBF-LB process parameters, and the major importance of understanding the relationship among process, structure and material properties of PBF-LB processed WE43.
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| 4. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Effect of layer thickness on spatter properties during laser powder bed fusion of Ti–6Al–4V
- 2023
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Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 66:4, s. 333-342
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Tidskriftsartikel (refereegranskat)abstract
- High layer thicknesses for laser powder bed fusion are promising for productivity increase. However, these are associated with increased process instability, spatter generation and powder degradation, crucial for alloys sensitive to oxygen. The effect of increasing layer thickness from 30 to 60 µm is studied focusing on Ti-6Al-4V spatter formation during LPBF and its characterisation, with scanning and transmission electron microscopy, combustion analysis and X-ray photoelectron spectroscopy. Results indicate that spatters are covered with a uniform Ti-Al-based oxide layer and Al-rich oxide particulates, the thickness of which is about twice that present on virgin powder. The oxygen content was about 60% higher in spatters compared to the virgin powder. The study highlights that increasing the layer thickness to 60 µm permits to reduce the total generation of spatters by ∼40%, while maintaining similar spatter characteristics and static tensile properties. Hence, this allows to increase build rate without compromising process robustness.
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