| 1. |
- Boz Noyan, Ezgi Ceren, 1990, et al.
(författare)
-
Rheological and Functional Properties of Mechanically Recycled Post-Consumer Rigid Polyethylene Packaging Waste
- 2024
-
Ingår i: Materials. - 1996-1944. ; 17:8
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of recycled post-consumer rigid polyethylene packaging waste were studied, using sorted waste washed in the laboratory with water alone and with added detergent, and compared with large-scale high-intensity washed flakes. The washed flakes were compounded using three different temperature profiles in a twin-screw extruder and then injection molded. A higher compounding temperature reduced the thermo-oxidative stability, the average molecular mass, and the viscosity of the samples. Rheological measurements suggested that changes in chain branching occurred at different compounding temperatures. The strength and the elongation at break were also influenced by the compounding temperature in both the molten and solid states. Detergent washing maintained the thermo-oxidative stability in contrast to washing with water. The large-scale washed samples had a relatively high thermo-oxidative stability, a higher melt elasticity, and a lower elongation at break in both the molten and solid states than the laboratory-scale washed samples. The thermal properties, melt elasticity, Young’s modulus, yield stress, and yield strain of the samples were not, however, significantly affected by either the compounding temperature or the washing medium and intensity. The results indicated that recycled post-consumer rigid polyethylene packaging waste has properties that can support further applications in new products.
|
|
| 2. |
- Enrico, Alessandro, et al.
(författare)
-
Cleanroom-Free Direct Laser Micropatterning of Polymers for Organic Electrochemical Transistors in Logic Circuits and Glucose Biosensors
- 2024
-
Ingår i: Advanced Science. - : Wiley. - 2198-3844.
-
Tidskriftsartikel (refereegranskat)abstract
- Organic electrochemical transistors (OECTs) are promising devices for bioelectronics, such as biosensors. However, current cleanroom-based microfabrication of OECTs hinders fast prototyping and widespread adoption of this technology for low-volume, low-cost applications. To address this limitation, a versatile and scalable approach for ultrafast laser microfabrication of OECTs is herein reported, where a femtosecond laser to pattern insulating polymers (such as parylene C or polyimide) is first used, exposing the underlying metal electrodes serving as transistor terminals (source, drain, or gate). After the first patterning step, conducting polymers, such as poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), or semiconducting polymers, are spin-coated on the device surface. Another femtosecond laser patterning step subsequently defines the active polymer area contributing to the OECT performance by disconnecting the channel and gate from the surrounding spin-coated film. The effective OECT width can be defined with high resolution (down to 2 mu m) in less than a second of exposure. Micropatterning the OECT channel area significantly improved the transistor switching performance in the case of PEDOT:PSS-based transistors, speeding up the devices by two orders of magnitude. The utility of this OECT manufacturing approach is demonstrated by fabricating complementary logic (inverters) and glucose biosensors, thereby showing its potential to accelerate OECT research. Ultrafast focused femtosecond laser has been introduced for the direct micropatterning of organic electrochemical transistors (OECTs), providing high resolution (2 mu m), selective cleanroom-free patterning of insulating and conjugated polymer layers while preserving device operation, and high flexibility in device design. The approach has been validated in the fabrication of complementary inverters and glucose biosensors.image
|
|
| 3. |
- Mansouri, Ebrahim
(författare)
-
Atomistic modelling of irradiation-induced microstructure evolution in Fe alloys
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nuclear reactors of the future require materials that are exceptionallyresistant to irradiation-induced degradation. This study presents a theoreticalframework, combining density functional theory and interatomic potentialmethods, to predict microstructural evolution in Fe-based alloys and oxides(Al2O3) subjected to damaging irradiation. Our research employs a powerfulcreation-relaxation algorithm to simulate defect formation and microstructuredevelopment under intense irradiation.We present the pioneering implementation of a first-principles quantummechanical approach for directly modelling the microstructural evolution ofmagnetic materials and ceramics under irradiation. A crucial aspect of studiesinvolves investigating the influence of the spatial distribution of Frenkel-pairs(FPs) on the microstructural evolution in Fe. Our findings reveal that spa-tially localised FP distributions, replicating low-energy transfer irradiationconditions, predict a significantly more moderate microstructure developmentcompared to uniform distributions. This highlights the importance of consid-ering the FP distribution for an accurate prediction of the formation andgrowth of the dislocation segments under low-energy irradiation conditions.Furthermore, first-principles calculations suggest that irradiation-inducedexcess energy can trigger polymorphism in bcc Fe, leading to magnetic insta-bilities, localised structural constriction, and ultimately local phase transfor-mations. Consequently, under extreme conditions, α-Fe undergoes local trans-formations into three-dimensional, non-parallel C15 Laves phase structureswith highly close-packed stacking and internal short-range ferromagnetism.Notably, the inclusion of antiferromagnetic chromium in bcc Fe significantlyenhances the stability of C15 interstitial clusters in concentrated FeCr alloys.Beyond these structural insights, the investigation delves into the intricateinterplay between atomic constituents and their profound impact on the non-linear magnetic properties of FeCr systems under irradiation. A striking cor-relation emerges, revealing that the chromium content directly influences theappearance of swelling, a key phenomenon following irradiation-induced dam-age. Increasing the chromium content mitigates irradiation-induced swellingby approximately 40%, compared to pure Fe, highlighting the profound effectof alloying in Fe-based alloys.In addition, our first-principles simulations of irradiation-induced damagein bcc FeCrAl and hcp Al2O3 predict that while there are relatively small dif-ferences in total defect number densities among bcc Fe and its alloys, there aresignificant discrepancies in defect concentrations between these bcc structuresand hexagonal Al2O3. Notably, the surviving FP content in alumina is seventimes higher than that recorded for FeCrAl alloys. Consequently, the differ-ent build-up of surviving damage in Fe alloys and alumina leads to diverselevels of swelling in the irradiated materials, with a remarkable three timeshigher swelling observed in alumina upon reaching a saturation state after anirradiation dose of approximately 1 displacement per atom (dpa). Further-more, our observations of amorphous phase formation in damaged corundumalumina, as predicted in this study, corroborate that there are significantirradiation-induced effects in alumina.These findings not only deepen our fundamental understanding of theresponses of structural materials to irradiation, but also pave the way foradvanced materials engineering with potential applications in near-future nu-clear reactor components.
|
|
| 4. |
- Wang, Dong, et al.
(författare)
-
Comparing the efficacy of GEP and MEP algorithms in predicting concrete strength incorporating waste eggshell and waste glass powder
- 2024
-
Ingår i: Developments in the Built Environment. - : Elsevier Ltd. - 2666-1659. ; 17
-
Tidskriftsartikel (refereegranskat)abstract
- The present study used the techniques of gene expression programming (GEP) and multi-expression programming (MEP) to assess the compressive strength (CS) and flexural strength (FS) and develop predictive models of sustainable mortar modified with waste eggshell powder (WEP) and waste glass powder (WGP) as a replacement of cement. In order to get more insights into the impact and relation of raw components on the CS and FS of a developed sustainable mortar, a comprehensive study using the SHapley Additive exPlanations (SHAP) methodology was performed. When comparing the efficiency of both employed models, it was seen that the MEP model exhibited superior performance with an R2 value of 0.871 and 0.894 for CS and FS, as compared to the GEP model, which had an R2 value of 0.842 and 0.845 for CS and FS respectively.
|
|
| 5. |
- Östmans, Rebecca, et al.
(författare)
-
Solidified water at room temperature hosting tailored fluidic channels by using highly anisotropic cellulose nanofibrils
- 2024
-
Ingår i: Materials Today Nano. - : Elsevier BV. - 2588-8420. ; 26
-
Tidskriftsartikel (refereegranskat)abstract
- Highly anisotropic cellulose nanofibrils can solidify liquid water, creating self-supporting structures by incorporating a tiny number of fibrils. These fibrillar hydrogels can contain as much as 99.99 wt% water. The structure and mechanical properties of fibrillar networks have so far not been completely understood, nor how they solidify the bulk water at such low particle concentrations. In this work, the mechanical properties of cellulose fibrillar hydrogels in the dilute regime from a wt% perspective have been studied, and an elastoplastic model describing the network structure and its mechanics is presented. A significant insight from this work is that the ability of the fibrils to solidify water is very dependent on particle stiffness and the number of contact points it can form in the network structure. The comparison between the experimental results and the theoretical model shows that the fibrillar networks in the dilute regime form via a non-stochastic process since the fibrils have the time and freedom to find contact points during network formation by translational and rotational diffusion. The formed, dilute fibrillar network deforms by sliding fibril contacts upon straining the network beyond its elastic limit. Our results also show that before macroscopic failure, the fibril contacts are restored once the load is released. The exceptional properties of this solidified water are exploited to host fluidic channels, allowing directed fluid transportation in water. Finally, the microfluidic channels formed in the hydrogels are tailored by the layer-by-layer technique to be interactive against external stimuli, a characteristic envisioned to be useful in biomedical applications.
|
|
| 6. |
- Edgren, Aina, 1995
(författare)
-
Microstructure and high temperature properties of Mo(Si,Al)2 - The effect of particle strengthening and alloying
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High temperature heating processes within the steel industries result in significant emissions of CO2, primarily due to the combustion of fossil fuels. Electrification of these processes, such as through the implementation of resistive heating elements, holds great promise for reducing emissions. However, a bottleneck in the transition to a more environmentally friendly industry is related to the materials used for these heating elements. Mo(Si,Al)2 is a ceramic material commonly used for heating elements in various high temperature furnaces and is being considered for large-scale industrial-scale applications. While its oxidation properties have been extensively studied, its mechanical properties, which are crucial when increasing the size of the heating elements, have received limited attention. In this thesis, the high temperature deformation behaviour of Mo(Si,Al)2-based materials, and potential routes for their improvement, have been investigated. This work has shown that diffusion-driven grain boundary sliding is the main deformation mechanism in polycrystalline Mo(Si,Al)2, particularly in fine-grained materials. In coarse-grained materials, the slip of dislocations also contributes to deformation. Moreover, coarse-grained Mo(Si,Al)2 relaxes through the formation of low-angle grain boundaries and dynamic recrystallization. The addition of Al2O3 particles, to achieve particle strengthening, results in a competition between a negative effect from grain refinement at low fractions (up to 15 wt.%), and a positive effect from inhibition of grain boundary sliding at higher fractions. Also alloying with W, Nb, Ta, and V has been studied, among which W was the most promising alternative. The solid solubility of W in Mo(Si,Al)2 was high, and it also led to a slight improvement in high temperature strength. The solubility of the alloying elements Nb, Ta, and V was found to be low in Mo(Si,Al)2. Instead, these elements were enriched in secondary phases. Additionally, Y alloying has been explored to investigate its effect on oxidation behaviour. However, the oxide adhesion was adversely affected.
|
|
| 7. |
- Gunnerek, Rasmus, 1992
(författare)
-
Increased Productivity of Ferrous Alloys Produced by Powder Bed Fusion - Laser Beam
- 2024
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low production speeds limit wider adoption of powder bed fusion – laser beam (PBF-LB) in cost sensitive industries as it correlates directly with high production costs. The main process parameters such as scan speed, hatch distance and layer thickness can be scaled up to increase build speed, but it often comes at a trade off in lower quality, i.e. surface roughness, porosity/density and mechanical properties. The objective of this thesis study was to investigate how large build rates influences microstructure and processability of two low alloy steels (4130 and 4140) and 316L stainless steel by detailed characterization of defects and porosity present in relation to process parameters applied. The initial study found that achieving consistent processability of low alloy steels across layer thicknesses, as indicated by the as-printed density, is better correlated with surface energy density (SED) J/mm2 rather than volumetric energy density (VED) J/mm3. Regions with high densities above 99.8% exhibited similar ranges of SED at different layer thicknesses, explained by the resulting melt pool depths being more similar than at similar ranges of VED. The second study addressed the impact of three- and four-factor increase in hatch distance and layer thickness compared with state of the art. It was observed that the influence of VED on density was poorly described as differences of up to 7.5% in density were measured at the same VED. More accurate representations of impact on main print parameters on density was found by regression analysis which also captured the interaction between laser power, scan speed and hatch distance at different layer thicknesses. Build rate increase can be realized by numerous combinations of basic laser parameters, however this results in distinctive porosity characteristics and even at the same levels of build rate increase, pore characteristics, such as orientation, aspect ratio and size, can differ significantly.
|
|
| 8. |
- Jabir Hussain, Ahmed Fardan, 1996, et al.
(författare)
-
Fine-Tuning Melt Pools and Microstructures: Taming Cracks in Powder Bed Fusion—Laser Beam of a non-weldable Ni-base Superalloy
- 2024
-
Ingår i: Materialia. - : ELSEVIER SCI LTD. - 2589-1529. ; 34
-
Tidskriftsartikel (refereegranskat)abstract
- Powder Bed Fusion – Laser Beam (PBF-LB) of high γ’ strengthened Ni-base superalloys, such as CM247LC, is of great interest for high temperature applications in gas turbines. However, PBF-LB of CM247LC is challenging due to the high cracking susceptibility during PBF-LB processing (solidification cracking) and heat treatment (strain age cracking, mostly caused by residual stresses). This study focuses on understanding the impact of process parameters on microstructure, residual stresses and solidification cracking. Laser power (P), speed (v) and hatch spacing (h) were varied while the layer thickness (t) was fixed. The melt pool size and shape were found to be key factors in minimizing solidification cracking. Narrower and shallower melt pools, achieved using a low line energy density (LED = P/v ≤ 0.1 J/mm), gave low crack densities (0.7 mm/mm2). A tight hatch spacing (h = 0.03 mm) resulted in reduced lack of fusion porosity. Electron backscatter diffraction investigations revealed that parameters giving finer microstructure with 〈100〉 crystallographic texture had low crack densities provided they were processed with a low LED. Atom probe tomography elucidated early stages of spinodal decomposition in the as-built condition, where Cr and Al cluster separately. The extent of spinodal decomposition was found to be affected by the LED and the hatch spacing. Samples with low LED and small hatch spacing showed higher degrees of spinodal decomposition. X-ray diffraction residual stress investigations revealed that the residual stress is proportional to the volumetric energy density (VED = P/(v. h. t)). Although low residual stresses can be achieved by using low VED, there is a high risk of lack of fusion. Hence, other parameters such as modified scan strategy, build plate pre-heating and pulsed laser mode, must be further explored to minimize the residual stresses to reduce the strain age cracking susceptibility.
|
|
| 9. |
- Tolvanen, Sakari, 1984, et al.
(författare)
-
Microstructure and Mechanical Properties of Ti-6Al-4V Welds Produced with Different Processes.
- 2024
-
Ingår i: Materials. - : MDPI. - 1996-1944. ; 17:4
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of defects and microstructure on the mechanical properties of Ti-6Al-4V welds produced by tungsten inert gas welding; plasma arc welding; electron beam welding; and laser beam welding was studied in the present work. The mechanical properties of different weld types were evaluated with respect to micro hardness; yield strength; ultimate tensile strength; ductility; and fatigue at room temperature and at elevated temperatures (200 °C and 250 °C). Metallographic investigation was carried out to characterize the microstructures of different weld types, and fractographic investigation was conducted to relate the effect of defects on fatigue performance. Electron and laser beam welding produced welds with finer microstructure, higher tensile ductility, and better fatigue performance than tungsten inert gas welding and plasma arc welding. Large pores, and pores located close to the specimen surface, were found to be most detrimental to fatigue life.
|
|
| 10. |
- Zissel, Kai, 1995
(författare)
-
Influence of the Processing Atmosphere on Binder Jetting of Stainless Steel: From Printing to Sintering
- 2024
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Binder Jetting (BJT) is considered a promising Additive Manufacutring (AM) technology for the production of complex metal components due to its high productivity and cost efficiency compared to other AM technologies. The BJT technology is a multi-step process that consists of printing, curing, depowdering, debinding and sintering. Each process step includes individual process parameters. One crucial variable across each step is the processing atmosphere. A robust process is a prerequisite for manufacturing consistent green parts. Printing in BJT is conducted at ambient temperature. The reusability of the metal powder is considered unproblematic since no oxidation is expected during printing. However, the impact of powder reuse and specifically curing on printing behavior has not been extensively studied in BJT. Therefore, the first part of this study investigated the influence of powder reuse on powder characteristics and printing results for 17‑4 PH stainless steel. Furthermore, different curing atmospheres were compared. The green densities obtained after printing decreased from 4.71 g/cm³ to 4.47 g/cm³ after 20 build jobs, which correlated with an oxygen pickup of the powder during curing. In addition, the median particle size increased by ~1 µm after 20 build jobs. Curing in inert environments such as nitrogen (N2) is shown as advantageous since oxidation of the powder is limited. The debinding process aims to remove the binder efficiently without contaminating the material. Debinding can be conducted in air to utilize oxygen (O2) for binder decomposition. The powder is, however, prone to oxidation at elevated debinding temperatures. Consequently, the decrease of the oxygen content in the debinding atmosphere at 300 °C for 2 h was studied. The results demonstrated that the carbon introduced by the binder can enhance oxide removal by carbothermal reduction. Debinding in inert argon (Ar) resulted in low binder removal, but led to nearly complete oxygen removal after sintering. The formation of δ-ferrite was prohibited due to the high carbon content resulting in low sintered densities of ~88 %. Debinding in 1 vol.% O2 + Ar reduced oxygen content by 46 % relative to the virgin powder. At the same time, high densities of ~98 % were obtained with no carbon pick-up after sintering. Debinding in 3 vol.% O2 to 20 vol.% O2 removed the binder almost completely. While oxygen reduction was measured from brown to sintered components, the oxidation caused during debinding was not sufficiently reversed by carbothermal reduction during sintering in an inert Ar atmosphere.
|
|
