During the last decade, friction stir welding has various applications in the automotive, shipbuilding, and aerospace industry due to its versatility. More recently, there have been trials to combine ...FSW with ceramic nanoparticle reinforcement in order to form MMCs locally on the weld line. This combination could result to potential applications on the above industries. In the present study, optical and electron microscopy, as well as microhardness and tensile testing, were used in order to determine the effect that SiC and TiC nanopowders have on the weld nugget of AA6082-T6 butt welds. It is the first time that such a thorough study via TEM in combination with EDS was conducted for this alloy. Emphasis was given on the distribution of dislocations and on the presence of the intermetallic and reinforcing particles in the weld. It was found that the grain size of all the specimens was dramatically decreased due to the dynamic recrystallization phenomenon. This also provoked the dilution of a lot of the intermetallic particles of the base metal and the multiplication of the dislocations. Between the two reinforced specimens, the SiC presented higher elongation while the TiC presented higher microhardness.
Hydrogen effect on an API 5L X65 low carbon ferritic-bainitic steel is investigated, by evaluating the fracture toughness parameters in air and in hydrogen environment. The hydrogen environment is ...manifested by in situ hydrogen charging of the X65 steel, using the electrolytic solution NS4, which simulates the electrolyte trapped between the pipeline steel and the coating in a buried pipeline. The fracture toughness results of the X65 are compared to two other pipeline steels with different microstructures, namely an X52 and an X70, possessing a banded ferritic-pearlitic and banded ferritic-mixed bainitic-pearlitic microstructure, respectively. The X65 steel exhibits significant reduction of fracture toughness parameter J0 integral due to hydrogen charging and insignificant variation of fracture toughness parameter KQ. Comparing the three steels, the lowest reduction of J0 integral due to hydrogen charging, is met on the X52 and the highest in the X65.
•X65 pipeline steel fracture toughness is in situ hydrogen tested.•X65 experiences larger reduction of J0 compared to banded ferrite-pearlite X52.•J0 reduction is also larger compared to banded ferrite-mixed bainite-pearlite X70.•Low carbon ferrite-bainite detrimental for hydrogen reduction of J0.•Martensite/austenite constituents also detrimental for hydrogen reduction of J0.
In the present work, similar and dissimilar friction stir welds have been produced on 6-mm-thick plates of AA6082-T6 and AA7075-T651. The microstructural characteristics and the mechanical response ...of both similar and dissimilar welds were investigated aiming to determine the major differences between them. Material mixing of the dissimilar weld nugget, which was created after the welding process, was studied in order to determine the produced different areas and their dominant alloying elements in this zone. Microstructural investigation was made in the welding zones of similar and dissimilar friction stir welds and indications of partial dynamic recrystallization were observed in the thermomechanically affected zone of the similar welds. Transverse and longitudinal microhardness distributions determined the heat affected zone as the weaker area in the welded specimen. After tensile testing, the fracture of the similar and the dissimilar welds at heat affected zone demonstrated the good bonding and weld quality of the similar and dissimilar weld nuggets.
Cancer research has made great progress in the recent years. With the increasing number of options in diagnosis and therapy the implementation of tumorboards (TUBs) has become standard procedure in ...the treatment of cancer patients. Adherence tests on tumor board decisions are intended to enable quality assurance and enhancement for work in tumor boards in order to continuously optimize treatment options for cancer patients.
Subject of this study was the adherence of the recommendations made in three of 14 tumorboards, which take place weekly in the Center for Integrated Oncology (CIO) at the University Hospital Bonn. In total, therapy recommendations of 3815 patient cases were checked on their implementation. A classification into four groups has been made according to the degree of implementation. A second classification followed regarding the reasons for differences between the recommendation and the therapy which the patient actually received.
The study showed that 80.1% of all recommendations in the three TUBs were implemented. 8.3% of all recommendations showed a deviance. Most important reasons for the deviances were patient wish (36.5%), patient death (26%) and doctoral decision, due to the patient's comorbidities or side effects of the treatment (24.1%).Interestingly, deviance in all three tumor boards in total significantly decreased over time.
Aim of the study was to clarify the use of tumor boards and find approaches to make them more efficient. Based on the results efficiency might be optimized by increased consideration of patients` preferences, improved presentation of patient-related data, more detailed documentation and further structuring of the tumor board meetings.
The aim of the present research is the fabrication of MWCNT-reinforced Al composite foams on localized regions of metallic parts using a novel friction stir processing (FSP) route. This route ...consists of friction stir processing passes for the integration of the foaming and the stabilizing agents in the aluminum matrix (precursor specimens) and a separate foaming stage at a laboratory furnace. The precursor specimens were manufactured by mixing a blowing agent powder (0.4%
w
/
w
TiH
2
) and a stabilization agent nanopowder (2%
w
/
w
MWCNT) into the aluminum alloy matrix (AA5083-H111), using the intense stirring action of FSP. The porous aluminum obtained at the foaming stage has a medium porosity of 54% with a high circularity of pores. The microstructural investigation was performed by means of optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) technique. All of the above were correlated with microhardness distribution in both the precursor and the foamed specimens. The microstructure was found to be closely related to microhardness distribution perpendicular to the traversing direction of the FSP tool for both precursor and foamed specimens.
The API 5L X70 and X52 pipeline steel weld fracture toughness parameters are measured in a hydrogen environment and compared to the ones in air. The hydrogen environment is created by in situ ...hydrogen charging, using as an electrolyte a simulated soil solution, with three current densities, namely 1, 5 and 10 mA/cm
2. A specially designed electrolytic cell mounted onto a three-point bending arrangement is used and hydrogen charging is performed during the monotonic loading of the specimens. Ductility is measured in terms of the
J
0 integral. In all cases a slight change in toughness was measured in terms of
K
Q. Reduction of ductility in the base metal is observed, which increases with increasing current density. A more complex phenomenon is observed in the heat affected zone metal, where a small reduction in ductility is observed for the two current densities (1 and 5 mA/cm
2) and a larger reduction for the third case (10 mA/cm
2). Regarding microstructure of tested X70 and X52 base and HAZ metal, it is observed that the hydrogen degradation effect is enhanced in banded ferrite–pearlite formations. The aforementioned procedure is used for calculating the fracture toughness parameters of a through-thickness pipeline crack.
► Pipeline steel welds fracture toughness is examined against hydrogen environment. ► In situ hydrogen charging is used using various current densities. ► Large reduction of
J
0 is observed for the base metal and small reduction for the HAZ. ► Banded ferrite–pearlite microstructure is detrimental for hydrogen reduction of
J
0. ► Damage type is hydrogen embrittlement.
The aluminum alloy AA5083 is a technologically important structural alloy as it is lightweight, with outstanding weldability and formability, moderate corrosion resistance and strength, making it ...suitable for a wide range of marine and transportation applications. In the present study, AA5083/nano-γAl
2
O
3
composite metal foam was fabricated using a friction stir processing route (FSP). More precisely, the paper presents a first attempt to use grooves for the integration of the foaming and stabilizing agent on the metal foam precursor by FSP. The implementation of grooves allows to control the amount of foaming, integrates the stabilizing particles within the precursor and permits the production of localized metal foams. Unlike the commonly used manufacturing processes, only one plate is required for the production of the precursor sample in the proposed process. Therefore, this process can be easily implemented in the industrial sector. Furthermore, γ-Al
2
O
3
nanostructured reinforcement, which is characterized by increased interfacial energy, was utilized as a stabilizing agent. The precursor specimens were manufactured by mixing blowing agent powder (0.4% w/w TiH
2
) and stabilization agent nanopowder (2% w/w γ-Al
2
O
3
) into the 5083 aluminum alloy matrix using FSP. The effects of the number of FSP passes and the foaming conditions (holding temperature and time) on the pore density, morphology and distribution were investigated. The microstructure and porosity evolution of the so-obtained metal foam was also examined and analyzed. Results indicate that, following the foaming procedure, a porosity of 60% and an equivalent pore diameter ranging from 0.2 to 3.3 mm can be achieved. Moreover, the microstructure was found to be closely related to microhardness distribution perpendicular to the traversing direction of the FSP tool for both precursor and foamed specimens.
In the present study, a new-developed method which leads to the determination of the number of beads in the single-V butt weld joint, is introduced and applied to robotic Flux-cored arc welding ...technique. The correlation between the wire feed rate, the wire variables, the torch welding speed, and the bead reinforcement area is investigated and determined via a mathematical formula. The investigation includes a theoretical section where the method is analyzed and several confirmation experiments where the theoretical function of the bead reinforcement area is verified. Moreover, the method is applied to a multipass weld of steel plates with preselected welding parameters, through the determination of a proposed weld profile based on the fundamental principles, standards, and rules of the welding technology. The methodology can be also expanded in the case of multipass welding joints with a different edge preparation such as J, U, or double-V in butt and tee weld joints.
The present study deals with the effect of the heat input on the tensile properties of AH-40 fatigue crack arrester steel (FCA). The joining process was implemented by the use of the robotic ...metal-cored arc welding technique with five heat input levels (0.5, 1.0, 1.5, 2.0, and 2.5 kJ/mm), which led to different microstructural and mechanical properties of the weldments. Initially, the microstructural characterization of the welds was carried out, followed by the measurement of the microhardness distribution, while appropriate coupons extracted from the welds were tested under uniaxial tensile loading and examined fractographically. The experimental results of the analysis correlate the selected operational parameters with the properties of the welds and principally with their tensile performance. Consequently, the obtained data result in the optimization of the structure, leading to the conclusion that the optimum heat input should be approximately 1.0 kJ/mm when AH-40 FCA steel plates of 13-mm thickness are welded.
In the present study, the feasibility of joining 2 mm thick plates of AA5754-H114 to mild steel was examined. Sound friction stir dissimilar butt welding was achieved between thin plates of the ...automotive grade 5754 aluminum alloy and mild steel for the first time. Moderate rotational speed and a rather slow traverse speed were used. The mechanical properties of the weld were close to the equivalent of the aluminum base metal and a rise in the microhardness of the weld nugget of around 40% compared to the equivalent of the mild steel base metal was presented. An interdiffusion layer with a width of around 5 μm was created at the interface of the two alloys, the extended width of which probably affects positively the mechanical properties of the welds.
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