Addition Of Active Elements Research Articles

Viability of Cathodic Protection for Preventing Corrosion of Stainless Steel 316H in Molten LiF-NaF-KF

Molten fluoride salts are candidate heat transfer fluids in a number of applications such as generation IV molten salt nuclear reactors and concentrated solar power plants. However, a chief concern in the design of these systems is the corrosion of structural materials that come in contact with these molten salts. Redox control methods such as the purification of salt, the addition of active elements, and applied electrochemical potential can be efficient methods for preventing the corrosion of structural materials in molten fluoride salts. Applied electrochemical potential as a redox control method for application in molten fluoride salts has rarely been explored. This study seeks to understand the viability of impressed current cathodic protection (CP) at various currents as a redox control method to prevent corrosion of stainless steel 316H in molten LiF-NaF-KF (FLiNaK) salt. Results show that application of CP can be an effective method to prevent corrosion of SS316H in molten FLiNaK salt, but the applied current will have to be optimized to prevent undesirable side effects such as reduction of salt constituents, salt deposition on electrodes, etc.

The progress in titanium alloys used as biomedical implants: From the view of reactive oxygen species.

Titanium and Titanium alloys are widely used as biomedical implants in oral and maxillofacial surgery, due to superior mechanical properties and biocompatibility. In specific clinical populations such as the elderly, diabetics and patients with metabolic diseases, the failure rate of medical metal implants is increased significantly, putting them at increased risk of revision surgery. Many studies show that the content of reactive oxygen species (ROS) in the microenvironment of bone tissue surrounding implant materials is increased in patients undergoing revision surgery. In addition, the size and shape of materials, the morphology, wettability, mechanical properties, and other properties play significant roles in the production of ROS. The accumulated ROS break the original balance of oxidation and anti-oxidation, resulting in host oxidative stress. It may accelerate implant degradation mainly by activating inflammatory cells. Peri-implantitis usually leads to a loss of bone mass around the implant, which tends to affect the long-term stability and longevity of implant. Therefore, a great deal of research is urgently needed to focus on developing antibacterial technologies. The addition of active elements to biomedical titanium and titanium alloys greatly reduce the risk of postoperative infection in patients. Besides, innovative technologies are developing new biomaterials surfaces conferring anti-infective properties that rely on the production of ROS. It can be considered that ROS may act as a messenger substance for the communication between the host and the implanted material, which run through the entire wound repair process and play a role that cannot be ignored. It is necessary to understand the interaction between oxidative stress and materials, the effects of oxidative stress products on osseointegration and implant life as well as ROS-induced bactericidal activity. This helps to facilitate the development of a new generation of well-biocompatible implant materials with ROS responsiveness, and ultimately prolong the lifespan of implants.

Improving the wettability of Ag/ZrB2 system by Ti, Zr and Hf addition: An insight from first-principle calculations

The addition of active elements is an excellent method to improve the wettability and interfacial bonding strength between Ag and ZrB2. To quantitatively evaluate the interfacial behavior and structure stability of Ag (1 1 1)/ZrB2 (0 0 0 1) interface, the role of Ti, Zr and Hf additions in the interfacial bonding strength and electronic properties was investigated comprehensively by first-principle calculations. The B-terminated ZrB2 (0 0 0 1) surface is more active than the Zr-terminated surface under the lower B chemical potential. For the Ag (1 1 1)/ZrB2 (0 0 0 1) interface, the interface with center-site presents the largest work of adhesion (Wa) and the lowest interfacial energy for both Zr- and B-terminations. The Ti, Zr and Hf additions can greatly improve the Wa for Ag/ZrB2 interface (especially with the B-termination) when the Ag atom in 1st layer of Ag slab is substituted by active elements. The calculation on the electronic structure shows that the ionic bonding across Ag/ZrB2 interface is further enhanced while adding the active elements due to the strong interactions between the active elements and the closest B atomics. These results provide crucial fundamental insights to enhance the wettability of Ag/ZrB2 system by the addition of active elements.

Hybrid Additive Manufacturing Technologies – An Analysis Regarding Potentials and Applications

Imposing the trend of mass customization of lightweight construction in industry, conventional manufacturing processes like forming technology and chipping production are pushed to their limits for economical manufacturing. More flexible processes are needed which were developed by the additive manufacturing technology. This toolless production principle offers a high geometrical freedom and an optimized utilization of the used material. Thus load adjusted lightweight components can be produced in small lot sizes in an economical way. To compensate disadvantages like inadequate accuracy and surface roughness hybrid machines combining additive and subtractive manufacturing are developed.Within this paper the principles of mainly used additive manufacturing processes of metals and their possibility to be integrated into a hybrid production machine are summarized. It is pointed out that in particular the integration of deposition processes into a CNC milling center supposes high potential for manufacturing larger parts with high accuracy. Furthermore the combination of additive and subtractive manufacturing allows the production of ready to use products within one single machine.Additionally actual research for the integration of additive manufacturing processes into the production chain will be analyzed. For the long manufacturing time of additive production processes the combination with conventional manufacturing processes like sheet or bulk metal forming seems an effective solution. Especially large volumes can be produced by conventional processes. In an additional production step active elements can be applied by additive manufacturing. This principle is also investigated for tool production to reduce chipping of the high strength material used for forming tools. The aim is the addition of active elements onto a geometrical simple basis by using Laser Metal Deposition. That process allows the utilization of several powder materials during one process what enables the tailoring of the tools materials mechanical properties. Another aspect is the possibility of Laser Alloying of the tools surface to reduce abrasive and adhesive wear. This technique is especially interesting for tools used in hot stamping production.

The effects of active element additions on the oxidation performance of a platinum aluminide coating at 1100°C

Abstract The beneficial effects of active element additions to both overlay coatings and β -NiAl intermetallics are well documented in the literature. The addition of such elements has been noted to increase the adherence of a protective oxide scale, decrease the oxide growth rate and improve the mechanical properties of the oxide. The present study aimed to assess the effects of the ion implantation of either Hf or Y to a platinum aluminide on a MarM002 substrate, to determine whether the additions would act to improve the coating's performance under hot oxidation conditions. The samples were isothermally exposed to laboratory air for 100, 250 and 500 h at 1100 °C. Their performance was assessed by comparing the oxide growth rate, adherence and composition to that formed by an untreated coating. The additions were found to have had no observable effects on the performance of the coating, promoting oxides that had a similar adhesion, growth rate and composition as were formed on untreated systems. However, the study did reveal the detrimental effects of excessive hafnium peg formation and their role in the degradation of the coatings.

Thermodynamic modelling of wetting at silicon nitride/NiCrSi alloy interfaces

Through thermodynamic modelling of the reaction at ceramic-metal interface, wetting of a sintered silicon nitride was investigated with a series of Ni-based brazing alloys without addition of active elements. The thermodynamic calculations showed that NiCrSi alloys with Ni/Cr ratio of 3.5 and X Si < 0.25 will react with and wet Si 3N 4 ceramics at 1220 °C (1493 K) and P N 2 = 15 Pa. Environment verifications using sessile drop method confirmed the validity of the calculations and the assumptions made in the wetting model.

Imaging modes for bilateral confocal scanning microscopy

SummaryThe bilateral scanning approach to confocal microscopy is characterized by the direct generation of the image on a two‐dimensional (2‐D) detector. This detector can be a photographic plate, a CCD detector or the human eye, the human eye permitting direct visualization of the confocal image. Unlike Nipkow‐type systems, laser light sources can be used for excitation. A design called a carousel has been developed, in which the bilateral confocal scan capability can be added to an existing microscope so that rapid exchange and comparison between confocal and non‐confocal imaging conditions is possible. The design permits independent adjustment of confocal sectioning properties with lateral resolutions better than, or, in the worst case equivalent to, those available in conventional microscopy. The carousel can be considered as a stationary optical path in which certain imaging conditions, such as confocality, are defined and operate on part of the imaging field. The action of the bilateral scan mirror then extends this image condition over the whole field. A number of optical arrangements for the carousel are presented which realize various forms of confocal fluorescence and reflection imaging, with point, multiple point or slit confocal detection arrangements. Through the addition of active elements to the carousel direct stereoscopic, ratio, time‐resolved and other types of imaging can be achieved, with direct image formation on a CCD, eye or other 2‐D detectors without the need to modify the host microscope. Depending on the photon flux available, these imaging modes can run in real‐time or can use a cooled CCD at (very) low light level for image integration over an extended period.

High temperature corrosion study on yttrium modified aluminide coatings on IN 713C

The addition of active elements in high temperature materials may improve corrosion resistance extensively. In general, the active elements are incorporated in the form of an alloying element either in the bulk or in overlay coatings, as an oxide dispersion, or by ion implantation. In this experiment, yttrium was incorporated by an ion plating method either before or after pack aluminizing to maximise the corrosion resistance of IN 713C. Various combinations of pack aluminizing and yttrium ion plating were examined with respect to coating sequence, aluminium activity, and corrosion environment. From all the various coating combinations examined, the best corrosion resistance was obtained from the H/A + Y (high activity aluminizing + Y-ion plating) type multilayer coatings. Uniformity of the Y deposition was greatly dependent upon the surface condition of the aluminide coating layer. The high activity aluminide coating gave better uniformity of Y deposition than did the low activity aluminide coating. Improvement of corrosion resistance by the Y-modified aluminide multilayer coatings of H/A + Y type may occur because Y present between the A12O3 columns improves the A12O3 scale adherence and substantially prohibits depletion of Al in the aluminide coating layer.

High temperature internal oxidation behaviour of dilute Ni-Al alloys

The internal oxidation of dilute Ni-Al alloys, either pure or containing small additions of tantalum or hafnium, was investigated at 1200° C in air. The advance of the precipitation zone followed a parabolic relationship at a slightly decreasing rate with increasing aluminium content. The presence of active elements had no appreciable effect on the growth rate. The precipitate shape, size and spacing depended upon the aluminium concentration and more significantly on the active element additions. The morphology varied from polyhedral crystallites and epitaxial platelets in the Ni-0.5 wt% Al alloy, to well defined cylindrical rods extending across the precipitation zone approximately normal to the reaction interface, in the alloys of higher aluminium content. An also continuous and similarly oriented plate-like morphology was observed in the active element-containing alloys. X-ray microanalysis indicated that the continuous precipitates consisted of NiAl2O4 and Al2O3. The former phase comprised approximately 65±5% of the outer region of the precipitation zone. Aluminium depletion in the alloy ahead of the precipitation front and a consequent enrichment in the form of oxide within the reaction zone inferred that growth was controlled by simultaneous outward aluminium and inward oxygen diffusion. No correlation was found between either the growth rate or oxygen permeability and the distribution of the precipitates. It was, therefore, concluded that the interfacial boundaries were ineffective in accelerating oxygen transport at this elevated temperature.

Erosion resistance of Co-Cr-Al coatings containing active element additions

Materials resistant to high temperature corrosion and small particle impact erosion are necessary in the design and construction of energy conversion systems. Al 2O 3-forming M-Cr-Al coatings with active element additions on an IN 738 substrate have exhibited enhanced resistance to erosion damage of their oxide scales owing to improved adherence of the scale. This improvement results from modifications of the scale morphology by the active element additions which encourage pegs of oxide that penetrate into the coating. Other active element additions cause a porous scale to form, increasing the erosion susceptibility. The thin alumina scales behave as a brittle material with the highest erosion rate occurring at an impingement angle of 90° and scale removal occurring by a chipping action.

The oxidation behavior of CoCrAI systems containing active element additions

The effect of small amounts of yttrium (up to 1 wt. %) and hafnium (up to 1.5 wt.%) on the oxidation behavior of Co-Cr-Al alloys in the temperature range 1000–1200°C for times up to 1000 hr in air has been studied. The major portion of the study has been concerned with Co-10Cr-11Al base alloys. Both isothermal and cyclic tests have been carried out; the cycle used consisted of 20 hr at temperature, followed by cooling to room temperature. Both additions reduce the overall oxidation, Hf somewhat more so than Y. In part, this is due to the improved adhesion between scale and alloy reducing scale spallation at temperature, and in part due to possible modification of the Al2O3 grain size. The former factor is far more critical under thermal cycling conditions. Under isothermal conditions the oxidation rate increases with increasing Hf content with all but the 1.5 wt.% alloy oxidizing more slowly than the Hf-free alloy; increase in Y content has the reverse effect. Under thermal cycling conditions the 0.3 and 1.0 wt.% Hf alloys show the lowest overall weight gain. Metallographic evidence suggests that the improved scale adhesion is due principally to a pegging mechanism; the active elements promote the growth of intrusions of Al2O3 into the alloy. However, if the intrusions are too large, they can act as initiators of scale failure.