The oxide growth during the decarburization process of non-oriented silicon steel sheets alloyed with 0.5 and 1 mass% of aluminium was studied using high-resolution auger electron spectroscopy ...(HRAES), the chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). The samples were annealed in a H
2–H
2O–N
2 gas mixture with different oxygen potential in the temperature range from 800 to 1050°C. We found that oxide scale was a mixture of FeO, Fe
3O
4 and SiO
2 and Fayalite (FeSi
2O
4). This oxide scale was porous. In the high Al alloyed sheets (2 mass% Si and 1 mass% Al) the oxide scale was a mixture of FeO, Fe
3O
4, and Al
2O
3 and also Hercynite (Fe Al
2O
4). In this case the oxide scale was compact. For thermodynamic calculations of Fayalite and Hercynite formation during the decarburization process the Gibbs energy minimization model (GPRO) was applied (Koroušić, Kovine zlitine tehnol 1994;28:609; Koroušić and Rosina, RadexRundsch 1994;1(2):523).
In this paper, we present the mechanisms of premature fracture of modular neck stems in two case studies: (I) when the neck and stem are both made of the same Ti6Al4V alloy, and (II) when the neck ...and stem are made from two different alloys, CoCrMo and Ti6Al4V alloy. Our study integrates two orthopedic patients who have undergone primary uncemented THA for usual indications in two orthopedic centers (Community Health Centre and University Medical Centre). Both centers are part of the national public health care system. Both surgeries were performed by two skilled orthopedic surgeons with more than 10 years of experience in THA. The survivorship of the modular neck of cast CoCrMo alloy was 24 months. The survivorship of the modular neck from Ti6Al4V alloy was 84 months. Multivariate analyses were performed to assess the differences in the fretting, corrosion, and fatigue of the two prematurely failed modular neck stems: stereo light microscopy (SLM), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). Patient demographic information, including sex, age, body mass index, survivorship of implants, and reason for the revision, was collected from medical records. We found that fretting and fatigue occurred on both neck-stem retrievals due to additional galvanic corrosion, but the CoCrMo/Ti6Al4V alloy system suffered more corrosion due to additional galvanic corrosion and fractured earlier than the Ti6Al4V/Ti6Al4V metal alloy system. Both metallic alloy systems used in this application are known to be highly corrosion-resistant, but the bio-tribo-corrosion processes need to be understood in detail and characterized so that appropriate improvements in design and materials can be made.
The surface, corrosion and wear properties of new and in vivo exposed nickel titanium (NiTi) and stainless steel (SS) archwires used in orthodontic treatment were investigated. Electrochemical and ...tribo-electrochemical tests in artificial saliva were performed in order to define corrosion properties and to estimate wear rate of new and in vivo exposed NiTi and SS archwires. The surface chemical analysis of the passive film on the NiTi and SS archwires before and after tribocorrosion tests was performed by Auger Electron Spectroscopy (AES). In vivo exposed NiTi and SS archwires had better electrochemical properties than new archwires due to the protective nature of oral deposits. Total wear and coefficients of friction were higher among in vivo exposed archwires and higher in NiTi archwires in comparison to SS archwires. The estimated thickness of the TiO2 passive film on as-received NiTi is 8 nm, while the passive Cr2O3 film on as-received SS is just 1–2 nm. On in vivo exposed NiTi archwire, a 60–80 nm thick organic film/dental plaque was observed, and on SS, it was thinner, at about 60 nm. This research shows the importance of combining AES with electrochemical testing, to characterize tribocorrosive properties of NiTi and SS orthodontic archwires.
During the recrystallization microalloyed Sn in non-oriented electrical steel segregates to the surface and on grain boundary and affects the texture development. In spite of the fact that the grain ...boundary segregation is much smaller compared to surface segregation, both have an influence on recrystallization and on texture development in electrical steel. Auger electron spectroscopy (AES) was used to measure the grain boundary and surface segregation of Sn in non-oriented electrical steels alloyed with different Sn weight contents (0.025, 0.05 and 0.1 %). The grain boundary segregation of the specimens, which were previously aged at 530ºC for various times and were fractured under UHV conditions, was measured. The surface segregation temperature dependence and its kinetics were followed in polycrystalline specimens in the temperature range from 400 to 900ºC on the grains of known crystallographic orientations: (100), (111) and (110). The textures were measured by X-ray texture goniometer and the results were presented as orientation distribution functions (ODF). By controlled surface and grain boundary segregation it is possible to achieve the selective grain growth which improves the electrical properties of non-oriented electrical steel. The best results were obtained by alloying it with 0.05 wt% Sn.
Different electron beam based techniques such us SEM/EDS and AES are very similar with regard to their imaging capabilities, but there are significant differences in the compositional information ...they can provide about the sample. In order to determine the usefulness of a technique for the identification of inclusions in spring steel the SEM/AES analysis techniques were used and are shown to be well suited for characterizing of these inclusions. From the results it was possible to evaluate the nature of inclusions, their location, size and chemical composition. It is evident from this study that applications of different techniques in inclusion determination are more representative and reflect inclusion size distribution in sample more objectively.
Nickel-titanium (NiTi) orthodontic archwires are crucial in the initial stages of orthodontic therapy when the movement of teeth and deflection of the archwire are the largest. Their great mechanical ...properties come with their main disadvantage—the leakage of nickel. Various in vitro studies measured nickel leakage from archwires that were only immersed in the medium with little or minimal simulation of all stress and deflection forces that affect them. This study aims to overcome that by simulating deflection forces that those archwires are exposed to inside the mouth of a patient. NiTi orthodontic archwires were immersed in CACO2-2 cell culture medium and then immediately loaded while using a simulator of multiaxial stress for 24 h. After the experiment, the surface of the NiTi orthodontic archwires were analysed while using scanning electron microscopy (SEM) and auger electron spectroscopy (AES). The observations showed significant microstructural and compositional changes within the first 51 nm thickness of the archwire surface. Furthermore, the released nickel and titanium concentrations in the CACO2-2 cell culture medium were measured while using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). It was found out that the level of released nickel ions was 1.310 µg/L, which can be assigned as statistically significant results. These data represent the first mention of the already detectable release of Ni ions after 24 h during the simulation of mechanical loading in the CACO2-2 cell culture medium, which is important for clinical orthodontic praxis.
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