Dynamic HVEM Observations of Metals and Alloys during in-Situ Helium Ion Irradiations
A 200 kV ion accelerator, with a PIG source for accelerating ionized gases, was coupled to a 500 kV transmission electron microscope in order to investigate the effects of helium irradiation on the development of microstructure in candidate fusion reactor first wall material. The microstructural evolution in nickel and in type 316 stainless steel bombarded by 80 keV helium ions was monitored via video recordings. The effect of specimen thickness and temperature and the effect of plastic deformation during irradiation was considered. In order to conduct these experiments a quantitative load-elongation hot tensile stage was constructed with a capability for monitoring specimen current continuously during the experiment. It was found that surface exfoliation and blistering may occur in specimens thinner than the mean projected range of helium ions. However, in the thinnest specimen regions, surface layer removal is replaced by the bending of individual grains. Blistering apparently can occur when underpressurization of bubbles exists. Plastic deformation during helium ion irradiation can lead to denuded layers adjacent to some grain boundaries and can produce removed surface layers whose thickness is several times greater than the project mean range of the incident helium ions.
In-situ HVEM Investigations under the Influence of Ion Beams
A 200 kV ion accelerator was coupled to a 500 kV TEM for in-situ studies of the 80 keV He+ irradiation of 316 stainless steel. Dynamic and static observations of bubble growth, exfoliation and blistering show that slip bands, incoherent twin boundaries and grain boundaries are preferred sites for helium bubble formation. Bubble growth is enhanced by plastic deformation during irradiation. Exfoliation and blistering occur in samples thinner than the projected range of 80 keV He+ ions. Crack propagation during tensile tests proceeds through the bubbles enlarging them in diameter by a factor of two. Bubble enlargement also accompanies the formation of a blister cap. Brittle intergranular failure, even in samples with a large bubble population on the grain boundaries, occurred only when tensile tests were performed at elevated temperatures. 
 
 
 
Ein 200-kV-Ionenbeschleuniger wurde an ein 500-kV-Transmissions-Elektronenmikroskop gekoppelt, um in-situ-Untersuchungen an rostfreiem Stahl 316 bei Bestrahlung mit He+-Ionen mit 80 kV durchzufuhren. Dynamische und statische Untersuchungen des Blasenwachstums, der Exfoliation und des Blistering-Phanomens zeigten, das Gleitbander, inkoharente Zwillingsgrenzen und Korngrenzen die bevorzugten Orte fur die Bildung von Heliumblasen sind. Das Blasenwachstum wird durch die plastische Deformation wahrend der Bestrahlung beschleunigt. Exfoliation und Blistering laufen in Proben ab, die dunner als die projizierte Reichweite der 80 keV-He+-Ionen sind. Wahrend der Zugversuche geht die Risausbreitung durch die Blasen weiter, wobei der Durchmesser der Blasen um das Doppelte erhoht wird. Korngrenzensprodbruch kommt sogar in Proben mit hoher Blasendichte nur dann vor, wenn Zugversuche bei erhohten Temperaturen durchgefuhrt werden.
Efficacy of Biodentine as an Apical Plug in Nonvital Permanent Teeth with Open Apices: An In Vitro Study
The aim of this study was to evaluate the apical microleakage of Biodentine and MTA orthograde apical plugs and to compare the effect of thickness of these biomaterials on their sealing ability. A total of eighty maxillary anterior teeth were used. The apices were removed by cutting with a diamond disc (Jota, Germany) 2 mm from the apical root end in an attempt to standardize the working length of all specimens to 15 ± 1 mm. Both materials were placed in 1–4 mm thickness as apical plugs root canal. Root canal leakage was evaluated by the fluid filtration technique. One-way ANOVA was used in order to determine normality of dispersal distribution of parameters; thereafter, results were analyzed by Kolmogorov-Smirnov test. Overall, between microleakage values of MTA and Biodentine regardless of apical plug thickness, no difference was observed. In terms of plug thickness, a statistically significant difference was observed between the subgroups of MTA and Biodentine (p < 0.05). The apical sealing ability of Biodentine was comparable to MTA at any apical plug thickness.