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 fracture studies of helium ion irradiated stainless steel
Abstract Tensile tests on helium ion irradiated stainless steel samples have been performed in a 500 kV transmission electron microscope. The tests were carried out to fracture while the specimen was under observation. The samples were irradiated with an 80 keV helium ion beam at fluxes of 3 × 1014cm−2sec−1 while the sample was being pulled in the microscope. The test temperatures were 25 and 600°C. Very considerable differences in specimen fracture behavior ranging from fairly ductile to extremely brittle were observed. The fracture tests at room temperature showed a coarsening of the slip lines during ductile failure. Fracture at 600°C produced a brittle intergranular fracture extending much deeper into the sample than the projected range of the helium. Room temperature fracture in samples with an extensive bubble population on the grain boundaries and in the grain interior was transgranular. Evidence of the role of helium along the grain boundaries included grain boundary ridges forming after fracture on the sample surfaces near the fracture edge and denuded zones of helium bubbles next to the grain boundaries. Athermal bubble enlargement accompanied crack propagation.
In Vivo Comparison of Synthetic Macroporous Filamentous and Sponge-like Skin Substitute Matrices Reveals Morphometric Features of the Foreign Body Reaction According to 3D Biomaterial Designs
Synthetic macroporous biomaterials are widely used in the field of skin tissue engineering to mimic membrane functions of the native dermis. Biomaterial designs can be subclassified with respect to their shape in fibrous designs, namely fibers, meshes or fleeces, respectively, and porous designs, such as sponges and foams. However, synthetic matrices often have limitations regarding unfavorable foreign body responses (FBRs). Severe FBRs can result in unfavorable disintegration and rejection of an implant, whereas mild FBRs can lead to an acceptable integration of a biomaterial. In this context, comparative in vivo studies of different three-dimensional (3D) matrix designs are rare. Especially, the differences regarding FBRs between synthetically derived filamentous fleeces and sponge-like constructs are unknown. In the present study, the FBRs on two 3D matrix designs were explored after 25 days of subcutaneous implantation in a porcine model. Cellular reactions were quantified histopathologically to investigate in which way the FBR is influenced by the biomaterial architecture. Our results show that FBR metrics (polymorph-nucleated cells and fibrotic reactions) were significantly affected according to the matrix designs. Our findings contribute to a better understanding of the 3D matrix tissue interactions and can be useful for future developments of synthetically derived skin substitute biomaterials.