Study of autoabsorption for total α and β counting

The RaMsEs Group (Radioprotection et Mesures Environnementales) of the IPHC performs research and offers services mainly in the field of radioactivity measurements and sample analysis. This report will describe some of our recent experience using a semiautomatic evaporation system to prepare large area thin deposits for total α and β counting and gives experimental and simulated results for the autoabsorption coefficients.     

High temperature creep of a hot-pressed β-sialon

The four-point bending creep properties of a hot-pressed β-sialon with Sm–melilite solid solution (denoted as M′) as intergranular phase have been studied in the temperature range 1250–1350°C in air. Creep rates plotted against stresses gave stress exponents of 1.45, 1.51 and 1.72 at 1250, 1300 and 1350°C, respectively, and Arrhenius plot between creep rate and temperature yielded a creep activation energy of 576 kJ mol⁻¹. Cavities were found to be mainly on the triple grain junctions. Diffusion coupled with grain boundary sliding and accompanied by the formation of wedge-shaped cavities was identified as the dominant creep mechanism.     

Microstructure and mechanical properties of a high nitrogen titanium alloy

High nitrogen titanium alloy with the chemical composition of Ti–4%Cr–0.6%N was produced by solution nitriding to nitrogen-free Ti–4%Cr alloy, and then its microstructure was controlled to have fine (α + β) dual phase structure by aging treatment to improve the ductility. As solution-nitrided specimen has a platelet hcp-martensitic structure (α′) and is characterized by hard but brittle nature that has been produced by solid solution of 0.6% of nitrogen. On the following aging treatment, fine β phase formed along the original plate boundaries, resulting in a fine (α + β) dual phase microstructure. X-ray and EELS analyses revealed that nitrogen is greatly concentrated in the tempered α′ phase. Although the hardness of as-quenched material gradually decreases during the aging treatment with increasing volume fraction of β, the hardness can be kept much higher than that of the aged Ti–4%Cr alloy without nitrogen. As a result of tensile testing, it was found that the aged Ti–4%Cr–0.6%N alloy has high tensile strength over 1 GPa with moderate ductility.     

Effects of precipitation phases on the hydrogen embrittlement sensitivity of Inconel 718

We investigated the effects of precipitation phases on the hydrogen embrittlement (HE) sensitivity of Inconel 718 by means of tensile tests. Hydrogen was charged into the test specimens via a cathodic charging process prior to the tensile tests. Various heat treatments were applied to conventionally aged specimens to fabricate specimens with different precipitation conditions for the γ″ phase and the δ phase. For each precipitation condition, we fabricated two specimens, one of which was charged with hydrogen before the tensile test. All specimens were tensioned under identical tensile conditions. The percent loss of the reduction of area (RA) caused by pre-charged hydrogen was used to assess HE sensitivity. Both the δ phase and the γ″ phase were found to play significant roles in altering HE sensitivity of Inconel 718. When these phases were totally dissolved, the HE sensitivity of the alloy was very low. The percent loss of RA decreased along with a decrease in the fractional volume of γ″. The δ-free aged alloy had greatly enhanced HE resistance, the same level as that of conventionally annealed alloy, and its strength was equal to that of the conventionally aged alloy. Fracture origins noted on the specimens were located on the surface layers and displayed brittle cleavage when pre-charged hydrogen was utilized. Local transgranular cleavages initiated from the δ/matrix were also observed in conventionally aged specimens, where there was a presence of pre-charged hydrogen. Therefore, the δ phase was considered to promote HE by initializing micro-cracks from δ/matrix interfaces. Since the δ-free aged alloy has both good strength and good ductility, we propose that it is advantageous for fabricating some hydrogen-containing parts.     

Identification of the anthelix motif in the TGF‐β superfamily by molecular 3D‐Rapid Prototyping

3D‐Rapid Prototyping (3D‐RP) is a novel technique for the construction of highly accurate three‐dimensional polyamide models of biomolecules. This method has been shown to be a valuable tool in the modeling of protein‐protein‐interactions as well as in the analysis of surface topography. Using this technique we were recently able to identify a so far unknown structure on the concave side of bone morphogenetic protein 2 (BMP‐2). Since this structure is the imprint of a left‐handed helix we have called this negative an unthelix. Obviously this novel structural feature of BMP‐2 may act as a binding side for endogenous ligands. BMP‐2 belongs to the highly conserved Transforming Growth Factor‐β (TGF‐β) superfamily, a large group of multifunctional peptides controlling differentiation, proliferation and repair in multicellular organism. The protomer structures of all members share a cystine‐knot motif as a characteristic feature. The question therefore arose whether a) the novel anthelical motif found in BMP‐2 is a common structural feature of this family and b) if there are any differences in terms of pitch and radius of the anthelix. As anthelical structures are difficult to visualize and nearly impossible to quantify using 3D molecular visualization software we constructed models of BMP‐2, BMP‐7 and TGF‐β2 from X‐ray crystallographic data by 3D‐Rapid Prototyping (3D‐RP). The anthelix motif was found in BMP‐2, BMP‐7 and TGF‐β2 with similar values for pitch (ca. 8‐10 nm) and radius (ca. 0.5‐0.7 nm). In contrast the anthelical motif was not found in a 3D‐RP model of human chorionic gonadotropin (HCG) which is also a member of the cystine‐knot family but doesn’t belong to the TGF‐β superfamily. These results were corroborated by measurements of the intersubunit angle of these dimeric proteins (141‐149°) and the distances between the center of mass (1.68‐1.96 nm) of the subunits both of which appear to be determinants of the anthelical pitch. We conclude that the anthelical groove on the concave side is a common structural motif of BMP‐2, BMP‐7 and TGF‐β2 and maybe of the whole group of the TGF‐β superfamily.