Effect of thermomechanical processing on the mechanical biofunctionality of a low modulus Ti-40Nb alloy

Different hardening strategies were evaluated regarding their potential to improve the mechanical biofunctionality of the cast and solution-treated low modulus β-Ti alloy Ti 40Nb. The strategies are based on thermomechanical treatments comprised of different hot- and cold-rolling steps, as well as annealing treatments aiming at the successive exploitation of different hardening mechanisms (grain boundary hardening, work hardening and precipitation hardening). Quasi-static tensile testing revealed that grain refinement by one order of magnitude has only a small impact on improving the mechanical biofunctionality of Ti-40Nb. However, work hardening effectively improves the tensile strength by 30% to a value of 650MPa, while retaining Young׳s modulus at 60GPa. The α-phase precipitation hardening was verified to have an increasing effect on both, strength and Young׳s modulus. Thereby, the change of Young׳s modulus dominates the change of the strength, even at low α-phase fractions. The pseudo-elastic behavior of Ti 40Nb is discussed under consideration of the microstructural changes due to the thermomechanical treatment. The texture changes evolving upon cold-rolling markedly influence the recrystallization behavior. However, the present results do not show a significant effect of the texture on the mechanical properties of Ti-40Nb.

K-Ar-Altersbestimmungen an Ultrabasiten des Baltischen Schildes

The K-Ar-ages of five ultrabasic rocks from the Baltic Shield were determined. K-Ar-ages of 3.7 to 8.8 x 109 y were obtained. Two samples were cut into fractions with different potassium content and a partial correlation of the argon content with the potassium content in the separated fractions was noticed. The question of extraneous argon causing higher age values is discussed. Taking into consideration the previous results obtained by GERLING et al., it may be said, that extremely high Ar40/K-ratios are the rule for ultrabasic rocks from the Baltic Shield. As a consequence of this fact, it is not likely that all these rocks have the age only of the precambrian pluton in which they are incorporated. Assuming that the alpinotype peridotites were transported upwards in the form of solid fractions from the upper mantle, it is possible, that actually radiogenic argon exists more or less in the sample.

The highest Ar40/K-ratios (according to ages ranging from 5.9 to 10.9 x 109 y) exhibit the samples with potassium contents below 100 ppm. Samples with potassium contents more than 1‰ have much smaller Ar40/K-ratios (according to ages from 4.2 to 5 x 109 y) . Excess argon probably causes the extremely high “ages” of more than 7 x 109 y. The ages from relative potassium-rich samples will eventuible show the true age. The most likely value for this age is 4.2 x 109 y, measured for a peridotite with 0.49% potassium content.

129I/127I: a Puzzling Early Solar System Chronometer

We report I-Xe ages and other relevant xenon data for seven ordinary chondrites from H and L-groups of petrologic types 4-6, which were selected on the basis of minimum weathering and shock effects. Nevertheless, no chronological order with respect to the I-Xe ages exists among the different petrologic types. We demonstrate, however, that the degree to which the 1-Xe record is preserved in these chondrites, but not necessarily the age, is dependent on the thermal metamorphic history. In order to explain the lack of chronological order among the chondrites, spatiotemporal variations in the condensation-accretion process or inhomogeneities in the isotopic composition of iodine in the solar nebula is required.

Direct measurement of the 7Be solar neutrino flux with 192 days of borexino data

We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49+/-3stat+/-4syst counts/(day.100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4sigma C.L. Our result is the first direct measurement of the survival probability for solar nu(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar nu(e), and the limit on the effective neutrino magnetic moment using solar neutrinos.

Terrestrial Ages of Four Allan Hills Meteorites: Consequences for Antarctic Ice

The terrestrial ages of three Allan Hills meteorites are between 3 x 10(4) and 3 x 10(5) years and one is (1.54(-0.28)(+0.14)) x 10(6) years old. The Antarctic ice sheet is therefore older than (1.54(-0.28)(+0.14)) x 10(6) years and the meteorite accumulation process at Allan Hills probably began between 3 x 10(4) and 3 x 10(5)years ago.

Rare Gases in Lunar Samples: Study of Distribution and Variations by a Microprobe Technique

The rare gas distribution in lunar soil, breccias, and rocks was studied with a micro-helium-probe. Gases are concentrated in grain surfaces and originate from solar wind. Helium-4 concentrations of different mineral components vary by more than a factor of 10 apart from individual fluctuations for each type. Also grains with no detectable helium-4 exist. Titanium-rich components have the highest, calcium-rich minerals the lowest concentrations. The solar wind was redistributed by diffusion. Mean gas layer thicknesses are 10, 6, and 5 microm for helium, neon, and argon respectively. Lithic fragments in breccias contain no solar gases. Glass pitted surfaces of crystalline rocks contain about 10(-2) cubic centimeter of helium-4 per square centimeter. Etched dust grains clearly show spallogenic and radiogenic components. The apparent mean exposure age of dust is approximately 500 x 10(6) years, its potassium-argon age is approximately 3.5 x 10(9) yerars. Cavities of crystalline rocks contain helium-4, radiogenic argon, H(2), and N(2).