Observations on Twinning in Zone-refined Tungsten

Observations on twinning in zone-refined tungste

Powder metallurgy approaches to high temperature components for gas turbine engines

Research is reported for the tensile strength, ductility, and heat performance characterisitics of powder metallurgy (p/m) superalloys. Oxide dispersion strengthened alloys were also evaluated for their strength during thermal processing. The mechanical attributes evident in both p/m supperalloys and dispersion strengthened alloys are discussed in terms of research into their possible combination

High gas velocity burner tests on silicon carbide and silicon nitride at 1200 C

Specimens of silicon carbide and silicon nitride were exposed to a Mach one gas velocity burner simulating a turbine engine environment. Cyclic tests up to 100 hour duration were conducted at specimen temperatures of 1200 C. A specimen geometry was used that develops thermal stresses during thermal cycling in a manner similar to blades and vanes of a gas turbine engine. Materials were compared on a basis of weight change, dimensional reductions, metallography, fluorescent penetrant inspection, X-ray diffraction analyses, failure mode, and general appearance. One hot pressed SiC, one reaction sintered SiC, and three hot pressed Si3N4 specimens survived the program goal of 100 one-hour cycle exposures. Of the materials that failed to meet the program goal, thermal fatigue was identified as the exclusive failure mode

High temperature mechanical properties of polycrystalline hafnium carbide and hafnium carbide containing 13-volume-percent hafnium diboride

High temperature mechanical properties of polycrystalline hafnium carbide containing 13- volume-percent hafnium diborid

Effects of crucible wetting during solidification of immiscible Pb-Zn

Many industrial uses for liquid phase miscibility gap alloys are proposed. However, the commercial production of these alloys into useful ingots with a reasonable amount of homogeneity is arduous because of their immiscibility in the liquid state. In the low-g environment of space gravitational settling forces are abated, thus solidification of an immiscible alloys with a uniform distribution of phases becomes feasible. Elimination of gravitational settling and coalescence processes in low-g also makes possible the study of other separation and coarsening mechanisms. Even with gravitational separation forces reduced, many low-g experiments have resulted in severely segregated structures. The segregation in many cases was due to preferential wetting of the crucible by one of the immiscible liquids. The objective was to analyze the wetting behavior of Pb-Zn alloys on various crucible materials in an effort to identify a crucible in which the fluid flow induced by preferential wetting is minimized. It is proposed that by choosing the crucible for a particular alloy so that the difference in surface energy between the solid and two liqud phases is minimized, the effects of preferential wetting can be diminished and possibly avoided. Qualitative experiments were conducted and have shown the competitive wetting behavior of the immiscible Pb-Zn system and 13 different crucible materials

Strontium as a tracer of weathering processes in a silicate catchment polluted by acid atmospheric inputs, Strengbach, France

This paper determines the weathering and atmospheric contributions of Ca in surface water from a small spruce forested silicate catchment (N–E France) receiving acid atmospheric inputs. The bedrock is a granite with K-feldspar and albite as dominant phases. The calcium content in plagioclase is low and the Ca/Na ratio in surface water is high, reflecting other sources of calcium from those expected from the weathering of major mineral phases. The biotite content is low. Only traces of apatite were detected while no calcite was found in spite of a major hydrothermal event having affected the granite. The strontium isotopic ratio 87Sr/86Sr and Sr content was used as a tracer of weathering and was determined in minerals and bulk bedrock, open field precipitation, throughfall, soil solution, spring and stream water. The Sr isotopic ratio of the reacting weathering end-member was predicted by simulating the alteration of the granite minerals by incorporating strontium into the water–rock interaction kinetic code KINDIS. In the early stages of water–rock interaction, K-feldspar and biotite strongly influence the isotopic composition of the weathering solution whereas, the Na-rich plagioclase appears to be the main long-term reactive weathering end-member. Approximately 50% of dissolved Sr in streamwater are atmospherically derived. The 87Sr/86Sr ratios of exchangeable Sr in the fine fraction at 1-m depth from a soil profile indicate that the amount of exchangeable Sr seems essentially controlled by atmospheric inputs. The exception is the deep saprolite where weathering processes could supply the Sr (and Ca). Na-Plagioclase weathering obviously control the chemistry and the isotopic composition of surface waters. The weathering of trace mineral plays a secondary role, the exception is for apatite when plagioclase is absent. Our hydrochemical, mineralogical and isotopic investigations show that a major part of the strong Ca losses detected in catchment hydrochemical budgets that result from the neutralization of acid precipitation has an atmospheric origin. Consequently, in the long term, in such areas, the availability of such an exchangeable base cation might be strongly limited and surface waters consequently acidified

Understanding How Components of Organisations Contribute to Attacks

Attacks on organisations today explore many different layers, including buildings infrastructure, IT infrastructure, and human factor – the physical, virtual, and social layer. Identifying possible attacks, understanding their impact, and attributing their origin and contributing factors is difficult. Recently, system models have been used for automatically identifying possible attacks on the modelled organisation. The generated attacks consider all three layers, making the contribution of building infrastructure, computer infrastructure, and humans (insiders and outsiders) explicit. However, this contribution is only visible in the attack trees as part of the performed steps; it cannot be mapped back to the model directly since the actions usually involve several elements (attacker and targeted actor or asset). Especially for large attack trees, understanding the relations between several model components quickly results in a large quantity of interrelations, which are hard to grasp. In this work we present several approaches for visualising attributes of attacks such as likelihood of success, impact, and required time or skill level. The resulting visualisations provide a link between attacks on an organisations and the contribution of parts of an organisation to the attack and its impact

A Study of the "toss Factor" in the Impact Testing of Cermets by the Izod Pendulum Test

The test method presented shows that the "toss energy" contributed by the apparatus for brittle materials is negligible. The total toss energy is considered to consist of two components. (a) recovered stored elastic energy and (b) kinetic energy contributed directly by the apparatus. The results were verified by high-speed motion pictures of the test in operation. From these photographs, velocities of tossed specimens were obtained and toss energy computed. In addition, impact energies of some titanium carbide base cermets and high-temperature alloys, as measured by the low-capacity Izod pendulum test, compare well with impact energies measured by the NACA drop test