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Summary of Prior Work on Joining of Oxide Dispersion-Strengthened Alloys
There is a range of joining techniques available for use with ODS alloys, but care should be exercised in matching the technique to the final duty requirements of the joint. The goal for joining ODS alloys is a joint with no local disruption of the distribution of the oxide dispersion, and no significant change in the size and orientation of the alloy microstructure. Not surprisingly, the fusion welding processes typically employed with wrought alloys produce the least satisfactory results with ODS alloys, but some versions, such as fusion spot welding, and the laser and electron-beam welding technologies, have demonstrated potential for producing sound joints. Welds made using solid-state spot welding reportedly have exhibited parent metal properties. Thus, it is possible to employ processes that result in significant disruption of the alloy microstructure, as long as the processing parameters are adjustment to minimize the extent of or influence of the changes in the alloy microstructure. Selection among these joining approaches largely depends on the particular application and component configuration, and an understanding of the relationships among processing, alloy microstructure, and final properties is key. Recent developments have resulted in friction welding evolving to be a prime method for joining ODS sheet products, and variants of brazing/diffusion bonding have shown excellent promise for use with tubes and pipes. The techniques that come closest to the goal defined above involve solid-state diffusion bonding and, in particular, it has been found that secondary recrystallization of joints made by pulsed plasma-assisted diffusion can produce the desired, continuous, large alloy grain structure through the joint. Such joints have exhibited creep rupture failure at >82% of the load needed to fail the monolithic parent alloy at 1000 C
Novel inhibitors of the calcineurin/NFATc hub - alternatives to CsA and FK506?
The drugs cyclosporine A (CsA) and tacrolimus (FK506) revolutionized organ transplantation. Both compounds are still widely used in the clinic as well as for basic research, even though they have dramatic side effects and modulate other pathways than calcineurin-NFATc, too. To answer the major open question - whether the adverse side effects are secondary to the actions of the drugs on the calcineurin-NFATc pathway - alternative inhibitors were developed. Ideal inhibitors should discriminate between the inhibition of (i) calcineurin and peptidyl-prolyl cis-trans isomerases (PPIases; the matchmaker proteins of CsA and FK506), (ii) calcineurin and the other Ser/Thr protein phosphatases, and (iii) NFATc and other transcription factors. In this review we summarize the current knowledge about novel inhibitors, synthesized or identified in the last decades, and focus on their mode of action, specificity, and biological effects
Icing: Supporting Fast-Math Style Optimizations in a Verified Compiler
Verified compilers like CompCert and CakeML offer increasingly sophisticated optimizations. However, their deterministic source semantics and strict IEEE 754 compliance prevent the verification of ``fast-math'' style floating-point optimizations. Developers often selectively use these optimizations in mainstream compilers like GCC and LLVM to improve the performance of computations over noisy inputs or for heuristics by allowing the compiler to perform intuitive but IEEE 754-unsound rewrites
The effects of milling conditions on the subsequent oxidation behaviour of mechanically alloyed FeAl-based powders
Mechanically alloyed, FeAl-based, oxide dispersion
strengthened alloys form a surface oxide scale during powder processing.
This scale becomes entrained in the consolidated alloy, and may have a
significant effect on subsequent recrystallisation behaviour. The high
oxidation rates found in these alloys are mainly due to the bulk alloy
composition. However, batch-to-batch differences in oxidation mass gain
occur in powders with ostensibly identical compositions. Batches PMWY2 and
PMWY3 were studied and parameters such as alloy composition and homogeneity,
powder surface area to volume ratios and scale thickening rates considered.
Batch PMWY2 showed 20-90% faster weight gain than PMWY3 and reached the
onset of breakaway oxidation approximately twice as quickly. PMWY2 was found
to contain aluminium-depleted regions, whereas PMWY3 is much more
homogeneous. The surface area to volume ratio for PMWY2 was 44% higher
than that of PMWY3, and batch PMWY2 was found to contain extremely fine
powder particles. The scale on batch PMWY2 thickened more quickly than that
on batch PMWY3, with rates 20-40% higher at different stages in the
oxidation. The major contributory factor to the difference in oxidation mass
gain between the two alloy batches is scale thickening rate and factors
influencing thickening rates are discussed
FEG-SEM investigation of -alumina scales formed on FeCrAlY alloys oxidised at 1200C
This work is part of an ongoing European funded project,
“SMILER”, with the aim of improving the performance of alumina forming
Fe-20Cr-5Al-Y alloys for high temperature industrial applications. One
aspect of the project is to investigate the influence of additives on the
oxidation behaviour of these alloys. During this study a LEO 1550 FESEM
(field emission scanning electron microscope), equipped with INCA X-ray
microanalysis facilities was used. Ultra-high-purity model alloys, where the
levels of additives (Hf, Zr, Ti, Si, La and Y) were carefully controlled,
and two commercial Aluchrom YHfAl and Kanthal AMPT alloys were oxidised at
1200C for up to 3100h (100h/cycle).
The YHfAl, (Y+Ti+Zr)- and (Y+Zr+Hf)-containing alloys showed the highest
oxidation rates when oxidised, whereas the La-containing alloy showed the
lowest oxidation rate. However, the La-containing alloy spalled the most,
while the (Y+Zr+Hf)-containing and YHfAl alloys showed little spallation,
and the additives appeared to have a major influence on the spallation of
the -alumina scale formed. On the alloys with La and Si
respectively, the scale spalled at the scale/metal interface (adhesively),
whereas on alloys containing (Y+Hf+Ti) and (Y+Hf+Zr) and the YHfAl alloy,
the scale spalled mainly in a cohesive manner (within the scale). Also, the
added elements affected the scale topography. In general the scale had a
columnar structure at the scale/metal interface, whereas the grains were
equiaxed at the scale/gas interface. However, in the case of YHfAl and
(Y+Zr+Hf)-containing alloys, a sunflower type structure was observed in both
fractured samples, in the regions where the scale spalled cohesively.
Preliminary EDX analyses revealed that, in the case of YHfAl, for example,
the center of the sunflower structure was rich in Mg. This suggests that
there may be inhomogeneities in the metal substrate, prior to oxidation,
where high concentrations of Mg increase the local oxide growth rate
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