We describe four criteria for the selection of alloying elements capable of producing castable, precipitation-strengthened Al alloys with high-temperature stability and strength: these alloying elements must (i) be capable of forming a suitable strengthening phase, (ii) show low solid solubility in Al, (iii) low diffusivity in Al, and (iv) retain the ability for the alloy to be conventionally solidified. With regard to criterion (i), we consider those systems forming Al3M trialuminide compounds with a cubic L12 crystal structure, which are chemically and structurally analogous to Ni3Al in the Ni-based superalloys. Eight elements, clustered in the same region of the periodic table, fulfill criterion (i): the first Group 3 transition metal (Sc), the three Group 4 transition metals (Ti, Zr, Hf) and the four latest lanthanide elements (Er, Tm, Yb, Lu). Based on a review of the existing literature, these elements are assessed in terms of criteria (ii) and (iii), which satisfy the need for a dispersion...

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Criteria for developing castable, creep-resistant aluminum-based alloys - A review

Ni-base amorphous alloys with the homogeneous dispersion of nanoscale fcc-Ni particles have been produced in the composition range of 5 to 14 at%Si and 7 to 15%B. The particle size and interparticle spacing are 10 and 20 nm, respectively. The alloys exhibit tensile fracture strength (σ f ), Young's modulus (E) and hardness (H v ) which are higher than those of the corresponding amorphous single phase alloys, accompanying an increase in fracture elongation (∈ f )

Increase in Mechanical Strength of Al–Y–Ni Amorphous Alloys by Dispersion of Nanoscale fcc-Al Particles

The influences of erbium (Er) on the microstructure and mechanical properties of Al–Mg–Mn–Zr alloys have been investigated. It has been found that about 0.2 wt.% Er can be dissolved in the matrix, excess Er atoms segregate at grain boundaries to form primary Al 3 Er. Addition of 0.4 wt.% Er refines the grain size of the as-cast alloy due to the formation of primary Al 3 Er. The solid solution decomposes to form a dispersion of secondary Al 3 Er, with facets parallel to {1 0 0} and {1 1 0} planes, during homogenization at 470 °C. The secondary Al 3 Er precipitates improve strength, especially the elevated temperature strength. The yield strength, at 150 °C, of the alloy with 0.2 wt.% Er is 50% higher than that of the Er-free alloy. The recrystallization temperature of the alloy with 0.4 wt.% Er is about 25 °C higher than that of the alloy without addition of Er.

The effect of erbium on the microstructure and mechanical properties of Al–Mg–Mn–Zr alloy

▪ Abstract Mate choice theory has become a major field of research in behavioral ecology. Tree crickets provide excellent opportunities for studying the diversity and variability of mate choice. The evidence for female mate choice in tree crickets is reviewed, and broad comparisons with other orthopteran groups are made. The evidence shows that female choice may occur during several different stages of mating and may target several different criteria. Song preferences are perhaps dominated by stabilizing preferences for the cues of species recognition, but there is a growing body of evidence for directional preferences based on sensory biases or mate quality. Mate rejection during courtship and forms of postcopulatory choice may favor males, based both on phenotypic quality and on the amount of nutritious courtship gifts they provide, and may differ with the value of mating incentives. Understanding the balance and trade-offs between different forms of mate choice may help in understanding their evolution...

Mate choice in tree crickets and their kin.

Alloys of compositions Al-6Nd, Al-9Ce, Al-16Nd and Al-22Ce (wt%) were prepared by chill-block melt-spinning at a surface speed of ∼ 29 m s−1 into ribbons of thickness between 20 and 70 μm. The melt-spun ribbons were heat treated for 2 h at 200, 300, 400 and 500 °C. The as-spun and heat-treated ribbons were tested for microhardness and investigated by optical and transmission electron microscopy and X-ray diffraction. Age hardening was not observed for any of the alloys, indicating only a limited amount of extended solid solubility as a result of the melt-spinning conditions used. Al-9Ce and Al-6Nd were found to be relatively stable at a hardness of ∼ 90 HK0.01 and 75–80 HK0.01, respectively, unaffected by heat treatment at up to 300 °C for 2 h, but heat treatment for 2 h at 400 or 500 °C caused softening. Al-6Nd and Al-9Ce as-solidified ribbons comprised a cellular Zone B structure with αAl cells (of size ∼ 0.5 μm) and intercellular orthorhombic αAl11(Nd, Ce)3. The hardness of Al-16Nd as-spun was measured as 330±20 HK0.01 unchanged by heat treatment at 200 °C for 2 h, while heat treatment for 2 h at higher temperatures caused softening. As-spun Al-16Nd consisted of Zone A only comprising αAl solid solution and orthorhombic α or tetragonal βAl11Nd3 partly coherent with the matrix. Al-22Ce had a hardness of 330±20 HK0.01 as-spun but softened on treatment for 2 h at 200 °C. As-spun Al-22Ce consisted partly of Zone A structure extending from the wheel side of the ribbon through half of the thickness. The remaining part of the ribbon consisted of cellular Zone B (cell size ∼ 0.2 μm) with intercellular αAl/αAl11Ce3 lamellar eutectic together with areas that were 100% lamellar eutectic (interlamellar spacing 0.09±0.02 μm). All the as-spun microstructures showed coarsening upon heat treatment at sufficiently high temperature. The resulting microstructure after treatment at 500 °C for 2 h consisted of a bimodal distribution of αAl11 (Nd, Ce)3 which formed as large particles on the grain boundaries and smaller ones in the grain interiors. The corresponding microstructure was less coarse for Al-16Nd and Al-22Ce.

Microstructure and thermal stability of melt-spun Al-Nd and Al-Ce alloy ribbons

The effect of the rapid-solidification melt-spinning process on an Al-4Er alloy has been studied Compared to the normally solidified master alloy, rapid-solidification processing promotes the formation of a eutectic suppressed, relatively refined microstructure Varying relative proportions of microstructures occupy the ribbon longitudinal transverse cross section: the featureless zone at the contact surface, the columnar zone in the middle and the equiaxed grains zone with degenerated dendrites at the free surface The presence of a finely dispersed, coherent Al3Er secondary equilibrium phase in the contact is evident Ribbon microhardness remains fairly stable up to 200 ° C and at further elevated temperatures retains higher mean values than the master alloy

https://link.springer.com/content/pdf/10.1007/BF00575385.pdf

Microstructure and thermal stability of a rapidly solidified Al-4Er alloy

The use of rapid solidification (RS) techniques to increase the thermal stability of aluminium and aluminium alloys is considered a promising processing route. The Al-La equilibrium binary system tends to form a high melting temperature intermetallic compound on the aluminium rich side. The limited solid solubility of solute, high solubility in the liquid and the relatively low solid state diffusivity, in general, of rare earth (RE) elements in aluminium suggests this system (as well as other Al-RE systems) as a suitable lightweight, dispersion-strengthened alloy candidate for elevated homological temperature applications. RS processing promotes the formation of a relatively finer microstructure in an Al-4La alloy, as well as the formation of a finely dispersed metastable phase. This metastable phase, is fairly stable up to 400° C. Lanthanum concentration in the ribbon bulk matrix, is considerably increased via RS process ing, and the formation of a heavy eutectic is suppressed.

A. Ruder

Papers

Microstructure and thermal stability of a rapidly solidified Al-4Er alloy

Microstructural transitions in an RS Al-4La alloy