Crystallographic information of intermediate phases in binary Mg-X (X=Sn, Y, Sc, Ag) alloys.
ABSTRACT: The compositions and structures of thermodynamically stable or metastable precipitations in binary Mg-X (X=Sn, Y, Sc, Ag) alloys are predicted using ab-initio evolutionary algorithm. The geometry optimizations of the predicted intermetallic compounds are carried out in the framework of density functional theory (DFT) . A complete list of the optimized crystallographic information (in cif format) of the predicted intermetallic phases is presented here. The data is related to "Predictions on the compositions, structures, and mechanical properties of intermediate phases in binary Mg-X (X=Sn, Y, Sc, Ag ) alloys" by Liu et al. .
Project description:Endohedral clusters count as molecular models for intermetallic compounds-a class of compounds in which bonding principles are scarcely understood. Herein we report soluble cluster anions with the highest charges on a single cluster to date. The clusters reflect the close analogy between intermetalloid clusters and corresponding coordination polyhedra in intermetallic compounds. We now establish Raman spectroscopy as a reliable probe to assign for the first time the presence of discrete, endohedrally filled clusters in intermetallic phases. The ternary precursor alloys with nominal compositions "K<sub>5</sub> Co<sub>1.2</sub> Ge<sub>9</sub> " and "K<sub>4</sub> Ru<sub>3</sub> Sn<sub>7</sub> " exhibit characteristic bonding modes originating from metal atoms in the center of polyhedral clusters, thus revealing that filled clusters are present in these alloys. We report also on the structural characterization of [Co@Ge<sub>9</sub> ]<sup>5-</sup> (1a) and [Ru@Sn<sub>9</sub> ]<sup>6-</sup> (2a) obtained from solutions of the respective alloys.
Project description:The paper presents the results of an experimental study of large (?0.6 kg) arc melted buttons of four Ti free Nb-silicide based alloys with Sn addition with nominal compositions (at.%) Nb-18Si-5Hf-5Sn (EZ1), Nb-18Si-5Al-5Sn (EZ7), Nb-18Si-5Cr-5Hf-5Sn (EZ3) and Nb-18Si-5Al-5Hf-5Sn (EZ4). The alloys were studied in the as-cast and heat treated conditions. In all the alloys there was macrosegregation of Si (MACSi). Among the single element additions Hf had the weakest and Sn the strongest effect on MACSi. The simultaneous presence of Cr and Hf in the alloy EZ3 had the strongest effect on MACSi. In all the alloys the ?Nb?Si? was the primary phase and was present after the heat treatment(s), the Nb?Si silicide was suppressed and the A15-Nb?Sn intermetallic was stable. The Nb<sub>ss</sub> was not stable in the alloys EZ7 and EZ4 and the C14-NbCr? Laves phase was stable in the alloy EZ3. Very Hf-rich Nb?Si? was stable in the alloy EZ4 after prolonged heat treatments. Eutectics were observed in all the alloys. These were binary eutectics in the alloys EZ1 and EZ7, where respectively they consisted of the Nb<sub>ss</sub> and ?Nb?Si?, and ?Nb?Si? and A15-Nb?Sn phases. Most likely ternary eutectics consisting of the Nb<sub>ss</sub>, C14-NbCr? and ?Nb?Si?, and Nb<sub>ss</sub>, ?Nb?Si? and A15-Nb?Sn phases were observed, respectively in the alloys EZ3 and EZ4. The addition of Al increased the vol% of the Nb?Si? and A15-Nb?Sn phases, particularly after the heat treatment(s). The lattice parameter of Nb respectively increased and decreased with the addition of Hf, and Al or Cr and the latter element had the stronger negative effect. Pest oxidation was not suppressed in the alloys of this study.
Project description:Using the evolutionary optimization algorithm, as implemented in the USPEX crystal predictor program, and first principles total energy calculations, the compositional phase diagrams for Al-Sc and Al-Ta alloy systems at zero temperature and pressure have been calculated. In addition to the known binary intermetallic phases, new potentially stable alloys, AlSc3 and AlTa7, have been identified in the Al-poor region of the phase diagram. The dynamic and thermal stability of their lattices has been confirmed from the calculated vibrational normal mode spectra in the harmonic approximation.
Project description:Enforced solid solution type Sn-Zn alloy films were electrochemically synthesized on Cu substrate from an aqueous solution containing citric acid complexes. The electrodeposition behavior of Sn-Zn alloys was classified to a normal co-deposition type, in which electrochemically nobler Sn deposits preferentially compared to Zn. Electrodeposited Sn-Zn alloy films were composed of a non-equilibrium phase, like an enforced solid solution, which was not observed in an equilibrium phase diagram of an Sn-Zn binary alloy system. By applying a thermal annealing process at 150 °C for 10 minutes, a pure Zn phase was precipitated from an electrodeposited Sn-based solid solution phase with excessively dissolved Zn atoms. During the soldering process, intermetallic phases such as Cu3Sn and Cu5Zn8 were formed at the interface between an Sn-Zn alloy and Cu substrate. Tensile strength and fracture elongation of solder-jointed Cu rods with Sn-8 at.%Zn alloy films reached ca. 40 MPa and 12%, respectively.
Project description:High-entropy alloys (HEAs) are promising materials for next-generation applications because of their mechanical properties, excellent high-temperature stability, and resistance against oxidation and corrosion. Although many researchers have investigated high-temperature HEA applications, few have considered low-temperature applications. Here we demonstrate an unprecedented intermetallic compound of (Fe, Cr, Co, Ni, Cu)Sn<sub>2</sub> at the interface between Sn-3.0Ag-0.5Cu (SAC) solder and FeCoNiCrCu<sub>0.5</sub> HEA substrate after reflow at 400?°C. Significantly suppressed growth of intermetallic compound without detachment from the substrate was observed during thermal aging at 150?°C for 150?h. Sn grains with an average grain size of at least 380 ?m are observed. The results reveal a completely new application for the fields of Sn-Ag-Cu solder and HEA materials.
Project description:Bulk ultrafine grained (UFG)/nanocrystal metals possess exceptional strength but normally poor ductility and thermal stability, which hinder their practical applications especially in high-temperature environments. Through microalloying strategy that enables the control of grains and precipitations in nanostructured regime, here we design and successfully produce a highly microstructure-stable UFG Al-Cu-Sc alloy with ~275% increment in ductility and simultaneously ~50% enhancement in yield strength compared with its Sc-free counterpart. Although the precipitations in UFG alloys are usually preferentially occurred at grain boundaries even at room temperature, minor Sc addition into the UFG Al-Cu alloys is found to effectively stabilize the as-processed microstructure, strongly suppress the ?-Al2Cu phase precipitation at grain boundary, and remarkably promote the ?'-Al2Cu nanoparticles dispersed in the grain interior in artificial aging. A similar microalloying strategy is expected to be equally effective for other UFG heat-treatable alloys.
Project description:We report the discovery of a unique micrometeorite, containing an exotic Al-Cu-Fe alloy composed of two intermixed phases: khatyrkite (CuAl2) and stolperite (CuAl) and both containing minor Fe (<1.4 wt%). These phases are dendritic and rapidly co-crystallized at the binary system's peritectic (~550 °C). The host micrometeorite is an otherwise typical S-type micro-porphyritic cosmic spherule containing relict olivine (Fo76-90, Cr2O3: 0.01-0.56 wt%, MnO: 0.03-0.32 wt% and CaO: 0.09-0.22 wt%) and a cumulate layered texture. These properties suggest the micrometeorite is derived from a carbonaceous chondrite (best matched to a CO chondrite) and entered the atmosphere a high speed (~16 kms-1), implying an origin from a highly eccentric orbit. This particle represents the second independent discovery of naturally occurring intermetallic Al-Cu-Fe alloys and is thus similar to the previously reported Khatyrka meteorite - a CV chondrite containing near-identical alloys and the only known natural quasicrystals. We did not observe quasicrystalline phases in this micrometeorite, likely due to the low amounts of Fe in the alloy, insufficient to stabilize quasicrystals. Our discovery confirms the existence of Al-Cu-Fe intermetallic alloys on chondritic parent bodies. These unusual phases require a currently unexplained formation process, we tentatively suggest this could represent the delivery of exotic interstellar material to the inner solar system via impact.
Project description:This paper presents the results of a systematic study of Nb-24Ti-18Si based alloys with 5 at.% Sn addition. Three alloys of nominal compositions (at.%), namely Nb-24Ti-18Si-5Cr-5Sn (ZX4), Nb-24Ti-18Si-5Al-5Sn (ZX6), and Nb-24Ti-18Si-5Al-5Cr-5Sn (ZX8), were studied to understand how the increased Sn concentration improved oxidation resistance. In all three alloys there was macrosegregation, which was most severe in ZX8 and the primary ?Nb5Si3 transformed completely to ?Nb5Si3 after heat treatment. The Nbss was not stable in ZX6, the Nb3Sn was stable in all three alloys, and the Nbss and C14-NbCr2 Laves phase were stable in ZX4 and ZX8. The 5 at.% Sn addition suppressed pest oxidation at 800 °C but not scale spallation at 1200 °C. At both temperatures, a Sn-rich area with Nb3Sn, Nb5Sn2Si, and NbSn2 compounds developed below the scale. This area was thicker and continuous after oxidation at 1200 °C and was contaminated by oxygen at both temperatures. The contamination of the Nbss by oxygen was most severe in the bulk of all three alloys. Nb-rich, Ti-rich and Nb and Si-rich oxides formed in the scales. The adhesion of the latter on ZX6 at 1200 °C was better, compared with the alloys ZX4 and ZX8. At both temperatures, the improved oxidation was accompanied by a decrease and increase respectively of the alloy parameters VEC (Valence Electron Concentration) and ?, in agreement with the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration). Comparison with similar alloys with 2 at.% Sn addition showed (a) that a higher Sn concentration is essential for the suppression of pest oxidation of Nb-24Ti-18Si based alloys with Cr and no Al additions, but not for alloys where Al and Cr are in synergy with Sn, (b) that the stability of Nb3Sn in the alloy is "assured" with 5 at.% Sn addition, which improves oxidation with/out the presence of the Laves phase and (c) that the synergy of Sn with Al presents the "best" oxidation behaviour with improved scale adhesion at high temperature.
Project description:Over the past several decades, it was generally believed that the strength of the industrially widely used cast Al-Si-Mg-Cu alloys enhanced monotonously with increasing Cu content. However, in this study using cast Al9Si0.5MgxCu (x = 0,0.2,0.4,0.6,0.85,1.0,1.25, in wt.%) alloys under T6 heat-treated condition, it was found that the hardness and yield strength of the heat-treated alloys showed a platform in the composition range from 0.4 wt.% to 0.85 wt.% Cu, while still increased with increasing Cu content before and after the platform. With increasing Cu content, the β-Mg2Si intermetallic phase decreased and disappeared at 0.85 wt.% Cu, while the Q-Al5Cu2Mg8Si6 and θ-Al2Cu intermetallic phases increased in the as-cast alloys. After heat treatment, the micron-scale intermetallic phases were dissolved into the Al matrix and precipitated as the nanoscale β″, Q' and θ' strengthening phases. With increasing Cu content, the β″ precipitate decreased and vanished at 0.85 wt.% Cu, while the Q' and θ' precipitates increased in the heat-treated alloys. The trade-off of the phases induces the platform in the strength of the heat-treated alloys, and further increase of the Cu content in this undetected trapped platform range is not favorited industrially as it only decreases ductility.
Project description:Alloying with Al, Cr, Sn, and Ti significantly improves the oxidation of Nb silicide-based alloys at intermediate and high temperatures. There is no agreement about what the concentration of Sn in the alloys should be. It has been suggested that with Sn ? 3 at.% the oxidation is improved and formation of the brittle A15-Nb?Sn compound is suppressed. Definite improvements in oxidation behaviour have been observed with 5 at.% Sn or even higher concentrations, up to 8 at.% Sn. The research reported in this paper is about three model alloys with low Sn concentration and nominal compositions Nb-24Ti-18Si-5Cr-2Sn (ZX3), Nb-24Ti-18Si-5Al-2Sn (ZX5), and Nb-24Ti-18Si-5Al-5Cr-2Sn (ZX7) that were studied to understand the effect of the 2 at.% Sn addition on as-cast and heat-treated microstructures and isothermal oxidation in air at 800 and 1200 °C for 100 h. There was macrosegregation of Si and Ti in the alloys ZX3 and ZX5 and only of Si in the alloy ZX7. The Nbss was stable in all alloys. Tin and Ti exhibited opposite partitioning behaviour in the Nbss. The ?Nb?Si? was the primary phase in all three cast alloys and had partially transformed to ?Nb?Si? in the alloy ZX3. Aluminium in synergy with Sn increased the sluggishness of the ?Nb?Si? to ?Nb?Si? transformation during solidification. After the heat treatment the transformation of ?Nb?Si? to ?Nb?Si? had been completed in all three alloys. Fine precipitates were observed inside some ?Nb?Si? grains in the alloys ZX5 and ZX7. In the latter alloys the A15-Nb?X (X = Al, Si, and Sn) formed after the heat treatment, i.e., the synergy of Al and Sn promoted the stability of A15-Nb?X intermetallic in these Nb-silicide-based alloys even at this low Sn concentration. A Nbss + Nb?Si? eutectic formed in all three alloys and there was evidence of anomalous eutectic in the parts of the alloys ZX3 and ZX7 that had solidified under high cooling rate and/or high melt undercooling. A very fine ternary Nbss + Nb?Si? + NbCr? eutectic was also observed in parts of the alloy ZX3 that had solidified under high cooling rate. At 800 °C none of the alloys suffered from catastrophic pest oxidation; ZX7 had a smaller oxidation rate constant. A thin Sn-rich layer formed continuously between the scale and Nbss in the alloys ZX3 and ZX5. At 1200 °C the scales formed on all three alloys spalled off, the alloys exhibited parabolic oxidation in the early stages followed by linear oxidation; the alloy ZX5 gave the smallest rate constant values. A thicker continuous Sn-rich zone formed between the scale and substrate in all three alloys. This Sn-rich zone was noticeably thicker near the corners of the specimen of the alloy ZX7 and continuous around the whole specimen. The Nb?Sn, Nb?Sn?Si, and NbSn? compounds were observed in the Sn-rich zone. At both temperatures the scales formed on all three alloys consisted of Nb-rich and Nb and Si-rich oxides, and Ti-rich oxide also was formed in the scales of the alloys ZX3 and ZX7 at 1200 °C. The formation of a Sn-rich layer/zone did not prevent the contamination of the bulk of the specimens by oxygen, as both Nbss and Nb?Si? were contaminated by oxygen, the former more severely than the latter.