High-purity Alloys Research Articles

Green and efficient recovery of valuable metals from waste copper slag via co-modification with CaO and Na2O

In this work, a novel carbon-free smelting reduction process is proposed to recover valuable metals from molten copper slag, in which secondary aluminum dross is used as the reductant via co-modification with CaO and Na2O additions. The influence of Na2O addition on the metal recovery and slag properties under different CaO/SiO2 ratios was investigated at 1550 °C. The results show that the modifier Na2O not only reduces the melting temperature of the slag, but also inhibits the precipitation of spinel and prevents the polymerization of aluminosilicate units to a certain extent by providing more O2-, which results in a relatively lower slag viscosity. These effects are more significant at the CaO/SiO2 of 0.9. The multiple strengthening mechanisms improve the kinetic conditions for smelting reduction, resulting in optimal results when the Na2O addition reaches 4 wt% at the CaO/SiO2 of 0.9, at which 99.1% of iron and 98.5% of copper in the slag can be recovered as the high-purity alloy. The leaching toxicity of the tailings is 2–3 orders of magnitude lower than the original slag, suggesting that they are clean sources for ceramic production. Furthermore, the assessment of the proposed process indicates that it is technically feasible even without an external energy supply, which indicates that the process is green, efficient, and cost-effective.

Study on the Fluorination Process of Sc2O3 by NH4HF2.

Research on rare-earth fluorides is of urgent and critical importance for the preparation and emerging applications of high-purity alloys. The fluorination of Sc2O3 by NH4HF2 to fabricate ScF3 is investigated. The effects of the fluorination temperature, time and mass ratio of reactant on the fluorination rate and fluoride are discussed in this work. The fluorination reaction was first confirmed using thermodynamic calculation. The thermal and mass stability of the fluorination process were analyzed by thermogravimetric and differential scanning calorimetric (TG-DSC). The as-obtained products at different fluorination temperatures were characterized by Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results indicated that the fluorination began at room temperature (RT) with the formation of (NH4)3ScF6. With the increase of temperature, the reaction proceeded sequentially through the formation of NH4ScF4, (NH4)2Sc3F11, and finally ScF3. The fluorination rate increased with the increase of fluorination temperature and holding time. ScF3 with a purity of 99.997 wt.% could be obtained by fluorination at 400 °C for 2 h.

The effect of Sr modification on the eutectic structure of AlSi7Mg alloys at different purity levels

The effect of different Sr levels on the solidification path and the microstructure of the Al-Si eutectic in AlSi7Mg alloys at 3 different levels of purity (high purity, commercial purity, and secondary alloy) was investigated. Thermal analysis technique was performed to obtain the cooling curves and characteristic temperatures of the eutectic reactions. Microstructural investigations were carried out to study the variation of the eutectic structure due to Sr addition and alloy’s purity. The results indicate how the commercially pure alloy shows the highest nucleation and growth temperatures among the unmodified alloys, while the secondary alloy has the lowest ones. Sr addition decreases the characteristic eutectic temperatures. Even though the growth temperature is similar after Sr modification in the commercial and high purity alloys, this last shows a finest eutectic structure. Different levels of Sr are required to fully modify the eutectic of the AlSi7Mg alloy at different purity grade.

Effect of trace impurity elements on the high-temperature oxidation resistance of a high-purity nickel-based superalloy

This study indicates that the kinetic rate constants of oxidation weight gain and thickening both increase with the increasing content of O, N and S impurities. The oxide layer of the low-purity alloy is not tight and easy to peel off. Internal oxidation becomes more serious with the increase of oxygen solubility. The microscopic mechanism of how impurity atoms affect the oxidation diffusion process was explained, and the models of the oxide layer growth process for high-purity alloys and low-purity alloys were constructed, which provide a reference for the improvement of high-temperature oxidation performance of superalloys in the future.

Manufacture of shape memory alloys NiTi and NiTiCu by casting method and studying the effect of adding the copper element in different proportions to the binary alloy on the microstructure, phase transformations and conductivity

Thanks to unique properties, such as light weight, good biocompatibility, high strength, and relatively low cost, shape memory alloys are of interest to researchers. In this work alloys NiTi and NiTiCu with different weight percents were made from the copper element using the casting method by (VAR) furnace. Where the elements were melted at (1350°C) without a crucible to obtain best alloys of high purity, and after that the manufactured ingots were cooled with ice water to obtain the best homogeneity. The melting process was followed by the annealing process by an electric furnace at (750°C). After completing the manufacturing process, specimens were prepared for microscopic and mechanical tests, and wires were drawn for the purpose of electrical testing. Several tests and examinations were carried out to ensure that the alloys manufactured are SMAs. The microscopic examinations that were performed via OM showed that the copper element is uniformly distributed within a NiTi matrix. The results showed FESEM that the microstructure is symmetric and homogeneous, and also showed phase (TI 002) and (Ti2Ni) and some defects. DSC examination showed the initial and final degrees of the austenite and martensite phase. In addition, the results of DSC showed that the best stable alloys are alloy NiTi and NiTiCu-3 and that the hysterical loop decreases with an increase in the percentage of copper. The results of the shape memory effect showed that the best SME was (88.98%) for alloy NiTiCu-3. As for the microhardness, it increased when the copper element was increased, so the maximum hardness of the specimen was at 2 wt.% Cu, and it seemed to decrease with the increase in the copper element. The electrical test that was performed using the 4T sensing method of wires showed that the conductivity value increases with the increase in ratio of Cu with the decrease in the resistance. The best conductivity ratio was for alloy NiTiCu-3 where the conduction ratio was 24096.4 (Ω.Cm)−1 and it had the lowest resistivity 41.5 (Ω.Cm)10−6. Strain rate was tested and the resistivity, so the increase in the strain rate was observed with the increase in the copper element and the decrease in the resistivity.

The decomposition process in high-purity Al-1.7\xa0at.% Cu alloys with trace elements: preservation of quenched-in vacancies by In, Sn and Pb influencing the theta , ' formation

Aluminium-copper alloys of the 2xxx type receive their excellent mechanical properties by the formation of copper-rich precipitates during hardening. Size, distribution and crystal structure of the formed precipitates determine the final strength of those alloys. Adding traces of certain elements, which bind to vacancies, significantly influences the decomposition behaviour, i.e. the diffusion of the copper atoms. For high-purity ternary alloys (Al-1.7 at.% Cu-X), we investigate the interaction of copper and trace element atoms (X=In, Sn, and Pb) with quenched-in vacancies by Positron Annihilation Lifetime Spectroscopy (PALS). By employing Vickers microhardness, Differential Scanning Calorimetry (DSC) and Small Angle X-Ray Scattering (SAXS) we obtain a comprehensive picture of the decomposition process: opposite to predicted binding energies to vacancies by ab-initio calculations we find during ageing at room and elevated temperature a more retarded clustering of copper in the presence of In rather than for Sn additions, while Pb, having the highest predicted binding to vacancies, shows nearly no retarding effect compared to pure Al-Cu. If the latter would be due to a limited solubility of lead, it had to be below 2 ppm. Transmission Electron Microscopy (TEM) as imaging method complements our findings. Annealing the quenched Al-1.7 at.% Cu-X-alloys containing 100 ppm In or Sn at 150,^circ {text {C}} leads to finely distributed theta , '-precipitates on the nanoscale, since due to the trace additions the formation temperature of theta , ' is lowered by more than 100,^circ {text {C}}. According to TEM small agglomerates of trace elements (In, Sn) may support the early nucleation for the theta , '-precipitates.

Interaction of Ca, P trace elements and Sr modification in AlSi5Cu1Mg alloys

Thermal and microscopy analyses were carried out to investigate the interaction of Sr modification with Ca and P trace elements in high-purity and commercial-purity Al–5Si–1Cu–Mg alloys. The results show how the addition of Sr to commercial-purity alloy induces significant changes in the nucleation and growth temperatures of eutectic Si since pre-eutectic Al2Si2(CaSr) intermetallics tend to poison AlP particles, making them inactive as nucleation sites for eutectic Si. In contrast, the addition of Sr to high-purity alloy shows no apparent influence on the characteristic temperatures of Al–Si eutectic reaction, even though the microstructural investigations reveal flake-to-fibrous transition in the eutectic Si structure. This indicates that the eutectic growth temperature, commonly used to predict eutectic modification level, is not a key feature of Sr modification, but it is indirectly caused due to the presence of additional impurities in commercial-purity alloys which affect the nucleation kinetics of eutectic Si.

Stable Light-Emitting Diodes Using Phase-Pure Ruddlesden-Popper Layered Perovskites.

State-of-the-art light-emitting diodes (LEDs) are made from high-purity alloys of III-V semiconductors, but high fabrication cost has limited their widespread use for large area solid-state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase-pure 2D Ruddlesden-Popper (RP) halide perovskites with a formula (CH3 (CH2 )3 NH3 )2 (CH3 NH3 )n-1 Pbn I3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr-1 cm-2 at 744 nm with an ultralow turn-on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase-pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm-2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes.

Cleaner production of spherical nanostructure chromium oxide (Cr2O3) via a facile combination membrane and hydrothermal approach

Chromium oxide is widely used in national defense, hard alloy, alloy, pigment, vacuum plating, consumables and high purity alloy and belong to one of the main products of chromate production industry. In the present study, a novel cleaner process is proposed to synthesize nanostructure chromium oxide (Cr2O3) from waste source containing chromium (VI). Hydrated chromic oxide was prepared by combination membrane and hydrothermal method. After calcined, chromium (III) compound: nanostructure chromium oxide (SNCO) was obtained. In the membrane electrolyte stage, this way can reduce the amount of acid added to adjust the solution pH. Besides, addition of CO2 into the cathode compartment could improve the current efficiency and desalination efficiency, while decrease the energy consumption. Then the products were characterized. Combined with the experiment results of TGA and XRD, the potential formation mechanism of hydrated chromic oxide was proposed. The fine structure of the product was analyzed by SEM and TEM. It was proved that the nanostructure chromium oxide with good crystallinity was obtained. The UV–Vis was used for optical properties, which proved that it had good optical properties.

ПРОИЗВОДСТВО МЕТАЛЛОПОРОШКОВЫХ КОМПОЗИЦИЙ ВЫСОКОЙ ЧИСТОТЫ ТИТАНОВЫХ СПЛАВОВ МЕТОДОМ ИНДУКЦИОННОЙ ГАЗОВОЙ АТОМИЗАЦИИ ДЛЯ АДДИТИВНЫХ ТЕХНОЛОГИЙ

ПРОИЗВОДСТВО МЕТАЛЛОПОРОШКОВЫХ КОМПОЗИЦИЙ ВЫСОКОЙ ЧИСТОТЫ ТИТАНОВЫХ СПЛАВОВ МЕТОДОМ ИНДУКЦИОННОЙ ГАЗОВОЙ АТОМИЗАЦИИ ДЛЯ АДДИТИВНЫХ ТЕХНОЛОГИЙ

Promoted nucleation of potent substrates assisted with Al-10Si-2Fe master alloy in Al-Si alloys

Cluster-assisted crystallization induced by Al-10Si-2Fe master alloy was investigated in Al-Si melts assisted with exogenous nucleation substrates. Al-Si-Fe master alloy can enhance nucleation immensely with the existence of AlP in high purity alloys and TiB2·AlP particles in commercial purity Al-Si alloys. TiB2 particles themselves in high purity alloys cannot cooperate with Al-10Si-2Fe master alloy and leave the alloys deep undercooling. In addition, swells on silicon surfaces provide the evidence of pre-nucleation clusters attachment during silicon crystallization. Conclusively, Al-10Si-2Fe master alloy can only function with abundant nucleation substrates and make more of them effective by alerting the crystallization of the Al-Si melts.

Printable metals forge ahead

A couple of recent developments show that additive manufacturing isn’t just for polymers. The Burlington, Mass.-based three-dimensional printing start-up Desktop Metal has received $45 million in a funding round led by BMW i Ventures, Lowe’s Ventures, and GV (formerly Google Ventures). The company has raised a total of $97 million since it was founded in October 2015. “Just as plastic 3-D printing paved the way for rapid prototyping, metal 3-D printing will make a profound impact on the way companies both prototype and mass-produce parts,” says Ric Fulop, Desktop Metal’s CEO. Separately, American Elements says it has completed an expansion of its Los Angeles plant for 3-D printing metals. The company says it can now make “several metric tons of high-purity alloys monthly.”

Modeling of Grain-Boundary Mobility and Nucleation Rate during Discontinuous Dynamic Recrystallization in Ni-Nb Alloys and a High-Purity Alloy Derived from SAE 304L

A simple mesoscale model has been developed for discontinuous dynamic recrystallization. Each grain is considered in turn as an inclusion, embedded in a homogeneous equivalent matrix, the properties of which are obtained by averaging over all the grains. The model includes: (i) a grain-boundary migration-equation driving the evolution of grain size via the mobility of grain boundaries, which is coupled with (ii) a single-internal-variable (dislocation density) constitutive model for strain hardening and dynamic recovery, and (iii) a nucleation equation governing the total number of grains by the nucleation of new grains. All the system variables tend to asymptotic values at large strains, in agreement with the experimentally observed steady-state regime.With some assumptions, both steady-state stress and grain-size are derived in closed forms, allowing immediate identification of the mobility of grain boundaries and the rate of nucleation. An application to Ni–Nb-pure-binary model alloys and high-purity 304L stainless steel with Nb addition is presented. More specifically on one hand, from experimental steady-state stresses and grain sizes, variations of the grain boundary mobility and the nucleation rate with niobium content are addressed in order to quantify the solute-drag effect of niobium in nickel. And on the other hand, the Derby exponents were investigated varying separately the strain rate or the temperature.

The role of dislocation channeling in IASCC initiation of neutron irradiated stainless steel

This study intended to understand how dislocation channeling affects IASCC initiation using a novel four-point bend test. Stainless steels used in this study (irradiated in the BOR-60 reactor) included a commercial purity 304L alloy irradiated to 5.5, 10.2, and 47.5 dpa, and two high purity alloys, Fe18Cr12Ni and Fe18Cr25Ni, irradiated to ∼10 dpa. IASCC was enhanced by MnS inclusions, which dissolve in the NWC environment and form oxide caps, creating a crevice condition with a high propensity for crack initiation. Stress concentration at the grain boundary intersecting these sites induced crack initiation, resulting from discontinuous dislocation channels (DC). Stress to initiate IASCC decreased with dose due to earlier DC initiation. The HP Fe18Cr12Ni alloy had low IASCC susceptibility and the high Ni alloy did not crack. The difference was attributed to the propensity for DCs to transmit across grain boundaries, which controls stress accumulation at DC – grain boundary intersections.

Corrosion and cell viability of high-purity Mg and Mg-1Ca alloy

Corrosion and cell viability of high-purity Mg and Mg-1Ca alloy

Significance of Si impurities on exceptional room-temperature superplasticity in a high-purity Zn-22%Al alloy

Recent numerous studies demonstrated the advantages of producing bulk metals with submicrometer grain sizes which provide the opportunity to demonstrate improved mechanical characteristics including superplastic properties. Besides the effort, although the impurity may cause low ductility due to grain boundary segregation, there are limited studies to date on the influence of general impurities upon flow behavior of conventional superplastic materials. Accordingly, the present report demonstrates the significance of Si impurity on superplastic properties in an ultrafine-grained high-purity Zn-22%Al eutectoid alloy at room temperature. The alloy was prepared to include different levels of Si contents up to 1500ppm in the high-purity alloy and the consistent fine grain sizes of ~0.60µm were introduced through a series of solutionizing followed by cold rolling. Tensile testing showed an occurrence of excellent room-temperature superplasticity and the maximum elongation of 500% was recorded at an optimal superplastic strain rate of 1.0×10−3s−1 in the alloy with less Si. Increasing Si contents reduced ductility without changing the strain rate sensitivity, thereby implying the consistency in the deformation mechanism for superplastic flow but the difference in the fracture mode. The present analysis estimates a threshold stress and demonstrate the validity of applying the conventional superplastic relationship for depicting the room-temperature superplastic flow in the high-purity Zn-22%Al alloy. Moreover, the separate fracture modes are proposed for the alloy with increasing Si impurity contents by taking fractographs after superplastic elongations.

One-dimensional migration of interstitial clusters in SUS316L and its model alloys at elevated temperatures

For self-interstitial atom (SIA) clusters in various concentrated alloys, one-dimensional (1D) migration is induced by electron irradiation around 300 K. But at elevated temperatures, the 1D migration frequency decreases to less than one-tenth of that around 300 K in iron-based bcc alloys. In this study, we examined mechanisms of 1D migration at elevated temperatures using in situ observation of SUS316L and its model alloys with high-voltage electron microscopy. First, for elevated temperatures, we examined the effects of annealing and short-term electron irradiation of SIA clusters on their subsequent 1D migration. In annealed SUS316L, 1D migration was suppressed and then recovered by prolonged irradiation at 300 K. In high-purity model alloy Fe-18Cr-13Ni, annealing or irradiation had no effect. Addition of carbon or oxygen to the model alloy suppressed 1D migration after annealing. Manganese and silicon did not suppress 1D migration after annealing but after short-term electron irradiation. The suppression was attributable to the pinning of SIA clusters by segregated solute elements, and the recovery was to the dissolution of the segregation by interatomic mixing under electron irradiation. Next, we examined 1D migration of SIA clusters in SUS316L under continuous electron irradiation at elevated temperatures. The 1D migration frequency at 673 K was proportional to the irradiation intensity. It was as high as half of that at 300 K. We proposed that 1D migration is controlled by the competition of two effects: induction of 1D migration by interatomic mixing and suppression by solute segregation.

Production and Quality Assessment of Superelastic Ti-Nb-Based Alloys for Medical Application

Superelastic biocompatible metallic materials Ti-22Nb-6Zr and Ti-22Nb-3Ta-3Zr (at %) were produced. Vacuum arc remelting (VAR) with manual control allowed to produce high‑purity alloys. X-ray fluorescence spectrometry (XRF) results showed that one remelt was not enough to obtain homogeneous Ti-Nb-Ta-Zr ingot. Ti-Nb-Zr and Ti-Nb-Ta-Zr alloys were remelted 3 times and turned upside down after each remelting. Scanning electron microscopy (SEM) with micro X‑ray spectral analysis showed that chemical composition of the alloys coincided with nominal chemical composition. SEM results also showed that the alloys were mostly homogeneous. Recommendations for optimization of VAR in terms of producing high-purity homogeneous superelastic titanium alloys were elaborated.

Comparison of the microstructure, deformation and crack initiation behavior of austenitic stainless steel irradiated in-reactor or with protons

The objective of this study was to compare the microstructures, microchemistry, hardening, susceptibility to IASCC initiation, and deformation behavior resulting from proton or reactor irradiation. Two commercial purity and six high purity austenitic stainless steels with various solute element additions were compared. Samples of each alloy were irradiated in the BOR-60 fast reactor at 320°C to doses between approximately 4 and 12dpa or by a 3.2MeV proton beam at 360°C to a dose of 5.5dpa. Irradiated microstructures consisted mainly of dislocation loops, which were similar in size but lower in density after proton irradiation. Both irradiation types resulted in the formation of Ni–Si rich precipitates in a high purity alloy with added Si, but several other high purity neutron irradiated alloys showed precipitation that was not observed after proton irradiation, likely due to their higher irradiation dose. Low densities of small voids were observed in several high purity proton irradiated alloys, and even lower densities in neutron irradiated alloys, implying void nucleation was in process. Elemental segregation at grain boundaries was very similar after each irradiation type. Constant extension rate tensile experiments on the alloys in simulated light water reactor environments showed excellent agreement in terms of the relative amounts of intergranular cracking, and an analysis of localized deformation after straining showed a similar response of cracking to surface step height after both irradiation types. Overall, excellent agreement was observed after proton and reactor irradiation, providing additional evidence that proton irradiation is a useful tool for accelerated testing of irradiation effects in austenitic stainless steel.

Appearance of anodised aluminium: Effect of alloy composition and prior surface finish

Effect of alloy composition and prior surface finish on the optical appearance of the anodised layer on aluminium alloys was investigated. Four commercial alloys namely AA1050, Peraluman 706, AA5754, and AA6082 were used for the investigation. Microstructure and surface morphology of the substrate prior to anodising were analysed using scanning electron microscopy and atomic force microscopy. The optical appearance of the anodised surface with and without sealing was investigated using a photography setup, photospectrometry and bidirectional reflectance distribution function. It was found that the roughness of the as-etched surface increases with the degree of alloying due to second phase particles making the reflection more diffused, and that the as-etched surface morphology is similar to the oxide–substrate interface after anodising. Proper polishing is achieved on hard alloys and the glossy appearance was kept for alloys of high purity. Sealing made the specular reflection of the mechanically polished specimens more distinct.