Nanocrystalline Solid Solution Research Articles

A promising perspective in improving corrosion and wear resistance of plain steel through electrodeposition of thick Ni–Mo–W ternary alloy

In this study, thick Ni–Mo–W ternary alloy coatings (∼24 μm) with 13–27 wt% Mo and 4–11 wt% W were electrodeposited from an alkaline citrate-ammonia bath using direct current. The effect of current density (20–100 mA/cm2) on the composition, current efficiency, morphology, structure, surface topography, tribological behavior, and corrosion resistance of coatings was investigated. The findings revealed an advantageous induced co-deposition of Mo in an electrolyte containing equimolar Mo and W ions. While increasing the current density decreased the Mo content of the coatings, they always had more Mo than W. Increasing the current density, according to SEM and AFM observations, changed the smooth and nodular morphology of Ni–Mo–W coatings to a relatively rough and cauliflower shape. The microhardness of the produced nanocrystalline solid solution coatings was 3.8–4.9 times higher than that of the plain carbon steel substrate. While the hardest coating (793 Hv) deposited at 100 mA/cm2 had the best wear resistance with a volume loss value of 0.04 mm3, it had the worst corrosion resistance among the coatings with icorr = 4.4 μA/cm2. The least hard coating (607 Hv), deposited at 40 mA/cm2, with the highest wear volume loss value of 0.11 mm3, however, was the most corrosion resistant sample with icorr = 1.9 μA/cm2.

Near-infrared reflective coatings based on Ca1-xNdxAl12-xNixO19 blue pigments, prepared by solution combustion synthesis

Blue pigments based on Ca1-xNdxAl12-xNixO19 (x = 0–0.7 apfu) were obtained by an ecological, fast and energy efficient approach, namely solution combustion synthesis. The formation of nanocrystalline solid solutions was confirmed by X-ray diffraction investigation results. Increasing the degree of substitution resulted in intensification of color, decrease in crystallite size, and decrease in total solar reflectance. The CIE L*/a*/b* values of the composition with x = 0.5 were 80.9/-8.8/-30.0, while the total solar reflectance was 70.0 %. The obtained pigments were used to develop NIR-reflective (cool) coatings, applied onto black and white opacity charts made of glossy cardboard, metal, fibercement and ceramic substrate. The dispersion media tested were: an aqueous acrylic resin, an epoxy resin, and a clear ceramic glaze. Pigments based on Ca1-xNdxAl12-xNixO19 showed very good stability in acidic and alkaline environments but were dissolved by the glaze-generating melt. Exposure of the films to near-infrared radiation demonstrated the thermo-reflective efficiency of Ca1-xNdxAl12-xNixO19-based pigments. The acrylic resin proved to be the most suitable dispersion environment for maximizing the thermo-reflective properties, being clearly superior to epoxy.

Study on dielectric relaxation and current–voltage characteristics of Mn-doped ZrO2 nanocrystalline solid solution at and above room temperature

Study on dielectric relaxation and current–voltage characteristics of Mn-doped ZrO2 nanocrystalline solid solution at and above room temperature

Tysonite Type Nanocrystalline Solid Solutions R1 – xScxF3 (R = La, Pr): Synthesis and Electrical Conductivity

Tysonite Type Nanocrystalline Solid Solutions R1 – xScxF3 (R = La, Pr): Synthesis and Electrical Conductivity

Tysonite Type Nanocrystalline Solid Solutions R1 – xScxF3 (R = La, Pr): Synthesis and Electrical Conductivity

The single-phase nanocrystalline R0.9Sc0.1F3 solutions (R = La, Pr) were synthesized by soft chemistry methods as transparent xerogels with the tysonite structure (space group). The ionic conductivity of ceramic samples prepared from these materials was 4.5 × 10–4 and 2.1 × 10–3 S/cm at 773 K for R = La and Pr, respectively. The activation energy of the ion transfer in ceramic samples was 0.43 (R = Pr) and 0.48 eV (R = La) in the high-temperature segment and 0.56 eV (R = Pr) in the low-temperature segment. It was shown that the isovalent replacement of La3+ (Pr3+) cations in the R0.9Sc0.1F3 tysonite solid solutions with Sc3+ leads to 3–4-fold decrease in the conductivity of the ceramic electrolytes.

Corrosion Resistance of Amorphous-Nanocrystalline Composite Structure Materials.

The purpose of this paper is to investigate the corrosion resistance of different nanoscale microstructures in the same material system and propose a novel method to obtain high-performance materials. During the last 2 decades, microstructure refinement and microalloying have become the main methods to prepare high-performance materials. The tensile strength of nanocrystalline solid solutions can reach 2.3 gigapascal, which is more than 1 fold the strength of traditional steel. However, there are few studies about the corrosion resistance of different nanoscale microstructures. In this paper, coatings with different microstructures (nanocrystalline, amorphous, and amorphous-nanocrystalline composite) have been successfully prepared by electrodeposition in the same material system (nickel-phosphorus alloy). Electrochemical test and high-pressure corrosion immersion test were carried out. The results show that the material loss of amorphous-nanocrystalline coating (P = 9.2 wt %) is about 1/4 that of crystalline coating at 8 MPa. In the range of 0.1 and 8 MPa, the average acceleration effect of hydrostatic pressure on the corrosion rate was calculated to be 1.611 × 10-6 g·cm-2·d-1·MPa-1.

Study of the structural and magnetic properties at high temperature of Ni-Co-Mn-Al Heusler alloy prepared by an unconventional route

ABSTRACT Ni, Co, Mn, and Al elemental powders have been ball milled in a planetary mill for various periods, up to 32 h. The obtained powder was characterized with XRD, SEM-EDS, DSC, high-temperature-XRD, and VSM techniques to study morphology, composition, thermal transitions, structural and magnetic changes occurring at high temperatures. At the end of the milling process, a particle mixture consisting of agglomerated grains with a rounded shape and an average size of about 60 µm was formed. XRD patterns of the as-milled powders revealed the presence of a nanocrystalline solid solution mixture with (L10) and (B2) structures. HT-In-situ XRD characterizations confirmed the complete formation of the B2 ordered structure from 573 K. The austenitic Heusler phase B2 remains stable during one hour of isothermal holding and its proportions increase between 648 and 773 K. Under the heating effect, crystallites size grows up greatly with increasing holding temperature, nevertheless the micro-strains decrease sharply from 0.98% at room temperature to 0.31% at 773 K. Magnetic features of the milled alloy enhance further during the heating process, making it magnetically soft with the most intriguing values of Ms, Mr, and Hc between 648 and 773 K. This is owing to the complete development of the homogeneous and ordered Heusler B2 phase and the significant increase in crystallite size with the relaxation of residual stresses resulting from the direct effects of temperature.

Effect of self-ion with high-energy irradiation on the surface morphology, microstructure and mechanical properties of nanocrystalline TiAlN coating

TiAlN coating are used as nuclear reactor cladding protective materials due to their good corrosion resistance. However, long-term exposure to an extremely harsh nuclear environment will cause degradation, and the threshold irradiation fluence is not clear. In this work, a nanocrystalline TiAlN coating was successfully deposited on 304 L stainless steel and silicon wafers by filtered cathodic vacuum arc (FCVA) technology. The effects of different fluences of Al 3+ irradiation performed by the GIC4117 tandem accelerator on the structure and mechanical properties of TiAlN coatings were studied. After irradiation with a fluence of 4.0 × 10 14 ions/cm 2 , the refinement of grain size and columnar structure of nanocrystalline TiAlN coatings was confirmed, which improved the hardness. The irradiation fluence of 4.0 × 10 16 ions/cm 2 reduces all mechanical properties and can be taken as the threshold for the degradation of the TiAlN coating. These nanocrystalline TiAlN coatings have high surface integrity with no destruction, such as flacking, exfoliation and blistering, and good mechanical properties after irradiation. • Ultra-hardness (>40 GPa) was obtained by the formation of nanocrystalline structure and solid solution phase. • The crystallites refined from the average size of 23 ± 2 nm for the initial state up to a size of 18 ± 2 nm. • The hardening effect was confirmed under ion irradiation and the hardness increases from 42.5 ± 1.3 GPa to 46.4 ± 1.4 GPa. • The TiAlN coating with nano-polycrystalline structure exhibits structural integrity without blistering or flaking effects after irradiation.

Photocatalytic properties of composites based on Y1-xBixFeO3 (0<x<0.15) nanocrystalline solid solutions with a hexagonal structure

Photocatalytic properties of composites based on Y1-xBixFeO3 (0<x<0.15) nanocrystalline solid solutions with a hexagonal structure

Thermodynamic analysis of nanocrystalline solid solutions formation in copper‐lead‐tin ternary immiscible system during mechanical alloying

AbstractIn this paper, copper‐15 wt.%‐lead‐1 wt.%‐tin (Cu‐15wt %Pb‐1wt %Sn), copper‐15 wt.%‐lead‐2 wt.%‐tin (Cu‐15wt %Pb‐2wt %Sn) and copper‐15 wt.%‐lead‐3 wt.%‐tin (Cu‐15wt %Pb‐3wt %Sn) powder mixtures were mechanically alloyed in order to study the solid solubility extension during the alloying process. Nanocrystalline supersaturated solid solutions have been prepared in copper‐lead‐tin (Cu−Pb−Sn) ternary immiscible system by mechanical alloying (MA). Based on the thermodynamic model, the Gibbs free energy changes in these alloys during the formation of solid solutions are calculated to be positive, which means that there are no driving force to form solid solutions in copper‐lead‐tin ternary immiscible system. It was found that a large fraction of grain boundaries and a high density of dislocations play a significant role in the solid solubility extension in copper‐lead‐tin ternary immiscible system.

Synthesis, Characterization and sintering of nanocrystalline (U1-yCey)O2±x

Nanocrystalline solid solutions of (U1-yCey)O2±x [y = 0.15, 0.22, 0.28, 0.35] have been synthesized by citrate gel-combustion route with a fuel to oxidant ratio of 1. The “as prepared” powders were calcined at 873 K in air for 6 h and were consolidated into pellets at 220 MPa. These green pellets were reduced at 1073 K under flowing hydrogen for 8 h and were sintered at 1873 K under flowing Ar+8% H2 for 6 h. All these powders were characterized for their X-ray crystallite size (XCS), specific surface area (SSA), particle size distribution (PSD), porosity, bulk density (BD) and residual carbon (RC). The morphology and microstructures of these powders were studied by using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM), respectively. The Hall–Williamson analysis of the X-ray diffraction (XRD) data revealed that the “as-prepared” powders consist of nano grains with a size of about 10 to 20 nm and the results have been substantiated by bright field HRTEM image analysis of these samples. These sintered pellets were characterized for their phase composition, density and microstructure. Presence of a single phase fluorite solid solution was confirmed by XRD. A sintered density of 95.88±0.62% of theoretical density (TD) could be achieved. A systematic study on the gel-combustion synthesis of nanocrystalline (U1-yCey)O2±x [y = 0.15, 0.22, 0.28, 0.35] powders is being reported for the first time.

Mechanical Dissolution of Cu5Zr Phase and Formation of Supersaturated Solid–Solution Nanocrystalline Structure by High–Pressure Torsion in a Hypoeutectic Cu–2.7at%Zr Alloy

Mechanical Dissolution of Cu₅Zr Phase and Formation of Supersaturated Solid–Solution Nanocrystalline Structure by High–Pressure Torsion in a Hypoeutectic Cu–2.7at%Zr Alloy

Síntesis y caracterización estructural del compuesto de refuerzo de Ti+Ni3Al+Al2O3 a base de Fe producido por aleación mecánica

La mezcla de polvo de Ti+Ni3Al+Al2O3 a base de Fe se alea mecánicamente en un molino de bolas Spex. Los compuestos con adición de Ti+Ni3Al+Al2O3 a base de Fe se produjeron a una temperatura de sinterización de 1000 °C durante un tiempo de 1 h. Las propiedades de estos compuestos se examinaron mediante microscopía electrónica de barrido (SEM), microscopía óptica (OM), espectroscopía de dispersión de energía (EDS), difracción de rayos X (XRD) y análisis de microdureza. El producto final producido por aleación mecánica fue una solución sólida rica en níquel nanocristalina, el tamaño promedio del cristal era de unos pocos nanómetros. El contenido de titanio en el refuerzo aumentó los valores de microdureza del composite. Los compuestos producidos incluían las fases Fe3Al, TiAl, NiAl, Al3Ni2, Al2O3 y Fe3O.

Metallurgical characterization of mechanically alloyed MoNiAl-WC reinforced Fe matrix composite

Abstract MoNiAl-WC reinforced Fe matrix composites were obtained by mechanical alloying. The effect of various reinforcement ratios on microstructure change, elemental characterization and phase transformation were examined by using optical microscopy, scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, elemental surface mapping and a microhardness test. Fe and MoNiAl-WC compound and powder mixtures were synthesized by MA and nanocrystalline solid solution was obtained. The increase in the reinforcement ratio reduced grain size in the structure and increased the carbide ratio. The composite demonstrated excellent metallurgical qualities and interface bonding. Moreover, it was found that the amount of porosities increased with increasing reinforcement. X-Ray analysis showed the formation of NiAl, Al3Ni and WC phases.

Metallurgical characterization of mechanically alloyed MoNiAl-WC reinforced Fe matrix composite

Abstract MoNiAl-WC reinforced Fe matrix composites were obtained by mechanical alloying. The effect of various reinforcement ratios on microstructure change, elemental characterization and phase transformation were examined by using optical microscopy, scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, elemental surface mapping and a microhardness test. Fe and MoNiAl-WC compound and powder mixtures were synthesized by MA and nanocrystalline solid solution was obtained. The increase in the reinforcement ratio reduced grain size in the structure and increased the carbide ratio. The composite demonstrated excellent metallurgical qualities and interface bonding. Moreover, it was found that the amount of porosities increased with increasing reinforcement. X-Ray analysis showed the formation of NiAl, Al3Ni and WC phases.

Tribo-mechanical properties of CrNbTiMoZr high-entropy alloy film synthesized by direct current magnetron sputtering

The deposition parameters of high-entropy alloy films significantly influence their performance due to effective control of their microstructure. Thus, these parameters have become a research hotspot. In this study, CrNbTiMoZr high-entropy alloy films of amorphous or nanocrystalline solid solution were synthesized by direct current magnetron sputtering on silicon wafers and 304 stainless steel under different substrate bias voltages. The films' microstructure and tribo-mechanical properties were studied in detail. Results showed that the microstructure of films transformed from columnar structure to featureless with increased substrate bias voltage. In the nanoindentation test, the film deposited at −150 V exhibited the highest hardness of 9.7 GPa. Nevertheless, the CrNbTiMoZr films displayed excellent tribological properties under low bias voltage. Overall, our findings can guide the design of other novel high-entropy alloy films.

The Mechanical Properties of the Novel Nanocrystalline Refractory Tantalum Alloys

The nanocrystalline tantalum alloys were investigated in terms of mechanical properties. The materials were obtained by powder metallurgy techniques—mechanical alloying (MA) and hot pressing (pulse plasma sintering mode). Pure powders of niobium, molybdenum, and tungsten were used for tantalum as an additive element in the concentration of 5, 10, 20, and 40 wt %. The analysis of XRD (Williamson–Hall equation) and TEM confirmed a significant reduction of the grain size (5.3–25.7 nm) for pure powders and (12.5–171.5 nm) for bulk hot-pressed elements. The nanoindentation test was used to study the mechanical properties. The load-displacement curves show high uniformity of the mechanical properties. The nanocrystalline alloys show very high hardness and stiffness. The highest value of hardness reached 1481 HV for Ta–10Mo composition. Significantly higher values of hardness compared to pure Ta-nano were measured for Ta–W system. The Young’s modulus increased twice up to 343 GPa for Ta–20Mo in comparison to the unalloyed nanocrystalline Ta (163 GPa). In the novel nanocrystalline tantalum alloys, both solid solution and grain boundary strengthening affected on high mechanical properties.

Evolution of synthesis of FCC nanocrystalline solid solution and amorphous phase in the Ti-Ta based alloy by high milling energy

Pure Ti and Ti-based alloys exhibit two equilibrium phases: at lower temperatures they have a hexagonal close packed (α-Ti) crystalline structure while at higher temperatures they possess a body-centered cubic (β-Ti) structure. However, in special conditions, they could exhibit a metastable face-centered cubic (γ-Ti) crystalline structure. This paper aims to investigate the influence of Sn amount and milling time on the formation of γ-Ti phase on the Ti-Ta based alloy. Four alloys with compositions Ti-13Ta-xSn (x: 3, 6, 9 and 12 at. %) were obtained by high energy milling. The alloys were analyzed by X-ray diffaction patterns, transmission and scanning electron microscopy. For the Ti-13Ta-3Sn alloy, the β-Ti phase is formed in greater quantity, ∼70% at 100 h. For the Ti-13Ta-6Sn and Ti-13Ta-9Sn alloys, the phase that is in greater quantity is γ-Ti, around 100% at 100h. The Ti-13Ta-6Sn alloy shows a greater tendency to form the γ-Ti phase, since the quantity is close to 100% at 50 h milling time. Thermodynamic calculations are comparable with experimental data. The calculations were made using the MAAT software based on Miedema’s model. The MAAT is a free software that can be download from www.rpm.usm.cl.

Microstructure Evolution and Mechanical Stability of Supersaturated Solid Solution Co-Rich Nanocrystalline Co-Cu Produced by Pulsed Electrodeposition.

Thick films of supersaturated solid solution nanocrystalline Co-Cu (28 at.% Cu) were synthesized through the pulsed electrodeposition technique. Microstructural changes of nanocrystalline Co-Cu were intensively studied at various annealing temperatures. Annealing at 300 °C results in a spinodal decomposition within the individual grains, with no grain coarsening. On the other hand, distinct phase separation of Co-Cu is detected at annealing temperatures beyond 400 °C. Static micro-bending tests show that the nanocrystalline Co-Cu alloy exhibits a very high yield strength and ductile behavior, with no crack formation. Static micro-bending tests also reported that a large plastic deformation is observed, but no microstructure change is detected. On the other hand, observation on the fatigue resistance of nanocrystalline Co-Cu shows that grain coarsening is observed after conducting the cyclic micro-bending test.

Structural studies on Ti–Cu alloy obtained by high-energy ball milling

ABSTRACTTi50Cu50 (at.-%) alloy has been produced from elemental Ti and Cu powders by high-energy ball milling in a planetary ball mill. Structural evolution of the alloy during milling and after subsequent heat treatment have been studied. It has been stated that high-energy ball milling of the investigated powder produces two nanocrystalline solid solutions: Cu(Ti) and Ti(Cu), both characterised by the fcc (Fm-3 m) structure. The transition of Ti structure from hcp (P63/mmc) to fcc (Fm-3 m) is observed during milling. Heat treatment of the milled powder leads to recrystallisation of Cu(Ti) and Ti(Cu) solid solutions.This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.