Spinodal Decomposition Structure Research Articles

Microstructural characterization and corrosion behaviour of AlCoCrFeNiTix high-entropy alloy coatings fabricated by laser cladding

High-entropy alloy (HEA) coatings of AlCoCrFeNiTix (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were fabricated on AISI1045 steel by laser cladding. X-Ray diffraction (XRD) was used to investigate the phase composition of the coatings. The microstructure of coatings was analyzed using a scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-Ray diffraction (XRD) was used to investigate the phase composition of the coatings. The potentiodynamic polarization behaviour of coatings and substrate was studied. The composition of passive film on the corroded surface of the coating was identified by X-Ray photoelectron spectroscopy (XPS). The phase composition analysis showed that the coating was mainly composed of disordered body-centered cubic (BCC) solid solution phase (Fe-Cr) and ordered BCC phase (Al-Ni). The microstructure of the coatings was mainly composed of equiaxed polygonal grains, micro-nano particles of TiC and nanoparticles of Al2O3. The spinodal decomposition structure of Fe-Cr enrichment and Al-Ni-Ti enrichment was found in grains. The introduction of Ti led to passivation behavior of the coating during corrosion process. The components of the passive film were Al2O3, TiO2, Ti2O3, Cr2O3 and Cr(OH)3. The AlCoCrFeNiTi HEA coating showed the best corrosion resistance.

Microstructure evolution and strengthening mechanism of Cux[Ni3Mo] alloys

ABSTRACTMo could be dissolved into Cu to increase its high-temperature stability via a Ni intermediate. The microstructure evolution and strengthening mechanism of Cux[Ni3Mo] (x = 1, 2, 3, 4, 5, 7, 9, 12) alloys were investigated. The results show that composition significantly affects strengthening mechanisms of the alloys. For x = 1 and 2, The strengthening mechanisms of the alloys are mainly precipitation strengthening derived from Ni2Mo and Ni4Mo nanophases, both of which coexist and coherently grow on the face-centered cubic matrix. For x = 3–5, the nanophases gradually decrease and spinodal decomposition structure increases, which transforms the strengthening mechanism to spinodal decomposition strengthening. For x = 7–12, spinodal decomposition structure and precipitates reduce significantly, the solution strengthening dominates namely.

Precipitation evolution in Cu [Ni3Cr1] spinodal alloys under mismatch control

Abstract Cu Ni Cr alloys have a typical spinodal decomposition structure. However, a systematic investigation of the correlation between the mismatch of the two decomposition phases, Cu-rich (γ1) and Ni-rich (γ2), and the γ2 morphology is lacking. In this study, the microstructure evolution of Cux[Ni3Cr1] (x = 1, 2, 3, 4, 5, 7, 9, and 12) alloys was investigated over a wide composition range. The results show that mismatch significantly affects the shape of the γ2 precipitates. The γ2 phase is cubic when the mismatch degree (η) is in the range 0.62%–0.75% and lath-shaped when η is in the range 1.08%–1.35%. With increasing Cu content, the proportion of the lath-shaped γ2 phase decreases and that of the cubic γ2 phase continuously increases. Cubic precipitates enhance the alloy strength, while lath-shaped precipitates show better corrosion resistance owing to their high packing density. Therefore, an appropriate x can be chosen according to the actual service conditions. In addition, the Cr state affects the microstructure and performance of the alloys. Cr in the solid solution state promotes spinodal decomposition, while a large amount of Cr-rich precipitates at the grain boundaries has a negative effect on the mechanical performance.

Influence of spinodal decomposition structures on the strength of Fe-Cr alloys: A dislocation dynamics study

This paper presents a numerical analysis of the influence of spinodal decomposition on the strength of Fe-Cr alloys using the dislocation dynamics (DD) method. In the DD simulations, the structure of a spinodally decomposed chromium distribution is approximated using a cosine function. Using the equation for internal stress distribution, the interaction between a dislocation and the internal stress distribution is precisely accounted for in the DD simulations. The structure of the spinodally decomposed chromium distribution is parameterized using four variables, including the magnitude of chromium concentration, wave length of chromium distribution, position of the slip plane of dislocation, and the dislocation character (angle between the dislocation line and Burgers vector). Using these variables, the influence of the structure of chromium distribution on the critical resolved shear stress (CRSS) is studied. Furthermore, we focused on two major slip systems of the BCC structure, {110}〈111〉 and {112}〈111〉, and discuss the difference in the influence between the different slip systems. In the {110}〈111〉 slip system, the ΔCRSS appears only for a mixed dislocation with θ = 54.7°, because of the stripe pattern of the resolved shear stress distribution. On the other hand, in the {112}〈111〉 slip system, the dislocations with θ = 39.2° and 90° have a large ΔCRSS. There is a plateau of ΔCRSS in a range of 39.2∘<θ<90∘. The slip plane position does not change the ΔCRSS. There is a dependence of ΔCRSS on the wave-length of the chromium distribution. The dependence of ΔCRSS on the wave-length can be found not with a straight dislocation but with a curved dislocation using the DD simulations. The information is a new finding, and is meaningful in understanding the relationship between the material strength and the structure of spinodal decomposition.

Effect of CeO2 Doping on Phase Structure and Microstructure of AlCoCuFeMnNi Alloy Coating

AlCoCuFeMnNi high-entropy alloy coating was prepared by plasma cladding method. The phase structure and microstructure of AlCoCuFeMnNi coating was investigated by XRD, SEM and EDS respectively. The results show that AlCoCuFeMnNi caotings have two BCC phase structure and typical dendrite structure and form good metallurgical bonding with substrate. The dendrite is the typical spinodal decomposition structure. After CeO2 doping, the change of peak intensity and FWHM is obvious due to the effect of Ce on the improvement of grain growth, microstructure and crystallinity. The addition of CeO2 is beneficial to reduce the cladding defect, make dendrite arm spacing enlarged and spinodal decomposition structure refined, and improve element segregation owing to the melioration effect in the temperature gradient, solidification rate, fluidity, wettability, and surface tension.

Effects of Annealing on the Microstructure and Wear Resistance of AlCoCrFeNiTi 0.5 High-entropy Alloy Coating Prepared by Laser Cladding

Annealing behavior of AlCoCrFeNiTi0.5 high entropy alloy coatings prepared by laser cladding was investigated. The specimens were annealed at 900 °C for 5 h. The microstructure and wear resistance of the as-annealed and as-cast specimens were investigated. The XRD results indicate that the as-annealed AlCoCrFeNiTi0.5 high entropy alloy coating is composed of Al80Cr13Co7, Co3Ti, and AlFe solid solution phase. The SEM results and EDS data show that a typical spinodal decomposition structure with uniform composition is formed after annealing treatment. The average Vickers micro-hardness of the as-annealed coatings could reach 9890 MPa which is increased by about 73.5% compared with that of the as-cast coatings. The abrasion resistance testing shows that the abrasion loss of the as-annealed coatings is reduced by 92.5% and the wear width is reduced by 50% compared with the values of as-cast coatings.

Effect of minor B addition on microstructure and properties of AlCoCrFeNi multi-compenent alloy

The influences of slight amount of B element on the microstructure and properties of AlCoCrFeNiBx high entropy alloys (x = 0, 0.01,…, 0.09 and 0.1, mole fraction) were investigated. The AlCoCrFeNi high entropy alloy exhibits equiaxed grain structures with obvious composition segregation. However, with the addition of B element, the alloys exhibit dendrite structures. Inside the dendrites, spinodal decomposition structure can be clearly observed. With the addition of B element, the crystal structures change from (B2 + BCC) to (B2 + BCC + FCC) structures, and the hardness firstly increases from HV 486.7 to HV 502.4, then declines to HV 460.7 (x ≥ 0.02). The compressive fracture strength firstly shows a trend of increasing, and then declining (x ≥ 0.08). The coercive forces and the specific saturation magnetizations of the alloys decrease as B addition contents increase, the decreasing coercive forces show a better soft magnetic behavior.

X-ray diffraction study of low temperature aging in U–5.8 wt.%Nb

In order to study the effect of low temperature on microstructure of U–Nb alloy α″ phase, and interpret the low temperature aging mechanism, the U–5.8wt.%Nb alloy was investigated during aging at 200°C using X-ray diffraction (XRD), in situ tensile test and transmission electron microscopy (TEM). The phase transformation of α″→γ° is found by XRD after aging 4h at 200°C. The γ° transforms to α″ during tensile test by stress-induced. The experimental results disclose that the phase transformation of γ°→α″ occurs at the stage of twinning (de-twinning) deformation. Therefore, the phase γ° formed during aging can hamper the deformation of twinning (de-twinning), and strengthens the alloy remarkably. The phase transformation between α″ and γ° is reversible nanoscale martensitic transitions. The microstructure of dark/bright striations was found in TEM image, which present in both as-quenched and aged samples. The striations, made up of dislocation, are different from the structure of spinodal decomposition. The crystallography relationship of low temperature aging mechanism was also discussed in this paper.

A Cahn Hilliard Modeling of Metal Oxide Thin Films for Advanced CMP Applications

Chemical mechanical planarization (CMP) process enables topographic selectivity through formation of a protective oxide thin film on the recessed locations of the deposited metal layer while a continuous chemical oxidation reaction is followed by mechanical abrasion takes place on the protruding locations [1]. This paper demonstrates a new approach to CMP process optimization in terms of slurry formulations by analyzing the nature of the protective metal oxide nano films and modeling their growth through a Cahn Hilliard Equation (CHE) approach [2]. The commonly utilized models on the material removal rate calculations are also revisited to address the differences from the typical approaches to the dynamic removal models at the elevated layers.In previous work we have demonstrated the formation and mechanical properties of the chemically modified metal oxide thin films in CMP and discussed the stresses develop at the interfaces delineating the stability and protective nature of the chemically altered films [3]. The preliminary model is developed on the very well established tungsten films by assuming a constant temperature and metal oxide thin film volume to apply the CHE approach. As the CMP nano metal oxide films of tungsten have been shown to be self-protective, these assumptions are valid. Thin film analyses were conducted through XRD, XRR and FTIR characterization and compared to the theoretical calculations for the modeling simulations. The atomic force microscopy surface structures observed on the tungsten wafers are shown to be predicted by the CHE approach as spinodal decomposition structures. This new modeling approach is going to help in formulating optimal slurries for the new generation CMP materials by considering not only the active material removal concept but also the very critical planarization requirement through enabling protective oxide layers for planarization.

Replication of spinodally decomposed structures with structural coloration from scales of the longhorn beetle Sphingnotus mirabilis

Scales of the longhorn beetle Sphingnotus mirabilis possess a disordered bicontinuous macroporous structure that resembles a structure formed by a phase-separation process of spinodal decomposition. By using the scales as templates, SiO2 and TiO2 structures were successfully replicated. Structural and optical characterizations show that the fabricated oxide structures are spinodal decomposition structures with only short-range order and display non-iridescent structural colors.

Ion transport studies on Al–Zn ferrite dispersed nano-composite polymer electrolyte

A ferrite dispersed PEO based nano-composite polymer electrolyte has been developed in the present work. Formation of nano-composites, change in the structural and microscopic properties of the system have been investigated by X-ray diffraction, optical microscopy and SEM imaging. Existence of spinodal decomposition structure indicates formation of nano sized composite polymer electrolyte. Increase in formation of crystalline domain has been evidenced in thermal studies upon dispersal of nano-sized filler particles in pristine electrolyte matrix. The ionic transport studies through impedance spectroscopy exhibit highest electrical conductivity for the composition [93PEO-7NH4SCN]:2 wt% Al–Zn ferrite, viz. is 1.22 × 10−4 S/cm at room temperature with ionic transference number in excess of 0.9. Arrhenius type thermally activated conduction process is reflected during temperature dependent conductivity studies on these electrolytes.

Pore Formation in Poly(divinylbenzene) Networks Derived from Organotellurium-Mediated Living Radical Polymerization

Macroporous cross-linked polymeric dried gels have been obtained by inducing phase separation in a homogeneous poly(divinylbenzene) (PDVB) network formed by organotellurium-mediated living radical polymerization (TERP). The living polymerization reaction of DVB with the coexistence of a nonreactive polymeric agent, poly(dimethylsiloxane) (PDMS), in solvent 1,3,5-trimethylbenzene (TMB) resulted in polymerization-induced phase separation (spinodal decomposition), and the transient structure of spinodal decomposition has been frozen by gelation. Well-defined macroporous monolithic dried gels with bicontinuous structure in the micrometer scale are obtained after removing PDMS and TMB by simple washing and drying. Inside the skeletons that comprise the macroporous structure, “skeletal pores” with various sizes in nanometer scale have also been found by gas sorption measurements. The skeletal pores are deduced to be formed by secondary phase separation in the skeletons due to the thermodynamic instability that ...

Preparation of Macroporous Poly(divinylbenzene) Gels via Living Radical Polymerization

AbstractMacroporous cross-linked polymeric dried gels have been obtained by inducing phase separation in a homogeneous poly(divinylbenzene) (PDVB) network formed by organotellurium-mediated living radical polymerization (TERP). The living polymerization reaction of DVB with the coexistence of a non-reactive polymeric agent, poly(dimethylsiloxane) (PDMS), in solvent 1,3,5-trimethylbenzene (TMB) resulted in polymerization-induced phase separation (spinodal decomposition), and the transient structure of spinodal decomposition has been frozen by gelation. Well-defined macroporous monolithic dried gels with bicontinuous structure in the micrometer scale are obtained after removing PDMS and TMB by simple washing and drying. The properties of the macropores have been controlled by changing starting composition.

Characteristic features of x-ray diffraction on natural titanomagnetites after their spinodal decomposition

The x-ray diffraction analysis of samples of the Siberian platform traps (doleritic outcrops of the Stolbovaya River) containing spinodally decomposed titanomagnetite is carried out. It is shown that the method of x-ray powder diffraction fails to determine the lattice parameter (and, accordingly, the composition) of the finely dispersed high-Ti titanomagnetite decomposition region, which is due to a significant elastic strain of the crystal lattice of this phase in the plane separating it from the low-Ti magnetite phase and to a coherent character of x-ray scattering by the phases under consideration. The results of this study do not exclude the possibility of applying x-ray diffractometry to the diagnosis of phase stratification of titanomagnetites at the stage of coarsening of spinodal decomposition structures.

Microstructure of sodium polysialate siloxo geopolymer

Scanning electron micrographs of a well-cured polysialate siloxo geopolymer (silica:alumina ratio 2:1) prepared from metakaolinite reveal a microstructure consisting of a glass-like matrix containing metakaolinite relicts and impurity quartz grains. This inhomogeneity probably results from viscosity increases during preparation militating against efficient mixing of the components, but does not appear to seriously degrade the physical properties of the product. The matrix composition, determined by EDAX, conforms closely to the expected molar ratio and is unchanged by heating at 1200 °C, which however, brings about the crystallization of mullite needles in areas of the geopolymer matrix, the dissolution of the quartz impurities and the depletion of silica from the metakaolinite relicts, leaving behind fine alumina grains. These previously unsuspected thermal reactions help to explain the exceptional stability of the geopolymer matrix. Transmission electron micrographs confirm the essentially amorphous nature of both the as-prepared and heated geopolymer samples, but unexpectedly reveal in the latter nanometre-sized features resembling spinodal decomposition structures in glass.

Silica–alumina catalysts prepared in sol–gel process of TEOS with organic additives

Amorphous silica–alumina catalysts were prepared in the sol–gel reaction of tetraethoxysilane in the presence of aluminium nitrate and various organic additives, and the effects of the additives on both pore formation and acid-site generation were investigated. Macropores with bicontinuous morphology are formed in the system with poly(ethylene oxide) (PEO) with an average molecular weight of 10 0000, when a transitional structure of spinodal decomposition is fixed by sol–gel transition of inorganic components. In the systems with other organic additives with low molecular weight, such as ethylene glycol oligomers and citric acid, silica–alumina is provided with only mesopores. Although their mesopore structures are not affected by organic additives, the catalytic activity varies depending on the kind of organic additives. It is found that organic additives with the ability to increase the interaction between silica oligomers and aluminium cations increase the dispersion of Al in the silica network, resulting in high catalytic activity in the cracking of cumene. PEO interacts with both silica and aluminium cations in the sol–gel solution, so that macroporous silica–alumina prepared in the presence of PEO shows excellent catalytic activity.

Phase Separation in Sol–Gel Process of Alkoxide‐Derived Silica‐Zirconia in the Presence of Polyethylene Oxide

Phase separation in a sol–gel process of SiO2–ZrO2 in the presence of polyethylene oxide is investigated. An amorphous gel with interconnected macroporous morphology is obtained when phase separation and sol–gel transition concur to fix a transitional structure of spinodal decomposition. Macropore size, together with connectivity of the pores and gel skeleton, can be controlled precisely by selecting an appropriate starting composition for preparation at a zirconium content ≤11.7 mol%. The macroporous gel retains additional mesopores &lt;4 nm and exhibits typical bimodal pore size distribution. The addition of ZrO2 in SiO2 improves the thermal stability of both macroporous and mesoporous structures.

Morphology Control of Macroporous Silica-Zirconia Gel Based on Phase Separation

Gels with interconnected porous morphology in micrometer range have been prepared in a silica-zirconia system containing 12.7 mass% of zirconia from metal alkoxides under coexistence of poly (ethylene oxide) (PEO) with an average molecular weight of 100000. The porous structure was formed when the transitional structure of spinodal decomposition was frozen-in by sol-gel transition of inorganic components. In the system, the driving force of phase separation was considered to be the repulsive interaction between solvent and PEO associated on inorganic oligomers. Although the addition of zirconium alkoxide has an effect to decrease the domain size of dried gel by the increase of condensation rate, the domain size could be controlled in the sizes ranging from 0.2 to 30μm by adjusting the compositions of other constituents in the reacting solution.

A small-angle x-ray scattering study of microstructure evolution during sintering of sol-gel-derived porous nanophase titania

The evolution of microstructure as a function of firing temperature in sol-gel derived porous titania xerogels was investigated by small-angle x-ray scattering (SAXS). SAXS curves for xerogels fired below 550 °C exhibit a well-defined structure peak. This peak indicates the presence of a high degree of order in the electron density correlations associated with the interparticle structure factor. Results from electron microscopy and SAXS give a primary particle mean diameter of 50 Å, while scaling analysis of the scattered intensity at large momentum transfer values yields the Porod exponent 4, indicating a sharp transition zone between the solid and void phases. The pore volume fraction of the unfired xerogel is consistent with random close-packing of spheres. The internal surface area decreases almost linearly with increasing firing temperature. Rapid grain growth and pore coarsening begin near 90% of theoretical density, and lead to a breakdown in pore interconnectedness and the development of isolated pores. Observed enhanced sintering properties may be attributed primarily to the large surface-to-mass ratio of the sol-gel particles. The SAXS curves were adequately fit using a bicontinuous phase model developed for late-stage spinodal decomposition structures. Alternatively, the microstructure can be described by a hierarchical close-packing of spheres model. SAXS results are compared with data from gas adsorption and electron microscopy.

Critical behavior of the binary fluids cyclohexane-methanol, deuterated cyclohexane-methanol and of their isodensity mixture: Application to microgravity simulations and wetting phenomena.

It is possible to adjust the density of cyclohexane by adding a small amount of deuterated cyclohexane. Then the mixture deuterated cyclohexane-cyclohexane-methanol can be made isopycnic. We have determined the critical properties of this system and of the systems cyclohexane-methanol and deuterated cyclohexane-methanol: coexistence curve, correlation length, and osmotic compressibility via refractive index and turbidity measurements. For that purpose, a detailed discussion of the validity of the volume additivity and of the Lorentz-Lorenz formula has been made. The main result is that the isopycnic system acts as a binary mixture for the phase transition properties as shown by the \ensuremath{\beta} exponent and the amplitude combinations (${R}_{\ensuremath{\xi}}^{+}$${R}_{c}^{\mathrm{\ensuremath{-}}1/3}$) which exhibit the universal values. Some aspects of microgravity conditions can then be created. We have studied in the isopycnic system the phase separation at critical concentration; new features are found after a thermal quench: macroscopic spinodal decomposition structures during the phase separation process and macroscopic wetting layers in the final equilibrium state.