Effect Of Second Phase Research Articles

A multidisciplinary approach to study precipitation kinetics and hardening in an Al-4Cu (wt. %) alloy

A multidisciplinary approach is presented to analyse the precipitation process in a model Al-Cu alloy. Although this topic has been extensively studied in the past, most of the investigations are focussed either on transmission electron microscopy or on thermal analysis of the processes. The information obtained from these techniques cannot, however, provide a coherent picture of all the complex transformations that take place during decomposition of supersaturated solid solution. Thermal analysis, high resolution dilatometry, (high resolution) transmission electron microscopy and density functional calculations are combined to study precipitation kinetics, interfacial energies, and the effect of second phase precipitates on the mechanical strength of the alloy. Data on both the coherent and semi-coherent orientations of the θ''/Al interface are reported for the first time. The combination of the different characterization and modelling techniques provides a detailed picture of the precipitation phenomena that take place during aging and of the different contributions to the strength of the alloy. This strategy can be used to analyse and design more complex alloys.

Effect of precipitates on nanostructuring and strengthening of high-strength aluminum alloys under high pressure torsion

Effects of secondary phases on the development of a nanocrystalline structure under severe plastic deformation (SPD) of two high-strength Al-Zn-Mg-Сu alloys with different additions of transition metals (TM) and on parameters of their hardness and tensile strength were investigated. The variety of heterogeneity of the alloy initial structure was conditioned by changes of sizes, densities and volume fractions of precipitates of TM aluminides and main strengthening phases, owing to alloying and heat treatment. Prior SPD the homogenized ingots were solution treated, water quenched and annealed in the temperature range of 170–250 °C to different times. Therewith in addition to coherent disk-shape 10–40 nm in diameter TM aluminides in the pre-quenched condition, further annealing led to formation of zones and precipitates of the main strengthening phases with equivalent diameter from several to about hundred nanometers. The disk-shape samples were further SPD processed by high-pressure torsion (HPT) via 10 revolutions under pressure of 6 GPa at room temperature. It was found that HPT of both alloys in the pre-quenched state, having nanosized precipitates of TM aluminides only, resulted in the most developed nanostructure with a (sub)grain size of about 80 ± 20 nm, and their maximum hardening. Straining of the pre-aged alloys, containing precipitates of the both types of fewer sizes and an order higher total density, on the contrary, completely suppressed grain refinement. Development of a work hardened, non-recrystallized structure was accompanied by the hardness and yield strength loss up to 25%. Preliminary overaging, leading to a strong coarsening and reduction in densities of main strengthening phases, activates nanostructuring of the alloys matrix. However, it was accompanied with formation of a bit coarser (sub)grains and demonstration of less hardness and strength than in the pre-quenched condition. Nature of the alloys structure and strength evolutions, depending on processing regimes and heterogeneity of the initial structure, have been discussed in details.

Effect of secondary phase on the electromagnetic shielding effectiveness of magnesium alloy

The microstructure, electrical conductivity, and electromagnetic interference (EMI) shielding effectiveness (SE) of Mg-xZn and Mg-xSn (x = 3,5) alloys prepared under different rolling and heat treatment conditions were systematically investigated to understand the effect of secondary-phase orientation on the electromagnetic-shielding property of magnesium alloys. Alloys were rolled to form basal textures and then subjected to different durations of solid-solution treatment and aging to induce the precipitation of secondary-phase particles along a specific direction. Experimental results indicated that in Mg-Zn and Mg-Sn alloys, secondary phases precipitated along directions perpendicular and parallel to the basal plane, respectively. When the direction of the incident electromagnetic wave is perpendicular to the basal plane, precipitates in Mg-Sn alloy parallel to the basal plane improve SE. The increment in SE is mainly attributed to the improvement in the reflection and multiple reflection losses of incident electromagnetic waves, which are caused by increasing the amounts of precipitates with specific orientations. Mg-5Sn alloy subjected to 16 h of solution treatment at 480 °C and 60 h of artificial aging at 170 °C for 60 h exhibited the maximum value of 107–89 dB and maximum increment in SE of 13 dB at 1200 MHz.

Effects of Secondary Phases on the High-Performance Colossal Permittivity in Titanium Dioxide Ceramics.

The intensive demands of microelectronics and energy-storage applications are driving the increasing investigations on the colossal permittivity (CP) materials. In this study, we designed a new system of Dy and Nb co-doped TiO2 ceramics [(Dy0.5Nb0.5)xTi1-xO2] with the formation of secondary phases, and then the enhancement of overall dielectric properties (εr ∼ 5.0-6.5 × 104 and tan δ < 8%) was realized in the broad composition range of 0.5 ≤ x ≤ 5%. More importantly, effects of secondary phases on microstructure, dielectric properties, and stability were explored from the views of defect-dipoles and internal barrier layer capacitance (IBLC) effect. According to the defect-dipoles theory, the CP should mainly originate from Nb5+, and the Dy3+ largely contributes to the decreased dielectric loss. Both CP and low dielectric loss were obtained for co-doping with Dy3+ and Nb5+. Besides, the Dy enrichment induced the formation of secondary phases, which were regarded as the low loss unit dispersed into the ceramic matrix, and largely facilitate the decreased dielectric loss. In particular, the analysis of temperature-dependent complex impedance spectra indicated that a stronger IBLC effect caused by the increased grain boundary resistance can also contribute to the optimized CP and low dielectric loss under appropriate contents of secondary phases.

The effect of graphene oxide on surface features, biological performance and bio-stability of calcium phosphate coating applied by pulse electrochemical deposition

In the current study, the effect of second phase of graphene oxide (GO) on the surface features and biological behavior of calcium phosphate (CaP) coating was evaluated. To do so, the GO-CaP composite coating was applied on TiO2 nanotubular arrays using pulse electrochemical deposition. The SEM and AFM images showed that, the CaP-based coating with uniform and refined microstructure could be formed through its compositing with GO sheets. The biological assessment of the coatings was also conducted by cell culture test and MTT assay. Based on findings, the GO-CaP coating showed the better biocompatibility compared to the CaP coating. This could be owing to the fact that the composite coating provided the lower roughness, moderately wettable surface with a contact angle of 23.5° ± 2.6° and the higher stability in the biological environments because of being involved with only the stable phase of CHA. However, in the CaP coating, spreading of cells could be limited by the plate-like crystals with larger size. The higher solubility of the CaP coating in the cell culture medium possibly owing to the existence of some metastable CaP phases like OCP in addition to the dominant phase of CHA in this coating could be another reason for its less biocompatibility. At last, the CaP coating showed the higher apatite-forming ability in SBF solution after its compositing with GO.

Effects of secondary phases on crystallographic preferred orientations in mylonites

Effects of secondary phases on crystallographic preferred orientations in mylonites

Effects of secondary phases on crystallographic preferred orientations in mylonites

Effects of secondary phases on crystallographic preferred orientations in mylonites

Effects of second phases on thermoelectric properties in copper sulfides with Sn addition

Abstract

The effects of second phases on superelastic behavior of TNTZ bio alloy

The present work was conducted to investigate the effects of second phases on the stability of β phase and superelastic behavior of a Ti–Nb–Ta–Zr (TNTZ) bio-alloy. For this purpose, the as-hot forged material was subjected to different thermal treatments. These included solution annealing, aging treatments at 500°C for 48h, and annealing at 850°C for 45min followed by quenching in water and ethanol solution, to obtain alpha (α) precipitate and α″ martensite, respectively, as the second phase in the β phase structure. These ended to different microstructures. The superelastic behavior of single β phase structure showed pseudoelastic (S) ratio of 20%. Furthermore, the precipitation of α phase reduced the S ratio to 6%. The α phase decreased the superelasticity by impeding the stress induced martensite (SIM) formation at the loading stage. On the other hand, the athermal α″ martensite, didn't significantly change superelasticity of β phase, (S ratio = 18%). The dissimilarity of α precipitate and α″ martensite in changing the superelastic behavior of the β phase was attributed to the their different mechanical and chemical stabilization potential. The TEM micrographs showed that the α precipitates hindered the growth of SIM needles, while the athermal α″ martensite was easily cut through by SIM. According to the EDS analysis, despite the presence of athermal α″ martensite, the segregation of β stabilizing elements from α precipitate to the β phase was traced; this was introduced as the second factor in spoiling the superelastic behavior of the β phase.

Influence of second phase on corrosion performance and formation mechanism of PEO coating on AZ91 Mg alloy

Plasma electrolytic oxidation (PEO) treatment has been performed on AZ91 Mg alloy in a silicate-containing alkaline electrolyte to disclose the relationship between second phase and resultant coating. The morphology and corrosion behavior were characterized for PEO coatings on three different AZ91 substrates with microstructures altered by heat treatment. In the presence of β phase, both the substrate and PEO coating exhibit enhanced corrosion resistance with finer and more evenly distributed β phase precipitates. In the as-cast AZ91, the anodized coating displays chemically and morphologically discontinuity on α and β phase with very coarse and defective regions on two-phase boundaries. In aged AZ91 with nano-sized β phase precipitates, the PEO coating shows no obvious difference on two-phase boundaries and is more homogenous with fewer pores and defects. The residual stress values given by X-ray diffraction (XRD) analysis indicate that PEO coating on aged AZ91 with finest β phase has the smallest stress which might be the reason for its improved corrosion resistance under synergetic effect of corrosive ions and residual stress. Conversely, in the absence of β phase, i.e. after solid solution treatment, the coating is characterized by the most inhomogeneous microstructure and the worst corrosion resistance, presumably owing to the absence of protective aluminum-containing oxides in the coating and more severe localized oxidation behavior adjacent to AlMn phase. Understanding the effect of second phase on PEO coating will enable us to optimize porous oxide structures for improved corrosion resistance by properly altering the substrate microstructure.

Microstructural and magnetic properties of Mn-Fe-P-Si (Fe2 P-type) magnetocaloric compounds

Fe2 P-based magnetocaloric compounds are an important and industrially relevant material class for magnetic refrigeration, yet their microstructure and its influence on the magnetic properties is hardly discussed in literature. We prepared Mn-Fe-P-Si-based samples using a powder metallurgical process and analyzed their microstructural and thermomagnetic properties. XRD, SEM, EDX and EBSD analysis reveal a phosphorous depleted cubic secondary phase in many samples with distinct microstructural properties giving an insight into the phase formation process. A porous morphology was found, hindering the direct application of the materials a magnetocaloric heat exchanger in bulk-like structures. The “virgin” effect could be in-situ observed for the first time on a macroscopic scale using temperature-dependent optical microscopy. Thermomagnetic measurements reveal a difference in transition temperature Tt in comparison to literature values which is attributed to a processing induced deviation from the nominal composition. The isothermal entropy change ΔST and adiabatic temperature change ΔTad were studied as well as their cyclic behavior. The effect of secondary phases is discussed and the importance of the metal/non-metal (M/NM)-ratio is shown. The article presents a road map for the preparation of Mn-Fe-Si-P-based alloys with highest quality.

Effect of secondary phases on thermoelectric properties of Cu2SnSe3

Cu2SnSe3 samples with different secondary phases are prepared from compositions of CuxSnSe3 (x=1.8–2.2) and Cu2SnySe3 (y=0.8–1.2), and their thermoelectric properties are investigated. For CuxSnSe3 samples, the secondary phase is SnSe2 for x=1.8 and 1.9 and SnSe for x=2.2, and nearly single-phase Cu2SnSe3 is obtained for x=2.0 and 2.1. For Cu2SnySe3 samples, the secondary phase is CuSe for y=0.8 and SnSe for x=1.1 and 1.2, and single-phase Cu2SnSe3 is produced for y=0.9 and 1.0. The lattice structure of synthesized Cu2SnSe3 depends on the x and y values, which is cubic for x≤2.0 or y≤1.0 and monoclinic for x>2.0 or y>1.0. Compared with the single-phase Cu2SnSe3 sample (ZT=0.42 at 773K), the samples with SnSe2 secondary phase show a greatly-enhanced ZT of 0.84 at 773K, which is likely the best result for un-doped Cu2SnSe3 up to now. The samples with SnSe secondary phase exhibit poor thermoelectric properties.

Influence of secondary phases on ferroelectric properties of Bi0.5Na0.5TiO3 ceramics

The effects of secondary phases on ferroelectric properties of Bi0.5Na0.5TiO3 (BNT) have been studied. Ceramic powders were prepared by solid state reaction employing different sintering temperatures and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy and impedance spectroscopy. The perovskite structure was detected by XRD; together with small peaks corresponding to a secondary phase assigned to the Na2Ti6O13-based phase in calcined powders. In addition, morphology and the content of the secondary phase were modified by the sintering temperatures, affecting the ferroelectric properties, and ac and dc conductivities. We believe that our results can benefit not only the understanding of BNT ceramics, but also expand the range of applications.

Effect of secondary phases on nanostructuring and hardness of severely deformed high-strength aluminum alloy

Effect of secondary phases on nanostructuring and hardness of severely deformed high-strength aluminum alloy

Effect of secondary phase on thermal behaviour and solid-state ion conduction in lithium doped N-ethyl-N-methylpyrrolidinium tetrafluoroborate organic ionic plastic crystal

Microstructural features significantly affecting lithium ion dynamics and conduction within the crystalline structure of pyrrolidinium based organic ionic plastic crystals.

Effects of sputtering period on the performance of Cu2ZnSnS4 solar cells

Currently, most of investigations about CZTS focus on the sulfurization conditions, the precursor stacking orders, and effects of secondary phases on the device performance. However, very few researchers have a detailed investigation of sputtering period. In this paper, the effects of sputtering period on the performance of Cu2ZnSnS4 solar cells are discussed. The crystal structure, morphology, chemical composition and phase purity of CZTS thin films prepared by different periods were characterized by X-Ray Diffraction(XRD), scanning electron microscopy(SEM) equipped with an energy dispersive spectrometer(EDS) and Raman spectroscopy. The results show that the performances of CZTS devices prepared by multi periods were better than that of using single period. Meanwhile, complete devices were fabricated using CZTS thin film based on different sputtering periods, and 2.02% efficiency of CZTS by single period, 3.19% efficiency by double periods and 3.6% efficiency by four periods were obtained, respectively.

Strengthening and elongation mechanism of Lanthanum-doped Titanium-Zirconium-Molybdenum alloy

The microstructural contributes to understand the strengthening and elongation mechanism in Lanthanum-doped Titanium-Zirconium-Molybdenum alloy. Lanthanum oxide particles not only act as heterogeneous nucleation core, but also act as the second phase to hinder the grain growth during sintering crystallization. The molybdenum substrate formed sub-grain under the effect of second phase when the alloy rolled to plate.

Defects annihilation behavior of neutron-irradiated SiC ceramics densified by liquid-phase-assisted method after post-irradiation annealing

Numerous studies on the recovery behavior of neutron-irradiated high-purity SiC have shown that most of the defects present in it are annihilated by post-irradiation annealing, if the neutron fluence is less than 1×1026 n/m2 (>0.1MeV) and the irradiation is performed at temperatures lower than 973K. However, the recovery behavior of SiC fabricated by the nanoinfiltrated and transient eutectic phase (NITE) process is not well understood. In this study, the effects of secondary phases on the irradiation-related swelling and recovery behavior of monolithic NITE-SiC after post-irradiation annealing were studied. The NITE-SiC specimens were irradiated in the BR2 reactor at fluences of up to 2.0–2.5×1024 n/m2 (E>0.1MeV) at 333–363K. This resulted in the specimens swelling up ∼1.3%, which is 0.1% higher than the increase seen in concurrently irradiated high-purity SiC. The recovery behaviors of the specimens after post-irradiation thermal annealing were examined using a precision dilatometer; the specimens were heated at temperatures of up to 1673K using a step-heating method. The recovery curves were analyzed using a first-order model, and the rate constants for each annealing step were obtained to determine the activation energy for volume recovery. The NITE-A specimen (containing 12 wt% sintering additives) recovered completely after annealing at ∼1573K; however, it shrank because of the volatilization of the oxide phases at 1673K. The NITE-B specimen (containing 18wt% sintering additives) did not recover fully, since the secondary phase (YAG) was crystallized during the annealing process. The recovery mechanism of NITE-A SiC was based on the recombination of the C and Si Frenkel pairs, which were very closely sited or only slightly separated at temperatures lower than 1223K, as well as the recombination of the slightly separated C Frenkel pairs and the migration of C and Si interstitials at temperatures of 1223–1573K. That is to say, the recovery mechanism was basically the same as that of pure SiC.

EFFECTS OF SECOND PHASES ON MICROARC OXIDATION PROCESS OF MAGNESIUM BASE MATERIALS

The effects of second phases on microarc oxidation (MAO, also named plasma electrolytic oxidation-PEO) behavior of Mg base materials were investigated and the related mechanism was discussed. The formation of barrier layer and its influence on sparking discharge behavior were characterized and analyzed on the base of systematic selecting and designing substrate materials. The variation of second phases at the early MAO stage was observed and analyzed by SEM and EDS, and then the effect mechanism of second phases on MAO behaviors was revealed. Voltage evolution trend during MAO were recorded to study the formation state of the barrier layer on the different Mg base materials. According to the growth mechanism of MAO film, the film growth process can be simplistically considered as a repeated breakdown and reconstruction process of a capacitor. Accordingly, the *国家自然科学基金项目51001036和国家国际科技合作专项项目2014DFR50560资助 收到初稿日期: 2015-09-25,收到修改稿日期: 2016-03-21 作者简介:王艳秋,女, 1979年生,讲师 DOI: 10.11900/0412.1961.2015.00500 第689-697页 pp.689-697

Grain boundary segregation and the formation mechanism of secondary-phase in (Ce,Nb)-codoped TiO2 ceramics

Secondary phases are common phenomena in doped titanium dioxide ceramics. Effects of secondary phases on the structure and performance of the doped TiO2 ceramic are crucial. Both boundaries segregation and formation mechanism of secondary phases should be comprehensively explored to enhance properties and application. (Ce,Nb)-codoped TiO2 ceramic samples were prepared from TiO2, Nb2O5, and CeO2 oxide powders by a traditional solid-state sintering method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and wavelength-dispersive X-ray spectroscopy (WDS) were conducted to determine the sample microstructures, crystal structures, ionic valences, and chemical composition. The point defect distributions at the grain boundaries were calculated via point defect thermodynamic analysis, and the effects of Ce4+ and Ce3+ on segregation at the grain boundaries were compared. The XPS analysis showed that both ions are present in the TiO2 ceramics, and that the Ce3+ content increases with increasing sintering temperature. Further, secondary phases originate from segregation of the NbTi· and Ce´Ti point defects at the grain boundaries. The driving force for segregation is primarily the elastic strain energy, and CeNbO4 and CeNbTiO6 secondary phases occur in the (Ce,Nb)-codoped TiO2 ceramics. With increased sintering temperature, the secondary phase transforms from CeNbO4 to CeNbTiO6.