Influence of Ru Content on Microstructural Stability and Stress Rupture Property of DD15 Alloy

A fourth generation single crystal(SC)nickel based cast superalloy DD15 with 1%Ru,3%Ru,5%Ru was prepared using vacuum induction single crystal furnace in order to optimize the properties and cost of DD15 alloy.The exposure experiment of three alloys was conducted at 1100℃for 1000 h.The stress rupture properties tests were performed at 1100℃temperature and 137 MPa pressure.The composition optimization of Ru element in DD15 alloy had been studied.It was found that the alloys with different Ru contents all consist of cuboidalγ′phase embedded coherent inγphase.Theγ′phase of the alloy all has a size of about 300-500 nm and a volume content of more than sixty percent.The dimension ofγ′precipitates is reduced and uniform with increase of Ru content.Ru element can reduce the distribution ratio of high melting point element,so the microstructural stability is enhanced with Ru content increasing.No topologically close-packed(TCP)phase precipitated in the 5%Ru alloy even after 1000 h exposure.The stress rupture life of the alloy is significantly improved as Ru content rising.The raft breadth decreases slightly as Ru content increases.The specimen with 1%Ru and 3%Ru exhibits the presence of TCP phases and without TCP phases precipitated in fracture specimen with 5%Ru.The density and integrity ofγ/γ′interfacial dislocation network increase as Ru content of the alloy rises.

Positron Annihilation Study on the Microstructural Stability in Rapidly Solidified Al_(92.3)Fe_(4.3)V_(0.7)Si_(1.7)Mm_(1.0) Alloy

Rapidly solidified Al92.3Fe4.3V0.7Si1.7Mm1.0 alloy has been studied by positron lifetime spectroscopy and the variations on the intedecial defects with the annealing temperature were revealed by an analysis of the lifetime results. The intedece characteristics derived from the positron-lifetime results could be used to give a satisfactory interpretation of the dependence of mechanical properties on the annealing temperature

Effect of Precipitating Phases on Tensile Strength and Microstructural Stability of a Spray-Deposited Al-Si-Fe-Mn-Cu-Mg Alloy

Spray deposition is a novel process which is used to manufacture rapidly solidified bulk and near-net-shape preforms. In this study, AI-20Si-5Fe-3Mn-3Cu-1Mg alloy was synthesized by spray deposition technique. The aging process of the alloy was investigated by differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM). The results show that two kinds of phases, i.e. S(Al2CuMg) and σ(Al5Cu6Mg2), precipitate from matrix and improve the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300℃). In addition, the σ-Al5Cu6Mg2 is a relatively stable phase which improves microstructural stability of the alloy.

Creep rupture properties and microstructure stability of the GH984G alloy tube

GH984G alloy is a significant candidate material for 650-700℃ ultra-supercritical coal-fired generating units.In this paper,creep rupture properties and microstructure stability of the GH984G alloy tube were studied,and the findings indicated excellent creep rupture properties at 700℃.Furthermore,the extrapolated strength for 100000 h was found to be 153.8 MPa,which satisfies the requirements for the long-term performance of high-temperature materials in power stations.Aging at 700℃ with the extension of time,the grain boundary carbides and the particle size of the γ′phase on the matrix gradually coarsen,but its spherical morphology remains uniformly distributed.However,no harmful phase precipitates were found even after aging at 700℃ for up to 19144 h.Excellent microstructure stability guarantees the 700℃ creep rupture properties of the GH984G alloy tube.

Effects of Al on microstructural stability and related stress-rupture properties of a third-generation single crystal superalloy

To examine the influences of minor modification of Al content on the microstructural stabilities and stress rupture properties,two alloys with minor difference in Al content were exposed isothermally at 1100℃for 100 h,500 h,and 1000 h,respectively.The microstructures were characterized before and after thermal exposure.It was found that when Al content was decreased by 0.4 wt%,the volume fractionγ'decreased by 4%,the size ofγ'increased by 40 nm,the matrix channel width increased by 5 nm,and the misfit degree ofγ/γ'phases increased by 0.006%after heat treatment(HT).During thermal exposure,the alloy with low Al content had a better resistance to coarsening ofγ'phase and precipitation ofμphase.Theγ'particles of the alloy with high AI content tended to connect each other and coarsened along<100>directions;however,theγ'particles of the alloy with low Al content remained cubic after 500 h.A serious coarsening behavior took place in the two alloys after aging for 1000 h.The structural stabilities were significantly improved.However,the change of 0.4 wt%Al content was found to have little effect on the high temperature stress-rupture properties.

Effects of Ni, Cr and W on the microstructural stability of multicomponent CoNi-base superalloys studied using CALPHAD and diffusion-multiple approaches

The alloying effects of Ni,W and Cron the microstructural stability of CoNi-base alloys were investigated using a multicomponent diffusion multiple after being aged at 1000℃ for 1000 h.The diffusion multiple was carefully designed based on thermodynamic calculations.The relationships between alloy compositions and microstructural characteristics were established over a large compositional range using this single sample,and the alloying effects of Ni,W and Cron the elemental partitioning behaviors betweenγ and γ' two phases were thermodynamically analyzed using high-throughput calculation.The results together show that an increase of Ni content increases the γ' volume faction in the long-term aged microstructures.However,the higher Ni content leads to the precipitation of the χ phase by promoting the partitioning of W from the γ' phase to the γ phase.The decrease of W content dramatically reduces theγ' volume faction,but the addition of Cr can properly counteract this effect by promoting the partitioning of Al and Ti from the γ phase to the γ' phase.This study will be helpful for accelerating the development of novel γ'-strengthened multicomponent CoNi-base alloys,as well as providing experimental data to improve the thermodynamic database.

Microstructural Evolution and Thermal Stability of Ultra-fine Grained Al-4Mg Alloy by Equal Channel Angular Pressing

Experiments were conducted to evaluate the grain refinement and thermal stability of ultra-fine grained Al-4Mgalloy introduced by equal-channel angular pressing (ECAP) at 473 K. The results show that the intensities of X-ray(111/222) and (200/400) peaks for the alloy processed by ECAP decrease significantly and the peak widths of halfheight become broadening compared with the corresponding value in the annealed alloy. The microstructure of 2passes ECAPed alloy consists of both elongated and equiaxed subgrains. The residual strain in the alloy increaseswith increasing passes numbers, that appears as increasing dislocation density and lattice constant of matrix. Anequiaxed ultra-fine grained structure of～0.2μm is obtained in the present alloy after 8 passes. The ultra-fine grainsare stable below 523 K, because the alloy retains extremely fine grain size of～1μm after static annealing at 523 Kfor 1 h.

Microstructure and thermal stability of mechanically alloyed Al_3Ti/Al alloy

The microstructure stability of Al 3Ti/Al alloy prepared by mechanical alloying (MA) was investigated in the simulating environment in which they may be used. The results show that the MA alloy possesses fine microstructure (the grain size is about 0.5 μm). After cycling loaded followed by heat exposure at 350 ℃ for 24 h, no microstructure coarsening of the alloy occurred, which means that the Al 3Ti/Al alloy behaves good microstructure stability at high temperature. The compression yield strength of the alloy reaches up to 247 MPa at 350 ℃. [

DIFFUSION PHENOMENA AND MICROSTRUCTURE STABILITY OF Ni－Cr－Al－Y－Si COATING ON THENi_3Al BASED ALLOY SUBSTRATE

In this paper, Ni-Cr-Al-Y-Si coating deposited by vacuum are deposition on the Ni_3Alalloy IC6, the typical use of which is for turbine blades and vanes, was examined.The results of the tests show that the tensile properties at room temperature and stress rupture properties at 1100℃ of the IC6 alloy were not obviously influenced by the coatings. At annealing state, limited element interdiffusion was observed. After stress rupture testing for 252 h at 1100℃/90 MPa, however,significant interdiffusion of Mo, Cr and Al took place between the coating layer and the substrate.The element diffustion did not result in the formation of brittle phases on the coating/substrate interface. No cracking and spallation in the coating were found.Therefore it can be concluded that the Ni-Cr-Al-Y-Si overlay coating was successful for protecting the IC6 alloy.

Effects of terbium sulfide addition on magnetic properties,microstructure and thermal stability of sintered Nd-Fe--B magnets

To increase coercivity and thermal stability of sintered Nd–Fe–B magnets for high-temperature applications, a novel terbium sulfide powder is added into（Pr（0.25）Nd（0.75））（30.6）Cu（0.15）Fe（bal）B1（wt.%） basic magnets. The effects of the addition of terbium sulfide on magnetic properties, microstructure, and thermal stability of sintered Nd–Fe–B magnets are investigated.The experimental results show that by adding 3 wt.% Tb2S3, the coercivity of the magnet is remarkably increased by about 54% without a considerable reduction in remanence and maximum energy product. By means of the electron probe microanalyzer（EPMA） technology, it is observed that Tb is mainly present in the outer region of 2：14：1 matrix grains and forms a well-developed Tb-shell phase, resulting in enhancement of HA, which accounts for the coercivity enhancement.Moreover, compared with Tb2S3-free magnets, the reversible temperature coefficients of remanence（α） and coercivity（β） and the irreversible flux loss of magnetic flow（hirr） values of Tb2S3-added magnets are improved, indicating that the thermal stability of the magnets is also effectively improved.

Microstructure and Stability of Fe_(73.5) Cu_1Nb_3Si_(13.5)B_9 Alloy at Different Stages of Phase Transformation

The microstructure and the stability of Fe_73.5Cu_1Nb_3Si_13.5B_9 alloy at different stages of phase transformation were investigated through the observation of X-ray difraction and transmission electron microscopy and the measurement of magnetic aftereffect (MAE). It was found that the dependence of the volume fraction of amorphous phase and the MAE in the samples annealed from 450 to 700℃ on the annealing temperature is similar.

Characterization of Microstructure and Stability of Precipitation in SIMP Steel Irradiated with Energetic Fe Ions

A type of home-made reduced activation martensitic steel, high silicon （SIMP） steel, is homogeneously irradiated with energetic Fe ions to the doses of 0.1, 0.25 and 1 displacement per atom （dpa）, respectively, at 300℃ and i dpa, at 400℃. MicrostructurM changes are investigated in detail by transmission electron microscopy with cross-section technique. Interstitial defects and defect dusters induced by Fe-ion irradiation are observed in ali the specimens under different conditions. It is found that with increasing irradiation temperature, size of defect clusters increases while the density drops quickly. The results of element chemical mapping from the STEM images indicate that the Si element enrichment and Ta element depletion occur inside the precipitates in the matrix of SIMP steel irradiated to a dose of 1 dpa at 300℃. Correlations between the microstructure and irradiation conditions are briefly discussed.

Stability/Instability of Solitary waves with Nonzero Asymptotic Value for a PDE in Microstructural Solid Materials

The present paper deals with results of stability/instability of solitary waves with nonzero asymptotic value for a microstructure PDE. By the exact solitary wave solutions and detailed computations, we set up the explicit expression for the discrimination d′′（c）. Finally, a complete study of orbital stablity/instablity for the explicit exact solutions is given.

Effect of Nb and Ti on second-phase precipitation and mechanical properties of 430 ferritic stainless steel

The influence of Ti and Nb on the microstructure,mechanical properties,and second-phase precipitation of 430 ferritic stainless steel was investigated.In addition to optical microscopy,transmission electron microscopy and X-ray diffraction analyses,tensile tests,and carbonitride extraction experiments were conducted to investigate the microscopic mechanisms.The results showed that the primary precipitates in SUS 430 ferritic stainless steel were Cr_（23）C_6,Mn_（23）C_6,and Cr_7C_3,and the primary strengthening mechanism was precipitation strengthening.When Ti was added separately,the main precipitates were TiC and TiN.However,coarse TiC adversely affected the mechanical properties of steel.When double-stabilized with Ti and Nb,coarse TiC was replaced by fine NbC.The type of precipitation was altered,and precipitation and solid solution strengthening occurred.Therefore,the tensile strength and plastic strain ratio（r-value） improved to 433.60 MPa and 1.37,respectively.

Creep-Induced Phase Instability and Microstructure Evolution of a Nearly Lamellar Ti–45Al–8.5Nb–(W, B, Y) Alloy

Microstructure degradation and stress-induced transformation of a high Nb-containing TiAl alloy with nearly lamellar microstructure during creep were investigated.Tensile creep experiments were performed at 800,850 and 900℃ under 150 MPa in air.Microstructures before and after creep tests were examined using scanning and transmission electron microscopy(SEM and TEM).Dislocations within the lamellar structure andβo(ω)region and twin intersection in massiveγgrains were investigated.Dislocation sliding played a critical role in the deformation ofωo phase,which preferentially occurred on the(0002)ωo plane.Possible deformation mechanisms were revealed.A stress-inducedγ→α2 phase transformation took place during the creep test at 850 and 900℃.α2 lamella could directly decompose into theωo phase at 850℃.The instability of high-temperature microstructure can weaken the creep resistance and promote the plastic deformation of the lamellar matrix,thus could be detrimental to the creep properties.The correlations between creep properties and microstructure instability were discussed.

Microstructure stability of γ’+β Ni-Al coated single-crystal superalloy N5 annealed at 1100℃

γ’+β Binary-phase Ni-Al coatings were prepared on second-generation single-crystal superalloy Rene N5(N5) substrates by electron beam physical vapor deposition.Inter-diffusion behavior between coatings and substrates at 1100℃ and its effects on microstructure stability of the substrates were investigated.A 3-μm-thick substrate diffusion zone(SDZ) layer forms beneath the coating/substrate interface after 5-h heat treatment.The SDZ layer is composed of γ’-Ni_(3) Al phases and needle-like precipitates growing along(100)(110) or(100) <■> direction.After100-h annealing,the thickness of the SDZ layer increases to~17 μm,much lower than that of the single β-NiAl-coated substrate,while keeping single-crystal microstructure.

Microstructure and Mechanical Properties of a CoFeNi_2V_(0.5)Nb_(0.75) Eutectic High Entropy Alloy in As-cast and Heat-treated Conditions

The eutectic CoFeNi2V0.5Nb0.75 high entropy alloys （HEAs） were heated at 500, 600, 700, 800 and 1000 ℃, respectively for 6 h and subsequently quenched in the water to investigate their thermal stability and phase transformation at high temperature. The microstructure and mechanical properties of the samples were investigated by scanning electron microscopy, X-ray diffraction, compressive and hardness tests. It was found that the as-cast CoFeNi2V0.5Nb0.75 HEAs showed a eutectic microstructure with alternating fcc solid solution phase and Fe2Nb-type Laves phase. The NbNi4-type intermetallic phase appeared when the heat-treated temperature was higher than 600 ℃. With increasing quenching temperature, the volume fraction of the NbNi4-type intermetallic phase increased while that of the eutectic regions decreased. The sample quenched at 800 ℃ showed the most excellent comprehensive mechanical properties; its fracture strength, yield strength and plastic strain were as high as 2586.76 MPa, 2075.18 MPa and 16.73%, respectively. Moreover, the eutectic CoFeNi2V0.5Nb0.75 HEAs exhibited apparent age hardening, especially quenched at 700 ℃, the hardness reached up to the maximum value of HV 727.52.

Density functional theory study on the influence of cation ratio on the host layer structure of Zn/Al double hydroxides

A density functional theory （DFT） study has been carried out for [Zn-1AI（OH2）n＋6（OH）2n-2]^3＋ （n=3-6） and [Znn-1AI（OH2）2n-2（OH）2n-2]^3＋ （n = 7） clusters, which include the basic structural information of the brucite-like lattice structure of Zn/Al layered double hydroxides （LDHs） with Zn/AI molar ratio （R） in the range 2-6, in order to understand the effect of the Zn/Al ratio on the structure and stability of binary Zn/Al LDHs. Based on systematic calculations of the geometric parameters and formation energies of the cluster models, it was found that it is possible for Zn^2＋ and Al^3＋ cations to replace Mg^2＋ isomorphously in the brucite-like structure with different R values, resulting in differences in microstructure of the clusters and unit cell parameter a of the Zn/Al LDHs. Analysis of the geometry and bonding around the trivalent Al^3＋ or divalent Zn^2＋ cations reveals that Al^3＋ plays a more significant role than Zn^2＋ in determining the microstructure properties, formation and bonding stability of the corresponding ZnRAl clusters when R〈5, while the influence of Zn^2＋ becomes the dominant factor in the case of R〉 5. These findings are in good agreement with experiments. This work provides a detailed electronic-level understanding of how the composition of cations affects the microstructure and stability of Zn-containing binary LDH layers.

Air stable Fe nanostructures with high magnetization prepared by reductive annealing

Monodispersed Fe nanospindles and nanoparticles were successfully synthesized through environmentfriendly reductive annealing ？-Fe OOH nanorods. Effects of annealing temperature and reaction atmosphere on microstructure, phase, and magnetic property of Fe nanostructures were investigated.The as-obtained pure Fe nanoparticles with mean size of 45 nm had a high saturation magnetization up to 207 emu/g, close to that of bulk material（218 emu/g）, which exhibited high air stability. After exposing in air for 2 and 7 days, the as synthesized Fe nanoparticles still showed high magnetization of 182 and141 emu/g, respectively.