Microstructure and creep behaviour of Mg-12Gd-3Y-1Zn-0.4Zr alloy

Microstructure and creep behaviour of Mg-12Gd-3Y-1Zn-0.4Zr alloy prepared by squeeze casting were investigated. Transmission electron microscope (TEM) observation revealed that a kind of lamellar-shaped morphologies 14h long-period stacking order structure (LPSO) and dense β’-phase precipitates were formed by heat treatment. The alloy exhibited good creep resistance. It was shown that the creep-resistant performance kept stable because of the restriction of dense β’-phase precipitates and LPSO phases to the movement of dislocations, and the formation of β-phase plates took responsibility for the softening of material during creep. Stress and temperature dependence of the steady-state creep rate were studied over stress range of 50-100 MPa and a temperature range of 250-300 oC, and a dislocation creep mechanism was proposed for the alloy.     

Microstructure evolution,mechanical properties and creep mechanisms of Mg-12Gd-1MM-0.6Zr (wt%) magnesium alloy

In this research, the microstructure evolution, mechanical properties, and creep mechanisms of Mg-12Gd-1MM-0.6Zr (wt%) alloy under different conditions were systematically studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile creep tests. Regarding the microstructure of the as-cast sample, the average grain size is about 42 μm, and the eutectic compounds were determined to be Mg₅(Gd_0.8MM_0.2). During homogenization, these eutectic compounds gradually dissolve, and Mg₁₂MM particles are precipitated. During hot extrusion, complete dynamic recrystallization (DRX) occurs, resulting in equiaxial grains with an average grain size of about 12 μm and the formation of streamlines consisting of Mg₁₂MM particles along the extrusion direction (ED). After T5 treatment (225 °C for 7 h), a large number of β′(Mg₇Gd) phases are precipitated on the {11–20}α habit plane and are interconnected, forming an interlaced network structure. The ultimate tensile strength (R_m = 405 MPa) and yield strength (R_P0.2 = 288 MPa) of the T5 sample are significantly higher than those of the as-extruded sample (R_m = 289 MPa, R_P0.2 = 185 MPa), but the elongation (A = 4%) was remarkably lower than that of the as-extruded sample (A = 18%). When crept at 225 °C under 100 MPa, the steady-state creep rates of the as-cast, as-extruded, and T5 samples are 1.59 × 10^–8, 1.08 × 10^–8, and 1.40 × 10^–8 s^–1, respectively, and their total strains within 100 h are respectively breaking, 0.81%, and 0.92%, indicating that the as-extruded alloy exhibits the best creep resistance. TEM analysis reveals that, during the creep process of the T5 sample, the β′ particles coarsen and the precipitate-free zones (PFZs) widen, which increase the steady-state creep rate and the total strain within 100 h as compared with the as-extruded sample.     

Effect of copper on magnetostriction and mechanical properties of TbDyFe alloys

The intrinsic brittleness of the TbDyFe alloy significantly decreases its mach inability and applications.This paper aims to improve the toughness of TbDyFe alloy by adding Cu. Various alloys of the type(Tb_(0.3)Dy_(0.7))_(0.37)Fe_(0.63-χ)Cu_χ(χ=0, 0,01.0.03, 0.05, 0.08, 0.1) were fabricated by an arc melting furnace under a high purity argon atmosphere. The microstructure, magnetostrictive properties and mechanical performance were studied systematically. The results show that the (Tb,Dy)Cu phase forms in these alloys upon the addition of Cu. Correspondingly, their toughness improves, attributed to the formation of a (Tb,Dy)Cu phase. Compared to the Cu-free alloy, the fracture toughness (Kic) increases 2-3 times with increasing Cu content. However, the magnetostriction performance of these alloys declines with Cu addition, due to the low-magnetic performance of the (Tb,Dy)Cu phase at room temperature. Compared with other alloys, the alloy with the addition of 1at%Cu shows the best compromise between the saturation magnetostriction and fracture toughness.     

Effects of heat treatments on microstructure and mechanical properties of Mg-15Gd-5Y-0.5Zr alloy

Microstructure and mechanical properties of Mg-15wt.%Gd-5 wt.%Y-0.5wt.% Zr alloy were investigated in a series of conditions. The eutectic was dissolved into the matrix and there was no evident grain growth after solntionized at 525 ℃ for 12 h. The evolution of the phase constituents from as-cast to cast-T4 was as follows： α-Mg solid solution＋Mg5（Gd,Y） entectic compound→α-Mg solid solution＋ spheroidized Mg5（Gd, Y） phase→α-Mg supersaturated solid solution＋cuboid-shaped compound （Mg2Y3Gd2）. And the precipitation sequences of Mg-15Gd-5Y-0.5Zr alloy were observed, according to the hardness response to isothermal ageing at 225-300 ℃ for 0-128 h.     

Microstructure and mechanical properties of as-cast and heat treated Mg-15Gd-3Y alloy

The microstructure evolution and mechanical properties of Mg-15Gd-3Y alloy were investigated in the as-cast and heat treated conditions.The microstructure evolution from as-cast to cast-T4 states involved α-Mg solid solution+Mg5(Gd,Y) phase→α-Mg supersatu-rated solid solution+rare earths compound Mg3(Gd1.26,Y0.74)→α-Mg supersaturated solid solution+rare earths compound Mg3(Gd0.745,Y1.255).It showed that 480 oC/4 h was the optimal solution treatment parameter.If the solution temperature was high or the holding time was long,such as 520 oC/16 h,an overheating phenomenon would be induced,which had a detrimental effect on the mechanical properties.When age-ing at 225 and 200 oC,the alloy would exhibit a significant age-hardening response and great long-time-age-hardening potential,respectively.The best mechanical properties were obtained at the parameters of 480 oC/4 h+225 oC/16 h,with the UTS of 257.0 MPa and elongation of 3.8%.     

Influences of different Zr/Sc ratios on microstructure and mechanical properties of Al-2Si alloy

The influences of different Zr/Sc ratios on the microstructural evolution and mechanical performances of Al-2 Si alloy were investigated in this paper.The as-cast samples were characterized and analyzed by the scanning electron microscope(SEM) with an energy dispersive spectrometer(EDS) to indicate the refining effect of the different Zr/Sc ratios on the α-Al and Si phases in Al-2 Si alloy.The results indicate that the α-Al phases are refined from coarse dendritic structure to relatively fine equiaxed grains when the Zr/Sc ratio is equal to 1:1.Meanwhile,the eutectic Si phase in Al-2 Si-0.2 Zr-0.2 Sc alloy is modified from the coarse plate and needle to fine fiber and partial granular structure,and the average roundness of eutectic Si is decreased by 75% from 16 to 4.With the refinement of α-Al phases and the modification of eutectic Si structure,the ultimate tensile strength(UTS) is improved by 53% and the elongation(EL) is increased by 64% when the Zr/Sc ratio is equal to 1:1.In addition,the UTS decreases and EL is enhanced with the increase of tensile temperature.Moreover,the fracture model of Al-2 Si-0.2 Zr-0.2 Sc alloy in250℃ changes into the ductile fracture.     

Enhancing (de)hydrogenation kinetics properties of the Mg/MgH_2 system by adding ANi_5(A=Ce,Nd,Pr,Sm,and Y) alloys via ball milling

Magnesium(Mg)-based alloys have already been widely studied as the hydrogen storage materials because of their high reversible hydrogen storage capacity,low cost,light weight,etc.However,the poor de/hydrogenation kinetic properties dramatically hinder the practical applications.In this work,the MgH_2-ANi_5(A=Ce,Nd,Pr,Sm,and Y) composites were prepared by a high-energy ball milling method.which can effectively refine the particle size thus improving the kinetic properties.Experimental results reveal that the MgH_2-ANi_5 composites mainly consist of Mg_2 NiH_4,MgH_2 and rare earth(RE) hydride,which will be dehydrogenated to form Mg_2 Ni,Mg and stable RE hydride reversibly.Accordingly,the asmilled MgH_2-ANi_5(A=Ce,Nd,Pr,Sm,and Y) composites with various A-elements can respectively contribute to a reversible hydrogen storage capacity of 6.16 wt%,5.7 wt%,6.21 wt%,6.38 wt%,and 6.5 wt%at a temperature of 300℃,and show much better kinetic properties in comparison to the pure MgH_2 without any additive.In-situ formed Mg_2 Ni and stable RE hydride(such as CeH_(2.73) and YH_2) might act as effective catalysts to significantly improve the hydrogen storage properties of MgH_2.The present work provides a guideline on improving the kinetic properties of the Mg-based hydrogen storage alloys.     

Corrosion resistance and mechanical properties of (Ho,Nd)FeB magnets

(Ho,Nd)FeB magnets with different Ho contents were prepared by Ho substitution for part of Nd during the casting process. Effects of Ho contents on the corrosion resistance and mechanical properties of (Ho,Nd)FeB magnets were analyzed by a highly accelerated aging tester, an electrochemical workstation, a microhardness tester, a bending tester, a scanning electron microscope and an X-ray diffractometer. Results show that the addition of Ho can change the main phase structure, optimize the distribution of rare-earth rich (RE-rich) phases in grain boundary, and improve the corrosion resistance and mechanical properties of NdFeB magnets. When the content of Ho increases from 0 to 21.0 wt%, the weight loss of magnets decreases from 2.672 to 0.933 mg/cm², and the microhardness and bending strength increase from 528.74 HV and 374.92 MPa to 633.84 HV and 459.80 MPa, respectively.     

First-principles study of structure,mechanical and optical properties of La-and Sc-doped Y_2O_3

The electronic,mechanical and optical properties of La-and Sc-doped Y_2O_3 were investigated using firstprinciples calculations.Two doping sites of Sc and La in Y_2O_3 were modeled.The calculated values of the energy of formation show that the most energetically favorable site for a La atom in Y_2O_3 is a d-site Y atom,while for Sc a b-site Y atom is the more stable position.The calculated band gap shows a slight decrease with increasing La or Sc concentration.The calculated results for the mechanical and optical properties of Y_(2-x)R_xO_3(R = Sc or La,0x ≤ 0.1875)show that La-or Sc-doped Y_2O_3 would have enhanced strength,and thus an ability of resisting external shocks,and increased hardness and mechanical toughness.These improved mechanical properties are achieved without sacrificing the optical properties of the doped compounds.So the doping of La or Sc in Y_2O_3 is permissible in the preparation of Y_2O_3 transparent ceramics,of course,doping of La or Sc will benefit the sintering of transparent ceramics.     

热处理及热挤压对Mg-10Gd-4.8Y-0.6Zr组织及常温力学性能的影响

通过力学和显微硬度测试、能谱和X射线衍射分析以及光学显微镜、扫描电镜和透射电镜观察,对Mg-10Gd-4.8Y-0.6Zr合金经均匀化、挤压变形及时效处理后的显微组织和常温力学性能进行研究。结果表明,铸态合金经520℃/16 h均匀化处理后网状共晶消除,并有黑色方块相生成,强度和塑性显著提高;挤压变形后的合金,抗拉强度σb达304.5 MPa,比挤压前提高25%,屈服强度σ0.2成倍增加,达268.7 MPa;在200℃时效20 h后峰值硬度达到137 HV;再经挤压和峰值时效后最终σb为370 MPa,比挤压态合金试样提高22%,屈服强度σ0.2为295.6 MPa,提高10%,但伸长率δ略有下降;该合金在室温下的断裂方式是脆性和韧性断裂兼有的混合断裂。     

Multiferroic properties of Bi5.75R0.25Fe1.4Ni0.6Ti3O18 (R = Eu,Sm, Nd,Bi and La) ceramics

An improved technique was used to prepare the ceramic samples of Bi_5.75R_0.25Fe_1.4Ni_0.6Ti₃O₁₈(BRFNT,R=Eu,Sm,Nd,Bi,and La).The five-layer Aurivillius phase of the samples was confirmed by X-ray diffraction(XRD)without detectable impurities.BRFNT samples exhibit the pseudo-tetragonal except the orthorhombic BSmFNT samples.The characteristic plate-like morphology was revealed by field emission transmission electron microscopy(FETEM)images.At ambient tempe rature,all the samples present both ferroelectric and magnetic properties and BEuFNT shows the best ferroelectric behavior with its remanent polarization as high as 14.9μC/cm²under 155 kV/cm,which is three times higher than that of Bi_5.75R_0.25Fe_1.4Ni_0.6Ti₃O₁₈.Moreover,the remanent magnetization of BEuFNT is increased up to 1.20 emu/g compared to that of Bi_5.75R_0.25Fe_1.4Ni_0.6Ti₃O₁₈which is only 0.53 emu/g.With increasing radius of the introduced A-site ions,the ferroelectric phase transition temperature(T_CE)is decreased while the magnetic phase transition temperature(T_CM)fluctuates.The decrease in both T_CEand T_CM corresponds to the upward shift of the related Raman modes and vice versa,indicating that the T_CEand the T_CM depend not only on the t factor,but also on the strength of the covalent bonds.     

Phase transition and magnetocaloric effect of Ni55.2Mn18.6Ga26.2-xGdx (x=0, 0.05, 0.15) alloys

Phase transition process and magnetic entropy change -ΔS of Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys were studied.Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys still underwent simultaneous structural and magnetic transitions and transform from ferro-magnetic martensitic phase to paramagnetic austenitic phase during heating. Under a field of 2 T, the maximum magnetic entropy change -ΔSM of Ni55.2Mn18.6Ga26.15Gd0.05 alloy was 7.7 J/kg.K at 317 K during heating and 8.6 J/kg.K at 314 K during cooling while it was 11.8 J/kg.K at 317 K in Ni55.2Mn18.6Ga26.05Gd0.15alloy during heating.     

Effect of wheel speed on phase formation and magnetic properties of (Nd0.4La0.6)-Fe-B melt-spun ribbons

The effect of wheel speed on phase formation and magnetic properties of (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 and (Nd_0.4La_0.6)_13.4Fe_79.9B_6.7 ribbons prepared by melt-spinning method was investigated experimentally. Based on X-ray diffraction results, all melt-spun ribbons consist of the main phase with the tetragonal 2:14:1 type structure and the minor α-Fe phase. Magnetic measurements show the maximum magnetic energy product ((BH)_max) and the remanence (M_r) increases firstly and then decreases with the increase of wheel speed, while the coercivity (H_ci) increases, resulting from the variation of the average volume fraction of the α-Fe phase and the average grain size in the melt-spun ribbons. Using Henkel plots, the interaction between the 2:14:1 phase and the α-Fe phase in the melt-spun ribbons was analyzed and the intergranular exchange coupling is manifested. Optimal magnetic properties of H_ci = 7.27 kOe, M_r = 90.94 emu/g and (BH)_max = 12.10 MGOe are achieved in the (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 ribbon with the wheel speed of 26 m/s. It indicates that magnetic properties of Nd-Fe-B melt-spun ribbons with highly abundant rare earth element La can be improved by optimizing alloy composition and preparation process.     

粉末冶金NiFe_(19)Al_(25)合金的组织与性能研究

用粉末冶金技术制备Ni-Fe-Al合金,将Ni、Fe、Al的元素粉与预合金粉等量混合后在500MPa下压制成形,于1280℃的温度烧结后进行热处理,对合金烧结态和淬火态进行密度、力学性能检测及X射线衍射分析、断口形貌及微观组织观察。结果表明:NiFe19Al25合金烧结态为(β+γ)双相组织,合金的密度达6.54g/cm3(相对密度为94.0%),抗拉强度达到771MPa,形变量为5.3%;合金淬火态处于(β′+γ)双相区,具有马氏体结构的NiFe19Al25合金在应力作用下呈现出线性超弹性,抗拉强度达到761MPa,形变量高达8.1%,最高形变恢复量超过4%。     

Facile synthesis and highly efficient selective adsorption properties of Y2Mo4O15 for methylene blue: Kinetics,thermodynamics and mechanical analyses

Y_2 Mo_4 O_(15) particles were prepared using a simple solution method(SSM) and used as a highly efficient selective adsorbent for methylene blue(MB) in aqueous solutions. The maximum adsorption capacity of the samples was determined based on the adsorption isotherms with different adsorbent doses at 298,318 and 338 K. The fittings of the temperature-dependent isotherms yield ΔrG_m~θ =-34.1 kJ/mol,Δ_rH_m~θ=-36.9 kJ/mol and Δ_rS_m~θ=-9.67 J/mol·K. The as-prepared Y_2 Mo_4 O_(15) has a very large maximum adsorption capacity(i.e., 198 mg/g) for MB at room temperature, and this value is only less than that of amorphous hardwood powder. Notably, 80 mg of adsorbent is able to completely decolorize 250 mL of30 mg/L MB aqueous solution. The kinetic parameters of the adsorption process were obtained from the temperature-dependent adsorption isotherm(i.e., E_1=26.9 kJ/mol and E_1 = 63.8 kJ/mol). The results of adsorption kinetics show that it is a pseudo-second-order reaction. The mechanism of the high selectivity and the large adsorption capacity is discussed based on competitive ion(CI) experiments and coordination theory.     

Synthesis and luminescence properties of CdSe:Eu NPs and their surface polymerization of poly(MMA-co-MQ)

CdSe:Eu nanoparticles(NPs) were synthesized using an oil phase method and the substitution of Cd~(2+)with Eu3+ was confirmed by XRD,TEM,UV-Vis absorption and fluorescence emission analyses.The CdSe:Eu NPs are monodispersed and uniform spherical particles with a diameter of 3.2 nm,bigger than the pure CdSe NPs(2.3 nm),but with a similar cubic structure as CdSe NPs.Compared with those of pure CdSe NPs,both emission spectrum and absorption spectrum of CdSe:Eu NPs are red-shifted.The CdSe:Eu NPs are incorporated into poly(MMA-co-MQ) to afford poly(MMA-co-MQ)-CdSe:Eu NPs with the cubic structure and particle size(～3-4 nm) similar to those of CdSe:Eu NPs.The TEM imaging suggests that the CdSe:Eu NPs are uniformly dispersed in poly(MMA-co-MQ,) without any obvious aggregation.The fluorescent emission peak and absorption peak of poly(MMA-co-MQ)-CdSe:Eu NPs are between those of CdSe:Eu NPs and poly(MMA-co-MQ),possibly due to the energy transfer caused by the interactions of Cd or Eu atoms on the surfaces of CdSe:Eu NPs with the N and O atoms of poly(MMA-co-MQ).These CdSe:Eu and poly(MMA-co-MQ)-CdSe:Eu NPs with tunable photoluminescence properties can be potentially used for the fabrication of optical and optoelectronic devices.     

Interfacial microstructure and mechanical properties of diffusion-bonded joints of titanium TC4 (Ti-6Al-4V) and Kovar (Fe-29Ni-17Co) alloys

Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature.Titanium alloy TC4(Ti-6 Al-4 V)and 4 J29 Kovar alloy(Fe-29 Ni-17 Co)were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min,under a pressure of 34.66 MPa.Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy,scanning electron microscopy,X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS).The elemental diffusion across the interface was revealed by electron probe microanalysis.Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength.Results of EDS and XRD indicated that(Fe,Co,Ni)-Ti,TiNi,Ti_2Ni,TiNi_2,Fe_2 Ti,Ti_(17) Mn_3 and Al_6 Ti_(19) were formed at the interface.When the bonding temperature was raised from 700 to 850°C,the voids of interface were reduced and intermetallic layers were widened.Maximum tensile strength of joints at 53.5 MPa was recorded by the sintering process at 850°C for 120 min.Fracture surface of the joint indicated brittle nature,and failure took place through interface of intermetallic compounds.Based on the mechanical properties and microstructure of the diffusion-bonded joints,diffusion mechanisms between Ti-6 Al-4 Vtitanium and Fe-29 Ni-17 Co Kovar alloys were analyzed in terms of elemental diffusion,nucleation and growth of grains,plastic deformation and formation of intermetallic compounds near the interface.     

Doping effect of rare-earth (lanthanum,neodymium and gadolinium) ions on structural,optical, dielectric and magnetic properties of copper nanoferrites

Copper and rare earth-doped (RE = La, Gd, Nd) CuFe_1.85RE_0.15O₄ nanoferrites were prepared using the sonochemical method. The effective doping of rare-earth (La³⁺, Nd³⁺, Gd³⁺) ions with copper nanoferrites was confirmed by X-ray diffraction. The tetrahedral and octahedral sites of the nanoferrites were identified through the Fourier transform infrared spectra. The doping of rare-earth elements enhances the optical bandgap energy of the nanoferrites that are observed through Ultraviolet–DRS spectra. The oxidation state of the elements Cu 2p, La 3d, Nd 3d, Gd 3d, Fe 2p and O 1s was analyzed. Scanning electron microscopy images indicate a spherical morphology with agglomeration to some elongate. The values of dielectric constant and conductivity decrease considerably due to doping rare-earth ions in copper nanoferrites. Low saturation magnetization and high coercivity values of rare earth-doped copper nanoferrites are observed from the typical hysteresis curves.     

Microstructure and mechanical properties of A356 alloy with yttrium addition processed by hot extrusion

The effects of the rare earth element yttrium(Y) and hot extrusion on the microstructure and mechanical properties of A356 alloy were investigated by mechanical properties testing and microstructure observation. The results indicate that the addition of Y improves the microstructure of the as-cast alloy. The distribution of primary α-Al is uniform and orderly. The long needle-like eutectic Si phases and β-Fe phases turn to strips and short rods. When the content of Y increases to 0.2 wt%, the mean diameter of aAl(40.3 μm) and the aspect ratio of the eutectic Si phase(2.3) reach the minimum values, which are68.9% and 86.1% lower, respectively, than that of the alloy without Y addition. Under extrusion stress, the shape of the eutectic Si phase is changed from long rod-like to near grain-like after solution treatment.The size of the eutectic Si phase is significantly reduced. The needle-like β-Fe phases are squeezed and broken. The mechanical properties of the as-extruded alloy are significantly improved compared to the as-cast alloy. When the rare earth content is 0.2 wt%, the ultimate tensile strength, hardness and elongation of the alloy reach the maximum values, which are 328.2 MPa, 110.4 HV and 21.3%, respectively, and increase by 42.01%, 37.71% and 481.91%, respectively, in comparison to the as-cast alloy without Y addition.