Ti – Cu– Zr–Fe– Nb ultrafine structur e-dendrite composites with good mechanical properties and biocompat ibility

Ti-Cu-Zr-Fe-Nb ultrafine structure-dendrite composites were designed by inducing Nb and more Ti to a Ti-Cu-Zr-Fe glass-forming alloy composition and prepared by copper mold casting.The composite alloys consist of β-Ti dendrites and ultrafine-structured CuTi₂ and CuTi phases as well as a trace amount of glassy phase.The volume fraction of β-Ti dendrites increases with the increase in content of Nb which acted as the β-Ti phase stabilizer in the alloys.The composites exhibit high compressive yield strength exceeding1200 MPa,maximum strength around 1800 MPa and low Young’s modulus around 48 GPa.The plasticity of the alloys is strongly influenced by the volume fraction and morphology of the dendritic β-Ti phase,and the compressive plastic strain was enlarged from 5.9%for the 4 at%Nb alloy to 9.2%for the 8 at%Nb alloy.The preliminary cell culture experiment indicated good biocompatibility of the composite alloys free from highly toxic elements Ni and Be.These Ti-based composite alloys are promising to have potential structural and biomedical applications due to the combination of good mechanical properties and biocompatibility.     

Microstructures and impact toughness behavior of Al 5083 alloy processed by cryorolling and afterwards annealing

The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvements in strength and hardness. The ultimate tensile strength increases up to 340 MPa and 390 MPa for the 30% and 50% cryorolled samples, respectively. The cryorolled samples, with 30% and 50% reduction, were subjected to Charpy impact testing at various temperatures from ?190℃ to 100℃. It is observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility. Annealing of samples after cryorolling shows remarkable increment in impact toughness through recovery and recrystallization. The average grain size of the 50% cryorolled sample (14 μm) after annealing at 350℃ for 1 h is found to be finer than that of the 30% cryorolled sample (25 μm). The scanning electron microscopy (SEM) analysis of fractured surfaces shows a large-size dimpled morphology, resembling the ductile fracture mechanism in the starting material and fibrous structure with very fine dimples in cryorolled samples corresponding to the brittle fracture mechanism.     

Effect of Ca modification on the elemental composition,microstructure and tensile properties of Al-7Si-0.3Mg alloy

The effect of Ca addition on the elemental composition, microstructure, Brinell hardness and tensile properties of Al-7Si-0.3Mg alloy were investigated. The residual content of Ca in the alloy linearly increased with the amount of Ca added to the melt. The optimal microstructure and properties were obtained by adding 0.06wt% Ca to Al-7Si-0.3Mg alloy. The secondary dendrite arm spacing (SDAS) of the primary α phase decreased from 44.41 μm to 19.4 μm, and the eutectic Si changed from coarse plates to fine coral. The length of the Fe-rich phase (β-Al₅FeSi) decreased from 30.2 μm to 3.8 μm, and the Brinell hardness can reach to 66.9. The ultimate tensile strength, yield strength, and elongation of the resulting alloy increased from 159.5 MPa, 79 MPa, and 2.5% to 212 MPa, 86.5 MPa, and 4.5%, respectively. The addition of Ca can effectively refine the primary α phase and modify the eutectic Si phase, likely because Ca enrichment at the front of the solid-liquid interface led to undercooling of the alloy, reduced the growth rate of the primary α phase, and refined the grain size. Also, it could increase the latent heat of crystallization, undercooling, and the nucleation rate of eutectic Si, which was beneficial to the improvement of the morphology of eutectic Si.     

Microstructure,thermal properties,and corrosion behaviors of FeSiBAlNi alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic FeSiBAlNi amorphous high-entropy alloy (HEA) was fabricated by mechanical alloying (MA). A fully amorphous phase was obtained in the FeSiBAlNi HEA after 240 h of MA. The bulk FeSiBAlNi samples were sintered by spark plasma sintering (SPS) at 520 and 1080℃ under a pressure of 80 MPa. The sample sintered at 520℃ exhibited an amorphous composite structure comprising solid-solution phases (body-centered cubic (bcc) and face-centered cubic (fcc) phases). When the as-milled amorphous HEA was consolidated at 1080℃, another fcc phase appeared and the amorphous phase disappeared. The sample sintered by SPS at 1080℃ exhibited a slightly higher melting temperature compared with those of the as-milled alloy and the bulk sample sintered at 520℃. The corrosion behaviors of the as-sintered samples were investigated by potentiodynamic polarization measurements and immersion tests in seawater solution. The results showed that the HEA obtained by SPS at 1080℃ exhibited better corrosion resistance than that obtained by SPS at 520℃.     

热轧和退火温度对SP-700合金组织和力学性能的影响

The effect of rolling temperature on both two- and single-phase regions and annealing in a temperature range of 700–950°C on the microstructure and mechanical properties of Ti?5Al?4V?2Fe?1Mo alloy was investigated. The results indicated that the best balance of strength and ductility is obtained by rolling in the two-phase region due to the globularization of the alpha phase and increase in its volume fraction. After rolling in the two-phase region, the ductility of the specimens annealed at 700 to 800°C increased because of the finer size and globularized alpha phase, while the reduction in strength was attributed to a decrease in the alpha phase volume fraction. However, at 950°C, the strength increased and ductility dropped by the formation of acicular alpha phase due to an increase in the phase boundary area. Annealing and aging after rolling in the beta-phase region increased the strength and decreased the ductility, which is attributed to the formation of a secondary alpha phase. A combination of favorable yield strength (1113 MPa) and elongation (13.3%) was obtained through rolling at 850°C followed by annealing at 750°C and aging at 570°C.     

Microstructure and mechanical properties of spark plasma sintered Ti-Mo alloys for dental applications

Ti-Mo alloys with various Mo contents from 6wt% to 14wt% were processed by spark plasma sintering based on elemental powders. The influence of sintering temperature and Mo content on the microstructure and mechanical properties of the resulting alloys were investigated. For each Mo concentration, the optimum sintering temperature was determined, resulting in a fully dense and uniform microstructure of the alloy. The optimized sintering temperature gradually increases in the range of 1100–1300℃ with the increase in Mo content. The microstructure of the Ti-(6–12)Mo alloy consists of acicular α phase surrounded by equiaxed grains of β phase, while the Ti-14Mo alloy only contains single β phase. A small amount of fine α lath precipitated from β phase contributes to the improvement in strength and hardness of the alloys. Under the sintering condition at 1250℃, the Ti-12Mo alloy is found to possess superior mechanical properties with the Vickers hardness of Hv 472, the compressive yield strength of 2182 MPa, the compression rate of 32.7%, and the elastic modulus of 72.1 GPa. These results demonstrate that Ti-Mo alloys fabricated via spark plasma sintering are indeed a perspective candidate alloy for dental applications.     

Microsegregation and Rayleigh number variation during the solidification of superalloy Inconel 718

The microstructure and composition of the residual liquid at different temperatures were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDX) associated with the Thermo-calc software calculation of the equilibrium phase diagrams of Inconel 718 and segregated liquid. The liquid density difference and Rayleigh number variation during solidification were estimated as well. It is found that the heavy segregation of Nb in liquid prompts the precipitation of δ and Laves phase directly from liquid and the resultant quenched liquid microstructure consists of pro-eutectic γ+eutectic,or complete eutectic according to the content of Nb from low to high. The liquid density increases with decreasing temperature during the solidification of Inconel 718 and the liquid density difference is positive. The largest relative Rayleigh number occurs at 1320℃ when the liquid fraction is about 40vol%.     

Effect of hot rolling and annealing temperatures on the microstructure and mechanical properties of SP-700 alloy

The effect of rolling temperature on both two-and single-phase regions and annealing in a temperature range of 700–950°C on the microstructure and mechanical properties of Ti-5 Al-4 V-2 Fe-1 Mo alloy was investigated. The results indicated that the best balance of strength and ductility is obtained by rolling in the two-phase region due to the globularization of the alpha phase and increase in its volume fraction. After rolling in the two-phase region, the ductility of the specimens annealed at 700 to 800°C increased because of the finer size and globularized alpha phase, while the reduction in strength was attributed to a decrease in the alpha phase volume fraction. However, at 950°C, the strength increased and ductility dropped by the formation of acicular alpha phase due to an increase in the phase boundary area. Annealing and aging after rolling in the beta-phase region increased the strength and decreased the ductility, which is attributed to the formation of a secondary alpha phase. A combination of favorable yield strength(1113 MPa) and elongation(13.3%) was obtained through rolling at 850°C followed by annealing at 750°C and aging at 570°C.     

Effects of P addition on the microstructure and mechanical properties of Mg–5%Sn–1.25%Si alloy

The effects of Al-P addition on the microstructure and mechanical properties of as-cast Mg–5%Sn–1.25%Si magnesium alloy were investigated. The results show that the phases of the as-cast alloy are composed of α-Mg, Mg2 Sn, Mg2 Si, little P, and AlP. The Chinese character shape Mg2 Si phase changes into a granular morphology by P addition because AlP can act as a heterogeneous nucleation core for the Mg2 Si phase. When 0.225wt% of Al–3.5%P alloy is added, the mechanical properties of the Mg–5%Sn–1.25%Si alloy are greatly improved, and the tensile strength increases from 156 to 191 MPa, an increase of 22.4% compared to the alloy without P addition. When the amount of Al–3.5%P reaches 0.300wt%, a segregation phenomenon occurs in the granular Mg2 Si phase, and the tensile strength and hardness decrease though the elongation increases.     

Influence of CeO_2 addition on the preparation of foamed glass-ceramics from high-titanium blast furnace slag

Foamed glass-ceramics doped with cerium oxide(CeO_2)were successfully prepared from high-titanium blast furnace slag by one-step sintering.The influence of CeO_2 addition(1.5wt%–3.5wt%)on the crystalline phases,microstructure,and properties of foamed glass-ceramics was studied.Results show that CeO_2 improves the stability of the glass phase and changes the two-dimensional crystallization mechanism into three-dimensional one.XRD analysis indicates the presence of Ca(Mg,Fe)Si_2O_6 and Ca(Ti,Mg,Al)(Si,Al)_2O_(6 )in all sintered samples.Added with CeO_2,Ti CeO_4 precipitates,and crystallinity increases,leading to increased thickness of pore walls and uniform pores.The comprehensive properties of foamed glass-ceramics are better than that of samples without CeO_2.In particular,the sample added with a suitable amount of CeO_2(2.5wt%)exhibits bulk density that is similar to and compressive strength(14.9 MPa)that is more than twice of foamed glass-ceramics without CeO_2.     

Microstructural evolution and mechanical properties of Nb-Si-Cr ternary alloys with a tri-phase Nb/Nb5Si3/Cr2Nb microstructure fabricated by spark plasma sintering

In this work, pure Nb, Nb₅Si₃ and Laves Cr₂Nb compound powders were used as raw materials to prepare Nb-Si-Cr ternary alloys by spark plasma sintering (SPS). A comprehensive estimation of the microstructure and properties, including room temperature fracture toughness, high temperature strength and oxidation resistance, of the Nb-Si-Cr ternary alloys as a function of the Nb/Nb₅Si₃/Cr₂Nb phase volume fraction combinations was conducted. The results showed that Nb-Si-Cr ternary samples with the relative density larger than 98.42% were obtained by SPS processing, and the samples all consisted of Nb, Nb₅Si₃ and Cr₂Nb phases that were distributed homogeneously. The fracture toughness K_Q of the Nb/Nb₅Si₃/Cr₂Nb microstructure, which was dominated by the Nb phase, naturally increased with the Nb fraction. As expected, the room-temperature Vickers hardness and the high-temperature strength of the bulk alloys increased monotonically with the increasing of the stiffening Nb₅Si₃ fraction. Interestingly, the binary Cr₂Nb phase played a positive role in the high temperature strength and oxidation resistance. Finally, the fracture modes of the typical Nb/Nb₅Si₃/Cr₂Nb microstructures under bending and compression conditions at room and high temperatures as well as the oxidation mechanism are described and discussed.     

Microstructure and growth kinetics of Ce and Y jointly modified silicide coatings for Nb–Ti–Si based ultrahigh temperature alloy

In order to protect Nb-Ti-Si based ultrahigh temperature alloy from oxidation, pack cementation processes were utilized to prepare Ce and Y jointly modified silicide coatings. The Ce and Y jointly modified silicide coating has a double-layer structure: a relatively thick (Nb, X)Si2 (X represents Ti, Cr and Hf elements) outer layer and a thin (Ti, Nb)5Si4 transitional layer. The pack cementation experiments at 1150 ℃ for 8 h proved that the addition of certain amounts of CeO2 and Y2O3 powders in the packs distinctly influenced the coating thickness, the contents of Si, Ce and Y in the (Nb, X)Si2 outer layers, and the density of cavities in the coatings. In order to study the effects of Ce and Y joint modification in the silicide coatings, both only Ce and only Y modified silicide coatings were also prepared for comparison. The mechanisms of the beneficial effects of Ce and Y are discussed. A pack mixture containing 1.5CeO2-0.75Y2O3 (wt%) powders was employed to investigate the growth kinetics of the Ce and Y jointly modified silicide coating at 1050, 1150 and 1250 ℃. It has been found that the growth kinetics obeyed parabolic laws and the parabolic rate constants were 109.20 mm2/h at 1050 ℃, 366.75 mm2/h at 1150 ℃ and 569.78 mm2/h at 1250 ℃, and the activation energy for the growth of the Ce and Y jointly modified silicide coating was 197.53 kJ/mol.     

Effects of alloying and high-temperature heat treatment on the microstructure of Nb–Ti–Si based ultrahigh temperatur e alloys

The phase co mpositions, microstructure and especi ally phase i nterfaces in the as-cast and heat-treated Nb– Ti–Si based ultrahigh temperature alloys have been investigated. It is shown that β(Nb,X)5Si3 and γ(Nb,X)5Si3 are the primary p hase s in the Nb–22Ti–16Si–5Cr–5Al (S1) (at%) and Nb–20Ti–16Si–6C r–4Al–5Hf–2B–0.06Y (S2) (at% ) alloys, respectively. The Nb solid solution (Nbss) is the primary phase in Nb–22Ti–14Si–5Hf–3Al–1. 5B –0.0 6Y (S3) (at%) alloy . An orientation relationship between Nbss and γ(Nb,X)5Si3 was determine d to be (1-10)Nb//(101-0)γ and [111]Nb//[0001]γ in the as-cast S2 and S3 alloys. Some original β(Nb,X)5Si3 transfor med into α(Nb,X)5Si3 because Al and Cr diffused from the β(Nb,X)5Si3 to Nbss during heattreatment at 1500 °C for 50 h in the S1 alloy. Mean while, Ti diffused from Nbss to β(Nb,X)5Si3, which induced a Ti to generate near the interface between Nbss and Ti-rich β(Nb,X)5Si3. The orientation relationship between the newl y-formed a Ti and previous Nbss was (110 )Nb//(1-10-1) αTi and [001]Nb//(12-3-1)αTi. Among the ( Nb,X)5Si3 phases , the contents o f Cr and Al in β(Nb,X)5Si3 are n earl y the same as those in γ(Nb,X)5Si3 but obviously hi gher than those in the α(Nb,X)5Si3, where as the content of Si in α(Nb,X)5Si3 is nearly the same a s that in γ(Nb,X)5Si3 but higher than that in the β(Nb,X)5Si3     

Effect of B2O3 on the aqueous tape casting and microwave properties of Li2O–Nb2O5–TiO2 ceramics

The effect of B2O3 addition on the aqueous tape casting, sintering, microstructure and microwave dielectric properties of Li2O-Nb2O5-TiO2 ceramics has been investigated. The tape casting slurries exhibit a typical shear-thinning behavior without thixotropy, but the addition of B2O3 increases the viscosity of the slurries significantly. It was found that doping of B2O3 can decrease the tensile strength, strain to failure and density of the green tapes. The sintering temperature could be lowed down to 900℃ with the addition of 2 wt% B2O3 due to the liquid phase effect. No secondary phase is observed. The addition of B2O3 does not induce much degradation on the microwave dielectric properties. Optimum microwave dielectric properties of εr 67, Q×f 6560 GHz are obtained for Li2O-Nb2O5-TiO2 ceramics containing 2 wt% B2O3 sintered at 900 1C. It represents that the ceramics could be promising for multilayer low-temperature co-fired ceramics (LTCC) application.     

Joining of Si3N4 ceramic using PdCo(Ni SiB)–V system brazingfi ller alloy and interfacial reactions

The wettability of V-active PdCo-based alloys on Si3N4ceramic was studied with the sessile drop method. And the alloy of Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6(wt%),was developed for Si3N4ceramic joining in the present investigation. The rapidly-solidified brazing foils were fabricated by the alloy Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6. The average room-temperature three-point bend strength of the Si3N4/Si3N4joints brazed at 1453 K for 10 min was 205.6 MPa,and the newly developed braze gives joint strengths of 210.9 MPa,206.6 MPa and 80.2 MPa at high temperatures of 973 K,1073 K and 1173 K respectively. The interfacial reaction products in the Si3N4/Si3N4joint brazed at 1453 K for10 min were identified to be VN and Pd2Si by XRD analysis. Based on the XEDS analysis result,the residual brazing alloy existing at the central part of the joint was verified as Co-rich phases,in which the concentration of element Pd was high up to 18.0–19.1 at%. The mechanism of the interfacial reactions was discussed. Pd should be a good choice as useful alloying element in newer high-temperature braze candidates for the joining of Si-based ceramics.     

Composition design of superhigh strength maraging stainless steels using a cluster model

The composition characteristics of maraging stainless steels were studied in the present work investigation using a cluster-plus-glue-atom model. The least solubility limit of high-temperature austenite to form martensite in basic Fe–Ni–Cr corresponds to the cluster formula [NiFe12]Cr3,where NiFe12is a cuboctahedron centered by Ni and surrounded by 12 Fe atoms in FCC structure and Cr serves as glue atoms. A cluster formula [NiFe12](Cr2Ni) with surplus Ni was then determined to ensure the second phase(Ni3M) precipitation,based on which new multicomponent alloys [(Ni,Cu)16Fe192](Cr32(Ni,Mo,Ti,Nb,Al,V)16) were designed. These alloys were prepared by copper mould suction casting method,then solid-solution treated at 1273 K for 1 h followed by water-quenching,and finally aged at 783 K for 3 h. The experimental results showed that the multi-element alloying results in Ni3M precipitation on the martensite,which enhances the strengths of alloys sharply after ageing treatment. Among them,the aged [(Cu4Ni12)Fe192](Cr32(Ni8.5Mo2Ti2Nb0.5Al1V1)) alloy(Fe74.91Ni8.82Cr11.62Mo1.34Ti0.67Nb0.32Al0.19V0.36Cu1.78wt%) has higher tensile strengths with YS?1456 MPa and UTS?1494 MPa. It also exhibits good corrosion-resistance in 3.5 wt% NaCl solution.     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Effect of CuO addition on the sintering temperature and microwave dielectric properties of CaSiO3– Al2O3 ceramics

CuO-doped CaSiO3–1 wt% Al2O3 ceramics were synthesized via a traditional solid-state reaction method, and their sintering behavior,microstructure and microwave dielectric properties were investigated. The results showed that appropriate CuO addition could accelerate the sintering process and assist the densification of CaSiO3–1 wt% Al2O3 ceramics, which could effectively lower the densification temperature from1250 1C to 1050 1C. However, the addition of CuO undermined the microwave dielectric properties. The optimal amount of CuO addition was found to be 0.8 wt%, and the derived CaSiO3–Al2O3ceramic sintered at 1100 1C presented good microwave dielectric properties of εr?7.27,Q f?16,850 GHz and τf? 39.53 ppm/1C, which is much better than those of pure CaSiO3 ceramic sintered at 1340oC(Q f?13,109 GHz).The chemical compatibility of the above ceramic with 30 Pd/70 Ag during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between palladium–silver alloys and ceramics.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Core loss analysis of Finemet type nanocrystalline alloy ribbon with different thickness

Nanocrystalline soft magnetic materials are widely used in power electronic applications due to their high permeability,magnetization and low core loss.In this paper,Fe_(73.5)Cu_1Nb_3Si_(15.5)B_7(at%)nanocrystalline alloy ribbons,with ultra-thin thickness of 14μm,and also 18 and 22μm,were prepared by a planar flow casting method with a single roller device.Soft magnetic properties of these ribbons were analyzed after nanocrystallization annealing.The experiments were conducted on toroidal samples using IWATSU B-H Analyzer over a frequency range of 10–100 kHz,at induction amplitudes of 100–500 m T,at room temperature.It was found that the excess eddy current loss P_(ex)was the dominant factor in the overall core loss above 10 k Hz.The toroidal samples made of the 14μm thickness ribbon exhibit very low total core loss of 48 W/kg at a frequency of100 kHz and magnetic flux density of 300 mT.The ratio of the P_(ex)was up to 89%at 100 kHz.The ribbon with lower thickness exhibits lower P_(ex)and therefore lower total core loss.The domain structure evidences were found.It indicates that the ribbons with small thickness are preferable for application in high frequency condition.