High-energy XRD study on temperature dependent mechanical stability of retained austenite in TRIP

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Ferroelectric and piezoelectric properties of tungsten substituted SrBi 2Ta 2O 9ferroelectric ceramicsIndrani Coondoo *,S.K.Agarwal a ,A.K.Jha ba Superconductivity and Cryogenics Division,National Physical Laboratory,Dr K.S.Krishnan Road,New Delhi 110012,India bDepartment of Applied Physics,Delhi College of Engineering,Bawana Road,Delhi 110042,India1.IntroductionDefects in crystals signiﬁcantly inﬂuence physical and various other properties of materials [1].For instance,as it is well known,doping by other elements leads to signiﬁcant changes in the electrical properties of silicon.Historically,‘‘defect engineering’’has been developed in the ﬁeld of semiconducting materials such as compound semiconductors as well as in diamond,Si and Ge [2–4].Subsequently,the concept of defect engineering has been applied to other functional materials,and the signiﬁcant improve-ment in material properties have been achieved in high transition-temperature superconductors [5],amorphous SiO 2[6],photonic crystals [7]and also in the ﬁeld of ferroelectrics,such as BaTiO 3,Pb(Ti,Zr)O 3(PZT),etc.[8,9].Various structural and electrical properties of bismuth layer-structured ferroelectrics (BLSF)are also strongly affected on deviation from stoichiometric composi-tions and defects have been recognized as a crucially important factor [10–13].It has been found that in BLSF small changes in chemical composition result in signiﬁcantly altered dielectric and ferroelectric properties including dielectric constant and remanent polarization.In SrBi 2Ta 2O 9(SBT)and SrBi 2Nb 2O 9(SBN),orthor-hombic structural distortions with non-centrosymmetric spacegroup A 21am cause spontaneous ferroelectric polarization (P s )along a axis [14,15].SBT,a member of the BLSF family,has occupied an important position among the Pb-free ferroelectric memory materials [16–18].Tungsten (W 6+)has recently been investigated as a dopant for bismuth titanates and lanthanum doped bismuth titanates,in which the remanent polarization was observed to enhance when a small amount of Ti 4+was substituted by W 6+[19,20].With the objective to improve structural,dielectric and ferroelectric proper-ties,the hexavalent tungsten (W 6+)was chosen as a donor cation for partial replacement of the pentavalent tantalum (Ta 5+)SBT.In this report,the effect of tungsten substitution in SBT (SBTW),on the microstructural,ferroelectric and piezoelectric properties is reported.The results including the improvement in polarization properties have been discussed.2.ExperimentalSamples of compositions SrBi 2(W x Ta 1Àx )2O 9(SBWT),with x =0.0,0.025,0.050,0.075,0.10and 0.20were synthesized by solid-state reaction method taking SrCO 3,Bi 2O 3,Ta 2O 5and WO 3(all from Aldrich)in their stoichiometric proportions.The powder mixtures were thoroughly ground and passed through sieve of appropriate size and then calcined at 9008C in air for 2h.The calcined mixtures were ground and admixed with about 1–1.5wt%polyvinyl alcohol (Aldrich)as a binder and then pressed at $300MPa into disk shaped pellets.The pellets were sintered at 12008C for 2h in air.Materials Research Bulletin 44(2009)1288–1292A R T I C L E I N F O Article history:Received 3October 2008Received in revised form 5December 2008Accepted 6January 2009Available online 15January 2009Keywords:A.CeramicsC.X-ray diffractionD.FerroelectricityA B S T R A C TTungsten substituted samples of compositions SrBi 2(W x Ta 1Àx )2O 9(x =0.0,0.025,0.050,0.075,0.10and 0.20)were synthesized by solid-state reaction method and studied for their microstructural,electrical conductivity,ferroelectric and piezoelectric properties.The X-ray diffractograms conﬁrm the formation of single phase layered perovskite structure in the samples with x up to 0.05.The temperaturedependence of dc conductivity vis-a`-vis tungsten content shows a decrease in conductivity,which is attributed to the suppression of oxygen vacancies.The ferroelectric and piezoelectric studies of the W-substituted SBT ceramics show that the remanent polarization and d 33values increases with increasing concentration of tungsten up to x 0.05.Such compositions with low conductivity and high P r values should be excellent materials for highly stable ferroelectric memory devices.ß2009Elsevier Ltd.All rights reserved.*Corresponding author.Present address:Liquid Crystal Group,National Physical Laboratory,Dr K.S.Krishnan Road,New Delhi 110012,India.Tel.:+919810361727;fax:+911125170387.E-mail address:indrani_coondoo@ (I.Coondoo).Contents lists available at ScienceDirectMaterials Research Bulletinj o ur n a l h o m e p a g e :w w w.e l se v i e r.c om /l oc a t e /m a t r e sb u0025-5408/$–see front matter ß2009Elsevier Ltd.All rights reserved.doi:10.1016/j.materresbull.2009.01.001X-ray diffractograms of the sintered samples were recorded using a Bruker diffractometer in the range 108 2u 708with CuK a radiation.The sintered pellets were polished to a thickness of 1mm and coated with silver paste on both sides for use as electrodes and cured at 5508C for half an hour.Electrical conductivity was performed using Keithley’s 6517A Electrometer.The polarization–electric ﬁeld (P –E )hysteresis measurements were done at room temperature using an automatic P –E loop tracer based on Sawyer–Tower circuit.Piezoelectric charge co-efﬁcient d 33was measured using a Berlincourt d 33meter after poling the samples in silicone–oil bath at 2008C for half an hour under a dc electric ﬁeld of 60–70kV/cm.3.Results and discussion3.1.Structural and micro-structural studiesThe phase formation and crystal structure of the ceramics were examined by X-ray diffraction (XRD),which is shown in Fig.1.The XRD patterns of the samples show the characteristic peaks of SBT.The peaks have been indexed with the help of a computer program–POWDIN [21]and the reﬁned lattice parameters are given in Table 1.It is observed that a single phase layered perovskite structure is maintained in the range 0.0 x 0.05.Owing to the same co-ordination number i.e.6and the smallerionic radius of W (0.60A˚)in comparison to Ta (0.64A ˚),there is a high possibility of tungsten occupying the tantalum site.The observance of unidentiﬁed peak of very low intensity in the compositions with x >0.05indicates the solubility limit of W concentration in SBT.The unidentiﬁed peak is possibly due to tungsten not occupying the Ta sites in the structure as the intensity of this peak is observed to increase with tungsten content.Composition and sintering temperature inﬂuences the micro-structure such as grain growth and densiﬁcation of the specimen,which in turn control other properties of the material [11,13].The effects of W substitution on the microstructure have been examined by SEM and the obtained micrographs are shown in Fig.2.It shows the microstructure of the fractured surface of the studied samples.It is clearly observed that W substitution has pronounced effect on the average grain size and homogeneity of the grains.Randomly oriented and anisotropic plate-like grains are observed in all the samples.It is also observed that the average grain size increases gradually with increasing W content.The average grain size in the sample with x =0.0is $2–3m m while that in the sample with x =0.20the size increases to $5–7m m.3.2.Electrical studiesThe electrical conductivity of ceramic materials encompasses a wide range of values.In insulators,the defects w.r.t.the perfect crystalline structure act as charge carriers and the consideration of charge transport leads necessarily to the consideration of point defects and their migration [22].Many mechanisms were put forward to explain the conductivity mechanism in ceramics.Most of them are approximately divided into three groups:electronic conduction,oxygen vacancies ionic conduction,and ionic and p-type mixed conduction [22].Intrinsic conductivity results from the movement of the component ions,whereas conduction resulting from the impurity ions present in the lattice is known as extrinsic conductivity.At low temperature region (ferroelectric phase),the conduction is dominated by the extrinsic conduction,whereas the conduction at the high-temperature paraelectric phase ($300–7008C)is dominated by the intrinsic ionic conduction [23,25].Fig.3shows the temperature dependence of dc conductivity (s dc )for the undoped and doped SBT samples.The curves show that the conductivity increases with temperature.This is indicative of negative temperature coefﬁcient of resistance (NTCR)behavior,a characteristic of dielectrics [22].It is observed in Fig.3that throughout the temperature range,the dc conductivity of the doped samples are nearly two to three orders lower than that of the undoped sample.Two predominant conduction mechanisms indicated by slope changes in the two different temperature regions are observed in Fig.3.Such changes in the slope in the vicinity of the ferro-paraelectric transition region have been observed in other ferroelectric materials as well [23,24].In addition,it is also observed (Table 2)that the activation energy calculated using the Arrhenius equation [22]in the paraelectric phase increase from $0.80eV for the undoped sample to $2eV for the doped samples.The X-ray photoemission spectroscopic study has conﬁrmed that when Bi 2O 3evaporates during high-temperature processing,vacancy complexes are formed in the (Bi 2O 2)2+layers [26].As a result,defective (Bi 2O 2)2+layers are inherently present in SBT.The undoped SBT shows n-type conductivity,since when oxygen vacancies are created,it leaves behind two trapped electrons [27]:O o !12O 2"þV o þ2e 0(1)where O o is an oxygen ion on an oxygen site,V o is a oxygen vacant site and e 0represents electron.The conductivity in the perovskites can be described as an ordered diffusion of oxygen vacancies [28].Their motion is manifested by enhanced ionic conductivity associated with an activation energy value of $1eV [26].These oxygen vacancies can be suppressed by addition of donors,since the donor oxide contains more oxygen per cation than the host oxide it replaces [29].It has been reported that conductivity in Bi 4Ti 3O 12(BIT)can be signiﬁcantly decreased,up to three orders of magnitude with the addition of donors,such as Nb 5+and Ta 5+at the Ti 4+sites [23,30].A few other studies on layered perovskites have also reported a decrease inconductivityFig.1.XRD patterns of SrBi 2(W x Ta 1Àx )2O 9samples sintered at 12008C.Table 1Lattice parameters of SrBi 2(W x Ta 1Àx )2O 9samples.Concentration of W a (A ˚)b (A ˚)c (A ˚)0.0 5.5212 5.513924.92230.025 5.5214 5.520225.10790.05 5.5217 5.519925.05850.075 5.5191 5.504525.05670.10 5.5142 5.506125.0850.205.51335.493925.0861I.Coondoo et al./Materials Research Bulletin 44(2009)1288–12921289with addition of donors [23,24,31].In the present study,the Ta 5+-site substitution by W 6+in SBT can be formulated using a defect chemistry expression as WO 3þV o!Ta 2O 512W Ta þ3O o (2)It shows that the oxygen vacancies are reduced upon the substitution of donor W 6+ions for Ta 5+ions.Hence,it is reasonable to believe that the conductivity in SBT is suppressed by donor addition.As per the above discussion,the high s dc observed in the undoped SBT (Fig.3)can be attributed to the motion of oxygen vacancies.As already discussed,the doped samples show reduced conductivity because the transport phenomena involving oxygen vacancies are greatly reduced.The high E a value of $1.75–2eVcorresponding to the high-temperature region in the doped ceramics is consistent with the fact that in the donor-doped materials,the ionic conduction reduces [32].The activation energy E a in the low temperature ferroelectric region (Table 2)corre-sponds to extrinsic conduction.At lower temperatures the extrinsic conductivity results from the migration of impurity ions in the lattice.Some of these impurities may also be associated with lattice defects.Pure SBT has large number of Schottky defects (oxygen vacancies)in addition to impurity ions whereas in the doped samples,due to charge neutrality,there is relatively less content of oxygen vacancies.Thus,in the doped samples the conductivity in the low temperature region is largely due to the impurity ions only.This explains the high activation energy in pure SBT in the low temperature region compared to doped samples (Table 2).In the high-temperature region,the value of E a in the doped samples is observed to increase with W concentration up to x =0.05but beyond that,it decreases (Table 2).The decrease in the activation energy for samples with x >0.05suggests an increase in the concentration of mobile charge carriers [33].This observation can be ascribed to the existence of multiple valence states of tungsten.Since tungsten is a transitional metal element,the valence state of W ions in a solid solution most likely varies from W 6+to W 4+depending on the surrounding chemical environment [34].When W 4+are substituted for the Ta 5+sites,oxygen vacancies would be created,i.e.one oxygen vacancy would be created for every two tetravalent W ions entering the crystal structure,whichFig.3.Variation of dc conductivity with temperature in SrBi 2(W x Ta 1Àx )2O 9samples.Fig.2.SEM micrographs of fractured surfaces of SrBi 2(W x Ta 1Àx )2O 9samples with (a)x =0.0,(b)x =0.025,(c)x =0.050,(d)x =0.075,(e)x =0.10and (f)x =0.20Table 2Activation energy (E a )in the high-temperature paraelectric region and low temperature ferroelectric region;Curie temperature (T c )in SrBi 2(W x Ta 1Àx )2O 9samples.Concentration of W E a (high temp.)(eV)E a (low temp.)(eV)T c (8C)0.00.790.893110.025 1.920.593080.05 1.960.543250.075 1.940.543380.10 1.860.573680.201.740.54390I.Coondoo et al./Materials Research Bulletin 44(2009)1288–12921290explains the increase in the concentration of mobile charge carriers which ultimately results in an decrease in the E a beyond x>0.05. Hence it is reasonable to conclude that W ions in the SBWT exists as a varying valency state,i.e.at lower doping concentration they exist in hexavalent state(W6+)and at a higher doping concentra-tion,they tend to exist in lower valency states[8].The P–E loops of SrBi2(Ta1Àx W x)2O9are shown in Fig.4.It is observed that W-doping results in formation of well-deﬁned hysteresis loops.Fig.5shows the compositional dependence of remanent polarization(2P r)and the coerciveﬁeld(2E c)of SrBi2(Ta1Àx W x)2O9samples.Both the parameters depend on W content of the samples.It is observed that2P rﬁrst increases with x and then decreases while2E cﬁrst decreases with x and then increases(Fig.5).The optimum tungsten content for maximum2P r ($25m C/cm2)is observed to be x=0.075.It is known that ferroelectric properties are affected by compositional modiﬁcation,microstructural variation and lattice defects like oxygen vacancies[10,35,36].In hard ferroelectrics, with lower valent substituents,the associated oxide vacancies are likely to assemble in the vicinity of domain walls[37,38].These domains are locked by the defects and their polarization switching is difﬁcult,leading to an increase in E c and decrease in P r[38]. On the other hand,in soft ferroelectrics,with higher valent substituents,the defects are cation vacancies whose generation in the structure generally increases P r.Similar observations have been made in many reports[38–41].Watanabe et al.[42]reported a remarkable improvement in ferroelectric properties in the Bi4Ti3O12ceramic by adding higher valent cation,V5+at the Ti4+ site.It has also been reported that cation vacancies generated by donor doping make domain motion easier and enhance the ferroelectric properties[43].Further,it is known that domain walls are relatively free in large grains and are inhibited in their movement as the grain size decreases[44].In the larger grains, domain motion is easier which results in larger P r.Also for the SBT-based system,it is known that with increase in the grain size the remanent polarization also increases[45,46].Based on the obtained results and above discussion,it can be understood that in the undoped SBT,the oxygen vacancies assemble at sites near domain boundaries leading to a strong domain pinning.Hence,as observed,well-saturated P–E loop for pure SBT is not obtained.But in the doped samples,the suppression of the oxygen vacancies reduces the pinning effect on the domain walls,leading to enhanced remanent polarization and lower coerciveﬁeld.Also,the increase in grain size in tungsten added SBT,as observed in SEM micrographs(Fig.2)contribute to the increase in polarization values.In the present study,the grain size is observed to increase with increasing W concentration.However, the2P r values do not monotonously increase and neither the E c decreases continuously with increasing W concentration(Fig.5). The variation of P r and E c beyond x>0.05,seems possibly affected by the presence of secondary phases(observed in XRD diffracto-grams),which hampers the switching process of polarization [47–50].Also,beyond x>0.05the increase in the number of charge carriers in the form of oxygen vacancies leads to pinning of domain walls and thus a reduction in the values of P r and increase in E c is observed.Fig.6shows the variation of piezoelectric charge coefﬁcient d33 with x in the SrBi2(Ta1Àx W x)2O9.The d33values increases with increase in W content up to x=0.05.A decrease in d33values is observed in the samples with x!0.075.The piezoelectric coefﬁcient,d33,increases from13pC/N in the sample with x=0.0to23pC/N in the sample with x=0.05.It is known that the major drawback of SBT is its relatively higher conductivity,which hinders proper poling[51].High resistivity is therefore important for maintenance of poling efﬁciency at high-temperature[52,53].The W-doped SBT samples show an electrical conductivity value up to three orders of magnitude lower than that of undoped sample(Fig.3).The positional variation of2P r and2E c in SrBi2(W x Ta1Àx)2O9samples.Fig.6.Variation of d33in SrBi2(W x Ta1Àx)2O9samples.Fig. 4.P–E hysteresis loops in SrBi2(W x Ta1Àx)2O9samples recorded at roomtemperature.I.Coondoo et al./Materials Research Bulletin44(2009)1288–12921291decrease in conductivity upon donor doping improve the poling efﬁciency resulting in the observed higher d33values.Moreover, since the grain size increases with W content in SBT,it is reasonable to believe that the increase in grain size will also contribute to the increase in d33values[54].The decrease in the value of d33for samples with x!0.075is possibly due to the presence of secondary phases as observed in diffractograms[1,51,55]and the increase in oxygen vacancies for samples with x>0.05.4.ConclusionsX-ray diffractograms of the samples reveal that the single phase layered perovskite structure is maintained in the samples with tungsten content x0.05.SEM micrographs reveal that the average grain size increases with increase in W concentration. The temperature dependence of the electrical conductivity shows that tungsten doping results in the decrease of conductivity by up to three order of magnitude compared to W free SBT.All the tungsten-doped ceramics have higher2P r than that of the undoped sample.The maximum2P r($25m C/cm2)is obtained in the composition with x=0.075.The reduced conductivity allows high-temperature poling of the doped samples.Such compositions with low loss and high P r values should be excellent materials for highly stable ferroelectric memory devices.The d33value is observed to increase with increasing W content up to x0.05.The value of d33 in the composition with x=0.05is$23pC/N as compared to$13 pC/N in the undoped sample.AcknowledgmentsThe authors sincerely thank Prof.P.B.Sharma,Dean,Delhi College of Engineering,India for his generous support and providing ample research infrastructure to carry out the research work.The authors are thankful to Dr.S.K.Singhal,Scientist, National Physical 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铁的氧化物的热膨胀系数及导热系数

Physical Properties of Iron-Oxide Scales on Si-Containing Steelsat High TemperatureMikako Takeda1,Takashi Onishi1,Shouhei Nakakubo1and Shinji Fujimoto21Materials Research Laboratory,Kobe Steel,Ltd.,Kobe651-2271,Japan2Graduate School of Engineering,Osaka University,Suita565-0871,JapanThe mechanical properties of oxide scales at high-temperature were studied in order to improve the surface quality of commercial Si-containing high strength steels.Speciﬁc oxides of Fe2O3,Fe3O4,FeO and Fe2SiO4were synthesized by powder metallurgy.The Vickers hardness,thermal expansion coeﬃcient and thermal conductivity were measured at high-temperatures.A series of measurements conﬁrmed that the physical properties of the synthesized oxides were diﬀerent each other.From the Vickers hardness measurements,it was veriﬁed that the hardness of each synthesized oxide was identical with the naturally-formed iron oxide,as observed in the cross-section of oxide scales on steels. The inﬂuence of the Fe2SiO4formed on Si-containing steels on the scale adhesion at high temperature and the surface property is discussed on the basis of the physical properties of the oxides.[doi:10.2320/matertrans.M2009097](Received March18,2009;Accepted June4,2009;Published August25,2009)Keywords:high-temperature oxidation,oxide hardness,oxide thermal expansion coeﬃcient,oxide thermal conductivity,silicon-containing steel,FeO,Fe3O4,Fe2O3,Fe2SiO4,adhesion,surface property1.IntroductionThe iron oxide scales that form on billets and slabs of hot-rolled steels are usually detached using a hydraulic descaling process.However,residual primary scales or secondary scales that form after the descaling process remain on the steel surface through subsequent hot-and cold-working,then inﬂuence the surface quality of theﬁnal products by modifying its mechanical properties,such as deformation, fracture and spalling.The residual scales may induce non-uniform surface temperature,which aﬀects theﬁnal scale structure and mechanical properties of the steel.Hence,it is of great importance to examine/understand the physical and mechanical properties of iron oxide scales in order to control their formation and properties,and ultimately to improve the quality of steels.The oxide scales that form on steels include Fe2O3,Fe3O4, FeO,which form in lamellar strata from the substrate towards the outer layer.In the case of Si-containing steels,which are widely used for automobile bodies and frames in the form of high-tensile steel sheets,the inner-most layer,mainly composed of fayalite(Fe2SiO4)and FeO,can form at the interface between scale and steel.1–4)Therefore,the high-temperature physical properties such as hardness,thermal expansion coeﬃcient,thermal conductivity,etc.of each oxide species need to be clariﬁed in order to understand the deformation and fracture behaviour of scale and its inﬂuence on the surface properties after rolling.The high-temperature deformation and fracture behaviour of these oxide species are not yet well summarised in the literature.Amano et al.5)reported the Vickers hardness of Fe2O3,Fe3O4,FeO and Fe2SiO4at RT(room temperature) and at1000 C,as measured by employing micro-indenta-tion.6)In this study,5)Vickers hardnesses were measured for the lamellar constituent oxides in cross-sections of Si-containing steels.In terms of the deformation behaviour of oxides,Hidaka et al.reported on the deformation of Fe2O3, Fe3O4and FeO at600–1250 C by measuring stress-strain curves.7,8)In these studies,tensile-test specimens of pure iron were completely oxidized underﬁxed conditions and tensile tests atﬁxed strain rates were conducted to obtain the deformation and fracture behaviour.Although knowledge of such high-temperature mechanical properties of oxide scales is beneﬁcial,their mechanical properties have been less extensively studied because high-purity specimens of speciﬁc iron oxides are required in order to measure these parameters with suﬃcient accuracy.This paper focuses on the hardness,thermal expansion coeﬃcients and thermal conductivities at high-temperatures of Fe2O3,Fe3O4,FeO and Fe2SiO4which were prepared by powder metallurgy and oxidation under a controlled atmo-sphere.Furthermore,the inﬂuence of the Fe2SiO4formed on the Si-containing steel on the scale adhesion at high-temperature,and surface property were investigated.2.Experimental2.1Preparation of speciﬁc oxide specimensIn this study,pure high-density FeO,Fe3O4,Fe2O3and Fe2SiO4were prepared by powder metallurgy and oxidation under a controlled atmosphere.Sintered compacts of each oxide were used as test specimens to measure the physical properties at high temperature.Each synthesized speciﬁc oxide of iron-oxide was prepared using the following process.FeO forms on Fe under limited oxygen partial pressures, ranging from2:8Â10À13Pa(equilibrium oxygen pressure of Fe2SiO4/FeO at850 C)to2:6Â10À13Pa(equilibrium oxygen pressure of FeO/Fe3O4at850 C).FeO is the stable phase at temperatures of570 C and above,but is not stable below570 C.9)Therefore,FeO may decompose into Fe and Fe3O4at RT.FeO that is formed at high temperature can be ‘frozen-in’by quenching,but this type of material is not suitable for measuring the mechanical properties in the high-temperature phase because numerous pores are present in such FeO specimens.Materials Transactions,Vol.50,No.9(2009)pp.2242to2246 #2009The Japan Institute of MetalsIn order to prepare an FeO specimen,ﬁnely-powdered Fe and Fe3O4were mixed in the ratio8:10by weight,and were then formed into blocks,55mm square by8mm thick.The shaped blocks were compacted by cold isostatic pressing under a constant load of150MPa,and then sintered at 1100 C for3.6ks in an Ar atmosphere.The sintered blocks were pressed in a graphite mould at900 C for3.6ks in vacuum,under a constant load of50MPa.Dense sintered compacts of pure FeO wereﬁnally obtained.On the other hand,Fe3O4forms on Fe over a wide range of oxygen pressures from2:6Â10À13Pa(equilibrium oxy-gen pressure of FeO/Fe3O4at850 C)to4:1Â10À3Pa (equilibrium oxygen pressure of Fe3O4/Fe2O3at850 C). Fe3O4is relatively stable,but can be oxidized to Fe2O3 under high partial pressures of oxygen,and is reduced to FeO under low oxygen partial pressures.In addition,Fe2O3 forms on Fe under limited partial pressures of oxygen above 4:1Â10À3Pa(equilibrium oxygen pressure of Fe3O4/Fe2O3 at850 C).Fe2O3is stable in high partial pressures of oxygen,but is unstable and can be reduced to Fe3O4under low partial pressures of oxygen,e.g.,in an inert atmosphere. The blocks ofﬁnely-powdered Fe3O4and Fe2O3were compacted by cold isostatic pressing under a constant load of300MPa,and then sintered at1100 C for3.6ks.The Fe3O4and Fe2O3were sintered in atmospheres of Ar and air,respectively.Si-containing steels promote the formation of lamellar fayalite:Fe2SiO4forms between the FeO layer and the steel substrate.Fe2SiO4forms in a narrow range of oxygen pressures between2:7Â10À14Pa(equilibrium oxygen pressure for SiO2/Fe2SiO4at850 C)and2:8Â10À13Pa (equilibrium oxygen pressure for Fe2SiO4/FeO at850 C), and therefore it is diﬃcult to obtain pure Fe2SiO4by the oxidation of Si-containing steels.Therefore,Fe2SiO4was prepared by the sintering of fayalite powder.The natural fayalite minerals were powdered and classiﬁed into the appropriateﬁneness(below150mesh),then formed into blocks.The shaped blocks were compacted by cold isostatic pressing under a constant load of150MPa,and were sintered at1130 C for3.6ks in vacuum.2.2Quantitative analysis of purity and sintering densityof synthesized speciﬁc oxide specimensThe synthesized oxide specimens were identiﬁed and were quantitatively analyzed by X-ray diﬀraction.In the quanti-tative analysis of the synthesized oxides,the main peaks of the X-ray diﬀraction spectra wereﬁtted to Gaussian curves, and the intensities of the main peaks were obtained.The relative concentrations of the synthesized speciﬁc oxide were calculated by substitution in the following equation for the peak intensity.C n¼A nÂY nÆðA iÂY iÞð1Þwhere C n is the relative concentration of component n,A n is the relative sensitivity coeﬃcient of component n,and Y n is the peak intensity of component n.The synthesized oxide specimens were machined and their densities were obtained at room temperature by measuring the volume-to-weight ratio.2.3Measurements of physical properties2.3.1HardnessThe synthesized oxides,Fe2O3,Fe3O4,FeO and Fe2SiO4, were machined into work-pieces with dimensions of 10Â20Â3mm3,and then polished with a series of emery papers up to1500grit,buﬀed,ﬁnally degreased in acetone. The hardnesses of the work pieces were measured by a high-temperature micro indenter(Nikon MQ type)at temperatures up to1000 C using square-based diamond and sapphire pyramids.A load of50g was applied for30s,and3 impressions were recorded for each sample.Oxide scales that were formed on iron and steel substrates were also prepared as reference standards,and the hardnesses of these scales were also measured similarly.10mmÂ20mmÂ2mm work-pieces of high-purity Fe(99.99%)and an Fe-3.0mass%-Si alloy were oxidized at1000 C for1.8ks in an O2atmosphere.Oxide scales of about600m m in thickness were formed under the oxidation condition.The hardnesses of oxide scales were measured using the square-based diamond and sapphire pyramids as indenters for the lamellar oxides in a cross section.5)2.3.2Thermal expansion coeﬃcientThe synthesized oxides were formed into3:5mmÂ3:5mmÂ18mm blocks,and were degreased in acetone. The thermal expansion coeﬃcients of the work pieces were measured between room temperature and1000 C using a thermo-mechanical analyzer(Rigaku TMA8140type)at a heating rate of5 C/min.A fused quartz bar was used as a reference in this measurement.The thermal expansion coeﬃcients of the synthesized oxides were measured in the air for Fe2O3,in an Ar atmosphere for Fe3O4and FeO,and in a He atmosphere for Fe2SiO4.2.3.3Thermal conductivityThe synthesized oxides were machined into work pieces with dimensions of 10mmÂ1:5mm,and were degreased in acetone prior to measurements.The thermal conductivities were measured at up to1000 C using a laserﬂash analyzer (ULVAC-RIKO TC-7000type).The speciﬁc heats were measured by diﬀerential scanning calorimetry in an Ar atmosphere.The thermal conductivities of the synthesized oxides were calculated using the thermal diﬀusion coeﬃ-cient,the speciﬁc heat and the sintering density.3.Results and Discussion3.1Purity and sintering density of iron oxide specimens The synthesized oxides were identiﬁed from X-ray diﬀraction spectra.Typical X-ray diﬀraction patterns of the synthesised oxides are shown in Figs.1to4.It was conﬁrmed that the synthesised Fe2O3,Fe3O4and Fe2SiO4were composed of a pure single phase.Although,slight inclusions of residual -Fe and Fe3O4were indicated for the synthesized FeO as shown in Table1,FeO was the predominant compound because the concentration of Fe3O4was below 2.0mass%.From these results,we could assume that the synthesized oxides were essentially composed of single oxide species.The densities of the synthesized oxides of Fe2O3, Fe3O4,FeO and Fe2SiO4were4.69gÁcmÀ3,5.08gÁcmÀ3, 6.27gÁcmÀ3and4.08gÁcmÀ3,respectively.Considering thatPhysical Properties of Iron-Oxide Scales on Si-containing Steels at High Temperature2243the densities of Fe 2O 3,Fe 3O 4,FeO and Fe 2SiO 4noted in the literature are 5.27g Ácm À3,5.18g Ácm À3,5.70g Ácm À3and 4.34g Ácm À3respectively,the sintering density of our synthesized Fe 2O 3was slightly low and that of the synthesized FeO was slightly high compared with the values available in the literature.10)3.2HardnessThe hardnesses of synthesized iron oxides at room-and high-temperatures are shown in Fig.5.The hardnesses of all of the oxides decrease with increasing temperature,with the magnitude of the decrease occurring approximately in the following order:Fe 2SiO 4,Fe 2O 3,Fe 3O 4and FeO.In particular,the hardnesses of Fe 2SiO 4and Fe 2O 3are remarkably high at room temperature,but are equivalent to the other oxides above 400 C.The hardness of FeO is lower than the other oxides in the range between room temperature and 1000 C.The hardness of Fe 2SiO 4can not be exactly measured at 1000 C because the melting point of Fe 2SiO 4is 1170 C and the material begins to soften at 1000 C.In order to conﬁrm the validity of these results,they were compared with the hardnesses of oxide scales formed on steels.The hardnesses of the synthesized iron oxides and of cross-sectional oxide scales on pure Fe and a Fe-3.0mass%Si alloy are listed in Table 2.Variation of hardness of the synthesized oxides is similar to that of scales formed on steels.Furthermore,the order of magnitude of thehardnessFig.1X-ray diﬀraction pattern of Fe 2O 3specimen.Fig.4X-ray diﬀraction pattern of Fe 2SiO 4specimen.Fig.2X-ray diﬀraction pattern of Fe 3O 4specimen.Fig.3X-ray diﬀraction pattern of FeO specimen.Table 1Concentration of oxide phase in FeO specimen (vol%).Fe 2O 3Fe 3O 4FeO -Fe 01.986.811.3Fig.5Hardness of the synthesized iron oxides at high-temperature.Table 2Comparison of Vickers hardness (GPa)of the respective iron oxide scales and the cross-sectional oxide scales on iron.TemperatureSample formSintered specimenScale formed on ironFeO RT 1.67 3.501000C 0.04360.05Fe 3O 4RT 1.64 4.001000 C 0.05050.08Fe 2O 3RT 3.27 6.701000 C 0.07340.53Fe 2SiO 4RT 3.29 5.501000 C—0.632244M.Takeda,T.Onishi,S.Nakakubo and S.Fujimotoof the synthesized oxides is consistent with that formed on the steels.However,the hardness of Fe 2O 3formed on the steel is much larger than synthesized Fe 2O 3at 1000 C.It is considered that the hardness of Fe 2O 3formed on the steel could not be measured precisely because its thickness is a few or several tens of m m .Therefore,it is concluded that the properties of synthesized iron oxides that had been fabricated with high purity and density corresponds to that of oxide scales formed on steels.3.3Thermal expansion coeﬃcientAs shown in Fig.6,the thermal expansion coeﬃcients of all of the synthesised oxides increase with increasing temperature,with magnitudes approximately in the following ascending order:FeO,Fe 3O 4,Fe 2O 3and Fe 2SiO 4.In particular,FeO exhibits the highest thermal expansion coeﬃcient in the temperature range below 400 C.The thermal expansion coeﬃcient of FeO abruptly increases at 600–700 C.This phenomenon may be caused by a stabiliza-tion of FeO,because FeO is becomes stable above 570 C.3.4Thermal conductivityThe temperature dependence of the thermal conductivity of the synthesized iron oxides is shown in Fig.7.The thermal conductivity is reduced approximately in the following ascending order:FeO,Fe 2O 3,Fe 3O 4and Fe 2SiO 4.A prominent feature is that FeO has the highest conductivity and Fe 2SiO 4shows the lowest in the temperature range between room temperature and 1000 C.The following is also noteworthy.The thermal conductivity of Fe 2O 3is the highest at RT,but changes remarkably smaller at high-temperature,while Fe 2SiO 4exhibits extremely reduced thermal conduc-tivity compared with FeO.3.5Inﬂuence of the physical properties of iron-oxide scales at high temperature on the surface properties of the Si-containing steelIt was shown in section 3.1–3.4that the high-temperature physical properties,such as hardness,thermal expansion coeﬃcient,and thermal conductivity,are signiﬁcantly diﬀer-ent for each oxide species.The scale structure and oxidation behaviour on the Si-containing steel have been described in many literatures.1–4)On the Si-containing steel,inner-most layer consisting of FeO–Fe 2SiO 4mixture is formed beneath the outer FeO layer.1–4)However,Fe 2SiO 4in the inner-most layer,the amount of which increases as the Si content increases,suppresses the outward diﬀusion of Fe ions from steels and hence the inner diﬀusion of oxygen ions predominates in the oxide growth.11)Therefore,as the Si content increase,the composition of outer scale layer changes from FeO to Fe 3O 4and Fe 2O 3.11)These results show that the fayalite (Fe 2SiO 4)aﬀects the structure of the outer and inner scale layers on Si-containing steel.In the following section,the inﬂuence of the fayalite (Fe 2SiO 4)formed on the high-Si steel on the scale adhesion at high temperature and surface properties are discussed on the basis of physical properties of iron-oxide scale.3.5.1The scale adhesion at high temperature of theSi-containing steelThe thermal stress generated by the diﬀerence in the thermal expansion coeﬃcient between inner-most layer and steel causes a spalling and cracking of the scale during the hot-rolling process.As described above,the inner-most layer on the high-Si steel is mainly composed of Fe 2SiO 4.Therefore,the scale adhesion of high-Si steel is inﬂuenced by the diﬀerence in the thermal expansion coeﬃcient between the Fe 2SiO 4and steel.As shown in Fig.6,the thermal expansion coeﬃcient of Fe 2SiO 4increases as the temperature increases.The thermal expansion coeﬃcient of Fe 2SiO 4at 1000 C is nearly equal to that of Fe(14:6Â10À6/ C at 800 C).12)By contrast,the diﬀerence in the thermal expansion coeﬃcient of FeO and Fe is large at 1000 C.It is also reported that the scale adhesion of Fe 2SiO 4on steel at high temperature is greater than that of FeO.11)Therefore,the Fe 2SiO 4might strongly adhere to the substrate steel and is not detached by the descalingprocess.Fig.6Thermal expansion coeﬃcients of the synthesized iron oxides athigh-temperature.Fig.7Thermal conductivities of the synthesized iron oxides at high-temperature.Physical Properties of Iron-Oxide Scales on Si-containing Steels at High Temperature 22453.5.2Surface property of the Si-containing steel afterrollingAs described above,the Fe2SiO4strongly adheres to the substrate steel,resulting in the deterioration of the descal-ability.The remaining Fe2SiO4suppresses the outward diﬀusion of Fe ions from the steel and hence the inner diﬀusion of oxygen ions predominates in the oxide growth.11) It is also shown in Fig.7that the thermal conductivity of Fe2SiO4is lower than that of other oxides.This result suggests that the remaining Fe2SiO4on the substrate steel brings about a reduction in the cooling rate and a rising of the surface temperature.As a result,the thick Fe2O3,which is a higher order oxide,is formed as the outer-most scale layer on the Fe2SiO4-coated substrate steel.Therefore,the fracture and deformation behaviour of Fe2O3may directly aﬀect the surface properties of high-Si steel.It is shown in Fig.5that the hardness of Fe2O3is greater than that of the other oxides at800 C.It is also reported that the ability to deform Fe2O3is lower than that of FeO.7,8)As a result,the outer-most scale surface,mainly composed of Fe2O3,is crushed because of its hardness and stiﬀness at 800 C,corresponding to the hot-rolling temperature.Finely-ground Fe2O3is often observed on high-Si steels,which frequently form red scales on their surfaces and degrade the surface property of the high-Si steel.4.ConclusionIn the present study,we measured the high temperature physical properties of various iron oxides,constituents of oxide scales on steels,in order to clarify the dynamic behavior of the oxide scales that occur on practical steels. We selected FeO,Fe3O4,Fe2O3and Fe2SiO4as typical oxide species that formed on Si-containing steels,and synthesized artiﬁcial specimens of each type of oxide.The specimens were composed of a single oxide species,and were used to measure the hardness,the thermal expansion coeﬃcient and the thermal conductivity over the temperature range between RT and1000 C.As a result,it was found that the physical properties of the synthesized iron oxides diﬀered signiﬁcantly from each other.The hardness of the synthe-sized iron oxides was identical with the naturally-formed corresponding iron oxide observed in cross-sectional oxide scales on practical steels.The experimental results from this study are conﬁrmed as reﬂecting the physical properties of the oxide scales that form on practical steels. Moreover,we discussed the relationship between the physical properties of oxides at high temperature and surface property after rolling the Si-containing steel.It is possible that Fe2SiO4aﬀects the high-temperature adhesion,surface temperature,and surface property of the Si-containing steel after rolling.REFERENCES1) C.W.Tuck:Corros.Sci.5(1965)631–643.2)W.W.Smeltzer,L.A.Morris and R.C.Logani:Can.Metall.Quart.9(1970)513–519.3)R.C.Logani and W.W.Smeltzer:Oxid.Met.3(1971)15–32.4)K.Yanagihara,S.Suzuki and S.Yamazaki:Oxid.Met.57(2002)281–296.5)T.Amano,M.Okazaki,Y.Takezawa,A.Shino,M.Takeda,T.Onishi,K.Seto,A.Ohkubo and T.Shishido:Mater.Sci.Forum522–523 (2006)469–476.6)G.R.Anstis,P.Chantikul,wn and D.B.Marshall:J.Am.Ceram.Soc.64(1981)533–538.7)Y.Hidaka,T.Anraku and N.Otsuka:Mater.Sci.Forum369–372(2001)555–562.8)Y.Hidaka,T.Anraku and N.Otsuka:Oxid.Met.59(2003)97–113.9)L.S.Darken and W.R.Gurry:Physical Chemistry of Metals,(McGrow-Hill Book Company,New York,1953)p.351.10)K.H.Hellwege ed.:Landolt Borstein numerical data tables,Group3,12,(Springer-Verlag,Berlin,1980)p.8.11)M.Takeda and T.Onishi:Mater.Sci.Forum522–523(2006)477–488.12)Metals Data Book,4th Edition,(Maruzen)p.14.2246M.Takeda,T.Onishi,S.Nakakubo and S.Fujimoto。

《热机械处理Al_xCoCrFeNi(x=0.1～0.8)高熵合金的显微组织及力学性能》范文

《热机械处理Al_xCoCrFeNi（x=0.1～0.8）高熵合金的显微组织及力学性能》篇一一、引言高熵合金作为一种新型的合金设计理念，其独特的物理和化学性质使其在众多领域中得到了广泛的应用。

Al_xCoCrFeNi高熵合金系列，通过调整Al元素的含量（x=0.1～0.8），可以获得不同的显微组织和力学性能。

本文旨在研究热机械处理对Al_xCoCrFeNi高熵合金显微组织和力学性能的影响。

二、材料与方法1. 材料准备实验所用的Al_xCoCrFeNi高熵合金由高质量的元素粉末通过高能球磨法混合均匀后，通过真空电弧熔炼制备而成。

合金中Al元素的含量通过调整原料配比进行控制，范围为x=0.1～0.8。

2. 热机械处理热机械处理包括固溶处理和形变热处理两个阶段。

首先，将合金在高温下进行固溶处理，使合金元素充分溶解；然后进行形变热处理，通过轧制、拉伸等工艺使合金发生形变。

3. 显微组织观察利用金相显微镜、扫描电子显微镜和透射电子显微镜对合金的显微组织进行观察，分析其相结构、晶粒大小和分布等。

4. 力学性能测试通过硬度测试、拉伸试验和冲击试验等方法，对合金的力学性能进行测试和分析。

三、结果与讨论1. 显微组织分析（1）相结构：随着Al含量的增加，Al_xCoCrFeNi高熵合金的相结构发生变化。

当x≤0.5时，合金主要由体心立方（BCC）相组成；当x≥0.6时，面心立方（FCC）相逐渐增多。

（2）晶粒大小与分布：热机械处理后，合金的晶粒大小得到细化，分布更加均匀。

随着Al含量的增加，晶粒细化效果更加明显。

2. 力学性能分析（1）硬度：随着Al含量的增加，合金的硬度先增加后降低。

在适当的Al含量下（如x=0.5），合金的硬度达到最大值。

这主要归因于合金相结构和晶粒大小的综合影响。

（2）拉伸性能：热机械处理后，合金的抗拉强度和延伸率均得到提高。

随着Al含量的增加，抗拉强度和延伸率呈现先增加后降低的趋势。

在适当的Al含量下，合金的拉伸性能达到最佳。

二硼化钛陶瓷在不同温度下的氧化行为_英文_

二硼化钛陶瓷在不同温度下的氧化行为黄飞，傅正义，王为民，王皓，王玉成，张金咏，张清杰(武汉理工大学，复合材料新技术国家重点实验室，武汉 430070)摘要：采用静态氧化法对不同温度下TiB2陶瓷的氧化行为进行研究，利用X射线衍射仪、扫描电镜、X射线光电子能谱仪对氧化前后的样品进行表征。

结果表明：低温下TiB2陶瓷氧化动力学满足抛物线规律，并在表面形成液相B2O3，阻止氧化反应的进一步进行，冷却后B2O3以玻璃态覆盖在表面。

高温下TiB2氧化反应在4h前满足抛物线规律，表面形成一层TiO2多孔结构；氧化4h后，随着氧扩散距离的延长，扩散阻力加大，从而使氧化速率降低，氧化反应不再满足抛物线规律。

关键词：二硼化钛；氧化动力学；微观结构中图分类号：TF123；TB332 文献标识码：A 文章编号：0454–5648(2008)05–0584–04OXIDATION BEHA VIOR OF TITANIUM DIBORIDE CERAMIC AT DIFFERENT TEMPERATURES HUANG Fei，FU Zhengyi，W ANG W eimin，W ANG Hao，W ANG Yucheng，ZHANG Jinyong，ZHANG Qinjie(State key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University ofTechnology, Wuhan 430070, China)Abstract: The oxidation behavior of TiB2 ceramics at different temperatures was investigated using the static oxidation kinetic method. The samples before and after oxidation have been characterized by X-ray diffractometer, scanning electron microscope and X-ray photoelectron spectrometer. The results show that the oxidation kinetics appear the parabolic law at low temperature. A liquid B2O3 coating on the surface of TiB2 ceramic could prevent from further oxidation. After the ceramic samples were cooled, their sur-faces were covered with glassy B2O3. At high temperature, the oxidation reaction of TiB2 ceramics showed the parabolic law only before 4h. Porous rutile TiO2 formed on the surface. But the oxidation behavior with the parabolic law for the TiB2 ceramics was not observed after oxidation for 4h because of the long path of diffusion, strong diffusion resistance and low reaction rate.Key words: titanium diboride; oxidation kinetics; microstructureTitanium diboride with P6/mmm structure is a uniquely stable compound of the boron element and tita-nium element.[1] TiB2 based materials have received wide attention because of their high hardness and elastic modulus, good abrasion resistance and superior thermal and electrical conductivity.[2–3] Potential applications in-clude high temperature structural materials, cutting tools, armor, electrodes in metal smelting and wear parts. De-spite its useful properties, the application of monolithic TiB2 is limited by poor sinterability, exaggerated grain growth at high temperature and poor oxidation resistance above 800.℃[4–5]The starting temperature to oxidize TiB2 ceramics is about 400℃ and oxidation kinetics is controlled by outward diffusion of interstitial titanium ions and inner diffusion of oxygen ions.[5–6] But there are conflicting viewpoints about the detailed oxidation process, for ex-ample, about the oxidation products and oxidation mechanism. Koh et al.[7] investigated the oxidation be-havior of dense TiB2 specimens with 2.5% in mass (the same below) Si3N4 and found that TiB2 exhibited two distinct oxidation behaviors depending on the tempera-ture. At temperatures below 1000℃, the oxidation layer comprised two layers: an inner layer of crystalline TiO2 and an outer layer mainly composed of B2O3. When the oxidation temperatures were higher than 1000℃, the收稿日期：2007–09–23。

钛合金tc11动态拉伸力学行为的实验研究

钛合金TC11动态拉伸力学行为的实验研究张军, 汪洋（中国科学技术大学近代力学系中科院材料力学行为和设计重点实验室安徽合肥 230027）摘要：利用MTS809材料试验机和旋转盘式间接杆杆型冲击拉伸实验装置，对双态组织两相钛合金TC11进行了应变率为0.001 s-1的准静态和190s-1的动态单向拉伸实验，获得了TC11等温和绝热拉伸应力-应变曲线；实施了应变率为190s-1的冲击拉伸复元实验，获得了TC11在高应变率下的等温应力-应变曲线。

试验结果表明，TC11的拉伸力学行为具有明显的应变硬化效应、应变率强化效应和绝热温升软化效应。

采用修正的Johnson-Cook模型较好地表征了TC11在试验应变率范围内的拉伸力学行为。

关键词：两相钛合金；动态拉伸；绝热温升软化；复元试验EXPERIMENTAL INVESTIGATION ON THE DYNAMIC TENSION BEHA VIOR OFTITANIUM ALLOY TC11Jun Zhang, Yang Wang(Department of Modern Mechanics, CAS Key Laboratory of Mechanical Behavior and Design of Materials, University of Science and Technology of China, Hefei, Anhui 230027, PR China)Abstract:Quasi-static and dynamic uniaxial tension tests for a titanium alloy TC11 with a duplex microstructure were performed using MTS809 testing system and rotating disk bar-bar tensile impact apparatus, respectively. The isothermal stress-strain curve at 0.001s-1 and the adiabatic stress-strain curve at 190s-1 were obtained. The dynamic tensile recovery test was carried out at the rate of 190s-1 and the isothermal stress-strain curve at the high strain rate was obtained. The experimental results indicate that there exists the strain hardening, strain-rate strengthening and adiabatic temperature-rise softening phenomenon in the tension behavior of TC11. A modified Johnson-Cook model was chosen to describe the tensile behavior of TC11 at different strain rates. The model results agree well with the experimental data.Keywords: Two phase titanium; Dynamic tension; Thermal softening; Recovery test0. 引言两相钛合金具有比强度高、高低温性能优异、耐腐蚀等优点，是航空、航天工程中广泛使用的结构材料。

钙钛矿型复合氧化物LaCrO3-δ的结构稳定性

第33卷第2期化学反应工程与工艺V ol 33, No 2 2017年4月 Chemical Reaction Engineering and Technology Apr. 2017文章编号：1001—7631 ( 2017 ) 02—0123—06 DOI: 10.11730/j.issn.1001-7631.2017.02.0123.06 钙钛矿型复合氧化物LaCrO3-δ的结构稳定性邓云香1,2，李扬1,2，朱贻安1,2，张敏1,2，周兴贵11.华东理工大学化学工程联合国家重点实验室，上海 2002372.上海市多相结构材料化学工程重点实验室，上海 200237摘要：为了研究氧空穴对LaCrO3-δ结构稳定性的影响，首先对LaCrO3结构中氧空穴的形成过程进行了分析，然后建立了不同氧空穴浓度下的LaCrO3-δ（δ为0.125～0.875）结构，并采用基于密度泛函理论的第一性原理对氧空穴形成能和LaCrO3-δ结构稳定性进行了研究。

结果表明，LaCrO3-δ的氧空穴形成能随着δ的升高不断增大，而结构稳定性也随之不断降低。

此外，根据氧空穴形成能的相对大小，发现在最稳定的LaCrO3-δ（δ为0.125～0.500）结构中，氧空穴都排布在CrO2层。

因此，LaCrO3-δ结构的稳定性不仅与氧空穴浓度有关，而且与氧空穴的排布方式有关。

关键词：钙钛矿密度泛函理论氧空穴结构稳定性中图分类号：TQ133.3；TQ136.1 文献标识码：A钙钛矿型复合氧化物具有成本低、催化活性和化学稳定性高等优点，是一种优良的氧化催化剂，可替代贵金属催化剂应用于化学反应过程中。

钙钛矿型复合氧化物作为氧载体可用于甲烷部分氧化反应，获得较高的甲烷转化率和一氧化碳选择性[1]。

钙钛矿型复合氧化物具有与钙钛矿（CaTiO3）相同的立方体或八面体结构，其通式为ABO3，其中A位的元素一般为稀土或碱土金属离子，B位的元素为过渡金属离子。

S32001双相型不锈钢高温力学性能试验

第50卷第6期2022年6月同济大学学报（自然科学版）

JOURNALOFTONGJIUNIVERSITY（NATURALSCIENCE）

Vol.50No.6

Jun.2022

论文拓展介绍

S32001双相型不锈钢高温力学性能试验楼国彪1，2，杨未1，陈武龙1，陶宇超1，王美南3（1.同济大学土木工程学院，上海200092；2.同济大学土木工程防灾国家实验室，上海200092；3.远大可建科技有限公司，湖南长沙430121）

摘要：对S32001双相型不锈钢进行了高温稳态拉伸试验研究，得到了高温下初始弹性模量、名义屈服强度、抗拉强度、断后伸长率等主要力学性能指标及其变化规律；利用试验数据研究了Rasmussen模型和Gardner模型的适用性，并基于Rasmussen模型提出了S32001不锈钢硬化指数的计算公式，

建立了高温下不锈钢材料本构关系表达式；对比分析了S32001不锈钢与其他种类不锈钢及Q235B结构钢的高温力

学性能。研究表明，S32001不锈钢的屈服强度和极限强度随温度升高下降，600℃时低于常温时的50%，但高温下材料强度明显高于S30408不锈钢，具有更加优越的抗火性能。该研究结果可用于结构受火性能研究和抗火设计。

关键词：双相型不锈钢；力学性能；本构关系；高温中图分类号：TU511.3文献标志码：A

ExperimentalInvestigationonMechanicalPropertiesofS32001DuplexStainlessSteelatElevatedTemperatures

LOUGuobiao1，2，YANGWei1，CHENWulong1，TAO

Yuchao1，WANGMeinan3

（1.CollegeofCivilEngineering，TongjiUniversity，Shanghai200092，China；2.StateKeyLaboratoryforDisasterReductioninCivilEngineering，TongjiUniversity，Shanghai200092，China；3.BroadSustainableBuilding，Changsha430121，Hunan，China）

Gd3+掺杂调控BiFeO3-BaTiO3高温无铅压电陶瓷的结构与性能

第 4 期第 43-53 页材料工程Vol.52Apr. 2024Journal of Materials EngineeringNo.4pp.43-53第 52 卷2024 年 4 月Gd 3+掺杂调控BiFeO 3-BaTiO 3高温无铅压电陶瓷的结构与性能Structures and properties of Gd 3+ doped modified BiFeO 3-BaTiO 3 high -temperature lead -free piezoelectric ceramics唐蓝馨1，王芳1，周治1，李双池1，左鑫1，李凌峰1，杨柳1，谭启2，陈渝1*（1 成都大学机械工程学院，成都 610106；2 广东以色列理工学院材料科学与工程系，广东汕头 515063）TANG Lanxin 1，WANG Fang 1，ZHOU Zhi 1，LI Shuangchi 1，ZUO Xin 1，LI Lingfeng 1，YANG Liu 1，TAN Daniel Q 2，CHEN Yu 1*（1 School of Mechanical Engineering ，Chengdu University ，Chengdu 610106，China ；2 Department of Materials Science and Engineering ，Guangdong Technion -Israel Institute of Technology ，Shantou 515063，Guangdong ，China ）摘要：用于监测航空发动机、重型燃气轮机等重大技术装备高温部件振动状态的压电加速度传感器，需要一种高居里温度压电陶瓷作为敏感元件，而电子元器件的无铅化是环境保护的迫切要求。

采用传统的固相反应法制备一种Gd/Mn 共掺杂的BF -BT （（0.67BiFeO 3-0.33Ba 1-x Gd x TiO 3）+0.5%（质量分数）MnO 2，x =0~0.02）高温无铅压电陶瓷，并研究Gd 3+掺杂浓度（x ）对BF -BT 陶瓷的相组成、微观结构、压电性能、介电弛豫行为及交流阻抗特征的影响。

高熵合金性能的研究现状

Metallurgical Engineering 冶金工程, 2018, 5(1), 17-24Published Online March 2018 in Hans. /journal/menghttps:///10.12677/meng.2018.51003Research Status of High EntropyAlloy PerformanceLijuan Lan, Yingying Gu, Tianjiao Pu, Heguo Zhu*School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing JiangsuReceived: Feb. 22nd, 2018; accepted: Mar. 8th, 2018; published: Mar. 19th, 2018AbstractDue to its high strength, high hardness, excellent wear and corrosion resistance, good thermal stability at high temperatures and high oxidation resistance properties, high-entropy alloy is a new alloy with great development potential in areas such as aerospace and electronic communi-cation. Research status on the properties of high-entropy alloys is reviewed, including mechanical properties, corrosion resistance and high temperature oxidation resistance. Main effective factors on properties are separately discussed, with alloy elements, preparation process, plastic deforma-tion and alloy ratio included. The deficiencies existed in high-entropy alloys’ researches are sum-marized. The prospects of the properties of high-entropy alloys are also proposed.KeywordsHigh Entropy Alloy, Mechanical Properties, Corrosion Resistance, Oxidation Resistance高熵合金性能的研究现状兰利娟，顾莹莹，濮天姣，朱和国*南京理工大学材料科学与工程学院，江苏南京收稿日期：2018年2月22日；录用日期：2018年3月8日；发布日期：2018年3月19日摘要高熵合金是一种新型合金，具有高的强度与硬度、优异的耐磨性与耐腐蚀性及强的热稳定性和抗氧化性*通讯作者。

《热机械处理Al_xCoCrFeNi(x=0.1～0.8)高熵合金的显微组织及力学性能》范文

《热机械处理Al_xCoCrFeNi（x=0.1～0.8）高熵合金的显微组织及力学性能》篇一一、引言高熵合金以其独特的多元合金化设计，成为近年来材料科学研究的热点。

Al_xCoCrFeNi系列高熵合金，由于铝元素的添加，具有优异的力学性能和广泛的潜在应用。

本文将重点探讨热机械处理对Al_xCoCrFeNi（x=0.1～0.8）高熵合金显微组织和力学性能的影响。

二、材料与方法1. 材料制备本研究所用材料为Al_xCoCrFeNi（x=0.1～0.8）高熵合金，通过真空电弧熔炼法制备。

2. 热机械处理对制备的高熵合金进行热机械处理，包括固溶处理、淬火和回火等工艺。

3. 显微组织观察利用光学显微镜、扫描电子显微镜和透射电子显微镜等手段，观察合金的显微组织。

4. 力学性能测试对合金进行硬度、拉伸、冲击等力学性能测试。

三、结果与讨论1. 显微组织观察（1）固溶处理后的显微组织经过固溶处理后，Al_xCoCrFeNi高熵合金的显微组织变得更加均匀，枝晶结构消失，合金元素充分固溶。

随着铝含量的增加，固溶体中的析出相也逐渐增多。

（2）淬火后的显微组织淬火处理后，合金中形成了大量的亚稳态结构，如马氏体等。

这些亚稳态结构的形成对合金的力学性能有重要影响。

（3）回火后的显微组织回火处理后，亚稳态结构逐渐转变为稳定的结构，如回火马氏体等。

同时，回火过程中还会发生析出相的析出和长大，对合金的力学性能产生影响。

2. 力学性能分析（1）硬度测试结果随着铝含量的增加，Al_xCoCrFeNi高熵合金的硬度先增加后减小。

这主要是由于铝元素的添加增加了合金的固溶强化作用，但过高的铝含量会导致析出相的增多，反而降低硬度。

经过热机械处理后，合金的硬度均有明显提高。

（2）拉伸性能测试结果热机械处理后，Al_xCoCrFeNi高熵合金的抗拉强度和延伸率均有所提高。

其中，适当的铝含量（x=0.3～0.5）有助于提高合金的拉伸性能。

随着铝含量的进一步增加，合金的拉伸性能反而降低。

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High-energyX-raydiﬀractionstudyonthetemperature-dependentmechanicalstabilityofretainedausteniteinlow-alloyedTRIPsteels

R.Blonde´a,b,⇑,E.Jimenez-Meleroa,L.Zhaob,c,J.P.Wrightd,E.Bru¨cka,S.vanderZwaage,N.H.vanDijka

aFundamentalAspectsofMaterialsandEnergy,FacultyofAppliedSciences,DelftUniversityofTechnology,Mekelweg15,2629JBDelft,TheNetherlands

bMaterialsInnovationInstitute,Mekelweg2,2628CDDelft,TheNetherlands

cDepartmentofMaterialsScienceandEngineering,DelftUniversityofTechnology,Mekelweg2,2628CDDelft,TheNetherlands

dEuropeanSynchrotronRadiationFacility,6RueJulesHorowitz,BP220,38043GrenobleCedex,France

eNovelAerospaceMaterialsGroup,FacultyofAerospaceEngineering,DelftUniversityofTechnology,Kluyverweg1,2629HSDelft,TheNetherlands

Received26September2011;accepted11October2011Availableonline22November2011

AbstractThestabilityoftheretainedaustenitehasbeenstudiedinsituinlow-alloyedtransformation-induced-plasticity(TRIP)steelsusinghigh-energyX-raydiﬀractionduringtensiletestsatvariabletemperaturesdownto153K.Adetailedpowderdiﬀractionanalysishasbeenperformedtoprobetheaustenite-to-martensitetransformationbycharacterizingtheevolutionofthephasefraction,loadpartitioningandtextureoftheconstituentphasessimultaneously.Ourresultsshowthatatlowertemperaturesthemechanicallyinducedaustenitetransformationissigniﬁcantlyenhancedandextendsoverawiderdeformationrange,resultinginahigherelongationatfracture.Lowcarboncontentgrainstransformﬁrst,leadingtoaninitialincreaseinaveragecarbonconcentrationoftheremainingaustenite.Laterthecarboncontentsaturateswhiletheaustenitestillcontinuestotransform.Intheelasticregimetheprobed{hkl}planesdevelopdiﬀerentstrainsreﬂectingtheelasticanisotropyoftheconstituentphases.Theobservedtextureevolutionindicatesthattheaustenitegrainsorientedwiththe{200}planealongtheloadingdirectionaretransformedpreferentiallyastheyshowthehighestresolvedshearstress.Forincreasingdegreesofplasticdeformationthecombinedpreferentialtransformationandgrainrotationresultsinthestandarddeformationtextureforaustenitewiththe{111}componentalongtheloadingdirection.ThemechanicalstabilityofretainedausteniteinTRIPsteelisfoundtobeacomplexinterplaybetweencarbonconcentrationintheaustenite,grainorientation,loadpartitioningandtemperature.Ó2011ActaMaterialiaInc.PublishedbyElsevierLtd.Allrightsreserved.

Keywords:TRIP-assistedsteel;Metastablephases;Martensitictransformation;Synchrotronradiation;Crystalorientation

1.IntroductionLow-alloyedtransformation-induced-plasticity(TRIP)steelsweredevelopedinthelate1980s[1–4]andhaveattractedsigniﬁcantinterestforautomotiveapplicationsduetotheiroutstandingcombinationofhighstrengthandformability[5–7].AtypicalTRIPsteelmicrostructurecontainsthreephasesatroomtemperature:ferrite,bainiteandmetastableaustenite[8,9].Theremarkablemechanicalpropertiesofthismaterialareattributedtothemultiphasemicrostructureaswellastothetransformationofthesoftmetastableaustenitephaseintothehardmartensitephaseuponactivationbymechanicaland/orthermalstimuli.Thisphenomenon,calledtheTRIPeﬀect,increasesthe

1359-6454/$36.00Ó2011ActaMaterialiaInc.PublishedbyElsevierLtd.Allrightsreserved.doi:10.1016/j.actamat.2011.10.019

⇑Correspondingauthorat:FundamentalAspectsofMaterialsand

Energy,FacultyofAppliedSciences,DelftUniversityofTechnology,Mekelweg15,2629JBDelft,TheNetherlands.Tel.:+31(0)152783793;fax:+31(0)152788303.E-mailaddress:R.J.P.Blonde@tudelft.nl(R.Blonde´).

www.elsevier.com/locate/actamatAvailableonlineatwww.sciencedirect.comActaMaterialia60(2012)565–577work-hardeningrateduringplasticdeformationanddelaysnecking[10,11].Alotofeﬀorthasbeendevotedinrecentyearstomax-imizeandtunetheretentionofausteniteatroomtempera-tureinordertoenhancetheTRIPeﬀect[12–15].InordertocreateasuﬃcientamountofretainedausteniteintheTRIPmicrostructure,athree-stepheattreatment(intercrit-icalannealing,bainiticholdingandﬁnallyquenchingtoroomtemperature)isimposed[16].Thisheattreatmentisonlyeﬀectiveifasuﬃcientconcentrationofalloyingele-ments(suchasSi,AlandP)retardingthecementiteforma-tionduringthebainiticholdingtreatmentispresent[17,18].Anoptimizedcompositionandheattreatmentleadstoaretainedaustenitefractionof10–15%.Thecarbonconcen-trationoftheretainedausteniteisaboutsixtoninetimesthenominalcarbonconcentration,butvariesfromgraintograin[19–21].Inpreviousinsitustudiestheaverageretainedaustenitebehaviorwasstudiedeitherasafunctionoftheundercooling(deﬁningthethermalstability)[22–24]orasafunctionoftheappliedloadatroomtemperature(deﬁningthemechanicalstability)[25–32].Inthesestudiessomeattentionwaspaidtothebehaviorofthenon-transformingferriticphaseaswell.TheseexperimentalresultsledtothedevelopmentofmicromechanicalmodelsfortheTRIPmultiphasemicro-structure[33–36].Anaccuratepredictionofthematerial’smechanicalresponseatvariabletemperaturesrequiresdetailedknowledgeabouttheinterplaybetweenthetrans-formationbehavior,thelocalloadredistributionbetweenthephases,thetextureevolutionandthedeformationbehav-iorofthenon-transformingferriticmatrixasafunctionofbothtemperatureanduniaxialload.Recentadvancesatsynchrotronradiationsourceshavepro-videdmaterialscientistswithintensehigh-energyX-raybeamsofmicrondimensionsthatareavaluabletoolforinsitustudiesduringthethermomechanicalprocessingofadvancedengineeringmaterials[37].InourprevioussynchrotronX-raydiﬀractionstud-ieswehaveprobedtheaustenitetransformationbehaviorinthebulkTRIPmicrostructureduringdeformationatroomtempera-ture[38]andduringcoolingdownto100K[21,24,39,40].Wefoundthattheaustenitestabilitydependsonboththelocalcarboncontentandthegrainsize.Inthiswork,acompleteinsitucharac-terizationofthecombinedthermalandmechanicalstabilityoftheretainedaustenitehasbeenperformedbyhighenergysynchrotronX-raydiﬀraction(XRD)duringtemperature-dependenttensiletests.Theinterplaybetweentensiledeformation,theorienta-tion-dependentaustenitetomartensitetransformationandgrainrotationhasbeenanalyzedbyaRietveldreﬁnementofthediﬀrac-tiondatacharacterizingtherelevantphasesandtheirtexturessimultaneously.