Oxidation Behavior of Fe-Ni-Co Based Superalloys and Influence of Yttrium Addition

1. IntroductionThe Fe-Ni-Co based 907 alloy is a controlled thermal expansion superalloy for use in casting rings andseals for aircraft gas turbine engines where the servicetemperature is up to 649oC. The coefficiellt of thermal expansion of this alloy is low, about half of that ofconventional superalloys. The absence of Cr in the alloy ensures the low thermal expansion, however leadsto an inherent lack of environmental resistance compared with other superalloys containing Cr[1]. Theoaldati…     

Characterization of Failure Mechanisms of Duplex and Graded Thermal Barrier Coatings Exposed to Thermal Shock Test

The beginning of failure of a (ZrO2-7%Y2O3)/(Ni-22%Co-17%Cr-12.5%Al-0.6%Y) duplex andgraded coating systems on lnconel 617 and IN738LC in burner rig tests has been characterized.The test conditions are 40 s heating up to 75O℃ substrate temperature followed by 80 s aircooling. Failure is considered at the appearance of the first bright spot during heating period.Stresses due to thermal expansion mismatch strains on cooling are the probable cause of life-limiting in this conditions of testing.     

Large anisotropic negative thermal expansion in Cu-TDPAT metalorganic framework:A combined in situ X-ray diffraction and DRIFTS study

Cu-TDPAT(H₆TDPAT=2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine),a stable nanoporous metal-organic framework with rht topology,has sparked broad interest as an adsorbent for several chemical separation processes.In this work,in situ synchrotron diffraction experiments followed by sequential LeBail refinements reveal that Cu-TDPAT shows unusually large anisotropic negative thermal expansion(NTE).The PASCal crystallography tool,used to analyze the magnitude of the NTE,reveals an average volumetric thermal expansion coefficientαv=-20.3 MK^-1.This value is significantly higher than the one reported for Cu-BTC(also known as HKUST-1),which contains the same Cu-paddlewheel building unit,αv=-12 MK^-1.In situ synchrotron single crystal X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)were employed to shed light on the NTE mechanism.Using these two methods,we were able to elucidate the three main structural motions that are responsible for the NTE effect.The more pronounced NTE behavior of Cu-TDPAT is attributed to the lower symmetry combined with the more complex ligand structure when compared to Cu-BTC.The knowledge obtained in this work is important for understanding the behavior of the adsorbent under transient variable temperature conditions in fixed adsorption beds.     

Effect of Grain Size on the Thermal Expansion of Isotropic Synthetic Graphites

The relationship is analyzed between the thermal expansion coefficient of synthetic graphites and the grain size of their filler. It is shown by examining a large number of commercial graphites of different classes that their thermal expansion coefficient increases from 2 × 10⁻⁶ to (7–8) × 10⁻⁶ K⁻¹ as the grain size decreases from 3000 to 1 μm. The strength of synthetic graphites also increases with increasing grain size and correlates with thermal expansion. The likely reason for the increase in thermal expansion coefficient is the better contact between neighboring microvolumes of the material. A model is proposed for the thermal expansion of synthetic graphites which considers microvolumes 0.1 to 0.5 μm in size, with a thermal expansion coefficient on the order of 8.3 × 10⁻⁶ K⁻¹, only a fraction of the microvolumes being involved in thermal-expansion transfer. The fraction of such microvolumes decreases with increasing grain size. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 12, 2005, pp. 1456–1462. Original Russian Text Copyright ? 2005 by Samoilov, Shilo.     

Diagnosis of the Thermal Bow of a Shaft in a Three Stage Centrifugal Compressor

In practice many turbo-machines driven by motors are started up to perational speed within a very short time,i.e.in less than 20 seconds .For this type of machines the compatibility of thermal deformaiton of the rotor stucture must be taken into account in the machine desing ,or the thermal defromation will be constrained and a huge resultant force can cause the shaft bending and consequently resulting in violent vibrations.In this paper,detection of thermal bow of a shaft in a three stage centrifugal compressor in a petrochemical plant is presented .The diagnostic results show that the thermal bow was induced by the incompatibility of axial thermal deformation of the rotor stucure.A remedial action allowing free axial thermal expansion of the outer parts of the rotor is suggested.     

Structure and Properties of Nanostructured Vacuum-Deposited Foils of Invar Fe–(35–38 wt%)Ni Alloys

The process of electron beam vacuum deposition of the Fe–(35–38 wt%)Ni alloys at substrate temperatures Ts from 300 to700 °C were used to produce vacuum-deposited foils with the FCC structure, differing by the size of characteristic microstructural elements(grains and subgrains). It was shown that refinement of foil microstructural elements to nanoscale is accompanied by their microhardness increase up to 4–5 GPa. The change of the thermal expansion coefficient(TEC) of the nanostructured(NS) foil of the Fe–35.1Ni alloy within the temperature range from-50 to 150 °C has some deviation from that observed for cast Invar alloy of the same composition. It has been found that the main factors affecting the peculiarities of thermal expansion of the NS foil can be related to the presence of small fraction of BCCphase in them, high level of crystalline lattice microstrains and inhomogeneous magnetic order in FCCphase. It was shown that as a result of additional thermal treatment of NS foils their invar properties become similar to that observed for cast Invar alloy but mechanical properties remain on the same level.     

Effect of CuO Addition on the Sintering Behavior and Electrical Conductivity of 3Y-TZP

Yttria stabilized tetragonal zirconia polycrystals （3Y-TZP） doped with CuO was prepared, to get two compositions, 0.3 and 1 mole fraction CuO, respectively. The dilatometric study of the samples showed sintering to be improved for the samples doped with 0.3 mole fraction CuO, and to be deteriorated for the samples doped with 1 mole fraction CuO. The 1 mole fraction CuO doped 3Y-TZP showed higher tetragonal/monoclinic phase transformation which was accompanied by grain growth. The electrical conductivity decreased with the addition of CuO.     

Thermomechanical Analysis of (Cu0.5Tl0.5)-1223 Substituted by Pr and La

The thermomechanical analysis (TMA) of Cu 0.5 Tl 0.5 Ba 2 Ca 2 x R x Cu 3 O 10 δ,where R=Pr and La,with 0.0≤x≤0.15,was carried out in temperature range from 450 to 1145 K.The samples were prepared by singlestep solid state reaction technique.The prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The superconductivity of the prepared samples was investigated by electrical resistivity measurement.The results showed that low substitution content enhanced the (Cu 0.5 Tl 0.5)1223 phase formation,while the higher substitution content degraded this phase.The higher superconducting transition temperatures T c were found to be 114 K and 109 K at x= 0.025 for Pr-and La-substitutions,respectively.The average linear thermal expansion coefficient increased as x increased,while the shrinkage temperature decreased as x increased.Those results were emphasized by porosity and Vickers microhardness calculations.Debye temperature θ D was calculated from the linear thermal expansion coefficient data and correlated to T c to estimate the electron-phonon coupling λ ep.     

Effect of Cu content on microstructure and mechanical properties of in-situ β phases reinforced Ti/Zr-based bulk metallic glass matrix composite by selective laser melting(SLM)

In this study,non-toxic in-situβphases of reinforced Ti/Zr-based bulk metallic glass matrix composites(BMGCs)of(Ti_0.65Zr_0.35)100-xCux(x=5,10,15 at.%)are fabricated via selective laser melting.The effect of Cu content on phase formation,microstructure,and mechanical properties is investigated.The average volume fraction and width of theβphase decreases with increasing Cu content,while a more amorphous phase and the(Ti,Zr)₂Cu phase forms.In the center zone of the molten pool,theβphase grows in the direction of the temperature gradient,and the amorphous phase distributes among theβphases.This occurs using:sphere morphology(for x=5),a more continuous elongated sphere and network morphology(for x=10),and network morphology(for x=15),respectively.In the edge zone of the molten pool,due to the smaller cooling rate and the existence of a partially molten zone,theβphase becomes coarser,and an amorphous phase forms for more continuous networks.Furthermore,the hardness improves significantly with increasing Cu content.No crack is found for x=5.Although the average volume fraction of theβphase for x=5 is about 90%,the compression yield strength is 1386±64 MPa,reaching to an average level of conventionally fabricated counterparts,due to finer microstructure,and twinning and martensitic transformation of theβphase.     

Magnetic Ordering and Exchange Interaction of Laves Compounds Sm0.9Pr0.1（Fe1—xCox）2

Structure,magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investi-gated by means of X-ray diffraction,a.c. initial susceptibility, extracting sample magnetometer,Mossbauer spec-troscopy and standard strain gauge techniques.The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration,deviating from the Vegardˊs law.Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0.The saturation magnetization Ms at temperatures 1.5K, 77K and 300K have the same variation tendency as the composition dependence of Curie temperature,in consistence with rigid-band model.The easy magnetization direction(EMD) od Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x≤0.6,and changes to [110] for x=0.8 ,while Sm0.9Pr0.1(Fe1-xCox)2 stays in the paramagnetic state at room temperature.The composition dependence of the average hyperfine field,Hhf,demonstrates a similar variation tendency as that of the saturation magnetiza-tion Ms and Curie temperature Tc .The spontaneous magnetostricton λ111 increases with increasing Co content.The saturation magnetostriction λs decreases monotonically with increasing x,which is caused by the increase of magnetostriction constant λ100 with opposite sign to that of λ111.A two-sublattice model has been proposed to understand the intermediate region between the [111]and [110] spin configurations ,which can also be used to explain the temperature dependence of magnetization.     

不同温度烧结的赝两元合金(PbTe)1-x(snTe)x电学性能

首次采用粉末冶金法在大成分范围内制备了赝两元合金(PbTe)_1-x(SnTe)_x(x=0～1),并对其电学性能进行了系统地研究.实验发现:经550℃烧结后,随合金中SnTe摩尔分数x增大,合金的最大Seebeck系数值减小.当摩尔分数x≤0.6时,最大Seebeck系数所对应的温度逐渐升高;摩尔分数x>0.6时基本不变.当摩尔分数x=0.6时电导率达最大值.经高温烧结后两参数值也有类似的变化规律,但摩尔分数>0.2的各合金Seebeck系数值高于550℃烧结后的合金,电导率降低.从而得出:烧结温度对赝两元合金(PbTe)_1-x(SnTe)_x的综合电学性能影响不大.     

Thermal Conductivity of Humid Air

In this article, measurements of the thermal conductivity of humid air as a function of pressure, temperature, and mole fraction of water, for pressures up to 5 MPa and temperatures up to 430 K, for different water contents (up to 10 % vapor mole fraction) are reported. Measurements were performed using a transient hot-wire apparatus capable of obtaining data with an uncertainty of 0.8 % for gases. However, as moist air becomes corrosive above 373 K and at pressures >5 MPa, the apparatus, namely, the pressure vessel and the cells had to be modified, by coating all stainless-steel parts with a titanium nitride thin film coating, about 4 μm thick, obtained by physical vapor deposition. The expanded uncertainty (coverage factor k = 2) of the present experimental thermal conductivity data is 1.7 %, while the uncertainty in the mole fraction is estimated to be better than 0.0006. Experimental details regarding the preparation of the samples, the precautions taken to avoid condensation in the tubes connected to the measuring cell, and the method developed for obtaining reliable values of the water content for the gas mixtures are discussed. A preliminary analysis of the application of the kinetic theory of transport properties in reacting mixtures to interpret the complex dependence of the thermal conductivity of humid air on water composition is addressed.     

热电材料CoSi和CrSi_2的晶格热膨胀性

利用动态高温X射线衍射技术分别对立方CoSi和六方CrSi2化合物在298~973 K温度范围内的晶格热膨胀性进行了研究。结果表明:化合物CoSi的点阵参数随温度升高呈线性增长关系,其平均线热膨胀系数aα和平均体热膨胀系数αV分别为1.14×10-5K-1和3.42×10-5K-1,两者之间符合立方晶系关系式,即3αa=αV;化合物CrSi2的点阵参数随温度升高而显著增大,其中沿a轴和c轴的平均线热膨胀系数及平均体热膨胀系数分别为αa=0.96×10-5K-1,cα=0.73×10-6K-1和αV=2.45×10-5K-1,三者之间符合六方晶系关系式,即2αa+cα=αV;化合物CrSi2沿a轴方向的线热膨胀系数远大于沿c轴方向的,呈较强的各向异性。     

New medium-temperature proton electrolytes based on CsH2PO4 and silicophosphate matrices

Silicophosphate gels ranging widely in P₂O₅ content and specific surface area have been synthesized by a sol-gel process. We have demonstrated the possibility of producing medium-temperature high-conductivity systems based on silicophosphate matrices and CsH₂PO₄. The thermal, structural, and transport properties of composite proton electrolytes have been investigated. The results indicate that the electrical conductivity of the composites based on matrices with Si : P = 1 : 0.5 increases by up to three and half or four orders of magnitude and that their proton conductivity is ～10^?3 to 3 × 10^?2 S/cm at temperatures from 90 to 220°C and a water vapor content of ?0.6–1 mol % in air. The additive suppresses the superionic phase transition of CsH₂PO₄. The increase in conductivity at low contents of the heterogeneous component is due to both CsH₂PO₄ dispersion and the presence of protonated centers on the matrix surface. When the mole fraction of the additive exceeds 0.3, the composites contain CsH₅(PO₄)₂, a compound with a lower thermal stability, which is responsible for their high conductivity in a limited temperature range.     

Electrical conductivity and infra red of CaTiO3 doped with CuO

The electrical conductivity of pure CaTiO3 and that containing 0.5～5.0 mole fraction CuO as dopant were measured in the temperature range 291～773 K. The conductivity values varied as a function of temperature and dopant concentration. The activation energy in the lower temperature range depended on the impurity content while in the high temperature range it indicated a value of energy gap width. The infrared absorption spectra in the range of 100～4000 cm-1revealed the presence of two main bands at 340 and 570 cm-1 which were assigned to TiO6 octahedral normal mode. Bands in the range of 106～270 cm-1 were due to the vibration of anion TiO-2. Some bands were observed at higher values due to the presence of lattice imperfections.There was a slight shift in band position with increasing dopant concentration which favors the formation of orthorhombic modification.     

Thermal Conductivities of Imidazolium-Based Ionic Liquid + CO<Subscript>2</Subscript> Mixtures

Experimental results for the thermal conductivities of imidazolium-based ionic liquid + CO₂ mixtures are reported. The thermal conductivities were measured with a transient short-hot-wire method. The experimental temperatures were from 294 K to 334 K, and pressures were 10.0 MPa and 20.0 MPa. The CO₂ mole fractions of the mixtures covered a range up to 0.42. It was found that the thermal conductivities of ionic liquids have a very small CO₂ mole fraction dependence.     

Etude des verres fluores dans les quaternaires ZnF2ThF4AlF3MF2 (M = Mg,Ca, Sr,Ba)

Fluoride glasses have been investigated in the ZnF₂AlF₃ThF₄MF₂ (M = Ba, Sr, Ca, Mg) systems. The vitreous areas are given for the basic ternary diagrams and at a constant 40 % ZnF₂ content. Small samples may be prepared for the compositions: 40 % ZnF₂, 20 % AlF₃, 20 % ThF₄, 20 % MF₂ (M = Ba, Sr, Ca). The glassy transition occurs between 310° C and 350° C and the fusion between 650° C and 750° C. The optical transmission range lies from 240 nm to 7500 nm. The average values of refractive index, thermal expansion coefficient and density are: n_D ～ 1.48, α ～ 15.10^?6° K^?1d ～ 5. The high compactness of the anion array is compared to that of close-packed crystalline fluorides.     

高体积分数粒子型铝基复合材料热膨胀性能的研究

测定了真空气压渗流法制备的三种高体积分数SiC_P/Al 复合材料在0～ 400℃间的热循环曲线及其在此温度区间的线膨胀系数值。测试结果表明复合材料的线膨胀系数值约为其基体的一半, 其值与Kerner 模型的计算值相接近; 复合材料的热循环曲线的特征明显不同于其基体, 三种基体复合材料的热循环曲线的特征也存在差异。对此应用塑性变形理论进行了解释。发现通过改变合金基体可改变热循环曲线的封闭性。      

K_2O对白榴石生成的影响

以钾长石、碳酸钾为主要原料,设计高、中、低3种不同钾含量的配方固相合成白榴石晶体,探讨K2O的含量对白榴石生成的影响。通过实验发现,适当地提高配方中K2O的含量对白榴石生成是有利的,但当配方中K2O远高于其在白榴石中的理论含量时,其在高温下完全熔融成玻璃熔态物质,没有白榴石晶体的生成;当K2O的含量为25.4%,在1250℃熔融保温60min,其热膨胀系数为20.74×10-6℃-1(30～700℃),平均晶粒尺寸为3μm。     

Sc2W3O12/ZrO2可控热膨胀复合材料的制备

采用固相法成功制备了纯度较高的各向异性负热膨胀材料Sc₂W₃O₁₂。将ZrO₂与Sc₂W₃O₁₂按一定体积比混合, 在1200 ℃烧结10 h制备Sc₂W₃O₁₂/ZrO₂复合材料。通过XRD、SEM、EDS和热膨胀仪对合成样品的晶体结构、断面形貌和热膨胀性能进行表征。结果表明: 样品组元为正交相Sc₂W₃O₁₂和单斜相ZrO₂; 在 30~600 ℃内, Sc₂W₃O₁₂/ZrO₂复合材料的热膨胀系数皆线性一致, 并且通过改变Sc₂W₃O₁₂的体积分数, 其热膨胀系数可以控制为正、负或零, 其中60%Sc₂W₃O₁₂/ZrO₂复合材料在30~600 ℃的平均热膨胀系数为0.026×10^-6 ℃^-1, 近似为0。