Phase diagram calculations of ZrO2-based ceramics with an emphasis on the reduction/oxidation equilibria of cerium ions in the ZrO2-YO1.5-CeO2-CeO1.5 system

Phase diagram calculations that were made previously for the ZrO₂-MO _m/2 (m = 2, 3, 4) systems and for the ZrO₂-YO_1.5-MO _m/2 (M = transition metals) systems have been extended to the ZrO₂-YO_1.5-CeO₂(-CeO_1.5) system to make an attempt to explain (1) thermogravimetric (TG) results as a function of oxygen potential, (2) electronic conductivity as a function of oxygen potential, and (3) a miscibility gap observed in air. The interaction parameters for the CeO₂-CeO_1.5-YO_1.5 system were obtained from the reported oxygen nonstoichiometry in CeO_2−x and rate earth doped ceria, (Ce,RE)O_2−δ . The interaction parameters for the ZrO₂-CeO₂ subsystem were obtained so as to reproduce the observed miscibility gap at 1273 K. Those thermodynamic properties can reproduce consistently the experimental behaviors of the electronic conductivity and the TG results in the (Zr_1−x Ce _x )_0.8Y_0.2O_1.9 solid solutions; these indicate the enhancement of reduction of CeO₂.     

Phase equilibria in the Fe–Rh–Ti system II. CVM calculations

Cluster Variation Method (CVM) calculations of phase equilibria in the bcc Fe–Rh–Ti system were performed in the irregular tetrahedron (IT) approximation including tetrahedron interactions. The energy parameters were obtained from a fit to recent experimental data on phase equilibria at 1000 °C and 800 °C. At these temperatures the ordering between first nearest neighbours dominates leading to large single-phase fields with B2 ordering. At lower temperatures the calculations predict additional ordering between second nearest neighbours of type D0₃. In the Fe–Ti system the second neighbour interactions are of segregation type leading to miscibility gaps between the disordered A2 and the ordered B2 phases extending from the binary Fe–Ti system into the ternary system. Calculated isothermal sections are presented at several temperatures. The complex ordering in the ternary system leads to strong variations of chemical potentials with composition. This is shown by calculated iso-chemical potential contours.     

超声磨削氧化锆陶瓷表面相变与残余应力特征实验研究

针对氧化锆陶瓷的易相变特点,通过对ZTA陶瓷和纳米氧化锆陶瓷进行对比实验,研究了氧化锆陶瓷磨削表面相变特性,分析了磨削表面的残余应力特征.实验结果表明,亚稳态四方相氧化锆的含量以及磨削应力是诱发氧化锆陶瓷产生马氏体相变的主要因素;陶瓷磨削过程中,砂轮的磨削深度越大、磨粒粒径越大,在材料基体中产生的磨削应力越大,从而马氏体相变率增大;纳米氧化锆陶瓷磨削表面产生的残余压应力值大于ZrO2增韧Al2O3(ZTA)陶瓷.通过分析磨削参数对残余应力的影响,验证了马氏体相变可在一定程度上促进残余压应力的产生,从而提高磨削表面的质量.     

ZrO2陶瓷t→m相变增韧的研究回顾与展望

回顾了国内外学者对ZrO2陶瓷相变增韧机制的理论研究,并对ZrO2陶瓷相变增韧机制的未来研究方向进行了展望.     

Phase equilibria in the Ti-rich corner of the Ti-Si-Ga system

Phase relations in the ternary Ti-Si-Ga system have been established experimentally by means of a study of alloy samples in the as-cast condition and annealed at 1350 °C. The alloys were prepared by arc melting. The investigation was carried out using physico chemical methods of analyses (metallography, X-ray powder diffraction, differential thermal analysis, and electron probe microanalysis over a limited composition range with samples containing less than 38 at.% Ga and more than 62 at.% Ti. Liquidus and solidus surface projections, the isothermal section at 1350 °C, and the isopleth at 68 at.% Ti are presented. Three surfaces of primary crystallization of phases have been established: extended ones for Ti₅(Si,Ga)₃ and β (Ti-base solid solution) and a narrow one of Ti₂Ga. The monovariant curves separating these are due to the eutectic reactions L↔β+Ti₅(Si,Ga)₃ and L↔β+Ti₂Ga and to the L+Ti₅(Si,Ga)₃↔Ti₂Ga peritectic reaction. The three-phase region (β+Ti₅(Si,Ga)₃+Ti₂Ga) results from the four-phase eutectic reaction L↔β+Ti₅(Si,Ga)₃+Ti₂Ga. The composition of the ternary eutectic point E and the compositions of the coexisting solid phases have been determined. The solubilities of Si in the gallides, and of Ga in Ti₅Si₃ and of both the elements in Ti are given.     

Phase diagram and thermodynamic properties of phases in the In-Te system

The In-Te phase diagram was refined in the composition range 0 to 71.77 at.% Te; the phases In₄Te₃, InTe, In₂Te₃, and In₂Te₅ were found to exist. Vaporization of In₂Te₃ and InTe was studied by the mass spectrometric method and the p _{Te 2} -T diagram was constructed. The standard molar enthalpies of formation of mentioned compounds were determined by direct synthesis calorimetry. The heat capacity of the solid In₂Te₃ was measured in a vacuum adiabatic calorimeter at 5 to 310 K, and the H ^o(T)-H ^o(0), S _T , and G ^o(T)-H ^o(0) functions were calculated.     

Phase diagram and thermodynamic properties of phases in the In-Te system

The In-Te phase diagram was refined in the composition range 0 to 71.77 at.% Te; the phases In₄Te₃, InTe, In₂Te₃, and In₂Te₅ were found to exist. Vaporization of In₂Te₃ and InTe was studied by the mass spectrometric method and the p _{Te 2} -T diagram was constructed. The standard molar enthalpies of formation of mentioned compounds were determined by direct synthesis calorimetry. The heat capacity of the solid In₂Te₃ was measured in a vacuum adiabatic calorimeter at 5 to 310 K, and the H ^o(T)-H ^o(0), S _T , and G ^o(T)-H ^o(0) functions were calculated.     

Phase diagram in the iron-rich corner of the Fe-Cr-Mo-V-C system below 1000 K

Relevant experimental phase equilibria were used with the THERMOCALC program to refine thermodynamic parameters for the low-temperature region, in the steels with composition 0.4 to 2.5 wt.% Cr, 0 to 1 wt.% Mo, and 0 to 0.5 wt.% V. The refined parameters were used to calculate phase relationships, which were then compared with experimental results. The main interest was focused on the temperature and concentration regions of existence of the chromium-rich carbides M₇C₃ and M₂₃C₆ and Mo-rich carbides M₆C and M₂C. Results of experiments indicate that M₇C₃ carbide replaces M₂₃C₆ carbide in the temperature region between 773 and 873 K. Similar behavior was also found for molybdenum-rich phases M₆C and M₂C. Some modifications of existing thermodynamic parameters in the low-temperature region, as well as the establishment of some new parameters, were necessary to obtain reasonable agreement between theoretical and experimental results.     

Phase equilibria in the AlVO4-Al2(MoO4)3 system

The phase equilibria established in the AlVO₄-Al₂(MoO₄)₃ system over the whole component concentration range up to 1000 °C have been investigated. A phase diagram has been constructed using the results of DTA and XRD methods. The AlVO₄-Al₂(MoO₄)₃ system is not a true two-component system, even in the subsolidus area.     

Phase equilibria in the Mg-rich corner of the Mg-Zn-La system at 350℃

The phase equilibria in the Mg-rich corner of the Mg-Zn-La system at 350℃ have been investigated by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. It has been shown that the linear compound (Mg,Zn)17La2 existed in the Mg-Zn-La system at 350℃. The linear compound (so-called T phase) was with the C-centred orthorhombic crystal structure induced by the solution of significant quantities of the third element. The three-phase region α(Mg) + MgZn(La) + T and the two-phase region composed of the α(Mg) and the linear-compound T phase existed in the Mg-rich corner of the Mg-Zn-La system at 350℃.     

Phase equilibria in the Ni-rich portion of the Ni–Ga binary system

The phase equilibria in the composition range from 0 to 60 at% Ga of the Ni–Ga system were determined by electron probe microanalysis (EPMA) using diffusion couples, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). It was found that while the phase equilibria between the α′ (L1₂: Ni₃Ga) and α (Ni-solid solution) or β (B2: NiGa) phases are basically in agreement with the diagram evaluated by Lee and Nash, those between γ (B8₁: Ni₁₃Ga₇), δ (Cmmm: Ni₅Ga₃) and ɛ (C2/m: Ni₁₃Ga₉) are topologically different from that diagram. Three eutectoid reactions (γ → δ + ɛ, β → γ + ɛ, β → α′ + γ) and one peritectoid reaction (α′ + γ → δ) were confirmed and the temperatures and concentrations of those invariant reactions were determined.     

Mo_2FeB_2基金属陶瓷液相烧结过程中硬质相晶粒生长的蒙特卡罗模拟

采用反应硼化烧结法制备了Mo_2FeB_2基金属陶瓷,通过蒙特卡罗模拟方法对Mo_2FeB_2基金属陶瓷在液相烧结过程中硬质相晶粒的生长进行了研究。模拟中分析了蒙特卡罗步、液相体积分数和固液界面能对硬质相晶粒形貌的影响,并通过扫描电镜(SEM)研究了Mo_2FeB_2基金属陶瓷显微组织中硬质相晶粒的形貌。将模拟结果同实验结果进行了对比,结果表明:硬质相晶粒生长受界面反应控制。硬质相晶粒平均长径比增大主要来源于高温液相烧结过程中硬质相不同晶面与液态粘接相之间的固液界面能的相对较大的差值。修正后的模拟结果与实验结果具有较好的一致性。     

Phase equilibria in the quasi-ternary system Ag2S–In2S3–CdS at 870 K

An isothermal section of the quasi-ternary system Ag₂S–CdS–In₂S₃ at 870 K was investigated using X-ray phase analysis. No quaternary intermediate phase was found. A continuous solid solution series between In₂S₃, AgIn₅S₈ and CdIn₂S₄ was discovered; a limited solid solution range of CdS is localized along the AgInS₂–CdS section.     

Thermodynamic evaluation of phase equilibria in the CaCl2-MgCl2-CaF2-MgF2 system

The phase diagram of the CaCl₂-CaF₂-MgCl₂-MgF₂ reciprocal ternary system was calculated thermodynamically from available data on the common-ion binary subsystems and from available data on the CaCl₂-MgF₂ join. This join is very nearly quasibinary and divides the system into two quasiternary systems: the CaCl₂-MgF₂-CaF₂ system with a ternary eutectic calculated at 724 +-5 °C and the CaC₂-MgF₂-MgCl₂ system with a ternary eutectic calculated at 561 +-5 °C.     

Phase diagram of magnetic structures in Fe/Cr/Fe films with nanoscale geometric inhomogeneities of interfaces

Results of an analysis of magnetic structures (mutual orientations of the iron-layer magnetizations) in three-layered Fe/Cr/Fe films formed due to the exchange interactions inside the layers of iron and chromium and on the Fe/Cr interfaces are given. The analysis was performed under the following assumptions: (1) the iron layers are ferromagnetic, and the magnetic structure of chromium layers has the form of transverse linearly polarized spin-density waves; (2) the iron-chromium exchange interaction is considered as a weak disturbance as compared to the exchange interactions inside the iron and chromium layers; therefore, they were considered as first-order and second-order perturbation-theory corrections; (3) the relative value of these corrections depends on the degree of roughness of the Fe/Cr interfaces; it was assumed that the roughness has a nanometer scale. With such approximations, the mutual orientation of the magnetizations of iron layers can be parallel, antiparallel, or noncollinear. The limits of stability of these structures depending on the thickness of the chromium interlayer and on the ratio of the first-to-second-order corrections have been determined. The main attention was paid to the conditions of the loss of stability with respect to changes in the phase of the spin-density wave, which can result in jumps in the curves of magnetization and magnetization reversal of the Fe/Cr films.     

Influence of cerium ions on the anatase-rutile phase transition of TiO2 prepared by sol-gel auto-igniting synthesis

The anatase-rutile phase transformation of TiO2 doped cerium up to 5 mol% was studied by X-ray diffraction and X-ray photoelectron spectroscopy. The samples were prepared by sol-gel auto-igniting synthesis process from a TiO(NO3)E-Ce(NO3)E-NH4NOE-citric acid complex compound system. The combusted amorphous powders were calcined at different temperatures. Significant structural changes were observed during the various stages of the phase transformation. It was concluded that at low dopant contents, cerium ions were incorporated into the TiO2 structure, and the anatase phase was stabilized; but at larger amounts, part of the dopant was segregated on the surface of TiO2 and the rutile formation was accelerated at elevated calcination temperature.     

Phase diagram of the Ba2YCu3O6-Ba2YCu3O7 system below 400°C

X-ray diffraction analysis and transmission electron microscopy have been used to study the low-temperature decomposition of the nonstoichiometric (in oxygen) HTSC compound Ba₂YCu₃O_{7 ? δ}. The phase diagram of the Ba₂YCu₃O₆-Ba₂YCu₃O₇ system below ≤400°C has been constructed. The temperature range corresponding to phase separation has been found to be divided into two portions. At T > 250°C, two orthorhombic phases characterized by different oxygen contents are formed; at the higher temperatures, the phase separation of the compound into a tetragonal and an orthorhombic phase takes place. The separation was also found to observe at T = 100°C; this indicates the possibility of natural aging for the Ba₂YCu₃O_{7 ? δ} compound at room temperature.