Papers by Keyword: Phase Diagram

Abstract: In the present research, seven multi-phase diffusion couples, with terminal alloys having different microstructural features, were prepared and annealed for 4 weeks at 335°C. The phase relations and change of morphological characteristics of each phase were studied along the diffusion zone by means of scanning electron microscopy/energy dispersive X-ray spectroscopy and quantitative electron probe microanalysis. Depending on the different terminal compositions of the diffusion couples, the morphological evolution in the diffusion zone can be: tooth-like, matrix phase with isolated and/or dendritic precipitates. Electron back-scattered diffraction analysis was carried out to investigate the crystal orientation of the ternary compounds and the crystal orientation relations at the interface of the diffusion zones.

Abstract: Zirconium rich corner’s isothermal section of the Zr-Sn-Nb system at 450°C was determined by using X-ray diffraction. Experiment results showed that this isothermal section consisted of 2 three-phase region: ((βNb) + Zr₄Sn + (αZr)) and (Zr₄Sn + (βNb) + Zr₅Sn₃), 3 two-phases region: ((βNb) + (αZr)), (Zr₄Sn + Zr₅Sn₃) and (Zr₄Sn + (αZr)), and 4 single-phase region: (βNb), (αZr), Zr₄Sn, Zr₅Sn₃.

Abstract: The phase equilibria in Al-rich corner of the Al-Zn-Ti ternary system at 400 °C were determined by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray powder diffraction (XRD). The results showed that this section consisted of three ternary-phase regions, namely, L+(Al)+τ, Ti₂Al₅+τ+(Al) and Ti₂Al₅+TiAl₃+(Al). The XRD patterns and EDS confirmed that a Ti₂Al₅-structured phase with containing 4 at.% Zn was stable at 400 °C. Furthermore, the ternary new phase (τ phase) was identified in samples and in equilibrium with (Al), Ti₂Al₅ and liquid, respectively.

Abstract: The isothermal section at 573 K of the Ni-Cu-La system was experimentally validated as well as the Mg-La-Cu system was thermodynamically evaluated. Four sample alloys in the Ni-Cu-La system were prepared and analyzed by ICP, XRD and BSE/EDS. All the experimental results were compared favorably with the calculated phase relationships. For the Mg-La-Cu ternary system, the isothermal section at 673 K was assessed on the basis of the available results in literatures, which showed a good agreement with the experimental data. Based on the thermodynamic models and parameters of the six binaries and four ternaries, the Mg-Ni-La-Cu system was finally modeled. The non-equilibrium solidification path La0.7Mg0.3Ni2.8-xCux (x=0-0.4) and the vertical section of LaNi5-Mg2Cu were calculated and analyzed from the viewpoint of hydrogen storage alloys design.

Abstract: The phase equilibrium of the LiCl-MgCl₂-Na₂­SiO₃-H₂O (LMNH) quaternary system at 150°C was studied and the phase diagram of the system was plotted, in order to synthesize hectorite with the nature brine, which was rich in lithium and magnesium. The solid phases were characterized by X-ray diffraction (XRD) and Energy Dispersive Spectrometer (EDS). It was found that hectorite, lithium silicate, karpinskite and brucite can be formed in this system.

Abstract: The equilibrium phase relationships and compositions of Ni - 51at.%Al/Ni - 26at.%Al diffusion couple heat treated at 650 °C for various times have been investigated by means of diffusion couple technique. Experimental results showed that Ni₅Al₃ phase was not only stable at 650 °C, but also had a large solubility range (45.3～40.6) at.% Al. The obtained relationships of NiAl/Ni₅Al₃ and Ni₅Al₃/Ni₃Al are in accordance with the current generally accepted Ni-Al binary system phase diagram, but their composition ranges are quite different from the presently accepted one, that is, the the phase boundaries of NiAl / (Ni₅Al₃ + NiAl), (Ni₅Al₃ + NiAl) / Ni₅Al₃ and Ni₅Al₃ / (Ni₃Al + Ni₅Al₃) significantly shift to the Al-rich side.

Abstract: First of all, the as-cast microstructures of Mo-rich Mo-Si-B ternary alloys were investigated around the triple junction point of the primary Mo solid solution, Mo5SiB2 and Mo2B in this work, based on the liquidus projections of the Mo-Si-B system which have been reported in earlier studies. Subsequently, their microstructural evolution through heat treatment was investigated. Since Mo2B crystallizes out during solidification into a primary or secondary phase even though the alloy composition lies in the triangle of Mo-Mo5SiB2-Mo3Si in the Mo-Si-B equilibrium phase diagram, the as-cast microstructures include the non-equilibrated Mo2B in wide compositional ranges. However, Mo2B was completely decomposed during heat treatment at 1800 °C for 24 h and this contributed to the development of homogeneous, fine microstructures. On the other hand, since Mo2B was not decomposed perfectly during 24 h of 1600 °C heat treatment, as-cast microstructures largely remained. Therefore, it is realized that the heat treatment at 1800 °C is necessary to obtain well-developed microstructures of Mo-Si-B alloys.

Abstract: The phase constituents of alloys from the (Ni,Co)85(Al,Ti)15 plane of the Ni-Co-Al-Ti quaternary system were investigated following prolonged exposure at 750°C. Microstructural investigations confirmed the existence of a continuous A1-L12 two-phase region in the Ni-Co-Al-Ti quaternary system between Ni-Ni3Al and Co-Co3Ti. The lattice misfits of alloys from this quaternary system were determined using neutron diffraction. With increasing contents of Ti the positive lattice misfit increases up to +0.79% in the Ti-containing alloys, which leads to an increasing tetragonal distortion of the  matrix phase due to the increasing coherency stresses.

Abstract: Short-range order formation in dilute Fe-Si and Fe-Al alloys has been investigated by statistical Monte Carlo simulations with effective interactions deduced from first principles calculations for different magnetic structures of bcc Fe. We find that the variation of the magnetic order from ferromagnetic to paramagnetic leads to significant changes in effective cluster interactions and, as follow, in short-range order parameters of alloys. It is shown in agreement with experiment the B2 type short-range order is formed above the Curie temperature, T_C, while the D0₃ type short-range order is preferred below T_C.

Abstract: Several samples of (U,Nd)O₂ with different Nd content (ranging from 2 to 50 in Nd₂O₃ mass. %) were prepared. For composition ranging from 6 to 20 in Nd₂O₃ mass %, two crystalline phases are unambiguously evidenced by X-ray and neutron diffraction, by optical microscopy, and by SEM-EDX and EPMA. The influence of the preparation route on the distribution of the domains made by these two phases is evidenced and discussed.