Change in the short-range order in binary Al-Mn melts during partial substitution of manganese atoms by nickel or cobalt

The structure of ternary melts Al₈₀Mn_14.7Ni_5.3 (at 1233 K) and Al_66.6Mn_16.7Co_16.7 (at 1393 K), the compositions of which correspond to ternary intermetallic compounds, is studied by X-ray diffraction. Structural models are constructed for the melts using experimental structure factor curves and the reverse Monte Carlo method. The structural models are analyzed by the Voronoi-Delaunay method of partitioning. Local atomic ordering is shown to change noticeably when passing from binary Al-Mn to the ternary melts. The causes of the appearance of a prepeak and the asymmetry of the second maximum in the experimental structure factor curves are discussed. Correlations between the short-range orders in the ternary melts and crystalline and pseudocrystalline phases are found.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Cu-Sn and Cu-Sn-Mn systems

The phase equilibria in the Cu-rich portion of the Cu-Sn binary and Cu-Sn-Mn ternary systems have been determined using the diffusion-couple method, differential scanning calorimetry (DSC), high-temperature electron diffraction (HTED), and high-temperature X-ray diffraction (HTXRD) techniques. The present experimental results on the binary Cu-Sn system show the presence of the two-stage, second-order reaction A2 → B2 → D0₃ in the bcc-phase region, rather than a two-phase equilibrium between the disordered bcc (A2) and the ordered bcc (D0₃) phases, as reported before. Phase equilibria in the Cu-Sn-Mn ternary system in the composition range of 0 to 30 at. pct Sn and 0 to 30 at. pct Mn at 550 °C, 600 °C, 650 °C, and 700 °C have been determined, and a ternary compound (Cu₄MnSn) with a very small solubility has been detected. A thermodynamic analysis of the Cu-Sn-Mn ternary system including the Cu-Sn and Mn-Sn binary systems has also been carried out by the CALPHAD (Calculation of Phase Diagrams) method, in which the Gibbs energy of the bcc phase is described by the two-sublattice model in order to take into account the second-order A2/B2 ordering reaction. A consistent set of optimized thermodynamic parameters for the Cu-Sn-Mn system for describing the Gibbs energy of each phase results in a better fit between calculation and experiment.     

Study on stability of RECo5 phases（RE=Dy,Gd）

The eutectoid decomposition reaction that occurred in RECo5 phases ( RE=Dy and Gd ) at low temperature was discussed and confirmed by X-ray powder diffraction (XRD), differential thermal analysis, and scanning electron microscopy. The decomposition temperature of the GdCo5 and DyCo5 were identified as 805.8 and 900℃, respectively. The GdCo5 and DyCo5 phases could not be found in the isothermal section of Gd-Dy-Co ternary system at 800 K. Reasons for the absence of the RE2Co7 phase in the XRD patterns were discussed in detail.     

Understanding the Magnesiothermic Reduction Mechanism of TiO<Subscript>2</Subscript> to Produce Ti

Titanium dioxide (TiO₂) powders in the mineral form of rutile were reduced to metallic and an intermediate phase via a magnesiothermic reaction in molten Mg at temperatures between 973 K and 1173 K (700 °C and 900 °C) under high-purity Ar atmosphere. The reaction behavior and pathway indicated intermediate phase formation during the magnesiothermic reduction of TiO₂ using XRD (X-ray diffraction), SEM (scanning electron microscope), and TEM (transmission electron microscope). Mg/TiO₂ = 2 resulted in various intermediate phases of oxygen containing titanium, including Ti₆O, Ti₃O, and Ti₂O, with metallic Ti present. MgTi₂O₄ ternary intermediate phases could also be observed, but they were dependent on the excess Mg present in the sample. Nevertheless, even with excessive amounts of Mg at Mg/TiO₂ = 10, complete reduction to metallic Ti could not be obtained and some Ti₆O intermediate phases were present. Although thermodynamics do not predict the formation of the MgTi₂O₄ spinel phase, detailed phase identification through XRD, SEM, and TEM showed significant amounts of this intermediate ternary phase even at excess Mg additions. Considering the stepwise reduction of TiO₂ by Mg and the pronounced amounts of MgTi₂O₄ phase observed, the rate-limiting reaction is likely the reduction of MgTi₂O₄ to the Ti_tO phase. Thus, an additional reduction step beyond thermodynamic predictions was developed.     

A lattice parameter study of the precipitates in Al-rich Al-Ag-Zn alloys

Precipitation of the metastable and equilibrium phases has been studied by X-ray diffraction in ternary aluminum rich Al-Ag-Zn alloys. The precipitation sequence was found to be GP zones → ∈ → ∈ Lattice mismatch between the GP zones, ∈, and ∈ phases was found to depend upon the solute content of the alloy. The lattice mismatch between the metastable precipitates and the matrix could be altered by alloying or aging at 150°C. Formerly Lecturer at the University of Manchester, Manchester, England is deceased     

Liquidus Projection of the Ternary Bi-Sb-Te Thermoelectric Material System

The ternary Bi-Sb-Te system is important for thermoelectric applications. Its liquidus projection is determined, except for the Bi-rich corner with various unconfirmed binary Bi-Te compounds. Fifty Bi-Sb-Te ternary alloys are prepared. Primary solidification phases are identified using metallographic observations and X-ray diffraction techniques. Phase transformation temperatures are determined using differential thermal analysis. No ternary compound is found. (Bi,Sb)₂Te₃ and (Bi,Sb) are continuous solid solutions. The Bi₂Te₃ and Sb₂Te₃ phases form a pseudo-binary section. Alloys of the primary solidification phases of Te, (Bi,Sb)₂Te₃, γ, δ, and (Bi,Sb) are determined and the boundaries of various primary solidification phases are delineated. The Bi-Sb-Te liquidus projection is also calculated with the CALPHAD method using preliminary thermodynamic models, and the calculated results are qualitatively in agreement with the experimental determinations.     

On the constitution of the system Al-Mn-Si

The constitution of the ternary system Al-Mn-Si over the entire composition range is investigated using metallography, X-ray diffraction (XRD), and differential thermal analysis (DTA). Ten stable ternary phase are identified and characterized. Isothermal sections for 550 °C and 700 °C, the liquidus projection, and a reaction scheme linking them are presented.     

Investigation of the phase equilibria in the Sn-Bi-In alloy system

This article presents an investigation of the phase equilibria in the Sn-Bi-In ternary alloy system, performed both by theoretical and experimental methods. Following the regular solution model and a standard thermochemical calculation, a theoretical evaluation of the phase equilibrium in the entire ternary system is conducted. The thermodynamic parameters required for the calculation are initially obtained by fitting the model to existing data available from prior studies. The theoretical results are then validated and further improved by experimental work in which alloys with several critical compositions were chosen and examined. In the experimental work, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) spectroscopy were jointly used to identify the transition temperatures and the phases in the microstructure. The resulting phase diagram agrees well both with the existing data and with the data from the current experiments. However, different from previous findings, this study finds a nonbinary nature of the Sn-BiIn and Sn-BiIn₂ quasi-binaries and nine invariant reactions, one eutectic, six peritectic and two peritectoid. The phase-reaction scheme (Scheil diagram), the liquidus projection, and the phase diagram, covering entire compositional ranges, are established.     

Microstructural characterization of the dispersed phases in Al-Ce-Fe system

Analytical electron microscopy studies were conducted on a rapidly solidified Al-8.8Fe-3.7Ce alloy and arc melted buttons of aluminum rich Al-Fe-Ce alloys to determine the characteristics of the metastable and equilibrium phases. The rapidly solidified alloy consisted of binary and ternary metastable phases in the as-extruded condition. The binary metastable phase was identified to be Al₆Fe, while the ternary metastable phases were identified to be Al₁₀Fe₂Ce and Al₂₀Fe₅Ce. The Al₂₀Fe₅Ce was a decagonal quasicrystal while the Al₁₀Fe₂Ce phase was determined to have an orthorhombic crystal structure belonging to space group Cmmm, Cmm2, or C222. Microscopy studies of RS alloy and cast buttons annealed at 700 K established the equilibrium phases to be Al₁₃Fe₄, Al₄Ce, and an Al₁₃Fe₃Ce ternary phase which was first identified in the present study. The crystal structure of the equilibrium ternary phase was determined to be orthorhombic with a Cmcm or Cmc2 space group. The details of X-ray microanalysis and convergent beam electron diffraction analysis are described.     

Activity-composition relations at 1100°C in the system calcium oxide-iron oxide-manganese oxide in contact with metallic iron

The extent of the solid miscibility gap in the system CaO−“FeO”−MnO at 1100°C has been determined termined by electron microprobe, point-counting, and X-ray diffraction analysis of coexisting phases within the miscibility gap. Activities of FeO in ternary solid solutions have been determined at 1100°C by equilibrating the solid solutions with metallic iron and a gas phase of known oxygen pressures. Activity-composition curves for CaO and MnO in the ternary system are calculated from a Gibbs-Duhem integration, and the data are extrapolated to the binary system CaO−MnO, which is shown to display a considerable positive deviation from ideality at 1100°C. NILS TIBERG, formerly Graduate Assistant, Department of metallurgy, The Pennsylvania State Univeristy, University Park, Pa.     

Growth characteristics of directionally solidified Al203/YAG/ZrO2 ternary hypereutectic in situ composites under ultra-high temperature gradient

Oxide eutectic ceramic in situ composites have attracted significant interest in the application of high-temperature structural materials because of their excellent high-temperature strength,oxidation and creep resistance,as well as outstanding microstructural stability.The directionally solidified ternary Al_2O_3/YAG/ZrO_2 hypereutectic in situ composite was successfully prepared by a laser zone remelting method,aiming to investigate the growth characteristic under ultra-high temperature gradient.The microstrucnrres and phase composition of the as-solidified hypereutectic were characterized by using scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD).The results show that the composite presents a typical hypereutectic lamellar microstructure consisting of fine A1203 and YAG phases,and the enriched ZrO_2 phases with smaller sizes are randomly distributed at the Al2O3/YAG interface and in Al_2O_3 phases.Laser power and scanning rate strongly affect the sample quality and microstructure characteristic.Additionally,coarse colony microstructures were also observed,and their formation and the effect of temperature gradient on the microstructure were discussed.     

Fabrication of an In Situ Bulk Metallic Glass Composite with High Magnesium Content

In this work, an in situ bulk metallic glass composite in the Mg-Ni-Gd ternary system with high Mg content (>80 at. pct) that contains a ductile Mg-rich crystalline phase was produced by copper mold casting. The stability and devitrification process of the amorphous matrix in the composite structure have been studied using scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. The precipitation of crystalline phases from the amorphous matrix and the volume fraction of these phases were found to be dependent on both cooling rate and melt composition.     

A 500 °C isothermal section for the Al-Au-Cu system

The Al-Au-Cu system and its associated ternary alloys and intermetallic compounds is surprisingly poorly known, and the authors could find no phase diagram for it in the literature. This article addresses this omission by presenting an isothermal section at 500 °C, derived with the aid of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), metallography, and hardness measurements. The samples studied had generally received an anneal of 2 hours at 500 °C, primarily in order to complete any transformations that occurred during solidification and cooling of the castings. The possibility of further changes on protracted annealing at 500 °C is not ruled out, and the diagram presented is, therefore, applicable only to material prepared by thermal processing of an industrial nature. The presence of a ternary β phase with a nominal stoichiometry of AlAu_2−x Cu_1−x (0≤x≤1) was confirmed, and its phase field at 500 °C was determined. A number of the binary intermetallic phases were found to exhibit some solid solubility of the ternary element. In particular, the γ-Al₄Cu₉ phase extends deep into the ternary and, in the vicinity of the commercially interesting 18-carat line, appears to exist in a ternary ordered form, designated here as γ ₂ .     

Investigation of the isothermal section of the Ce-Co-Al ternary system at 573 K

The isothermal section of the Ce-Co-Al ternary system at 573 K was investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. It consisted of 19 single-phase regions, 46 two-phase regions and 25 three-phase regions. Four ternary compounds, namely CeCoAl, Ce2Co15Al2, CeCoAl4, CeCo2Al8, were confirmed in this system. At 573 K, the maximum solid solubilities of Co in CeAl2 and Al in CeCo2 were about 10.4 at.% and 10.0 at.%, resp...     

新化合物Al14Gd5Si的晶体结构及其Rietveld精修

利用X射线粉末衍射技术和Rietveld结构修正方法对Al14Gd5Si进行了研究,新三元化合物Al14Gd5Si具有Ni3Sn结构类型,空间群为P63/mmc(No.194).点阵参数为a=0.63022 (1)nm,c=0.45856 (1)nm,指标化的可靠性因子F30=218.1(33).用Rietveld方法对该化合物的晶体结构成功地进行了精化修正,精修得到的R因子为Rp=0.119,Rwp=0.157.     

Structure of mechanically alloyed Ti-Al-Nb powders

Ti-Al-Nb ternary powder mixtures containing 24Al-11Nb, 25Al-25Nb, 37.5Al-12.5Nb, and 28.5Al-23.9Nb (at. pct) were mechanically alloyed in a SPEX 8000 mixer mill using a ball-to-powder weight ratio of 10:1. The structural evolution in these alloys was investigated by X-ray diffraction and transmission electron microscopy techniques. A solid solution of Al and Nb in Ti was formed at an early stage of milling, followed by the B2/body-centered cubic (bec) and amorphous phases at longer milling times. The stability of these phases and their transformation to other phases have been investigated by heat treating these powders at different temperatures. The B2/bcc phase transformed into an orthorhombic (O-Ti₂AlNb) or a mixture of the orthorhombic (O) and hexagonal close-packed (α₂-Ti₃Al) phases, the proportion of phases being dependent on the powder composition. Milling beyond the amorphous phase formation resulted in the formation of an fee phase in all the powders, which appears to be TiN, formed as a result of contamination of the powder. Formerly Graduate Student, University of Idaho     

Analysis of heat-affected zone phase transformations usingin situ spatially resolved x-ray diffraction with synchrotron radiation

Spatially resolved X-ray diffraction (SRXRD) consists of producing a submillimeter size X-ray beam from an intense synchrotron radiation source to perform real-time diffraction measurements on solid materials. This technique was used in this study to investigate the crystal phases surrounding a liquid weld pool in commercial purity titanium and to determine the location of the phase boundary separating the high-temperature body-centered-cubic (bcc) β phase from the low-temperature hexagonalclose-packed (hcp) α phase. The experiments were carried out at the Stanford Synchrotron Radiation Laboratory (SSRL) using a 0.25 × 0.50 mm X-ray probe that could be positioned with 10-μm precision on the surface of a quasistationary gas tungsten arc weld (GTAW). The SRXRD patterns were collected using a position-sensitive photodiode array in a φ-2φ geometry. For this probe size, integration times of 10 s/scan at each location on the specimen were found adequate to produce high signal-to-noise (S/N) ratios and quality diffraction patterns for phase identification, thus allowing real-time diffraction measurements to be made during welding. The SRXRD results showed characteristic hcp, bcc, and liquid diffraction patterns at various points along the sample, starting from the base metal through the heat-affected zone (HAZ) and into the weld pool, respectively. Analyses of the SRXRD data show the coexistence of bcc and hcp phases in the partially transformed (outer) region of the HAZ and single-phase bcc in the fully transformed (inner) region of the HAZ. Postweld metallographic examinations of the HAZ, combined with a conduction-based thermal model of the weld, were correlated with the SRXRD results. Finally, analysis of the diffraction intensities of the hcp and bcc phases was performed on the SRXRD data to provide additional information about the microstructural conditions that may exist in the HAZ at temperature during welding. This work represents the first directin situ mapping of phase boundaries in fusion welds.     

Metallographic and structural observations in the pseudo-binary section Ni3Si-Ni3Ti of the Ni-Si-Ti system

The metallographic and structural features of the alloys in the pseudo-binary section between Ni₃Si (L1₂) and Ni₃Ti (D0₂₄) were investigated. The L1₂ phase (γ′) extended along a pseudo-binary line between the two phases with Ti solubility of about 11 at.%. Also, the L1₂ phase expanded up to about 80 at.% Ni at high Ti concentration. Consistent with previous observations, the addition of the Ti elements into the Ni₃Si alloy led to congruent melting of L1₂ phase. Based on the observations of X-ray diffraction and an electron channeling technique aided with EDX (Energy Dispersive X-ray spectrometer), it was shown that the alloying element, Ti, substituted for the component element of Si the ternary alloy Ni₃(Si, Ti) was highly ordered. The solubility limit of boron in Ni₃(Si, Ti) was shown to be very low, i.e. less than 50 ppm.