Iridium-based refractory superalloys by pulse electric current sintering process: Part 1. Elemental powder

Pulse electric current sintering (PECS) was tried as a novel powder metallurgy (PM) process for five Ir-based elemental powder mixtures. Sintering was carried out at 1800 °C for 4 h for all the samples. Specimens with a relative density, more than 90% theoretical density, were obtained after sintering. More than two phases were found; however, a single phase (L1₂ or B2) was expected, according to the phase diagram. The densification mechanism is discussed briefly, and remaining problems are presented.     

On the phase diagram of erbium

We have examined the magnetic phase diagram of single crystal erbium in applied magnetic fields up to 5.5 T along the c and b-axes using electrical resistance versus temperature and magnetoresistance measurements. The phase diagram for the field along the c-axis generally agrees well with the previous neutron scattering studies by Lin et al. (Phys. Rev. B., 45 (1992) 12873) and McMorrow et al. (J. Phys. Condens. Matter, 4 (1992) 8599). We have observed a splitting of the longitudinal Néel transition as a function of applied magnetic field, and a multicritical point at a field of 2.65 T and 71 K leading to previously unobserved magnetic phases. The phase diagram for the field along the b-axis of Erbium has been determined for the first time. Recently, Jehan et al. (Phys. Rev. B, 50 (1994) 3085) have studied the a-axis phase diagram using neutron scattering. We have used their data along the a-axis in identifying the magnetic structure of our phase diagram for Er along the b-axis.     

Influence of coupling with calculation of phase diagrams on microsegregation forming simulation of Al-4.5%Cu alloy

The effect of coupling with calculation of phase diagrams on microsegregation forming simulation was investigated. The traditional simplified phase diagram and calculated phase diagram were introduced into the numerical models respectively and simulation on microsegregation forming of the Al-4.5%Cu alloy ingot was also presented. The simulation results were both compared with the experiment results. The results show that the calculated sencondary arm spacing with these two kinds of phase diagram are almost the same because relationship between the coarsening model and the information of phase diagram is not close. The calculated eutectic phase volume fractions of different locations in the ingot coupled with different phase diagrams are discrepant. The calculated volume fractions are consistent with the experiment results when calculated phase diagram couples, but are far from the experiment results and obviously inacceptable when traditional simplified phase diagram couples. So, coupling with accurate calculated phase diagrams is very significant for microsegregation forming simulation since much information of the phase diagram is used in the models and it can improve the precision of simulation results.     

Phase studies on the quasi-binary thallium(I) selenide-thallium(I) telluride system

The phase diagram for the system Tl₂Te-Tl₂Se has been determined on the basis of the results of studies by means of common thermal analysis. The diagram has been compared with diagrams published earlier. Some regularities have been presented for the quasi-binary chalcogenide systems with common cation.     

Phase studies on the quasi-binary thallium(I) selenide-thallium(I) telluride system

The phase diagram for the system Tl₂Te-Tl₂Se has been determined on the basis of the results of studies by means of common thermal analysis. The diagram has been compared with diagrams published earlier. Some regularities have been presented for the quasi-binary chalcogenide systems with common cation.     

Experimental determination of NH<Subscript>4</Subscript>NO<Subscript>3</Subscript>-KNO<Subscript>3</Subscript> binary phase diagram

The solid-state phase transitions in ammonium nitrate (AN)-potassium nitrate (KN) system, and the equilibrium AN-KN phase diagram have been determined by using differential scanning calorimetry and high-temperature in situ x-ray diffractometry. Sample preparation was performed in a special “dry room” with very low humidity. A single phase region (AN III) with no phase transitions to 373 K was observed in the composition range 5 to 20% KN; this is critical for use in air bag gas generators. The high-temperature KN phase (KN I) has a wide range of stability from 20 to 100 wt.% KN. There are one eutectic, two eutectoid, three peritectoid, and one congruent transformations in this phase diagram. Two new nonstoichiometric phases were found at lower temperatures in the mid-composition range between the AN and KN terminal solid solutions. Details of the phase equilibria are presented.     

Topology of potential phase diagrams composed of three chemical elements

A detailed analysis of the topology of two-dimensional isothermal potential phase diagrams for systems composed of three chemical elements is presented. Chemical potentials (or derived properties as activities or partial pressures) of two independent components or their combinations are used as coordinates of such diagrams. The chemical potentials of other species are constant at the given temperature (i.e., stoichiometric, single-species condensed phases, or components of a multicomponent phase of fixed composition). It was shown that only invariant point can change the topology of the diagram. A method for the determination of invariant points is proposed. The set of invariant points is divided into four classes, and each class is demonstrated by a practical example.     

Widmanstatten Structure of Carbon Steels

The effect of the main factors responsible for the formation of Widmanstatten structure in steel, i.e., the size of austenite grains, the cooling rate, and the chemical composition, is investigated. A generalizing diagram illustrating the susceptibility of steels to formation of Widmanstatten structure is presented as a function of their place in the Fe – C phase diagram. The mechanism of crystallization of Widmanstatten structures is considered.     

Hendrik-Willem Bakhuis Roozeboom: Equilibrium and phase topology

Hendrik-Willem Bakhuis Roozeboom (1854–1907) is well known for his applications of the phase rule to the study of heterogeneous equilibrium and its representation using the projection of the P-T-x space into the P-T and T-x planes. Together with van der Waals, he put Gibbs’ abstract studies of phase equilibrium in a language that any chemist could understand and use. The graphical representation of the phenomena of equilibrium had a profound influence in the study of the phase rule and the variety of its applications. With its help, Bakhuis Roozeboom was able to improve significantly the original phase diagram for the system iron-carbon presented by Roberts-Austen. Bakhuis Roozeboom may well be considered one of the pioneers of phase topology.     

Hendrik-Willem Bakhuis Roozeboom: Equilibrium and phase topology

Hendrik-Willem Bakhuis Roozeboom (1854–1907) is well known for his applications of the phase rule to the study of heterogeneous equilibrium and its representation using the projection of the P-T-x space into the P-T and T-x planes. Together with van der Waals, he put Gibbs’ abstract studies of phase equilibrium in a language that any chemist could understand and use. The graphical representation of the phenomena of equilibrium had a profound influence in the study of the phase rule and the variety of its applications. With its help, Bakhuis Roozeboom was able to improve significantly the original phase diagram for the system iron-carbon presented by Roberts-Austen. Bakhuis Roozeboom may well be considered one of the pioneers of phase topology.     

相图及其在钛电解新工艺和钛合金设计中的应用

相图是材料设计的指导书、冶金工作者的地图和热力学数据的源泉。简要概述了近年来相图计算研究的进展,举例说明了Ti-C-O三元系及其亚二元系相图在钛电解新工艺研究中的应用及Ti-Al相图在钛合金设计中的应用,并在文献中列出了新的可靠的合金和化合物相图的来源。最后指出,进一步测定Ti-C-O三元系中TiC-TiO固溶体的精确固溶范围及其与其它相的相关系对于直接电解TiO2提取金属钛新工艺的工业化有重要意义。     

Binary alloy phase diagrams requiring further studies

Binary Alloy Phase Diagrams , 2nd ed. 90Mas, covering ∼3000 systems and ∼2200 phase diagrams, is the most current compilation of binary systems. However, ∼500 of them include thermodynamically unlikely features. These problems are classified into more than 30 groups, and a few typical examples are shown for each group. If a phase diagram shows an improbable feature, it implies that either the phase diagram is erroneous or a very unique phase diagram situation is occurring in the system. In either case, it is worthwhile to investigate the system in more detail.     

Phase equilibria in the Nb-Ga-As system below 1000 °C

The Nb-Ga-As solid state equilibrium phase diagram was determined at 600 °C with the use of powder X-ray diffraction (XRD), electron probe microanalysis (EPMA), and scanning electron microscopy (SEM). No ternary Nb-Ga-As phases were found, and limited solid solubilities were measured in the constituent binary Nb-Ga and Nb-As compounds. The phases GaAs, NbGa₃, and NbAs coexist with each other to form a three-phase equilibrium that dominates the GaAs side of the phase diagram. The phase diagram is in agreement with interfacial reaction studies, which have shown that NbGas and NbAs are the stable phases when Nb thin films are reacted to completion on GaAs.     

Binary alloy phase diagrams requiring further studies

Binary Alloy Phase Diagrams , 2nd ed. 90Mas, covering ∼3000 systems and ∼2200 phase diagrams, is the most current compilation of binary systems. However, ∼500 of them include thermodynamically unlikely features. These problems are classified into more than 30 groups, and a few typical examples are shown for each group. If a phase diagram shows an improbable feature, it implies that either the phase diagram is erroneous or a very unique phase diagram situation is occurring in the system. In either case, it is worthwhile to investigate the system in more detail.     

New investigation of phase equilibria in the system Al-Cu-Si

The phase equilibria and invariant reactions in the system Al-Cu-Si were investigated by a combination of optical microscopy, powder X-ray diffraction (XRD), differential thermal analysis (DTA) and electron probe micro analysis (EPMA). Isothermal phase equilibria were investigated within two isothermal sections. The isothermal section at 500?°C covers the whole ternary composition range and largely confirms the findings of previous phase diagram investigations. The isothermal section at 700?°C describes phase equilibria only in the complex Cu-rich part of the phase diagram. A new ternary compound τ was found in the region between (Al,Cu)-γ(1) and (Cu,Si)-γ and its solubility range was determined. The solubility of Al in κ-CuSi was found to be extremely high at 700?°C. In contrast, no ternary solubility in the β-phase of Cu-Al was found, although this phase is supposed to form a complete solid solution according to previous phase diagram assessments. Two isopleths, at 10 and 40?at.% Si, were investigated by means of DTA and a partial ternary reaction scheme (Scheil diagram) was constructed, based on the current work and the latest findings in the binary systems Al-Cu and Cu-Si. The current study shows that the high temperature equilibria in the Cu-rich corner are still poorly understood and additional studies in this area would be favorable.     

Case-Study Inverse Thermal Analyses of Al2139 Laser Welds

Case study inverse thermal analyses of A12139 laser welds are presented. These analyses employ a numerical methodology that is in terms of analytic and numerical basis functions for inverse thermal analysis of steady state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and their associated software implementations. In addition, these weld temperature histories will be useful for construction of numerical basis functions that can be adopted for inverse analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes.     

Case-Study Inverse Thermal Analyses of Al2198 Laser Welds

In this article, case-study inverse thermal analyses of Al2198 laser welds are presented. These analyses employ a numerical methodology, that is, in terms of analytic and numerical basis functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and their associated software implementations. In addition, these weld temperature histories can be used for construction of numerical basis functions that can be adopted for inverse analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes.     

Ni—Zr二元相图计算

优化和计算了ＮｉＺｒ二元相图。液相用缔合物模型、端际固溶体用替换溶液模型描述，Ｎｉ５Ｚｒ和Ｎｉ１０Ｚｒ７则分别选用了（Ｎｉ）１（Ｎｉ，Ｖａ）４（Ｎｉ，Ｚｒ）１和（Ｎｉ，Ｚｒ）１０Ｚｒ７的亚点阵模型。计算结果与大部分相图和热力学数据相吻合     

Structural energies and phase stability in Ni-Cr alloys

The structural energy difference between stable bcc and metastable fcc structures of Cr are investigated via a detailed first-principles and phenomenological study of the thermodynamic properties of Ni-Cr alloys. Our work focuses on the large discrepancies between the first-principles calculations of structural energies and those obtained from phase diagram studies. For the Ni-Cr system, we find that the existing phase diagram and thermochemical data are insufficient to assess accurately the structural energies of Cr. Electronic structure calculations based on a tight-binding (TB) approximation for the alloy Hamiltonian are used, together with available thermochemical data, to obtain more reliable estimates of structural energies. This research was funded by the National Science Foundation under grant No. DMR 85-10594.