Prediction of the densities of liquid Ni-based superalloys

The molar volume of nickel and the partial molar volumes of Cr, Co, W, Ta, Al, Mo, and Re are computed from the densities of liquid nickel and liquid Ni-based binary alloys measured by the modified sessile drop method (MSDM) and the modified pycnometric method (MPM). The molar volumes of Hf, Nb, and Ti are calculated from the literature density values of these elements. A prediction model for the densities of liquid Ni-based alloys is developed based on the obtained molar/partial molar volumes of the elements in liquid Ni-based alloys. The validity of this model is verified by the density data of liquid Ni-based ternary (Ni-Co-Al), quaternary (Ni-Co-Al-Cr, Ni-Co-Al-Mo, and Ni-Cr-Al-Mo), and commercial alloys measured by both MSDM and MPM. It is also verified by the density values of liquid Ni-based commercial alloys in the literature. It has been shown that the present model can provide reasonable estimation for the density and its temperature dependency of liquid Ni-based alloys. The difference between the predicted value and the measured/cited value is within ±2.5 pct.     

Measurement of liquid permeability in the mushy zones of aluminum-copper alloys

Measurements of liquid permeability in the mushy zones of Al-15.42 pct Cu and Al-8.68 pct Cu alloy samples were performed isothermally just above the eutectic temperature, using eutectic liquid as the fluid. A modified method was developed to determine the specific permeability as a function of time (K _s) during the test from the data collected on these alloys. Factors affecting permeability measurements are discussed. The permeabilities are observed to vary throughout the experiment. This is attributed to microstructural coarsening and channeling that occur in the sample during the experiment. Coarsening rates are determined for the isothermal coarsening tests without fluid flow, and the results are observed to be less than the rates indicated from permeability tests where fluid flow is present. Careful measurement of the volume fraction of liquid (g _L) shows that g _L decreases during the test. The permeability is then related to the microstructure of the sample using the Kozeny-Carman equation. The correlation between the measured K _S, g _L, and specific solid surface area (S _V) improves markedly when compared to previous studies, when microstructural parameters at the initial stage of the test are used.     

Measurement of viscosity,density and surface tension of metal melts

A modified procedure for measuring viscosity, surface tension and density of metallic melts, using a gas bubble viscosimeter, is presented. The principle of measurement is based on the relation between rate of ascent of a gas bubble in the melt and the melt viscosity. The rate of bubble ascent is determined by registering the moment of detachment by pressure measurement in the lance and the moment of arrival of the bubble at the melt surface by video film and an image processing system. The procedure is tested and the limits of its application are determined by comparative measurements on reference metals. After tests on reference metals, measurements are taken of the viscosity, density and surface tension of Al-Cu alloys in the temperature range 960 – 1465 K with copper contents of 12.23 to 58.5%. The relationships between these values and temperature and composition of the melt are investigated, and corresponding approximation formulae derived.     

A new experimental method for determining liquid density and surface tension

A summary concerning the measurement of liquid density relying on the Archimedes principle has been presented, based on which a new effective method with a specially designed bob for determining liquid density has been suggested. The application of this method to ethyl alcohol solution and liquid glycerol, as well as a theoretical error analysis, shows that this new method is significant, because not only can it simplify the procedure of measurement but it can also offer more precise results. Besides, this method can further provide surface tension or contact angle simultaneously. It is expected that this new method will find its application in hightemperature melts. leave from Thermodynamics and Phase Diagram Lab, University of Science and Technology Beijing     

The density and surface tension of dilute liquid Na-In alloys and comparison with liquid Na-Cd alloys

The density and surface tension of five liquid Na-ln alloys, containing between 0.5 and 7 at. pct In, have been measured in the temperature range 170° to 400°C using a maximum bubble pressure technique which incorporates an automatic pressure measuring and recording device. The results are compared with corresponding data reported previously for Na-Cd alloys. The gram-atomic volumes of the Na-ln alloys, calculated from the densities, indicate a substantial contraction on alloying which is, on average, about double that for the Na-Cd alloys and qualitatively consistent with thermodynamic data for the two systems. The surface tension of liquid sodium is increased slightly on adding indium, indicating a lower indium concentration in the surface than in the bulk, in contrast to the marked surface active behavior of cadmium. The surface excess concentrations of indium and cadmium are calculated using Gibbs’ adsorption equation. The surface excess entropy, estimated from the temperature dependence of the surface tension, is compared and briefly discussed for the two systems.     

On the mechanism of serrated grain boundary formation in Ni-based superalloys

Grain boundary serration is studied as a function of cooling rate in a number of Ni-based superalloys, e.g. IN 738, Nimonic 115 and Nimonic 105. The mechanism is related to γ′ precipitation in these alloys and a higher γ′ solvus temperature than the M₂₃C₆ solvus temperature appears to be a prerequisite for the development of serrations. A model based on the grain boundary primary γ′ particle movement causing the displacement of the local grain boundary segment and initiating serrated grain boundary formation has been proposed.     

Surface segregation and surface tension of liquid mixtures

A model has been developed in which surfaces are treated as separate phases with a thickness corresponding to a monolayer. It is argued that the surface tension of liquids is a measure of the excess surface chemical potential of the surface atoms relative to the bulk atoms. Equations for the calculation of the surface composition and surface tension of liquid mixtures are developed. Using only the surface tension and molar volume data of the pure components, excellent correspondence between calculated and experimental surface tension values was obtained. The method was also tested on liquid systems showing immiscibility. The surface coverage calculated from the present model is compared with that calculated using Gibbs adsorption equation. The surface coverage of the solute species increases with increasing solute concentration. However, depending on the surface properties of the system, the excess surface coverage may pass through a maximum value and then decrease with increasing solute concentration.     

The surface tension of liquid nickel-silicon alloys

Summary A study was made of the effect of composition on the surface tension of nickel-silicon alloys with up to 50 at.% Si. An inflection was observed on the isotherm at 28 at.% Si. The unusual shape of the surface tension versus composition curve is ascribed to a microheterogeneous structure of the melt and the presence in the latter of short-range order.     

镍基高温合金真空感应熔炼脱氧

研究了使用CaO坩埚真空感应熔炼Ni-6Cr-2MO-6W-5Co合金时C与Al的脱氧作用.从热力学上计算了Al-O反应的平衡值,计算结果表明,Al-O反应在1773 K能使氧的质量分数降至6×10-6以下.计算了Ni-Al-C-O平衡,结果表明,C与Al2O3的反应在真空感应熔炼条件下可以进行,从而导致合金液精炼期C含量下降值大于脱氧所需值.     

Effect of W on formation and properties of precipitates in Ni-based superalloys

The formation and properties of precipitates in wrought Ni-based superalloys with different W contents during long-term exposure to high temperatures were inves...     

The density and surface tension isotherms of manganese-silicon melts

Summary Density measurements carried out at 1350 and 1550°C confirmed that Mn-Si melts strongly deviate from Raoult's equation. In the range 20–80 at.% Si, the partial-molar volumes undergo a substantial change: ¯V_mn decreases from 9.97 to 6.5 cm³/g-mole, while V_Si increases from 6.60 to 11.06 cm³/g-mole.The surface tension isotherm has a maximum near Mn₂Si-Mn₅Si₃, which attains 1150 ergs/cm², and an inflection point near MnSi. The temperature coefficients of the alloys of this system are practically equal (0.2 ergs/cm²-deg C).     

Serrated grain boundary formation potential of Ni-based superalloys and its implications

The serrated grain boundary formation potential of a large number of conventionally forged, powder processed, and investment cast Ni-based superalloys is reviewed. A mechanism of serrated grain boundary formation by which grain boundaryγ′ particles move and displace the local grain boundary segment is discussed and the prerequisite conditions for its occurrence are highlighted. The practical implications of the serrated grain boundary formation are also discussed. It is suggested that modifying the existing heat-treatment cycles in some investment cast and powder processed Ni-based superalloys would improve their properties. The possibility of minimizing weld cracking in superalloys by creating serrated grain boundaries in the base metal and the heat affected zone is also discussed.     

Effect of slag inclusions on the density and the surface tension of liquid 32G2 and 32G1 steels

The density and the surface tension of liquid 32G2 and 32G1 steels are experimentally studied. Samples are cut from oil-and-gas pipes having different degrees of imperfection. The experimental results are used to find the effect of the defects detected by magnetic-powder and ultrasonic inspection methods on the temperature dependences of the density and the surface tension of liquid 32G2 and 32G1 steels. The results obtained are interpreted in terms of the concepts of a microheterogeneous structure of metallic melts. Microheterogeneities are irreversibly destroyed when the liquid 32G2 steel is heated to 1700°C and the 32G1 steel, to 1750°C.