Thermophysical properties for the solid and liquid phases of several Ni based superalloys (CMSX-4, CMSX-10, CM186LC, IN 738 and Rene 80) have been measured. The following properties were measured: heat capacity and enthalpy, thermal expansion coefficient and density, thermal diffusivity, viscosity and surface tension. Analysis of these measurements showed that that γ′ phase (Ni3Al) affected the values for the following properties; C p, enthalpy, electrical resistivity, thermal diffusivity and conductivity. Relationships have been identified between properties and the γ′ phase content (which can be represented by mass% Al in the alloy). These relations were then used to calculate property values of the alloys from chemical composition. Other relations were developed to estimate the viscosities and surface tensions of Ni based superalloys. The predicted property values were found to be in good agreement with the measured values.

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Measurement and estimation of thermophysical properties of nickel based superalloys

Thermal conductivity data for molten metals, published since the review of Touloukian et al. in 1970, are collated and evaluated. Where possible recommended values are given. Where availability of data permits, the Wiedemann-Franz-Lorenz equation relating electrical and thermal conductivities has been assessed. It has been found to be valid for most pure metals at their melting point.

Thermal conductivities of molten metals: Part 1 Pure metals

Enthalpy, resistivity, density, specific heat capacity, and normal spectral emissivity as a function of temperature of Inconel 718 alloy were measured by a fast resistive pulse heating technique up into the liquid phase, thus obtaining data on thermal conductivity and thermal diffusivity. The high-speed measurements are compared with results of quasistatic measurements of specific heat obtained by differential-scanning calorimetry and expansion measurements by dilatometry.

Thermophysical properties of solid and liquidInconel 718 Alloy

Laser powder bed fusion (LPBF) has broad application prospects due to its high fabrication accuracy and excellent performance, but the dynamic mechanical properties of LPBF components are relatively low due to defects of the melt track such as protrusions and depressions, whose generation mechanisms remain unclear. In this work, we investigate the correlation between the ex situ melt track properties and the in situ high-speed, high-resolution characterization. We correlate the protrusion at the starting position of the melt track with the droplet ejection behaviour and backward surging melt. We also reveal that the inclination angles of the depression walls are consistent with the ejection angles of the backward-ejected spatter. Furthermore, we quantify the vapour recoil pressure by in situ characterization of the deflection of the typical forward-ejected spatter. Our results clarify the intrinsic correlation of the melt track properties, which is important for the stable LPBF formation with few defects.

Correlation between forming quality and spatter dynamics in laser powder bed fusion

Reliable thermophysical data of Ni-based superalloys are needed for the mathematical modelling of solidification in casting applications. This paper derives equations and procedures to calculate the following properties of these alloys from chemical composition of the alloy: the γ′ phase content, liquidus and solidus temperatures, density and thermal expansion coefficient, heat capacity and enthalpy, electrical resistivity, thermal diffusivity and conductivity, viscosity, surface tension and contact angle. Estimates are also for the diffusion coefficient and emissivity. This work has revealed an urgent need for reliable property measurements on liquid Ni-based alloys for the following: heat capacity, electrical resistivity, thermal diffusivity and conductivity, emissivity and diffusion coefficients.

Calculation of Thermophysical Properties of Ni-based Superalloys

Data on the physical properties of alloys at high temperatures are urgently needed for the mathematical modeling of high-temperature processes such as casting, welding, secondary refining, dip melting, spray forming, and metal powder production. Data are required for those properties which are involved in heat and fluid flow in high-temperature processes. Levitated drop methods have been adopted to measure the surface tensions, densities, and enthalpies of commercial alloys, and rapid, transient methods have been developed to measure thermal conductivities to avoid the problem of convection. The results obtained for the properties of commercial alloys for the liquid and “mushy” states are discussed.

A. J. Barnicoat

Papers

The physical properties of alloys in the liquid and ``mushy'' states