The Effect of Aluminium Content on Thermophysical Properties of Ni-based Superalloys

Abstract

Ni 3 Al is the principal component in the gЈ phase formed in Ni-based superalloys but Ni 3 Cr and Ni 3 Fe can also contribute to the gЈ phase at temperatures below 820 K. Approximate values for the gЈ phase content can be derived from a relationship based on (mass% Al). In a previous publication it was shown that the density in both the solid and liquid alloys was dependent upon the gЈ phase (or Al) contents in the alloy. Consequently, the effect of the gЈ phase on other thermophysical properties (C p , enthalpy, electrical resistivity, thermal conductivity and diffusivity) have been investigated. Linear relations were found between the property values around 300 K and the mass% Al. It was also found that property-temperature relationships were also affected by the gЈ phase (or Al) contents. Although it is known that the strong bonding between Ni and Al atoms affects the density of liquid alloys, we were unable to establish any such relationship for the other properties for liquid alloys because of the large experimental uncertainties in the measurements of these properties. This study has revealed that there is an urgent need for accurate values for C p , electrical resistivity, thermal diffusivity and conductivity for liquid, Ni-based superalloys.KEY WORDS: Ni-based superalloys; gЈ phase; heat capacity; enthalpy; electrical resistivity; thermal conductivity; thermal diffusivity. structural factors in the alloy when compared with other properties. Consequently, it would be expected that other properties may be affected by the gЈ phase content. In this paper we examine the effect of gЈ phase (via the Al content) on other thermophysical properties for solid and liquid Ni-based superalloys. Database and Treatment of DataThermophysical property data have been reported for a number of Ni-based superalloys; the chemical compositions for these alloys are given in Table 1.In this paper all temperatures are expressed as thermody- 3. Thermal Expansion Coefficient (a a ) and Density (r r )The density and the linear thermal expansion coefficient (a) were found to be functions of the gЈ phase content (or Al content).3) The difference in density, Dr 296 ϭr 298 meas Ϫ r 298 ideal , was found to increase with increasing gЈ phase and/or Al contents, (Eqs. (4) and (5), respectively). The thermal expansion coefficients for solid alloys were found to decrease with increasing gЈ phase or Al content as can be seen from Fig. 2. Thermal expansion data were collated and divided into three groups based on the Al content, namely, (0-0.5 mass%), (3-4 mass%) and (5-5.8 mass%). Vol. 46 (2006) The mean values for each group were determined and are shown in Fig. 2. It can also be seen from this figure that the slope of all three curves flatten around 870 K and that the coarsening and dissolution of the gЈ phase is accompanied by an increase in slope for the alloys with high gЈ content (CMSX 4 and Rene 80). Heat Capacity (C p ) and Enthalpy (H T ؊H 298 )The enthalpy and C p are not particularly sensitive to structure and consequently, Kopp's...

Calculation of Thermophysical Properties of Ni-based Superalloys

“…(2) and (3), respectively) were also found to be functions of the Al content. It was also reported 2) that:…”

“…In recent papers 1,2) it was found that: (i) physical properties of Ni-based superalloys were dependent upon the amount of gЈ phase formed. (ii) the amount of gЈ phase can be related to the Al content of the alloy.…”

Surface Tension and Viscosity of the Ni-Based Superalloys LEK94 and CMSX-10 Measured by the Oscillating Drop Method on Board a Parabolic Flight

“…The reduction of the surface tension of the alloys relative to that of pure Ni is seen to result from the presence of Al although the reduction is much less than expected from an ideal mixing. In the bulk phase, the viscosity is dominated by the presence of the heavy alloying elements, while the effect of Al on the viscosity appears to be minimal [58] in comparison to what would be expected from an ideal mixture giving further evidence that in the liquid phase the composition of the free surface of the Ni-based superalloys is different from that of the bulk.…”

“…[9][10][11] Because of the large variety of Ni-based superalloys, predictive models for the values of a variety of thermophysical properties have been developed. [12] The models require reliable input data at selected alloy compositions to allow for proper scaling over a larger concentration range.…”

Thermal Diffusivity Measurements of CMSX-4 Alloy by the Laser-Flash Method

“…where κ is the thermal conductivity in W · m −1 · K −1 , σ e is the electrical conductivity in −1 · m −1 , and T is the absolute temperature in K. By using the Wiedemann-Franz law, the thermal conductivity of CMSX-4 alloy was calculated at room temperature to be 4.755 W · m −1 · K −1 , from the electrical-conductivity value of 65.13×10 4 −1 · m −1 [16]. At 1200 K, the thermal conductivity was 16.554 W · m −1 · K −1 , estimated from the electrical-conductivity value of 226.74 × 10 4 −1 · m −1 [16].…”