Total hemispherical emissivity of Inconel 718

Abstract

Total hemispherical emissivity for Inconel 718 was measured in anticipation of its application in Very High Temperature Gas Reactors (VHTRs). A majority of current emissivity data for Inconel 718 is in the form of spectral measurements. The data presented here were obtained with an experimental apparatus based on the standard ASTM C835-06 for total hemispherical emittance. Measurements of Inconel 718 were made for four different surface types including: (i) 'as-received' from the manufacturer (ii) oxidized in air and humidified helium, (iii) sandblasted with aluminum oxide powder, and (iv) with a thin coating of nuclear grade graphite powder (grade NGB-18). The emissivity for the 'as-received' sample ranged from 0.21 to 0.28 in the temperature interval from 760 K to 1275 K. Oxidation in air at 1073 K resulted in an increase in emissivity into the range from 0.2 at 650 K to 0.52 at 1200 K. There was no dependence on the oxidation times studied here. Oxidation with humidified helium at 1073 K produced less of an increase in emissivity than the oxidation in air but there was an increase up to the range from 0.2 at 600 K to 0.35 at 1200 K. Sandblasting of Inconel 718 was also observed to increase the emissivity up to the range from 0.43 at 780 K to 0.53 at 1270 K when 60 grit sized powder was used and up to the range from 0.45 at 683 K to 0.57 at 1267 K when 120 and 220 grit sized powders were used. Coating of graphite powder onto the 'as-received' Inconel 718 showed no increase in the emissivity whereas the coating of graphite powder onto the 220 grit sandblasted Inconel 718 did show an increase in emissivity up to the range from 0.60 at 650

Strategies for Increasing the Productivity of Pulsed Laser Cladding of Hot-Crack Susceptible Nickel-Base Superalloy Inconel 738 LC

“…This result is in accordance with Ref. [19,20]. The emissivity curve was also claimed for HS 282 in the numerical simulation.…”

Microstructure Evolution of Selective Laser Melted Inconel 718: Influence of High Heating Rates

“…The analysis was based on a one-dimensional heat conduction equation for a round bar of infinite length and used direct local temperature measurements corroborated by microstructural observations, as in the present study. Using the above model and considering similar physical properties for IN718 and SLM IN718 (e.g., thermal conductivity, thermal convection, and emissivity [52]) the radial thermal gradient from the surface to center was estimated for heating rates of 100 • C/s and 200 • C/s and the results are reported in Figure 11. In this figure, (∆T) represents the difference between the temperature applied to the sample surface (1000 • C, measured by the thermocouple) and the center of the sample during the heating cycle defined in the radial direction (based on the model proposed in reference [49]).…”

“…On the basis of the above discussion, the diffusion distance (x) of Nb from the Laves phase in the interdendritic regions to the γ-matrix (core of the dendrites) is controlled by t e which can be determined using Fick's second law, x = √ D e t e . In the above equations, the diffusion coefficient of Nb in Ni was calculated according to the following equation, obtained from the literature [30,[52][53][54][55]:…”

Scaling effects of a novel solar receiver for a micro gas-turbine based solar dish system

“…For this analysis the austenitic superalloy 253MA is chosen for the metallic components of the receiver due its operating temperature of up to 1150°C, its machinability, weldability, and availability for the manufacturing of a prototype. As no absorptivity values are available for this superalloy it is estimated by the total hemispherical emissivity of fully oxidized Inconel 718 for temperature in the region of 1000°C as 90% [53] [54]. Rays that are absorbed on the absorber side wall contribute to the surface heat source ̇ whereas the rays reflected continue their path and are subsequently absorbed inside the volume or pass through the absorber altogether.…”