Oxidation of Inconel 718 in Air at Temperatures From 973k to 1620k.

Abstract

As part of the APT project, it was necessary to quantify the release of tungsten from the APT spallation target during postulated accident conditions in order to develop accident source terms for accident consequence characterization. Experiments with tungsten rods at high temperatures in a flowing steam environment characteristic of postulated accidents revealed that considerable vaporization of the tungsten occurred as a result of reactions with the steam and that the aerosols which formed were readily transported away from the tungsten surfaces, thus exposing fresh tungsten to react with more steam. The resulting tungsten release fractions and source terms were undesirable and it was decided to clad the tungsten target with Inconel718 in order to protect it from contact with steam during an accident and mitigate the accident source term and the consequences.As part of the material selection criteria, experiments were conducted with Inconel 718 at high temperatures to evaluate the rate of oxidation of the proposed clad material over as wide a temperature range as possible, as well as to determine the high-temperature failure limit of the material. Samples of Inconel718 were inserted into a preheated furnace at temperatures ranging from 973 K to 1620 K and oxidized in air for varying periods of time. After oxidizing in air at a constant temperature for the prescribed time and then being allowed to cool, the samples would be reweighed to determine their weight gain due to the uptake of oxygen. From these weight gain measurements, it was possible to identify three regimes of oxidation for Inconel 718: a lowtemperature regime in which the samples became passivated after the initial oxidation, an intermediate-temperature regime in which the rate of oxidation was limited by diffusion and exhibited a constant parabolic rate dependence, and a high-temperature regime in which material deformation and damage accompanied an accelerated oxidation rate above the parabolic regime.At temperatures below 1173 K, the rate of oxidation of the Inconel 718 surface was found to decrease markedly with time; the parabolic oxidation rate coefficient was not a constant but decreased with time. This was taken to indicate that the oxide film on the surface was having a passivating effect on oxygen transport through the oxide to the underlying metal. For temperatures in the range 1173 K to 1573 K, the time-dependent rate of oxidation as determined once again by weight-gain measurements was found to display the classical parabolic rate behavior, indicating that the rate of transport of reactants through the oxide was controlled by diffusion through the growing oxide layer. Parabolic rate coefficients were determined by least-squares analysis of time

High temperature oxidation of IN 718 manufactured by laser beam melting and electron beam melting: Effect of surface topography

“…In aircraft applications, this material is commonly employed at operating temperatures below 650°C [8]. During air oxidation between 700°C and 950°C [42,43], transient oxidation occurred during the first 24 h of the experiment, followed by slow oxidation kinetic during steady state. Between 900°C and 1300°C [42], oxidation kinetics have been shown to follow a parabolic rate dependence, ranging from 6.3 × 10 −6 mg².…”

“…Above 1270°C, the oxidation became catastrophic, the oxide layer can be spalled easily. At temperature above 1300°C, the material was rapidly consumed [42]. Furthermore, looking at oxidation layer composition, small amounts of TiO 2 , MnCr 2 O 4 spinel [43], and CrNbO 4 [44] were found during the early stages of the 900°C air oxidation test.…”

Thermal Management at Hypersonic Leading Edges

“…212 ________________________________________________________________________ standoff distance of 146mm, significant deterioration at the tip of the evacuated sample was observed due to high temperature oxidation [134]. As a result, smaller standoffs were not attempted.…”

In-Service Oxidation and Microstructural Evolution of a Nickel Superalloy in a Formula 1 Car Exhaust

“…To understand such effects, previous studies on this and similar alloys have examined oxidation and surface degradation behaviour using a variety of model exposures [6][7][8][9][10][11]. The benefits of protective coatings have also been studied [12,13], along with the effects of corrosion following exposure to salts simulating gas turbine [14] and fuel cell [15] operation.…”