Thermodynamic characteristics and numerical modeling of internal nitridation of nickel base alloys

Abstract

Kinetics and thermodynamics of the process of internal nitridation of various nickel-base alloys have been investigated in oxygenfree nitrogen atmospheres. Furthermore, the influence of formation and spalling of a protective oxide scale on the internal nitridation behavior of the alloys was studied by isothermal and cyclic oxidation tests in air. In general, nitridation kinetics of model nickel-base alloys of the system Ni-Cr-Ti was found to obey a parabolic rate law indicating that the nitridation process is diffusion-controlled. The temperature dependence of the nitridation rate constants is well described by an equation of the Arrhenius type. A thermodynamic calculation of the Ni-Cr-Ti-Al-N system was used to determine the nitrogen solubility in respective alloys as a function of temperature and alloy composition. The results show that a higher chromium content gives rise to an increase in the nitrogen solubility of Ni-Cr-Ti alloys leading to an increased nitridation rate in accordance with the experimental observations. From the calculated values for the nitrogen solubility, the diffusion coefficients of nitrogen were assessed using Wagner's classical theory of internal oxidation. A computer model of internal nitridation was developed that combines a commercial thermodynamic software (ChemApp) with a finite-difference diffusion calculation. It was found that this model describes the internal nitridation process in reasonable agreement with the experimental results and allows to treat the case of simultaneous formation of different nitrides. The dependence of internal nitridation behavior on spalling and cracking of the oxide was incorporated into the simulation on the basis of simple assumptions showing that this calculation method successfully applies also to complex internal corrosion processes.

Properties of Alumina/Chromia Scales in N2-Containing Low Oxygen Activity Environment Investigated by Experiment and Theory

“…Here, the high thermodynamic stability of alumina relative to AlN [4] is emphasized, making Al 2 O 3 -forming alloys useful also in low oxygen activity nitriding environments. However, internal nitridation is an important mode of corrosion for Al 2 O 3 -forming alloys in environments where low oxygen activity (low dew point) is combined with a high availability of nitrogen-containing species [5]. For example, FeCrAl's have been successful in some alloy heat treatment applications [6] but were reported to suffer nitridation in very dry N 2 ?…”

Influence of Fe/Cr on nitrogen doped carbon nanotube growth

“…Low levels of Cr doping may be a way to produce heterogeneous high concentration nitrogen doped tubes. We note that Cr doping Ni is known to both increase its nitrogen solubility and diffusivity [12].…”

Internal corrosion of engineering alloys: Experiment and computer simulation

“…7 representing results obtained Fig. 7 Arrhenius-type plot of the maximum dissolved N concentration in various Ni-Cr alloys versus the reciprocal temperature [19] Fig. 6 (a) Internal nitridation of Ni-5wt.%Cr-2wt.%Ti and Ni-20wt.%Cr-2wt.%Ti alloys (100 h, 1100°C, N 2 ) and (b) corresponding nitridation constants k N (according to the internal oxidation constant in Eq 7) [17] Section I: Basic and Applied Research by thermodynamic calculations using the commercial software ChemSage/FactSage (GTT Technologies, Herzogenrath, Germany) in combination with a database for the system Ni-Cr-Al-Ti-N.…”