Oxidation behaviour of NiAl intermetallics with embedded Cr and Mo

Golnar Geramifard,Camelia Gombola,Peter Franke,Hans J Seifert

doi:10.1016/j.corsci.2020.108956

Abstract

The isothermal oxidation of directionally solidified NiAl-34Cr and NiAl alloys with embedded Cr bar and Mo wire were studied in a thermobalance at 800 °C, 1200 °C and 1300 °C for 50 h (Ar/ 13 vol.% O2). NiAl-Cr showed formation of a continuous Al2O3-Cr2O3 solid solution in the vicinity of the interface of NiAl and Cr in which the composition changed from almost pure Al2O3 near the metal matrix to almost pure Cr2O3 near the gas surface. DS NiAl-34Cr showed more spallation compared to NiAl-Cr. In case of NiAl-Mo, a weight loss was observed due to formation of volatile oxides.

Highlights

In the past few decades, gas turbine manufacturers used Ni-based superalloys to increase the tolerated gas inlet temperature in the com bustion chamber and, to increase the operational effi ciency
At a temperature of 800 ◦C, the mass gain of NiAl and the coarse com posite of NiAl-Cr show parabolic behav iour which indicates that the kinetics of oxide growth is diffusion controlled [20,21,22]
As shown in the processed image from energy dispersive X-ray analysis (EDX) and electron backscatter diffraction (EBSD) in Fig. 16, the results indicate the formation of a mixed oxide in which the composition varies from the metal surface to the gas surface

Summary

Introduction

In the past few decades, gas turbine manufacturers used Ni-based superalloys to increase the tolerated gas inlet temperature in the com bustion chamber and, to increase the operational effi ciency. The NiAl has a higher melting temperature than the solidus tem perature of Ni-based superalloys. Directionally solidified metal-matrix composites of NiAl alloy, in which fibres of chromium or molybdenum are embedded, show much better mechanical properties than pure NiAl [3,4,5,6,7,8,9]. This makes these composites candidates for high-temperature applications in turbines since they exhibit good thermodynamic stability and chemical compatibility between the NiAl matrix and the strengthening fibres

Methods

Results

Conclusion