Consequences of Different Mechanical Surface Preparation of Ni-Base Alloys during High Temperature Oxidation.

Wojciech J Nowak,Krzysztof Siemek,Bartek Wierzba,Barbara Kościelniak,Kamil Ochał

doi:10.3390/ma13163529

Abstract

The influence of surface roughness on its high temperature oxidation for an Ni-base superalloy was studied using laser profilometry, atomic force microscopy, mass change measurements, glow-discharge optical emission spectrometry, scanning electron microscopy, X-ray diffraction, and positron annihilation methods. The isothermal and cyclic air oxidation tests were performed at 1000 °C and showed dependence of oxidation behavior on surface roughness. Smoother surfaces oxidation resulted in the formation of a multilayered oxide scale consisting of NiO, Cr2O3, and internally oxidized Al2O3 while a rougher surface formed protective Al2O3 scale. The factors responsible for different oxidation behaviors were determined as higher concentration of vacancies and increased residual stresses in the near-surface region of studied alloys.

Highlights

The materials used for the production of machinery elements working at high temperature, e.g., in gas turbines of jet engines or stationary gas turbines, have to fulfil a number of outstanding properties such as suitable ductility at low temperature, high creep strength, and high oxidation resistance over a wide range of operating temperatures, environments, and loading conditions
Investigation of commercial Ni-base superalloy was performed to illustrate the effect of surface preparation method on its oxidation behavior during high temperature exposure while high purity ternary Ni-Cr-Al model alloy was used to elucidate the factors responsible for different oxidation behaviors observed on commercial alloy
To avoid the influence of anisotropy on surface roughness parameters, Ra values were calculated using the profile taken in a direction perpendicular to the grinding direction

Summary

Introduction

The materials used for the production of machinery elements working at high temperature, e.g., in gas turbines of jet engines or stationary gas turbines, have to fulfil a number of outstanding properties such as suitable ductility at low temperature, high creep strength, and high oxidation resistance over a wide range of operating temperatures, environments, and loading conditions. One type of material meeting such requirements is the Ni-base superalloys family. Using metallic alloys at high temperature results in their degradation due to high temperature corrosion, mainly by the reaction between the metal and oxygen [1]. The high temperature oxidation resistance of used alloy is of major importance in terms of the component lifetime. According to Giggins and Pettit [2], the alloys can be classified into three types, namely NiO, Cr2 O3 (chromia), and Al2 O3 (alumina) forming alloys. Considering the oxidation kinetics, the most protective oxide scale is an alumina scale [3]

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