Abstract
The Ni-base superalloys facing high temperature require further protection against high temperature oxidation. One of the most common methods providing high temperature oxidation resistance is the production of aluminide layers (NiAl-coatings). It is known that the thickness of produced diffusion layer can be controlled by the temperature and time of aluminization process. However, no research on the effect of surface roughness on aluminization kinetics was conducted so far. Then, to elucidate the effect of surface roughness on aluminization kinetics, diffusion layers were obtained by an in-pack aluminization method on the IN 617 alloy with differently prepared surfaces, namely polished, ground using 220 grit SiC paper and 80 grit SiC paper. The obtained results revealed that different surface preparation does not affect the chemical and phase composition of produced layers. However, a strong influence of surface preparation method on aluminide layers thicknesses was observed. Namely, it was found that the increase in substrate surface roughness results in an increase of aluminization kinetics. The dependence between surface roughness and thickness of aluminide layers was found to be logarithmic. Moreover, it was found that the aluminization kinetics is influenced, especially at early stages of the aluminization process.
Highlights
The metallic materials experiencing high temperatures suffer due to high temperature oxidation i.e., they start oxidizing, i.e., the metals react with oxygen to produce so-called oxide scales
The scanning electron microscope (SEM)/energy dispersive spectrometer (EDS) point analysis revealed that the bright precipitates are enriched in Cr and Mo in comparison with a dark grey matrix, which is rich in Ni and Al
Since the thickness of an outer NiAl-coating is higher than 20 μm, measurement of the phases present in the interdiffusion zone (IDZ) is hardly possible for this type of analysis
Summary
The metallic materials experiencing high temperatures suffer due to high temperature oxidation i.e., they start oxidizing, i.e., the metals react with oxygen to produce so-called oxide scales. Repetition of spalling and re-growth of the oxide scale leads to reducing of the component wall thicknesses The latter causes a decrease in mechanical properties of metallic components, which in turn leads to catastrophic failure. Despite the protective properties of chromia scale, chromia forming alloys cannot be successively used at temperatures above 1050 ◦C, due to relatively high volatilization of chromia species [3]. Sreenath et al [24] investigated the influence of surface roughness of low alloyed steel on the thickness of an aluminide layer produced by pack diffusion aluminization. In the work of Dong et al [25], the effect of substrate surface roughness on the thickness of an aluminide layers formed on 316L stainless steel was found. The authors found that the thickness of FeAl-coatings decreased with increasing gradation of SiC paper used for substrate surface preparation prior to the aluminizing process
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