Kinetic study on NaF-activated pack-aluminizing of pure titanium at 950–1100 °C

Zarchi, H.R. Karimi; Soltanieh, M.; Aboutalebi, M.R.; Guo, Xinyun

doi:10.1016/s1003-6326(14)63277-5

“…Figure 6 presents a schematic diagram illustrating the mechanism of activated atom generation. In the pack cementation process, the rise in temperature leads to the conversion of NaF into a gaseous state and decomposition [36]:…”

Section: Gas Phase Reactionmentioning

confidence: 99%

Formation Mechanism of Ti–Si Multi-Layer Coatings on the Surface of Ti–6Al–4V Alloy

Zhao,

Liang,

Zhang

et al. 2024

Coatings

0

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Titanium alloys are widely used in aerospace applications due to their high specific strength and exceptional corrosion resistance. In this study, a silicide coating with a multi-layer structure was designed and prepared via a pack cementation process to improve the high-temperature oxidation resistance of titanium alloy. A new theory based on the Le Chatelier’s principle is proposed to explain the generation mechanism of active Si atoms. Taking the chemical potential as a bridge, a functional model of the relationship between the diffusion driving force and the change in the Gibbs free energy of reaction diffusion is established. Experimental results indicate that the depth of the silicide coating increases with the siliconization temperature (1000–1100 °C) and time (0–5 h). The multi-layer coating prepared at 1075 °C for 3 h exhibits a thick and dense structure with a thickness of 23.52 μm. This coating consists of an outer layer of TiSi2 (9.40 μm), a middle layer of TiSi (3.36 μm), and an inner layer of Ti5Si3 (10.76 μm). Under this preparation parameter, increasing the temperature or prolonging the holding time will cause the outward diffusion flux of atoms in the substrate to be much larger than the diffusion flux of silicon atoms to the substrate, thus forming pores in the coating. The calculated value of the diffusion driving force FTiSi = 2.012S is significantly smaller than that of FTiSi2 = 13.120S and FTi5Si3 = 14.552S, which perfectly reveals the relationship between the thickness of each layer in the Ti–Si multi-layer coating.

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“…The Fe-Al intermetallic phases, FeAl 3 and Fe 2 Al 5, were detected clearly due to the powder pack contained high Al amount up to 25 wt.% [16][17][18]. Also, the aluminized layers increase with increasing aluminizing time taking into account diffusion theory [19][20][21][22][23]. The squared thickness of aluminized layer as a function of time can be explained in Eq.…”

Section: Non-deep Rolled Austenitic Stainless Steel Aisi 304mentioning

confidence: 99%

Diffusion enhancement of low-temperature pack aluminizing on austenitic stainless steel AISI 304 by deep rolling process

YUTANORM¹,

JUIJERM²

2021

km

1

0

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The deep rolling process is a mechanical surface treatment which plastically deforms only the surface and near-surface regions. The deep rolled AISI 304 austenitic stainless steel has been investigated to illustrate the near-surface plastic deformation effect on the aluminium diffusion rate in the low-temperature pack aluminizing process. Near-surface properties such as residual stresses and full width at half maximum (FWHM) values were measured using the X-ray diffractometer (XRD). The deep rolled, and non-deep rolled specimens were aluminized using powder pack method at the relatively low temperature of 550 • C for about 2-8 h. A scanning electron microscope (SEM) with energy dispersive X-ray spectrometer (EDS) and XRD were used to characterize the surface layers. It was found that the deep rolled condition shows the higher diffusion coefficient as compared to the non-deep rolled condition. Finally, it can be mentioned that the deep rolling process can enhance the diffusion rate of the pack aluminizing treatment at the temperature of 550 • C.

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“…The Fe-Al intermetallic phases, FeAl 3 and Fe 2 Al 5, were detected clearly due to the powder pack contained high Al amount up to 25 wt.% [16][17][18]. Also, the aluminized layers increase with increasing aluminizing time taking into account diffusion theory [19][20][21][22][23]. The squared thickness of aluminized layer as a function of time can be explained in Eq.…”

Section: Non-deep Rolled Austenitic Stainless Steel Aisi 304mentioning

confidence: 99%

Diffusion enhancement of low-temperature pack aluminizing on austenitic stainless steel AISI 304 by deep rolling process

Yutanorm¹,

Juijerm²

2016

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The deep rolling process is a mechanical surface treatment which plastically deforms only the surface and near-surface regions. The deep rolled AISI 304 austenitic stainless steel has been investigated to illustrate the near-surface plastic deformation effect on the aluminium diffusion rate in the low-temperature pack aluminizing process. Near-surface properties such as residual stresses and full width at half maximum (FWHM) values were measured using the X-ray diffractometer (XRD). The deep rolled, and non-deep rolled specimens were aluminized using powder pack method at the relatively low temperature of 550 • C for about 2-8 h. A scanning electron microscope (SEM) with energy dispersive X-ray spectrometer (EDS) and XRD were used to characterize the surface layers. It was found that the deep rolled condition shows the higher diffusion coefficient as compared to the non-deep rolled condition. Finally, it can be mentioned that the deep rolling process can enhance the diffusion rate of the pack aluminizing treatment at the temperature of 550 • C.

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Kinetic study on NaF-activated pack-aluminizing of pure titanium at 950–1100 °C

Cited by 8 publications

References 27 publications

Formation Mechanism of Ti–Si Multi-Layer Coatings on the Surface of Ti–6Al–4V Alloy

Formation Mechanism of Ti–Si Multi-Layer Coatings on the Surface of Ti–6Al–4V Alloy

Diffusion enhancement of low-temperature pack aluminizing on austenitic stainless steel AISI 304 by deep rolling process

Diffusion enhancement of low-temperature pack aluminizing on austenitic stainless steel AISI 304 by deep rolling process

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