Design model for diffusion coatings formed via pack cementation

2013 ◽  
Vol 65 (3) ◽  
pp. 312-318 ◽  
Author(s):  
A. Naji ◽  
M. C. Galetz ◽  
M. Schütze
Keyword(s):  
Pack Cementation ◽  
Design Model ◽  
Diffusion Coatings

scholarly journals Microstructural investigation of the coatings prepared by simultaneous aluminizing and siliconizing process on γ-TiAl

2019 ◽  
Vol 55 (2) ◽  
pp. 217-225
Author(s):  
S. Nouri ◽  
M. Azadeh
Keyword(s):  
Powder Mixture ◽  
Pack Cementation ◽  
Chemical Compositions ◽  
Powder Mixtures ◽  
Microstructural Investigation ◽  
Diffusion Coatings ◽  
Sequential Mechanism ◽  
First Time ◽  
Pack Cementation Process ◽  
Segregated Structure

In this research, formation of aluminide/silicide diffusion coatings on ?-TiAl[Ti-48Al-2Nb?2Cr (at.%)] alloy using gasphase diffusion pack cementation process has been investigated. The application of powder mixtures with various chemical compositions in the pack cementation process performed at 1000oC for 6 hours in order to achieve simultaneous diffusion of Al and Si, showed that the composition of the powder mixture could have a significant effect on the structure and thickness of the aluminide/silicide coatings. The identification and analysis of aluminide/silicide microstructures formed as a result of simultaneous diffusion of Al and Si, which was comprehensively and qualitatively done for the first time in this study, showed that the sequential mechanism is dominant in the formation of the above-mentioned coatings. Furthermore, Kirkendall phenomenon and volumetric changes caused by the formation of Ti5Si3 and Ti5Si4, were considered as the two dominant mechanisms in the formation of porous segregated structure in these coatings. In this study, the effect of decreasing the activity of Si, through two approaches of reducing the amount of Si in the powder mixture and using Al- 20wt.%Si alloyed powder instead of pure Al and Si depositing elements, on the microstructural modification coatings was investigated. The results showed that reducing the Si activity at the surface of the coating and, consequently, reducing the flux of active silicon atoms (JSi), has a significant effect on the formation of coating with an ideal structure.

Aluminide and silicide diffusion coatings by pack cementation for Nb-Ti-Al alloy

2020 ◽  
Vol 389 ◽  
pp. 125675
Author(s):  
N. Chaia ◽  
P.L. Cury ◽  
G. Rodrigues ◽  
G.C. Coelho ◽  
C.A. Nunes
Keyword(s):  
Pack Cementation ◽  
Al Alloy ◽  
Diffusion Coatings

scholarly journals Formation Mechanism of Aluminide Diffusion Coatings on Ti and Ti-6Al-4V Alloy at the Early Stages of Deposition by Pack Cementation

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3097
Author(s):  
Hailiang Du ◽  
Ning Tan ◽  
Li Fan ◽  
Jiajie Zhuang ◽  
Zhichao Qiu ◽  
...  
Keyword(s):  
Outer Layer ◽  
Aluminide Coating ◽  
Energy Dispersive Spectrometer ◽  
Pack Cementation ◽  
X Ray Diffraction ◽  
Diffusion Coatings ◽  
Early Stages ◽  
Outward Migration ◽  
Kinetics Of ◽  
Precision Balance

The diffusion coatings were deposited on commercially pure Ti and Ti-6Al-4V alloy at up to 1000 °C for up to 10 h using the pack cementation method. The pack powders consisted of 4 wt% Al (Al reservoir) and 4 wt% NH4Cl (activator) which were balanced with Al2O3 (inert filler). The growth kinetics of coatings were gravimetrically measured by a high precision balance. The aluminised specimens were characterised by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). At the early stages of deposition, a TiO2 (rutile) scale, other than aluminide coating, was developed on both materials at <900 °C. As the experimental temperature arose above 900 °C, the rutile layer became unstable and reduced to the low oxidation state of Ti oxides. When the temperature increased to 1000 °C, the TiO2 scale dissociated almost completely and the aluminide coating began to develop. After a triple-layered coating was generated, the coating growth was governed by the outward migration of Ti species from the substrates and obeyed the parabolic law. The coating formed consisted of an outer layer of Al3Ti, a mid-layer of Al2Ti and an inner layer of AlTi. The outer layer of Al3Ti dominated the thickness of the aluminide coating.

Diffusion Layers with Ti and Ti+Al Formed on 316L Austenitic Steel by a Pack Cementation Procedure

2011 ◽  
Vol 312-315 ◽  
pp. 13-19 ◽  
Author(s):  
Iulia Mirela Britchi ◽  
Mircea Olteanu ◽  
Niculae Ene ◽  
Petru Nita
Keyword(s):  
Activation Energy ◽  
Powder Mixture ◽  
Pack Cementation ◽  
X Ray Diffraction ◽  
Powder Mixtures ◽  
X Ray ◽  
Diffusion Coatings ◽  
Diffusion Layers ◽  
316L Steel ◽  
Temperature Activation

Pack cementation procedure implies the use of a powder mixture containing the diffusive elements, which in our case are either Ti or Ti+Al, Al2O3 and NHCl as activator. In the case of titanizing the powder mixture contained 77% in weight Ti, while for alumino-titanizing Al/Ti = 1/5 ratio was employed. NH4Cl content was 3% in weight in all cases. Aluminium additions to the powder mixtures led to a decrease of the process temperature. Activation energy for the aluminizing of austenitic 316L steel is 73.87 KJ/mol, much smaller than for the titanizing, 257.86 KJ/mol. Activation energy for alumino-titanizing, in the same conditions, is 146.01 KJ/mol. All diffusion coatings, in the Ti – 316L and Ti+Al – 316L couples are formed of two layers having different structures and compositions. All couples were investigated by optical microscopy, electron microscopy (SEM and EDX), X-ray diffraction and microhardness trials.

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