• Journal of the Korean Society for Heat Treatment
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• v.8 no.1
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• pp.3-11
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• 1995

A theoretical model which combines gaseous transport and solid state diffusion was used to study aluminide coating process by pack cementation. The aluminide coatings were applied in the high activity pack containing $NH_4Cl$ activator with Ni substrate under argon atmosphere. On the basis of the process conditions, the suggested model allows the surface composition, the growth rate of coating layers and the aluminium concentration profiles in coatings to be calculated. In the case of $NH_4Cl$ activator, careful consideration was required in the analysis, because activator contains nitrogen and hydrogen as well as halogen element to activate the pack. A good agreement is obtained between the theoretical predictions and the experimental results.

• Korean Journal of Materials Research
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• v.28 no.3
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• pp.135-141
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• 2018

Stainless steel is being used in various industries such as automobile and aerospace for its cheap manufacturing cost and excellent mechanical properties. However, stainless steel failed to stably protect a specimen with a $Cr_2O_3$ protective layer at temperatures above $1000^{\circ}C$. Thus, improving the high temperature flame resistance of the specimen through additional surface coating was needed. In this study, multilayer coatings of YSZ and $Al_2O_3$ were performed on SUS 304 specimens using pack cementation coatings and thermal plasma spray. The multilayer coated specimen showed enhanced thermal properties due to the coated layers. The microstructures and phase stability are discussed together with flame conditions at $1350^{\circ}C$.

• Journal of the Korean institute of surface engineering
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• v.20 no.3
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• pp.95-105
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• 1987

For the purpose of improving the hot corrosion resistance of Ni-base superalloy, Inconel 600, aluminide and chromium-aluminide coatings by pack cementation process were studied. The morphology of these coatings is dependent on the type of process employed. And their overall composition depends on the composition of the base alloy and on the nature of the cement. Therefore the different aluminide and chromium-aluminide coatings obtained on a superalloy do not possess the same resistance to oxidation and hot corrosion. The mechanisms governing the formation of the coatings and the composition of the coating were varied by pack composition and temperature, and cyclic hot corrosion resistance of the auluminide coating formed by one-step process was inferior to that of the coating formed by two-step process. and Cr-Al composite coating showed good resistance for cyclic hot corrosion.

• Journal of the Korean institute of surface engineering
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• v.28 no.3
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• pp.152-163
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• 1995

A theoretical model which combines gaseous transport and solid state diffusion with the multi-component equilibrium at the gas/pack and gas/coating interfaces was used to study the kinetics of diffusion aluminide coating. The diffusion aluminide coatings were applied by pack cementation with Ni substrate under argon atmosphere in the high activity and the low activity pack containing $NH_4CL$ or $AlF_3$ activator. On the basis of the process conditions, the suggested model allows the surface composition, the growth rate of coating layers and the aluminium concentration profiles in coatings to be calculated. In the case of $NH_4$Cl activator, careful consideration was required in the analysis, because activator contains nitrogen and hydrogen as well as halogen element to activate the pack. A good agreement is obtained between the theoretical predictions and the experimental results.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.2
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• pp.129-138
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• 1994

The purpose of this study is to clarify the influence of the reaction temperature and $AlCl_3$ content on the aluminide coating formation on Ni-based superalloy IN713C in CVD process and to compare its throwing power with that of Pack Cementation process. Aluminide coating was formed by CVD in hot-wall stainless tube reactor from an $AlCl_3-H_2$ mixture in the temperature range $850{\sim}1050^{\circ}C$. At reaction temperature $850^{\circ}C$, the coating thickness and the content of aluminium at the surface were increased as $AlCl_3$ heating temperature was raised. At reaction temperature $1050^{\circ}C$, they were not influenced by the variation of $AlCl_3$ heating temperature. When $AlCl_3$ heating temperature was fixed $125^{\circ}C$, the phases of the coatings were varied from $Ni_2Al_3$ to Al-rich NiAl and to Ni-rich NiAl with the reaction temperature. Therefore, in this study the reaction temperature has been found to be a major factor in determining the phase formed in CVD process. The throwing power of CVD was superior to that of Pack Cementation.

• Journal of the Korean institute of surface engineering
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• v.51 no.5
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• pp.297-302
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• 2018

The important drawback of hardware fasteners consisted of 304 stainless steel (STS) is a frequent galling caused by a combination of friction and adhesion between the sliding surface. To improve the anti-galling effect, Sn-Al coatings by a thermal diffusion have been developed. The thermal diffusion by pack cementation with an $AlCl_3$ activator at $250^{\circ}C$ for 1 hour produced an Sn-Al alloy coating layer with an average thickness of $9.9{\pm}0.5{\mu}m$ on the surface of 304 STS fasteners. Compared with the galling frequency of the 304 STS fasteners, Sn-Al coatings on the surface of 304 STS fasteners demonstrated about 2.8-time reduction of the galling frequency.

• Journal of the Korean institute of surface engineering
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• v.20 no.2
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• pp.60-73
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• 1987

For the purpose of improving the cyclic oxidation resistance of Ni-base superalloy, Inconel 600, aluminide coating methods are studied. The formation rate of aluminide coating layers is measured as a function of time and pack composition to find out the optimum coating condition. The evaluation of cyclic oxidation is established by the change in weight, the microphotography and EPMA of cross sectional area during $200^{\circ}C\;{\leftrightarrow}\;950^{\circ}C\;and\;200^{\circ}C\;{\leftrightarrow}\;1100^{\circ}C$, respectively. The thickness of coating layer and weight gains are parabolic behavior in propotion to time and Al contents. In pack of low aluminum contents, 2 wt%, however, weight gain is decreased when activator, $NH_4Cl$ is higher than 2 wt%. The cyclic oxidation resistance of the coating carried out at 1100$^{\circ}C$ are superior to those of the coating diffusion-treated after pack cementation at 800$^{\circ}C$. Aluminide oxide, which is formed in external scale, is barrier to the cyclic oxidation.

• Corrosion Science and Technology
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• v.7 no.4
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• pp.233-236
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• 2008

Halide-activated pack cementation was utilized to deposit B-doped silicide coating. The pack powders were consisted of $3Wt.c/oNH_4Cl$, 7Wt.c/oSi, $90Wt.c/oAl_2O_3+TiB_2$. B-doped silicide coating was consisted of two layers, an outer layer of $NbSi_2$ and an inner layer of $Nb_5Si_3$. Isothermal oxidation resistance of B-doped silicide coating was tested at $1250^{\circ}C$ in static air. B-doped silicide coating had excellent oxidation resistance, because continuous $SiO_2$ scale which serves as obstacle of oxygen diffusion was formed after oxidation.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.211-217
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• 2016

Boride coating applied on steam turbine parts of power plants has provided good particle erosion resistance under temperature of $550^{\circ}C$, but it isn't able to protect the parts effectively any more in ultra super critical (USC) steam turbine which is being operated up to temperature of $650^{\circ}C$. To ensure stable durability for USC steam turbine parts, an alternative coating replacing boride coating should be developed. In this study, multi-component boride coatings containing elements such as chromium (Cr) and vanadium (V) were formed on base metal (B50A365B) using thermochemical treatment method called by pack cementation. The thermochemical treatments involve consecutive diffusion of boron(B) and Cr or/and V using pack powders containing diffusion element sources, activators and diluents. The top layer of Cr-boride coating is primarily consisted of $Cr_2B_3$ and $Cr_5B_3$, while that of V-boride coating is mostly consisted of $VB_2$ and $V_2B_3$. The (Cr,V)-boride coating is consisted of $Cr_2B_3$, $Cr_5B_3$ and $V_2B_3$ mostly. The top surfaces of 3 multi-component boride coatings show hardness of $3200-3400H_v$, which is much higher than that of boride, about $1600-2000H_v$. In 5 wt.% NaCl solution immersion tests, the multi-component boride coatings show much better corrosion resistance than boride coating.

• Corrosion Science and Technology
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• v.2 no.1
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• pp.53-57
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• 2003

The MarM247 based superalloy (8wt.%Cr- 9wt.%Co- 3wt.%Ta- 1.5wt.%Hf- 5.6%wt.Al- 9.5wt.%W- Bal. Ni) specimens were diffusion aluminized by for types of pack cementation methods, and their coating structure and their high temperature oxidation resistance were investigated. The coated specimens treated at 973K in high aluminum concentration pack had a coating layer containing large hafunium rich precipitates, which were originally included in substrate alloy. After the high temperature oxidation test in air containing 30 vol.% $H_2O$ at 1273K ~ 323K, the deep localized corrosion which reached to the substrate were observed along with these hafnium rich precipitates. On the other hand, the coated specimens treated at 1323K using low aluminum concentration pack showed the coating layer without the large hafunium rich precipitates, and after the high temperature oxidation test at 1273K for 1800 ksec, it did not show the deep localized corrosion. The nickel electroplating before the aluminizing forms thick hafnium free area, and its high temperature oxidation resistance were comparable to platinum modified aluminizing coatings at 1273K.