• Journal of the Korean institute of surface engineering
• /
• v.49 no.2
• /
• pp.211-217
• /
• 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
• /
• v.14 no.2
• /
• pp.76-84
• /
• 2015

The components in ultra super critical (USC) steam turbine, which is under development for high efficient power generation, are encountering harsher solid particle erosion by iron oxide scales than ones in the existing steam turbines. Therefore, the currently used boride coating will not be able to hold effective protection from particle erosion in USC system and should be replaced by new particle erosion resistant coatings. One of the best protective coatings developed for USC steam turbine parts was found to be vanadium-boride (V-boride) coating which has a hardness of about 3000 HV, much higher than that of boride, 1600~2000 HV. In order to evaluate particle erosion resistance of the various coatings such as V-boride, boride and Cr-carbide coatings at high temperature, particle erosion test equipments were designed and manufactured. In addition, erosion particle velocity was simulated using FLUENT software based on semi-implicity method for pressure linked equations revised (SIMPLER). Based on experimental results of this work, the vanadium-boride coating was found to be superior to others and to be a candidate coating to replace the boride coating.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 1999.05a
• /
• pp.58-59
• /
• 1999

• Journal of the Korean institute of surface engineering
• /
• v.36 no.4
• /
• pp.291-295
• /
• 2003

Many steam turbine components encounter solid particle erosion damage. It has been reported that particle erosion damage is caused by oxide scale exfoliation from boiler tubes. One of the most effective solutions to combat the erosion damage is the application of erosion resistant coatings on the turbine components. In this study, particle erosion resistance for various hard coatings such as nitride, Cr carbide and boride coatings was evaluated under the simulated erosion conditions of steam turbines. Based on the particle erosion tests, the boride coating was found to be more superior to others.

• Journal of the Korean institute of surface engineering
• /
• v.35 no.6
• /
• pp.371-376
• /
• 2002

Steam turbine components of power generators are subjected to severe damages from the particle erosion by iron oxides (mainly $Fe_3$$O_4$) which are formed due to the oxidation of boiler tubes, causing high costs for maintaining and repairing. One of the practical ways to minimize the particle erosion is to apply the erosion resistant boride coating on the turbine components which is composed of boride apply. But the evaluation of its performance has not been carried out. A particle erosion tester, which can offer the erosion condition of steam turbine components, was developed to evaluate the performances of the boronized Cr/Mo alloy. The result showed that the boronized Cr/Mo alloy showed superior resistance to particle erosion to the bare Cr/Mo alloy in all test conditions.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 1997.10a
• /
• pp.118-118
• /
• 1997

• Journal of the Korean institute of surface engineering
• /
• v.29 no.5
• /
• pp.478-481
• /
• 1996

Disproportionation reaction is very important and interesting reaction to be applied to such surface treatment as metal, alloy, compound coating, a surface etching and so on. In gaseous system, the reaction of Al chloride is applied to Al and Al alloy coating, and the similar reaction of Ti chloride is also used for Ti, Ti alloy and Ti compound coating. As for aqueous system, this reaction is utilized to such metal coat as Sn etc. and metal etching such as Cu, Fe and so on. Also in molten salts system, this reaction has many application for surface treatment like metal, alloy and compound coatings for corrosion, wear, heat resistance and so forth. For instance, carbide film, nitride film, boride film, alloy film, quite new different film from the components of substrate material are coated in single and multiple component film system by the disproportionation reaction.

• Journal of the Korean Ceramic Society
• /
• v.43 no.6 s.289
• /
• pp.358-361
• /
• 2006

A two-step plasma-assisted boronizing process was carried out on the AISI 1045 steel substrate to reduce the pore density introduced by a conventional single plasma boronizing process. The specimens were plasma boronized for 1 h at $650^{\circ}C$ and subsequently far 7 h at $800^{\circ}C$ in an atmosphere of $BCl_3-H_2-Ar$. The boride layer thickness was parabolic in boronizing time, a high HV reading of 1540 was found up to the boride layer thickness of $25{\mu}m$. It was found that the morphology of the boride layer prepared by the two-step boronizing process was changed from a columnar to a tooth-like structure and the pores in the borided steel were eliminated completely in comparison to those synthesized by the conventional single boronizing process, implying that it is highly applicable for enhancing the dense and compact coating properties of the low-alloy steel.