• 한국표면공학회지
• /
• 제40권4호
• /
• pp.175-179
• /
• 2007

An Fe-Ni-Co based superalloy Incoloy 909 (Incoloy 909) has been used for gas turbine engine component material. This alloy is susceptible to high temperature oxidation and corrosion because of the absence of corrosion resistant Cr. For the improvement of durability of the component of Incoloy 909 aluminizing-chromate coating by pack cementation process has been investigated at relatively low temperature of about $550^{\circ}C$ to protect the surface microstructure and properties of Incoloy 909 substrate. As a previous study to aluminizing-chromate coating by pack cementation of Incoloy 909, the optimal aluminizing process has been investigated. The size effects of source Al powder and inert filler $Al_O_3$ powder and activator selection have been studied. And the dependence of coating growth rate on aluminizing temperature and time has also been studied. The optimal aluminizing process for the coating growth rate is that the mixing ratio of source Al powder, activator $NH_4Cl$ and filler $Al_O_3$ are 80%, 1% and 19% respectively at aluminizing temperature $552^{\circ}C$ and time 20 hours.

• 한국재료학회지
• /
• 제19권4호
• /
• pp.207-211
• /
• 2009

In this study, we attempted to develop a convenient aluminizing process, using Al-Ti mixed slurry as an aluminum source, to control the Al content of the aluminized layer as a result of a one-step process and can be widely adopted for coating complex-shaped components. The aluminizing process was carried out by the heat treatment on disc and rod shaped S45C steel substrates with Al-Ti mixed slurries that were composed of various mixed ratios (wt%) of Al and Ti powders. The surface of the resultant aluminized layer was relatively smooth with no obvious cracks. The aluminized layers mainly contain an Fe-Al compound as the bulk phase. However, the Al concentration and the thickness of the aluminized layer gradually decrease as the Ti proportion among Al-Ti mixed slurries increases. It has also been shown that the Al-Ti compound layer, which formed on the substrate during heat treatment, easily separates from the substrate. In addition, the incorporation of Ti into the substrate surface during heat treatment was not observed.

• 한국표면공학회지
• /
• 제39권4호
• /
• pp.173-178
• /
• 2006

Incoloy alloy 909 is an Fe-Ni-Co based superalloy that is attractive for gas turbine engine applications. The absence of chromium, however, makes the alloy more susceptible to oxidation in high temperature. To improve the oxidation resistance aluminizing was performed by high activity low temperature pack cementation process. Aluminizing condition was examined with different times and temperatures. Optimum aluminizing conditions were at the temperature of $552^{\circ}C$ for 20 hrs. In the optimized condition, the thickness of the aluminized layer was about $20{\mu}m$. Also, the aluminized layer made the alloy to increase the resistance to the corrosion.

• 한국표면공학회지
• /
• 제31권6호
• /
• pp.325-333
• /
• 1998

A duplex surface treatment process of simultaneous aluminizing-chromizing process followed by plasma nitriding was performed on AISI HI3 steel and STS 403 steel. The properties of these duplex-treated steels were investigated and were compared with those of steels treated by single process of either simultaneous aluminizing-chromizing or plasma nilriding, in terms of microstructure, microhardness and high temperature wear resistance. Sim~dtaneous alumizing-chromizing process was done using a 2-step coating cycle and plasma nitriding process was done at $530^{\circ}C$ for 1.5 hour. AISI HI3 steel and STS 403 steel showed a FeA1 compound layer of approximately 350$\mu\textrm{m}$ thickness on the surface after simultaneous diffusion coating and nitrided layer of approximately 70-80$\mu\textrm{m}$ formed after the subsequent plasma nitriding process. The microhardness was improved much more by the duplex surface heatment than only by plasma nitriding. In addition the duplex treated specimens showed an improved high temperature wear resistance.

• 한국표면공학회지
• /
• 제29권2호
• /
• pp.120-131
• /
• 1996

In order to improve the mechanical properties and the high temperature oxidation resistance, aluminizing was carried out at a temperature range between $850^{\circ}C$ and $1050^{\circ}C$. The pack cementation process was used to produce uniform layer. After each treatment, the microhardness and the characteristics of high temperature oxidation were tested to evaluate the properties of the aluminide layer. The aluminide layer consisted of FeAl above $1000^{\circ}C$, and $Fe_2Al_5$ below $900^{\circ}C$, and the mixed phase of FeAl and $Fe_2Al_5$ between 90$0^{\circ}C$ and $1000^{\circ}C$ in case of the mixture powder consisted of 5%Al+5%$NH_4Cl+90%AL_2O_3$. The microhardness of $Fe_2Al_5$ was obtained much as the twice as that of FeAl. As the aluminizing temperature and time increased, the thickness of aluminide increased. After aluminizing, the high temperature oxidation resistance was remarkably improved. The high temperature oxidation resistance of FeAl was superior to the resistance of high temperature oxidation of $Fe_2Al_5$.

• 한국주조공학회지
• /
• 제31권2호
• /
• pp.66-70
• /
• 2011

Hot dip aluminizing (HDA) is widely used in industry for improving corrosion resistance of material. The formation of intermetallic compound layers during the contact between dissimilar materials at high temperature is common phenomenon. Generally, intermetallic compound layers of $Fe_2Al_5$ and $FeAl_3$ are formed at the Al alloy and Fe substrate interface. In case of cast iron, high contact angle of graphite existed in the matrix inhibits the formation of intermetallic compound layer, which carry with it the disadvantage of a reduced reaction area and mechanical properties. In present work, the process for the removal of graphite existed on the surface of specimen has been investigated. And also HDA was proceeded at $800^{\circ}C$ for 3 minutes in aluminum alloy melt. The efficiency of graphite removal was increased with the reduction of particle size in sanding process. Graphite appears to be present both in the region of melting followed by re-solidification and in the intermetallic compound layer, which could be attributed to the fact that the surface of cast iron is melted down by the formation of low melting point phase with the diffusion of Al and Si to the cast iron. Intermetallic compound layer consisted of $Fe(Al,Si)_3$ and $Fe_2Al_5Si$, the layer formed at cast iron side contained lower amount of Si.

• Corrosion Science and Technology
• /
• 제20권6호
• /
• pp.384-390
• /
• 2021

In this paper, durability evaluation and surface damage mechanism were investigated through solid particle erosion (SPE) test after applying hot-dip aluminizing (HDA) technology for the purpose of maintenance of marine economizer tube. Damaged surface shape was analyzed using SEM and 3D microscope. Compositional changes and microstructure of the HDA layer were analyzed through EDS and XRD. Durability was evaluated by analyzing weight loss and surface damage depth after SPE. HDA was confirmed to have a two-layer structure of Al and Al₅Fe₂. HDA+HT was made into a single alloy layer of Al₅Fe₂ by diffusion treatment. In the microstructure of HDA+HT, void and crack defect were induced during the crystal phase transformation process. The SPE damage mechanism depends on material properties. Plastic deformation occurred in the substrate and HDA due to ductility, whereas weight loss due to brittleness occurred significantly in HDA+HT. As a result, the substrate and HDA showed better SPE resistance than HDA+HT.

• 분석과학
• /
• 제6권2호
• /
• pp.167-180
• /
• 1993

Pack cementation법을 이용하여 한국과학기술연구원에서 개발한 세계 최강의 고운 단조용 초내열합금인 KM 1557에 내산화성이 우수한 알루미나이드 코팅층 제조시 코팅처리 변수들이 코팅층의 형성과정에 미치는 영향을 연구하였다. 알루미나이드 코팅처리는 pure 알루미늄 분말을 사용한 high-activity process와 Codep 합금분말을 사용한 low-activity process로 나누어 실시하였다. High-activity process의 경우 활성제의 종류와 첨가량 및 알루미늄의 첨가량에 따라 알루미늄의 증착속도와 알루미나이드 코팅층의 형성속도 및 단면조직은 큰 영향을 받는다. Low-activity process의 경우 알루미늄의 증착속도와 알루미나이드 코팅층의 형성속도 및 단면조직은 활성제의 종류에 전혀 영향을 받지 않으며 단조 활성제의 첨가량에 영향을 받는다. 그러나 활성제의 종류에 따라 코팅층의 표면조직의 결정립 크기가 달라진다. 알루미늄의 활동도에 관계없이 알루미늄의 증착속도는 시간의 평방근에 비례하며, 활성제의 종류에 따라 parabolic rate constants인 $K_p$값이 달라진다. High-activity process의 경우 알루미늄 증착에 필요한 활성화에너지는 활성제의 종류에 따라 달라지나, low-activity process의 경우 활성제의 종류에 관계없이 알루미늄의 증착에 필요한 활성화에너지는 약 12~14 Kcal/mole 정도의 값이 된다.