STUDY OF HOT CORROSION RESISTANCE OF NI-20CR-8MO-2,5TI-1,5AL SUPERALLOY WITH MAXIMUM 0,8% ZIRCONIUM ADDITION VARIATION AT 900°C
The number of population are more and more increasing and industries are more and more developing make the need of electricity bigger. The capacity of electricity in Indonesia in 2015 was 55 GW with 43% coming from coal-fired steam power plants (PLTU). PLTU generally have an efficiency of 40%. The e...
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| Format: | Final Project |
| Language: | Indonesia |
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| Online Access: | https://digilib.itb.ac.id/gdl/view/41078 |
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| Institution: | Institut Teknologi Bandung |
| Language: | Indonesia |
| Summary: | The number of population are more and more increasing and industries are more and more developing make the need of electricity bigger. The capacity of electricity in Indonesia in 2015 was 55 GW with 43% coming from coal-fired steam power plants (PLTU). PLTU generally have an efficiency of 40%. The efficiency of the PLTU is influenced by two operating parameters, namely temperature and vapor pressure so that by increasing both operating parameters it can increase the efficiency of the power plant. To increase the operating temperature of the power plant, an alloy that is resistant to high temperatures is needed, one of which is nickel superalloy. However, the corrosive environment causes metal alloys to become susceptible to hot corrosion. In this study a series of experiments were conducted to determine the effect of zirconium and the number of cycles on the hot corrosion of nickel superalloy and to determine the behavior of hot corrosion and oxide characteristics formed on nickel superalloy. The alloy composition used is Ni-20Cr-8Mo-2,5Ti-1,5Al with zirconium variation of 0%, 0,17%, 0,42%, and 0,81%.
The experiment was started by making Ni-20Cr-8Mo-2,5Ti-1,5Al alloy button sample using a mini DC electric arc furnace. Furthermore, button was homogenized using a horizontal tube furnace to remove residual stress due to the melting process. The buttons are then cut into smaller sizes and polished before testing. After that, the cyclic hot corrosion test was carried out on samples using horizontal tube furnace at 900°C up to 25 cycles. The samples from the hot corrosion test were characterized using x-ray diffraction (XRD) and scanning electron microscope (SEM) - energy dispersive spectroscopy (EDS).
In sample without zirconium addition showed the characteristics of hot corrosion type I with an acid flux mechanism. Molybdenum deposits is found on the surface of that sample which caused the salt around the oxide-salt interface to become acidic. In addition, the sample also has very massive chromium depletion, so that the alloy is not protective and occurs in large amounts of spalling. Another sample with the addition of zirconium has an improvement in the resistance of hot corrosion by not showing significant spalling. Zirconium decreases the diffusion rate of chromium to the surface of the sample, increases metal-oxide adhesion and prevents aluminum diffusion to the surface. Addition of 0.42% by weight of zirconium to Ni-20Cr-8Mo-2,5Ti-1,5Al superalloy has the best hot corrosion resistance. |
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