Perpustakaan Digital ITB

Turbine blades of an aircraft's engine are made of high temperature corrosion resistant material. In order to meet this criteria, a lot of researches have been done to investigate chromaluminide coating on Ni-based superalloy substrate. The assessment of chromaluminide coating on pure Ni substrate has been conducted using duplex method, which is a two stage diffusion coating. The initial stage is cromizing process, and the second stage is an aluminizing process with high Alactivity. Result of duplex coating process mentioned above is a chromaluminide coating, wich consist of -NiAI phase, 6-Ni2A13 phase, and a-Cr precipitates. These results are obtained through chromizing process at 1100 °C for 4 hours using 3 % NH4C1 activator, and alumunizing process at 900 °C for 30 – 100 minutes, using the mixed activator of 1 % NH4CI + 4 % NaCl. Isothermal and cyclic oxidation tests, as well as hot corrosion test in a Na2SO4 salt bath have been conducted in still air at 900 °C during 4-16 hours, toward the chromaluminide coated samples. The oxides for med consist of Al203, Cr203, NiCr2O4 spinel and Ni Al204. From the experimental results, it is concluded that : a. Dupex coating method on Ni results in aluminide coating wich consist of a-Cr precipitates. b. The chromaluminide coating is found to be resistant to isothermal oxidation at 900 °C for 16 hours. c. The chromaluminide coating is found to be resistant to cyclic oxidation until 35 cycles ( 1 hour in furnance, 15 minutes outside furnance ). d. The chromaluminide coating is oxidized and form spine] ( NiCr2O4, NiAl2O4) at 900 °C in Na2SO4 salt bath in amount of 1,9 – 2,0 mg/cm2 for 12 hours. By using larger amount of salt bath (3,5 – 3, 8 mg/cm2) the chromaluminida coating is tend to suffer hot corrosion attack.