EFFECT OF YYTRIUM ADDITION ON EARLY CYCLIC OXIDATION STAGE OF TI-62AL AT 900°C

• Main Author: Wahyu Suryohutomo, Nosa
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/61912
• Institution: Institut Teknologi Bandung

Material application on high temperature as found in coal-fired boiler and aircraft jet engine needs good combination of properties such as mechanical properties, microstructure stability, and high temperature corrosion resistance. Research regarding intermetallic TiAl based alloys is continuously developing in order to replace steel and superalloy that being used nowadays. TiAl based alloys has high melting point, low density, high specific strength, and good oxidation resistance that considered to be suitable for high temperature applications. Nevertheless, TiAl alloys suffer severe oxidation when the temperature comes to 750°C. The oxidation of TiAl alloys forms oxide scale that composed of mainly TiO2 and Al2O3. This mixture of oxides tends to be nonprotective scale that more aluminum is added to enhance the oxidation resistance since Al2O3 forms more protective scale. The formation of these oxide scales is also affected by alloying elements being added. Current study discusses how yttrium addition affects oxidation behavior of specific Ti-62Al alloy. This study comprises the fabrication of Ti-62Al up to cyclic oxidation testing. The alloy button was made using DC arc melting furnace, homogenized at 1000°C for six hours, then cut into small specimens for microstructural analysis and cyclic oxidation testing. The test was conducted in 900°C for 25 cycles. One cycle covers one hour oxidation inside horizontal tube furnace, then weighed after 20 minutes air cooling. The analysis of this study includes the specimens’ weight change during 25 cycles of oxidation, also the observation of post-oxidized specimens using XRD and SEM-EDS. Investigation using XRD and SEM-EDS shows the oxidation product formed during oxidation process consists of amorphous layer of Al2O3 and coarse grained TiO2 on the outside, while mixture of Al2O3 and TiO2 found on the inner side. Kinetic oxidation curve shows alloy without Y addition experienced dynamic weight change during oxidation. In contrast, alloy with 0.3 at.% Y addition found to be the most oxidation resistant since this alloy shows the smallest weight change with nearly no spallation occurred. The oxide scale observed on 0,3 at.% added Y composed of thin amorphous Al2O3 while layered oxide structure found on the alloy with no Y addition which more susceptible to undergo spallation. The addition of 0.3 at.% Y is expected to suppress TiO2 growth and maintain the formation of protective Al2O3 that responsible for increasing oxidation resistance.