INTERDIFUSSION COEFFECIENTS DETERMINATION OF ALUMINIDE COATED TI-47AL-2CR-2NB-0,5ZR-0,5Y INTERMETALIK ALLOY TO PREDICT CONCENTRATION PROFILES AND THE THICKNESS OF INTERDIFFUSION LAYER.

• Main Author: Muhammad, Fadhli
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/78495
• Institution: Institut Teknologi Bandung

Titanium aluminides have attracted considerable interest among industrial companies in the last two decades for their attractive properties at high temperature applications such as aeroengine and automotive engine. Due to their lower density (a half of nickel based superalloy density), high yield strength at high temperature, good creep resistance, and good oxidation/corrosion resistance. These intermetallic alloys regarded as strong substitute candidates for conventional titanium alloy in the compressor part of aerospace gas turbine engines and also Ni-Based superalloys in the lower pressure turbine part. A two phase ?2-Ti3Al/?-TiAl intermetallic alloys has relatively poor oxidation resistance at the temperature above 700°C. In order to increase their oxidation and hot corrosion resistance, these alloys are protected by aluminum coating on their surface. However, the use of aluminide coatings at high temperatures may cause interdiffusion between the coating layer and the substrate so it could decrease the coating thickness. In this study, the interdiffusion model was constructed for aluminide coated Ti-47Al-2Cr-2Nb-0.5Zr-0.5Y intermetallic alloy to determine the values of interdiffusion coefficient at several temperatures as well as predict the thickness of interdiffusion layer along with time. A series of experiments of pack aluminizing and interdiffusion was conducted on substrate Ti-47Al-2Cr-2Nb-0.5Zr-0.5Y intermetallic alloy. Pack aluminizing was conducted at temperature 900°C for 10 hours with the pack composition consist of 2% NH4Cl, 20% Al powder, and 78% inert filler Al2O3. Interdiffusion investigations were carried out at inert environment (closed system) to prevent the oxidation of the specimen during the process. The investigations were done at temperature 800°C, 900°C, and 1,000°C with 3 variance of time to determine the average thickness of interdiffusion layer so that the interdiffusion growth rate can be measured and calculated. In addition, SEM/EDS analyses were also conducted to provide the information on morphology and concentration profiles. EDS analyses data have been used to determine the values of interdiffusion coefficient using Boltzmann-matano technique. The interdiffusion coefficient are 7.091 x 10-14, 1.650 x 10-12, and 5.261 x 10-12 cm2/s for temperature 800°C, 900°C, and 1,000°C respectively. Both analytical methods and numerical methods can be used to quantitatively predict the profile of interdiffusion layer thickness as well as the lifetime of the coating layer. Moreover, the addition of micro-alloying elements such as Cr, Nb, Zr, and Y can significantly inhibit the interdiffusion growth rate between coating layer and the substrate.