Effect of Thermal Exposure on Long-Term Heated Microstructures at 900°C of Nickel Base Superalloy Turbine Blades, Grade Udimet 500

Abstract

In this research, 5 superalloys Udimet-500 samples were reheat-treated under simulation of 2 working conditions. First, they were heated at 900oC for 400 hours of each heating cycle from the beginning until accumulated heating time reached 1600 hours, these samples were collected and examined the microstructures for size and shape of gamma prime particles. Another heating condition, they had an additional over thermal exposure heating at 1125oC for 1 hour after heating at 900oC of each 400 hours-heating cycle. Then the results were analyzed from 2 working conditions. It was found that the area fraction, average area of gamma prime particle values of nickel base superalloy turbine blade, grade Udimet-500 happened in the same directions in first heating program. However, with the over thermal exposure heating at 1125oC for 1 hour after every heating at 900oC for 400 hours-heating, the obtained results show rates of the area fraction, average area of gamma prime particle values had changed more slowly because the temperature 1125oC at the end of each 900C heating could solutioning some coarse gamma prime phase back to the matrix in some degree. Therefore, the rate of ripening of gamma particle size was slower due to that the microstructural rejuvenation was always performed after each heating cycle and also allowed the reprecipitation of uniform finer gamma prime particles providing longer service time than those of first heating condition.