Microstructural change and impact toughness property of Inconel 738LC after 12years of service

Abstract

The Domestic and Foreign Object Damage (DOD & FOD) are knownas serious problems for many heavy duty (or high temperature) device such as compressor, different turbine sections of jet engines and gas turbine, therefore the impact resistance study plays an important role to prevent any catastrophic failures. In this study a V94.2 Siemens gas turbine blade was used, which has been exposed to hot gases, heating the material to a temperature of 800–900°C in 105,120 operating hours. Initial metallographic investigation confirmed microstructural damage in the airfoil compared with the root of turbine blade.Charpy V-Notch tests were made according to the specification ASTM-E23 in ambient and service temperature (900°C). The fracture surfaces of the Charpy specimens were analyzed with the scanning electron microscopy,in order to identify the fracture mechanisms. The results showed that, with increasing the test temperature from 25 to 900°C, the impact energy of the root in both temperatures were relatively equal and far from airfoil. The microstructural investigation confirmed that the microstructure of airfoil was damaged due to the long operation at high temperature. Also, rafting behavior is observed in airfoil section.Fractographic investigations showed fracture mechanism of transgranular cleavage and dimples in the airfoil and root specimens in both temperatures.