Abstract
The technical condition of gas turbine blades of the turbine engine has a significant impact on the reliability and life span of the turbine and the entire engine. In order to assess the blades technical condition, a visual method, with the use of optoelectronic devices, is used. In order to verify this assessment, metallographic tests are conducted. The paper presents the results of microstructural tests of the turbine rotor blades made of nickel-based monocrystalline super alloys. The aim of these tests was to determine the consequences of impacting high exhaust gas temperature and stresses occurring during operation on the stability of the blade microstructure. The progress level of the blade microstructure changes in the post-operational stage for different sections towards the blade vertical axis and was compared with the blade microstructure on delivery made of the same super alloy. A varied degree of the microstructure degradation for different blade sections was shown. The changes typical of the high-temperature creep process – γ phase directional growth (rafting), were observed only for the thinnest walls of the upper section of the turbine blade leaf.
Highlights
A turbine is a rotor turbomachine converting enthalpy of the work factor, called the thermodynamic factor, into mechanical work making the rotor rotate
Increasing exhaust gas temperature is limited by the material properties of the turbines: their resistance to creeping, microstructure change, thermal fatigue, high temperature corrosion, etc. [1, 5, 14]
The super alloys used to operate at a temperature above the limit temperature Tg are called the heatresistant ones
Summary
A turbine is a rotor turbomachine converting enthalpy of the work factor, called the thermodynamic factor, into mechanical work making the rotor rotate. Increasing exhaust gas temperature is limited by the material properties of the turbines: their resistance to creeping, microstructure change (overheating), thermal fatigue, high temperature corrosion, etc. It leads to the additional heating of the turbine blade leaf front, the result of which is the increased turbine blade leaf expansion, as well as unfavourable changes of its microstructure, and the need to repair the turbines [1, 4] As it is clear from the above analysis, despite using many endeavours in order to improve the efficiency of the gas turbine operation, its durability and reliability, over the long-term operation process, there are still all kinds of damages to turbine elements, especially their blades (Fig. 1). The important reasons include improper fuel atomization in the combustion chamber, as well as its diminished physical-chemical properties [3]
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