Use of ball indentation technique to evaluate room temperature mechanical properties of a gas turbine blade

Abstract

Ball indentation technique (BIT) has been used to explore its usefulness in revealing the effect of high temperature exposure on mechanical properties of a gas turbine (GT) blade of Ni base super alloy. The dependence of yield strength (YS), ultimate tensile strength (UTS), strength coefficient (K) and strain hardening exponent (n) values on different exposure time are available from the BIT results and they are validated with the standard conventional test results. It is found that while exposing at high temperature (760 °C), the room temperature mechanical properties of the virgin blade have diminished. The diminishing of mechanical properties of the exposed blade (15,000 h) is due to the average size increment of the γ/ particle. Again, the average grain size of the 15,000 h exposed blades is greater than the virgin one and it might be another cause for decreasing the YS and UTS. No further significant changes of mechanical properties were observed when the exposure time was increased to 30,000 h at the same temperature. Overall, it is found that BIT can be effectively used to determine the minute changes of mechanical properties due to microstructural variation.