Analysis on Notch Sensitivity of Low Thermal Expansion Superalloys GH2909

Superalloy GH2909 bars produced by a Chinese supplier present high notch sensitivity during high temperature creep performance test.In order to understand the reason for this issue,the imported and studied GH2909 alloy bars had been compared in terms of their chemical compositions,microstructures and mechanical properties,and the microstructure development of studied alloy during processes from forging to heat treatment had been investigated as well.Chemical composition analysis results showed there was no apparent difference between imported and studied alloys.However,microstructure observation indicated two alloys present remarkable difference.For the studied alloy,the notch sensitivity is attributed to the random distribution of Laves phase inside the grain,which is expected to be caused by the inappropriate forging process.Based on the research results,an improved forging process was proposed. By increasing the final forging temperature,controlling recrystallization of the alloy and precipitating Laves phase along the grain boundary,a new GH2909 alloy bar with suitable microstructure and excellent properties was successfully prepared,and the problem of notch sensitivity of domestic GH2909 alloy bar was solved.