Novel Fractgraphy of Ni-Based Alloy by SEM/EBSD Method

Alloy 718 superalloy has been used for blades of air craft jet engine and gas turbine. The failures of these parts derive from fatigue and creep, but it is difficult to estimate applied stress from observation of samples from damaged parts. Oxidation and crush on fracture surfaces prevent from the estimation by fractgraphy especially. Therefore, we established the novel observation of the microstructure on the cross section beneath cracks by using EBSD. Tensile test, fatigue test and creep test were performed, and the change in dislocation density and the difference of strain contour of these specimens were specified by the new method. Finally the applied stress could be estimated and the test temperature could be also estimated.