On methodology of residual stress measurement in Ni-based single crystal superalloys using neutron diffraction

Residual stress is one of the main factors affecting the high temperature mechanical properties of blades. At present, there is no publicly reported research on the accurate measurement of three-dimensional stress of nickel-based single crystal superalloy blades. In this study, a method which can accurately measure the three-dimensional stress of nickel-based single crystal superalloys by neutron diffraction was established. Based on the elasticity theory, the relationship between the lattice strain in the laboratory coordinate system and the macroscopic stress in the sample coordinate system was established according to the relationship between strain and stress in the single crystal coordinate system. By measuring the strain of multiple crystal planes, the method of multiple linear regression equation was used to calculate the three-dimensional stress of nickel-based single crystal superalloy. In-situ tensile experiments were designed to obtain the stress components of Nickel-based single crystal superalloys under different tensile forces. Comparing the known stress with the measured stress it was found that the difference between the two was very small, which was within the allowable error range of the neutron diffraction experiment. This verified the reliability of the three-dimensional stress test method of neutron diffraction nickel-based single crystal superalloy. Finally, the influence of crystal plane combination on the stress test results was studied. This study provides an experimental basis for subsequent single crystal blade measurement.