Acoustic Nonlinearity and Loss Associated with Unbonded Interfaces and Dislocations in Additively Manufactured CoCrMo Parts with Complex Geometries

Complex geometries of additively manufactured (AM) metal parts present challenges for rapid post-build part qualification with most conventional nondestructive measurement techniques. This study explores the potential of nonlinear reverberation spectroscopy (NRS) for detecting defects in parts with complex geometries. It focuses on measurements of two CoCrMo hollow pentagonal star-shaped specimens with and without designed-in mesoscale cavities and trapped unmelted powder. Nonlinearity and loss of the specimen with cavities are found to be greater than those of the specimen without cavities, and these differences are found to increase after six years of aging at room temperature. Different behavior of the two specimens with respect to aging and extended acoustic excitation lead to the conclusion that the dominant sources of nonlinearity and loss in the two specimens are different: contacting unbonded internal interfaces in the specimen with cavities, and dislocations in the other specimen. This conclusion is partly supported by calculations showing that the time scale of an aging-induced decrease in nonlinearity of the specimen without cavities is consistent with expected rates of migration of vacancies and nitrogen interstitials to dislocations. The results support the idea that NRS measurements would be useful for rapid nondestructive qualification of AM parts with complex geometries.