Quantitative Percussion Diagnostics for Evaluating Porosity and Surface Roughness of Cold Sprayed and Laser Deposited Materials

Quantitative percussion diagnostics (QPD) is a non-destructive evaluation method that has been used successfully in a number of applications. This technique involves a rod that is actuated to impact a specimen with a given amount of kinetic energy and the resulting mechanical response of the specimen as a function of time is measured using a piezoelectric force sensor. The mechanical energy returned to the rod is then analyzed. Because contact with the specimen is on the order of a few hundred microseconds, QPD can be used in situations and for specimen conditions (e.g. high temperature) that are not feasible for other nondestructive testing methods. The objective of the present study was to evaluate the use of QPD for characterization of defects in specimens fabricated using two additive manufacturing methods, i.e. cold spray deposition and laser powder directed energy deposition (LPDED). Cold spray specimens were produced using commercially pure nickel with varied process conditions including gas type (i.e. helium and nitrogen) and deposition rate. In addition, a Ti–6Al–4V specimen was manufactured using LPDED with varying porosity content. All specimens were characterized using both QPD and destructive methods (i.e. cross-sectional metallography) to compare results for observed defect characteristics. Cold spray specimens exhibited a lower energy return when they contained more porosity and/or surface roughness. Microscopic plastic deformation at highly porous surfaces was indicated during percussion testing that reached a saturation level after repeated percussion. Overall, the results showed that QPD can effectively evaluate cold spray and LPDED specimens for porosity and surface roughness.