Laser ultrasonic detection of submillimeter artificial holes in laser powder bed fusion manufactured alloys

In the development of additive manufacturing (AM) technology, laser powder bed fusion (LPBF) is one of the important processing methods. However, the hole defects in the fabricated samples limit the development. Laser ultrasonic (LU) technology plays a major role in the detection of LPBF parts with tiny defects, which has the advantages of non-contact and non-destructive. In this work, the detection of submillimeter internal defects in four typical LPBF alloys by LU technology is studied numerically and experimentally. A multiphysics simulation model of LU detection is established to investigate the propagation characteristics of excited ultrasonic waves in different LPBF alloys and their interaction with submillimeter artificial defects. Simulation results show that the amplitude of longitudinal (L) wave at the defect is the largest in AlSi10Mg alloy, and the amplitude of L wave in the 316L alloy, Ti6Al4V alloy and In718 alloy are very close, but their phases are slightly different. The amplitude of L wave tends to decrease nearly linearly with the increase in defect diameter. Then, four typical LPBF alloys are fabricated and measured by the LU through-transmission detection. The geometric information of artificial holes with a diameter larger than 0.2 mm are clearly characterized by the LU C-scan results, indicating the prominent applicability and feasibility of LU detection on different materials fabricated by LPBF.