Nondestructive evaluation of micro-oxide inclusions in additively manufactured metal parts using nonlinear ultrasonic technique

Abstract

Additive manufacturing (AM), commonly known as 3D printing, is an emerging technology for manufacturing metal parts. Recently, micro-oxide inclusions, which are inevitably generated during AM processes owing to the high-temperature environment, have been noted to enhance the mechanical strength of AM metal parts. However, an explicit nondestructive testing (NDT) method to assess the micro-oxide inclusions of AM metal parts has not been reported yet owing to the difficulty of sensing micro-inclusions. In this study, the micro-oxide inclusions of AM metal parts were evaluated nondestructively using a nonlinear ultrasonic technique. The uniqueness and advantages of this study are (1) the development of a micro-oxide inclusion evaluation technique for AM metal parts, (2) superior evaluation ability for micro-inclusions compared to conventional NDT; (3) applicability of the proposed method in assessing the strengthening of the mechanical properties of the AM parts by the inclusions; and (4) potential for nondestructive online monitoring. The performance of the proposed method was validated using specimens fabricated under various 3D printing conditions. The results of the micro-oxide inclusions assessed by the proposed method were consistent with the metallography and tensile testing results. Furthermore, the performance of the proposed method was better than that of conventional NDT.