Inter-pass peening for residual stress control in additive manufacturing: validation using ultrasonic, X-ray and contour method

• This study investigates inter-pass peening as an in-process residual stress mitigation technique for WAAM Ti-6Al-4V components. • A novel ultrasonic method, PAURS, was applied for residual stress measurement using phased array probes and Full Matrix Capture. • Validation was performed by comparing PAURS results with X-ray Diffraction and the Contour Method on corresponding WAAM samples. • PAURS measurements were carried out along the bottom surface of as-deposited and inter-pass peened samples, while the Contour Method and X-ray Diffraction provided validation. In this study, round-robin experiments were carried out to evaluate the effectiveness of inter-pass peening as an in-process residual stress (RS) mitigation technique for Wire Arc Additive Manufacturing (WAAM) of Ti-6Al-4V components. A newly developed method, Phased Array Ultrasonics for Residual Stress Measurement (PAURS), was evaluated for its capability to accurately characterise residual stress distributions. To validate PAURS, two established techniques, X-ray Diffraction (XRD), a non-destructive method, and the Contour Method (CM), a destructive technique, were employed. PAURS, particularly when implemented with Full Matrix Capture (FMC), demonstrated enhanced accuracy through improved data redundancy and outlier rejection. Results from PAURS and XRD showed good qualitative agreement with finite element (FE) models derived from CM data, despite some quantitative differences. Inter-pass peening was found to significantly reduce tensile RS in the heat-affected zone, with performance comparable to post-process peening. These findings support the use of inter-pass peening as an effective in-process RS mitigation strategy and highlight the potential of PAURS as a reliable, non-destructive RS measurement method for WAAM Ti-6Al-4V components.