Miniaturised Charpy Impact Toughness Testing for the Characterisation of Laser Powder Bed Fusion - Built and Laser Shock Peened Ti-6Al-4V

Abstract

Laser Powder Bed Fusion (L-PBF) Additive Manufacturing (AM) might produce inconsistent results that require testing and documentation for qualification and, eventually, certification for aerospace applications. Literature has shown that the inconsistent results in part mechanical performance could be attributed to part features such as porosity and imperfections, residual stresses, microstructure, surface integrity, and microhardness. These inconsistencies can compromise the reliability, safety, and performance of aerospace components, necessitating rigorous testing and documentation to ensure compliance with stringent industry standards. Therefore, a preliminary testing method called the Miniaturised Charpy V-Notch (MCVN) impact testing is used to qualitatively assess the integrity of the parts produced. It also assesses the variations in the identified features that result from the manufacturing technique. Ti-6Al-4V test samples were manufactured with the intentional variation of the hatch spacing distance, stress-relieved, and prepared according to specification. Laser Shock Peening (LSP) post-processing was also selectively performed on some samples. MCVN tests, which were performed on the modified and recalibrated equipment, revealed that increasing hatch spacing of ideal settings by around 80% resulted in a significant and discernible impact toughness difference. The corresponding peened samples, tested under the same conditions, indicated a slight improvement in the recorded absorbed energy values. While the microstructural structure remained the same for both sample sets, the % porosity, the surface average, and the microhardness showed some changes. Another significant contributing factor was also the induction of compressive residual stresses recorded post-LSP, which was beneficial in countering crack propagation. This work provides significant information on the subject matter that can help as a stepping stone to achieve a standard procedure in the preliminary qualification of parts at minimal costs.