Influence of NaCl environment on stress corrosion cracking of additive manufactured Ti-6Al-4V alloy

A slow strain rate test (SSRT) was performed to evaluate the stress corrosion cracking (SCC) of the Ti-6Al-4V alloy specimens developed by the Laser Powder Bed Fusion (LPBF) process. The test environment was open-air and 3.5% aqueous NaCl solutions. To study the crack growth mechanism and induced microstructure, a test was performed on the as-prepared specimen, the results were then compared with the heat-treated specimen. The strain rate was set to analyze the susceptibility of LPBF processed Ti-6Al-4V alloy specimens for stress corrosion cracking and its effect on the microstructure. The fractography analysis revealed that the shallow dimple was formed with the breaking planes of the alpha-lath separation and the geometry of the border profile of beta-grains on the heat-treated specimen. Whereas, for the as-prepared specimen, the crack profile of the alpha'-martensite structure was distinctly viewed. From the stress vs. strain and time curves of the SSRT results, this study provides an overview of the variation in the internal geometry of the Ti-6Al-6V alloy produced by the additive manufacturing process, which is hardly identified through rapid tensile testing. When comparing the SSRT results of the open air and aqueous NaCl solution, the dissolution of the passive layer from the surface of the additively produced Ti-6Al-4V alloy specimen in NaCl solution has significantly varied the tensile performance during the SSRT test. The dissolution was also confirmed by the XPS and the weight loss analysis.