Enhancing the fatigue performance of AM metals via conformal coatings that activate uniform surface remelting and smoothening

Mitigating surface roughness is a key to improving the fatigue performance of AM metals. However, current surface treatment options are not sufficient for complex AM parts, such as internal channels or microlattices. Surface treatments for the geometries need to be able to address beyond line-of-sight surfaces, as well as uniformly treat all component surfaces for predictable fatigue performance (e.g., not creating "weak links" in microlattices via nonuniform material removal). This work introduces a new surface treatment strategy through a transient surface remelting process. Surface remelting is triggered during heat treatment with a uniform, highly conformal coating, such as films fabricated with atomic layer deposition or electroplating. During heat treatment, the coating triggers local melting by activating a eutectic reaction, resulting in smoother surfaces and better fatigue performance. This talk will describe this new class of surface treatments with the specific case of AM Ti-6Al-4V. By using conformal coatings, we have demonstrated pronounced surface smoothening that increases the fatigue strength by approximately 30%.