Investigation of the influence of process interruption on mechanical properties of metal additive manufacturing parts

Fabrication methods of metals range from traditional subtractive methods to the new and emerging additive manufacturing technologies. As expected, these different metal fabrication and processing methods have a significant impact on the material structure and mechanical properties of final products. While the impact of the manufacturing process on the mechanical properties of metals is well understood for traditional manufacturing methods, the relationship between the additive manufacturing process and product characteristics is quite complex and still an ongoing research topic. Accordingly, many research studies on the material structure and mechanical properties of parts produced using additive manufacturing have been conducted in recent years. However, current literature considers ideal operating conditions while neglecting to consider the impact of printing process interruption on metal additive manufacturing parts. Additive manufacturing processes rely on continuous layer by layer printing of material, with strict melting and solidification requirements. When the printing process is interrupted, thermal dynamics governing binding strength and defect generation within layers are disturbed. It is expected that additive manufacturing process interruptions impact layer binding, which in turn jeopardizes the development of uniform microstructures and mechanical properties of metal parts. Accordingly, in this paper the impact of process interruption on the microstructure and mechanical properties of titanium samples printed using Wire Arc Additive Manufacturing (WAAM) is investigated. Various tests on the sample specimens are conducted including: Acoustic Resonance testing, Nanomechanical testing, X-ray Computed Tomography, and Ultrasonic nondestructive testing (NDT). The results indicate that additive manufacturing process interruption results in serious defects such as porosities and cracking that impact the mechanical properties of additive manufacturing metal parts.