Additively Manufactured Materials Allowables for Critical Applications

Laser powder bed fusion, an additive manufacturing technique, brings significant opportunities for manufacturing in terms of new structural designs, higher performance, and a reduction in weight and material required. Among the various high-performance alloys adapted for laser powder bed fusion, Inconel 718, a precipitation-strengthened nickel-based superalloy renowned for its exceptional mechanical strength and thermal stability, has generated significant interest for aerospace and nuclear applications. However, for this potential to be unlocked, industry requires the creation of high calibre datasets to enable design and product certification. This requires a deep understanding and evaluation of the effect of defects, appropriate adoption of test methods, and relating the process of creating additive manufactured material to the microstructure and lifing of a component in-service. Investigation into the mechanical and microstructural performance of laser powder bed fused Inconel 718 against conventionally wrought material, with emphasis on evaluation of the influence of varying post-processing heat treatment routes on powder bed fused Inconel 718, was conducted. Variants for laser powder bed fusion included a non-heat treated variant, and two heat treated variants to improve varying mechanical properties (fatigue and creep). Microstructural analysis via advanced electron microscopy showed grain characteristics and phase variation between the additive variants and a contrast to the wrought Inconel 718. The different microstructures directly related to the mechanical properties, which were evaluated via room and elevated temperature: tensile, strain control low cycle fatigue, constant load creep testing, alongside hardness testing and small scale techniques – small punch tensile and small punch creep. Overall, the additively manufactured variants, particularly the heat treated variants, exhibited mechanical superiority compared to the wrought Inconel 718.However, the heat treatment implemented did not typically show the intended desired properties. Additionally, small scale test techniques showed general trends could be gathered but direct correlations to uniaxial tests were not accurate. Consequently, conclusions advise the need for further research into AM specific HTs and the use of small-scale testing.