We have also invited certain notable guests to share their expertise in the field of 3D printing and its future applications.

Bonnie Attard
Department of Metallurgy & Materials Engineering, Faculty of Engineering, University of Malta
Functionally-graded Inconel 718 microstructures through Laser Powder Bed Fusion: characterisation of local mechanical properties and defect formation

Abstract: Additive manufacturing is an attractive technique to manufacture bespoke, complex components. Despite the flexibility of Powder Bed Fusion (PBF), microstructural manipulation has still not been fully investigated. The use of additive manufacturing in tailoring mechanical properties can be applied to areas where concerns such as stress shielding are prevalent. This study investigates the viability of using scanning strategies rather than heat source parameters in laser powder bed fusion to modify the mechanical properties of Inconel 718 through a variation of microstructure. Both grain size and preferred orientation were successfully tailored. Graded microstructures were developed using various laser parameters with varying interfaces and their mechanical behaviour was investigated. Digital image correlation together with electron backscatter diffraction and scanning electron microscopy was used to investigate the tensile behaviour of graded structures under loading and associate this behaviour with the microstructural features generated from the grading. Mechanical testing indicated that the scanning strategy was a successful approach to functionally grade the microstructure and through that varying the mechanical behaviour. Larger grains and a more [001] preferred alignment resulted in lower Young’s modulus and strength while smaller grains with a more random orientation led to a higher Young’s modulus. Digital image correlation showed that strain in graded structures was concentrated in highly textured areas. The ductility was highly variable due to lack of fusion defects which formed due to thin Al oxides folded and entrained in the melt pool. Such defects are known to form in casting but have not been discussed in depth in the context of additive manufacturing. Melt pool motion due to Marangoni flow and recoil effects can be entraining these young aluminium oxide films in the melt pool. Such issues could also be evident with other alloys containing Al as an element in limited quantities.