Achieving high quality nitinol parts with minimised input thermal energy by optimised pulse wave laser powder bed fusion process
Muhannad Ahmed Obeidi
Abstract
Nitinol alloys have great applications especially in the biomedical industry due to their unique super-elastic and shape memory properties which depends on the balance between the element composition Ni–Ti. For this reason, controlling the applied volumetric thermal energy (VED) during the manufacturing process is very essential in order to identify the final part's property. It is known that the boiling temperature of nickel is far less than that of titanium thus is easier to vaporise and alter the chemical composition of the alloy. In this study, pulse operating mode was employed in a Laser-Powder Bed Fusion (L-PBF) process to produce additively manufactured (AM) parts with high density and high mechanical properties with minimised input thermal energy. The aim was always to achieve full melting situation and to maintain the original chemical composition of the virgin powder. It has been shown that fully dens parts with significant compression strength, comparative modulus of elasticity, and stable chemical composition can be produced by modulating the laser pulse by 50% duty cycle. This means reducing the applied VED by 50% and working in low levels of ∼6.5 J/mm3, avoiding excessive heating and vaporization of metals and enhancing the sustainability of the process. All the tested samples exhibit a catastrophic fracture accompanied by loud noise and spark during compression. A new approach was used to calculate the VED in a more accurate way by calculating the pulse energy and the exact number of pulses per unit area.