| Abstract Scope |
Inhomogeneous non-equilibrium microstructures of NiTi alloys can be induced by additive manufacturing (AM), resulting in compromised performance and impeded functional applications. NiTi alloys with varying gradient compositions have been in-situ alloyed using directed energy deposition (DED): mixed powder NiTi, graded Ti/Ni, and graded Ti/NiTi, to achieve tailored microstructure gradients. The printability of these graded materials was evaluated to control intermetallic phase distribution. Systematic investigations of microstructural characterisation, phase transformation, and mechanical properties have been performed to obtain tailored microstructure. Computational modelling unveils the mechanisms governing dynamic temperature fluctuations, as well as thermal and mass transport within melt pools. Effective control over the formation and distribution of intermetallic compounds has been achieved by a broadening of the martensitic transformation interval through microstructure gradient design. This study provides valuable insights into the fabrication of AM graded NiTi alloys, thus enabling intricate structural designs tailored to meet specific functional requirements. |