Fabrication And Characterization Of Ni Mn Ga Thin Films From Binder Jetting Additive Manufactured Sputtering Target

Ni-Mn-Ga thin films have attracted significant attention over the past two decades due to its multifunctional properties, leveraging these characteristics in applications such as actuators, sensors, and micro-electromechanical systems (MEMS). The most favorable deposition technique for making Ni-Mn-Ga thin films is magnetron sputtering where the target used is near stoichiometric Ni2MnGa alloy. Ni-Mn-Ga alloy target manufacturing has been challenging and costly due to design constraints, process optimization issues and inefficient target utilization resulting in compounded negative economics. To address these problems, this research aimed at investigating and demonstrating the viability of a cost-effective, modern technology known as binder jetting additive manufacturing (BJAM) technique to produce targets with excellent target consumption efficiency based on proposed target design. The additive manufactured Ni-Mn-Ga alloy target process began with ball-milled Ni-Mn-Ga powder having bimodal particle distribution to ensure an increased packing density and mechanical strength after the determination of optimized 3D printing parameters. The printed targets were post-processed through curing, de-binding and sintering. Sintering was conducted in an inert/argon atmosphere to safeguard essential material properties which were benchmarked through characterization. Backscattered electron (BSE) micrographs showed AM targets were homogenous with martensitic twin microstructures necessary for shape memory behavior. The XRD results showed that the martensitic twin microstructures were mostly tetragonal and monoclinic crystal structures. The martensitic transformation temperatures for Ni-Mn-Ga targets ranged from 79.3 to 148.1°C and possessed a maximum density of 87.18%. Using the direct current (DC) magnetron sputtering, Ni-Mn-Ga thin films were deposited on Si (100) substrates at discharge currents ranging from 0.05 to 0.15 A and substrate temperatures 20°C to 700°C. The effect of discharge current and substrate temperature on surface morphology, composition, crystal structure of Ni-Mn-Ga thin films on silicon substrates were investigated. As the discharge current increased, the film showed increased grain size. The grain morphology, as appeared from the investigation of the film planar surface was of elongated grains. The film crystallinity also increased with increased discharge current, as proved by XRD investigations. The most important effect of maintaining the discharge current value constant and increasing the substrate temperature was the change in chemistry and crystallography of the obtained Ni-Mn-Ga thin films. The film deposited at 700°C showed the closest chemical composition to the target composition. For the other substrate temperatures, the high oxygen contamination, due perhaps to not-so-optimum deposition conditions, drastically altered the film composition. By increasing the substrate temperature, the film crystal structure changed from Heusler L2I cubic (high temperature phase) to monoclinic (low temperature phase). It was also demonstrated that, 3D printed sputtering targets of different geometrical designs are potential for improving target utilization efficiency and film properties.