Directed Energy Deposition of Ni-Mn-Ga Magnetic Shape Memory Alloy

Processing of magnetic shape memory alloys – active materials that show strains of up to 12 % in a magnetic field and that are being targeted for application as actuators, sensors and energy harvesters – suffers from challenges including time intensive production and macrosegregation that leads to reduced yield. Furthermore, the brittle mechanical behavior of these materials largely eliminates the possibility of machining for a desired shape. This work explores directed energy deposition, an additive manufacturing or “3D printing” process, as an alternative processing route for Ni Mn Ga magnetic shape memory alloy. The magnetic properties, transformation behavior, and composition of the feedstock powder and deposits resulting from a laser metal deposition process are investigated against varied laser power. All samples are seen to possess favorable magnetic behavior and potentially favorable phase for magnetic field induced strain (MFIS) to take place. Additionally, the microstructure of the deposited samples is observed and its special features that may aid MFIS are discussed. Most notably, this thesis presents possible evidence of twin variants crossing deposition layers and of twin boundary motion in a magnetic field. Finally, a connection between lower laser power and reduced loss of Mn is considered