Material Characterization of NiTi Based Memory Alloys Fabricated by the Laser Direct Metal Deposition Process

Abstract

Shape memory alloys (SMAs) are used in a wide variety of applications including medical stents, couplings, actuators, jointless monolithic structures for actuation and manipulation, etc. Due to the SMA’s poor machinability it is advantageous to use rapid prototyping (RP) techniques for the manufacturing of SMA structures. However, the influence of the RP process on the properties of the SMA is not fully explored yet. A laser based direct metal deposition (DMD) RP process was used in this work to manufacture NiTi SMA samples and to investigate their physical properties using optical microscopy, differential scanning calorimetry (DSC), chemical analysis with secondary ion mass spectrometry (SIMS), and energy dispersive x-ray spectrometry (EDS) with a scanning electron microscope (SEM). DSC analysis has shown that the thermally treated parts possess smooth and pronounced reversible martensite-austenite transformation peaks that are the prerequisite for the shape memory effect (SME) in SMAs. DSC has also shown that quenching affects the peaks. The density of the produced parts was close to the theoretical density of the material as determined by porosity measurements. Finally, SIMS depth profile analysis has shown very low amounts of contamination in the material manufactured by DMD. The major conclusion is that the DMD RP process can be used to manufacture high-quality SMA structures from SMA powders.