Additive manufacturing of high-temperature shape memory alloys: effect of laser parameters and aging

Additive manufacturing (AM) techniques have emerged as a promising path to producing shape memory alloys (SMAs) where processability and machinability can be challenging (e.g., limited ductility or complex shapes). Additionally, AM presents an opportunity to tune SMA properties in situ as the material is being produced. In order to take advantage of such tool, it is vital to determine the process parameters (PP) and boundary conditions that can yield a useful material with the desired properties. This presentation aims to use AM to produce Ni-rich and Ti-rich NiTiHf alloys using various PPs. Multiple coupons of NiTiHf were fabricated through a powder bed machine and effect of different process parameters such as power and scanning velocity on multiple build factors are discussed. It is shown that near dense parts were fabricated without any cracks or delamination by identifying a satisfactory printability zone. Multiple aspects are considered for the fabrication evaluation and it is shown that each PP may affect one of the characteristics dominantly. More importantly, multiple ranges of TTs were achieved which indicated AM as a tailoring method to adjust shape memory behavior. Linear energy density of 0.25 J/mm was found to be an optimum value; thus, a large window of laser power and scanning speed could be used to produce defect-free parts which showed phase transformation and functionality. Initial results of aging of AM NiTiHf alloys will also be presented.