October_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 0 3 9 FEATURE Fig. 2 — In a 3D printing, or more accurately, additive-manufacturing process, material is deposited in a sequential, layer-wise manner and fabricated directly into the (near) final part geometry. In this study, the laser directed energy deposition (DED) 3D printing technology was used, also known as laser engineered net shaping, or LENS. (a) In this process, powders are blown through a nozzle into the focal point of a laser and melted onto a substrate by the laser. A computer numerical control (CNC) bedmanipulates the substrate beneath the laser in a path that forms the desired part geometry. The direction of the deposition path may be alternated in subsequent layer to improve the isotropy of the material performance in the final part geometry. Simple geometries such as (b-c) rods and (d-e) tubes may be fabricated, in addition to more complex geometries such as (f-g) honeycombs, which for solid-state cooling technologies, can be optimized to improve heat exchange between the elastocaloric SMA and its surrounding environment. Adapted fromHou et al. [1] with permission. (a) (b) (c) (f) (d) (e) (g) Fig. 3 — Using the laser-DED 3D printing technology to process blended Ni and Ti powders resulted in (a-b) nanocomposite microstructures composed primarily of NiTi and Ni 3 Ti phases. The curved, well dispersed nature of the nanocomposite interfaces serves to strengthen the ma- terial against fatigue, and also limits the hysteresis. Normally, using conventional processingmethods, (c) Ni 3 Ti phase forms as more heteroge- neously distributed micro-inclusions, (d) often concentrated at grain boundaries, which promotes fracture and limits the cyclic performance. Figures a and b reproduced with permission fromHou et al. [1] and Figs. c and d reproduced from Benafan et al. [7] with permission. (a) (b) (c) (d) 9