Towards an understanding of the functional properties of NiTi produced by powder bed fusion

Abstract

In this work, near fully dense NiTi components have been fabricated using a 55.2Ni-Ti (wt.%) powder through selective laser beam melting. The effect of the manufacturing process on mechanical and functional properties of the selected NiTi alloy has been systematically investigated by tuning the hatching distance, h, and the scanning speed, v, in order to define a set of twelve NiTi families. The as-built NiTi parts present phase transformation temperatures higher than those of the feedstock, ascribed to the depletion of Ni during the process. Pseudoelasticity and shape memory responses have been evaluated through uniaxial compression and bending measurements, respectively. Both quasi-static and dynamic analyses have been considered. It is shown that the resulting material may exhibit distinct damping and strain recovery responses depending on the used process parameters.

A Study on Damping Property of NiTi Elements Produced by Selective Laser‐Beam Melting

“…It is worth to notice that the 12 parameters’ sets enable an increase in the transformation temperatures with respect to that of the feedstock powder ( A f = 28 °C) due to Ni loss during the process attributed to both Ni evaporation and the formation of Ni‐rich precipitates. [ 48 ]…”

“…The presented results show that NiTi parts fabricated through SLM may guarantee mechanical properties and dynamic characteristics suitable for damping vibrations spanning from low to high amplitude levels at low frequencies. The occurrence of Ni loss during the process [ 48 ] results in 12 NiTi families with specific microstructure, thermal characteristic (see A f of Table 1) and damping response. Figure shows a comparison between the maximum loss factor of the studied NiTi parts and the one of different materials produced through traditional processing.…”

“…Several NiTi bars (3 × 3 × 15 mm 3 ) were produced from a NiTi micrometric powder (TLS Spezialpuver gmbh) with 55.2 wt% Ni ( A f = 28 °C [ 48 ] ) through a Renishaw AM400 SLM machine which works with a pulsed wave emission Ytterbium fiber laser. The process parameters were selected to obtain near fully dense and defect‐free specimens according to a previous study: [ 48 ] the laser power and the layer thickness were kept constant at 250 W and 30 μm, respectively. In addition, three values of laser speed were considered (1000, 1250, 1500 mm s −1 ) and four hatching distance values were investigated (50, 75, 100, and 120 μm).…”

“…[ 43 ] For NiTi alloys, values of E in the range of 55 to 222 J mm −3 provide high density and low porosity level within the produced samples. [ 36–39,44–48 ] Despite the extensive literature on NiTi components produced by SLM, many issues are still open or have not been completely explored; so far, damping has received very little attention. An interesting work on damping is reported by Wang et al [ 12 ] that found an excellent damping response of a layer‐structured NiTi sample produced by alternating two sets of SLM process parameters during printing.…”

Use of 4D-printing and shape memory alloys to fabricate customized metal jewels with functional properties

“…power [W] 250 Layer thickness [lm] 30 Hatch distance [lm] 100 Scan speed [mm/s]1,000 Source:(Nespoli et al, 2021) …”