Properties of Cu-Based Shape-Memory Alloys Prepared by Selective Laser Melting

Abstract

Two shape-memory alloys with the nominal compositions (in wt.%) Cu-11.85Al-3.2Ni-3Mn and Cu-11.35Al-3.2Ni-3Mn-0.5Zr were prepared by selective laser melting (SLM). The parameters were optimised to identify the process window, in which almost fully dense samples can be obtained. Their microstructures were analysed and correlated with the shape-memory behaviour as well as the mechanical properties. Suction-cast specimens were also produced for comparison. Mainly, b 1 0 martensite forms in all samples, but 0.5 wt.% of Zr stabilises the Y phase (Cu 2 AlZr), and its morphology depends on the thermal history and cooling rate. After annealing, the Y phase is primarily found at the grain boundaries hampering grain coarsening. Due to the relative high cooling rates applied here, Zr is mostly dissolved in the martensite in the as-prepared samples and it has a grainrefining effect only up to a critical cooling rate. The Zrcontaining samples have increased transformation temperatures, and the Y phase seems to be responsible for the jerky martensite-to-austenite transformation. All the samples are relatively ductile because they mostly fracture in a transgranular manner, exhibiting the typical double yielding. Selective laser melting allows the adjustment of the transformation temperatures and the mechanical properties already during processing without the need of a subsequent heat treatment.

Elastocaloric cooling of additive manufactured shape memory alloys with large latent heat

“…The SLS is the first commercialized additive manufacturing technique and thus far, it is the technique of choice for most of reported 3D printed TiNi, [30] as well as some Cu-based alloys. [32] The flow-based approach, on the other hand, injects flux of powders into a molten pool while simultaneously a laser beam is pointed at the injected powders. A typical flow-based technique is Laser Engineered Net Shaping (LENS).…”

Cu-Based Shape Memory Alloys: Modified Structures and Their Related Properties

“…Additionally, the high temperatures of the β-phase for the Cu-Al-Ni alloys have a disordered bcc structure similar to the Cu-Zn-Al alloys [37]. In the Cu-Al-Ni alloys, two types of thermally induced martensites (β′ 1 and γ′ 1 ) form, depending on the alloy's composition and heat treatment [38][39][40][41]. The stability of the β-phase decreases with decreasing temperature.…”

Additive Manufacturing from the Point of View of Materials Research

“…Mechanically produced powder Mechanical shape memory functionality was proven with a force range of 10-100 mN [119] Quality of deposited Ni-Ti was improved by increasing the scanning speed [120] E-PBF PREP atomized powder No visible shape memory and pseudoplastic effect seen [121] The authors did not recommend E-PBF for Ni-Ti alloys. Preheating was required [97] E-PBF process resulted in better tensile properties than L-DED and L-PBF [97,122] PAD Pre-alloyed powder Linear superelasticity [123] Quasi-linear superelasticity with narrow hysteresis [123,124] WAAM Wire High hardness and tensile strength [125] Cu-Al-Ni L-PBF Elemental powders High aluminum content led to dendrites and high hardness [126] Cu-Al-Ni-Mn Gas atomized powder High relative density (>92%) achieved [127][128][129] Reversible martensitic transformation with the formation of β 1 '-martensite [127][128][129] Large strain recovery after unloading (up to 18%) [127] Strong distribution of pores produced by the L-PBF sample [127,128] Additional re-melting led to smaller grain size and yielded a deformability of 14% [129] Higher strength and improved plasticity was observed for both samples (Cu-Al-Ni-Mn and Cu-Al-Ni-Mn-Zr) [128][129][130] For the Cu-Al-Ni-Mn-Zr sample, Zr-rich phase was found to precipitate at the grain boundaries during the annealing process [130] Cu-Al-Ni-Mn-Zr Cu-Al-Ni-Ti Copper alloy with Ti addition had a high hardness of about 280 HV due to the grain refinement. The relative density exceeded 99% [131] Fe-Mn-Al-Ni Reversible martensitic transformation and pseudo-elastic effect [132] MSMA Ni-Mn-Ga 3D ink printing Ink with elemental powders Reversible martensitic transformation [133] Martensitic twins [134] Binder jetting Mechanically produced powder Martensitic twins and reversible martensitic transformation after post-processing [135,…”