Effect of Quarterly Element Addition of Cobalt on Phase Transformation Characteristics of Cu-Al-Ni Shape Memory Alloys

Abstract

In the current study, a new type of Cu-based shape memory alloys with the function of shape memory effect was successfully produced with the introduction of high-purity Co precipitates between the phases of Cu-Al-Ni shape memory alloy. The microstructure, transformation characteristics, and mechanical properties were systematically investigated by means of differential scanning calorimetry, field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy, X-ray diffraction (XRD), a tensile test, a hardness test, and a shape memory effect test. The typical microstructures show that a new phase was formed, known as the c 2 phase, and the volume friction and the size of this phase were gradually increased with the increasing Co content. According to the results of the XRD and EDS, it was confirmed that the c 2 phase represents a compound of Al 75 Co 22 Ni 3 . However, the presence of c 2 phase in the modified alloys was found to result in an increase of the transformation temperatures in comparison with the unmodified alloy. Nevertheless, it was found that with 1 wt pct of Co addition, a maximum ductility of 7 pct was achieved, corresponding to an increase in the strain recovery by the shape memory effect to 95 pct with respect to the unmodified alloy of 50 pct.

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

“…For this reason, there is major interest in another group of HTSMAs derived from Cu-based alloys (e.g. Cu-Zn-Al and Cu-Al-Ni) due to their relatively low manufacturing costs, good processability as well as good shape-memory properties [1][2][3][4][5][6][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…Hence, especially Cu-Al-Ni SMAs, which are less prone to ageing (i.e. the precipitation of c 2 or other phases) than Cu-Zn-Al SMAs for instance, with small grain sizes and enhanced deformability have been subject of research in the past decades [2,4,7,9,10,[18][19][20].…”

“…The propensity to early failure in coarse-grained Cubased SMAs can be avoided by selecting the proper processing conditions or alloy composition. It has been shown that the poor workability of Cu-Al-Ni SMAs caused by brittle intergranular fracture can be reduced by refining the microstructure through the addition of Co [10], Mn [9], Ti [2, 10-13, 19, 20] or Zr [2,13,14]. When Ti or Zr is dissolved in the melt, it reduces the grain growth rate and thus refines the microstructure [19,21,22].…”

“…These factors, in turn, determine the details of the phase transformation [2,3,11,13,18,39]. With decreasing grain size, the transformation temperatures of Cu-based SMAs have been found to become lower [2,4,5,10,16,18,20]. This makes SLM a very attractive tool for processing Cu-based SMAs because the resulting grain sizes are rather small and, hence, these specimens exhibit an improved deformability [7].…”

Effects of Gd addition on the microstructure, mechanical properties and shape memory effect of polycrystalline Cu-Al-Ni shape memory alloy

“…However, polycrystalline Cu-Al-Ni alloys suffer from high brittleness, which is associated with large elastic anisotropy, intergranular cracking and large grain size [16,17]. Some methods were adopted to improve the mechanical properties of polycrystalline Cu-Al-Ni, including grain refinement [18] and fourth element addition [3,[19][20][21]. Published results showed that rare earth Gd addition can tailor the microstructure and mechanical properties of shape memory alloys [22][23][24], and accordingly, Gd is added into Cu-13.0Al-4.0Ni HTSMA to improve its plastic in the present work.…”