Determining the liquidus and ordering temperatures of the ternary NiMn-Ga and quaternary Ni-Mn-Ga-Fe/Cu alloys

Abstract

Abstract. The were studied for the practical melting and annealing purposes. At first the chemical compositions (SEM-EDS) and the martensitic and magnetic transition temperatures (DSC, ac magnetic susceptibility) of the alloys were determined. High temperature DSC measurements were made in argon with 10 K/min. Two first measurements were carried out in the solid state (301 -1273 K) and in the third measurement the material was melted (max meas. temp. 1573 K). The ordering temperature was obtained from the measurements in the solid state. As the e/a ratio was above 7.53 the ordering temperature was in the range of 1019-1039 K, otherwise a clear change was observed. The variation in heating and cooling was less than 5 K with small quaternary additions, but alloying of 8% Fe increased this difference to 18 K. Alloys with close Ni/Mn/Ga-ratio showed only minor differences in solidus and liquidus temperatures, but if there was a clear change in the Ni/Mn-ratio even those alloys having close e/a ratios showed a clear difference in melting behavior. When Ni/Mn is 1.5--with higher values not clear region could be determined.

Microstructure and properties of Ni–Mn–Ga alloys produced by rapid solidification and pulsed electric current sintering

“…Conventional processing of these materials takes place via a melt route including casting of the polycrystalline master alloy with correct chemical composition and growing of the single crystal. There is a strong segregation tendency in these alloys [7,8], and therefore long homogenizing and ordering heat treatments are required before their use [9,10]. This conventional fabrication process is costly and time consuming, and thus, other possible fabrication routes are of interest.…”

In-situ characterization of ferromagnetic shape memory alloy / silicon bimorph nanoactuators

“…5), we can use the melting temperature of Ni-Mn-Ga to estimate the combined κ of the bimorph. For this purpose, we use the solidus temperature T S =1380 K of a similar Ni-Mn-Ga composition, Ni 49.7 Mn 28.7 Ga 21.6 as the melting temperature [12]. Assuming that the maximum temperature at the tip for the critical power equals the solidus temperature, T(L,P melt )=T S , Equation (1) yields κ≈10 Wm -1 K -1 .…”

NiMnGa/Si Shape Memory Bimorph Nanoactuation

“…Thereby, only those regions are considered to contribute to the SME that keep in the range of lower and upper stress limit. This approach may underestimate the fraction of non-contributing material, as additional effects such as creep occurring at high deposition temperatures may also induce stress relaxation [35,36]. A typical stress profile of a NiMnGa/Si bimorph actuator along thickness direction is shown in the Appendix.…”