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

Abstract
The high temperature transformations (e.g. liquidus, ordering temperature) of the alloys Ni_47.7Mn_31.2Ga_21.1, Ni_49.7Mn_28.7Ga_21.6, and Ni_49.6Mn_24.0Ga_26.6, Ni_47.3Mn_30.3Ga_20.3Fe_2.1, Ni_49.9Mn_28.3Ga_20.1Fe_1.7, Ni_51.3Mn_14.4Ga_26.3Fe_8.0, Ni_47.3Mn_25.5Ga_24.5Cu_2.7, Ni_48.3Mn_29.7Ga_21.1Cu_0.9, and Ni_49.4Mn_23.3Ga_25.6Cu_1.7 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 1.5-1.6 the liquidus was 1364±2 K, and with 1.7-1.8 it is 1384±5 K, while with higher values not clear region could be determined.