Temperature-minimum line in the Cu-Ni-Mn phase diagram

Abstract

225 The phase diagram of the Cu–Ni–Mn system has been studied for a long time. In Fig. 1, we show iso therms on the liquidus and solidus surfaces of the dia gram established by Parravano in 1913 [1]. Note the temperature minima in the diagrams of the Cu–Mn and Ni–Mn systems, where there are general regions corresponding to solid solutions with a bcc structure on the copper and nickel sides, and the unlimited solubility in the Cu–Ni system. This raises the question of whether there is a contact line of the liquidus and soli dus surfaces in the ternary Cu–Ni–Mn diagram, con necting the minima in the binary Cu–Mn and Ni–Mn diagrams. On that line, there should be a continuous series of ternary alloys solidifying at constant tempera ture, with values ranging from 1020°C (the minimum on the Ni–Mn diagram) to 870°C (the minimum on the Cu–Mn diagram). Nothing has been reported regarding the existence of such a line in metallic systems as yet. Ternary Cu–Ni–Mn alloys with a small control lable temperature range of solidification are encoun tered as solder for use up to 800°C. According to the fundamental texts on physico chemical analysis [1, 2], the isotherms on the ternary Cu–Ni–Mn diagram indicate that the minima in the binary Cu–Mn and Ni–Mn systems are connected along a line running along the liquidus and solidus sur faces of the ternary system. This, in turn, indicates that those surfaces touch along this line. The liquidus and solidus surfaces do not touch in the ternary Cu–Ni–Mn diagram presented in [3]. Verification of the data in [3]—by plotting three dimensional diagrams using 3D Studio Max 9.0 soft ware—indicates that the diagrams and isotherms in [3] are not consistent and, in fact, the liquidus and solidus surfaces do meet along the line connecting the minima in the binary Cu–Mn and Ni–Mn diagrams. It is not a straight line. There are depressions on the liquidus and solidus sur faces of the ternary Cu–Ni–Mn diagram determined by the minima in the binary Cu–Mn and Ni–Mn systems, according to [4]. We conclude that the liquidus and solidus surfaces do not touch on the basis of the ter Temperature Minimum Line in the Cu–Ni–Mn Phase Diagram