Computer model of Cu-Ni-Mn isobaric phase diagram: verification of crystallisation intervals and change of the three-phase reaction type

The purpose of article was to show the possibilities of spatial computer models of phase diagrams in solving of the problems of digitalization of materials science. The study of the high-temperature part of the isobaric phase diagram for the Cu–Ni–Mn system was carried out taking into account two polymorphic modifications of manganese (dMn and gMn). For a better understanding of the phase diagram structure, at the first stage, its prototype was developed with increased temperature and concentration intervals between binary points with the preservation of topological structure, which is then modified into the model of phase diagram corresponding to the real system. The phase diagram of Cu-Mn-Ni system above 800°C was formed by three pairs of liquidus, solidus, and transus surfaces and three ruled surfaces with a horizontal arrangement of the forming segment. Experimental part: the effect of changing the peritectic equilibrium (L + dMn → gMn) to the metatectic one (dMn → L + gMn) was revealed. The crystallisation features at the change of three-phase transformation type were considered, the surface of change of melt mass increment sign and the vertical mass balances for the three-phase region L + dMn + gMn were constructed. The surface of two-phase reaction, on which the change of three-phase reaction type occurs, is a ruled surface and is determined, using the algorithm for calculating the change in sign of the mass increment of liquid phase. Three-phase region, taking into account the surface of type change of three-phase reaction, is divided into six concentration fields when projecting into the triangle of compositions. Four concentration fields differ in the crystallisation stages and the formed set of microstructures. Isothermal sections were calculated in the temperature range between two minimum points arranged in the Cu–Mn and Mn–Ni systems at zero crystallisation interval between the valleys of the liquidus and solidus surfaces and taking into account the crystallisation interval. The spatial model of phase diagram greatly expands the possibilities of computer-aided design of materials. In particular, a solution for the problem of type changing of three-phase reaction was obtained, which cannot be realised either by thermodynamic calculations or by calculations from first principles.