STRUCTURAL CHANGES IN MELTS OF HEAT-RESISTANT NICKEL ALLOYS
Melts of heat-resistant nickel alloys immediately after melting are macro-homogeneous, but micro-inhomogeneous in structure. Further heating of the melt causes structural changes. The kinetics of changes is recorded on polytherms of physical properties: specific electrical resistivity, kinematic viscosity and density. The measurements were performed on heating and cooling. More than 50 grades of nickel base alloys were investigated. All polytherms after heating to a certain temperature are characterized by the discrepancy between forward and reverse operation - the hysteresis phenomenon. After heating to the following temperature specific for each alloy composition the mismatch of the branches becomes maximum and constant. In accordance with the Arkharov - Novokhatsky model the melts near the melting points consist of atomic microgroupings with the middle order and the disordered zone. The composition of atomic clusters follows the structure of the solid metal. Because the principal excess phases in these alloys are intermetallic precipitates based on Ni3(Al,Ti) and MC type carbides, the clusters of the melt will consist of the same elements. Heating of the melt leads to a decrease in the size of clusters and increase in inter-cluster space. A second heating above a certain temperature, recorded as a result of studying the physical properties, will lead to the complete decomposition of atomic groups, the distribution of alloying elements becoming even in the entire volume of the melt. The liquid metal becomes more equilibrium. This state is characterized by macro- and micro-homogeneity. This effect is a base of the technology of high temperature melt treatment, significantly improving the quality of metal products.