T-X-Y Diagrams With Kinematical Surfaces For Lead-free Soldering Systems

Abstract:

Atlas, containing description of 20 ternary systems for lead alloys substitution, has been published. In spite of enormous work fulfilled, it contains only liquidus projections, invariant reactions tables, 2-3 isotherms and some isopleths for every T-x-y diagram. Obviously, it is not a real device to design the heterogeneous materials. Special technology to reconstruct a space T-x-y diagram with all set of its geometrical elements in dependence of a scope of experimental and calculated data (beginning from phase transformation scheme via primitive template as surfaces set, given by their additive contours, to perfect thermodynamically regulated computer model) has been elaborated. Every surface is given by interpolate Lagrange polynomial and is constructed cinematically. Main difficulties of T-x-y diagrams computer models were connected with the fact that the liquidus does not contain all information about the system properties. Computer models of Au-Bi-Sb, Bi-In-Sn, Ag-Cu-Sn systems had been designed by incomplete data of the Atlas. Additional efforts were made for the sub-solidus regions, low-temperature allotropies and exothermic compounds. So, 3 from 8 binary compounds of the Ag-Cu-Sn system has not exit on the liquidus. Two from them have upper and low temperatures of decomposition and third one is the low-temperature allotropy and participates in the eutectoid transformation with a Sn modification. In Ag-Cu-Sn system there are 14 invariant and 37 monovariant transformations, its T-x-y diagram consists of 233 surfaces and 81 phase regions. Reconstructed (and verified by 2 isotherms and 5 isopleths of the Atlas) computer model helped to detect some errors: homogeneous regions of Ag and one binary compound are degenerated on some isotherms, but according to the invariant reactions they must present on corresponding sections.Such kind of computer models help to calculate mass balances on different crystallization stage and detect the origin of crystals, to search the mistakes in the graphics of real diagrams sections.

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