The isothermal section (500 °C) of the phase diagram of the ternary system Cu-Sn-Y

The isothermal section (500 °C) of the phase diagram of the ternary system Cu-Sn-Y (40 at.% Y or less) was investigated by X-ray diffraction, differential thermal microanalysis, optical microanalysis and electron probe microanalysis techniques. The isothermal section consists of 12 single-phase regions, 25 two-phase regions and 14 three-phase regions. Three new ternary compounds were found in this isothermal section: the θ phase (Y₈Cu₇Sn₅), the β phase (Y₃Cu₄Sn₃) and the γ phase (Y₁₉Cu₆₆Sn₁₅). They are all non-variable compounds. The θ phase is an orthorhombic system with $\text{a = 9.702}\text{A}\text{̊}$, $\text{b = 7.285}\text{A}\text{̊}$ and $\text{c = 6.545}\text{A}\text{̊}$.

The maximum solid solubility of tin in α-Cu at 500 °C is about 9.0 at.% and that of yttrium in α-Cu at 500 °C (with 4.3 at.% Sn) is about 1.5 at.%.