Composition: Sn-10%Sb.

Processing: Sand casting.

Etching: 10 s immersion in FeCl₃ alcoholic solution.

The macrograph reveals large columnar grains decorated with black crystals of primary  δ phase (SnSb intermetallic compound), indicating incomplete peritectic reaction. This intermetallic are square, however, depending on the sectioning plane, they appear as trapezoids or with triangular shapes. The dark β phase that is visible in the micrographs is a solid solution of Sb in Sn and it is originated from both the peritectic reaction and direct solidification. At higher magnifications, small white crystals of δ phase are visible at the grain boundaries and within the β phase. These are formed when entering in the β+δ field. Note that the solubility of Sb in Sn significantly decreases with decreasing temperatures.

Sn-Sb diagram

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