Reversible “Wetting” of grain boundaries by the second solid phase in the Cu-In system

The reversible wetting of grain boundaries by the second solid phase in the copper-indium system has been observed. With an increase in the temperature, the contact angle θ between the (Cu)/(Cu) grain boundary in a Cu-based solid solution based and particles of the δ-phase (Cu70In30) decreases gradually. Above T W = 370°C, the first (Cu)/(Cu) grain boundaries completely “wetted” by the δ phase appear in Cu-In polycrystals. In other words, the δ phase forms continuous layers along grain boundaries and θ = 0. At 440°C, the fraction of completely wetted grain boundaries reaches a maximum (93%), whereas the average contact angle reaches a minimum (θ = 2°). With a further increase in the temperature, the fraction of completely wetted grain boundaries decreases and vanishes again at T DW = 520°C. This phenomenon can be explained by an anomalous shape of the solubility limit curve of indium in a solid solution (Cu).

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