Perfection et stabilité thermique des structures lamellaires de l'eutectique Pb–Sn

In directionally solidified Pb–Sn eutectic, prepared by the Bridgman technique, it has been found that it is possible to obtain grains of nearly perfect lamellar structure and stable at elevated temperatures. The interlamellar spacing λ is 1 μm and the mean distance between fault lines 20 λ whereas they are respectively 1.5 μm and 7 λ in neighbouring grains. The orientation relation is: growth direction || [21]_Pb and ⊥ (12)_Sn, lamellar interfaces || (47)_Pb and (523)_Sn. The spacing between planes perpendicular to the growth direction is the same in both phases. By studing the orientation relation with Bollmann's theory, zero planes and interfaces are found to be parallel. The coherent interphase boundary can explain the particularities of these grains. Their origin is discussed and related to the nucleation conditions.