Comparative TEM study on as-cast ingot and nodular bainite of Cu-14.9%Sn alloy

Abstract

We have investigated microstructure and orientation relationship (OR) of the α and δ phases in an as-cast ingot and nodular bainite of Cu-14.9 at.% Sn alloy by using transmission electron microscopy. Proeutectoid α grains and surrounding δ phase (prior β phase) possess well-defined (1 1 1)_α//(1 1 0)_δ, OR, that is, Kurdjumov–Sach (K–S) OR, while these two phases formed by eutectoid decomposition exhibit some deviation from K–S OR. On the other hand, the α and δ phases in nodular bainite exhibit (1 1 1)_α//(1 1 0)_δ, , which is Nishiyama–Wassermann (N–W) OR, as well as K–S OR. The emergence and variations of these ORs between the α and δ phases have been interpreted from the viewpoints of (i) matching of interplanar spacing of {1 1 1}_α, {1 1 0}_β and {6 6 0}_δ planes, (ii) minimum strain criteria based on the invariant line concept for K–S OR and (iii) correspondence of atomic positions in the relevant phases by employing the structural ledge concept for N–W OR.

Keywords:

• copper-tin alloy
• phase transformation
• solidification
• precipitation behaviour
• transmission electron microscopy
• orientation relationship