Mechanism of peritectic reactions and transformations

Abstract

The following peritectic reactions in the Cu–Sn, Ag–Sn, and Al–Mn systems were studied by a unidirectional solidification technique <disp-formula> <mml:math> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>+</mml:mo> <mml:mi>L</mml:mi> <mml:mo>→</mml:mo> <mml:mi>β</mml:mi> <mml:mo>(</mml:mo> <mml:mtext>Cu</mml:mtext> <mml:mo>–</mml:mo> <mml:mtext>Sn</mml:mtext> <mml:mo>)</mml:mo> <mml:mo>,</mml:mo> <mml:mtext> </mml:mtext> <mml:mi>ɛ</mml:mi> <mml:mo>+</mml:mo> <mml:mi>L</mml:mi> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:mo>(</mml:mo> <mml:mtext>Cu</mml:mtext> <mml:mo>–</mml:mo> <mml:mtext>Sn</mml:mtext> <mml:mo>)</mml:mo> <mml:mo>,</mml:mo> </mml:mrow> </mml:math> </disp-formula> <disp-formula> <mml:math> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>+</mml:mo> <mml:mi>L</mml:mi> <mml:mo>→</mml:mo> <mml:mi>ζ</mml:mi> <mml:mo>(</mml:mo> <mml:mtext>Ag</mml:mtext> <mml:mo>–</mml:mo> <mml:mtext>Sn</mml:mtext> <mml:mo>)</mml:mo> <mml:mo>,</mml:mo> <mml:mtext> </mml:mtext> <mml:mi>γ</mml:mi> <mml:mo>+</mml:mo> <mml:mi>L</mml:mi> <mml:mo>→</mml:mo> <mml:mi>β</mml:mi> <mml:mo>(</mml:mo> <mml:mtext>Al</mml:mtext> <mml:mo>–</mml:mo> <mml:mtext>Mn</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> </disp-formula> It was found that in the peritectic reaction a border of the secondary phase formed around the primary phase in the first three cases. It was experimentally and theoretically shown that a peritectic transformation occurred in the first and third reactions by diffusion through the secondary phase boundary. In the Al–Mn alloys the peritectic reaction took place by a precipitation of β and a dissolution of γ, both in contact with the liquid. All reactions were theoretically analysed.