The Density Discontinuity Associated with the Precipitation of the Second Phase in Pb + 7.45 At.% Sn Alloy


Associated with the precipitation of an Sn-rich phase from a Pb + 7.45 at.% Sn alloy during cooling at a constant rate from an elevated temperature well above the solvus temperature, there is a measurable and precipitous decline in density which begins at a temperature slightly below the solvus temperature for this alloy. This decline takes place over a limited temperature range and is attributed to the formation of excess vacancies created during the nucleation of the precipitation reaction. A similar formation of excess vacancies has been observed using positron annihilation spectrometry in a similar alloy during cooling through the solvus temperature. During this decline in density, the concentration of these vacancies much exceeds the equilibrium vacancy concentration for this alloy. The excess vacancies are unstable and, with continued cooling, quickly anneal out over a narrow temperature range allowing the versus temperature curve to regain linearity. © 1997 Elsevier Science S.A.


Materials Science and Engineering

Keywords and Phrases

Pb-Sn alloys; Ramp cooling; Vacancy formation; β-Sn precipitation

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Article - Journal

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Publication Date

01 Jan 1997