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Discontinuous precipitation initiated at interphase boundaries in a Zn-rich Zn-6.3 at.% Ag alloy

“…It can be seen that the reaction front velocity of discontinuous precipitation initiated at the Z 0 =Z 0 grain boundary is 12± 90% higher than that of discontinuous precipitation initiated at the Z 0 =e interphase boundary. This is slightly di erent from the conclusion obtained by Manna et al (1991) in Cu± 12 at.% In alloy in which the steady-state growth of discontinuous precipitation is assumed to be independent of the nucleation site once the reaction has initiated. The dependence of interlamellar spacing on ageing temperature is shown in ® gure 6, which indicates that the interlamellar spacing maintains an approximately constant value (0.5 mm † for discontinuous precipitate colonies grown from the Z 0 =e interphase or Z 0 =Z 0 grain boundaries at ageing temperatures studied except at higher temperatures (above 466 K).…”

“…In fact the discontinuous precipitation reaction a 0 ! a ‡ d in the above-mentioned study (Manna et al 1991) has occurred at d=a 0 interphase boundaries and advanced into supersaturated matrix a 0 . Unlike the Cu± In phase diagram including eutectoid transf ormation, no eutectoid transf ormation exists in the composition region corresponding to the two-phase Zn± 6.3 at.% Ag alloy in the present study.…”

“…In the study of Cu± 12 at.% In alloy (Manna et al 1991) on discontinuous precipitation, they have reported that the d=a 0 interphase boundaries are equally capable of initiating discontinuous precipitation (a 0 ! a ‡ d) in the supersaturated matrix a 0 as the grain boundaries.…”

“…Despite this, most of the studies so far have been con® ned to discontinuous precipitation initiated at grain boundaries (Tu and Turnbull 1967, Fournelle and Clark 1972, Williams and Edington 1976, Solorzano et al 1984 rather than interphase boundaries. We are not aware of any reports on discontinuous precipitation initiated at interphase boundaries except for one attempt with a Cu± 12 at.% In alloy (Manna et al 1991). In that study, the matrix± precipitate type of phase boundary between a supersaturated matrix (a 0 ) and a eutectoid colony (a 0 ‡ d) has the ability to initiate discontinuous precipitation in the a 0 matrix as does the a 0 =a 0 grain boundary.…”

“…Dependence of reaction front velocity on the reciprocal ageing temperature.Results ofManna et al (1999) for a single-phase Zn± 4 at.% Ag alloy are shown for comparison.…”