Interlamellar spacing in discontinuous precipitation

After reviewing the behavior of a number of systems exhibiting discontinuous precipitation, the theoretical treatment of the process is discussed, with emphasis on the problem of the interlamellar (or inter-rod) spacing. The case of the minimum, or critical, spacing is discussed for lamellar and rod products, as is a possible criterion for the maximum accessible spacing. The problem of the optimal spacing is then addressed, mainly from an experimental point-of-view. Experimental data for Al-Zn and Mg-Al alloys are analyzed and related to the discussion. This paper is based on a presentation made at the symposium “Establishment of Microstructural Spacing during Dendritic and Cooperative Growth” held at the annual meeting of the AIME in Atlanta, Georgia on March 7, 1983 under the joint sponsorship of the ASM-MSD Phase Transformations Committee and the TMS-AIME Solidification Committee. formerly with the Department of Metallurgy and Materials Science, McMaster University.