Microstructural descriptors and the effects of nuclei clustering on recrystallization path kinetics

Two stereologically based, microstructural path descriptors (left angle bracket)(lambda)(right angle bracket), the mean chord length, sometimes called the intercept free-grain length and C(alpha)(alpha), the contiguity ratio, are discussed from an experimental and kinetics modelling point of view for cases of recrystallization and phase transformation where the new product grains are nucleated in clusters rather than being randomly distributed. The microstructural partial path (MP) function, (left angle bracket)(lambda)(right angle bracket)versus volume fraction, is derived for three kinetics models based on different patterns of impingement: either (i) the new grains are randomly dispersed or where nuclei are heterogeneously distributed in idealized clusters in (ii) linear or (iii) planar arrays. The model formulations compared favorably with previous experiments on recrystallization of cold and hot worked commercial aluminum. Also, the contiguity ratio was determined experimentally for three cases where clustered nucleation behavior was thought to be prevalent. Positive deviation of C(alpha)(alpha) from C(alpha)(alpha) ~ Vv at low Vv was clearly evident in each example.