Correlations between the minimum grain size produced by milling and material parameters

Synthesis of nanocrystalline Zn-22 Pct Al using cryomilling

“…Several investigators [15,17,[35][36][37][38] have argued that d min scales with the melting temperature. For some fcc metals, d min scales inversely with melting temperature, T m , while for bcc and hcp metals, and for fcc metals with higher melting temperatures, d min exhibits essentially constant values with T m .…”

“…[16] It was reported that d min scales inversely with melting temperature for selected fcc metals, whereas in bcc and hcp metals, d min is constant with respect to melting temperature. [17] It had been suggested [16] that for pure metals, the limiting grain size is determined by the minimum grain size that can sustain a dislocation pileup within a grain and the rate of dislocation recovery.…”

Characteristics of face-centered cubic metals processed by equal-channel angular pressing

“…According to the experimental data, which show rather a monotonously changing slope of the HallPetch relation obtained for a wide range of grain sizes [34,44], it is reasonable to suppose that in general the value of r pile is a power law function of the normalized effective shear stress of the form…”

“…1 The maximum yield strength, r p,max /l, obtained by ECAP versus the absolute melting temperature, T m , for fcc metals Al 120 [14] 122 [22] 119 [22] Au 245 [25] 237 [unpublished] Cu 395 [14] 380 [26] 390 [27] 383 [22] Ni -1138 [unpublished] decrease in yield stress with decreasing grain size indicating a softening effect at very fine grain sizes [32,[34][35][36][37]. While the current models [32,34,35,[38][39][40][41] explaining the softening process are quite different and inconclusive, the Hall-Petch type of behavior is basically interpreted by the concept of dislocation pile-ups formed at grain boundaries [34,[42][43][44]. In this context, it is considered that dislocations are generated by Frank-Read sources and then arrested at the grain boundaries of grains having a size of d. At the proper effective shear stress, s e , the pile-up of these dislocations then results in a maximum normalized dimensionless stress, r pile , having a value equal to [42]:…”

“…For very fine grain sizes (d < 100 nm), the numbers of dislocations in the pile-ups tend to one giving pile-up breakdown [34,44], and the value of r pile is now proportional to the normalized shear stress so that…”