Particle size effects on dislocation density, microstructure, and phase transformation for high-entropy alloy powders

Abstract

Recrystallization and phase transformation reactions are driven by energy stored in the parent phase due to previous processing history. Grain boundaries, lattice strain, and dislocation networks may affect subsequent microstructural evolution, especially during metal powder consolidation processes. In this work, AlCrFe2Ni2 eutectic high-entropy alloy powders over a wide range of size distribution were used to investigate the correlation between dislocation density and microstructure as a function of particle size. Line profile analysis of the X-ray diffraction patterns of the as-received (quenched) samples shows that the dislocation density increases linearly with decreasing particle size. Based on microstructure analysis of the as-quenched and the annealed samples, it is found that the correlation is associated with the grain boundary length which increases with decreasing particle size, revealing that the key source of dislocation density is dislocations within the grain boundaries. The grain boundary energy acts as a driving force for the metastable to stable phase transformation of AlCrFe2Ni2, showing that the phase transformation kinetics is a function of particle size. This work shows a direct experimental observation and quantitative analysis that in metallic powder systems particle size is one of the key parameters which affects the dislocation density and the phase transformation kinetics most probably due to the different cooling rates achieved during powder production.