Microstructural evolution and chemical redistribution in Fe-Cr-W-Ti-Y2O3 nanostructured powders prepared by ball milling

Microstructural, chemical and hardness changes of 14YWT ODS nanostructured powders prepared by mechanical alloying in different milling times (5, 20, 35, 50 and 80 h) were investigated by light and electron microscopy, X-ray diffraction analysis (modified Willamson-Hall equation) and microhardness tester. It was observed that morphology and structure of powders experienced five different stages during milling and a qualitative mechanism based on them was proposed. The morphology of powders through theses stages followed this sequence: particles with core-rim structure - loosely bound clusters - equiaxed particles - plate-like particles - chemically homogenized equiaxed particles. The layered structure inside powders firstly appeared in the third stage (between 20 and 35 h) which was associated with the onset of Fe-based solid solution formation and reduction in lattice parameter value. According to metallographic and XRD analyses, in the first three stages (from beginning to 35 h), the milling chiefly resulted in severe deformation and grain refinement of powders, while in two later stages (after 35 h), alloying was progressed. Also, the relationship between hardness and crystallite size of powders in different milling times was found to show the Hall-Petch type behavior.