In-situ TEM annealing of amorphous Fe-24at.%W coatings and the effect of crystallization on hardness

This paper describes the crystallization which occurs upon annealing of an amorphous Fe-24at.%W coatings, electrodeposited from a glycolate-citrate plating bath. A combination of Differential Scanning Calorimetry and in-situ Transmission Electron Microscopy annealing is used to study the onset of crystallization of the amorphous coating. The in-situ TEM analyses reveal the formation of first crystallites after annealing at 400\ua0\ub0C for 30\ua0min. Upon a temperature increase to 500–600\ua0\ub0C, the crystallites develop into Fe-rich nanocrystals with ~ 40\ua0nm grain size. The nanocrystals are dispersed in the remaining amorphous Fe-W matrix, which results in the formation of a mixed nanocrystalline-amorphous structure. The observed crystallization can be held responsible for the increase in the hardness obtained upon annealing of Fe-24at.%W coatings. In fact, the hardness of the as-deposited material increases from 11 to 13\ua0GPa after annealing at 400\ua0\ub0C, and it reaches the maximum value of 16.5\ua0GPa after annealing at 600\ua0\ub0C