Yoshikiyo Ogino

Nanocrystallization and Mechanical Properties of an Amorphous Electrodeposited Ni75W25 Alloy

An amorphous Ni-W alloy containing about 25 at. % W has been prepared by electrodeposition. Nanocrystallization behavior of this alloy has been studied by X-ray diffraction, high resolution transmission electron microscopy (HR-TEM) and small angle X-ray scattering. The Hall-Petch strengthening mechanism was observed for the hardness extending to a finest grain size of about 10 nm. When the grain size is less than about 10 nm, decrease of the hardness was observed. This decrease may be due to the significant increase of the intercrystalline volume fraction, especially the fraction associated with the triple junction.

Effect of grain boundary migration in solution treatment on grain boundary precipitation of Al-Fe dilute alloys

Grain boundary internal friction in the Al-0.002 wt.% Fe alloy was measured to examine an interaction between moving boundaries and solute atoms. When both the alloys solution treated for a short time at 773K in which grains are growing and solution treated for a prolonged time in which grain growth has been ceased are subsequently aged at 593K, grain boundary precipitation occurs within a shorter time in the former. This fact is in consistent with the assumption that greater quantities of solute atoms segregate in moving boundaries than in stationary boundaries. If the alloy is solution treated at elevated temperatures above 823K, however, longer times are required for grain boundary precipitation when grains are growing in the solution treatment. This may be due to the breaking away of the moving boundary from the solute atmosphere.