Effect of Applied Stress on α^′′ Precipitation in Fe-N Alloys

Abstract

Two step aging (stress aging and free aging) has been carried out on single crystals of iron-nitrogen solid solutions. It has been confirmed that the stress orienting effect of α^′′ precipitates (Fe₁₆N₂) is due to preferential nucleation on a particular habit plane of α^′′ which is favored by the stress. A critical nucleus of α^′′ which can grow spontaneously at 100°C is estimated to have not more than 30 nitrogen atoms. Growth kinetics of α^′′ has been determined by measurement of length change which is induced by growth of preferentially nucleated α^′′ during the stress aging and has been shown to have the time exponent 2.