Effects of aging on precipitation and shape memory of Fe–Mn–Si–Cr–Ni based alloy with V and N addition

Abstract

The effects of aging on the precipitation of the second phase and the shape memory effect (SME) of an Fe–Mn–Si–Cr–Ni based alloy containing V and N elements (0·9 wt-%) have been investigated. The results showed that VN particles, precipitated during aging, could improve the shape recovery ratio to 56%, compared with that of only 25% for the solution treated samples when the V and N bearing alloy was aged for 24 h. It was further confirmed by X-ray diffraction that the fitting relationship between shape recovery and martensite content is practically in agreement with linearity. Electron microscopic observation has shown that aging treatment gives rise to an increasing amount of VN precipitates, among which the small ones uniformly precipitated inside grains but would aggregate and grew quite remarkably to be large ones at the grain boundaries. These large particles do not appear to have much negative effects on the SME, whereas it is the fine nanosize VN particles inside grains that are the key factor to act as preferential nucleation sites for martensite, improving the SME.