Effect Of C,N On Stacking Fault Probability And Hrem Characterization Of Microstructures In Fe-Mn-Si Alloy

Because of its low price and good mechanical machining property, Fe-Mn-Si-based shape memory alloy (SMA) has great potential and been the hotspot of SMA research in recent years. Its shape memory effect (SME) relies on fcc→hcp matensitic transformation and its reverse transformation, which nucleates in the austenite by stacking faults, then multiply. Therefore, methods to improve SME of Fe-Mn-Si alloys concentrate on the matensitic transformation and its reverse transformation, for instance, obtaining themoelastic matensite; introducing new heat treatment process"training"; adding alloying elements and so on. Many scientists have already studied the effects of C,N elements on stacking fault probability(SFP) and SME experimentally and theoretically, but there is no final conclusion.In order to get a deep understanding of the mechanism of C,N elements, the relationship between SFP and SME, SFP has been determined by XRD peak shift, peak broadening and electronic diffraction spot shift methods; the relationship between C,N elements and SFP has been analyzed; and stacking faults and interfaces has also been characterized by HREM. Moreover, long period stacking structures in Fe-Mn-Si and Ni-Mn-Ga alloy have been discovered in the experiments.In the XRD measurements, Psf was obtained by substitute instrument linewidth via Jade software for instrument linewidth via Al standard sample. In addition, errors of peak shift method have also been discussed. The fact that high dense stacking faults induced electronic diffraction spots shift has been discovered. Two orders difference between local region SFP and average SFP, indicates that stacking faults distribute nonhomogeneously in these alloys, and also support the stacking faults nucleation mechanism.There is no clear relationship between SFP and SME by comparing the results of SFP and SME. As Cωt% increasing, SFP rises and then decline. When C content came close to 0.1%, SFP reached a peak. Otherwise, when C content is lager than 0.3%, SFP will not change a lot. Moreover, There is a linear relationship between C%+N% and shape memory alloy. In HREM characterization of the stacking faults and very thin matensitic plates, long period stacking structures that were formed by periodically overlapped (111) planes of austenite, were discovered the stacking sequence of which is ABCABABCAB…….In addition, two dimensional long period stacking structure has been discovered in Ni-Mn-Ga alloy by HREM characterization.