Surface hardening and precipitation behaviors in plasma-nitrided Fe-(2-x) at%Al-x at%Ti alloys

Synopsis: The alloying effects of Ti, which is strongly attracted to nitrogen (N), on nitride precipitation and the resultant surface hardening in nitrided Fe-Al-Ti alloys, were investigated using three-dimensional atom probe tomography. Ti addition promotes nucleation of Al nitrides, which leads to substantial surface hardening. As the amount of added Ti increases, the hardness near the surface increases because the nucleation of Al nitrides is promoted, likely due to the higher density of Ti-N clusters. However, the effect of Ti on surface hardening by nitriding in Fe-Al alloys is weaker than that of V addition, as reported previously, although Ti is a stronger cluster-forming element than V. These results suggest that, in addition to the ability to form clusters, the potency of clusters for AlN nucleation needs to be considered to control AlN precipitation by solute clustering.