The Role of Microstructure on Strength and Ductility of Hot-Extruded Mechanically Alloyed NiAl

Processing and properties of mechanically alloyed Ni(Fe)Al-Al2O3-AlN

“…Considering the average grain size of 0.3 pm in this material, the driving force for SRx in the form of grain boundary energy may be thought to be enough in comparison to the previous result of the mechanically alloyed NiA1 containing 3% of A1203 [17]. Thus, it is reasonable to assume that the unique break-away process of the SRx mechanism [ 17] is constrained due to the relatively higher content of dispersoids or lack of high mobility coincident to the lattice site (CSL) boundaries acting as SRx seeds in this material [4,17,20]. The present alloy system is expected to have an adequate combination of ambient temperature ductility and high temperature creep resistance.…”

“…However, this is not applicable to NiAI since planar slip is not generally observed. Dispersoi~s will raise the yield strength of the material and this can result in the operation of additional slip systems resulting in improved ductility [4]. As discussed above, dispersoids produce refined grain structures and ductility was shown to have improved below a critical grain size in NiA1 [12][13].…”

“…In addition to this alloy design philosophy, a solid solution with the addition of Fe and the precipitation of the phase in this material have been considered in order to improve room temperature ductility [9] as well as creep resistance [11 ]. The addition of dispersoids to a brittle material should have a beneficial effect on ductility through the homogenization of slip [4]. However, this is not applicable to NiAI since planar slip is not generally observed.…”

“…Recent studies [3][4][5][6][7][8] have demonstrated that, by permitting AI to react with residual oxygen through milling in an argon filled attritor, ultra fine A1203 dispersoids could be incorporated into the NiA1 matrix having grain sizes of less than 1 ~tm. The in situ formed A1203 dispersoids acted as obstacles to the dislocation motion, leading to a significant improvement in mechanical properties, including compressive ductility at ambient temperature and creep resistance at high temperature [3][4][5][6][7][8].…”

“…The in situ formed A1203 dispersoids acted as obstacles to the dislocation motion, leading to a significant improvement in mechanical properties, including compressive ductility at ambient temperature and creep resistance at high temperature [3][4][5][6][7][8]. As yet, there is no direct measurement of the coarsening rate of particular dispersoids in NiAI and initially A1203 was used as the major dispersoid phase.…”