Surface nanocrystallization of Ni3Al by surface mechanical attrition treatment

The mechanical property and microstructure evolutions of Ni3Al intermetallic compound subjected to surface mechanical attrition treatment (SMAT) were investigated in relation to surface nanocrystalization. Grain size in topmost surface of SMATed Ni3Al alloy was refined to a minimum size of about 10 nm, and then increased with the enhancement of the depth from surface to matrix. The original ordered L12 phase transformed to Ni (Al) solid solution with a disordered face-centered cubic structure. The maximum nanohardness of the deformed Ni3Al alloy was near 12 GPa. The microstructure evolution including the variation of defects during the SMAT as well as post-annealing processes showed that the surface nanocrystallization of Ni3Al intermetallic compound was predominantly controlled by dislocations which divided the coarse grains. The different microstructures at each sublayer illustrated that the nanocrystallization process was decided by the accumulated energy resulted from plastic strain.