18 - Mechanical properties of B2 nanostructures

Abstract

Nanocrystalline NiAl was fabricated by mechanical alloying and vacuum hot-pressing sintering technique. Increase in yield stress, ultimate tensile stress (UTS), and fracture strain with increasing strain can be attributed to the grain refinement. The high compressive strain is associated with ductile fracture. Also the microhardness increases by the grain refinement. Cracking is not observed around the indentations, which suggests significant plastic deformation during the indentation. Hall–Petch plot can be used for nanostructures also. Strengthening is a result of forest dislocation inhibiting dislocation motion. Increasing temperature induces grain growth and at 180nm hardness decreases. The hardness indicates an inverse Hall–Petch effect in nano-polycrystalline NiAl. The Hall–Petch relation is applied to FeAl nanostructures also. The effect of temperature is similar to that in NiAl. Increased strength properties of nanostructures in FeAl did not significantly improve the ductility. In most of the cases reported brittle behavior is found even at very small grain sizes and ductility and toughness are about the same as in macroscopic material.