Structural Stability of Nanocrystalline NiAl

Abstract

<jats:p>NiAl is an important high temperature structural material, with a high melting point (1640°C), low density and excellent high temperature oxidation resistance. The room temperature ductility of NiAl may potentially be improved with the use of nanocrystalline grain size. However, a key question concerning the application of nanostructured NiAl is about its structural stability at high temperature. The current study is thus focused on the investigation of the structural stability of nanocrystalline NiAl using in-situ transmission electron microscopy (TEM) and differential thermal analysis (DTA).</jats:p><jats:p>Nanocrystalline B2-NiAl was prepared by ball milling (24 hrs) from elemental Ni and Al powders. Subsequent consolidation into bulk form was performed using dynamic consolidation employing a 3-capsule plate-impact fixture at approximately 400 m/s [1-3]. Powder nanocrystalline NiAl was dispersed on a holey carbon film for TEM observation. TEM specimens of shock compacted bulk NiAl nanocrystals were prepared by cutting, polishing, dimpling and ion milling.</jats:p>

The Microstructure of Oxidized Consolidated Nanocrystalline NiAl

“…Nanophased NiAl specimens were prepared by mechanical alloying followed by shock wave consolidation, which yielded consolidated material with an average grain size of 11 ±8 nm [2]. Thermogravimetric analysis (TGA) of nanosized NiAl was used to characterize the material's oxidation resistance, and performed for three different times (0.5 h, 5 h, 48 h) in compressed air at 1373 K. It was found that the thickness of the scale increased with increasing oxidation time, in accordance with parabolic oxidation kinetics.…”