Thermal stability of nanocrystalline fcc and hcp Ni(Si) synthesized by mechanical alloying of Ni90Si10

The thermal stability of nanocrystalline fcc and hcp Ni(Si), obtained by me chanical alloying of Ni90Si10, has been studied. The allotropic transformat ion from fee to hcp Ni(Si) is accompanied by a volume expansion of 8.6% and is observed when fee Ni(Si) reaches a critical crystallite size of 10 nm. The hcp phase transforms to stable fcc Ni(Si) at 573 K. It has been identif ied that the lattice distortion in nanometre-sized crystallites from the eq uilibrium configuration and the decrease in the interfacial energy with gra in refinement act as self obstacles in controlling the grain growth of nano crystalline materials.