SYNTHESIS AND CHARACTERIZATION OF NANOCRYSTALLINE NI-TI AND NI-CR POWDERS BY MECHANICAL ALLOYING

Nanocrystalline powders in the Ni-Ti and Ni-Cr systems were prepared b y mechanical alloying (MA) of elemental crystalline powders in an iner t atmosphere. The microstructure of the mechanically alloyed powders w ere characterized by XRD and TEM. The ball-milling process results in a drastic decrease of the crystallite size to the nanometer scale. X-r ay diffraction analysis reveals that in the Ni-Cr system, no diffracti on peaks from NiCr compound were observed even after 20 h of bail mill ing; while the lattice parameter of Ni increased with the milling time . In the Ni-Ti system, amorphous alloy was formed. Crystalline interme tallic compounds were obtained by post heat treatment of the amorphous alloy. The crystallization temperature of the amorphous NiTi alloy wa s obtained by DSC measurement.