Microstructural Evolution of Ti-Mo-Ni-C Powder by Mechanical Alloying

Abstract

The microstructural evolution of (Ti,Mo)C-Ni powder by mechanical alloying of pure titanium, nickel, carbon and molybdenum as starting powder with the composition of TiC-20 Mo2C-20 Ni in mass% were investigated by X-ray diffraction (XRD) using CuKradiation, field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) with EDS. The powders were mixed gradually and the size of the mechanically alloyed particles was of sub-micrometer order. The TiC structure, which indicated smaller lattice constant than TiC, clearly appeared after 100 h milling time. The particles consisted of fine grains of about 5 nm size. The nickel was transformed from crystallized phase into an amorphous phase by mechanical alloying. The molybdenum was dissolved into TiC structure and Mo/Ti ratio in (Ti,Mo)C was about 3/7. (doi:10.2320/matertrans.MRA2008280) The powders were milled for various times, and were then analyzed to determine the change of the phase compositions and morphologies by means of X-ray diffraction using CuKradiation, field emission scanning electron micros- copy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) with EDS. The crystallite size of the TiC structure for powder after 700 h milling was estimated, based on the half-width of the X-ray diffraction pattern of the specimen using Scherrer's formula. The powders for FE-SEM with EDS observation were embedded in polymer and Cu powders for conductivity and then were mechanically polished. The lattice constants for the powder and the sintered compact were estimated by means of selected area diffraction pattern (SADP). The as-synthesized powders after 700 h milling time were pressed into pellets under 100 MPa to pellets. These green pellets were then sintered at 1723 K for 1 h under vacuum. The sintered compact was also analyzed by X-ray diffraction, FE-SEM and TEM-EDS. 3. Results and Discussion The XRD patterns of the milled powders for different times are shown in Fig. 1. Peaks of crystalline titanium,