Effect of mechanical milling of elemental powders on interface formation in TiN-Ni cermets prepared by pulsed current sintering

Interfaces of TiN-Ni cermets prepared by mechanical milling (MM) of TiN and Ni powders and the pulsed current sintering (PCS) method were investigated using TEM and high resolution TEM. The MM is an effective method for the formation of the TiN/Ni interface. Coherent TiN/Ni interfaces were observed in the sintered sample. The orientation relationship of the coherent interface was (111)TiN/(111)Ni. This coherent interface was formed by the Ni lattice expansion due to the introduction of the dislocations. Therefore, the Ni energy state in the cermet was metastable. The MM can excite the Ni energy state to a higher state rather than the metastable state in the cermet, and subsequent PCS leads to the Ni metastable state by relaxation of the exited energy; presuming that this process requires the lower activation energy compared with the amount that the Ni energy is excited to the metastable state from the stable (non-milled) state.