Morphologies and growth mechanism of TiN in ceramic surface layers prepared by nitrogen arc

The titanium nitride(TiN) ceramic surface layers were in-situ prepared by nitrogen arc melting on the surface of pure titanium substrates. The formation mechanism of the ceramic layers, the growth morphologies and mechanism of the TiN phase were investigated. The results show that the nitrogen arc melting is a non-equilibrium rapid cooling process and the cooling rate can be as high as 10²~10³ K/s. The micro growth modes of the TiN phase in ceramic surface layers exhibit the diversity. The TiN crystal grows up by the spiral dislocation lateral growth mode at the location of low undercooling in the molten pool. Because of the undercooling increased at the bottom of the molten pool, the micro growth mode changes to the alternating between the continuous growth and the lateral growth.