|M.Sc Student||Mashall Ido|
|Subject||Reactive Surface Modification of Nickel Alloys by Treatment|
in Titanium and Nitrogen
|Department||Department of Materials Science and Engineering||Supervisors||Mr. Leonid Klinger|
|Professor Emeritus Elazar Gutmanas (Deceased)|
|Dr. Irena Gotman|
In the present research, a two-stage titanization-nitriding process has been developed with the goal to grow a wear- and oxidation-resistant TiN coating on the surface of nickel alloys. The process is based on the Powder Immersion Reaction Assisted Coating (PIRAC) method originally developed for the coating on non-oxide ceramics.
At the first stage, Ni surface was enriched in Ti by PIRAC annealing in a halogen-activated Ti powder. This resulted in the formation of a multi-layer coating consisting of different Ti-Ni compound layers. The treatment temperature did not exceed 900ºC to avoid liquid formation (the low melting Ti-Ti2Ni eutectic). The kinetics of different layers growth at 700-900ºC was found to be controlled by diffusion and obeyed the parabolic growth law. The activation energies of the process as a whole and of separate layers growth have been measured. The effect of different processing parameters (amount of halogen, shape and size of Ti powder, etc.) on the formation of Ni-Ti surface layers has been studied.
The Ti-enriched surface was subsequently transformed into a titanium nitride layer by PIRAC nitriding - a process based on annealing the sample under a low nitrogen pressure formed by selective diffusion of the atmospheric nitrogen. The thickness of the TiN layer did not exceed 1 mm even after 16 h long PIRAC treatment at 900ºC. During nitriding, the significant growth of the Ni3Ti layer and the shrinkage of the Ti2Ni and NiTi layers (all formed during the titanization procedure) were observed. Several peculiarities of layers growth were observed both during titanization and during nitriding PIRAC procedures.
The applicability of the TiN PIRAC coating process to Iron- and copper-base alloys has also been demonstrated.