INVESTIGATION OF THE NITROGEN-NICKEL-TITANIUM SYSTEM - THE ISOTHERMALSECTION AT 900-DEGREES-C

Phase relations in the ternary system N-Ni-Ti have been established ex perimentally for the 900 degrees C isothermal section assisted by ther modynamic modeling. Phase equilibria are characterized by an appreciab le amount of up to similar to 11 at. % N dissolved in the octahedral i nterstices of the crystal structure of Ti2Ni. Two-phase equilibria are formed at 900 degrees C among the pairs Ti2N + Ti2NiNx, TiN1-x + Ti2N iNx, TiN1-x + TiNi3, and TiN1-x + Ni(Ti)(x). The investigation is base d on X-ray powder diffraction, metallography, scanning electron micros copy, and electron probe microanalysis techniques on about 50 alloys, which were prepared by an: melting or high-frequency levitation meltin g of appropriate blends of Ti,Ni-powders with TiN used to introduce ni trogen. Key experiments related to the N solubility in the Ti2Ni phase have been triggered by an interactively performed thermodynamic model ing. The experimental results are in fine agreement with the thermodyn amic calculation.