Thermodynamic Study on Nitrogen Solubility and TiN Formation in Molten Ni-Ti-N Alloys

In the temperature range of 1773 K to 1873 K, nitrogen solubility and TiN formation in molten nickel were studied using melt-gas and melt-gas-nitride equilibrium at atmospheric nitrogen pressure. The nitrogen solubility increased with the increase of Ti content in molten nickel. TiN was formed when titanium and nitrogen in molten nickel reach critical contents. The critical titanium and nitrogen contents for TiN formation were significantly increased with the increase of melt temperature. Thermodynamic analysis of the experimental results was carried out in the form of Wagner interaction parameter. The standard Gibbs free energy change of nitrogen dissolution reaction in molten nickel was obtained as \(\Delta G_{{\text{N}}}^{0} = 53803 + 27.76T{\text{ (J/mol)}}\) $\mathrm{\Delta }{G}_{\text{N}}^0=53803+27.76T\text{(J/mol)}$ . Based on the study of nitrogen solubility in molten Ni-Ti-N alloys, the temperature dependence of interaction parameters between N and Ti can be expressed as \(e_{{\text{N}}}^{{{\text{Ti}}}} = - 800/T + 0.25\) $e_{\text{N}}^{\text{Ti}}=-800/T+0.25$ and \(e_{{{\text{Ti}}}}^{{\text{N}}} = - 2728/T + 0.85\) $e_{\text{Ti}}^{\text{N}}=-2728/T+0.85$ . According to the thermodynamic study of TiN formation in molten Ni-Ti-N alloys, the standard Gibbs free energy change of TiN formation was \(\Delta G_{{{\text{TiN}}}}^{0} = - 203553 + 65.29T \, ({\text{J/mol}})\) $\mathrm{\Delta }{G}_{\text{TiN}}^0=-203553+65.29T(\text{J/mol})$ , and the interaction parameter of Ti on itself was obtained as \(e_{{{\text{Ti}}}}^{{{\text{Ti}}}} = 0.046 \, (1773{\text{ to }}1873{\text{ K}})\) $e_{\text{Ti}}^{\text{Ti}}=0.046(1773\text{to}1873\text{K})$ .