Mitsuhiro Hasebe

Calculation of phase diagrams of the iron-copper and cobalt-copper systems☆

Abstract Synthesis of phase diagrams has been made on Fe-Cu and Co-Cu systems using thermodynamic parameters obtained by analysis of data on phase boundaries and thermodynamic properties. An anomaly in solubility of copper due to the magnetic transition was confirmed to occur in αFe as well as γCo. It was also detected that the solidus curves in both the systems exhibit remarkable retrograde solubility.

Calculation of the Fe-C-Ti ternary phase diagram

Abstract A thermodynamic analysis of phase equilibria in the Fe-Ti, Ti-C, and Fe-C-Ti systems has been carried out. The Gibbs energy has been expressed by the two-sublattice model being separated into the paramagnetic and ferromagnetic terms. In particular, the equilibrium between austenite and NaCl type Ti-carbide has been treated as a portion of the miscibility gap in the fcc phase. The thermodynamic parameters for each phase were evaluated on the basis of experimental phase equilibrium and activity data. The calculated phase boundary of austenite in equilibrium with Ti-carbide exhibited a characteristic shape, not only in the isothermal but also in the vertical section.

Effect of magnetic transition on solubility of carbon in bcc Fe and fee Co-Ni alloys

The solubility of carbon in bcc Fe and fcc Co-Ni alloys has been examined by the diffusion couple method, and a thermodynamic analysis of the data has been carried out, taking into account the effect of magnetic transition. It has been detected that the solubility slightly deviates from the ordinary linear relation between log [pct C] and 1/T below the Curie point. The deviation has been well explained by the magnetic effect on the Gibbs energy for the bcc Fe-C and fcc Co-Ni-C phases.

Calculation of the FeCNb ternary phase diagram

Abstract Phase equilibria in the Fe-rich portion of the FeCNb ternary system were analyzed on the basis of experimental and thermodynamic data. The Gibbs energy of the Nb-carbide and solution phases was approximated by the two-sublattice model, being separated into the paramagnetic and ferromagnetic terms. In particular, the two phase equilibrium between austenite and cubic Nb-carbide was treated as a portion of the miscibility gap in the fcc FeCNb phase. The calculated phase boundary of austenite in equilibrium with the Nb-carbide showed a characteristic shape, as was the case in the FeCTi system.

Further study on phase diagram of the iron-copper system

Abstract Partition of copper between austenite and ferrite in Fe-Cu-Si system at 1000°C and 1300°C was examined, and the interaction parameter, ΩαFeCu, as a function of temperature and composition was evaluated. Using a newly revised parameter, the phase diagram of Fe-Cu system has been re-calculated.