Chengying Tang

Thermodynamic description of the C-Fe-Mn system with key experiments and its practical applications

Abstract Based on the critically reviewed experimental data available in the literature, new phase transition temperatures and phase equilibria at 800 °C close to the Cu-Fe side of the Cu-Fe-Mn system were measured in the present work. The composition-invariant (γFe, γMn) → (αFe) massive transformations were observed in the two quenched alloys in the Fe-rich region. A set of consistent thermodynamic parameters of the Cu-Fe-Mn system was then obtained by taking into account all kinds of experimental data. Comparisons between the calculated and measured phase diagrams indicate that most of the experimental information is satisfactorily described by the present thermodynamic modeling. The liquidus isolines, liquidus projection and reaction scheme of this ternary system are also presented. Significant improvements have been made, compared with the previous assessments. The presently obtained parameters were applied in successfully solving the !surface fissure during hot rolling of steel and controlling the micro-structure of the Cu-Fe based alloys in rapid solidification.

Thermodynamic modeling of the Sc-Zn system coupled with first-principles calculation

The Sc-Zn system has been critically reviewed and assessed by means of n CALPHAD (CALculation of PHAse Diagram) approach. By means of first-principles n calculation, the enthalpies of formation at 0 K for the ScZn, ScZn2, n Sc17Zn58, Sc3Zn17 and ScZn12 have been computed with the desire to assist n thermodynamic modeling. A set of self-consistent thermodynamic parameters for n the Sc-Zn system is then obtained. The calculated phase diagram and n thermodynamic properties agree well with the experimental data and n first-principles calculations, respectively.

Phase equilibria and thermal analysis in the Fe–Mn–Ni system

Abstract Based on the critical review of the experimental data available in the literature, 7 decisive ternary alloys were prepared. New phase transition temperatures and phase equilibria at 800°C in the Fe – Mn – Ni system were measured. An effective method to accurately determine phase transition temperatures from differential thermal analysis curves with overlapped peaks and nonlevel baselines within a narrow temperature range was developed. A massive transformation was observed in one quenched Fe-rich alloy. In order to make the fcc_A1 phase always in the fully disordered state in the ternary system, the effect of the binary reciprocal parameter on the Gibbs energy of ternary ordered L12 phase was considered. It was found that the introduction of only one parameter could describe all reliable experimental data in the Fe – Mn – Ni system satisfactorily. The presently obtained parameters were successfully applied in two practical cases.

Interdiffusion in bcc_B2 Ni–Al–Cu alloys at 1 173 K

Abstract The interdiffusion behavior of bcc_B2 Ni–Al–Cu alloys at 1173 K was experimentally investigated on the basis of six groups of bulk diffusion couples. With the electron probe microanalysis technique and the Matano–Kirkaldy method, the composition-dependent mole-fraction interdiffusion coefficients and the interdiffusion fluxes in bcc_B2 Ni–Al–Cu alloys at 1173 K were determined. The reliability of the presently obtained interdiffusivities was verified by the thermodynamic stability constraints, comparison with the interdiffusion coefficients in boundary binary bcc_B2 Ni–Al alloys as well as numerical simulations based on Ficks second law.

Atomic mobilities in fcc Cu–Mn–Ni–Zn alloys and their characterizations of uphill diffusion and zero-flux plane phenomena

Abstract An effective approach to establish the atomic mobility parameters of quaternary Cu-rich fcc Cu–Mn–Ni–Zn alloys is presented through assessments of the critically-reviewed experimental diffusivities available in the literature by means of DICTRA (DIffusion Controlled TRAnsformation) software. In the quaternary Cu-rich fcc Cu–Mn–Ni–Zn alloys, atomic mobilities in ternary fcc Cu–Mn–Ni and Cu–Ni–Zn boundary systems were directly taken from our previous work, while atomic mobilities in ternary fcc Cu–Mn–Zn boudnary system were assessed as a function of temperature and composition in this work. Since no experimental data were available, the atomic mobility database for fcc Ni–Mn–Zn alloys was not assessed but just directly extrapolated based on the three constituent binary alloys. Considering that the accurate quaternary interdiffusion coefficients were usually absent in the literature, atomic mobilities in fcc Cu–Mn–Ni–Zn alloys were extrapolated based on the assessed atomic mobilities in the 4 ternary boundary systems. On the basis of the obtained mobility parameters, simulations of a series of ternary and quaternary diffusion couple experiments were performed. The concentration profiles and the diffusion paths in diffusion couples were well reproduced by the presently obtained parameters. Furthermore, 3D views of the concentration profiles, diffusion fluxes, chemical potential and quaternary interdiffusion coefficients surfaces were calculated with the obtained atomic mobilities to analyze the uphill diffusion and zero-flux plane phenomenon in some quaternary diffusion couples. In addition, simple criteria for judging whether the uphill diffusion and/or zero-flux plane can occur are also proposed.