Experimental and Computational Study of Diffusion Mobilities for fcc Ni-Cr-Mo Alloys
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NI-BASED superalloys have been widely used as ideal materials for jet engines, gas turbines, etc., due to their attractive combination of high strength, good oxidation, and corrosion resistance under high temperatures as well as good weldability.[1–3] Knowledge on both thermodynamics and diffusion kinetics of the Ni-based systems is of critical importance both in determining the alloy stability under long-term service conditions and in processing design. The Ni-Cr-Mo system, which is one of the key ternary systems in the multi-component Ni-based database for designing commercial superalloys such as Alloy 22, Alloy 59, and C-4, is chosen as the target in the present work. Turchi et al.[4,5] conducted phase stability and kinetic studies of Ni-Cr-Mo-based alloys using the CALPHAD approach. The thermodynamic properties of the Ni-Mo system quoted in Turchi et al.’s work[4] were assessed by Frisk.[6] However, a new self-consistent thermodynamic description of this binary system was obtained by integrating the first-principles calculations and CALPHAD approach in Zhou et al’s work.[7] The diffusion mobility corresponding to the Ni self-diffusion coefficient was updated by Zhang et al.[8] recently. Furthermore, no assessment of the diffusion mobilities in fcc Ni-Cr-Mo ternary system has been carried out up to now. Thus, a modified Ni-Cr-Mo thermodynamic database was established so as to reassess the diffusion mobilities for fcc Ni-Mo, Ni-Cr, and Ni-Cr-Mo systems by means of the PARROT module incorporated in the DICTRA (DIffusion Controlled TRAnsformation) software package[9] in the present work.
NAQIONG ZHU and JINCAI LI, Researchers, XIAO-GANG LU, YANLIN HE, and JIEYU ZHANG, Professors, are with the School of Materials Science and Engineering, Shanghai University, Shanghai 200444, P.R. China. Contact e-mail: [email protected] Manuscript submitted January 31, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
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EVALUATION OF EXPERIMENTAL DIFFUSIVITIES
Various experimental diffusivities are needed to assess the mobility parameters. All the experimental information for fcc Ni-Mo, Ni-Cr, and Ni-Cr-Mo alloys available in the literature is categorized as follows. A. The Ni-Mo System Using the Ni/Ni-10 wt pct Mo diffusion couples, Karunaratne and Ree[10] measured the interdiffusion coefficients in fcc Ni-Mo alloys from 1173 K to 1573 K (900 °C to 1300 °C) and derived the impurity diffusion coefficients of Mo in Ni. Minamino et al.[11] measured the concentration profiles of Ni/Ni-2.97 at. pct Mo diffusion couples from 1323 K to 1623 K (1050 °C to 1350 °C) by the electron probe microanalysis (EPMA) and determined the impurity coefficients of Mo in Ni using the Hall method. Heijwegen and Rieck[12] determined the impurity diffusion coefficients of Mo in Ni by measuring the diffusion layer growth in Ni/Mo and Ni/ Ni-38 at. pct Mo diffusion couples in the temperature range of 1273 K to 1573 K (1000 °C to 1300 °C). Ugaste and Pimenov[13] explored the interdiffusion coefficients and derived the impurity diffusion coefficients of Mo in Ni from 1443 K to 1563 K (1170
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