A New Relationship Among Self- and Impurity Diffusion Coefficients in Binary Solution Phases
- PDF / 872,303 Bytes
- 5 Pages / 593.972 x 792 pts Page_size
- 43 Downloads / 185 Views
undamental to regulate materials properties and processes during synthesis and in service. Experimental methods, such as diffusion couple, capillary, and quasielastic neutron scattering, are traditionally utilized to measure diffusion coefficients.[1] However, accurate measurements of diffusivity are challenging due to, for example, the purity of samples and the appearance of metastable phases. Theoretical methods, such as the density functional theory (DFT)[2,3]-based calculations and Diffusion Controlled TRAnsformation (DICTRA)type modeling,[4] are effective.[5–8] Nevertheless, theoretical calculations are limited by either computational resources or available experimental data. In order to obtain effectively the missing diffusivities, which may be difficult to be determined via experiment and
JINGHUA XIN, Ph.D. Candidate, JIANCHUAN WANG, Lecturer, and BAIYUN HUANG, Professor, are with the State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083, P.R. China. YONG DU, Professor, is with the State Key Laboratory of Powder Metallurgy, Central South University, and also with the Sino-German Cooperation Group ’’Microstructure in Al alloys’’, Changsha, Hunan, 410083, P.R. China. Contact e-mail: [email protected] SHUNLI SHANG, Research Associate, and ZIKUI LIU, Professor, are with the Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802. SENLIN CUI, Ph.D. Candidate, is with the Department of Mining and Materials Engineering, McGill University, 3610 University Street, Montreal, Quebec, H3A 0C5, Canada. Manuscript submitted January 11, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
computational modeling, several empirical approaches were proposed in the literature.[9–14] For instance, there exist four widely used empirical relationships[9–12] to estimate the self-diffusion coefficient. Correlations between activation energy and the melting point by Askill[9] or with the valence and crystal structure of materials by Sherby and Simnad[10] and LeClaire[11] are available. Combined with the estimation of pre-exponential factor promoted by Dushman and Langmuir,[12] the self-diffusion coefficient is empirically predicted. On the contrary, only one empirical relationship was proposed by Lazarus[13] and LeClaire[14] to estimate one approximate trend for impurity diffusion, according to which activation energy of impurity diffusion decreases as the valence of impurity solutes increases. So far, quantitative estimation of diffusion coefficient is not available for impurity diffusion.[9] Due to the lack of empirical models for predicting impurity diffusivity, it is often assumed that the impurity diffusion coefficient equals to the self-diffusion coefficient.[8] However, recent DFT calculations indicate that this approximation is not always valid. For example, both the calculated impurity diffusion coefficients for W in hcp Mg[15] and in fcc Al[16] are orders of magnitude smaller than the self-diffusion coefficient of the solvent. Hence the aim of the present communication i
Data Loading...
