Grain Boundary Diffusion und Grain Boundary Segregation in Cu and Cu-Based Alloys

• Applicant: Professor Dr. Guido Schmitz
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Synthesis and Properties of Functional Materials
• Term: from 2004 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5431168

• Final Report Year: 2007

Final Report Abstract

Grain boundary diffusion of Ni and Fe in high-purity polycrystalline Cu is investigated by the radiotracer technique in a wide temperature interval from 0.35 to 0.93 of the melting point of copper. By combination of low- and high temperature measurements, the GB segregation behaviour of Ni (and partially of Fe) was determined in true dilute limit conditions. Whereas Ni and Cu are completely miscible in solid state, a distinct although moderate GB segregation is established for Ni in Cu with the segregation enthalpy of-17kJ/mol. This fact indicates the existence of a irascibility gap in the system. Fe segregates surprisingly strong at Cu GBs even taking into account its low solubility in solid Cu. Such behaviour complicated substantially the analysis of high-temperature data for Fe GB diffusion. A fundamentally new phenomenon was established for Fe GB diffusion in Cu at temperatures above 0.8 of the melting point of copper revealing penetration profiles which formally correspond to low temperature diffusion conditions. The combination of detailed experiments and atomistic simulation by molecular dynamics is suggested for drawing more insight into this problem. Furthermore, we extended the investigations beyond the dilute limit for solute segregation. Nonlinear segregation phenomena were provoked in specially designed radiotracer experiments on bicrystals and were quantitatively evaluated. As a result, the complete solute segregation isotherms were determined from radiotracer diffusion experiments. Strong solute segregation invokes also new effects. A GB wetting transition in the Cu-Bi system was investigated by radiotracer diffusion. A pronounced increase of the GB diffusivity was observed in the two-phase (solid+liquid) region of the corresponding phase diagram. Such a GB diffusion enhancement exists even in the single phase (solid solution in Cu) region manifesting the existence of a pre-wetting GB phase transition in this system.

Publications

• Grain-boundary melting phase transition in the Cu-Bi system. Phys. Rev. B 71 (2005) 104104
  Divinski S.V., Lohmann M., Herzig Chr., Straumal B., Baretzky B., Gust W.
  
• Quantitative experiments on the transition between linear to non-linear segregation of Ag in Cu bicrystals studied by radiotracer grain on boundary diffusion. Z. Metallkd. 96 (2005) 1181
  Divinski S.V., Lohmann M., Prokofjev S., Herzig Chr.
  
• Radiotracer grain boundary diffusion experiment on bicrystal - a tool to study non-linear segregation quantitatively. International Workshop on Surface and Interface Segregation, IWStS 2005, Nove Hrady, Czech Republic, July 2005
  
  
• Segregation, pre-melting, and melting phenomena in the Cu-Bi system studied by radiotracer grain boundary diffusion. Symposium "Point Defects" by TMS Annual Meeting, San Antonio, Texas, USA, March 2006
  
  
• Grain boundary diffusion and segregation of Ni in Cu. Acta Mater. 55 (2007) 3337
  Divinski S.V., Ribbe J., Schmilz G., Herzig Chr.
  
• Radiotracer investigation of diffusion, segregation and -wetting phenomena in grain boundaries. 12th International Conference on Intergranular and Interphase Boundaries, Barcelona, Spain, July 2007
  
  
• Segregation phenomena studied by interface diffusion measurements. 4th International Workshop on Diffusion and Diffusional Transformations in Alloys, Cherkassy, Ukraine, July 2007
  
  
• Systematics of grain boundary diffusion and solute segregation in copper poly- and bicrystals. 3rd International Conference on Diffusion in Solids and Liquids, Alvor, Portugal, July 2007