Thin intergranular films and solid-state activated sintering in nickel-doped tungsten

Vivek K. Gupta; Dang Hyok Yoon; Harry M. Meyer; Jian Luo

doi:10.1016/j.actamat.2007.01.017

Thin intergranular films and solid-state activated sintering in nickel-doped tungsten

Vivek K. Gupta, Dang Hyok Yoon, Harry M. Meyer, Jian Luo

Research output: Contribution to journal › Article › peer-review

201 Scopus citations

Abstract

Nickel-doped tungsten specimens were prepared with high purity chemicals and sintered. Although activated sintering starts more than 400 °C below the bulk eutectic temperature, the nickel-rich crystalline secondary phase does not wet the tungsten grain boundaries in the solid state. These results contrast with the classical activated sintering model whereby the secondary crystalline phase was presumed to wet grain boundaries completely. High resolution transmission electron microscopy and Auger electron spectroscopy revealed the presence of nanometer-thick, nickel-enriched, disordered films at grain boundaries well below the bulk eutectic temperature. These interfacial films can be regarded as metallic counterparts to widely observed equilibrium-thickness intergranular films in ceramics. Assuming they form at a true thermodynamic equilibrium, these films can alternatively be understood as a class of combined grain boundary disordering and adsorption structures resulting from coupled premelting and prewetting transitions. It is concluded that enhanced diffusion in these thin intergranular films is responsible for solid-state activated sintering.

Original language	English
Pages (from-to)	3131-3142
Number of pages	12
Journal	Acta Materialia
Volume	55
Issue number	9
DOIs	https://doi.org/10.1016/j.actamat.2007.01.017
State	Published - May 2007
Externally published	Yes

Funding

This research was in part supported by a Ralph E. Powe Junior Faculty Enhancement Award from Oak Ridge Associated Universities. J.L. also acknowledges an NSF CAREER award (DMR-0448879) and an AFOSR Young Investigator award. Auger analysis was sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Freedom CAR and Vehicle Technologies, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the US Department of Energy under Contract Number DE-AC05-00OR22725. The authors thank M. Tang and Prof. Y.-M. Chiang for insightful discussions and Dr. J. Hudson, Dr. Y. Ding and Y. Berta for some assistance regarding TEM. We thank an anonymous reviewer for useful comments. J.L. is indebted to Dr. R.M. Cannon (who sadly passed away in April 2006) for many stimulating discussions, his enthusiastic support to this research and his long-term mentorship and friendship.

Funders	Funder number
Office of Freedom Car
National Science Foundation	DMR-0448879
U.S. Department of Energy	DE-AC05-00OR22725
Air Force Office of Scientific Research
Office of Energy Efficiency and Renewable Energy
Oak Ridge Associated Universities
Oak Ridge National Laboratory

Keywords

Grain boundary diffusion
Grain boundary wetting
Interface segregation
Refractory metals
Sintering

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10.1016/j.actamat.2007.01.017

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abstract = "Nickel-doped tungsten specimens were prepared with high purity chemicals and sintered. Although activated sintering starts more than 400 °C below the bulk eutectic temperature, the nickel-rich crystalline secondary phase does not wet the tungsten grain boundaries in the solid state. These results contrast with the classical activated sintering model whereby the secondary crystalline phase was presumed to wet grain boundaries completely. High resolution transmission electron microscopy and Auger electron spectroscopy revealed the presence of nanometer-thick, nickel-enriched, disordered films at grain boundaries well below the bulk eutectic temperature. These interfacial films can be regarded as metallic counterparts to widely observed equilibrium-thickness intergranular films in ceramics. Assuming they form at a true thermodynamic equilibrium, these films can alternatively be understood as a class of combined grain boundary disordering and adsorption structures resulting from coupled premelting and prewetting transitions. It is concluded that enhanced diffusion in these thin intergranular films is responsible for solid-state activated sintering.",

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Thin intergranular films and solid-state activated sintering in nickel-doped tungsten

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