CC BY
6Hydrogen in metals and alloys
ON THE ROLE OF THE HYDRIDE-LIKE NANOSEGREGATION AT DISLOCATIONS AND GRAIN BOUNDARIES IN PALLADIUM AND SOME OTHER METALS IN HYDROGEN DIFFUSIVITY, SOLUBILITY, CRACKING, BLISTERING, EMBRITTLEMENT AND PLASTIFICATION
Yu. S. Nechaev, G. A. Filippov
I. P. Bardin Central Research Institute of Ferrous Metallurgy, Vtoraja Baumanskaja St. 9/23, Moscow, 105005 Russia E-mail: netchaev@online.ru
On the basis of the multi-factor analysis of the known most representative experimental data on solubility, electrical resistivity and diffusivity of hydrogen in palladium specimens with high and low dislocation densities, it has been shown [1] that the structure, composition, diameter (up to several nm), contribution to electrical resistivity, thermodynamic and diffusion characteristics of the hydride-like segregation at dislocations (and grain boundaries) in palladium can vary in a wide diapason depending on concentration and thermodynamic activity of hydrogen dissolved in the normal lattice metal.
The formation of hydride-like segregation at dislocations occurs at large degrees of the undersaturation of the solutions (several orders) with respect to the hydride precipitation within the normal lattice of palladium. This means that the specific phase diagram [2, 3] can be considered for the system of «the near-dislocation segregation Pd-regions — hydrogen», in comparison with the generally used phase diagram of «palladium-hydrogen».
Similar results on the hydride-like nanosegregation at dislocations and grain boundaries have been obtained for a series of metals and alloys (iron and steels [4-6], palladium, niobium, vanadium and tantalum [7]).
The obtained results can be used for a description of the effective concentration and distribution of hydrogen between the normal crystalline lattice and the lattice defects' regions in the material specimens produced by different ways of processing and treatments [7-10].
The results can be used for an interpretation of the hydrogen influence on physical and mechanical properties of metallic materials, for revealing of the micromech-anisms of their cracking, blistering, embrittlement and plastification (superplasticity), and the ways of an optimization of regimes of the thermal-hydrogen treatment and governing hydro-phase hardening of metals and alloys [7-10].
References
1. Nechaev Yu. S. Characteristics of the hydridelike segregation of hydrogen at dislocations in palladium. Physics Uspekhi (Progresses of Physical Sciences) 2001; 171(11): 1251-1261.
2. Nechaev Yu. S. The phase transitions in the segregation nanoregions of high pressure at dislocations in metals. In: The abstract booklet of The Russian Conference on Phase Transitions at High Pressures, 20-22 May 2002, Institute of Solid State Physics, Chernogolovka, p. 21/7.
3. Nechaev Yu. S. Transformation of the segregation phases at dislocations in the hydride-like ones in steels under hydrogen charging. In: The Extended Abstracts Booklet of the ICHMS'2001, VII International Conference, ADEF-Ukraine, Kiev - 2001, pp. 78-81.
4. Nechaev Yu. S., Filippov G. A. Hydride-like segregation at dislocations in iron electrolytically charged by hydrogen. Perspectivnie Materialy (Journal of Advanced Materials). 2000;(2): 63-71.
5. Nechaev Yu. S., Filippov G. A. Hydride-like segregation at dislocations in Fe and steels. Defect & Diffusion Forum. 2001;194-199:1099-1104.
6. Nechaev Yu. S. On the hydrogen fugacity in metals under electrolytic charging. In: Veziroglu N. et al. editors. Hydrogen Materials Sciences and Chemistry of Metal Hydrides. NATO Science Series 2002; 82: 161-164.
7. Ephimenko S. P., Nechaev Yu. S., Karelin F. P., et. al. On the mechanisms of the influence of the thermal-hydrogen treatment on properties of transition metals and alloys. Fizika i Khimija Obrabotki Materialov (Physics and Chemistry of Materials Treatment). 1997; (5): 101-108.
8. Nechaev Yu. S., Filippov G. A. Micromecha-nisms of the influence of small additions of hydrogen on mechanical properties of metals. Materials Sciences Transactions. 2001; (11): 40-45.
9. Nechaev Yu. S., Filippov G. A. The hydrogen fugacity in iron and steels under electrolytic charging, in the connection with blistering and cracking. In: Transactions of the III International Conference «Hydrogen Treatment of Metals», Donetsk, Ukraine, 2001, Part II, pp. 281-283.
10. Nechaev Yu. S., Filippov G. A. The role of the hydride-like segregation at dislocations and grain boundaries in the delayed fracture of steels. Ibid., 2001, pp. 264-286.
ISJAEE Special issue (2003)
