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1 -Phase in Fe-Cr and Fe-V Systems Stanislaw M. Dubiel * Faculty of Physics & Applied Computer Science, AGH University, Kraków *

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Presentation on theme: "1 -Phase in Fe-Cr and Fe-V Systems Stanislaw M. Dubiel * Faculty of Physics & Applied Computer Science, AGH University, Kraków *"— Presentation transcript:

1 1 -Phase in Fe-Cr and Fe-V Systems Stanislaw M. Dubiel * Faculty of Physics & Applied Computer Science, AGH University, Kraków *

2 2 -Phase The -phase (tetragonal structure, space group D 14 4h – P4 2 /mnm) is known to exist only in alloy systems. Among 53 members of the -phase family in binary alloys only two i.e. Fe-Cr and Fe-V have well documented magnetic properties [1]. The -FeCr seems to be the most known member of the family not only as the archetype, but also for technological reasons. The latter follows from a deteriorating effect of the phase precipitation on mechanical and corrosive properties of technologically important materials based on Fe-Cr alloys e. g. loss of corrosion resistance and reduction of ductility and toughness. Although the -FeCr and -FeV have been known since many years, their physical properties, and, in particular, magnetic ones, are not known satisfactorily, and the Debye temperature was determined for the first time only recently [2]. There are only very few theoretical papers on the issue available, which in a combination with a complex crystallographic structure (30 atoms distributed randomly over five different crystallographic sites with high coordination numbers) makes the interpretation of experimental results very difficult. [1] E. O. Hall and S. H. Algie, Metall. Rev., 11 (1966) 61 [2] J. Cieslak et al., Phys. Rev. B, 65 (2002) The -phase (tetragonal structure, space group D 14 4h – P4 2 /mnm) is known to exist only in alloy systems. Among 53 members of the -phase family in binary alloys only two i.e. Fe-Cr and Fe-V have well documented magnetic properties [1]. The -FeCr seems to be the most known member of the family not only as the archetype, but also for technological reasons. The latter follows from a deteriorating effect of the phase precipitation on mechanical and corrosive properties of technologically important materials based on Fe-Cr alloys e. g. loss of corrosion resistance and reduction of ductility and toughness. Although the -FeCr and -FeV have been known since many years, their physical properties, and, in particular, magnetic ones, are not known satisfactorily, and the Debye temperature was determined for the first time only recently [2]. There are only very few theoretical papers on the issue available, which in a combination with a complex crystallographic structure (30 atoms distributed randomly over five different crystallographic sites with high coordination numbers) makes the interpretation of experimental results very difficult. [1] E. O. Hall and S. H. Algie, Metall. Rev., 11 (1966) 61 [2] J. Cieslak et al., Phys. Rev. B, 65 (2002)

3 3 Outline Crystallographic structure and -phase family Short history of -FeCr Formation and identification of -FeCr Debye temperature, D Curie temperature, T C Hyperfine field, B Correlations between B and Magnetism of -phase in Fe-Cr and Fe-V systems

4 4 Structure – Unit Cell A C E DEDE B

5 5 Structure – Sites Site number Site code CNON [nm] 1A B C D E CN - coordination number; ON- occupation number; - average nearest-neighbour distance

6 6 Structure – Sites The plot shows all 5 sites with all their NN-neighbours. The geometry of the NN-atoms is preserved. Note that atoms at B, D and E sites have all 5 different atoms as their NN-neighbours, but atoms at A miss A and C NN-atoms, and those at C sites miss A NN-atoms. A B C D E

7 7 Structure – Site Occupancy Mössbauer spectroscopy ( -FeCr) B a = 13.5 T; T = 4.2 K Five different sites occupied by Fe atoms J. Cieslak, M. Reissner, S. M. Dubiel, W. Steiner, 6th Seeheim Workshop on MS, 2006

8 8 Structure - Site Occupancy Neutron diffraction (---- Fe x V; Fe x Cr) J. Cieslak et al., J. Alloys Comp., 460 (2008) 20

9 9 -Phase Family 53 cases in binary alloys e.g. FeV, FeNb, FeTa, FeCr, FeMo, FeTc, FeRe

10 10 Phase Diagram - FeV System

11 11 History of -FeCr 1923: Bain observed hard, brittle and nonmagnetic phase (B-constituent) in FeCrNi alloy 1936: Jette & Foote gave the name sigma 1943: Cook & Jones recorded first XRD pattern 1954: Bergmann & Shoemaker established its crystal structure 1981: Yakel determined site occupancy 1995: Kawazoe et al. published first theoretical paper E. O. Hall and S. H. Algie, Metall. Rev., 11 (1966) 61

12 12 Identification of -FeCr T = 295 K XRDME NEUTRONS J. Cieslak et al.. J. Alloys Comp., 460 (2008) 20 The difference in the isomer shift between and amounts to ca mm/s

13 13 Kinetics of Transformation Isothermal annealing at ~ 530 T ~ 830 o C E = 196 ± 2 kJ/mol -FeCr T a = 700 o C A. Blachowski, S. M. Dubiel and J. Zukrowski, Intermetallics, 9 (2001) 493

14 14 Debye Temperature, Θ D T[K] FeCr

15 15 Debye Temperature, Θ D -FeV + -FeCr J. Cieslak et al., J. Phys.: Condens. Matter., 17 (2005) 6889 There is a linear increase of T D with x for x 45 for both V and Cr Θ D [K]

16 16 Curie Temperature, T c Mössbauer effect ( -FeCr) - from line width, G (a) x = 45.0, (b) x = 46.2 and (c) x = 48.0 (a) 4.2 K; (b) 295 K J. Cieslak et al., J. Magn. Magn. Mater., (2004) 534

17 17 Curie Temperature, T c Mössbauer effect ( -FeV 34 ) - from average hf. field J. Cieslak, B. F. O. Costa, S. M. Dubiel, M. Reissner, W. Steiner, ICAME2008 T C = 323 K

18 18 Curie Temperature, T c -FeV -FeCr J. Cieslak, B. F. O. Costa, S. M. Dubiel, M. Reissner, W. Steiner, ICAME2008 There is a non-linear decrease of T C with vanadium content

19 19 - Relationship a = a + B CEP J. Cieslak, B. F. O. Costa, S. M. Dubiel, M. Reissner, W. Steiner, ICAME2008 Lack of linearily speaks for important contribution from conduction electrons

20 20 Models of -FeCr Magnetism Ferrimagnetism 1 = 2.0 B 2 = 1.5 B B 1 = 18 T B 2 = 13 T B exp 4 T Band-magnetism

21 21 Band-magnetism Lack of saturationRhodes - Wohlfarth plot 4K4K Models of -FeCr Magnetism -FeCr Both plots give evidence for itinerant magnetism in the -FeCr

22 22 Rhodes – Wohlfarth plot Fe 50.5 Cr 49.5 Fe 53.8 Cr 46.2 µ eff /µ s Models of -FeCr Magnetism Systems for which eff / s > 1 have itinerant character of magnetism

23 23 Conclusions Mössbauer spectroscopy is very useful to study magnetic and dynamic properties of the -phase in Fe-Cr and Fe-V systems, as well as the kinetics of -to- transformation. All measured quantities (T D, T C, and ) depend sensitively on Cr, V content, x); T D increases at the rate of ~15 K/at% (x 45) for both systems T C and decrease non-linearly with x is non-lineraly correlated with Magnetism of -FeCr (V) seems to obey itinerant model due to; lack of saturation Rhodes - Wohlfarth plot non-linear relationship -. Mössbauer spectroscopy is very useful to study magnetic and dynamic properties of the -phase in Fe-Cr and Fe-V systems, as well as the kinetics of -to- transformation. All measured quantities (T D, T C, and ) depend sensitively on Cr, V content, x); T D increases at the rate of ~15 K/at% (x 45) for both systems T C and decrease non-linearly with x is non-lineraly correlated with Magnetism of -FeCr (V) seems to obey itinerant model due to; lack of saturation Rhodes - Wohlfarth plot non-linear relationship -.

24 24 More to read G. Bergman and D. P. Shoemaker, Acta Cryst., 7 (1954) 857 H. L. Yakel, Acta Cryst., B39 (1983) 20; ibid, B39 (1983) 28 H. H. Ettwig and W. Pepperhoff, Arch. Eisenhuttenwes., 43 (1972) 271 Y. Sumimoto et al., J. Phys. Soc. Jpn., 35 (1973) 461 A. M. van der Kraan et al., Phys. Stat. Sol. (a), 88 (1985) 231 R. Vilar and G. Cizeron, Acta Metall., 35 (1987) 1229 A. Gupta et al., Hyper. Inter., 54 (1990) 805 B. F. O. Costa and S. M. Dubiel, Phys. Stat. Sol. (a), 139 (1993) 83 B. F. O. Costa et al., Phys. Stat. Sol. (a), 161 (1997) 349 J. Cieslak, S. M. Dubiel and B. Sepiol, Sol. Stat. Commun., 111 (1999) 613 J. Cieslak, S. M. Dubiel and B. Sepiol, Hyper. Inter., 126 (2000) 187 A. Blachowski et al., J. Alloys Comp., 308 (2000) 189; ibid, 313 (2000) 182 A. Blachowski et al., Intermetallics, 8 (2000) 963 J. Cieslak et al., J. Alloys Comp., 460 (2008) 20 J. Cieslak et al., J. Phys.: Condens Matter., 20 (2008)


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