Z.Q. Liu et al.: Microstructural investigation of four kinds of ␥Ј–Fe4N nitrides in ion-nitrided pure iron
nucleated from nitrogen-rich substrate areas with the ori-
entation relationship of (100)␥Ј//(110)␣ [011]␥Ј//[111]␣,
used in this study. The financial support from the Na-
tional Natural Science Foundation of China (Grant No.
50071063) is also appreciated.
¯
which has been described in the inset of Fig. 6 and re-
ported by others.8,33 According to this orientation rela-
tionship, the misfit degree between {010}␥Ј and {110}␣
planes is only 6.57%. This degree is homogeneous and
lower than the average degree in the ␣Љ → ␥Ј transfor-
mation (see Sec. C); thus, the small stacking faults could
be generated on different sets of {111}␥Ј planes without
preference. Since little information was reported on this
kind of ␥Ј hitherto, more efforts should be made to
clarify its precipitation mechanism.
REFERENCES
1. T. Bell, Heat Treat. Met. 2, 39 (1975).
2. K. Sachs and D.B. Clayton, Heat Treat. Met. 6, 29 (1979).
3. D.L. Guan and Z.W. Yu, in Mechanical Behaviour of Materials—
VI, edited by M. Jono and T. Inoue (Pergamon Press, Elmsford,
New York, 1991), p. 295.
4. M.K. Lei and Z.L. Zhang, J. Mater. Sci. Lett. 16, 1567 (1997).
5. G.B. Li, G.Q. Li, M.K. Lei, and B.Z. Liu, Surf. Coat. Technol. 96,
34 (1997).
6. G.R. Booker, J. Norbury, and A.L. Sutton, Journal of the Iron and Steel
IV. CONCLUSIONS
Institute 187, 205 (1957).
7. D. Geradin, J.P. Morniroli, H. Michel, and M. Gantois, J. Mater.
Sci. 16, 159 (1981).
8. D. Gerardin, H. Michel, J.P. Morniroli, and M. Gantois, Mem.
Sci. Rev. Metall. 74, 457 (1977).
9. X.L. Xu, L. Wang, Z.W. Yu, and Z.K. Hei, Metall. Mater. Trans.
A 27, 1347 (1996).
10. J. D’Haen, C. Quaeyhaegens, G. Knuyt, M. D’Olieslaeger, and
L.M. Stals, Surf. Coat. Technol. 74–75, 405 (1995).
11. X.L. Xu, L. Wang, Z.W. Yu, and Z.K. Hei, Acta Metall. Sin.
(Engl. Lett.) 11, 183 (1998).
12. K.H. Jack, Proc. R. Soc. A 195, 34 (1948).
13. G.R. Booker, Acta Metall. 9, 590 (1961).
14. U. Dahmen, P. Ferguson, and K.H. Westmacott, Acta Metall. 35,
1037 (1987).
15. Z.Q. Liu, D.X. Li, Z.K. Hei, and H. Hashimoto, Scr. Mater. 45,
455 (2001).
16. M.A.J. Somers and E.J. Mittemeijer. Metall. Mater. Trans. A 26,
57 (1995).
(1) Four kinds of ␥Ј–Fe4N nitrides with different mor-
phologies and microstructures were formed in the ni-
trided layer of polycrystalline pure iron due to different
precipitation mechanisms.
(2) In the columnar compound layer ␥Ј plates precipi-
tated from ⑀–Fe2−3N columnar grains with orientation
¯
¯
relationship of (111)␥Ј//(0001)⑀ and [011]␥Ј//[1210]⑀,
and resulted in a lamellar structure in the grain. HREM
observation indicates that ␥Ј plates (3–12-nm thickness)
and ⑀ plates (25–115-nm thickness) array alternatively in
each lamellar grain and a twin relationship only occurs
between different ␥Ј plates. In spite of interfacial steps,
the planar interface between ⑀ and ␥Ј plates is coherent.
(3) The ␥Ј nitrides in the transition compound layer
appeared as equiaxed grains (1–1.5 m), which nucle-
ated and grew from ␣–Fe substrate during nitriding at
high temperature and then were maintained in the fol-
lowing cooling process.
17. J.P. Hirth and R.C. Pond, Acta Mater. 44, 4749 (1996).
18. R.C. Pond, P. Shang, T.T. Cheng, and M. Aindow, Acta Mater.
48, 1047 (2000).
19. M.A.J. Somers, N.M. van der Pers. D. Schalkoord, and
E.J. Mittemeijer, Metall. Mater. Trans. A 20, 1533 (1989).
20. K.H. Jack, Proc. R. Soc. A 208, 200 (1951).
21. G. Hagg, Z. Phys. Chem. 8, 455 (1930).
(4) In the diffusion layer, the lenticular ␥Ј with parallel
striations was fully filled with a high density of stacking
faults generated on only one set of {111}␥Ј plane. This
striated ␥Ј nitride precipitated from the ␣Љ–Fe16N2 lattice
22. B. Rauschenbach, A. Kolitsch, and K. Hohmuth, Phys. Status
Solidi A 80, 471 (1983).
¯
with the orientation relationship of (100)␥Ј//(110)␣Љ and
23. G.J. Mahon and J.M. Howe, Metall. Trans. A 21, 1655 (1990).
24. P. Shang, T.T. Cheng, and M. Aindow, Philos. Mag. A 79, 2553
(1999).
25. X.W. Du, J. Zhu, X. Zhang, Z.Y. Cheng, and Y.W. Kim, Scr.
Mater. 43, 597 (2000).
[011]␥//[111]␣Љ. The sliding took place on the other set
of {111}␥Ј plane without stacking faults, which divided
the nitride into several parts.
(5) The unstriated ␥Ј nitrides in the diffusion layer also
had lenticular morphology and precipitated from the ␣
26. K. Hashimoto, M. Kimura, and Y. Mizuhara, Intermetallics 6, 667
(1998).
¯
27. J.M. Howe, U. Dahmen, and R. Gronsky, Philos. Mag. A 56, 31 (1987).
28. H.S. Fang and C.M. Li, Metall. Trans. A 25, 2615 (1994).
29. W. Krakow and D.A. Smith, Ultramicroscopy 22, 47 (1987).
30. Z.Q. Liu, Y.X. Chen, Z.K. Hei, D.X. Li, and H. Hashimoto, Met-
all. Mater. Trans. A 32, 2681 (2001).
substrate with orientation relationship of (100)␥Ј//(110)␣
and [011]␥Ј//[111]␣. The short stacking faults on differ-
ent sets of {111}␥Ј planes and a misoriented grain were
observed with HREM.
31. Z.Q. Liu, X.L. Xu, Z.K. Hei, R.N. Guan, R.S. Li, and D.X. Li,
ACKNOWLEDGMENTS
Acta Metall. Sin. A 36, 7 (2000).
32. Z.Q. Liu, D.X. Li, X.L. Xu, L. Wang, and Z.K. Hei, J. Mater. Sci.
Technol. 16, 362 (2000).
The authors give grateful thanks to Mr. J.X. Wang
(Institute of Materials and Technology, Dalian Maritime
University, Dalian, China) for nitriding the specimens
33. G. Hinojosa, J. Oseguera, and P.S. Schabes-Retchkiman, Thin
Solid Films 349, 171 (1999).
J. Mater. Res., Vol. 17, No. 10, Oct 2002
2627
Downloaded: 19 Mar 2015
IP address: 144.173.6.37