- Email: [email protected]
Effect of surface crystallographic orientation on the oxidation behavior of Ni-based alloy
Accepted Manuscript Title: Effect of surface crystallographic orientation on the oxidation behavior of Ni-based alloy Author: Xu Wang Szpunar J.A. Lina Zhang PII: DOI: Reference:
S0169-4332(14)02624-5 http://dx.doi.org/doi:10.1016/j.apsusc.2014.11.126 APSUSC 29172
To appear in:
APSUSC
Received date: Revised date: Accepted date:
20-6-2014 6-10-2014 21-11-2014
Please cite this article as: X. Wang, S. J.A., L. Zhang, Effect of surface crystallographic orientation on the oxidation behavior of Ni-based alloy, Applied Surface Science (2014), http://dx.doi.org/10.1016/j.apsusc.2014.11.126 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights We attempted to find a more direct way to study the effect of orientation on the
ip t
initial oxidation behavior of materials. EBSD orientation maps before and after oxidation were compared at the same
cr
area.
us
The degree of crystallographic orientation dependence was quantitatively
Ac ce p
te
d
M
an
analyzed by grains deviation angle from ideal principle <111> orientation.
Page 1 of 12
Xu Wanga*, Szpunar J.Aa, Lina Zhangb
College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK,S7N 5A9 Canada b
cr
a
ip t
Effect of surface crystallographic orientation on the oxidation behavior of Ni-based alloy
School of Materials Science and Engineering, University of Science and Technology Beijing, China
us
ABSTRACT
an
Dependence of initial oxidation behavior on crystalline orientation of Haynes 230 at 900°C was investigated by a novel method. Analysis of oxidation rate reveals that the
M
oxide thicknesses are different for grains having different orientations. Orientation mapping was performed on oxidized specimen and grains having near {111} were easily
d
indexed by electron backscattered diffraction. We determined that planes with deviation
te
angle lower than 20° were all well indexed after oxidation. Results demonstrate that substrate orientation plays an important role on oxidation rate during the initial stage.
Ac ce p
Keywords: Oxidation; Ni-based superalloy; Electron backscattered diffraction; Texture; Deviation angle
1. Introduction
Crystallographic orientation of materials has a significant influence on numerous properties like deformation [1], hardness [2], electrochemical activity [3], corrosion [4] and oxidation [5]. Many works were published on correlation between these properties and the crystallographic orientation of pure Fe [4], Cu [6] and Ni [7]. It was suggested that oxides on the (100) face produce higher number of high-angle grain boundaries which can be considered as short-circuit diffusion paths for metal ions and therefore they
Page 2 of 12
accelerate the oxidation process. Furthermore, it was demonstrated that the grain boundary concentration on grains with (100) orientation is much higher than that on grains with (111) orientation.
behavior of alloys mainly focused on single crystals [8,9].
1
ip t
Until now, most of the studies about the effect of surface orientation on the oxidation Recently, researchers
cr
attempted to investigate this dependence on polycrystalline materials[10,11]. However,
us
most of these works were carried out by combining electron backscattered diffraction (EBSD) with several other material characterization techniques like atomic force
an
microscope (AFM) [10], scanning electron microscope (SEM) [11] and optical microscope (OM) [12]. Here, we made attempt to find a novel method that will allows us
M
directly inspect the effect of crystallographic orientation on the early stage of oxidation of
te
2. Experimental
d
different alloys.
Ni-based superalloy Haynes 230 with chemical composition (wt.%) of Ni-22Cr-14W-
Ac ce p
2Mo-3Fe-5Co-0.5Mn-0.4Si-0.3Al-0.02La-0.015B provided by Haynes company was examined. Rectangular specimen with dimensions of 15mm×10mm×1.5mm was used. Prior to EBSD measurement, the specimen was polished up to 1μm diamond polishing and polished by using 0.04μm colloidal silica solution for 30minutes. Then specimen was polished in VibroMet2 Vibratory polisher for 10h by colloidal silica slurry to produce a strain free surface. After polishing, crystallographic texture of the specimen was determined by EBSD installed on Hitachi SU6600 scanning electron microscope (SEM). To produce an orientation map, an accelerating voltage of 20kV with a step size of 1.4μm was used. * Corresponding author. Tel: +1 3062615408; E-mail: [email protected]
Page 3 of 12
Then the sample was oxidized in air at 900°C for 5min. Finally, crystallographic texture of oxidized sample was measured by EBSD again on the same area as previous. In order to compare the results of orientation measurements, parameters for EBSD measurements
ip t
were kept the same. For visualization of EBSD data, HKL Channel 5 software was used.
Raman spectra from the oxidized sample were obtained from a Renishaw 2000 Raman
cr
Microscope with laser source wavelength of 785 nm. Energy dispersive spectroscopy
us
(EDS) mounted on Hitachi SU6600 was used to determine the oxide chemical components at 15KV in this experiment. Finally, sample was mounted for cross-section
an
investigation. The cross-section sample was polished along the same way as described above. Then EBSD was done on the cross-section sample to see the effect of substrate
M
grain orientation on the oxide thicknesses formed on grains.
d
To observe the same area where EBSD was done, sample was marked as shown in
te
Fig.1 (a). A rectangle (blue rectangle) mark was stamped on the specimen surface by a steel scriber. The enlarged image of this area is shown on the right image. Then a series
Ac ce p
of Wickers hardness indentations were imprinted in the area. EBSD patterns were recorded in the marked area where contains several indentations. Fig.1 (b) and (c) show the EBSD image quality (IQ) maps before and after oxidation. Crystallographic texture of an area with dimensions 450μm × 330μm was scanned. Four grains labeled with “A” to “D” are shown in these figures. This is made to demonstrate that the grains in these two areas are identical and they did not change their size and shape after oxidation. Small black un-indexed areas in Fig.1 (b) are corresponding to the carbides that segregated mainly at grain boundaries, these segregations were also observed in Haynes 230 by other authors [13]. Nevertheless, most of the grain
Page 4 of 12
orientations are well differentiated before oxidation. In case of after oxidation, most of grain orientations in this region cannot be identified as shown by dark black areas. The reason of this is discussed later.
us
cr
ip t
(a)
(c)
d
M
an
(b)
te
Fig. 1. (a) Method for marking and EBSD quality maps (b) before and (c) after oxidation.
3. Results and discussions
Ac ce p
Fig.2 (a) and (b) depict the orientation maps before and after oxidation. In these color maps, each color corresponds to a specific orientation which represents the normal vector of the crystal plane that is parallel to the normal direction (ND) of the specimen. The legend of these colors is shown in Fig.2 (c). Specifically, blue color grains are near (111) orientation, green color grains have near (110) orientation and red grains are close to (100). To illustrate this, the Euler Angles of grains “A” to “D” determined from HKL Channel 5 software are converted to ideal Miller indices. The Miller indexes of grains from “A” to “D” are (223)[ 12], (233)[ 21], (233)[ 41] and (324)[32 ] respectively. Twin grains in grains “A” to “C” have Miller indices as (237)[8
], (016)[
1] and
Page 5 of 12
(012)[ 00]. As seen from Fig.2 (a), all these grains and twin grains are indexed and marked with different colors before oxidation. According to Fig.2 (b) that display the same area after oxidation, almost all the grains with near (111) orientation (blue color)
ip t
are indexed. However, the grains near (110) and (100) orientation cannot be detected. Further, orientations of grains “A” to “D” which are all near (111) orientation are
cr
properly identified, but the orientation of twin grains in grains “A” to “C” cannot be
us
identified. This may indicate that grains with near (111) orientations are forming only a thin layer of oxide, while other grains oxidized faster since the EBSD diffraction patterns
an
from the substrate cannot be recorded.
(b)
Ac ce p
te
d
M
(a)
(d)
(c)
(e)
(f)
Fig. 2. (a) Orientation map before oxidation (b) orientation map after oxidation (c) legend of orientation map (d) IPF before oxidation (e) IPF after oxidation (f) IPF of grain “A” to “E” and twins in “A” to “C”.
Page 6 of 12
To clearly illustrate this result, the inverse pole figures (IPFs) of the same area are depicted in Fig.2 (d) to (f). The difference between IPF before oxidation Fig.2 (d) and IPF after oxidation Fig.2 (e) is clearly recorded. All orientations of the grains in this area
ip t
are indentified and represented by different colors in Fig.2 (d). However, in Fig.2 (e), only grains with near (111) orientation are identified after oxidation. This means that near
cr
(111) planes have lower oxidation rate than planes near (100) and (110) orientation in the
us
early stage of oxidation. In addition, the orientations of grain “A” to “D” and twin grains in grains “A” to “C” are re-plotted in a standard stereographic triangle in Fig.2 (f). It is
an
clearly evident which grain orientations are detected by EBSD system after oxidation and which are not when comparing Fig.2 (e) with Fig.2 (f). Those grains which are located in
M
the area close to <111> depicted by Fig.2 (e) are indexed, however, grains which are not 1] is
d
in this area are total un-indexed. Also grain E with Miller indices of (101)[
te
identified in Fig.2 (d) while not shown in Fig.2 (e). EBSD, as a surface technique, is used to examine surface characteristics like grain
Ac ce p
orientation, grain size distribution and phase distribution. Small scratches, contaminations and oxide layers will affect the quality of EBSD maps. It was demonstrated that the amorphous or semi-conductive oxide layer after oxidation will prevent the elastic electrons escape from the substrate crystal [14]. Therefore, EBSD detector may not recognize the crystallographic orientation of the substrate grains either because the obstacle effect or the absorption problems from the thick oxide layer. As a high content Cr (22wt.%) alloy, Haynes 230 is a Cr2O3-forming alloy[15,16]. Fig.3 (a) shows the comparison Raman spectrum results before and after oxidation. Several Raman shift peaks were observed between 500 and 700 cm-1. This area was
Page 7 of 12
selected and fitted with Lorentzian equation. Three peaks shown around 530, 551 and 650 cm-1 attributed to Cr-O vibration modes present the formation of Cr2O3 [17]and peak around 685 cm-1 was attributed to the formation of MnCr2O4. For this work, it is
ip t
reasonable to assume that oxides are favourably formed on the grains that are not close to (111) orientation. Consequently, the orientations of these grains cannot be identified
cr
again by EBSD and the area they occupied is marked as white in Fig.2 (b). This may
us
indicate that oxide layers formed on grains with near (111) orientations are much thinner than the other grains. Further, this assumption is confirmed by the EBSD result from the
an
cross-section as shown in Fig.3 (b) and (c). Fig.3 (b) depicts a small area with its orientation map in which grain 1 has a near (111) orientation and grain 2 has a near (100)
M
orientation. From Fig.3 (c) which shows the SEM image of the same area as (b), the
d
thickness of the oxide layer formed on grain 1 is much thinner than that on grain 2.
te
Judging from all the evidence, we may conclude that grains with near (111) orientations
Ac ce p
are more oxidation resistant than other grains. (b)
(a)
(c)
Fig. 3. (a) Raman spectrum result for oxide phase (b) EBSD result of cross-section (c) SEM image of cross-section
Page 8 of 12
Anisotropy behaviors of different grains with variation of texture under corrosion and oxidation atmosphere are numerously discussed. It was attributed to the different binding energy of atoms in individual crystal faces [18,19]. It is acceptable to expect that near
ip t
(111) planes will have slower oxidation rate since these planes have higher atomic densities in face centered cubic (FCC) materials. Surface free energy of planes tends to
cr
decrease for higher atomic density which may result in better resistance properties in
us
severe service environment.
Orme et.al [20,21] characterized the oxidation rate of different orientations by
an
measuring the deviation angle of a plane from the <111> orientation. For this work, particularly, the deviation angles from <111> direction for grains “A” to “E” are 11.4°,
M
10°, 10°, 15.2° and 35.3°, respectively. Deviation angles of twin grains in grains “A” to
d
“C” are 28.4°, 48.4° and 39.2°. In our experiments only those grains (“A”~“D”) with a
te
small deviation angle from <111> orientation can be indexed. After investigating all the grains indexed in this work, orientations of grains with deviation angles lower than
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around 20° were all indexed after oxidation. This means grains with deviation angles that are lower than 20° tend to have lower initial oxidation rate in air at temperature 900°C. In addition, EDS mapping was done on the area where contains three grains close to different orientations named as (111), (110) and (100) as shown in Fig.4 (a). Fig.4 (b) to (f) depicts the element distribution results of Ni, Cr, O, W and Mn, respectively. Cr and Mn seems homogeneously distributed inside these three grains, however, O seems concentrated on grains with orientation close to (110) and (100). The grain close to (111) gets less oxygen content than the other two grains. Fig.4 (g) is
[T1] the
typical EDS
spectrums from grains close to (111), (100) and (110). The normalized intensity for O
Page 9 of 12
increases as grains close to (111) < (110) < (100). [T2]It is clear to see the oxygen content difference which is identical with the trend described above. These results may further indicate that grain with orientation near (111) is more oxidation resistant.
ip t
4. Conclusions
The crystallographic orientation on oxidation behavior was investigated in a more
cr
direct way. Results indicate that crystallographic orientations of grains strongly affect the
us
oxidation rate at the early stage of oxidation of Haynes 230 at 900°C. Comparison of EBSD maps before and after oxidation determines the crystalline planes that have slow
an
oxidation rate. It was demonstrated that grains with deviation from <111> orientation less
M
than 20°are expected to have low oxidation rate in this study. (b)
(c)
(e)
(f)
Ac ce p
(d)
te
d
(a)
(g)
[T3]
Page 10 of 12
cr
ip t
Fig.4 EDS results measured from grains with different orientations
[T4]
us
[T5]
(j) Fig.4 EDS results measured from grains with different orientations
an
Acknowledgements
The authors gratefully acknowledge the financial support from Canadian
M
National Science and Engineering Research Council (NSERC). Xu Wang gratefully
[2] [3] [4] [5]
A.S. Taylor, P. Cizek, P.D. Hodgson, Acta Mater. 60 (2012) 1548.
Ac ce p
[1]
te
Reference
d
thanks financial support from China Scholarship Council (CSC).
S.-N. Luo, J.G. Swadener, C. Ma, O. Tschauner, Phys. B Condens. Matter 399 (2007) 138. E. Martinez-Lombardia, Y. Gonzalez-Garcia, L. Lapeire, I. De Graeve, K. Verbeken, L. Kestens, J.M.C. Mol, H. Terryn, Electrochim. Acta 116 (2014) 89.
A. Schreiber, J.W. Schultze, M.M. Lohrengel, F. Kármán, E. Kálmán, Electrochim. Acta 51 (2006) 2625. L. Hu, D. Hovis, A.H. Heuer, Scr. Mater. 61 (2009) 157.
[6]
F.W. Young, J. V Cathcart, A.T. Gwathmey, Acta Metall. 4 (1956) 145.
[7]
F. Czerwinski, a Zhilyaev, J.. Szpunar, Corros. Sci. 41 (1999) 1703.
[8]
F.H. Yuan, E.H. Han, C.Y. Jo, T.F. Li, Z.Q. Hu, Oxid. Met. 60 (2003) 211.
[9]
F.H. Latief, K. Kakehi, X. Fu, Y. Tashiro, 7 (2012) 8369.
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L.P. Bonfrisco, M. Frary, J. Mater. Sci. 45 (2009) 1663.
[11]
R. Bès, S. Gavarini, N. Millard-Pinard, S. Cardinal, a. Perrat-Mabilon, C. Peaucelle, T. Douillard, J. Nucl. Mater. 427 (2012) 415.
[12]
M.V. Diamanti, M.P. Pedeferri, C. a. Schuh, Metall. Mater. Trans. A 39 (2008) 2143.
[13]
H.M. Tawancy, J. Mater. Sci. 27 (1992) 6481.
ip t
[10]
cr
[14] C.J. Boehlert, R.K. Schulze, J.N. Mitchell, T.G. Zocco, Scr. Mater. 45 (2001) 1107. H.M. Tawancy, Oxid. Met. 45 (1996) 323.
[16]
L. Jian, P. Jian, H. Bing, G. Xie, J. Power Sources 159 (2006) 641.
us
[15]
an
[17] P.M. Sousa, a. J. Silvestre, N. Popovici, O. Conde, Appl. Surf. Sci. 247 (2005) 423. D.P. Burke, R.L. Higginson, 42 (2000) 277.
[19]
H. Park, J. a. Szpunar, Corros. Sci. 40 (1998) 525.
[20]
C. a. Schuh, K. Anderson, C. Orme, Surf. Sci. 544 (2003) 183.
[21]
J.J. Gray, B.S. El Dasher, C.A. Orme, Surf. Sci. 600 (2006) 2488.
Ac ce p
te
d
M
[18]
Page 12 of 12
S0169-4332(14)02624-5 http://dx.doi.org/doi:10.1016/j.apsusc.2014.11.126 APSUSC 29172
To appear in:
APSUSC
Received date: Revised date: Accepted date:
20-6-2014 6-10-2014 21-11-2014
Please cite this article as: X. Wang, S. J.A., L. Zhang, Effect of surface crystallographic orientation on the oxidation behavior of Ni-based alloy, Applied Surface Science (2014), http://dx.doi.org/10.1016/j.apsusc.2014.11.126 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights We attempted to find a more direct way to study the effect of orientation on the
ip t
initial oxidation behavior of materials. EBSD orientation maps before and after oxidation were compared at the same
cr
area.
us
The degree of crystallographic orientation dependence was quantitatively
Ac ce p
te
d
M
an
analyzed by grains deviation angle from ideal principle <111> orientation.
Page 1 of 12
Xu Wanga*, Szpunar J.Aa, Lina Zhangb
College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK,S7N 5A9 Canada b
cr
a
ip t
Effect of surface crystallographic orientation on the oxidation behavior of Ni-based alloy
School of Materials Science and Engineering, University of Science and Technology Beijing, China
us
ABSTRACT
an
Dependence of initial oxidation behavior on crystalline orientation of Haynes 230 at 900°C was investigated by a novel method. Analysis of oxidation rate reveals that the
M
oxide thicknesses are different for grains having different orientations. Orientation mapping was performed on oxidized specimen and grains having near {111} were easily
d
indexed by electron backscattered diffraction. We determined that planes with deviation
te
angle lower than 20° were all well indexed after oxidation. Results demonstrate that substrate orientation plays an important role on oxidation rate during the initial stage.
Ac ce p
Keywords: Oxidation; Ni-based superalloy; Electron backscattered diffraction; Texture; Deviation angle
1. Introduction
Crystallographic orientation of materials has a significant influence on numerous properties like deformation [1], hardness [2], electrochemical activity [3], corrosion [4] and oxidation [5]. Many works were published on correlation between these properties and the crystallographic orientation of pure Fe [4], Cu [6] and Ni [7]. It was suggested that oxides on the (100) face produce higher number of high-angle grain boundaries which can be considered as short-circuit diffusion paths for metal ions and therefore they
Page 2 of 12
accelerate the oxidation process. Furthermore, it was demonstrated that the grain boundary concentration on grains with (100) orientation is much higher than that on grains with (111) orientation.
behavior of alloys mainly focused on single crystals [8,9].
1
ip t
Until now, most of the studies about the effect of surface orientation on the oxidation Recently, researchers
cr
attempted to investigate this dependence on polycrystalline materials[10,11]. However,
us
most of these works were carried out by combining electron backscattered diffraction (EBSD) with several other material characterization techniques like atomic force
an
microscope (AFM) [10], scanning electron microscope (SEM) [11] and optical microscope (OM) [12]. Here, we made attempt to find a novel method that will allows us
M
directly inspect the effect of crystallographic orientation on the early stage of oxidation of
te
2. Experimental
d
different alloys.
Ni-based superalloy Haynes 230 with chemical composition (wt.%) of Ni-22Cr-14W-
Ac ce p
2Mo-3Fe-5Co-0.5Mn-0.4Si-0.3Al-0.02La-0.015B provided by Haynes company was examined. Rectangular specimen with dimensions of 15mm×10mm×1.5mm was used. Prior to EBSD measurement, the specimen was polished up to 1μm diamond polishing and polished by using 0.04μm colloidal silica solution for 30minutes. Then specimen was polished in VibroMet2 Vibratory polisher for 10h by colloidal silica slurry to produce a strain free surface. After polishing, crystallographic texture of the specimen was determined by EBSD installed on Hitachi SU6600 scanning electron microscope (SEM). To produce an orientation map, an accelerating voltage of 20kV with a step size of 1.4μm was used. * Corresponding author. Tel: +1 3062615408; E-mail: [email protected]
Page 3 of 12
Then the sample was oxidized in air at 900°C for 5min. Finally, crystallographic texture of oxidized sample was measured by EBSD again on the same area as previous. In order to compare the results of orientation measurements, parameters for EBSD measurements
ip t
were kept the same. For visualization of EBSD data, HKL Channel 5 software was used.
Raman spectra from the oxidized sample were obtained from a Renishaw 2000 Raman
cr
Microscope with laser source wavelength of 785 nm. Energy dispersive spectroscopy
us
(EDS) mounted on Hitachi SU6600 was used to determine the oxide chemical components at 15KV in this experiment. Finally, sample was mounted for cross-section
an
investigation. The cross-section sample was polished along the same way as described above. Then EBSD was done on the cross-section sample to see the effect of substrate
M
grain orientation on the oxide thicknesses formed on grains.
d
To observe the same area where EBSD was done, sample was marked as shown in
te
Fig.1 (a). A rectangle (blue rectangle) mark was stamped on the specimen surface by a steel scriber. The enlarged image of this area is shown on the right image. Then a series
Ac ce p
of Wickers hardness indentations were imprinted in the area. EBSD patterns were recorded in the marked area where contains several indentations. Fig.1 (b) and (c) show the EBSD image quality (IQ) maps before and after oxidation. Crystallographic texture of an area with dimensions 450μm × 330μm was scanned. Four grains labeled with “A” to “D” are shown in these figures. This is made to demonstrate that the grains in these two areas are identical and they did not change their size and shape after oxidation. Small black un-indexed areas in Fig.1 (b) are corresponding to the carbides that segregated mainly at grain boundaries, these segregations were also observed in Haynes 230 by other authors [13]. Nevertheless, most of the grain
Page 4 of 12
orientations are well differentiated before oxidation. In case of after oxidation, most of grain orientations in this region cannot be identified as shown by dark black areas. The reason of this is discussed later.
us
cr
ip t
(a)
(c)
d
M
an
(b)
te
Fig. 1. (a) Method for marking and EBSD quality maps (b) before and (c) after oxidation.
3. Results and discussions
Ac ce p
Fig.2 (a) and (b) depict the orientation maps before and after oxidation. In these color maps, each color corresponds to a specific orientation which represents the normal vector of the crystal plane that is parallel to the normal direction (ND) of the specimen. The legend of these colors is shown in Fig.2 (c). Specifically, blue color grains are near (111) orientation, green color grains have near (110) orientation and red grains are close to (100). To illustrate this, the Euler Angles of grains “A” to “D” determined from HKL Channel 5 software are converted to ideal Miller indices. The Miller indexes of grains from “A” to “D” are (223)[ 12], (233)[ 21], (233)[ 41] and (324)[32 ] respectively. Twin grains in grains “A” to “C” have Miller indices as (237)[8
], (016)[
1] and
Page 5 of 12
(012)[ 00]. As seen from Fig.2 (a), all these grains and twin grains are indexed and marked with different colors before oxidation. According to Fig.2 (b) that display the same area after oxidation, almost all the grains with near (111) orientation (blue color)
ip t
are indexed. However, the grains near (110) and (100) orientation cannot be detected. Further, orientations of grains “A” to “D” which are all near (111) orientation are
cr
properly identified, but the orientation of twin grains in grains “A” to “C” cannot be
us
identified. This may indicate that grains with near (111) orientations are forming only a thin layer of oxide, while other grains oxidized faster since the EBSD diffraction patterns
an
from the substrate cannot be recorded.
(b)
Ac ce p
te
d
M
(a)
(d)
(c)
(e)
(f)
Fig. 2. (a) Orientation map before oxidation (b) orientation map after oxidation (c) legend of orientation map (d) IPF before oxidation (e) IPF after oxidation (f) IPF of grain “A” to “E” and twins in “A” to “C”.
Page 6 of 12
To clearly illustrate this result, the inverse pole figures (IPFs) of the same area are depicted in Fig.2 (d) to (f). The difference between IPF before oxidation Fig.2 (d) and IPF after oxidation Fig.2 (e) is clearly recorded. All orientations of the grains in this area
ip t
are indentified and represented by different colors in Fig.2 (d). However, in Fig.2 (e), only grains with near (111) orientation are identified after oxidation. This means that near
cr
(111) planes have lower oxidation rate than planes near (100) and (110) orientation in the
us
early stage of oxidation. In addition, the orientations of grain “A” to “D” and twin grains in grains “A” to “C” are re-plotted in a standard stereographic triangle in Fig.2 (f). It is
an
clearly evident which grain orientations are detected by EBSD system after oxidation and which are not when comparing Fig.2 (e) with Fig.2 (f). Those grains which are located in
M
the area close to <111> depicted by Fig.2 (e) are indexed, however, grains which are not 1] is
d
in this area are total un-indexed. Also grain E with Miller indices of (101)[
te
identified in Fig.2 (d) while not shown in Fig.2 (e). EBSD, as a surface technique, is used to examine surface characteristics like grain
Ac ce p
orientation, grain size distribution and phase distribution. Small scratches, contaminations and oxide layers will affect the quality of EBSD maps. It was demonstrated that the amorphous or semi-conductive oxide layer after oxidation will prevent the elastic electrons escape from the substrate crystal [14]. Therefore, EBSD detector may not recognize the crystallographic orientation of the substrate grains either because the obstacle effect or the absorption problems from the thick oxide layer. As a high content Cr (22wt.%) alloy, Haynes 230 is a Cr2O3-forming alloy[15,16]. Fig.3 (a) shows the comparison Raman spectrum results before and after oxidation. Several Raman shift peaks were observed between 500 and 700 cm-1. This area was
Page 7 of 12
selected and fitted with Lorentzian equation. Three peaks shown around 530, 551 and 650 cm-1 attributed to Cr-O vibration modes present the formation of Cr2O3 [17]and peak around 685 cm-1 was attributed to the formation of MnCr2O4. For this work, it is
ip t
reasonable to assume that oxides are favourably formed on the grains that are not close to (111) orientation. Consequently, the orientations of these grains cannot be identified
cr
again by EBSD and the area they occupied is marked as white in Fig.2 (b). This may
us
indicate that oxide layers formed on grains with near (111) orientations are much thinner than the other grains. Further, this assumption is confirmed by the EBSD result from the
an
cross-section as shown in Fig.3 (b) and (c). Fig.3 (b) depicts a small area with its orientation map in which grain 1 has a near (111) orientation and grain 2 has a near (100)
M
orientation. From Fig.3 (c) which shows the SEM image of the same area as (b), the
d
thickness of the oxide layer formed on grain 1 is much thinner than that on grain 2.
te
Judging from all the evidence, we may conclude that grains with near (111) orientations
Ac ce p
are more oxidation resistant than other grains. (b)
(a)
(c)
Fig. 3. (a) Raman spectrum result for oxide phase (b) EBSD result of cross-section (c) SEM image of cross-section
Page 8 of 12
Anisotropy behaviors of different grains with variation of texture under corrosion and oxidation atmosphere are numerously discussed. It was attributed to the different binding energy of atoms in individual crystal faces [18,19]. It is acceptable to expect that near
ip t
(111) planes will have slower oxidation rate since these planes have higher atomic densities in face centered cubic (FCC) materials. Surface free energy of planes tends to
cr
decrease for higher atomic density which may result in better resistance properties in
us
severe service environment.
Orme et.al [20,21] characterized the oxidation rate of different orientations by
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measuring the deviation angle of a plane from the <111> orientation. For this work, particularly, the deviation angles from <111> direction for grains “A” to “E” are 11.4°,
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10°, 10°, 15.2° and 35.3°, respectively. Deviation angles of twin grains in grains “A” to
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“C” are 28.4°, 48.4° and 39.2°. In our experiments only those grains (“A”~“D”) with a
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small deviation angle from <111> orientation can be indexed. After investigating all the grains indexed in this work, orientations of grains with deviation angles lower than
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around 20° were all indexed after oxidation. This means grains with deviation angles that are lower than 20° tend to have lower initial oxidation rate in air at temperature 900°C. In addition, EDS mapping was done on the area where contains three grains close to different orientations named as (111), (110) and (100) as shown in Fig.4 (a). Fig.4 (b) to (f) depicts the element distribution results of Ni, Cr, O, W and Mn, respectively. Cr and Mn seems homogeneously distributed inside these three grains, however, O seems concentrated on grains with orientation close to (110) and (100). The grain close to (111) gets less oxygen content than the other two grains. Fig.4 (g) is
[T1] the
typical EDS
spectrums from grains close to (111), (100) and (110). The normalized intensity for O
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increases as grains close to (111) < (110) < (100). [T2]It is clear to see the oxygen content difference which is identical with the trend described above. These results may further indicate that grain with orientation near (111) is more oxidation resistant.
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4. Conclusions
The crystallographic orientation on oxidation behavior was investigated in a more
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direct way. Results indicate that crystallographic orientations of grains strongly affect the
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oxidation rate at the early stage of oxidation of Haynes 230 at 900°C. Comparison of EBSD maps before and after oxidation determines the crystalline planes that have slow
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oxidation rate. It was demonstrated that grains with deviation from <111> orientation less
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than 20°are expected to have low oxidation rate in this study. (b)
(c)
(e)
(f)
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(d)
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d
(a)
(g)
[T3]
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cr
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Fig.4 EDS results measured from grains with different orientations
[T4]
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[T5]
(j) Fig.4 EDS results measured from grains with different orientations
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Acknowledgements
The authors gratefully acknowledge the financial support from Canadian
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National Science and Engineering Research Council (NSERC). Xu Wang gratefully
[2] [3] [4] [5]
A.S. Taylor, P. Cizek, P.D. Hodgson, Acta Mater. 60 (2012) 1548.
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[1]
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