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Non-equilibrium phosphorus grain boundary segregation and its effect on embrittlement in a niobium-stabilized interstitial-free steel
Materials Letters 140 (2015) 20–22
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Non-equilibrium phosphorus grain boundary segregation and its effect on embrittlement in a niobium-stabilized interstitial-free steel S.-H. Song a,n, Yu Zhao a, Hong Si b a b
Shenzhen Key Laboratory of Advanced Materials, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China Central Iron and Steel Research Institute, Beijing 100081, China
art ic l e i nf o
a b s t r a c t
Article history: Received 10 October 2014 Accepted 31 October 2014 Available online 8 November 2014
Grain boundary segregation of phosphorus in an Nb-stabilized and P-strengthened interstitial-free steel was investigated using Auger electron spectroscopy after the steel specimens were quenched from 880 1C and aged at 680 1C for different times. The segregation initially increased with increasing aging time until reaching a maximum value and then decreased gradually to its equilibrium value with further increasing aging time, demonstrating a non-equilibrium segregation kinetic characteristic with a critical time of around 30 min. The ductile-to-brittle transition temperatures (DBTTs) of the aged specimens were determined through fracture appearance measurements. There was a linear relationship between DBTT and phosphorus boundary concentration (Cp, at%): DBTT(1C) ¼ 4.39Cp 64.06, suggesting that a P-strengthened IF steel should avoid slow cooling or staying in the intermediate temperature range so as to avoid apparent phosphorus grain boundary segregation and in turn to avoid embrittling. & 2014 Elsevier B.V. All rights reserved.
Keywords: Grain boundaries Segregation Metals and alloys Interfaces
1. Introduction In order to meet the industrial needs for high strength deep drawing steel, interstitial-free (IF) steel is usually hardened by solid solution strengthening with P, Si and Mn [1]. P is the best choice for this purpose because it has the highest strengthening effect without considerable cost of the deep drawability. However, P usually tends to segregate at grain boundaries, thereby causing a sharp increase in cold brittleness. The embrittlement induced by P grain boundary segregation is non-hardening embrittlement and it would increase the ductile-to-brittle transition temperature (DBTT) of the steel [2]. Previous studies have shown that solute grain boundary segregation, which includes equilibrium segregation and non-equilibrium segregation, can be caused by thermal induction, deformation, and irradiation [3]. Chen et al. [4] studied equilibrium grain boundary segregation of P in a Ti-stabilized IF steel and established a relationship between DBTT and P boundary concentration. Until now, there have been no reports on thermal non-equilibrium grain boundary segregation of P and its effect on DBTT for an IF steel. In the present work, thermal non-equilibrium grain boundary segregation of P in an Nb-stabilized and P-strengthened IF steel was investigated using Auger electron spectroscopy (AES). DBTTs of the steel with different phosphorus grain boundary n
Corresponding author. Tel.: þ 86 755 26033465; fax: þ 86 755 26033504. E-mail address: [email protected] (S.-H. Song).
http://dx.doi.org/10.1016/j.matlet.2014.10.158 0167-577X/& 2014 Elsevier B.V. All rights reserved.
concentrations were determined through fracture appearance transition measurements, thereby establishing a relationship between DBTT and non-equilibrium phosphorus grain boundary segregation.
2. Experimental An IF steel with chemical composition (wt%) of 0.0017C, 0.0018N, 0.002S, 0.044P, 0.036Nb, 0.35Mn, and 0.064Si was prepared by vacuum induction melting. Clearly, the steel was Nbstabilized and P-strengthened. Resulting ingot was hot rolled into a plate 5 mm in thickness. Then the plate was machined into samples with a size of 50 mm 50 mm 5 mm. These samples were initially austenitized at 960 1C for 15 min and then waterquenched to room temperature. After that, they were heated at 880 1C for 30 min, followed by ice-water quenching, so that a unified microstructure of ferrite with supersaturated vacancies was obtained. Finally, the samples were aged at 680 1C in a salt bath for different times to induce non-equilibrium grain boundary segregation of P. To evaluate the concentration of P at the grain boundary, an Auger electron spectrometer (AES) was employed. Cylindrical AES specimens with a sharp notch (3.8 mm 31.7 mm in size) were machined from the aged samples. The specimens were maintained at liquid-nitrogen temperature in the AES system for at last 30 min and then immediately fractured by impact to obtain intergranular
S.-H. Song et al. / Materials Letters 140 (2015) 20–22
fracture surfaces for AES measurements. Not less than 18 grain boundaries were measured for each condition and the mean value was taken as the measured result. Details on AES analysis can be seen elsewhere [5–8]. To examine the effect of non-equilibrium P grain boundary segregation on DBTT for the present IF steel, DBTTs of the aged samples were measured using impact tests in conjunction with fracture appearance observation. Rectangular specimens with a size of 50 mm 2.5 mm 2.5 mm and a sharp V-notch (1 mm deep) were machined from the aged samples. The specimens were cooled in liquid nitrogen-adjusted alcohol to different test temperatures. After soaking there for 10 min, they were immediately fractured by impact. Then, the fracture surfaces were analyzed using scanning electron microscopy (S-4700 SEM) and the temperature corresponding to 50% brittle fracture and 50% ductile fracture was determined as DBTT. In addition, a Vickers hardness testing machine with a load of 19.6 N was chosen to measure the hardness values of different samples and optical microscopy was employed to observe microstructures.
3. Results and discussion Fig. 1a shows a typical fractograph for the specimen aged at 680 1C for 5 min and fractured in the AES system by impact at liquid nitrogen temperature. Obviously, there are many intergranular facets, which are suitable for AES grain boundary microanalysis. A typical AES spectrum for this specimen is shown in Fig. 1b. As seen,
21
P has apparently segregated at the grain boundary. Fig. 2a shows P grain boundary concentrations as a function of aging time, which was determined by AES analysis. Obviously, during aging, the boundary concentration of P increases evidently with increasing aging time until reaching a maximum value in approximately 30 min and then decreases gradually with further increasing aging time. Finally, the boundary concentration comes to its equilibrium level in approximately 90 min. The kinetic curve of P segregation shown in Fig. 2a is a solid experimental verification of the nonequilibrium grain boundary segregation theory [9–11] and it is also the first observation of thermal non-equilibrium grain boundary segregation of P in an IF steel. According to the isothermal kinetic model of non-equilibrium grain boundary segregation, non-equilibrium segregation includes two processes: segregation process and desegregation process [11]. In the segregation process, P segregates to the grain boundary by a vacancy–solute complex diffusion mechanism, leading to an increase of P boundary concentration with increasing aging time. This diffusion is driven by the complex concentration gradient established by quenching-induced supersaturated vacancies. In the desegregation process, the backward diffusion of P from the grain boundary to the grain interior is dominant so that P boundary concentration decreases until reaching its equilibrium level with further increasing aging time. Xu [12] put forward that the most notable feature of isothermal non-equilibrium grain boundary segregation is its critical time which is defined as the time at which the segregation reaches a maximum level. Clearly, the grain boundary concentration of P reaches its peak value at
a P boundary concentration (at.%)
27
24
21
18
15
12
(b)
0
20
40
60
80
100
120
Aging time (min)
b 32
P
Fe
24
o
DBTT ( C)
dN(E)/dE
40
16
Fe 8
100
200
300
400
500
600
700
800
900
Kinetic energy (eV) Fig. 1. (a) Typical SEM fractograph and (b) corresponding AES spectrum for the specimen aged at 680 oC for 5 min and fractured by impact at liquid-nitrogen temperature in the AES system.
0
0
20
40
60
80
100
120
Aging time (min) Fig. 2. (a) Grain boundary concentrations of phosphorus in the specimens aged at 680 oC for different times and (b) corresponding DBTTs. Error bars represent the 95% confidence interval.
22
S.-H. Song et al. / Materials Letters 140 (2015) 20–22
about 30 min (see Fig. 2a). The critical time (tc) is expressed as
35
t c ¼ B2 lnðDc =Di Þ=½4δðDc Di Þ
30
ð1Þ
DBTTðo CÞ ¼ 4:39C p 64:06
ð2Þ
Consequently, for non-equilibrium grain boundary segregation of P, there is also a linear relationship between DBTT and P boundary concentration when the hardness and grain size are fixed. As can be seen in Eq. (2), grain boundary segregation of P can considerably raise DBTT for the present Nb-stabilized IF steel. It is therefore suggested that the P-strengthened IF steel should avoid slow cooling or staying in the intermediate temperature range so as to avoid apparent phosphorus grain boundary segregation and in turn to avoid embrittling. In addition, in terms of an investigation into the effect of boron on phosphorus-induced temper embrittlement [15], a trace quantity of boron could be doped in the P-strengthened IF steel to suppress P-induced embrittlement.
2
( R = 0.9704)
25 o
DBTT ( C)
where B is the grain size and δ is a constant; Dc and Di are the diffusion coefficients of vacancy–solute complexes and solute atoms in the matrix, respectively. Metallographic analysis indicated that there was no apparent difference in grain size between different aging times, being approximately 225 μm. This is reasonable because all the samples were heat-treated at 880 1C for 30 min after quenching from 960 1C, resulting in a unified microstructure prior to aging treatment. With Dc ¼1.7 10 5exp( 1.60/ kT), Di ¼1.83 10 5exp( 2.38/kT) [13], and δ ¼1162 [14], the critical time may be calculated as around 29 min, which is rather close to the present experimental value. Therefore, the segregation does have a non-equilibrium kinetic characteristic. Some previous studies [4,7] show that P is a strong embrittling element in the ferritic steels and its grain boundary segregation can shift DBTT of the steels to higher temperatures. The DBTTs of the specimens aged for different times are shown in Fig. 2b. It is interesting to note that the variation of DBTT with aging time is similar to that of P boundary concentration. This implies that the changes in DBTT are mainly caused by those in P boundary segregation. Embrittlement of a ferritic steel is divided into two types: hardening embrittlement and non-hardening embrittlement [7]. Normally, the hardening embrittlement comes with alloy strengthening, such as precipitation strengthening and strain hardening. The non-hardening embrittlement is mainly induced by grain boundary segregation of impurity elements such as P, Sn and Sb without an apparent change in hardness or strength. Hence, DBTT of the present steel may be affected not only by P grain boundary segregation but also by hardness and grain size. As with the same reason for the unified grain size, hardness measurements showed that there was also no apparent difference in hardness between different aging times, being approximately 92 HV. Accordingly, the embrittlement of the steel is mainly induced by grain boundary segregation of P as shown in Fig. 2a. In terms of the data shown in Fig. 2, the relation of DBTT to P boundary concentration (Cp, at%) is plotted in Fig. 3, clearly indicating that there is a linear relationship between them with an R-square value of 0.97, which is expressed as
DBTT = 4.39CP - 64.06
20
15
10
5
16
17
18
19
20
21
22
23
P boundary concentration (at.%) Fig. 3. DBTT as a function of phosphorus grain boundary concentration.
4. Conclusions Grain boundary segregation of P in the experimental Nbstabilized IF steel aged at 680 1C for different times after quenching from 880 1C is examined by AES measurements. The segregation exhibits a non-equilibrium kinetic characteristic with a critical time of approximately 30 min at which there is a maximum segregation level. DBTTs of the steel specimens are determined by impact tests along with fracture appearance observation. A relation of DBTT to phosphorus grain boundary concentration is established, which can be expressed asDBTTðo CÞ ¼ 4:39C p 64:06, where Cp is the phosphorus boundary concentration in at%.
Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant no. 51071060) and the Science and Technology Foundation of Shenzhen (Grant no. JCYJ20120613 115121482). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
Ray RK, Ghosh P, Bhattacharjee D. Mater Sci Technol 2009;25:1154–67. Chen XM, Song SH, Weng LQ, Wang K. Mater Lett 2012;67:107–9. Busby JT, Was GS, Kenik EA. J Nucl Mater 2002;302:20–40. Chen XM, Song SH, Weng LQ, Liu SJ, Wang K. Mater Sci Eng A 2011;528:8299–304. Davis LE, McDonald NC, Palmberg PW, Riach GE, Weber RE. Handbook of Auger electron spectroscopy. Minnesota: Physical Electronics Inc; 1976. Sevc P, Janovec J, Koutnik M, Vyrostkova A. Acta Metall Mater 1995;43:251–8. Shen DD, Song SH, Yuan ZX, Weng LQ. Mater Sci Eng A 2005;394:53–9. Song SH, Wu J, Wang DY, Weng LQ, Zheng L. Mater Sci Eng A 2006;430:320–5. Faulkner RGJ. Mater Sci 1981;16:373–83. Xu TD, Song SH. Acta Metall 1989;37:2499–506. Xu TD, Cheng BY. Prog Mater Sci 2004;49:109–208. Xu TD. Mater Sci Technol 1999;15:659–65. Song SH, Weng LQ. Mater Sci Technol 2005;21:305–10. Guo AM, Yuan ZX, Shen DD, Wu JJ. Rare Earth 2003;21:210–4. Song SH, Faulkner RG, Flewitt PEJ. J Mater Sci 1999;34:5549–56.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Non-equilibrium phosphorus grain boundary segregation and its effect on embrittlement in a niobium-stabilized interstitial-free steel S.-H. Song a,n, Yu Zhao a, Hong Si b a b
Shenzhen Key Laboratory of Advanced Materials, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China Central Iron and Steel Research Institute, Beijing 100081, China
art ic l e i nf o
a b s t r a c t
Article history: Received 10 October 2014 Accepted 31 October 2014 Available online 8 November 2014
Grain boundary segregation of phosphorus in an Nb-stabilized and P-strengthened interstitial-free steel was investigated using Auger electron spectroscopy after the steel specimens were quenched from 880 1C and aged at 680 1C for different times. The segregation initially increased with increasing aging time until reaching a maximum value and then decreased gradually to its equilibrium value with further increasing aging time, demonstrating a non-equilibrium segregation kinetic characteristic with a critical time of around 30 min. The ductile-to-brittle transition temperatures (DBTTs) of the aged specimens were determined through fracture appearance measurements. There was a linear relationship between DBTT and phosphorus boundary concentration (Cp, at%): DBTT(1C) ¼ 4.39Cp 64.06, suggesting that a P-strengthened IF steel should avoid slow cooling or staying in the intermediate temperature range so as to avoid apparent phosphorus grain boundary segregation and in turn to avoid embrittling. & 2014 Elsevier B.V. All rights reserved.
Keywords: Grain boundaries Segregation Metals and alloys Interfaces
1. Introduction In order to meet the industrial needs for high strength deep drawing steel, interstitial-free (IF) steel is usually hardened by solid solution strengthening with P, Si and Mn [1]. P is the best choice for this purpose because it has the highest strengthening effect without considerable cost of the deep drawability. However, P usually tends to segregate at grain boundaries, thereby causing a sharp increase in cold brittleness. The embrittlement induced by P grain boundary segregation is non-hardening embrittlement and it would increase the ductile-to-brittle transition temperature (DBTT) of the steel [2]. Previous studies have shown that solute grain boundary segregation, which includes equilibrium segregation and non-equilibrium segregation, can be caused by thermal induction, deformation, and irradiation [3]. Chen et al. [4] studied equilibrium grain boundary segregation of P in a Ti-stabilized IF steel and established a relationship between DBTT and P boundary concentration. Until now, there have been no reports on thermal non-equilibrium grain boundary segregation of P and its effect on DBTT for an IF steel. In the present work, thermal non-equilibrium grain boundary segregation of P in an Nb-stabilized and P-strengthened IF steel was investigated using Auger electron spectroscopy (AES). DBTTs of the steel with different phosphorus grain boundary n
Corresponding author. Tel.: þ 86 755 26033465; fax: þ 86 755 26033504. E-mail address: [email protected] (S.-H. Song).
http://dx.doi.org/10.1016/j.matlet.2014.10.158 0167-577X/& 2014 Elsevier B.V. All rights reserved.
concentrations were determined through fracture appearance transition measurements, thereby establishing a relationship between DBTT and non-equilibrium phosphorus grain boundary segregation.
2. Experimental An IF steel with chemical composition (wt%) of 0.0017C, 0.0018N, 0.002S, 0.044P, 0.036Nb, 0.35Mn, and 0.064Si was prepared by vacuum induction melting. Clearly, the steel was Nbstabilized and P-strengthened. Resulting ingot was hot rolled into a plate 5 mm in thickness. Then the plate was machined into samples with a size of 50 mm 50 mm 5 mm. These samples were initially austenitized at 960 1C for 15 min and then waterquenched to room temperature. After that, they were heated at 880 1C for 30 min, followed by ice-water quenching, so that a unified microstructure of ferrite with supersaturated vacancies was obtained. Finally, the samples were aged at 680 1C in a salt bath for different times to induce non-equilibrium grain boundary segregation of P. To evaluate the concentration of P at the grain boundary, an Auger electron spectrometer (AES) was employed. Cylindrical AES specimens with a sharp notch (3.8 mm 31.7 mm in size) were machined from the aged samples. The specimens were maintained at liquid-nitrogen temperature in the AES system for at last 30 min and then immediately fractured by impact to obtain intergranular
S.-H. Song et al. / Materials Letters 140 (2015) 20–22
fracture surfaces for AES measurements. Not less than 18 grain boundaries were measured for each condition and the mean value was taken as the measured result. Details on AES analysis can be seen elsewhere [5–8]. To examine the effect of non-equilibrium P grain boundary segregation on DBTT for the present IF steel, DBTTs of the aged samples were measured using impact tests in conjunction with fracture appearance observation. Rectangular specimens with a size of 50 mm 2.5 mm 2.5 mm and a sharp V-notch (1 mm deep) were machined from the aged samples. The specimens were cooled in liquid nitrogen-adjusted alcohol to different test temperatures. After soaking there for 10 min, they were immediately fractured by impact. Then, the fracture surfaces were analyzed using scanning electron microscopy (S-4700 SEM) and the temperature corresponding to 50% brittle fracture and 50% ductile fracture was determined as DBTT. In addition, a Vickers hardness testing machine with a load of 19.6 N was chosen to measure the hardness values of different samples and optical microscopy was employed to observe microstructures.
3. Results and discussion Fig. 1a shows a typical fractograph for the specimen aged at 680 1C for 5 min and fractured in the AES system by impact at liquid nitrogen temperature. Obviously, there are many intergranular facets, which are suitable for AES grain boundary microanalysis. A typical AES spectrum for this specimen is shown in Fig. 1b. As seen,
21
P has apparently segregated at the grain boundary. Fig. 2a shows P grain boundary concentrations as a function of aging time, which was determined by AES analysis. Obviously, during aging, the boundary concentration of P increases evidently with increasing aging time until reaching a maximum value in approximately 30 min and then decreases gradually with further increasing aging time. Finally, the boundary concentration comes to its equilibrium level in approximately 90 min. The kinetic curve of P segregation shown in Fig. 2a is a solid experimental verification of the nonequilibrium grain boundary segregation theory [9–11] and it is also the first observation of thermal non-equilibrium grain boundary segregation of P in an IF steel. According to the isothermal kinetic model of non-equilibrium grain boundary segregation, non-equilibrium segregation includes two processes: segregation process and desegregation process [11]. In the segregation process, P segregates to the grain boundary by a vacancy–solute complex diffusion mechanism, leading to an increase of P boundary concentration with increasing aging time. This diffusion is driven by the complex concentration gradient established by quenching-induced supersaturated vacancies. In the desegregation process, the backward diffusion of P from the grain boundary to the grain interior is dominant so that P boundary concentration decreases until reaching its equilibrium level with further increasing aging time. Xu [12] put forward that the most notable feature of isothermal non-equilibrium grain boundary segregation is its critical time which is defined as the time at which the segregation reaches a maximum level. Clearly, the grain boundary concentration of P reaches its peak value at
a P boundary concentration (at.%)
27
24
21
18
15
12
(b)
0
20
40
60
80
100
120
Aging time (min)
b 32
P
Fe
24
o
DBTT ( C)
dN(E)/dE
40
16
Fe 8
100
200
300
400
500
600
700
800
900
Kinetic energy (eV) Fig. 1. (a) Typical SEM fractograph and (b) corresponding AES spectrum for the specimen aged at 680 oC for 5 min and fractured by impact at liquid-nitrogen temperature in the AES system.
0
0
20
40
60
80
100
120
Aging time (min) Fig. 2. (a) Grain boundary concentrations of phosphorus in the specimens aged at 680 oC for different times and (b) corresponding DBTTs. Error bars represent the 95% confidence interval.
22
S.-H. Song et al. / Materials Letters 140 (2015) 20–22
about 30 min (see Fig. 2a). The critical time (tc) is expressed as
35
t c ¼ B2 lnðDc =Di Þ=½4δðDc Di Þ
30
ð1Þ
DBTTðo CÞ ¼ 4:39C p 64:06
ð2Þ
Consequently, for non-equilibrium grain boundary segregation of P, there is also a linear relationship between DBTT and P boundary concentration when the hardness and grain size are fixed. As can be seen in Eq. (2), grain boundary segregation of P can considerably raise DBTT for the present Nb-stabilized IF steel. It is therefore suggested that the P-strengthened IF steel should avoid slow cooling or staying in the intermediate temperature range so as to avoid apparent phosphorus grain boundary segregation and in turn to avoid embrittling. In addition, in terms of an investigation into the effect of boron on phosphorus-induced temper embrittlement [15], a trace quantity of boron could be doped in the P-strengthened IF steel to suppress P-induced embrittlement.
2
( R = 0.9704)
25 o
DBTT ( C)
where B is the grain size and δ is a constant; Dc and Di are the diffusion coefficients of vacancy–solute complexes and solute atoms in the matrix, respectively. Metallographic analysis indicated that there was no apparent difference in grain size between different aging times, being approximately 225 μm. This is reasonable because all the samples were heat-treated at 880 1C for 30 min after quenching from 960 1C, resulting in a unified microstructure prior to aging treatment. With Dc ¼1.7 10 5exp( 1.60/ kT), Di ¼1.83 10 5exp( 2.38/kT) [13], and δ ¼1162 [14], the critical time may be calculated as around 29 min, which is rather close to the present experimental value. Therefore, the segregation does have a non-equilibrium kinetic characteristic. Some previous studies [4,7] show that P is a strong embrittling element in the ferritic steels and its grain boundary segregation can shift DBTT of the steels to higher temperatures. The DBTTs of the specimens aged for different times are shown in Fig. 2b. It is interesting to note that the variation of DBTT with aging time is similar to that of P boundary concentration. This implies that the changes in DBTT are mainly caused by those in P boundary segregation. Embrittlement of a ferritic steel is divided into two types: hardening embrittlement and non-hardening embrittlement [7]. Normally, the hardening embrittlement comes with alloy strengthening, such as precipitation strengthening and strain hardening. The non-hardening embrittlement is mainly induced by grain boundary segregation of impurity elements such as P, Sn and Sb without an apparent change in hardness or strength. Hence, DBTT of the present steel may be affected not only by P grain boundary segregation but also by hardness and grain size. As with the same reason for the unified grain size, hardness measurements showed that there was also no apparent difference in hardness between different aging times, being approximately 92 HV. Accordingly, the embrittlement of the steel is mainly induced by grain boundary segregation of P as shown in Fig. 2a. In terms of the data shown in Fig. 2, the relation of DBTT to P boundary concentration (Cp, at%) is plotted in Fig. 3, clearly indicating that there is a linear relationship between them with an R-square value of 0.97, which is expressed as
DBTT = 4.39CP - 64.06
20
15
10
5
16
17
18
19
20
21
22
23
P boundary concentration (at.%) Fig. 3. DBTT as a function of phosphorus grain boundary concentration.
4. Conclusions Grain boundary segregation of P in the experimental Nbstabilized IF steel aged at 680 1C for different times after quenching from 880 1C is examined by AES measurements. The segregation exhibits a non-equilibrium kinetic characteristic with a critical time of approximately 30 min at which there is a maximum segregation level. DBTTs of the steel specimens are determined by impact tests along with fracture appearance observation. A relation of DBTT to phosphorus grain boundary concentration is established, which can be expressed asDBTTðo CÞ ¼ 4:39C p 64:06, where Cp is the phosphorus boundary concentration in at%.
Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant no. 51071060) and the Science and Technology Foundation of Shenzhen (Grant no. JCYJ20120613 115121482). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
Ray RK, Ghosh P, Bhattacharjee D. Mater Sci Technol 2009;25:1154–67. Chen XM, Song SH, Weng LQ, Wang K. Mater Lett 2012;67:107–9. Busby JT, Was GS, Kenik EA. J Nucl Mater 2002;302:20–40. Chen XM, Song SH, Weng LQ, Liu SJ, Wang K. Mater Sci Eng A 2011;528:8299–304. Davis LE, McDonald NC, Palmberg PW, Riach GE, Weber RE. Handbook of Auger electron spectroscopy. Minnesota: Physical Electronics Inc; 1976. Sevc P, Janovec J, Koutnik M, Vyrostkova A. Acta Metall Mater 1995;43:251–8. Shen DD, Song SH, Yuan ZX, Weng LQ. Mater Sci Eng A 2005;394:53–9. Song SH, Wu J, Wang DY, Weng LQ, Zheng L. Mater Sci Eng A 2006;430:320–5. Faulkner RGJ. Mater Sci 1981;16:373–83. Xu TD, Song SH. Acta Metall 1989;37:2499–506. Xu TD, Cheng BY. Prog Mater Sci 2004;49:109–208. Xu TD. Mater Sci Technol 1999;15:659–65. Song SH, Weng LQ. Mater Sci Technol 2005;21:305–10. Guo AM, Yuan ZX, Shen DD, Wu JJ. Rare Earth 2003;21:210–4. Song SH, Faulkner RG, Flewitt PEJ. J Mater Sci 1999;34:5549–56.