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Influence of process control agents on the performance of Ni3Al by mechanical alloying
RARE METALS, Vol. 27, No. 6, Dec 2008, p. 648
Influence of process control agents on the performance of Ni3Al by mechanical alloying LIAN Jiqionga, MENG Jieb, and JIA Chengchanga a b
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China
Received 8 December 2007; received in revised form 22 January 2008; accepted 6 February 2008
Abstract The influence of process control agents (PCAs) on the mechanical properties of Ni3Al intermetallic compounds by mechanical alloying was investigated in order to develop oxide deposition reinforced intermetallics. The PCAs in mechanical alloying were pure ligroin, 75 vol.% ligroin + 25 vol.% alcohol, 50 vol.% ligroin + 50 vol.% alcohol, 25 vol.% ligroin + 75 vol.% alcohol, and pure alcohol. The normal composition is Ni-22.9at.%Al-0.5at.%B, the ball-to-powder weight ratio is 10 1, and the milling time is 30 min. Then, the powders were sintered by spark plasma sintering under 40 MPa for 5 min at 1000qC. The results show that a higher bending strength and a higher hardness were obtained when the PCAs were 75% ligroin + 25% alcohol in mechanical alloying. The bending strength is about 2700 MPa and the hardness (HV) is more than 6 GPa. Keywords: intermetallic compounds; mechanical properties; mechanical alloying; process control agent; spark plasma sintering
1. Introduction Ni-Al based intermetallic compounds possess advantageous properties: high tensile strength and yield point, low density, high-temperature creep resistance, good corrosion, and oxidation resistance at elevated temperatures [1-3]. One of the intermetallics for high-temperature applications is Ni3Al with fcc order L12 structure [1, 4]. The yield strength of the Ni3Al increases with increasing temperature up to 600-800qC [5]. However, there are many limitations in its application as engineering materials because of the extreme brittleness of polycrystalline Ni3Al at room temperature, especially the fabrication of Ni3Al by conventional cast is difficult and costly to process as structural components [6-7]. Mechanical alloying (MA) is an alternative technique for producing metallic powders in solid state [8-9]. Using MA for the preparation of Ni3Al results in the occurrence of metastable states and dispersed microstructures that significantly change the properties of the alloy [10]. In this article, the microstructure and characteristics of mechanical alloying powder with a normal composition of Ni-22.9at.%Al-0.5at.%B has been investigated. The effect of process control agents (PCAs) on the performance of the powder has been studied. The properties include the density Corresponding author: JIA Chengchang
E-mail: [email protected]
of sintered samples by spark plasma sintering (SPS), bending strength, and hardness.
2. Experimental The powders of Ni, Al, and B were mixed to obtain the normal composition of Ni-22.9at.%Al-0.5at.%B. The particle size and purity of the powders are shown in Table 1. Mechanical alloying was performed at room temperature in air using vibratory milling. The powders and the hardened stainless steel milling balls were sealed in a hardened stainless steel vial. To decrease the agglomeration and adhering, pure ligroin, 75 vol.% ligroin + 25 vol.% alcohol, 50 vol.% ligroin + 50 vol.% alcohol, 25 vol.% ligroin + 75 vol.% alcohol, and pure alcohol were each added to the mixture as PCAs. The ball-to-powder weight ratio was 10 1. The milling time selected was 30 min. Then, the powders were sintered by SPS under 40 MPa for 5 min at 1000qC. Table 1. Size and purity of powders as raw materials Powder
Size / Pm
Purity / %
Ni
2
99.9
Al
2
99.5
B
3-5
98.0
Lian J.Q. et al., Influence of process control agents on the performance of Ni3Al by mechanical alloying
X-ray diffraction patterns of the powders and sintered samples were recorded using a Philips 330 diffractometer with Cu KD radiation at 40 kV and 25 mA. Scanning electron microscopy with energy dispersive spectrometer (EDS) was used to investigate the microstructure of the samples. The densities of sintered samples were determined by the buoyancy method applying the Archimedes Principle. Bending specimens with 16 mm in gauge length, 3 mm in width, and 3 mm in thickness were prepared from the samples. Bending test was done at a constant strain rate of 0.5 s1 at room temperature. Micro hardness test was carried out
649
at a load of 20 N.
3. Results and discussion The densities of the samples are shown in Table 2. It can be seen that the density decreases along with the increase in the alcohol content of the PCA, and the maximum density can reach 7.496 g/cm3, near to the theoretical density of Ni3Al (7.5 g/cm3). The reason is that the oxygen content of the powders increases along with the alcohol content of the PCA, which results in the increase in the pore of the samples.
Table 2. Density of the samples Samples
PCA
m1 / g
m2 / g
Theoretical density / (gcm3)
Density / (gcm3)
Relative density / %
1#
100 vol.%L
16.5383
14.3319
7.5
7.496
99.90
2#
75vol.%L-25vol.%A
16.3623
14.1326
7.5
7.338
97.84
3#
50vol.%L-50vol.%A
14.9614
12.8475
7.5
7.078
94.40
4#
25vol.%L-75vol.%A
14.6544
12.5700
7.5
7.031
93.70
5#
100 vol.%A
14.7108
12.6246
7.5
7.051
94 .00
Note: L is ligroin, A is alcohol, m1 is the mass of the sample in air, and m2 is the mass of the sample in water.
The characterization of X-ray diffraction patterns of the sintered powders and bodies were shown in Figs. 1 and 2, respectively. In Fig. 1 it can be seen that some Al remains. It suggested that a supersaturated solution of Al in Ni was obtained after milling. While Fig. 2 shows that Ni3Al was formed by spark plasma sintering (SPS) under 40 MPa for 5 min at 1000qC. During milling, Fe as a pollution was brought in, but it cannot be seen in the characterization of X-ray diffraction patterns because of very little.
and the alcohol content are shown in Figs. 4 and 5, respectively.
Fig. 2. X-ray diffraction patterns of bodies.
Fig. 1. X-ray diffraction patterns of the as-milled powders.
Fig. 3 shows the microstructures of samples 1#, 2#, 3#, 4#, and 5#. More pores exist in sample 2# than in sample 1#. So the density of sample 2# is lower than that of 1#. But the dispersed Al2O3 increased the strength and hardness of samples. However, the pores can be seen in the intergranular from Fig. 3(c) to Fig. 3(e). This results in a lower strength and hardness of samples 3#, 4#, and 5#. The relationship between the bending strength and the alcohol content, and the relationship between the hardness
Fig. 4 shows that the maximum bending strength is 2768 MPa with 75 vol.% ligroin mixed with 25 vol.% alcohol as PCA. It can be observed that the maximum hardness (HV) is more than 6 GPa with 75 vol.% ligroin mixed with 25 vol.% alcohol as PCA (Fig. 5). The oxygen of the sample with 100% ligroin is from milling, that of the other samples (sintered with 75 vol.% ligroin + 25 vol.% alcohol, 50 vol.% ligroin + 50 vol.% alcohol, 25 vol.% ligroin + 75 vol.% alcohol and pure alcohol as PCAs) are from milling and alcohol. The oxygen content of the sample with 100% ligroin is 0.20 wt.%, and that with 100% alcohol is 0.61 wt.%. The oxygen content increased with the increase in alcohol. Fig. 6 shows the composition of compacts with powder milled for 30 min by EDS. Fig. 6(a) shows the point scanning of second phase; Fig. 6(b) shows the area scanning of matrix. Obviously, the oxygen content
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RARE METALS, Vol. 27, No. 6, Dec 2008
increased in the second phase. In Ni-rich Ni-Al alloys, the selective oxidation of Al should be promoted, for the formation of Al2O3 instead of Ni oxides [11-15]. A few of Al2O3 dispersed during the intergranular (Fig. 7). The dispersion of
Al2O3 increases the strength and hardness of the sample and improves the ductility. But the density decreases and glomeration is formed with the increase in the oxygen content, so the strength and hardness decreases by degrees.
Fig. 3. SEM micrographs of the samples: (a) 1#; (b) 2#; (c) 3#; (d) 4#;(e) 5#.
Fig. 4. Relationship between bending strength and alcohol content.
Fig. 5. Relationship between hardness and alcohol content.
Fig. 6. Composition of compacts with powder milled for 30 min by EDS: (a) points scanning of second phase; (b) area scanning of matrix.
Lian J.Q. et al., Influence of process control agents on the performance of Ni3Al by mechanical alloying
651
Fig. 6. Bright field image (a) and selected area electron diffraction (SAD) pattern (b) of the sintered sample with milled powders.
4. Conclusions (1) A solution of Al in Ni was obtained after mechanical alloying of elemental powder with the normal composition of Ni-22.9at.%Al-0.5at.%B. (2) PCAs have influence on the mechanical properties of Ni3Al intermetallic compounds. The optimal proportion is 75 vol.% ligroin mixed with 25 vol.% alcohol. (3) The density of sintered samples is 97.84%, the bending strength is 2768 MPa, and the hardness (HV) is more than 6 GPa.
References [1] Krasnowski M., Antolak A., and Kulik T., Nanocrystalline Ni3Al alloy produced by mechanical alloying of nickel aluminides and hot-pressing consolidation, J. Alloys Compd., 2007, 434-435: 344. [2] Deevi S.C. and Sikka V.K., Nickel and iron aluminides: an overview on properties, processing, and application, Intermetallics, 1996, 4: 357. [3] Deevi S.C., Sikka V.K., and Liu C.T., Processing, properties, and application of nickel and iron aluminides, Prog. Mater. Sci., 1997, 42 (1-4): 177. [4] Paidar V., Pope D.P., and Vitek V., A theory of the anomalous yield behavior in L12 ordered alloys, Acta Metall., 1984, 32 (3): 435. [5] Enayati M.H., Sadeghian Z., Salehi M., and Saidi A., The effect of milling parameters on the synthesis of Ni3Al inter-metallic compound by mechanical alloying, Mater. Sci.
Eng. A, 2004, 375-377: 809. [6] Meng J., Jia C.C., and He Q., Fabrication of Ni3Al by hot pressing from element powders, Rare Met., 2007, 26 (3): 222. [7] George E.P., Liu C.T., Lin H., and Pope D.P., Environmental embrittlement and other causes of brittle grain boundary fracture in Ni3Al, Mater. Sci. Eng. A, 1995, 192/193: 277. [8] Suryanrayana C., Mechanical alloying and milling, Prog. Mater. Sci., 2001, 46 (1-2): 1. [9] Li L. and Lai M.O., Formation of new materials in the solid state by mechanical alloying, Mater. Des., 1995, 16 (1): 33. [10] Portnoy V.K., Blinov A.M., Tomilin I.A., Kuznetsov V.N., and Kulik T., Formation of nickel aluminides by mechanical alloying and thermo dynamics of interaction, J. Alloys Compd., 2002, 336: 196. [11] Cao G.J., Geng L., Zheng Z.Z., and Naka M., The oxidation of nanocrystalline Ni3Al fabricated by mechanical alloying and spark plasma sintering, Intermetallics, 2007, 15 (12): 1672. [12] Liu Z.Y., Gao W., Dahm Karl L., and Wang F.H., Oxidation behaviour of sputter-deposited Ni-Cr-Al micro-crystalline coating, Acta Mater., 1998, 46: 1691. [13] Chen G.F. and Lou H.Y., The effect of nanocrystallization on the oxide formation on Ni-11Cr-8Al alloy, Scripta Mater., 2000, 43 (2-3):119. [14] Zhou Y., Peng X., and Wang F., Oxidation of a novel electrodeposited Ni-Al nanocomposite file at 1050qC, Scripta Mater., 2004, 50: 1429. [15] Kima S.H., Ohb M.H., Kishidac K., Hiranoc T., and Weea D.M., Deposition of NiAl coating for improvement of oxidation resistance of cold-rolled Ni3Al foils, Intermetallics, 2005, 13: 129.
Influence of process control agents on the performance of Ni3Al by mechanical alloying LIAN Jiqionga, MENG Jieb, and JIA Chengchanga a b
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China
Received 8 December 2007; received in revised form 22 January 2008; accepted 6 February 2008
Abstract The influence of process control agents (PCAs) on the mechanical properties of Ni3Al intermetallic compounds by mechanical alloying was investigated in order to develop oxide deposition reinforced intermetallics. The PCAs in mechanical alloying were pure ligroin, 75 vol.% ligroin + 25 vol.% alcohol, 50 vol.% ligroin + 50 vol.% alcohol, 25 vol.% ligroin + 75 vol.% alcohol, and pure alcohol. The normal composition is Ni-22.9at.%Al-0.5at.%B, the ball-to-powder weight ratio is 10 1, and the milling time is 30 min. Then, the powders were sintered by spark plasma sintering under 40 MPa for 5 min at 1000qC. The results show that a higher bending strength and a higher hardness were obtained when the PCAs were 75% ligroin + 25% alcohol in mechanical alloying. The bending strength is about 2700 MPa and the hardness (HV) is more than 6 GPa. Keywords: intermetallic compounds; mechanical properties; mechanical alloying; process control agent; spark plasma sintering
1. Introduction Ni-Al based intermetallic compounds possess advantageous properties: high tensile strength and yield point, low density, high-temperature creep resistance, good corrosion, and oxidation resistance at elevated temperatures [1-3]. One of the intermetallics for high-temperature applications is Ni3Al with fcc order L12 structure [1, 4]. The yield strength of the Ni3Al increases with increasing temperature up to 600-800qC [5]. However, there are many limitations in its application as engineering materials because of the extreme brittleness of polycrystalline Ni3Al at room temperature, especially the fabrication of Ni3Al by conventional cast is difficult and costly to process as structural components [6-7]. Mechanical alloying (MA) is an alternative technique for producing metallic powders in solid state [8-9]. Using MA for the preparation of Ni3Al results in the occurrence of metastable states and dispersed microstructures that significantly change the properties of the alloy [10]. In this article, the microstructure and characteristics of mechanical alloying powder with a normal composition of Ni-22.9at.%Al-0.5at.%B has been investigated. The effect of process control agents (PCAs) on the performance of the powder has been studied. The properties include the density Corresponding author: JIA Chengchang
E-mail: [email protected]
of sintered samples by spark plasma sintering (SPS), bending strength, and hardness.
2. Experimental The powders of Ni, Al, and B were mixed to obtain the normal composition of Ni-22.9at.%Al-0.5at.%B. The particle size and purity of the powders are shown in Table 1. Mechanical alloying was performed at room temperature in air using vibratory milling. The powders and the hardened stainless steel milling balls were sealed in a hardened stainless steel vial. To decrease the agglomeration and adhering, pure ligroin, 75 vol.% ligroin + 25 vol.% alcohol, 50 vol.% ligroin + 50 vol.% alcohol, 25 vol.% ligroin + 75 vol.% alcohol, and pure alcohol were each added to the mixture as PCAs. The ball-to-powder weight ratio was 10 1. The milling time selected was 30 min. Then, the powders were sintered by SPS under 40 MPa for 5 min at 1000qC. Table 1. Size and purity of powders as raw materials Powder
Size / Pm
Purity / %
Ni
2
99.9
Al
2
99.5
B
3-5
98.0
Lian J.Q. et al., Influence of process control agents on the performance of Ni3Al by mechanical alloying
X-ray diffraction patterns of the powders and sintered samples were recorded using a Philips 330 diffractometer with Cu KD radiation at 40 kV and 25 mA. Scanning electron microscopy with energy dispersive spectrometer (EDS) was used to investigate the microstructure of the samples. The densities of sintered samples were determined by the buoyancy method applying the Archimedes Principle. Bending specimens with 16 mm in gauge length, 3 mm in width, and 3 mm in thickness were prepared from the samples. Bending test was done at a constant strain rate of 0.5 s1 at room temperature. Micro hardness test was carried out
649
at a load of 20 N.
3. Results and discussion The densities of the samples are shown in Table 2. It can be seen that the density decreases along with the increase in the alcohol content of the PCA, and the maximum density can reach 7.496 g/cm3, near to the theoretical density of Ni3Al (7.5 g/cm3). The reason is that the oxygen content of the powders increases along with the alcohol content of the PCA, which results in the increase in the pore of the samples.
Table 2. Density of the samples Samples
PCA
m1 / g
m2 / g
Theoretical density / (gcm3)
Density / (gcm3)
Relative density / %
1#
100 vol.%L
16.5383
14.3319
7.5
7.496
99.90
2#
75vol.%L-25vol.%A
16.3623
14.1326
7.5
7.338
97.84
3#
50vol.%L-50vol.%A
14.9614
12.8475
7.5
7.078
94.40
4#
25vol.%L-75vol.%A
14.6544
12.5700
7.5
7.031
93.70
5#
100 vol.%A
14.7108
12.6246
7.5
7.051
94 .00
Note: L is ligroin, A is alcohol, m1 is the mass of the sample in air, and m2 is the mass of the sample in water.
The characterization of X-ray diffraction patterns of the sintered powders and bodies were shown in Figs. 1 and 2, respectively. In Fig. 1 it can be seen that some Al remains. It suggested that a supersaturated solution of Al in Ni was obtained after milling. While Fig. 2 shows that Ni3Al was formed by spark plasma sintering (SPS) under 40 MPa for 5 min at 1000qC. During milling, Fe as a pollution was brought in, but it cannot be seen in the characterization of X-ray diffraction patterns because of very little.
and the alcohol content are shown in Figs. 4 and 5, respectively.
Fig. 2. X-ray diffraction patterns of bodies.
Fig. 1. X-ray diffraction patterns of the as-milled powders.
Fig. 3 shows the microstructures of samples 1#, 2#, 3#, 4#, and 5#. More pores exist in sample 2# than in sample 1#. So the density of sample 2# is lower than that of 1#. But the dispersed Al2O3 increased the strength and hardness of samples. However, the pores can be seen in the intergranular from Fig. 3(c) to Fig. 3(e). This results in a lower strength and hardness of samples 3#, 4#, and 5#. The relationship between the bending strength and the alcohol content, and the relationship between the hardness
Fig. 4 shows that the maximum bending strength is 2768 MPa with 75 vol.% ligroin mixed with 25 vol.% alcohol as PCA. It can be observed that the maximum hardness (HV) is more than 6 GPa with 75 vol.% ligroin mixed with 25 vol.% alcohol as PCA (Fig. 5). The oxygen of the sample with 100% ligroin is from milling, that of the other samples (sintered with 75 vol.% ligroin + 25 vol.% alcohol, 50 vol.% ligroin + 50 vol.% alcohol, 25 vol.% ligroin + 75 vol.% alcohol and pure alcohol as PCAs) are from milling and alcohol. The oxygen content of the sample with 100% ligroin is 0.20 wt.%, and that with 100% alcohol is 0.61 wt.%. The oxygen content increased with the increase in alcohol. Fig. 6 shows the composition of compacts with powder milled for 30 min by EDS. Fig. 6(a) shows the point scanning of second phase; Fig. 6(b) shows the area scanning of matrix. Obviously, the oxygen content
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RARE METALS, Vol. 27, No. 6, Dec 2008
increased in the second phase. In Ni-rich Ni-Al alloys, the selective oxidation of Al should be promoted, for the formation of Al2O3 instead of Ni oxides [11-15]. A few of Al2O3 dispersed during the intergranular (Fig. 7). The dispersion of
Al2O3 increases the strength and hardness of the sample and improves the ductility. But the density decreases and glomeration is formed with the increase in the oxygen content, so the strength and hardness decreases by degrees.
Fig. 3. SEM micrographs of the samples: (a) 1#; (b) 2#; (c) 3#; (d) 4#;(e) 5#.
Fig. 4. Relationship between bending strength and alcohol content.
Fig. 5. Relationship between hardness and alcohol content.
Fig. 6. Composition of compacts with powder milled for 30 min by EDS: (a) points scanning of second phase; (b) area scanning of matrix.
Lian J.Q. et al., Influence of process control agents on the performance of Ni3Al by mechanical alloying
651
Fig. 6. Bright field image (a) and selected area electron diffraction (SAD) pattern (b) of the sintered sample with milled powders.
4. Conclusions (1) A solution of Al in Ni was obtained after mechanical alloying of elemental powder with the normal composition of Ni-22.9at.%Al-0.5at.%B. (2) PCAs have influence on the mechanical properties of Ni3Al intermetallic compounds. The optimal proportion is 75 vol.% ligroin mixed with 25 vol.% alcohol. (3) The density of sintered samples is 97.84%, the bending strength is 2768 MPa, and the hardness (HV) is more than 6 GPa.
References [1] Krasnowski M., Antolak A., and Kulik T., Nanocrystalline Ni3Al alloy produced by mechanical alloying of nickel aluminides and hot-pressing consolidation, J. Alloys Compd., 2007, 434-435: 344. [2] Deevi S.C. and Sikka V.K., Nickel and iron aluminides: an overview on properties, processing, and application, Intermetallics, 1996, 4: 357. [3] Deevi S.C., Sikka V.K., and Liu C.T., Processing, properties, and application of nickel and iron aluminides, Prog. Mater. Sci., 1997, 42 (1-4): 177. [4] Paidar V., Pope D.P., and Vitek V., A theory of the anomalous yield behavior in L12 ordered alloys, Acta Metall., 1984, 32 (3): 435. [5] Enayati M.H., Sadeghian Z., Salehi M., and Saidi A., The effect of milling parameters on the synthesis of Ni3Al inter-metallic compound by mechanical alloying, Mater. Sci.
Eng. A, 2004, 375-377: 809. [6] Meng J., Jia C.C., and He Q., Fabrication of Ni3Al by hot pressing from element powders, Rare Met., 2007, 26 (3): 222. [7] George E.P., Liu C.T., Lin H., and Pope D.P., Environmental embrittlement and other causes of brittle grain boundary fracture in Ni3Al, Mater. Sci. Eng. A, 1995, 192/193: 277. [8] Suryanrayana C., Mechanical alloying and milling, Prog. Mater. Sci., 2001, 46 (1-2): 1. [9] Li L. and Lai M.O., Formation of new materials in the solid state by mechanical alloying, Mater. Des., 1995, 16 (1): 33. [10] Portnoy V.K., Blinov A.M., Tomilin I.A., Kuznetsov V.N., and Kulik T., Formation of nickel aluminides by mechanical alloying and thermo dynamics of interaction, J. Alloys Compd., 2002, 336: 196. [11] Cao G.J., Geng L., Zheng Z.Z., and Naka M., The oxidation of nanocrystalline Ni3Al fabricated by mechanical alloying and spark plasma sintering, Intermetallics, 2007, 15 (12): 1672. [12] Liu Z.Y., Gao W., Dahm Karl L., and Wang F.H., Oxidation behaviour of sputter-deposited Ni-Cr-Al micro-crystalline coating, Acta Mater., 1998, 46: 1691. [13] Chen G.F. and Lou H.Y., The effect of nanocrystallization on the oxide formation on Ni-11Cr-8Al alloy, Scripta Mater., 2000, 43 (2-3):119. [14] Zhou Y., Peng X., and Wang F., Oxidation of a novel electrodeposited Ni-Al nanocomposite file at 1050qC, Scripta Mater., 2004, 50: 1429. [15] Kima S.H., Ohb M.H., Kishidac K., Hiranoc T., and Weea D.M., Deposition of NiAl coating for improvement of oxidation resistance of cold-rolled Ni3Al foils, Intermetallics, 2005, 13: 129.