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Preparation of bulk Zr55Al10Ni5Cu30 metallic glass ring by centrifugal casting method
Intermetallics 10 (2002) 1197–1201 www.elsevier.com/locate/intermet
Preparation of bulk Zr55Al10Ni5Cu30 metallic glass ring by centrifugal casting method Q.S. Zhang*, D.Y. Guo, A.M. Wang, H.F. Zhang, B.Z. Ding, Z.Q. Hu Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, Shenyang, 110016, PR China Accepted 8 July 2002
Abstract In this work, a conventional centrifugal casting method was used to produce bulk amorphous Zr55Al10Ni5Cu30 rings. The 1-mm thick amorphous ring of the Zr55Al10Ni5Cu30 alloy was successfully prepared by this method. With increasing thickness of the rings, no crystalline phase can be seen on the transverse section near the outer surface of the rings. However, Zr2Cu and Zr2Ni particles precipitated from the amorphous matrix near the inner surface for the rings with thicknesses of 1.5 or 2 mm. For the 1 mm thick ring, the hardness showed no evident variation along the whole cross section. The hardness increased with increasing distance from the outer surface to the inner surface for the rings with thicknesses of 1.5 and 2 mm. Centrifugal casting is a useful process to produce amorphous alloy parts, such as amorphous tube and graded amorphous matrix composites. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: B. Glasses, metallic; C. Casting
1. Introduction In the last decade, a series of Zr-based alloys with a wide supercooled liquid region and large glass-forming ability (GFA) have been discovered [1,2]. Such alloys can be easily cast into bulk amorphous samples with dimensions of several centimeters by conventional casting processes at cooling rates as low as 1–100 K/s. Due to their high mechanical strength, Zr-based bulk amorphous alloys have promising application for structural materials. Many methods for the net-shape fabrication of bulk amorphous alloy have been developed, such as copper mold casting, die casting, and suction casting [3]. The golf clubs of Zr-based amorphous alloys have been successfully produced by a ‘‘mold-clamp casting method’’ [4]. Also, the large viscous flow in the supercooled liquid enables the fabrication of amorphous alloys in the form of small gears [5]. More recently, Zhang and Inoue [6]. had developed a rotating disk casting method to produce the Zr-based amorphous wire with a maximum diameter of 1.5 mm. Uriarte et al [7]. developed a centrifugal force casting device for the * Corresponding author. E-mail address: [email protected] (Q.S. Zhang).
preparation of net-shape bulk metallic glasses. Based on their ideas, we replaced the rotating disk by a copper mold and produced bulk amorphous rings using the conventional centrifugal casting method. This paper is intended to present this modified centrifugal casting method and investigate the formation of Zr-based bulk amorphous rings.
2. Experimental procedure A Zr55Al10Ni5Cu30 (at.%) alloy was used in the present study for its high glass forming ability. The ingot was prepared by arc melting a mixture of pure metals in argon atmosphere. Fig. 1 shows a schematic illustration of the centrifugal casting method used for the production of bulk amorphous rings. Bulk amorphous rings 25 mm in diameter and 20 mm high were prepared by injection casting of the melt into a copper mold with a rotating speed of 3000 rpm. The thickness of the ring was controlled by changing the weight of the master alloy. The amorphous structure of the inner and outer surface was identified by X-ray diffractometry. The cross section of the samples was electrolytically polished and etched at a voltage of 16–20 V DC in a solution of
0966-9795/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0966-9795(02)00158-9
1198
Q.S. Zhang et al. / Intermetallics 10 (2002) 1197–1201
70% perchloric acid in acetic acid for 3 min at room temperature and examined by optical microscopy. Vickers hardness was determined by indenting specimens at a load of 50 N, averaged over at least eight indents.
3. Results and discussion
Fig. 1. Schematic illustration of the centrifugal casting method.
Fig. 2. Photograph of the Zr55Al10Ni5Cu30 alloy rings with the thicknesses of 1 and 1.5 mm produced by the centrifugal casting method.
Fig. 2 shows the surface appearance of two as-cast Zr55Al10Ni5Cu30 rings with an outer diameter of 25, 1.5 and 1 mm in thicknesses, which exhibit a good luster. Fig. 3 shows the X-ray diffraction patterns taken from the outer surface and inner surface of the bulky Zr55Al10Ni5Cu30 rings with the thicknesses of 1 and 2 mm. The patterns from outer and inner surfaces consist only of halo peaks and no distinct crystalline peak is seen for the 1-mm thick ring. These results indicate that this ring is composed of a single amorphous phase. For the 2-mm thick ring, as shown in Fig. 3, the diffraction pattern of the outer surface is characterized by a halo peak. However, Zr2Cu and Zr2Ni phases were observed on the inner surface, which seemed to be formed by primary crystallization process from the melt. To confirm the formation of the amorphous ring, transverse sections of the rings were examined by optical microscopy. Fig. 4(a) shows an optical micrograph of the 1-mm thick Zr55Al10Ni5Cu30 ring. As shown in Fig. 4(a), no contrast corresponding to the precipitation of any crystallite was seen over the entire section. This indicated that this ring was composed of a single amorphous phase, in agreement with the results obtained by X-ray diffractometry. Fig. 4(b) shows an optical micrograph of
Fig. 3. X-ray diffraction profiles of the outer surface and inner surface for the rings with the thicknesses of 1 and 2 mm.
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Fig. 4. Optical photograph of the cross section for the rings with the thicknesses of (a) 1 mm, (b) 1.5 mm and (c) 2 mm.
the 1.5-mm thick Zr55Al10Ni5Cu30 ring. The quenchedin crystallites precipitated from the amorphous matrix in two stripe regions near the outer surface and inner surface respectively, and almost no crystallite was seen in the central region. Fig. 4(c) shows an optical micrograph of 2-mm thick Zr55Al10Ni5Cu30 ring. It is clearly seen that the transition from glassy to crystalline phase takes place with an increasing of distance from the outer surface to the inner surface. The formation of the nonequilibrium Zr2Cu and Zr2Ni phases near the inner surface indicates that the cooling rate in this region during solidification is not sufficient to vitrify the melt without crystallization. Hardness profiles as an increasing of distance from the outer surface to the inner surface for the as-cast rings are shown in Fig. 5. For the 1-mm thick ring, the hardness had no evident variation along the whole cross section.
However, great fluctuation of the hardness values has taken place along the cross section for the 1.5-mm thick ring owing to the precipitated phases in two stripe regions. The hardness value increased from the outer surface to the inner surface for the 2-mm thick ring, resulting from the precipitation of Zr2Cu and Zr2Ni phases [8]. In summary, bulk amorphous metallic rings can be prepared by conventional centrifugal casting method. Besides the high glass forming ability of the Zr55Al10Ni5Cu30 alloy, the success of forming the bulk amorphous ring with a thickness of 1 mm is mainly attributed to high cooling rate of the rotating copper mold to form the amorphous phase without crystallization. To simply analyze the solidification process, the cooling rates for the inner surfaces of the rings during solidification were estimated with a finite element method. A schematic model representation of the system of centrifugal casting
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Q.S. Zhang et al. / Intermetallics 10 (2002) 1197–1201
Fig. 5. Hardness profiles as a function of distance from the outer surface to the inner surface for the as-cast rings with different thickness (R/Ro is the nominal distance).
is shown in Fig. 6. The equation that describes the heat transfer of the solidification process is @ cp T 1 @ k @T 1@ @T ¼ kr þ ð1Þ @t r @ r @ r @r @r where t is time, is the density, k is the thermal conductivity, cp is the specific heat, and r and are the polar coordinates. The boundary condition at the interface between air and copper mold can be written as q ¼ h T Tf ð2Þ where Tf =25 C (Tf is environmental temperature), h is heat-transfer coefficient. The air gap is not taken into account at the interface between the melt and copper mold during solidification. The boundary condition at the interface between air and the melt is @T ¼0 ð3Þ @r
Fig. 6. Schematic representations of the system of centrifugal casting, D=150 mm and d=25 mm.
Taking cp=4 J/cm3 K1, k=0.1 W/cm s1 K1, =6.8 g/cm3, Tpour=1000 C and Tmold=25 C. A finite element method (ANSYS5.6) was used to solve Eq. (1). Fig. 7 shows the dependence of the cooling rate on the time for the inner surface of the rings after the melt was injected into the mold. For the 1-mm thick ring, upon casting of the melt, the initial cooling rate of was 30 K/s, and the maximum cooling rate was obtained at the first second immediately. From 1 to 4 s the cooling rate of
the inner surface was more than 80 K/s, which exceeds the critical cooling rate (about 10 K/s) for glass formation of the Zr55Al10Ni5Cu30 alloy. Since the melt has been cooled from 1000 C to room temperature during this period (from 0 to 4 s), the fully amorphous ring with a thickness of 1 mm was successfully obtained by centrifugal casting method without any crystallites. For the 1.5-mm thick ring, the initial cooling rate was about 6 K/s, and the maximum cooling rate of 80 K/s was
Q.S. Zhang et al. / Intermetallics 10 (2002) 1197–1201
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Fig. 7. The dependence of the cooling rate of the inner surface for the rings with the thicknesses of 1, 1.5, and 2 mm on time calculated with ANSYS 5.6.
obtained at the third second. During initial cooling stage, the cooling rate was about the same as the critical cooling rate and not enough to vitrify the melt, which seemed to be the main reason for the precipitation of crystalline phases (Fig. 4(b)). In addition, turbulent flow occurred during centrifugal casting probably resulted in the distribution of crystalline phases in two stripe regions. For the 2-mm thick ring, during the period of the first second after casting, the cooling rate at the inner surface had only reached 8 K/s, lower than the critical cooling rate. Moreover, it took about 4 s to increase the cooling rate at the inner surface from 0 to 40 K/s. Therefore, it is very difficult to form a fully amorphous ring for the sample with a thickness of 2 mm. Centrifugal casting is a process specifically adapted to the production of cylindrical parts. The casting solidifies from the outside and the inner surface feeds the necessary metal to the remainder of the casting as required. So some defects such as voids can be eliminated by centrifugal action. It is further expected that the amorphous rings of other multicomponent alloys with high GFA can be produced by the centrifugal casting method, which can also be used to produce graded amorphous matrix composites and amorphous tubes.
4. Summary A fully amorphous ring with a thickness of 1 mm of the Zr55Al10Ni5Cu30 alloy has been successfully
prepared by conventional centrifugal casting method. For the rings with a thickness of 1.5 and 2 mm, Zr2Cu and Zr2Ni phases precipitated from the amorphous matrix. Centrifugal casting method is an important process for producing amorphous alloy parts, such as amorphous tube and graded amorphous matrix composites.
Acknowledgements This work was supported by the National Key Project for Basic Research under Grant No. G2000067201 and National Development Project for High Technology under Grant No. 2001AA331010.
References [1] Zhang T, Inoue A, Masumoto T. Mater Trans JIM 1991;32:1005. [2] Peter A, Johnson WL. Appl Phys Lett 1993;63:2342. [3] Inoue A. Bulk amorphous alloy. Aedermansdorf, Switzerland: Trans Tech Publications; 1998. [4] Kakiuchi H, Inoue A, Onuki M, Takano Y, Yamaguchi T. Mater Trans 2001;42:678. [5] Inoue A, Kavamura Y, Shibata T, Sasamori K. Mater Trans JIM 1996;37:1337. [6] Zhang T, Inoue A. Mater Trans JIM 2000;41:1463. [7] Uriarte JL, Le Moulec A, Yavari AR. Mater Sci Forum 2001; 360–362:91. [8] Wang JG, Choi BW, Nieh TG, Liu CT. J Mater Res 2000; 15:798.
Preparation of bulk Zr55Al10Ni5Cu30 metallic glass ring by centrifugal casting method Q.S. Zhang*, D.Y. Guo, A.M. Wang, H.F. Zhang, B.Z. Ding, Z.Q. Hu Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, Shenyang, 110016, PR China Accepted 8 July 2002
Abstract In this work, a conventional centrifugal casting method was used to produce bulk amorphous Zr55Al10Ni5Cu30 rings. The 1-mm thick amorphous ring of the Zr55Al10Ni5Cu30 alloy was successfully prepared by this method. With increasing thickness of the rings, no crystalline phase can be seen on the transverse section near the outer surface of the rings. However, Zr2Cu and Zr2Ni particles precipitated from the amorphous matrix near the inner surface for the rings with thicknesses of 1.5 or 2 mm. For the 1 mm thick ring, the hardness showed no evident variation along the whole cross section. The hardness increased with increasing distance from the outer surface to the inner surface for the rings with thicknesses of 1.5 and 2 mm. Centrifugal casting is a useful process to produce amorphous alloy parts, such as amorphous tube and graded amorphous matrix composites. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: B. Glasses, metallic; C. Casting
1. Introduction In the last decade, a series of Zr-based alloys with a wide supercooled liquid region and large glass-forming ability (GFA) have been discovered [1,2]. Such alloys can be easily cast into bulk amorphous samples with dimensions of several centimeters by conventional casting processes at cooling rates as low as 1–100 K/s. Due to their high mechanical strength, Zr-based bulk amorphous alloys have promising application for structural materials. Many methods for the net-shape fabrication of bulk amorphous alloy have been developed, such as copper mold casting, die casting, and suction casting [3]. The golf clubs of Zr-based amorphous alloys have been successfully produced by a ‘‘mold-clamp casting method’’ [4]. Also, the large viscous flow in the supercooled liquid enables the fabrication of amorphous alloys in the form of small gears [5]. More recently, Zhang and Inoue [6]. had developed a rotating disk casting method to produce the Zr-based amorphous wire with a maximum diameter of 1.5 mm. Uriarte et al [7]. developed a centrifugal force casting device for the * Corresponding author. E-mail address: [email protected] (Q.S. Zhang).
preparation of net-shape bulk metallic glasses. Based on their ideas, we replaced the rotating disk by a copper mold and produced bulk amorphous rings using the conventional centrifugal casting method. This paper is intended to present this modified centrifugal casting method and investigate the formation of Zr-based bulk amorphous rings.
2. Experimental procedure A Zr55Al10Ni5Cu30 (at.%) alloy was used in the present study for its high glass forming ability. The ingot was prepared by arc melting a mixture of pure metals in argon atmosphere. Fig. 1 shows a schematic illustration of the centrifugal casting method used for the production of bulk amorphous rings. Bulk amorphous rings 25 mm in diameter and 20 mm high were prepared by injection casting of the melt into a copper mold with a rotating speed of 3000 rpm. The thickness of the ring was controlled by changing the weight of the master alloy. The amorphous structure of the inner and outer surface was identified by X-ray diffractometry. The cross section of the samples was electrolytically polished and etched at a voltage of 16–20 V DC in a solution of
0966-9795/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0966-9795(02)00158-9
1198
Q.S. Zhang et al. / Intermetallics 10 (2002) 1197–1201
70% perchloric acid in acetic acid for 3 min at room temperature and examined by optical microscopy. Vickers hardness was determined by indenting specimens at a load of 50 N, averaged over at least eight indents.
3. Results and discussion
Fig. 1. Schematic illustration of the centrifugal casting method.
Fig. 2. Photograph of the Zr55Al10Ni5Cu30 alloy rings with the thicknesses of 1 and 1.5 mm produced by the centrifugal casting method.
Fig. 2 shows the surface appearance of two as-cast Zr55Al10Ni5Cu30 rings with an outer diameter of 25, 1.5 and 1 mm in thicknesses, which exhibit a good luster. Fig. 3 shows the X-ray diffraction patterns taken from the outer surface and inner surface of the bulky Zr55Al10Ni5Cu30 rings with the thicknesses of 1 and 2 mm. The patterns from outer and inner surfaces consist only of halo peaks and no distinct crystalline peak is seen for the 1-mm thick ring. These results indicate that this ring is composed of a single amorphous phase. For the 2-mm thick ring, as shown in Fig. 3, the diffraction pattern of the outer surface is characterized by a halo peak. However, Zr2Cu and Zr2Ni phases were observed on the inner surface, which seemed to be formed by primary crystallization process from the melt. To confirm the formation of the amorphous ring, transverse sections of the rings were examined by optical microscopy. Fig. 4(a) shows an optical micrograph of the 1-mm thick Zr55Al10Ni5Cu30 ring. As shown in Fig. 4(a), no contrast corresponding to the precipitation of any crystallite was seen over the entire section. This indicated that this ring was composed of a single amorphous phase, in agreement with the results obtained by X-ray diffractometry. Fig. 4(b) shows an optical micrograph of
Fig. 3. X-ray diffraction profiles of the outer surface and inner surface for the rings with the thicknesses of 1 and 2 mm.
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Fig. 4. Optical photograph of the cross section for the rings with the thicknesses of (a) 1 mm, (b) 1.5 mm and (c) 2 mm.
the 1.5-mm thick Zr55Al10Ni5Cu30 ring. The quenchedin crystallites precipitated from the amorphous matrix in two stripe regions near the outer surface and inner surface respectively, and almost no crystallite was seen in the central region. Fig. 4(c) shows an optical micrograph of 2-mm thick Zr55Al10Ni5Cu30 ring. It is clearly seen that the transition from glassy to crystalline phase takes place with an increasing of distance from the outer surface to the inner surface. The formation of the nonequilibrium Zr2Cu and Zr2Ni phases near the inner surface indicates that the cooling rate in this region during solidification is not sufficient to vitrify the melt without crystallization. Hardness profiles as an increasing of distance from the outer surface to the inner surface for the as-cast rings are shown in Fig. 5. For the 1-mm thick ring, the hardness had no evident variation along the whole cross section.
However, great fluctuation of the hardness values has taken place along the cross section for the 1.5-mm thick ring owing to the precipitated phases in two stripe regions. The hardness value increased from the outer surface to the inner surface for the 2-mm thick ring, resulting from the precipitation of Zr2Cu and Zr2Ni phases [8]. In summary, bulk amorphous metallic rings can be prepared by conventional centrifugal casting method. Besides the high glass forming ability of the Zr55Al10Ni5Cu30 alloy, the success of forming the bulk amorphous ring with a thickness of 1 mm is mainly attributed to high cooling rate of the rotating copper mold to form the amorphous phase without crystallization. To simply analyze the solidification process, the cooling rates for the inner surfaces of the rings during solidification were estimated with a finite element method. A schematic model representation of the system of centrifugal casting
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Fig. 5. Hardness profiles as a function of distance from the outer surface to the inner surface for the as-cast rings with different thickness (R/Ro is the nominal distance).
is shown in Fig. 6. The equation that describes the heat transfer of the solidification process is @ cp T 1 @ k @T 1@ @T ¼ kr þ ð1Þ @t r @ r @ r @r @r where t is time, is the density, k is the thermal conductivity, cp is the specific heat, and r and are the polar coordinates. The boundary condition at the interface between air and copper mold can be written as q ¼ h T Tf ð2Þ where Tf =25 C (Tf is environmental temperature), h is heat-transfer coefficient. The air gap is not taken into account at the interface between the melt and copper mold during solidification. The boundary condition at the interface between air and the melt is @T ¼0 ð3Þ @r
Fig. 6. Schematic representations of the system of centrifugal casting, D=150 mm and d=25 mm.
Taking cp=4 J/cm3 K1, k=0.1 W/cm s1 K1, =6.8 g/cm3, Tpour=1000 C and Tmold=25 C. A finite element method (ANSYS5.6) was used to solve Eq. (1). Fig. 7 shows the dependence of the cooling rate on the time for the inner surface of the rings after the melt was injected into the mold. For the 1-mm thick ring, upon casting of the melt, the initial cooling rate of was 30 K/s, and the maximum cooling rate was obtained at the first second immediately. From 1 to 4 s the cooling rate of
the inner surface was more than 80 K/s, which exceeds the critical cooling rate (about 10 K/s) for glass formation of the Zr55Al10Ni5Cu30 alloy. Since the melt has been cooled from 1000 C to room temperature during this period (from 0 to 4 s), the fully amorphous ring with a thickness of 1 mm was successfully obtained by centrifugal casting method without any crystallites. For the 1.5-mm thick ring, the initial cooling rate was about 6 K/s, and the maximum cooling rate of 80 K/s was
Q.S. Zhang et al. / Intermetallics 10 (2002) 1197–1201
1201
Fig. 7. The dependence of the cooling rate of the inner surface for the rings with the thicknesses of 1, 1.5, and 2 mm on time calculated with ANSYS 5.6.
obtained at the third second. During initial cooling stage, the cooling rate was about the same as the critical cooling rate and not enough to vitrify the melt, which seemed to be the main reason for the precipitation of crystalline phases (Fig. 4(b)). In addition, turbulent flow occurred during centrifugal casting probably resulted in the distribution of crystalline phases in two stripe regions. For the 2-mm thick ring, during the period of the first second after casting, the cooling rate at the inner surface had only reached 8 K/s, lower than the critical cooling rate. Moreover, it took about 4 s to increase the cooling rate at the inner surface from 0 to 40 K/s. Therefore, it is very difficult to form a fully amorphous ring for the sample with a thickness of 2 mm. Centrifugal casting is a process specifically adapted to the production of cylindrical parts. The casting solidifies from the outside and the inner surface feeds the necessary metal to the remainder of the casting as required. So some defects such as voids can be eliminated by centrifugal action. It is further expected that the amorphous rings of other multicomponent alloys with high GFA can be produced by the centrifugal casting method, which can also be used to produce graded amorphous matrix composites and amorphous tubes.
4. Summary A fully amorphous ring with a thickness of 1 mm of the Zr55Al10Ni5Cu30 alloy has been successfully
prepared by conventional centrifugal casting method. For the rings with a thickness of 1.5 and 2 mm, Zr2Cu and Zr2Ni phases precipitated from the amorphous matrix. Centrifugal casting method is an important process for producing amorphous alloy parts, such as amorphous tube and graded amorphous matrix composites.
Acknowledgements This work was supported by the National Key Project for Basic Research under Grant No. G2000067201 and National Development Project for High Technology under Grant No. 2001AA331010.
References [1] Zhang T, Inoue A, Masumoto T. Mater Trans JIM 1991;32:1005. [2] Peter A, Johnson WL. Appl Phys Lett 1993;63:2342. [3] Inoue A. Bulk amorphous alloy. Aedermansdorf, Switzerland: Trans Tech Publications; 1998. [4] Kakiuchi H, Inoue A, Onuki M, Takano Y, Yamaguchi T. Mater Trans 2001;42:678. [5] Inoue A, Kavamura Y, Shibata T, Sasamori K. Mater Trans JIM 1996;37:1337. [6] Zhang T, Inoue A. Mater Trans JIM 2000;41:1463. [7] Uriarte JL, Le Moulec A, Yavari AR. Mater Sci Forum 2001; 360–362:91. [8] Wang JG, Choi BW, Nieh TG, Liu CT. J Mater Res 2000; 15:798.