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Fabrication and characterization of Coriolis mass flowmeter made from Ti-based glassy tubes
Materials Science and Engineering A 407 (2005) 201–206
Fabrication and characterization of Coriolis mass flowmeter made from Ti-based glassy tubes Chaoli Ma a,∗ , Nobuyuki Nishiyama a , Akihisa Inoue b a
R&D Institute of Metals and Composites for Future Industries (RIMCOF), Kathira 2-1-1, Aoba-ku, Sendai, Miyagi, 980-8577, Japan b Institute for Materials Research, Tohoku University, Japan Received in revised form 29 June 2005; accepted 15 July 2005
Abstract Bulk metallic glasses (BMGs) have potential applications for both structural and functional components owing to their good mechanical properties. With the aim of demonstrating great engineering value of BMGs, we have developed a direct melt-forming technique based on suction casting for the production of glassy alloy tubes. We have examined the fabrication, structure, geometry, properties and sensor performance of the tubes. We have observed that the Coriolis mass flowmeters using the Ti-based glassy alloy sensor tube exhibit excellent measurement sensitivity compared to the conventional flowmeter manufactured using stainless steel (SUS316) tube. © 2005 Elsevier B.V. All rights reserved. Keywords: Metallic glass; Suction casting; Tube; Coriolis mass flowmeter; Sensitivity
1. Introduction Recent advances in materials science and technology have placed strong demand for the development of functional materials with stringent requirements for the precise control of geometry of various components. Based on this demand, a new material design that simultaneously satisfies some factors of processing, shape, structure, properties and performance has been employed in machine-parts fabrications [1]. Bulk metallic glasses (BMGs) are a new kind of advanced materials that started to draw attention at the end of 1980s [2,3]. Since then, considerable endeavor has been exercised to the development of new materials [4–6]. BMGs have high stability of supercooled liquid against crystallization and possess unique dense random-packed atomic configurations, which are the origin of their superior mechanical, chemical and magnetic properties [6]. The details of the atomic configurations may vary depending upon alloy compositions [6], enabling one to tailor the properties of BMGs [7]. BMGs ∗
Corresponding author. Tel.: +81 22 215 2840; fax: +81 22 215 2841. E-mail address: [email protected] (N. Nishiyama).
0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.07.037
also have technological interest because they can be easily synthesized by various liquid-to-solid cooling methods [7]. These direct fabrication processes from molten alloys into near-net or net shaped machine-parts can lead to great reductions of process cost, e.g., consumption of energy. Moreover, the resulting products thus fabricated may exhibit an interesting combination of essential properties, i.e., high strength, high flexibility, large elastic limit, high corrosion resistance and good viscous fluidity which serves as the prerequisite for the sensing elements in precision apparatuses. The simple fabrication process and beneficial combination of properties of BMGs lend us the possibility to use them as high performance materials in structural and functional applications. Therefore, we reckon that BMGs can be good materials for the investigation of the relationship among processing, shape, structure, properties and performance. We have recently developed a casting process to fabricate a glassy alloy tube and found that the glassy alloy tubes in Zr- and Ti-based systems exhibit excellent performance for a highly sensitive Coriolis mass flowmeter. In this paper we present the fabrication, shape, structure, properties and performance of Ti-based glassy alloy tubes.
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C. Ma et al. / Materials Science and Engineering A 407 (2005) 201–206
2. Background of metallic glass sensor tube 2.1. Sensor tube of Coriolis mass flowmeter (CMF) The CMF has been known as a unique flowmeter that can directly measure the mass of fluid [8]. In addition, the CMF originates from a novel principle and the measurement value is independent of environmental temperature as well as the structure of the measured fluid. This feature leads to significantly increasing requirement for applications of semiconductor industry, biomedical technology and medical science, etc. A schematic illustration of the CMF is shown in Fig. 1(a) [8]. The flowmeter consists of a sensor tube through which a fluid to be measured flows, and a vibration generator which gives a primary flexural vibration to the sensor tube. When the sensor tube is vibrated, as illustrated in Fig. 1(b), the mass of fluid at “A” strikes against the tube wall at “A”, resulting in the generation of a Corioli’s force (Fc ) upward. While the mass of fluid at “B” strikes against the tube wall at “B”, a downward force, Fc is generated. Such Corioli’s forces with opposite direction are proportional to the mass of the liquid, and they cause a sine-wave shaped elastic deformation of the sensor tube as shown in Fig. 1(c). By measuring the maximum elastic deformation δmax (amplitude of elastic deformation) of the sensor tube, one can calculate the Corioli’s force Fc and, consequently, determine the mass of the measured fluid. The measurement sensitivity of the CMF is
Fig. 1. (a) Plain view of a Coriolis mass flowmeter consisting the sensor tube and a vibration generator; (b) schematic graph showing the generation of Coriolis force (Fc ) when the sensor tube is vibrated; (c) the elastic deformation of sensor tube caused by Fc .
mainly determined by δmax of the sensor tube. The larger the δmax , the higher the measurement sensitivity. δmax can be expressed by: δmax =
4Fc l3 3πE(d24 − d14 )
(1)
where Fc , E, d1 , d2 and l are the Corioli’s force, the Young’s modulus, the interior and outer diameters and the length of the sensor tube, respectively. Equation (1) indicates that δmax is inversely proportional to the Young’s modulus. It means that higher sensitivity of flowmeter can be obtained by using the sensor tube with lower Young’s modulus. 2.2. Metallic glasses Metallic glasses are well known to possess lower Young’ modulus, large elastic elongation and higher strength compared to the conventional crystalline counterparts [6]. These features enable us to use metallic glasses as stressor strain-sensor material for various precision instruments. To obtain a better understanding of this, the tensile (or compressive) stress–strain plots for crystalline and glassy phase alloys are schematically shown in Fig. 2 [9]. Here, it is illustrated that the Young’s modulus of a crystalline alloy is much higher than that of a glassy alloy, and hence the elastic part of the stress–strain curves of a crystalline alloy lies above that of a glassy alloy. If the two types of alloys are loaded to the same tensile or compressive stress, σ i , a much larger elastic strain is to be expected in the glassy alloy, viz. εglass > εcrystal . This feature renders the glassy alloy to behave as an “amplifier” of elastic strain and hence satisfies one of the main requirements for a high-sensitivity sensor tube. Although the relationship between δmax and the strength of the tube material is not explicitly expressed by equation (1), the relatively high strength of a glassy alloy allows us to produce the sensor tube with smaller size compared to the conventional crystalline one and give large δmax , leading to high performance of CMF. Guided by this principle we then set out to search for an appropriate glassy alloy for this purpose.
Fig. 2. Schematic illustration of different load responses for crystalline and glassy phases with different Young’s moduli.
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Fig. 3. Young’s modulus–strength map of several metallic glasses and general industry crystalline materials [7].
Fig. 3 shows the Young’s modulus–strength map of several glassy and conventional crystalline alloys [6]. At present, the majority of the conventional sensor tubes are manufactured by stainless steel (SUS316). As can be seen in Fig. 3, the Young’s modulus of a typical stainless steel is about 200 GPa, which is significantly higher than those of most metallic glasses, including Fe-, Ni-, Ti-, Zr-, Pd- and Mgbased glasses etc. The Ti-, Zr- and Pd-based glasses exhibit nearly half the Young’s modulus as compared with that of the stainless steel. Especially the Ti-based glassy alloys do not need expensive elements and can be regarded as candidate materials to manufacture cost-effective, highly sensitive stress- or strain-sensor. In this study, a Ti-based glassy alloy with composition of Ti50 Cu25 Ni15 Zr5 Sn5 [11] was used to fabricate metallic glass tubes. In what follows, we will first present the production, structure and mechanical properties of the Ti-based glassy alloy tubes, followed by evaluation of the performance of CMF.
3. Fabrication of metallic glass tube The Ti-based glassy alloy tube was produced by a suction casting method [12]. Fig. 4(a and b) shows a schematic illustration of the suction casting equipment and its operating principle. The equipment consists of a carbon crucible, a mobile pipe-shape copper mold and a water-cooling system. The alloy ingot in the crucible is first induction heated to above the melting point and then the mobile copper mold is pushed down into the melt to certain depth. At the same time, a negative pressure is applied at the other end of the mobile copper mold and instantaneously the melt is sucked up into the copper mold. The melt in contact with the mold surface is then rapidly cooled down to below the melting point and starts to solidify. Meanwhile, the temperature of the melt at the center of the mold is still high and the viscosity is very
Fig. 4. Graphs schematically showing (a) the suction casting equipment and (b) the operation principle of the suction casting process.
low. The temperature gradient sustains continuous movement of the melt, leading to the formation of a tube. Here, if the melt in contact with the surface of mold is quickly quenched to below the glass temperature so as to avert crystallization, a glassy alloy tube can be produced. By using the suction casting method, Ti50 Cu25 Ni15 Zr5 Sn5 glassy alloy tubes with outer diameters of 6 mm and 2 mm were produced. The outer shapes of the two kinds of cast alloy tubes are shown in Fig. 5(a and b). The thickness of the cast alloy tube is affected by suction temperature, time, pressure, cooling rate and solidification mode, etc. In the present study, the suction temperature, time and pressure were 1447 K, 0.2 s and 0.1 MPa, respectively. Under such conditions, the thickness was about 0.8 mm for the 6 mm tube and about 0.2 mm for the 2 mm tube.
4. Structure and mechanical properties of the cast alloy tube The microstructure of the cast alloy tubes was examined by X-ray diffraction (XRD) and optical microscopy (OM). The thermal behavior of the cast structure was analyzed with a differential scanning calorimeter (DSC). Fig. 6 shows the XRD patterns of the cast alloy tubes. The corresponding DSC curves are given in Fig. 7. The 2 mm tube exhibits a typical amorphous halo in the XRD pattern and a distinct glass transition, indicating that the 2 mm tube is composed of a fully glassy structure. On the other hand, some diffraction peaks are observed in the XRD pattern of the 6 mm tube and no glass
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Fig. 5. Outer appearance of Ti-based glassy tubes with outer diameters of (a) 6 mm and (b) 2 mm produced by a suction casting method.
transition is present in the DSC curve. These results indicate that the 6 mm tube is mainly composed of a crystalline structure. In addition, voids and cavities were occasionally observed in the outer surface of the 6 mm tube, whereas no distinct contrast due to these defects was observed on the surface of the 2 mm tube. Fig. 8 shows an optical micrograph of the 6 mm tube, revealing such cast defects. These casting-
induced defects may play as a detrimental factor, which yields some adverse effects on the measurement precision and sensitivity of CMF. Mechanical properties of the Ti-based alloy tubes were measured by compression test in comparison with those of the SUS316 tube with an outer diameter of 6 mm, which has generally been used as the sensor tube for CMF. The gauge dimension of the samples used for the test was 6 mm in outer diameter and 15 mm in length. The yield strength was 800 MPa for the 6 mm Ti-based alloy tube and 230 MPa for the SUS316 tube. The wall thickness of 2 mm Ti-based glassy alloy tube is too small (about 0.2 mm in thickness) to measure its strength by the conventional compression test. The Vickers hardness of the 2 mm glassy alloy tube was 650 [DPN]. Considering that the hardness (Hv) and strength (σ) of glassy alloys follows usually an empirical relation of
Fig. 6. XRD patterns of Ti-based glassy tubes.
Fig. 7. DSC curves of Ti-based glassy tubes.
Fig. 8. Optical micrographs of Ti-based glassy tubes with an outer diameter of 6 mm.
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Hv = 3σ, the strength of the 2 mm glassy alloy tube is estimated to be about 217 kg/mm2 (∼2123 MPa). The Young’s moduli of all the alloy tubes were measured by an acoustic method. The resulting Young’s moduli were 85 GPa for the 6 mm Ti-based alloy tube, 82 GPa for the 2 mm Ti-based glassy alloy tube and 221 GPa for the 6 mm SUS316 alloy tube.
5. Performance of Coriolis mass flowmeter To evaluate the performance of the glassy alloy tube, the measurement precision and the sensitivity of a CMF using the glassy alloy tube were examined in comparison with those of the conventional SUS316 sensor tube. For descriptions hereafter, the CMFs using the Ti-based alloy tubes with 2 mm and 6 mm in outer diameter are referred to as CMF-T2 and CMF-T6, respectively, and the one using the 6 mm SUS316 tube is denoted by CMF-S6. 5.1. Measurement precision We selected an electromagnetic flowmeter (EF) having high measurement precision as a reference flowmeter. Fig. 9 shows a schematic illustration of how to evaluate the measurement precision of various CMFs. The EF was connected in series with the CMF. Distilled water was used as the test fluid. The flowrate (Q) of distilled water was simultaneously measured by the CMF and the EF. If the value of flowrate measured by the CMF exhibits good linear correlation with that measured by EF, the measurement precision of CMF is comparable to that of EF. The data so obtained are summarized in Fig. 10. The black and the hollow circles represent the flowrate (Q) of water measured by the CMF-T2 and CMF-T6,
Fig. 10. Illustration of the linear correlation of experimental data measured by CMFs using various sensor tubes.
respectively, while the hollow triangles represent that measured by the CMF-S6. The linear correlation coefficients of the data measured by each CMF are evaluated to be 0.9997 for CMF-T2, 0.995 for CMF-T6 and 0.997 for CMF-S6. It can be said that the measurement precision of these CMFs decreases in the order of CMF-T2 > CMF-S6 > CMF-T6. That is, the metallic glass tube (CMF-T2) possesses the highest performance among the sensor tubes examined in the present study. 5.2. Measurement sensitivity In Section 2, we mentioned that the amplitude of elastic deformation (δmax ) of the sensor tube is a dominant factor for the measurement sensitivity of a CMF. That is, the larger the δmax , the higher the measurement sensitivity. To obtain a better quantitative understanding, a simple calculation is given here. The material and the geometric parameters of the sensor tubes are summarized in Table 1. Based on equation (1), the elastic deformation ratios (EDRcalc : δmax-T(2 or 6) /δmax-SUS316 ) of the Ti-based alloy tubes (2 mm and 6 mm) to the SUS316 tube (6 mm) are calculated and listed in this table. It is evident that the value of δmax-T2 /δmax-SUS316 is as high as 33, indicating that the sensitivity of CMF could be greatly improved by the use of the Ti-based glassy alloy sensor tube. The experimental sensitivity ratios (SRexpt ) of the CMFs using the Ti-based glassy tubes (2 mm and 6 mm) to the SUS316 tube (6 mm) are also listed in the table. The sensitivity of the 6 mm Ti-
Table 1 Materials and geometric parameters of various sensor tubes
Fig. 9. Apparatus for studying the measurement precision of various Coriolis mass flowmeters.
Sensor tube
E (GPa)
d1 (mm)
d2 (mm)
l (mm)
SUS316 T6 (crystal) T2 (BMG)
221 85 82
4.4 4.4 1.6
6.0 6.0 2.0
140 140 70
EDRcalc – ∼2.6 ∼33
SRexpt 1.9 28.5
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based tube with a crystalline structure is about two times higher than that of the SUS316 tube. It is noted that the 2 mm Ti-based glassy alloy tube exhibits excellent sensitivity, about 28.5 times higher than that of the stainless steel tube. 6. Summary With the aim of opening up a new application area for metallic glass materials, the Coriolis mass flowmeter characteristics of Ti50 Cu25 Ni15 Zr5 Sn5 glassy alloy tubes were examined as well as microstructure and mechanical properties of the glassy alloy tubes. The Ti-based glassy alloy tube with an outer diameter of 2 mm was produced by a suction casting method. Compared with the conventional process to produce stainless steel tubes, the suction casting process is much simpler and can substantially reduce the process cost. The glassy alloy tube exhibits good mechanical properties, i.e., high strength of 2123 MPa and low Young’s modulus of 82 GPa. In addition, the Coriolis mass flowmeter using this glassy alloy tube exhibited significant improvement of measurement precision and measurement sensitivity as compared with that using the conventional stainless steel (SUS316) tube. The measurement sensitivity of the Coriolis mass flowmeter is 28.5 times higher than that of the conventional one, demonstrating that the Ti-based glassy
alloy tube has great potential as high performance sensor material.
Acknowledgement This research was supported by a grant from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.
References [1] G.B. Olson, Science 277 (1997) 1237–1242. [2] A. Inoue, K. Ohtera, K. Kita, T. Masumoto, Jpn. J. Appl. Phys. 27 (1988) L2248–L2251. [3] A. Inoue, T. Zhang, T. Mosumoto, Mater. Trans., JIM 30 (1989) 965–972. [4] A. Inoue, Mater. Trans. JIM 36 (1995) 866–875. [5] W.L. Johnson, MRS Bull. 24 (1999) 42–56. [6] A. Inoue, Acta Mater. 28 (2000) 279–306. [7] Y. Yokoyama, K. Yamono, K. Fukaura, H. Sunada, A. Inoue, Mater. Trans., JIM 40 (1999) 1018–1065. [8] K. Ohnishi, Y. Tomikawa, Coriolis Flowmeter, United States Patent, US 6,684,716 B2, Feb. 3, 2004. [9] C.L. Ma, A. Inoue, Mater. Trans. 44 (2003) 188–196. [11] T. Zhang, A. Inoue, Mater. Trans., JIM 39 (1998) 1001–1006. [12] A. Inoue, E. Makabe, Production of Glassy metal and Apparatus, Japan Patent, P2000-271730A, Oct. 3, 2000.
Fabrication and characterization of Coriolis mass flowmeter made from Ti-based glassy tubes Chaoli Ma a,∗ , Nobuyuki Nishiyama a , Akihisa Inoue b a
R&D Institute of Metals and Composites for Future Industries (RIMCOF), Kathira 2-1-1, Aoba-ku, Sendai, Miyagi, 980-8577, Japan b Institute for Materials Research, Tohoku University, Japan Received in revised form 29 June 2005; accepted 15 July 2005
Abstract Bulk metallic glasses (BMGs) have potential applications for both structural and functional components owing to their good mechanical properties. With the aim of demonstrating great engineering value of BMGs, we have developed a direct melt-forming technique based on suction casting for the production of glassy alloy tubes. We have examined the fabrication, structure, geometry, properties and sensor performance of the tubes. We have observed that the Coriolis mass flowmeters using the Ti-based glassy alloy sensor tube exhibit excellent measurement sensitivity compared to the conventional flowmeter manufactured using stainless steel (SUS316) tube. © 2005 Elsevier B.V. All rights reserved. Keywords: Metallic glass; Suction casting; Tube; Coriolis mass flowmeter; Sensitivity
1. Introduction Recent advances in materials science and technology have placed strong demand for the development of functional materials with stringent requirements for the precise control of geometry of various components. Based on this demand, a new material design that simultaneously satisfies some factors of processing, shape, structure, properties and performance has been employed in machine-parts fabrications [1]. Bulk metallic glasses (BMGs) are a new kind of advanced materials that started to draw attention at the end of 1980s [2,3]. Since then, considerable endeavor has been exercised to the development of new materials [4–6]. BMGs have high stability of supercooled liquid against crystallization and possess unique dense random-packed atomic configurations, which are the origin of their superior mechanical, chemical and magnetic properties [6]. The details of the atomic configurations may vary depending upon alloy compositions [6], enabling one to tailor the properties of BMGs [7]. BMGs ∗
Corresponding author. Tel.: +81 22 215 2840; fax: +81 22 215 2841. E-mail address: [email protected] (N. Nishiyama).
0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.07.037
also have technological interest because they can be easily synthesized by various liquid-to-solid cooling methods [7]. These direct fabrication processes from molten alloys into near-net or net shaped machine-parts can lead to great reductions of process cost, e.g., consumption of energy. Moreover, the resulting products thus fabricated may exhibit an interesting combination of essential properties, i.e., high strength, high flexibility, large elastic limit, high corrosion resistance and good viscous fluidity which serves as the prerequisite for the sensing elements in precision apparatuses. The simple fabrication process and beneficial combination of properties of BMGs lend us the possibility to use them as high performance materials in structural and functional applications. Therefore, we reckon that BMGs can be good materials for the investigation of the relationship among processing, shape, structure, properties and performance. We have recently developed a casting process to fabricate a glassy alloy tube and found that the glassy alloy tubes in Zr- and Ti-based systems exhibit excellent performance for a highly sensitive Coriolis mass flowmeter. In this paper we present the fabrication, shape, structure, properties and performance of Ti-based glassy alloy tubes.
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2. Background of metallic glass sensor tube 2.1. Sensor tube of Coriolis mass flowmeter (CMF) The CMF has been known as a unique flowmeter that can directly measure the mass of fluid [8]. In addition, the CMF originates from a novel principle and the measurement value is independent of environmental temperature as well as the structure of the measured fluid. This feature leads to significantly increasing requirement for applications of semiconductor industry, biomedical technology and medical science, etc. A schematic illustration of the CMF is shown in Fig. 1(a) [8]. The flowmeter consists of a sensor tube through which a fluid to be measured flows, and a vibration generator which gives a primary flexural vibration to the sensor tube. When the sensor tube is vibrated, as illustrated in Fig. 1(b), the mass of fluid at “A” strikes against the tube wall at “A”, resulting in the generation of a Corioli’s force (Fc ) upward. While the mass of fluid at “B” strikes against the tube wall at “B”, a downward force, Fc is generated. Such Corioli’s forces with opposite direction are proportional to the mass of the liquid, and they cause a sine-wave shaped elastic deformation of the sensor tube as shown in Fig. 1(c). By measuring the maximum elastic deformation δmax (amplitude of elastic deformation) of the sensor tube, one can calculate the Corioli’s force Fc and, consequently, determine the mass of the measured fluid. The measurement sensitivity of the CMF is
Fig. 1. (a) Plain view of a Coriolis mass flowmeter consisting the sensor tube and a vibration generator; (b) schematic graph showing the generation of Coriolis force (Fc ) when the sensor tube is vibrated; (c) the elastic deformation of sensor tube caused by Fc .
mainly determined by δmax of the sensor tube. The larger the δmax , the higher the measurement sensitivity. δmax can be expressed by: δmax =
4Fc l3 3πE(d24 − d14 )
(1)
where Fc , E, d1 , d2 and l are the Corioli’s force, the Young’s modulus, the interior and outer diameters and the length of the sensor tube, respectively. Equation (1) indicates that δmax is inversely proportional to the Young’s modulus. It means that higher sensitivity of flowmeter can be obtained by using the sensor tube with lower Young’s modulus. 2.2. Metallic glasses Metallic glasses are well known to possess lower Young’ modulus, large elastic elongation and higher strength compared to the conventional crystalline counterparts [6]. These features enable us to use metallic glasses as stressor strain-sensor material for various precision instruments. To obtain a better understanding of this, the tensile (or compressive) stress–strain plots for crystalline and glassy phase alloys are schematically shown in Fig. 2 [9]. Here, it is illustrated that the Young’s modulus of a crystalline alloy is much higher than that of a glassy alloy, and hence the elastic part of the stress–strain curves of a crystalline alloy lies above that of a glassy alloy. If the two types of alloys are loaded to the same tensile or compressive stress, σ i , a much larger elastic strain is to be expected in the glassy alloy, viz. εglass > εcrystal . This feature renders the glassy alloy to behave as an “amplifier” of elastic strain and hence satisfies one of the main requirements for a high-sensitivity sensor tube. Although the relationship between δmax and the strength of the tube material is not explicitly expressed by equation (1), the relatively high strength of a glassy alloy allows us to produce the sensor tube with smaller size compared to the conventional crystalline one and give large δmax , leading to high performance of CMF. Guided by this principle we then set out to search for an appropriate glassy alloy for this purpose.
Fig. 2. Schematic illustration of different load responses for crystalline and glassy phases with different Young’s moduli.
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Fig. 3. Young’s modulus–strength map of several metallic glasses and general industry crystalline materials [7].
Fig. 3 shows the Young’s modulus–strength map of several glassy and conventional crystalline alloys [6]. At present, the majority of the conventional sensor tubes are manufactured by stainless steel (SUS316). As can be seen in Fig. 3, the Young’s modulus of a typical stainless steel is about 200 GPa, which is significantly higher than those of most metallic glasses, including Fe-, Ni-, Ti-, Zr-, Pd- and Mgbased glasses etc. The Ti-, Zr- and Pd-based glasses exhibit nearly half the Young’s modulus as compared with that of the stainless steel. Especially the Ti-based glassy alloys do not need expensive elements and can be regarded as candidate materials to manufacture cost-effective, highly sensitive stress- or strain-sensor. In this study, a Ti-based glassy alloy with composition of Ti50 Cu25 Ni15 Zr5 Sn5 [11] was used to fabricate metallic glass tubes. In what follows, we will first present the production, structure and mechanical properties of the Ti-based glassy alloy tubes, followed by evaluation of the performance of CMF.
3. Fabrication of metallic glass tube The Ti-based glassy alloy tube was produced by a suction casting method [12]. Fig. 4(a and b) shows a schematic illustration of the suction casting equipment and its operating principle. The equipment consists of a carbon crucible, a mobile pipe-shape copper mold and a water-cooling system. The alloy ingot in the crucible is first induction heated to above the melting point and then the mobile copper mold is pushed down into the melt to certain depth. At the same time, a negative pressure is applied at the other end of the mobile copper mold and instantaneously the melt is sucked up into the copper mold. The melt in contact with the mold surface is then rapidly cooled down to below the melting point and starts to solidify. Meanwhile, the temperature of the melt at the center of the mold is still high and the viscosity is very
Fig. 4. Graphs schematically showing (a) the suction casting equipment and (b) the operation principle of the suction casting process.
low. The temperature gradient sustains continuous movement of the melt, leading to the formation of a tube. Here, if the melt in contact with the surface of mold is quickly quenched to below the glass temperature so as to avert crystallization, a glassy alloy tube can be produced. By using the suction casting method, Ti50 Cu25 Ni15 Zr5 Sn5 glassy alloy tubes with outer diameters of 6 mm and 2 mm were produced. The outer shapes of the two kinds of cast alloy tubes are shown in Fig. 5(a and b). The thickness of the cast alloy tube is affected by suction temperature, time, pressure, cooling rate and solidification mode, etc. In the present study, the suction temperature, time and pressure were 1447 K, 0.2 s and 0.1 MPa, respectively. Under such conditions, the thickness was about 0.8 mm for the 6 mm tube and about 0.2 mm for the 2 mm tube.
4. Structure and mechanical properties of the cast alloy tube The microstructure of the cast alloy tubes was examined by X-ray diffraction (XRD) and optical microscopy (OM). The thermal behavior of the cast structure was analyzed with a differential scanning calorimeter (DSC). Fig. 6 shows the XRD patterns of the cast alloy tubes. The corresponding DSC curves are given in Fig. 7. The 2 mm tube exhibits a typical amorphous halo in the XRD pattern and a distinct glass transition, indicating that the 2 mm tube is composed of a fully glassy structure. On the other hand, some diffraction peaks are observed in the XRD pattern of the 6 mm tube and no glass
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Fig. 5. Outer appearance of Ti-based glassy tubes with outer diameters of (a) 6 mm and (b) 2 mm produced by a suction casting method.
transition is present in the DSC curve. These results indicate that the 6 mm tube is mainly composed of a crystalline structure. In addition, voids and cavities were occasionally observed in the outer surface of the 6 mm tube, whereas no distinct contrast due to these defects was observed on the surface of the 2 mm tube. Fig. 8 shows an optical micrograph of the 6 mm tube, revealing such cast defects. These casting-
induced defects may play as a detrimental factor, which yields some adverse effects on the measurement precision and sensitivity of CMF. Mechanical properties of the Ti-based alloy tubes were measured by compression test in comparison with those of the SUS316 tube with an outer diameter of 6 mm, which has generally been used as the sensor tube for CMF. The gauge dimension of the samples used for the test was 6 mm in outer diameter and 15 mm in length. The yield strength was 800 MPa for the 6 mm Ti-based alloy tube and 230 MPa for the SUS316 tube. The wall thickness of 2 mm Ti-based glassy alloy tube is too small (about 0.2 mm in thickness) to measure its strength by the conventional compression test. The Vickers hardness of the 2 mm glassy alloy tube was 650 [DPN]. Considering that the hardness (Hv) and strength (σ) of glassy alloys follows usually an empirical relation of
Fig. 6. XRD patterns of Ti-based glassy tubes.
Fig. 7. DSC curves of Ti-based glassy tubes.
Fig. 8. Optical micrographs of Ti-based glassy tubes with an outer diameter of 6 mm.
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Hv = 3σ, the strength of the 2 mm glassy alloy tube is estimated to be about 217 kg/mm2 (∼2123 MPa). The Young’s moduli of all the alloy tubes were measured by an acoustic method. The resulting Young’s moduli were 85 GPa for the 6 mm Ti-based alloy tube, 82 GPa for the 2 mm Ti-based glassy alloy tube and 221 GPa for the 6 mm SUS316 alloy tube.
5. Performance of Coriolis mass flowmeter To evaluate the performance of the glassy alloy tube, the measurement precision and the sensitivity of a CMF using the glassy alloy tube were examined in comparison with those of the conventional SUS316 sensor tube. For descriptions hereafter, the CMFs using the Ti-based alloy tubes with 2 mm and 6 mm in outer diameter are referred to as CMF-T2 and CMF-T6, respectively, and the one using the 6 mm SUS316 tube is denoted by CMF-S6. 5.1. Measurement precision We selected an electromagnetic flowmeter (EF) having high measurement precision as a reference flowmeter. Fig. 9 shows a schematic illustration of how to evaluate the measurement precision of various CMFs. The EF was connected in series with the CMF. Distilled water was used as the test fluid. The flowrate (Q) of distilled water was simultaneously measured by the CMF and the EF. If the value of flowrate measured by the CMF exhibits good linear correlation with that measured by EF, the measurement precision of CMF is comparable to that of EF. The data so obtained are summarized in Fig. 10. The black and the hollow circles represent the flowrate (Q) of water measured by the CMF-T2 and CMF-T6,
Fig. 10. Illustration of the linear correlation of experimental data measured by CMFs using various sensor tubes.
respectively, while the hollow triangles represent that measured by the CMF-S6. The linear correlation coefficients of the data measured by each CMF are evaluated to be 0.9997 for CMF-T2, 0.995 for CMF-T6 and 0.997 for CMF-S6. It can be said that the measurement precision of these CMFs decreases in the order of CMF-T2 > CMF-S6 > CMF-T6. That is, the metallic glass tube (CMF-T2) possesses the highest performance among the sensor tubes examined in the present study. 5.2. Measurement sensitivity In Section 2, we mentioned that the amplitude of elastic deformation (δmax ) of the sensor tube is a dominant factor for the measurement sensitivity of a CMF. That is, the larger the δmax , the higher the measurement sensitivity. To obtain a better quantitative understanding, a simple calculation is given here. The material and the geometric parameters of the sensor tubes are summarized in Table 1. Based on equation (1), the elastic deformation ratios (EDRcalc : δmax-T(2 or 6) /δmax-SUS316 ) of the Ti-based alloy tubes (2 mm and 6 mm) to the SUS316 tube (6 mm) are calculated and listed in this table. It is evident that the value of δmax-T2 /δmax-SUS316 is as high as 33, indicating that the sensitivity of CMF could be greatly improved by the use of the Ti-based glassy alloy sensor tube. The experimental sensitivity ratios (SRexpt ) of the CMFs using the Ti-based glassy tubes (2 mm and 6 mm) to the SUS316 tube (6 mm) are also listed in the table. The sensitivity of the 6 mm Ti-
Table 1 Materials and geometric parameters of various sensor tubes
Fig. 9. Apparatus for studying the measurement precision of various Coriolis mass flowmeters.
Sensor tube
E (GPa)
d1 (mm)
d2 (mm)
l (mm)
SUS316 T6 (crystal) T2 (BMG)
221 85 82
4.4 4.4 1.6
6.0 6.0 2.0
140 140 70
EDRcalc – ∼2.6 ∼33
SRexpt 1.9 28.5
206
C. Ma et al. / Materials Science and Engineering A 407 (2005) 201–206
based tube with a crystalline structure is about two times higher than that of the SUS316 tube. It is noted that the 2 mm Ti-based glassy alloy tube exhibits excellent sensitivity, about 28.5 times higher than that of the stainless steel tube. 6. Summary With the aim of opening up a new application area for metallic glass materials, the Coriolis mass flowmeter characteristics of Ti50 Cu25 Ni15 Zr5 Sn5 glassy alloy tubes were examined as well as microstructure and mechanical properties of the glassy alloy tubes. The Ti-based glassy alloy tube with an outer diameter of 2 mm was produced by a suction casting method. Compared with the conventional process to produce stainless steel tubes, the suction casting process is much simpler and can substantially reduce the process cost. The glassy alloy tube exhibits good mechanical properties, i.e., high strength of 2123 MPa and low Young’s modulus of 82 GPa. In addition, the Coriolis mass flowmeter using this glassy alloy tube exhibited significant improvement of measurement precision and measurement sensitivity as compared with that using the conventional stainless steel (SUS316) tube. The measurement sensitivity of the Coriolis mass flowmeter is 28.5 times higher than that of the conventional one, demonstrating that the Ti-based glassy
alloy tube has great potential as high performance sensor material.
Acknowledgement This research was supported by a grant from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.
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