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Manufacturing of High Tc Superconducting Ceramic Wires by Hot Extrusion
Manufacturing of High TcSuperconducting Ceramic Wires by Hot Extrusion Shyam K. Samanta (2); National Science Foundation / USA; I-Wei Chen, X. W u and T. Y. Tien; University of Michigan, Ann Arbor Received on February 2,1988
/ USA
Sumnery: In the current work high temnerature extrusion technique is develoned for making wires ofl-2-3 superconducting ceramic material. To overcome the difficulties in forming YBa Cu 0 ceramic, caused by its chemical activity, high yield strength and poor ductility, a high temoerature extrusion devi?e Aag been expressly designed, and a variety o f extrusion parameters such as temneratures, die angles and lubrications are being investigated. The feasibility o f using h o t extrusion for producing superconducting wire with high current density will be assessed based on these experiments. Keywords: Superconductor Material, High Tc, Wires, Hot Extrusion
INTRODUCTION
EXPEUIMENTAL PROCEDURE
The recent discovery of high TC superconducting ceramics by Bendroz and Muller in 1986 (1) has provoked some of the most exciting prospects for engineering development. Within the past year, the discovery of ternary metal oxide ceramic superconducting materials has led to a sudden burst of research activity all over the world. ROUtine observations of transition temperatures (Tc) above 90K (-29O'F) have been made in oxides of barium, lanthanum OK yttrium, and copper. Potential applications for these materials include high-field magnets for highspeed levitation trains, power transmission lines, and magnetic coils for storage of electricity, electrical machinery, fusion, high energy particle accelerators and magnetic resonance imaging for medical systems.
Billet Preparation
The most common techniques for manufacturing these 90Kt superconductors, YBa2Cu30, composites is to sintermicron sized particles of the individual metal oxide precursors, produced by free precipitation in aqueous solutions. The resulting ceramics are porous, brittle, non-homogeneous and have unacceptably low current density. Processinq of these ceramics into useful forms such as wires, r o d s , strips, etc. woula require lnnovatlve processing methods and interdisciplinary research in materials science, materials processing and manufacturing. Commonly taken approaches via deformation processing typically involve cold or warm extrusion or drawing of powders, followed by sintering. Recently, Murr et al. ( 2 ) have shown that powders and powder mixtures, including ceramic powders, can be consolidated into contiguous monoliths by dynamic compaction using explosively generated shock waves. We prefer to use hot deformation in processing, however, since it offers the advantage of a better control of density and texture. This concept was demonstrated in our earlier work (3). The main problems of forming this material are: they are extremely brittle, they have very high strength at room temperature (hardness 570 MPa in fully dense form), and they are chemically unstable. Pronounced textures have been found to develop during hot extrusion and hot pressing of YBa2Cu30, powders. The basal plane is preferentially oriented normal to the maximum compression axis in hot deformation. In particular, the extrusion texture of this ceramic material provides a favorable grain orientation such that the superconducting planes are parallel to the extrusion axis. The texture can be retained during subsequent annealing, which may effect a reversible tetragonal-to-orthorhombic transformation. This finding ( 3 ) suggests that judicious exploitation of such textures could result in drawn or extruded wires with favorable superconducting currentcarrying capability.
To pursue this approach at high extrusion rates, we have proposedtousehydrostaticextrusionwhichcaneliminate
die-wall friction and achieve better efficiency. Center cracking, often encountered in extrusion of hard materials ( 4 , 51, can also be avoided in this process by a careful design of die geometry ( 5 , 6 ) . Thus the present program was established to study the feasibility of extrusion of high T ceramics at high temperatures. To achieve this objecave, we have initially concentrated our efforts on finding a favorable processing condition, in terms of temperature, pressure, and geometry for extrusion. Since the condition is expected to be very similar for both conventional and hydrostatic extrusion processes, our preliminary experiments have been carried out using conventional extrusion method.
Annals of the CIRP Vol. 37/1/1988
YBa~Cu30, powderswerepreparedby solid-state reaction. The superconducting phase was identified by X-ray diffraction. Hot-pressing was performed using cylindrical dies made of WC in an environmental chamber of controlled atmosphere at 850°C and 100 MPa pressure. To avoid the direct contact of YBa2CujOx with WC die at high temperature, a thin wall copper tube with 3/8 in. outer diameter and .33 in. inner diameter was used to coat the powder. Usingthis system, w e h a v e h o t - p r e s s e d b i l l e t s to nearly theoretical density. It was found that the copper jacket not only protected the tooling (from chemically attacking by 1-2-3 material) but also acted as solid lubricant. Extrusion Tests We have developed a tooling arrangement, see Fig. 1, for extruding this high Tc superconductors at below looooc. After initial experimenting with Sic, TZM, and wc, we are now using WC containers, dies and punches almost exclusively in this system. Experiments were performed in Argon atmospheres, using conical dies (30', 4 5 O and 6 0 " semi-cone angles) with an extrusion ratio of 9 to 1. Fig. 2 shows a hot-pressed billet along with the extruded product. Provisions were made in the design for its later c o n v e r s i o n i n t o a h y d r o s t a t i c extrusion system. RESULTS Using the above mentioned extrusion system several hotpressed billets were extruded at rates up to 1 mm/min between 825OC and 895OC. The extruded rod, as shown in Fig. 2 , has a diameter of 3mm. The results, ram pressure, P, vs. extrusion speed, V are summarized in Figs. 3 and 4 . As expected, a smaller die angle lowers the force requirement for extrusion very significantly, so does a higher temperature. However, extrusion rates at 895OC were actually lower than those obtained at 875OC. We also noted a change of the stress exponent from approximately one to two at 5 0 0 MPa, at 85Ooc with 45' semi-cone angle dies, see Fig. 3. It is our hypothesis that a substantial contribution to the plasticity under the present extrusion conditions may be attributed to diffusional creep, and that a rapid grain growth at 895"C caused the slower extrusion rates observed. Long-range research is needed to gain fundamental understanding of the deformation mechanism of this material. Ftg. 5 shows the polished cross section of an extruded wire, extruded through a die of semi-cone angle 4 5 ' . Though, for 45' die we have observed central macrocrack, no such crack was observed in extrusions through the 30' die. We should emphasize at this point that in this preliminary work, the lengths of the extruded wire were very small in most cases (except for the one shown in Fig. 2 ) . Based on the above results, the condition of 85OoC, 300 MPa, and 30' semi-cone angle die was identified as a feasible and favorable extrusion condition. We are currently testing high pressure lubricants and their compatibility and sealing properties in preparation of this operation, which we hope to demonstrate very soon. From quality consideration, it may be necessary to develop hydrostatic extrusion method using streamlined dies. It has been shown ( 6 ) that extrusion through dies with streamlined shapes, for which the divergence of the stream lines is moderate and velocity field is continuous, should yield higher process efficiency and better
259
quality than the conventional dies. This work is in progress.
conical
and
square
CONCLUSIONS We have demonstrated that superconducting wires of 1-2-3 materials can be extruded at 85OoC under 300 MPa pressure. It is, however. necessary that for successful operations hot hydrostatic extrusion method has to be employed and intensive research in materials science, materials processing, design and manufacturing is needed for developing a processing technique of this difficult-to-form material. ACRNOWLEDGEMENT This work has been supported by a grant from the National Science Foundation, MSM-8718692. We greatly appreciate this support and the support of Dr. Ranga Komandur I . REFERENCES Huller, K. A., 1986, Possible Bednorz, J. G., High Tc Superconductivity in the Ba-La-Cu-0 System, Zeitschrift fur Physik B-Condensed Matter, 64:189-193. Murr, L. E., Hare, A. W., Eror, N. G., 1987, Introducing the Metal-Matrix High-Temperature Superconductor, Advanced Materials and Processes, 132:37-43. Wu, X., Keating, C. Y., Keating, Chen, I. W . , S., Johnson, P.. Tien, T. Y., Texture Development in YBa2CujOx by Hot Extrusion and Hot Pressing, American Ceramic Society, C:388-390. Pugh, H.Ll.D., Green, D., 1958, Progress Report on the Behavior of Materials under High Hydrostatic Pressure, MERL Plasticity Report NO. 147, NEL, East Kilbride, Glasgow.
Fig. 2. Hot-pressed billet along with the extruded product
.
H dro Inoue, N., Nishihara, M., (eds.), 1985 static Extrusion: Theory and ApDlicatiok,* vier Applied Science Publishers, New York. Samanta, S. K., 1970, Slip Line Field for Extrusion through Cosine-Shaped Dies, Journal of the Mechanics and Physics of Solids, 18:311-318.
.
=m=
I
-
contmllr
0.001
10
1000
100
RAM PRESSURe P (ma)
II -7
Fig. 3. Relationship between ram pressure vs. extrusion speed. 1
12
aisoc
..
'
D i e Angle = 30"
0.01 10
Fig. 1. Extrusion tooling: 1. Load cell: 2. Push rod: 3. Container: 4. Ram: 5.1-2-3 Ceramic billet: 6. Die: 7. Die Spacer: 8. Spacer: 9. Hollow Support for the die: 10. Base: 11. Quartz tube; 12. Furnace.
260
100
1000
RAM PRESSURE P
(MW Fig. 4.
Relationship between ram pressure vs. extrusion speed.
Fig. 5.
Cross sectional view of an extruded wire with macrocrack.
261
/ USA
Sumnery: In the current work high temnerature extrusion technique is develoned for making wires ofl-2-3 superconducting ceramic material. To overcome the difficulties in forming YBa Cu 0 ceramic, caused by its chemical activity, high yield strength and poor ductility, a high temoerature extrusion devi?e Aag been expressly designed, and a variety o f extrusion parameters such as temneratures, die angles and lubrications are being investigated. The feasibility o f using h o t extrusion for producing superconducting wire with high current density will be assessed based on these experiments. Keywords: Superconductor Material, High Tc, Wires, Hot Extrusion
INTRODUCTION
EXPEUIMENTAL PROCEDURE
The recent discovery of high TC superconducting ceramics by Bendroz and Muller in 1986 (1) has provoked some of the most exciting prospects for engineering development. Within the past year, the discovery of ternary metal oxide ceramic superconducting materials has led to a sudden burst of research activity all over the world. ROUtine observations of transition temperatures (Tc) above 90K (-29O'F) have been made in oxides of barium, lanthanum OK yttrium, and copper. Potential applications for these materials include high-field magnets for highspeed levitation trains, power transmission lines, and magnetic coils for storage of electricity, electrical machinery, fusion, high energy particle accelerators and magnetic resonance imaging for medical systems.
Billet Preparation
The most common techniques for manufacturing these 90Kt superconductors, YBa2Cu30, composites is to sintermicron sized particles of the individual metal oxide precursors, produced by free precipitation in aqueous solutions. The resulting ceramics are porous, brittle, non-homogeneous and have unacceptably low current density. Processinq of these ceramics into useful forms such as wires, r o d s , strips, etc. woula require lnnovatlve processing methods and interdisciplinary research in materials science, materials processing and manufacturing. Commonly taken approaches via deformation processing typically involve cold or warm extrusion or drawing of powders, followed by sintering. Recently, Murr et al. ( 2 ) have shown that powders and powder mixtures, including ceramic powders, can be consolidated into contiguous monoliths by dynamic compaction using explosively generated shock waves. We prefer to use hot deformation in processing, however, since it offers the advantage of a better control of density and texture. This concept was demonstrated in our earlier work (3). The main problems of forming this material are: they are extremely brittle, they have very high strength at room temperature (hardness 570 MPa in fully dense form), and they are chemically unstable. Pronounced textures have been found to develop during hot extrusion and hot pressing of YBa2Cu30, powders. The basal plane is preferentially oriented normal to the maximum compression axis in hot deformation. In particular, the extrusion texture of this ceramic material provides a favorable grain orientation such that the superconducting planes are parallel to the extrusion axis. The texture can be retained during subsequent annealing, which may effect a reversible tetragonal-to-orthorhombic transformation. This finding ( 3 ) suggests that judicious exploitation of such textures could result in drawn or extruded wires with favorable superconducting currentcarrying capability.
To pursue this approach at high extrusion rates, we have proposedtousehydrostaticextrusionwhichcaneliminate
die-wall friction and achieve better efficiency. Center cracking, often encountered in extrusion of hard materials ( 4 , 51, can also be avoided in this process by a careful design of die geometry ( 5 , 6 ) . Thus the present program was established to study the feasibility of extrusion of high T ceramics at high temperatures. To achieve this objecave, we have initially concentrated our efforts on finding a favorable processing condition, in terms of temperature, pressure, and geometry for extrusion. Since the condition is expected to be very similar for both conventional and hydrostatic extrusion processes, our preliminary experiments have been carried out using conventional extrusion method.
Annals of the CIRP Vol. 37/1/1988
YBa~Cu30, powderswerepreparedby solid-state reaction. The superconducting phase was identified by X-ray diffraction. Hot-pressing was performed using cylindrical dies made of WC in an environmental chamber of controlled atmosphere at 850°C and 100 MPa pressure. To avoid the direct contact of YBa2CujOx with WC die at high temperature, a thin wall copper tube with 3/8 in. outer diameter and .33 in. inner diameter was used to coat the powder. Usingthis system, w e h a v e h o t - p r e s s e d b i l l e t s to nearly theoretical density. It was found that the copper jacket not only protected the tooling (from chemically attacking by 1-2-3 material) but also acted as solid lubricant. Extrusion Tests We have developed a tooling arrangement, see Fig. 1, for extruding this high Tc superconductors at below looooc. After initial experimenting with Sic, TZM, and wc, we are now using WC containers, dies and punches almost exclusively in this system. Experiments were performed in Argon atmospheres, using conical dies (30', 4 5 O and 6 0 " semi-cone angles) with an extrusion ratio of 9 to 1. Fig. 2 shows a hot-pressed billet along with the extruded product. Provisions were made in the design for its later c o n v e r s i o n i n t o a h y d r o s t a t i c extrusion system. RESULTS Using the above mentioned extrusion system several hotpressed billets were extruded at rates up to 1 mm/min between 825OC and 895OC. The extruded rod, as shown in Fig. 2 , has a diameter of 3mm. The results, ram pressure, P, vs. extrusion speed, V are summarized in Figs. 3 and 4 . As expected, a smaller die angle lowers the force requirement for extrusion very significantly, so does a higher temperature. However, extrusion rates at 895OC were actually lower than those obtained at 875OC. We also noted a change of the stress exponent from approximately one to two at 5 0 0 MPa, at 85Ooc with 45' semi-cone angle dies, see Fig. 3. It is our hypothesis that a substantial contribution to the plasticity under the present extrusion conditions may be attributed to diffusional creep, and that a rapid grain growth at 895"C caused the slower extrusion rates observed. Long-range research is needed to gain fundamental understanding of the deformation mechanism of this material. Ftg. 5 shows the polished cross section of an extruded wire, extruded through a die of semi-cone angle 4 5 ' . Though, for 45' die we have observed central macrocrack, no such crack was observed in extrusions through the 30' die. We should emphasize at this point that in this preliminary work, the lengths of the extruded wire were very small in most cases (except for the one shown in Fig. 2 ) . Based on the above results, the condition of 85OoC, 300 MPa, and 30' semi-cone angle die was identified as a feasible and favorable extrusion condition. We are currently testing high pressure lubricants and their compatibility and sealing properties in preparation of this operation, which we hope to demonstrate very soon. From quality consideration, it may be necessary to develop hydrostatic extrusion method using streamlined dies. It has been shown ( 6 ) that extrusion through dies with streamlined shapes, for which the divergence of the stream lines is moderate and velocity field is continuous, should yield higher process efficiency and better
259
quality than the conventional dies. This work is in progress.
conical
and
square
CONCLUSIONS We have demonstrated that superconducting wires of 1-2-3 materials can be extruded at 85OoC under 300 MPa pressure. It is, however. necessary that for successful operations hot hydrostatic extrusion method has to be employed and intensive research in materials science, materials processing, design and manufacturing is needed for developing a processing technique of this difficult-to-form material. ACRNOWLEDGEMENT This work has been supported by a grant from the National Science Foundation, MSM-8718692. We greatly appreciate this support and the support of Dr. Ranga Komandur I . REFERENCES Huller, K. A., 1986, Possible Bednorz, J. G., High Tc Superconductivity in the Ba-La-Cu-0 System, Zeitschrift fur Physik B-Condensed Matter, 64:189-193. Murr, L. E., Hare, A. W., Eror, N. G., 1987, Introducing the Metal-Matrix High-Temperature Superconductor, Advanced Materials and Processes, 132:37-43. Wu, X., Keating, C. Y., Keating, Chen, I. W . , S., Johnson, P.. Tien, T. Y., Texture Development in YBa2CujOx by Hot Extrusion and Hot Pressing, American Ceramic Society, C:388-390. Pugh, H.Ll.D., Green, D., 1958, Progress Report on the Behavior of Materials under High Hydrostatic Pressure, MERL Plasticity Report NO. 147, NEL, East Kilbride, Glasgow.
Fig. 2. Hot-pressed billet along with the extruded product
.
H dro Inoue, N., Nishihara, M., (eds.), 1985 static Extrusion: Theory and ApDlicatiok,* vier Applied Science Publishers, New York. Samanta, S. K., 1970, Slip Line Field for Extrusion through Cosine-Shaped Dies, Journal of the Mechanics and Physics of Solids, 18:311-318.
.
=m=
I
-
contmllr
0.001
10
1000
100
RAM PRESSURe P (ma)
II -7
Fig. 3. Relationship between ram pressure vs. extrusion speed. 1
12
aisoc
..
'
D i e Angle = 30"
0.01 10
Fig. 1. Extrusion tooling: 1. Load cell: 2. Push rod: 3. Container: 4. Ram: 5.1-2-3 Ceramic billet: 6. Die: 7. Die Spacer: 8. Spacer: 9. Hollow Support for the die: 10. Base: 11. Quartz tube; 12. Furnace.
260
100
1000
RAM PRESSURE P
(MW Fig. 4.
Relationship between ram pressure vs. extrusion speed.
Fig. 5.
Cross sectional view of an extruded wire with macrocrack.
261