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Fabrication and tensile properties of rapidly solidified Cu-10wt.%Ni alloy
Materials Science and Engineering, A158 (1992) 7-10
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Fabrication and tensile properties of rapidly solidified Cu- 10wt.%Ni
alloy D a n i e l Baril*, R o c h A n g e r s a n d J o c e l y n B a r i l t
Department of Mining and Metallurgy, Laval University, Ste-Foy, Q ue. G1K 7P4 (Canada) (Received July 22, 1991; in revised form March 23, 1992)
Abstract Cu-10wt.%Ni ribbons were produced by melt spinning and cut into small particles with a blade cutter mill. The powders were then hot consolidated to full density by hot pressing followed by hot extrusion. Tensile properties of the resulting pieces were measured. Cu-10wt.% Ni cast ingots were also hot extruded and mechanically tested to compare with the rapidly solidified alloy and to evaluate the possible benefits brought by the rapid solidification process.
I. Introduction Cu-Ni alloys are especially suitable in marine environment [ 1, 2] because of their good corrosion resistance to sea water, their good erosion corrosion resistance, their antifouling capability and their relatively high strength. In this work, the evolution of the microstructure of a Cu-10Ni alloy (where the composition is in weight per cent) made from rapidly solidified powders through a two-step hot-consolidation process will be studied. The mechanical properties of this alloy will also be compared with those of an alloy produced by conventional casting. High cooling rates lead to a better chemical homogeneity, a higher solubility of alloying elements and a finer microstructure. Hence, better mechanical properties and better corrosion resistance should be expected in metallic alloys processed by rapid solidification [3-8].
2. Experimental procedure Rapidly solidified Cu-10Ni ribbons were produced by melt spinning under argon with a copper wheel. The *Present address: Alcan International, 1955 Mellon Boulevard, Jonquiere, Que. G7S 4K8, Canada. tPresent address: Les Aciers Amsco Inc., 620 Laval Street, Joliette, Que. J6E 6H5, Canada. 0921-5093/92/$5.00
tangential velocity of the wheel was between 12 and 13 m s -1. The melting of the alloy was done in a graphite crucible fixed into a VycorTM tube and the ejection nozzle was made of boron nitride with a 0.75 mm orifice. The ejection overpressure was 20 kPa. Under these conditions, it was possible to produce long uniform ribbons about 80 /~m thick (standard deviation of 10 ~m) and 1-3 mm wide. The solidification rate of these ribbons should be higher than 105 K s[9]. The pulverization of the ribbons into powders was done in a blade cutter mill [10] under a protective argon atmosphere. The resulting powders were separated by sieving into two size fractions: a 50-160/~m fraction and a 160-355 /zm fraction. These two different fractions were selected to investigate the influence of particle size on the mechanical properties of the final product. The powders were then hot consolidated. They were first hot pressed in a cylindrical graphite die at 700 °C at a 45 MPa uniaxial pressure for 45 min under a protective atmosphere of argon. Hot-pressed billets were 3.0-3.5 cm long and 3.2 cm in diameter and contained less than 1% porosity. Afterward, the billets were preheated at 800 °C for 20 rain and were hot extruded into rods 1.27 cm in diameter. The extrusion die diameter was 3.81 cm and the extrusion ratio was 9 to 1. Cu-10Ni alloy billets were also cast and hot extruded under the same conditions as those used with the hot-pressed billets for comparison purposes. Tensile standard [11] specimens (0.635 cm round) were machined from the extruded rods for mechanical © 1992 - Elsevier Sequoia. All rights reserved
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D. Baril et al.
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Rapidly solidified Cu-lOwt. %Ni
Fig. 1. Microstructureof melt-spun ribbons.
Fig. 3. Microstructureof a hot-pressed billets.
Fig. 2. Microstructureof powder (polishedsection).
Fig. 4. Microstructureof rods extruded from cast billets.
properties measurements. The tensile tests used a cross-head speed of 0.25 cm min- 1.
be explained by the heterogeneous nature of the plastic deformation that occurred during milling of the ribbons. It is possible to distinguish original particles in the microstructure of the hot-pressed billets (dark thick interfaces in Fig. 3). Figure 4 illustrates the microstructure of rods extruded from cast billets while Fig. 5 shows the microstructure of rods extruded from hot-pressed billets. In the latter rods, it can be observed (dark thick interfaces) that the deformation produced by hot extrusion brings about considerable elongation of the original powder particles along the extrusion axis. Anisotropic properties should be expected because of this fibrous structure. Both types of rod exhibit some recrystallization of the alloy. Table 1 reports average measured tensile properties. This table shows that the yield strength of the rapidly solidified alloy improved by about 30% over the conventionally cast alloy. The ultimate tensile strength is about the same for both types of alloy but elongation is
3. Results
The microstructure of the melt-spun ribbons is shown in Fig. 1. As expected, the microstructure is very fine. At the lower portion of the ribbon, which was solidified by direct contact with the rotating copper wheel, a columnar grain structure is observed. Milling of the rapidly solidified ribbons produces rounded particles because of the rolling up of small ribbon pieces. The resulting powders are free flowing and easy to handle. Their microstructure is shown in Fig. 2. It can be seen that important plastic deformation occurred during milling. The microstructure of the hot-pressed billets is illustrated in Fig. 3. Recrystallization occurred during hot pressing, and grain growth was not uniform. This can
D. Baril et al.
/
Rapidly solidified Cu-lOwt. %Ni
TABLE 1. Tensile properties of Cu-10Ni alloys Specimen
Number Yield of specimens strength tested (MPa)
Extruded from cast billets Extruded from hot-pressed billets, 50-160/~m powders Extruded from hot-pressed billets, 160-355/~m powders
3 2 2
114 147 150
Tensile strength (MPa)
Elastic modulus (GPa)
Elongation (%)
283 275 290
64 66 60
44 36 36
noted that measurements of the porosity at various stages of hot pressing showed that 98% of the compaction was achieved in less than 10 min. Hence, the hotpressing time and/or temperature could have been reduced significantly which would have reduced grain growth and led to a more uniform grain size in the hotpressed billets.
5. Conclusions
Fig. 5. Microstructure of rods extruded from hot-pressed billets.
higher for rods extruded from the cast alloy. It can also be noticed that extruded rods made from the 160-355 /zm size fraction gave slightly better mechanical properties than those obtained from the 5 0 - 1 6 0 / ~ m fraction.
4. Discussion The mechanism leading to the increase in the yield strength of the alloys produced by the rapid solidification technique is not clearly understood. The higher yield strength and the lower elongation of these alloys are similar to what is observed with cold-worked, conventionally cast alloys. The presence of dark interfaces around original particles in the alloys hot pressed from rapidly solidified powders (Fig. 3) is a characteristic that could explain their different mechanical properties. Further studies would be required to understand better the reinforcement mechanisms achieved by the rapid solidification technique. They should be focused on the processing parameters and on the composition of the dark interfaces. Alloys made from coarser C u - 1 0 N i powders seem to have slightly better mechanical properties, but the effect of the size of the powders on the mechanical properties is not really significant. It should also be
A higher yield strength but a lower elongation were obtained in Cu-10Ni alloys produced from rapidly solidified powders compared with alloys obtained by casting. The parameters of the powder metallurgy process could be modified to achieve better properties. For example, hot-pressing and hot-extrusion parameters should be closely controlled to obtain optimal microstructure and mechanical properties.
References 1 T. J. Giover and B. B. Moreton, Corrosion and Fouling Resistance of Cupro-Nickel in Marine Environments, Institution of Corrosion Science and Technology, 1982, pp. 105-108. 2 V. Callcut, Copper alloys in marine environments, Metallurgia, 55 (1988) 38-40. 3 P.R. Holiday, A. R. Cox and R. J. Patterson II, Rapid solidification effects on alloy structures, in R. Mehrabian, B. H. Kear and M. Coken (eds.), Proc. Int. Conf. on Rapid Solidification Processing: Principle and Technologies, Claitor's Publishing Division, Baton Rouge, LA, 1977, pp. 246-257. 4 S.J. Savage and E H. Froes, Production of rapidly solidified metals and alloys, J. Met., 36 (1984) 20-33. 5 Zhi-cheng Qui, R. Angers and E. Ghali, Effect of rapid solidification processing on corrosion resistance of Cu-Ni-Cr alloys, Mater. Lett., 7 ( 1988) 149-151. 6 C. Ceasar and U. Ktster, Microstructure and mechanical properties of rapidly solidified CuNil0 alloys, Proc. 7th Int. Conf. on the Strength of Metals and Alloys, Vol. 2, Pergamon, Oxford, 1986, pp. 201-213. 7 S. H. Lo, W. M. Gibbon and R. S. Hollingshead, Corrosion resistance enhancement of marine alloys by rapid solidification, J. Mater Sci., 22 (1987) 3293-3296. 8 W. A. Palko, Characterization of first-generation rapidly solidified copper-nickel alloys for marine applications,
10
Powder Metallurgy in Defense Powder Industries Federation, 133-152. 9 R. W. Jech, T. J. Moore, T. K. Rapid solidification via melt
D. Baril et al.
/
Rapidly solidified Cu-lOwt. %Ni
Technology, Vol. 6, Met~ Princeton, NJ, 1985, pp. Glasgow and N. W. Orth, spinning: equipment and
techniques, J. Met., 36(1984)41-45. 10 C. G61inas, R. Angers and S. Pelletier, Production of metal powders from rapidly solidified ductile ribbons, Mater. Lett., 6 (1988) 359-361. 11 ASTM Stand. B 557, 1984.
7
Fabrication and tensile properties of rapidly solidified Cu- 10wt.%Ni
alloy D a n i e l Baril*, R o c h A n g e r s a n d J o c e l y n B a r i l t
Department of Mining and Metallurgy, Laval University, Ste-Foy, Q ue. G1K 7P4 (Canada) (Received July 22, 1991; in revised form March 23, 1992)
Abstract Cu-10wt.%Ni ribbons were produced by melt spinning and cut into small particles with a blade cutter mill. The powders were then hot consolidated to full density by hot pressing followed by hot extrusion. Tensile properties of the resulting pieces were measured. Cu-10wt.% Ni cast ingots were also hot extruded and mechanically tested to compare with the rapidly solidified alloy and to evaluate the possible benefits brought by the rapid solidification process.
I. Introduction Cu-Ni alloys are especially suitable in marine environment [ 1, 2] because of their good corrosion resistance to sea water, their good erosion corrosion resistance, their antifouling capability and their relatively high strength. In this work, the evolution of the microstructure of a Cu-10Ni alloy (where the composition is in weight per cent) made from rapidly solidified powders through a two-step hot-consolidation process will be studied. The mechanical properties of this alloy will also be compared with those of an alloy produced by conventional casting. High cooling rates lead to a better chemical homogeneity, a higher solubility of alloying elements and a finer microstructure. Hence, better mechanical properties and better corrosion resistance should be expected in metallic alloys processed by rapid solidification [3-8].
2. Experimental procedure Rapidly solidified Cu-10Ni ribbons were produced by melt spinning under argon with a copper wheel. The *Present address: Alcan International, 1955 Mellon Boulevard, Jonquiere, Que. G7S 4K8, Canada. tPresent address: Les Aciers Amsco Inc., 620 Laval Street, Joliette, Que. J6E 6H5, Canada. 0921-5093/92/$5.00
tangential velocity of the wheel was between 12 and 13 m s -1. The melting of the alloy was done in a graphite crucible fixed into a VycorTM tube and the ejection nozzle was made of boron nitride with a 0.75 mm orifice. The ejection overpressure was 20 kPa. Under these conditions, it was possible to produce long uniform ribbons about 80 /~m thick (standard deviation of 10 ~m) and 1-3 mm wide. The solidification rate of these ribbons should be higher than 105 K s[9]. The pulverization of the ribbons into powders was done in a blade cutter mill [10] under a protective argon atmosphere. The resulting powders were separated by sieving into two size fractions: a 50-160/~m fraction and a 160-355 /zm fraction. These two different fractions were selected to investigate the influence of particle size on the mechanical properties of the final product. The powders were then hot consolidated. They were first hot pressed in a cylindrical graphite die at 700 °C at a 45 MPa uniaxial pressure for 45 min under a protective atmosphere of argon. Hot-pressed billets were 3.0-3.5 cm long and 3.2 cm in diameter and contained less than 1% porosity. Afterward, the billets were preheated at 800 °C for 20 rain and were hot extruded into rods 1.27 cm in diameter. The extrusion die diameter was 3.81 cm and the extrusion ratio was 9 to 1. Cu-10Ni alloy billets were also cast and hot extruded under the same conditions as those used with the hot-pressed billets for comparison purposes. Tensile standard [11] specimens (0.635 cm round) were machined from the extruded rods for mechanical © 1992 - Elsevier Sequoia. All rights reserved
8
D. Baril et al.
/
Rapidly solidified Cu-lOwt. %Ni
Fig. 1. Microstructureof melt-spun ribbons.
Fig. 3. Microstructureof a hot-pressed billets.
Fig. 2. Microstructureof powder (polishedsection).
Fig. 4. Microstructureof rods extruded from cast billets.
properties measurements. The tensile tests used a cross-head speed of 0.25 cm min- 1.
be explained by the heterogeneous nature of the plastic deformation that occurred during milling of the ribbons. It is possible to distinguish original particles in the microstructure of the hot-pressed billets (dark thick interfaces in Fig. 3). Figure 4 illustrates the microstructure of rods extruded from cast billets while Fig. 5 shows the microstructure of rods extruded from hot-pressed billets. In the latter rods, it can be observed (dark thick interfaces) that the deformation produced by hot extrusion brings about considerable elongation of the original powder particles along the extrusion axis. Anisotropic properties should be expected because of this fibrous structure. Both types of rod exhibit some recrystallization of the alloy. Table 1 reports average measured tensile properties. This table shows that the yield strength of the rapidly solidified alloy improved by about 30% over the conventionally cast alloy. The ultimate tensile strength is about the same for both types of alloy but elongation is
3. Results
The microstructure of the melt-spun ribbons is shown in Fig. 1. As expected, the microstructure is very fine. At the lower portion of the ribbon, which was solidified by direct contact with the rotating copper wheel, a columnar grain structure is observed. Milling of the rapidly solidified ribbons produces rounded particles because of the rolling up of small ribbon pieces. The resulting powders are free flowing and easy to handle. Their microstructure is shown in Fig. 2. It can be seen that important plastic deformation occurred during milling. The microstructure of the hot-pressed billets is illustrated in Fig. 3. Recrystallization occurred during hot pressing, and grain growth was not uniform. This can
D. Baril et al.
/
Rapidly solidified Cu-lOwt. %Ni
TABLE 1. Tensile properties of Cu-10Ni alloys Specimen
Number Yield of specimens strength tested (MPa)
Extruded from cast billets Extruded from hot-pressed billets, 50-160/~m powders Extruded from hot-pressed billets, 160-355/~m powders
3 2 2
114 147 150
Tensile strength (MPa)
Elastic modulus (GPa)
Elongation (%)
283 275 290
64 66 60
44 36 36
noted that measurements of the porosity at various stages of hot pressing showed that 98% of the compaction was achieved in less than 10 min. Hence, the hotpressing time and/or temperature could have been reduced significantly which would have reduced grain growth and led to a more uniform grain size in the hotpressed billets.
5. Conclusions
Fig. 5. Microstructure of rods extruded from hot-pressed billets.
higher for rods extruded from the cast alloy. It can also be noticed that extruded rods made from the 160-355 /zm size fraction gave slightly better mechanical properties than those obtained from the 5 0 - 1 6 0 / ~ m fraction.
4. Discussion The mechanism leading to the increase in the yield strength of the alloys produced by the rapid solidification technique is not clearly understood. The higher yield strength and the lower elongation of these alloys are similar to what is observed with cold-worked, conventionally cast alloys. The presence of dark interfaces around original particles in the alloys hot pressed from rapidly solidified powders (Fig. 3) is a characteristic that could explain their different mechanical properties. Further studies would be required to understand better the reinforcement mechanisms achieved by the rapid solidification technique. They should be focused on the processing parameters and on the composition of the dark interfaces. Alloys made from coarser C u - 1 0 N i powders seem to have slightly better mechanical properties, but the effect of the size of the powders on the mechanical properties is not really significant. It should also be
A higher yield strength but a lower elongation were obtained in Cu-10Ni alloys produced from rapidly solidified powders compared with alloys obtained by casting. The parameters of the powder metallurgy process could be modified to achieve better properties. For example, hot-pressing and hot-extrusion parameters should be closely controlled to obtain optimal microstructure and mechanical properties.
References 1 T. J. Giover and B. B. Moreton, Corrosion and Fouling Resistance of Cupro-Nickel in Marine Environments, Institution of Corrosion Science and Technology, 1982, pp. 105-108. 2 V. Callcut, Copper alloys in marine environments, Metallurgia, 55 (1988) 38-40. 3 P.R. Holiday, A. R. Cox and R. J. Patterson II, Rapid solidification effects on alloy structures, in R. Mehrabian, B. H. Kear and M. Coken (eds.), Proc. Int. Conf. on Rapid Solidification Processing: Principle and Technologies, Claitor's Publishing Division, Baton Rouge, LA, 1977, pp. 246-257. 4 S.J. Savage and E H. Froes, Production of rapidly solidified metals and alloys, J. Met., 36 (1984) 20-33. 5 Zhi-cheng Qui, R. Angers and E. Ghali, Effect of rapid solidification processing on corrosion resistance of Cu-Ni-Cr alloys, Mater. Lett., 7 ( 1988) 149-151. 6 C. Ceasar and U. Ktster, Microstructure and mechanical properties of rapidly solidified CuNil0 alloys, Proc. 7th Int. Conf. on the Strength of Metals and Alloys, Vol. 2, Pergamon, Oxford, 1986, pp. 201-213. 7 S. H. Lo, W. M. Gibbon and R. S. Hollingshead, Corrosion resistance enhancement of marine alloys by rapid solidification, J. Mater Sci., 22 (1987) 3293-3296. 8 W. A. Palko, Characterization of first-generation rapidly solidified copper-nickel alloys for marine applications,
10
Powder Metallurgy in Defense Powder Industries Federation, 133-152. 9 R. W. Jech, T. J. Moore, T. K. Rapid solidification via melt
D. Baril et al.
/
Rapidly solidified Cu-lOwt. %Ni
Technology, Vol. 6, Met~ Princeton, NJ, 1985, pp. Glasgow and N. W. Orth, spinning: equipment and
techniques, J. Met., 36(1984)41-45. 10 C. G61inas, R. Angers and S. Pelletier, Production of metal powders from rapidly solidified ductile ribbons, Mater. Lett., 6 (1988) 359-361. 11 ASTM Stand. B 557, 1984.