Patent Application
20080289730
The present invention relates to a ferromagnetic material having a high elastic deformation composed of Co-based alloy which has a high elastic deformation capability and is capable of displacement control by applied magnetic field.
Titanium alloys have drawn attention as materials having a low Young's modulus and high elastic deformation capability and have been used in a dental implant, an artificial bone, and an eyeglass frame. For example, Patent documents 1 and 2 introduce a titanium alloy containing elements of Groups 4A and 5A, which exhibits a low Young's modulus and has a high elastic deformation capability.
External factors that cause material deformation are temperature and magnetic field, in addition to external force described in Patent documents 1 and 2.
A shape memory alloy is known for displacement control by temperature and a small percentage of change in dimension can be obtained. Shape memory effect is a phenomenon in which an original shape is recovered by utilizing the martensite reverse transformation occurred when a deformed material is heated to a predetermined temperature or higher. The shape memory effect allows the shape memory alloy to be used as a heat driven actuator. However, temperature control is required and further changes in shape during the cooling-down period are rate-limited by thermal diffusion, and thus the responsiveness is bad.
Ferromagnetic shape memory alloys have also been attracting attention as actuator materials. In the ferromagnetic shape memory alloys, a small percentage of change in dimension which exceeds conventional magnetostriction materials can be obtained by application of an external magnetic field. Low responsiveness which is a defect of heat-driven shape memory alloy is also reduced. As a ferromagnetic shape memory alloy, for example, Ni—Mn—Ga system is listed, and Patent document 3 introduces actuator materials which deform in response to an applied magnetic field. Patent documents 4 and 5 introduce Co—Ni—Al system, and further Patent document 6 introduces Co system alloy.
However, the material of Ni—Mn—Ga system is inferior inductility, and thus it is hard to be formed into a complicated and precise shape which is required for machine parts. The ductility of Co—Ni—Al system alloy is improved by using a γ-phase as a second phase, however, the intensity of magnetization is low. Although the Co system alloy is relatively excellent in ductility and intensity of magnetization and heat driven shape memory effect is obtained, magnetostrictive characteristics are insufficient and super elastic characteristics cannot be obtained.
Patent document 1: Japanese Patent Application Laid-Open (JP-A) No. 2002-332531
Patent document 2: JP-A No. 2002-249836
Patent document 3: U.S. Pat. No. 5,958,154
Patent document 4: JP-A No. 2002-129273
Patent document 5: JP-A No. 2004-277865
Patent document 6: JP-A No. 2004-238720
The present inventors investigated and examined various materials which are ferromagnetic and can be driven by the magnetic field while maintaining high elastic deformation capability, and further have a good ductility in view of the defects of conventional titanium alloys and Ni—Mn—Ga system alloy. As a result, they found that a Co-based alloy having a high elastic deformation capability can be obtained by using cobalt as a basic material, properly selecting alloy content and composition, and forming an appropriate amount of an ε-phase of h.c.p. structure.
An objective of the present invention is to provide Co-based alloy having a high elastic deformation capability and good ductility and workability which is obtained by controlling the level of production of the ε-phase in the component system to which one or more members selected from Fe, Ni, and Mn are added, on the basis of the findings.
The Co-based alloy of the present invention includes, on the basis of mass percent, one or more members selected from 0.01 to 10% of Fe, 0.01 to 30% of Ni, and 0.01 to 25% of Mn. When two or three members selected from Fe, Ni, and Mn are added, it is preferable that the total content is set to the range of 0.02 to 50%. Hereinafter, the mass ratio is simply expressed as %.
Further, the Co-based alloy of the present invention may include, in addition to Fe, Ni, and Mn, one or more members selected from 0.01 to 10% of Al, 0.01 to 35% of Cr, 0.01 to 20% of V, 0.01 to 15% of Ti, 0.01 to 30% of Mo, 0.01 to 10% of Nb, 0.01 to 3% of Zr, 0.01 to 30% of W, 0.01 to 10% of Ta, 0.01 to 5% of Hf, 0.01 to 8% of Si, 0.001 to 3% of C, 0.001 to 3% of B, 0.001 to 3% of P, and 0.001 to 3% of misch metal in a total of 0.001 to 50%.
The proposed Co-based alloy is ferromagnetic at least ordinary temperature and the ε-phase of h.c.p. structure induced by heat or stress is distributed in the alloy. The proportion of the ε-phase is 10% by volume or more and can be controlled by adjusting the components and production conditions.
A metallic structure in which the ε-phase of h.c.p. structure is distributed is formed by solution-treating Co-based alloy with a predetermined composition at 900 to 1400° C. After the solution treatment, working may be performed at a working ratio of 10% or more, and further aging treatment may be performed at 300 to 800° C.
The present inventors added various alloy elements to cobalt which is a ferromagnetic element and then investigated and examined the relationship amongst the structure, the elastic deformation capability, and the magnetic properties in order to develop materials which have a high elastic deformation capability and are capable of displacement control by application or removal of magnetic field and workable. As a result, it is found out that when an appropriate amount of at least one member selected from Fe, Ni, and Mn is alloyed with cobalt, a ferromagnetic alloy having a high elastic deformation capability in which the workability is enhanced is produced.
Ferromagnetic materials are known to be displaced by forces due to the magnetic gradient in accordance with the equation, F=−M(dH/dx). The equation means that a force F obtained by a predetermined magnetic gradient dH/dx is proportional to an intensity of magnetization M. The amount of strain to be obtained is larger as the force F applied to materials is larger. Therefore, a large intensity of magnetization M is better to increase the amount of strain. When the force required for deformation is high, the amount of strain due to the magnetic field becomes small, and thus it is desirable that the Young's modulus is small. However, when the elastic deformation capability is low, the strain is remained by removing the magnetic gradient. For that reason, a large elastic deformation capability is needed in order to obtain a large reversible strain by application or removal of the magnetic gradient.
Cobalt is a ferromagnetic element with a high Curie temperature, however, pure cobalt is lack of workability and has a low magnetic susceptibility. The Cobalt has the γ-phase of f.c.c. structure at high temperature and is transformed to a martensitic ε-phase of h.c.p. structure at around 420° C. during cooling. Various alloy elements are added to cobalt and then the phase stability of the γ- and ε-phases are investigated. As a result, the γ-phase could be stabilized and various elements capable of improving workability could be identified.
The γ-phase has a good workability because of f.c.c. of unordered structure. Although the ε-phase has an effect of increasing the amount of elastic deformation, it is easily work-hardened and allows defects such as working cracks to be generated. Thus, when an element to be dissolved in the γ-phase and stabilize is added, the γ-phase remains even at an ordinary temperature. Therefore, the improvement in the workability of the Co-based alloy can be expected. Particularly, Fe, Ni, and Mn which have magnetic moments are effective for enhancement of magnetic characteristics of the Co-based alloy in addition to the improvement in workability.
When the proportion of the ε-phase is adjusted to 10% by volume or more by adjusting the components and production conditions, an effect of high elastic deformation becomes remarkable. However, excessive distribution of the ε-phase compensates for workability-improving effects of the residual γ-phase. Therefore, the upper limit of the ε-phase is set to 99% by volume. Basically, the Co-based alloy has a diploid structure consisting of the ε-phase of h.c.p. structure and the remainder being γ-phase of f.c.c. structure. The Co-based alloy permits a heterophase to be present as long as the phase does not have an adverse influence on the high elastic characteristics, magnetic properties, and workability. Examples of the heterophase include an intermetallic compound produced by addition of a third component, a carbide, and an α-phase (b.c.c. structure).
The Co alloy to which Fe is added exhibits particularly excellent magnetic properties. In the use as a displacement control element by applied magnetic field, it is preferable that a large intensity of magnetization is obtained by a relatively low magnetic field. When the magnetization curve of the Co-based alloy in the present invention is determined, the intensity of magnetization is 30 emu/g or more to an external magnetic field of 0.2T (Tesla). It can be said that the material is promising as the displacement control element. Although Ni and Mn have effects which reduce the intensity of magnetization, the intensity of magnetization is still maintained at high level. Thus, demand characteristics as the displacement control elements are given.
On the other hand, the following facts were revealed by the result of investigation of the relation between the structure and the elastic deformation behavior.
The elastic limit strain of annealed metallic materials such as Fe and Co is normally about 0.3%. When cold working is performed, the materials are work-hardened and sliding deformation is suppressed. Thus, the hardness and tensile strength are increased, and further the yield stress and elastic limit are increased. On the other hand, in the Co-based alloy of the present invention, based on, for example, 1% of bending deformation, 0.4% or more of strain that exceeds the normal amount of elastic strain is recovered. In addition, a large temperature range from −196° C. (liquid nitrogen temperature) to 400° C. is applicable.
However, it is difficult to obtain the displacement by the magnetic field when the force required for deformation is high. Therefore, it is desirable that the Young's modulus is low. The Young's modulus is a value of physical properties related to cohesive force between atoms. It is considered that it is hard to control by working or heat treatment. In this regard, a low Young's modulus is attained by lattice softening at the time of martensitic transformation or controlling the direction of the martensite variant in the present invention.
In the martensitic transformation, a lattice softening phenomenon where the elastic constant is reduced in the range from the martensitic transformation temperature to about several 10 to 100° C. is observed as one of the precursor phenomena accompanying the transformation. When the lattice softening is used for the Co-based alloy, the reduction in the Young's modulus is expected in the vicinity of the martensitic transformation temperature Ms.
In the pure cobalt, the lattice softening by the martensitic transformation is brought about in the vicinity of 420° C. However, the transformation temperature is decreased by the addition of Fe, Ni, and Mn. In accordance with the decrease in the transformation temperature, a low Young's modulus is obtained in the desired temperature range. Further, the martensitic transformation of Co—X (X: Fe, Ni, Mn) system is non-thermoelastic, and thus the hysteresis is about 150° C. Since the hysteresis further grows by the working, it is suitable to realize the low Young's modulus with a large temperature width.
As for the martensitic transformation of the Co-based alloy, even if the Co-based alloy is sufficiently cooled to the Ms temperature or less in the same manner as that of the Fe alloy, the whole sample is not necessarily transformed into a martensitic phase and a certain amount of the mother phase remains. Thus, the martensitic phase is stress-induced by working after the solution treatment. The largest variant of Schmid factor to the stress is preferentially generated. Further, when the stress is applied to the martensitic phase thermally-induced, a part of the martensitic phase is rearranged in the variant preferential to the direction of the stress. Such a preferential variant exhibits a low deforming stress against the direction of the stress, which is considered as one of the causes that the Co-based alloy exhibits a low Young's modulus.
The Co—Ni—Al system alloy (Patent documents 4 and 5) has a structure of the β-phase or β+γ phase and the martensitic transformation and reverse transformation of the β-phase is used to impart a shape memory property. However, the γ-phase is not transformed to the ε-phase. Although the presence of the β-phase of B2 structure with a low ductility causes the reduction in workability, it can be said that the material is excellent in ductility from the viewpoint that the β-phase is not present in the Co-based alloy of the present invention. In addition, the Co-based alloy of the present invention has an extremely high intensity of magnetization compared with the Co—Ni—Al system alloy being ferromagnetic and having a low intensity of magnetization. Thus, the Co-based alloy of the present invention exhibits excellent capacity when performing displacement control by the magnetic gradient.
The Co-based alloy with a shape memory property described in Patent document 6 is excellent in shape memory effect. However, superelasticity is not obtained and the displacement control by the magnetic field is also difficult because of extremely small magnetostriction. This is because the displacement control by the shape memory effect, superelasticity, or magnetic field is respectively resulted from different phenomena. That is, the shape memory effect is a phenomenon where the deformation is given in the martensitic phase state and the shape is recovered by allowing the mother phase to be martensite reverse-transformed. The superelasticity is a phenomenon where stress-induced martensitic transformation is exhibited when the stress is given in the state of the mother phase, and martensite reverse transformation to the mother phase occurs when the stress is unloaded, thereby recovering the shape. On the other hand, a large magnetostriction in the ferromagnetic shape memory alloys is a phenomenon that is given by rearrangement of the martensite variant by a uniform magnetic field or magnetic-field-induced martensitic transformation.
In the Co-based alloy of the present patent application, a high elastic deformation capability is realized mainly by work hardening, which essentially differs from the superelasticity in the respect that martensitic reversible transformation or reverse transformation is not clearly detected by stress loading or unloading. While a martensitic phase (ε-phase) has a low Young's modulus, it only supports the elastic deformation capability. Further the workability is enhanced and the intensity of magnetization is also increased. Thus, the Co-based alloy exhibits an excellent function as a material in which displacement control can be performed by application or removal of the magnetic gradient.
The Co-based alloy of the present invention has a basic composition which includes one or more selected from 0.01 to 10% of Fe, 0.01 to 30% of Ni, and 0.01 to 25% of Mn.
Fe, Ni, and Mn reduce the martensitic transformation temperature, contribute to the improvement in ductility and workability, and are effective in increasing the magnetic susceptibility. Such effects become significant when 0.01% or more of Fe, Ni, or Mn is added. However, an excessive addition thereof reduces the martensite transformation temperature and magnetic transformation temperature to below room temperature, thereby inhibiting the production of the ε-phase and reduction in magnetic properties. Thus, the upper limits of Fe, Ni, and Mn are set to 10%, 30%, and 25%, respectively. When two or three members selected from Fe, Ni, and Mn are added, it is preferable that the total content is set to the range of 0.02 to 50%. Each content of Fe, Ni, and Mn is set to preferably in the range of 1 to 8%, 1 to 25%, or 1 to 20%, more preferably in the range of 2 to 6%, 5 to 20%, or 5 to 15%.
One or more third components selected from Al, Cr, V, Ti, Mo, Nb, Zr, W, Ta, Hf, Si, C, B, P, and misch metal can be added to Co— (Fe, Mn, Ni) system if necessary. In the case of addition of a plurality of third components, the total content is selected in the range of 0.002 to 50% (preferably in the range of 0.005 to 30%).
Al, V, and Ti are components which reduce the martensitic transformation temperature. However, an excessive amount thereof allows the γ-phase to be stabilized and reduces the volume fraction of the E-phase. Thus, when Al, V, and Ti are added, the content of Al, V, and Ti is selected in the range of 0.01 to 10%, in the range of 0.01 to 20%, and in the range of 0.01 to 15%, respectively.
Cr and Mo are components effective in improving corrosion resistance, however, the addition of an excessive amount thereof leads to a significant deterioration in ductility. When Cr and Mo are added, the Cr content is selected in the range of 0.01 to 35% and the Mo content is selected in the range of 0.01 to 30%.
Nb, Zr, W, Ta, and Hf are components effective in strengthening materials, however, the addition of an excessive amount thereof leads to a significant deterioration in ductility. When Nb, Zr, W, Ta, and Hf are added, the content of Nb, Zr, W, Ta, and Hf is selected in the range of 0.01 to 10%, in the range of 0.01 to 3%, in the range of 0.01 to 30%, in the range of 0.01 to 10%, and in the range of 0.01 to 5%, respectively.
Si is a component which increases the martensitic transformation temperature, however, the addition of an excessive amount thereof leads to a significant deterioration in ductility. When Si is added, the Si content is selected in the range of 0.01 to 8%.
C, B, P, and misch metal are components effective in allowing crystal grains to form a fine-grained structure, however, the addition of an excessive amount thereof leads to a significant deterioration in ductility. Thus, when C, B, P, and misch metal are added, the content of C, B, P, and misch metal is selected in the range of 0.001 to 3%, in the range of 0.001 to 3%, in the range of 0.001 to 3%, and in the range of 0.001 to 3%, respectively.
The Co-based alloy adjusted to a predetermined composition is dissolved, followed by casting, forging, and hot-rolling. The resulting alloy is subjected to cold working, such as rolling, drawing, and forging so as to be formed into a plate member, a wire member, a pipe member, and the like, with a target size. When the Co-based alloy after the cold working is subjected to solution treatment at 900 to 1400° C., the strain introduced until the cold working process is removed and the quality of materials is uniformed. The solution-treatment temperature is sufficiently required to be the recrystallization temperature or higher. Therefore, it is set to 900° C. or higher and below melting point (specifically 1400° C. or less). Preferably, it is set to the range of 1000 to 1250° C.
In the process of cooling from the solution-treatment temperature to room temperature, the γ-phase of f.c.c. structure is transformed to a martensitic γ-phase of h.c.p. structure. Even when the martensitic transformation point (Ms temperature) is higher than room temperature, the γ-phase is stabilized by Fe, Ni, and Mn. Thus, the structure after the cooling is not transformed to a single ε-phase.
The Co-based alloy after the solution treatment may be subjected to rolling, forging, bending, and drawing. The working temperature is usually set to an ordinary temperature. It can be set to 700° C. or less. Examples of the martensitic transformation include stress induced transformation in addition to the heat induced transformation caused by cooling to the Ms temperature or less. The working is an effective means for the increase of the volume fraction of the E-phase.
The stress induced transformation is caused when the stress is applied under the environment at the Ms temperature or more. The hot working that concerns about dynamic recrystallization and precipitation accompanying the working is not preferable.
Taking into consideration that the hot working is usually defined as working at 0.6 TM (TM: melting point) or more, the working temperature is set to 0.6 TM or less, specifically 700° C. or less. An inductive effect of the ε-phase becomes remarkable due to the increase in the working ratio. Therefore, the working ratio at the time of cold working is set to 10% or more. The upper limit of the working ratio is determined depending on the capability of the processing plant. However, an excessive working ratio makes the burdens involved in the processing plant greater. Therefore, it is preferable that the upper limit is set to 90%.
Effect of the ε-phase on the improvement in the elastic deformation capability and the reduction in Young's modulus becomes significant when the ε-phase accounts for 10% by volume or more of the total metallic structure. However, excessive distribution of the ε-phase weakens the effect of the reduction in Young's modulus and this has the opposite effect of relatively reducing the volume fraction of the γ-phase which is effective for the improvement in workability. Therefore, the upper limit of the ε-phase is set to 99% by volume.
Solution treatment is performed at 900 to 1400° C. and working is performed at 700 or less. When 10% or more of the work is finished, aging temperature may be carried out at 300 to 800° C. (preferably at 400 to 700° C.). When aging treatment is performed, the strength can be increased or decreased by the strain-aging effect or the recovery and recrystallization. The strength is increased in the case where the Cottrell effect or the Suzuki effect occurs, while the strength is decreased in the case where the recovery or recrystallization occurs. At least short-range atomic diffusion is required for aging treatment, and thus the aging temperature is set to 300° C. or more. However, high-temperature heating at greater than 800° C. does not allow for a sufficient elastic strain.
Hereinafter, the actions and effects of the present invention will be specifically described with reference to Examples. Needless to say, Examples help to make the present invention easier to understand specifically and the technical scope of the present invention shall not be affected thereby.
Co-based alloys of Tables 1 to 3 were dissolved, followed by casting and hot-rolling. Then, each alloy was cold-rolled to a plate thickness of 0.5 mm and further subjected to solution-treatment at 1200° C. for 15 minutes.
F1 to F8 of Table 1 have alloy designs based on Co—Fe systems, N1 to N8 of Table 2 have alloy designs based on Co—Ni systems, and M1 to M8 of Table 3 have alloy designs based on Co—Mn systems.
Results of the volume fraction of the ε-phase, amount of recovered strain, and intensity of magnetization as to each Co-based alloy which were examined at room temperature are shown in Tables 1 to 3. For the purpose of comparison, the same characteristics of pure cobalt, pure iron, and SUS316L are shown in Table 4. Further, effects of Fe, Ni, and Mn on the volume fraction of the E-phase, amount of recovered strain, and intensity of magnetization were graphed and shown in
Volume fraction Xε of the ε-phase is calculated by substituting integrated intensities I(200)γ and I(10
The amount of recovered strain is an amount of strain in the shape recovered when unloaded after applying an amount of bending strain (1%) in three-point bending test.
The intensity of magnetization was defined as the intensity of magnetization obtained when a magnetic field of 0.2 T was applied by using a vibrating sample magnetometer.
As shown in Tables 1 to 3 and
As shown in
In the Co—Fe system, the intensity of magnetization is increased with a weighting amount of Fe. When the amount of Fe was 7.61% (No. F4), the maximum value of the intensity was shown, which was excellent magnetic properties. In the Co—Ni system and the Co—Mn system, the decrease in intensity of magnetization was observed depending on the weighting of Ni and Mn. However, a large intensity of magnetization of 43.9 emu/g or more was still maintained.
On the other hand, the ε-phase accounted for 93% by volume of the total in Comparative example C1 (pure cobalt), however, the amount of recovered strain was lower than that of the material of the present invention. Although the intensity of magnetization in Comparative example C2 (pure iron) was large, the ε-phase was not present and the amount of recovered strain was also still low. In Comparative example C3 (SUS316L), which was a paramagnetic material, the intensity of magnetization was close to about 0 when a magnetic field of 0.2 T was applied. The amount of recovered strain also showed a low value.
Next, each Co-based alloy solution-treated at 1200° C. for 15 minutes was cold-rolled at a rolling reduction of 40% and then the volume fraction of the ε-phase, the amount of recovered strain, and the intensity of magnetization were determined with the same test. The research results are shown in Tables 5 to 7.
In any alloy system of Co—Fe, Co—Ni, and Co—Mn, the volume fraction of the ε-phase was increased as compared with that of materials (Tables 1 to 3) without cold-rolling. Further, as shown in the stress/strain diagram (
On the other hand, in Comparative examples C1 and C2, any change in the volume fraction of the ε-phase caused by cold rolling was not observed. The amount of recovered strain was small as compared with the material of the present invention. In the case of C3, a large amount of recovered strain was obtained, however, the intensity of magnetization was almost zero when an external magnetic field of 0.2T was applied.
F2 of Table 1, N4 of Table 2, and M3 of Table 3 were selected as representatives of Co—Fe system alloy, Co—Ni system alloy, and Co—Mn system alloy, respectively, which were subjected to cold working and aging treatment after the solution treatment.
The relation between production conditions and values of physical properties is shown in Table 9. Further, with reference to each of the Co—Fe system, Co—Ni system, and Co—Mn system, effects of solution treatment conditions on the volume fraction of the ε-phase, amount of recovered strain, and intensity of magnetization (cold working ratio: 40%, aging treatment condition: at 700° C. for 2 hours), effects of cold working ratio (solution-treatment conditions: at 1200° C. for 15 minutes, aging treatment condition: 700° C. for 2 hours, these conditions were fixed), and effects of aging treatment conditions (solution-treatment conditions: 1200° C. for 15 minutes, cold working ratio: 40% or 80%, these conditions were fixed) were graphed and shown in
In Test Nos. 4, 6, and 7, the cold working ratio and aging treatment conditions were fixed and the solution treatment temperature was changed. However, great changes in the volume fraction of the ε-phase, amount of recovered strain, and intensity of magnetization were not observed. The relation was the same as that of Test Nos. 12 and 13 as well as Test Nos. 19 and 20. It can be understood from
In Test No. 2 where the solution treatment temperature was too high, a liquid phase appeared and partial melting occurred.
In Test Nos. 11, 12, 14, and 15, the solution treatment conditions and aging treatment conditions were fixed and the cold working ratio was changed. The volume fraction of the ε-phase was higher as the cold working ratio was higher, and the amount of recovered strain was also larger. Although the intensity of magnetization was reduced slightly, the reduction was not large. The relation was observed in Test Nos. 4 and 5 as well as Test Nos. 19 and 21. It can be understood from
In Test Nos. 16 to 19, 22, and 23, the solution treatment conditions and aging treatment conditions were fixed and the aging treatment conditions were changed. The volume fraction of the ε-phase and the amount of recovered strain tended to be reduced with the increase of the aging temperature. The amount of recovered strain was small as compared with materials left after the cold working. In Test Nos. 17 to 19 and 22, the value was intermediate between the amount of recovered strain obtained by materials left after the solution treatment and the amount of recovered strain obtained by materials given by solution treatment and cold working. Remarkable changes in the intensity of magnetization were not observed. The relation was the same as that of Test Nos. 1, 3, and 4 as well as Test Nos. 8, 10, and 12.
In Test Nos. 9 and 15 where the working ratio was as large as 80%, the amount of recovered strain was increased by aging treatment. On the other hand, in Test No. 23, the amount of recovered strain which was obtained by aging after the cold working was equivalent to one before the working (shown in Table 3). Thus, remarkable aging effects were not obtained.
The above-described results suggest that the amount of recovered strain can be controlled by proper aging, which is supported by
Co-alloy containing 2.05% of Fe, Co-alloy containing 10% of Ni, and Co-alloy containing 5% of Mn were basic compositions of Co—Fe system, Co—Ni system, and Co—Mn system, respectively. The third component was added to prepare various Co-based alloys. Each alloy was dissolved, followed by casting and hot-rolling in the same manner as described in Example 1. Then, each alloy was cold-rolled to a plate thickness of 0.5 mm, which was subjected to solution treatment, cold rolling, and aging treatment.
The volume fraction of the ε-phase, the amount of recovered strain, and the intensity of magnetization as to each of the obtained Co-based alloys were measured. The results are shown in Table 10 (Co—Fe system), Table 11 (Co—Ni system), and Table 12 (Co—Mn system).
As is apparent from the research results in Tables 10 to 12, in the Co-based alloy in which the ductility, magnetism, corrosion resistance, and strength were enhanced by the addition of the third component, 50% by volume or more of ε-phase was present in any solution-treated materials and 0.41% or more of recovered strain was obtained when 1% of strain was applied. Further, when a magnetic field of 0.2 T was applied, the intensity of magnetization was 69.9 emu/g or more. Each volume fraction of the ε-phase was increased by 40% of cold rolling and a large amount of recovered strain (around 0.6%) was obtained without greatly reducing the intensity of magnetization. Further, the amount of recovered strain was controlled by performing aging treatment.
F2 alloy of Table 1 was selected, followed by casting and hot-rolling. Then, the alloy was cold-rolled to a plate thickness of 0.33 mm, which was subjected to solution treatment at 1200° C. for 15 minutes and finally cold-rolled at a rolling reduction of 20%.
With reference to the obtained Co—Fe system alloy, the volume fraction of the E-phase, the amount of recovered strain, and the intensity of magnetization (under conditions of −50° C., 25° C., 100° C., and 200° C.) were determined. The amount of recovered strain is an amount of strain in the shape recovered when unloaded after applying an amount of bending strain (1%) in tensile test at each temperature. The volume fraction of the ε-phase, the amount of recovered strain, and the intensity of magnetization were determined at each temperature in the same manner as described in Example 1.
As is apparent from the research results in Table 13, the volume fraction of the ε-phase was not largely changed in the range of −50° C. to 200° C. The amount of recovered strain tended to be reduced when the test temperature was increased. However, the amount of recovered strain was still large at 200° C.
In the shape memory alloy, the deforming stress varies largely with temperature. For example, the temperature dependence of the apparent yield stress in Ti—Ni system alloy is about 5 MPa/° C. On the other hand, as shown in the stress/strain diagram (
Effects of temperatures on N4 alloy cold-rolled material of Table 2 produced under the same conditions and M3 alloy cold-rolled material of Table 3 were investigated with the same test and the research results were shown in Table 13. In the case of Co—Ni system and Co—Mn system, the ε-phase constitutes a large majority of metallic structures, and the amount of recovered strain and the intensity of magnetization were large.
As described above, the Co-based alloy with a high elastic deformation capability was given by adding an appropriate amount of one or more members selected from Fe, Ni, and Mn and controlling the level of production of the ε-phase. When the magnetic properties of the obtained Co-based alloy are used, a functional material which is useful as a sensor or actuator capable of displacement control by an applied magnetic field is provided.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-350431 | Dec 2005 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2006/323877 | Nov 2006 | US |
| Child | 12112513 | US |
