JPWO2007043687A1 - High-strength Co-based alloy with improved workability and method for producing the same - Google Patents

Abstract

Co-base alloy useful as a spring, spring, wire, cable guide, steel belt, cladding material, guide wire, stent, catheter, etc., and Al: 3-13% Co—Al binary system with Ni: 0. 01 to 50%, Fe: 0.01 to 40%, Mn: 0.01 to 30% selected from one or more workability improving elements added, f. c. c. The structure has a lamellar structure in which the α phase and β (B2) phase repeat in layers. The lamellar structure has an occupancy ratio of 30% by volume or more in the entire structure and a layer interval of 100 μm or less. One or two or more optional components selected from Ga, Cr, V, Ti, Mo, Nb, Zr, W, Ta, Hf, Si, Rh, Pd, Ir, Pt, Au, B, C, P Total: 0.01 to 60% may be added.

Description

  The present invention relates to a Co-base alloy that is expected to be used for high-strength applications, wear-resistant applications, heat-resistant applications, medical instruments / tools, biomaterials, and the like, and further, a Co-base alloy with improved workability and a method for producing the same About.

Co-base alloys used in heat-resistant materials, wear-resistant materials, biomaterials, medical instruments and tools, etc. are Cr, Ni, Fe for improving corrosion resistance, oxidation resistance, stabilizing α phase, strengthening materials, etc. , Mo, C, and the like are added, and are strengthened by various methods such as solid solution strengthening, precipitation strengthening, work hardening and the like in order to obtain the required strength.
All of the conventional strengthening methods and material improvements are based on a metal structure in which the α single phase or the second phase is continuously precipitated in the α phase (References 1 and 2). However, in addition to the harsh use environment, it is required to be applied to applications in which further thinning and miniaturization have been promoted, and much higher strength is required than the Co alloy reinforced by the conventional method.
In other alloy systems, strengthening by lamellar structure is also adopted, and a typical example is the pearlite transformation found in steel materials. When a lamellar structure of ferrite and cementite is formed by pearlite transformation, the strength is increased to satisfy the required characteristics as a piano wire.
Regarding material strengthening using a lamellar structure, the present inventors have also introduced Cu-Mn-Al-Ni-based alloys in Reference 3, and Lamellar organization of Co-Al binary alloys has also been reported in Reference 4. .
Reference 1: JP 7-179967 A
Reference 2: JP 10-140279 A
Reference 3: JP 5-25568 A
Reference 4: P.M. Zieba, Acta material. Vol. 46, no. 1 (1998) p. 369-377
The lamellar textured Co-Al binary alloy has a multiphase structure in which hard precipitated phases are laminated in layers at very fine intervals on a soft α-phase matrix, and is expected to achieve both strength and toughness at a high level. it can. However, the ductility is extremely low as compared with ordinary metal materials, and cracks starting from the precipitation phase or the α phase / precipitation phase interface are likely to occur in cold working with a high workability. As a measure to overcome difficult workability and enable processing to the target shape by cold working such as rolling, drawing, swaging, etc., the machining process is divided into multiple stages, and distortion is removed by intermediate annealing between each process. It is possible to do. However, multi-stage cold working with intermediate annealing is not an effective solution because it complicates the manufacturing process and increases manufacturing costs. There is also concern that the lamellar structure collapses during intermediate annealing, and the original properties of the lamellar structure are impaired.

ｆ．ｃ．ｃ．構造のα相とβ（Ｂ２）相が微小間隔で繰り返されるラメラー組織は、Ｃｏ基合金を溶解した後、凝固過程での制御冷却や熱処理で生成する。凝固過程の制御冷却による場合、１５００〜６００℃の温度域を平均冷却速度：５００℃／分以下で凝固冷却する。熱処理による場合、９００〜１４００℃の溶体化後に５００〜９００℃で時効処理する。凝固冷却，熱処理の組合せでラメラー組織化，更には組織制御することも可能である。
制御冷却又は時効処理でラメラー組織が生成したＣｏ基合金に圧延，引抜き，スエージング等の冷間加工を加工率：１０％以上で施すと、ラメラー組織が加工方向に伸長し、一層の組織微細化，加工硬化が図られ強度，耐磨耗性が向上する。しかも、Ｎｉ，Ｆｅ，Ｍｎの添加で加工性が改善されているので、加工率：１０％以上でもクラック等の加工欠陥が発生せず、目標形状に冷間加工できる。When the lamellar textured Co-Al binary alloy can be cold-worked into the target shape, the excellent properties inherent in the lamellar texture can be utilized, and combined with the excellent corrosion resistance of Co, can be used for a wide range of applications of Co-Al alloys. Can be expected.
Therefore, we investigated and studied the workability improvement of Co-Al alloys from various viewpoints, such as the addition of a third component, the improvement of heat treatment conditions, and processing conditions. As a result, it has been found that the addition of Ni, Fe, Mn, etc. improves the ductility of the Co—Al alloy and suppresses the occurrence of cracks even in cold working at a high working rate.
The present invention has been completed on the basis of such knowledge. By adding Ni, Fe, and Mn, the ductility of the Co-Al alloy, and hence the workability, can be improved without damaging the properties of the lamellar structure. The object is to provide a Co-based alloy that can be cold worked into a shape and is useful as a material for various parts and members.
The Co-based alloy of the present invention is selected from Al: 3 to 13% by mass, Ni: 0.01 to 50% by mass, Fe: 0.01 to 40% by mass, and Mn: 0.01 to 30% by mass. Based on a component system containing one or more workability improving elements in a total content of 0.01 to 60% by mass, f. c. c. The structure has a lamellar structure in which the α phase and β (B2) phase of the structure overlap each other at a minute interval. Since the workability is improved by the addition of Ni, Fe and / or Mn, it can be thinned and thinned, and exhibits excellent strength and wear resistance derived from a lamellar structure even after processing.
Hereinafter, the content of the alloy component is simply expressed as%, and other ratios are expressed as volume%, area%, and the like.
The lamellar structure is generated by controlled cooling in the solidification process and aging treatment after solution treatment. In this component system, f. c. c. The α phase and β (B2) phase of the structure is a multiphase structure in which the layer interval is 100 μm or less and overlaps each other, and the occupation ratio with respect to the entire metal structure is adjusted to 30% by volume or more. Since the workability is improved by adding Ni, Fe, and Mn, it is possible to perform cold work of 10% or more on the La-structured Co-based alloy.
The Co-based alloy of the present invention has a basic composition in which a workability improving element such as Ni, Fe, Mn or the like is added to a Co—Al binary system, but can contain other elements as optional components. The optional component includes one or more selected from Table 1. One or more optional components are added within a range of 0.001 to 60% in total. Table 1 shows the relationship between workability improving elements, arbitrary components, and main precipitates.

f. c. c. A lamellar structure in which the α phase and β (B2) phase of the structure are repeated at a minute interval is generated by controlled cooling or heat treatment in the solidification process after the Co-based alloy is dissolved. In the case of controlled cooling in the solidification process, solidification cooling is performed at a temperature range of 1500 to 600 ° C. at an average cooling rate of 500 ° C./min or less. In the case of heat treatment, aging treatment is performed at 500 to 900 ° C. after solution treatment at 900 to 1400 ° C. It is possible to form a lamellar structure and control the structure by a combination of solidification cooling and heat treatment.
When a cold working such as rolling, drawing, swaging, etc., is performed on a Co-based alloy with a lamellar structure formed by controlled cooling or aging treatment at a processing rate of 10% or more, the lamellar structure expands in the processing direction, resulting in a further finer structure. Strengthening and work-hardening improve strength and wear resistance. Moreover, since the workability is improved by adding Ni, Fe, and Mn, even if the processing rate is 10% or more, processing defects such as cracks do not occur, and cold processing can be performed to the target shape.

1 is a Co—Al binary phase diagram. FIG. FIG. 3 is an optical microscope image showing a lamellar structure of a swept Co—Al—Ni alloy.

In order to realize a lamellar structure similar to the pearlite structure of steel in the Co system, an alloy element having a high solid solubility in Co at a high temperature range and a small temperature at a low temperature range is necessary so that discontinuous precipitation occurs. From this point of view, Al is most suitable for lamellar organization of the Co-based alloy. Specifically, by subjecting a Co—Al binary alloy containing an appropriate amount of Al to controlled cooling or aging treatment, f. c. c. A lamellar structure in which the α phase and β (B2) phase of the structure are repeated at a minute interval is obtained.
The α phase is f. c. c. It has a (face-centered cubic) crystal structure and is a phase in which Al is dissolved in Co as can be seen from the Co-Al binary phase diagram (FIG. 1). c. p. The structure may undergo martensitic transformation. crystallized phase or precipitated phase to produce the α phase is, Ni, Fe, although the Co-Al system containing Mn which is β-phase crystal structure type B2, the Co-Al system include any component L1 ₂ structure Γ ′ phase, D0 ₁₉ type phase, M ₂₃ C ₆ type carbide, and the like also become precipitates. These precipitates can be identified by X-ray diffraction, TEM observation or the like. Hereinafter, L1 ₂ structure gamma 'phase, _{D0 19} -type _phase, thereby appropriately represent the _M 23 _{C 6} type carbide and the like in β phase.
The lamellar structure is a multiphase structure in which the α phase and the crystallization phase or the precipitation phase are repeated in layers, and the finer the layer interval (lamellar interval) between the α phase and the crystallization phase or the precipitation phase, the better the toughness. .
The lamellar structure is formed by discontinuous precipitation represented by α ′ → α + β. The α ′ phase and the α phase are the same phase, but there is a concentration gap at the interface, and the solute concentration in the parent phase does not change. In the Co—Al binary system of FIG. 1, discontinuous precipitation occurs when heat treatment is performed in an α single-phase region and then heat treatment is performed in a predetermined α + β two-phase region.
In discontinuous precipitation, in most cases, two phases grow from a grain boundary as a starting point to form a group called a colony, and a lamellar structure in which an α phase and a β phase are repeated in layers is formed.
Various mechanisms for generating lamellar structures have been proposed. For example,
・ Because the precipitates precipitated at the grain boundaries are inconsistent with the grain boundaries and matched or semi-matched with the parent phase, the grain boundaries are oriented in the direction of the precipitate / grain boundary based on the energy imbalance. The theory that it moves and repeats to form a lamellar structure ・ Intergranular movement occurs, and the precipitate that forms in the grain boundary in the process becomes a lamellar structure due to further grain boundary movement The interface between the mother phase and the precipitated phase Elucidation of the mechanism is complicated because various factors such as energy, strain energy, melting point difference and temperature are related to the lamellar organization reaction, but in any case, it is a grain boundary reaction type precipitation. Body diffusion (lattice diffusion) in which atoms jump and diffuse while occupying the position on the crystal lattice or between the crystal lattices is dominant on the high temperature side with 0.75-0.8 Tm (Tm: absolute temperature of melting point) as the boundary. Assuming the general rule that grain boundary diffusion is dominant on the low temperature side, it is necessary to perform heat treatment at a relatively low temperature in order to form a lamellar structure as a result of the grain boundary reaction. However, if the driving force for precipitation (in other words, the degree of supercooling from the single-phase region) is small, the precipitation reaction becomes slow, and it is necessary to increase the degree of supercooling to some extent.
The Co—Al binary phase diagram (FIG. 1) shows that the solid solubility of the α phase is greatly reduced below the magnetic transformation temperature. Due to a significant change in solid solubility of the α phase at the boundary of the magnetic transformation temperature, the difference in solid solubility in the Co—Al binary alloy increases between the high temperature range and the low temperature range, resulting in an increase in the driving force for precipitation. As a result, a lamellar structure can be sufficiently formed by heat treatment at a low temperature.
It is known that a lamellar structure is also generated by a eutectic reaction. The eutectic reaction is expressed as L → α + β. In the Co—Al binary system (FIG. 1), the eutectic reaction occurs when an alloy containing about 10% Al is solidified. In the eutectic reaction, an α phase and a β phase are crystallized simultaneously, solute atoms diffuse throughout the solidified surface, and two adjacent phases grow at the same time, so that a lamellar structure or a rod-like structure is formed. When the volume fractions of both phases are almost equal, a lamellar structure is formed. When there is a large difference in volume fractions, a rod-shaped structure tends to be formed. In the Al: 3 to 13% Co—Al alloy, a lamellar structure is formed because there is no significant difference in the volume fraction between the α phase and the β phase in the high temperature region where the metal structure is formed.
In the Co—Al binary system, the α phase is h. c. p. It has transformed into the martensitic phase of the structure. h. c. p. The structure generally tends to be inferior in workability, but f. c. c. The α phase of the structure is excellent in workability. Processability improving elements such as Ni, Fe and Mn are h. c. p. From structure f. c. c. Has the effect of stabilizing the structure, h. c. p. Suppresses transformation of structure to martensite phase to improve workability. On the other hand, the β phase of the Co—Al based alloy tends to be softened as the ratio of Co: Ni, Co: Fe, Co: Mn increases. Therefore, Ni, Fe, Mn, etc. contribute to the improvement of the workability of both the α and β phases, and the workability of the Co—Al base alloy having the α-phase and β-phase lamellar structures is improved. In addition, since Ni, Fe, and Mn do not greatly decrease the magnetic transformation temperature, they do not significantly inhibit the formation of lamellar structures.
It does not occur in Co-Al binary alloys or Co-based alloys with added workability improving elements such as Ni, Fe, Mn, etc., but lamellar structures are formed even in eutectoid reactions and continuous precipitation in systems containing the optional components listed above. The In normal continuous precipitation, a lamellar structure cannot be obtained, but a lamellar structure tends to be formed when a directional precipitation reaction proceeds.
The Co-based alloy of the present invention is basically based on a component system in which one or more of Ni, Fe, and Mn are added as a workability improving element to a Co—Al binary system containing Al: 3 to 13%. With the optimal alloy design, cold working can be achieved with a working rate of 99.9%, and the number of cold working steps required to obtain the target shape can be greatly reduced.
Al is an essential component for the formation of a lamellar structure in which the β (B2) phase is crystallized or precipitated in layers, and lamellar organization is observed at an Al content of 3% or more. However, when an excessive amount of Al exceeding 13% is contained, the matrix becomes β phase and the ratio of the lamellar structure is remarkably reduced. Preferably, the Al content is selected in the range of 4 to 10%.
Ni, Fe, and Mn are effective components for stabilizing the α phase and contribute to the improvement of ductility. However, excessive addition adversely affects the formation of lamellar structure, so Ni: 0.01 to 50% (preferably 5 to 40%), Fe: 0.01 to 40% (preferably 2 to 30%) , Mn: The content of Ni, Fe, Mn is determined in the range of 0.01 to 30% (preferably 2 to 20%). When two or three of Ni, Fe and Mn are added simultaneously, the total addition amount is 0.01 to 60% (preferably 2 to 40%, more preferably 5 to 25%) for the same reason. Select.
Cr, Mo, and Si are effective components for improving the corrosion resistance, but excessive addition causes a significant deterioration in ductility. When adding Cr, Mo, Si, Cr: 0.01 to 40% (preferably 5 to 30%), Mo: 0.01 to 30% (preferably 1 to 20%), Si: 0. The content is selected in the range of 01 to 5% (preferably 1 to 3%).
W, Zr, Ta, and Hf are effective components for improving the strength. However, excessive addition causes a significant deterioration in ductility. When W, Zr, Ta, and Hf are added, W: 0.01 to 30% (preferably 1 to 20%), Zr: 0.01 to 10% (preferably 0.1 to 2%), The content is selected in the range of Ta: 0.01 to 15% (preferably 0.1 to 10%) and Hf: 0.01 to 10% (preferably 0.1 to 2%).
Ga, V, Ti, Nb, and C have an effect of promoting the formation of precipitates and crystallized substances. However, when excessively added, the occupation ratio of the lamellar structure with respect to the entire metal structure tends to decrease. When adding, Ga: 0.01-20% (preferably 5-15%), V: 0.01-20% (preferably 0.1-15%). Ti: 0.01 to 12% (preferably 0.1 to 10%), Nb: 0.01 to 20% (preferably 0.1 to 7%), C: 0.001 to 3% (preferably Is selected in the range of 0.05 to 2%).
Rh, Pd, Ir, Pt, and Au are effective components for improving X-ray contrast properties, corrosion resistance, and oxidation resistance. However, when added excessively, the generation of lamellar tissue tends to be suppressed. When added, Rh: 0.01 to 20% (preferably 1 to 15%), Pd: 0.01 to 20% (preferably 1 to 15%), Ir: 0.01 to 20% (preferably 1-15%), Pt: 0.01-20% (preferably 1-15%), Au: 0.01-10% (preferably 1-5%) To do.
B is an effective component for crystal grain refinement, but if an excessive amount of B is contained, the ductility is remarkably lowered. Therefore, when B is added, the B content is selected in the range of 0.001 to 1% (preferably 0.005 to 0.1%).
P is an effective component for deoxidation, but if an excessive amount of P is contained, the ductility is significantly lowered. When added, the P content is selected in the range of 0.001 to 1% (preferably 0.01 to 0.5%).
When a Co-based alloy adjusted to a predetermined composition is melted and then cast and cooled, f. c. c. The α phase and β (B2) phase of the structure crystallize while forming a lamellar structure. Assuming that the growth rate is V, the lamellar interval is proportional to V ^−1/2 , so that the growth rate V, and hence the lamellar interval, can be controlled by the cooling rate. From the relationship between the cooling rate and the lamellar interval, it can be said that the higher the cooling rate, the finer the lamellar interval. However, in order to stably form a lamellar structure, a temperature range of 1500 to 600 ° C is averaged at 500 ° C / min. It is preferable to solidify at a cooling rate below (preferably 10 to 450 ° C./min).
Although sufficiently satisfactory properties can be obtained even with a cast material, it is possible to improve the properties by hot working, cold working, strain relief annealing, and the like. The cast material is subjected to forging and hot rolling as necessary, and is formed into a target-size plate, wire, tube, or the like by cold working such as rolling, drawing, or swaging.
When a lamellar structure is produced by heat treatment, it undergoes steps of solution treatment and aging treatment.
First, the cold-worked Co-based alloy is subjected to a solution treatment at a temperature of 900 to 1400 ° C. The precipitate is solid-dissolved in the matrix by the solution treatment, the strain introduced in the process up to the cold working is removed, and the material is homogenized. Since the solution temperature needs to be set sufficiently higher than the recrystallization temperature, it is set to 900 ° C. or higher and the melting point (1400 ° C.) or lower. Preferably, the solution temperature is set in the range of 1000 to 1300 ° C.
When the solution-treated Co-based alloy is subjected to an aging treatment at a temperature of 500 to 900 ° C., a lamellar structure in which a β (B2) phase and the like are deposited in layers in an α-phase matrix is formed. In order to promote layered precipitation, the aging temperature is set to 500 ° C. or more at which sufficient diffusion occurs. However, high-temperature heating exceeding 900 ° C. is governed by body diffusion, and precipitates are formed mainly inside the crystal grains, which are generated by grain boundary reactions. Precipitates in a form different from the layered precipitates are easily formed. Therefore, the aging temperature is selected in the range of 500 to 900 ° C. (preferably 550 to 750 ° C.). Prior to the aging treatment, cold working may be performed in order to promote lamellar structure formation. Generally, when the aging temperature is lowered, the layer spacing becomes fine, and the volume fraction of precipitates including the β (B2) phase increases. Miniaturization of the layer spacing can also be achieved by shortening the aging time.
Furthermore, when cold processing such as rolling, drawing, swaging, etc. is performed on the Co-based alloy in which the lamellar structure is formed, the lamellar structure is stretched along the processing direction, and the structure refinement and work hardening further progress. High strength is imparted. The effect of cold working on strength improvement is seen at a processing rate of 10% or more, but an excessive processing rate increases the burden on processing equipment, so it is preferable to set the upper limit to about 99%.
The fact that it can be formed into the target shape by cold working after lamellar organization is the effect of adding workability improving elements such as Ni, Fe, Mn, etc., and is important for the development of applications of Co-based alloys with excellent strength and wear resistance It will give the performance. Although annealing may be performed in the middle of processing or while annealing may be performed, the final shape may be either processed or heat-treated. Specifically, the required characteristics differ depending on the application, but the degree of refinement of the lamellar structure required for the required characteristics can be adjusted by the degree of processing during cold working and the heat treatment conditions before and after.
Regardless of whether controlled cooling during casting or aging treatment, the heating conditions are controlled so that the ratio of the lamellar structure in the entire metal structure is 30% by volume or more, resulting in high strength, high toughness, etc. derived from the lamellar structure The characteristics are given. F. c. c. When the layer interval between the α phase and β (B2) phase of the structure is 100 μm or less, the characteristics resulting from the lamellar structure can be effectively utilized.
The lamellar structure produced in the solidification process is relatively coarse, and the lamellar structure produced by the aging treatment is relatively fine. Thus, when combining the formation of a lamellar structure by solidification and aging, a composite structure having both a coarse lamellar structure and a fine lamellar structure is also possible. However, in a structure in which the layer interval exceeds 100 μm, there is a possibility that the performance unique to the lamellar structure cannot be sufficiently exhibited.
The excellent properties often depend on a fine lamellar structure and are homogenized throughout the Co-based alloy. In addition, the inherent corrosion resistance of the Co-base alloy, which is superior to that of austenitic stainless steel, can be utilized. Therefore, constant characteristics can be obtained even if the wire is thinned and miniaturized, so springs, springs, wires, cable guides, steel belts, bearings, overlaying materials and guidewires, stents, catheters and other medical devices, artificial tooth roots, Used as a product with high quality and reliability, such as biomaterials such as artificial bones.
Next, the present invention will be specifically described by way of examples with reference to the drawings.

ラメラー組織の占有率が１００体積％に達した試験Ｎｏ．５（熱処理によるラメラー組織化），試験Ｎｏ．７（凝固冷却の制御によるラメラー組織化）を基本系とし、Ｎｉ，Ｆｅ，Ｍｎ等が加工性改善に及ぼす影響を調査した。表３には、試験Ｎｏ．５，７のＣｏ−Ａｌ二元合金に対する加工性改善元素の種類，添加量及び物性を示すが、試験Ｎｏ．５，７とＡｌ含有量が異なるＣｏ基合金でもＮｉ，Ｆｅ，Ｍｎ添加による同様な傾向が確認された。
表３にみられるように、ラメラー組織がＳＥＭ像の視野全域に生成したＣｏ−Ａｌ合金を冷間加工するとラメラー組織の層間隔が狭まり、強度，耐摩耗性の改善が図られた。強度，耐磨耗性向上に及ぼす加工性の影響は１０％以上の加工率が必要であるが、所定量のＮｉ，Ｆｅ，Ｍｎ添加によりクラック等の加工欠陥なく目標形状に加工できることが判る。これは、Ｎｉ，Ｆｅ，Ｍｎ等でα相が軟質化されて加工時に必要なメタルフローが確保された結果と推察される。
表３中、強度に関してはＪＩＳ Ｚ２２４１に準拠した引張試験で求めた。
耐摩耗性に関しては、ＳＵＪ−２を相手材とし大越式摩耗試験機で摩耗量を測定し、摩耗量の測定値から演算された比摩耗量を指標とした。比摩耗量：１×１０^−６ｍｍ^２／ｋｇ以下を◎，（１．０〜５．０）×１０^−６ｍｍ^２／ｋｇを○，（５．０〜１０）×１０^−６ｍｍ^２／ｋｇを△，１０×１０^−６ｍｍ^２／ｋｇ以上を×として耐摩耗性を評価した。
冷間加工性試験では、冷間圧延，引抜き，据込み鍛造で試験片が破断するまで加工率を上げ、破断時の加工率を求めた。何れの加工法による場合も、圧下率，断面減少率，減厚率が２０％未満を×，２０％以上で４０％未満を△，４０％以上を○として加工性を評価した。

Co-Al binary alloys to which Al was added in various proportions were melted and cast. Test No. In Nos. 7 to 9, the cast structure generated in the solidification / cooling process was kept as it was. Test No. In Nos. 1-6, the steel sheet was cold-rolled to a thickness of 1 mm through hot rolling, and the cold-rolled sheet was made into a lamellar structure by a heat treatment of solution treatment: 1200 ° C. × 15 minutes, aging: 600 ° C. × 12 hours.
The Co-Al alloy plate subjected to aging treatment was observed with a microscope, and the precipitation state of the β (B2) phase was investigated. As can be seen from the results of the investigation in Table 2, the test No. 1 maintained the Al content in the range of 3 to 13%. For 2-6 Co-Al alloys, f. c. c. A β (B2) phase was deposited in a layered manner on the α phase matrix of the structure. As a result, test no. A clear lamellar structure was formed as seen in FIG.
Test No. In the case of the Co-Al alloys Nos. 7 and 8, the crystallization reaction is controlled by the cooling conditions of the solidification process. c. c. The structure had a lamellar structure in which the α phase and β (B2) phase were repeated. Test No. As compared with test No. 7, test No. In 8, the layer spacing was widened.
On the other hand, Test No. with Al content of less than 3%. In the case of Co-Al alloy No. 1, precipitation of the β (B2) phase was insufficient and the structure was substantially an α single phase. Conversely, No. containing an excess amount of Al exceeding 13%. In the 9, 10 Co—Al alloys, the matrix became β (B2) phase, and the ratio of the lamellar structure was extremely reduced in both cases of controlled cooling and aging treatment in the casting solidification process.
Table 2 also shows the volume ratio and the layer spacing converted from the area ratio of the lamellar structure determined by the image processing of the SEM image.

Test No. in which the occupancy of the lamellar structure reached 100% by volume. 5 (lamellar organization by heat treatment), test no. 7 (lamellar organization by control of solidification cooling) was used as a basic system, and the influence of Ni, Fe, Mn, etc. on workability improvement was investigated. Table 3 shows the test no. The type, amount and physical properties of workability improving elements for Co-Al binary alloys Nos. 5 and 7 are shown. The same tendency due to the addition of Ni, Fe and Mn was confirmed even in Co-based alloys having different Al contents from 5,7.
As shown in Table 3, when the Co-Al alloy having a lamellar structure generated in the entire field of view of the SEM image was cold worked, the layer spacing of the lamellar structure was narrowed, and the strength and wear resistance were improved. The effect of workability on strength and wear resistance improvement requires a processing rate of 10% or more, but it can be seen that a predetermined amount of Ni, Fe, Mn can be processed into a target shape without processing defects such as cracks. This is presumed to be a result of the α-phase being softened by Ni, Fe, Mn, etc. and the necessary metal flow being ensured during processing.
In Table 3, the strength was determined by a tensile test based on JIS Z2241.
Regarding the wear resistance, the wear amount was measured with an Ogoshi type wear tester using SUJ-2 as a counterpart material, and the specific wear amount calculated from the measured value of the wear amount was used as an index. Specific wear amount: 1 × 10 ⁻⁶ mm ² / kg or less ◎, (1.0 to 5.0) × 10 ⁻⁶ mm ² / kg ○, (5.0 to 10) × 10 ⁻⁶ mm ² Abrasion resistance was evaluated with Δ / kg being Δ and 10 × 10 ⁻⁶ mm ² / kg or more being ×.
In the cold workability test, the work rate was increased until the test piece broke by cold rolling, drawing, and upset forging, and the work rate at break was determined. In any of the processing methods, the workability was evaluated assuming that the rolling reduction, the cross-sectional reduction rate, and the thickness reduction rate were less than 20% x, 20% or more and less than 40% Δ, and 40% or more ○.

更に、ラメラー組織が形成された試験Ｎｏ．２４，２５，２８の熱処理ままの合金を種々の加工度でスエージングし、加工によるラメラー組織，物性の変化を調査した。
表５の調査結果にみられるように、ラメラー組織がスエージング方向に伸長し、ラメラー組織が一層微細化した（図３）。ラメラー組織の微細化は加工硬化と相俟って、Ｃｏ基合金の物性向上にも有効であった。このような冷間加工の効果は、１０％以上の断面減少率でみられ、断面減少率が大きくなるほど顕著になった。

Test No. 1 in which the densest lamellar structure was produced in Example 1 was obtained. Taking 12 Co-based alloys as an example, the effect of temperature conditions of solution treatment and aging treatment on the layered precipitation of β (B2) phase was investigated.
As seen in the investigation results in Table 4, the layered precipitation of β (B2) phase is promoted under the conditions satisfying the solution temperature: 900 to 1400 ° C. and the aging temperature: 500 to 900 ° C., and the target lamellar structure is Obtained. Also, the blending of Ni stabilizes the ductile rich α phase and softens the β (B2) phase, so the ductility is greatly improved, and the lamellar without microcracks even after cold rolling into a predetermined shape at a processing rate of 40%. Tissue was observed.
At an aging temperature of less than 500 ° C., the formation and growth of the β (B2) phase was insufficient and no lamellar texture was formed, and at an aging temperature of more than 900 ° C., the β (B2) phase was no longer layered. In addition, test No. that did not reach the solution temperature. In No. 21, since the precipitate was not a solid solution sufficiently and was subjected to aging treatment, the residue of the precipitate inhibited the generation of the lamellar structure. However, when the solution treatment was performed at a high temperature exceeding 1400 ° C., a liquid phase appeared due to partial melting, so that the liquid-derived mass was mixed with the layer.

Furthermore, Test No. in which a lamellar structure was formed. 24, 25, and 28 as-treated alloys were swaged at various degrees of processing, and changes in lamellar structure and physical properties due to processing were investigated.
As seen in the investigation results in Table 5, the lamellar structure was elongated in the swaging direction, and the lamellar structure was further refined (FIG. 3). The refinement of the lamellar structure was effective in improving the physical properties of the Co-based alloy in combination with work hardening. The effect of such cold working was seen at a cross-sectional reduction rate of 10% or more, and became more prominent as the cross-sectional reduction rate increased.

An optional component was added to a Co-6.9% Al-21.6% Ni alloy, and the influence of the optional component on lamellar structure and mechanical properties was investigated. In the corrosion test, the passive holding current density at 0 V vs SCE was measured by an anodic polarization test using a PBS (−) solution at 25 ° C., and the passive holding current density was 0.05 A / m ² or less. the .05~0.1A / ^{m 2} ○, the 0.1~0.3A / ^{m 2} △, was evaluated the corrosion resistance as × a 0.3 a / ^{m 2} or more.
In addition, workability was evaluated according to the same criteria as in Example 1.
As can be seen from the investigation results in Table 6, the lamellar structure was maintained in any of the tests of the present invention examples, and the corrosion resistance, strength, elongation, and the like were improved by the addition of optional components. For this reason, even if cold working was performed at a working rate exceeding 10%, there was no working defect such as a crack, and the target shape could be obtained.

  As explained above, a Co-based alloy in which Ni, Fe, and Mn are added as a workability improving element to a Co—Al binary system of Al: 3 to 13% is obtained after controlled cooling or solution treatment after casting. It is aging and lamellar texture, and it is a material that shows sufficient strength even if it is thinned and refined. In addition, since the workability is improved, even if cold working such as rolling, drawing or swaging is performed, it can be formed into a predetermined shape without any processing defects. Therefore, it can be processed into the target shape necessary for various applications without impairing the characteristics of the Co-Al binary alloy due to the fine lamellar structure, spring, spring, wire, cable guide, steel belt, bearing, overlay material, It is used in a wide range of fields such as guide wires, stents, catheters, artificial bones, and artificial tooth roots.

Claims (5)

One or more workability improving elements selected from Ni: 0.01 to 50%, Fe: 0.01 to 40%, Mn: 0.01 to 30% by mass ratio: 0.01 to 60% And Al: 3 to 13%, with the balance being the basic composition of Co and impurities,
f. c. c. A high-strength Co-based alloy characterized by a metal structure in which a lamellar structure in which the α phase of the structure and the B2 type β phase are repeated at a layer interval of 100 μm or less accounts for 30% by volume or more. In addition to Al: 3 to 13% and workability improving element: 0.01 to 60% by mass ratio, Cr: 0.01 to 40%, Mo: 0.01 to 30%, Si: 0.01 to 5 %, W: 0.01-30%, Zr: 0.01-10%, Ta: 0.01-15%, Hf: 0.01-10%, Ga: 0.01-20%, V: 0 .01-20%, Ti: 0.01-12%, Nb: 0.01-20%, C: 0.001-3%, Rh: 0.01-20%, Pd: 0.01-20% , Ir: 0.01-20%, Pt: 0.01-20%, Au: 0.01-10%, B: 0.001-1%, P: 0.001-1% Or a total of 0.001 to 60% of two or more, with the balance having the composition of Co excluding inevitable impurities, f. c. c. Α phase and B2 type β-phase structure, L1 ₂ type gamma 'phase, _{D0 19} type precipitates and / or _M 23 _{C 6} type carbide and the layer spacing: having a lamellar structure repeated at 100μm or less A high-strength Co-based alloy characterized in that a lamellar structure occupies 30% by volume or more of the entire metal structure. After melting the Co-based alloy having the composition according to claim 1 or 2, the temperature range of 1500 to 600 ° C is cooled and solidified at an average cooling rate of 500 ° C / min or less, f. c. c. Α phase and B2 type β-phase structure, and characterized in that the lamellar structure of and L1 ₂ type gamma 'phase, D0 ₁₉ type precipitates and / or M ₂₃ and C ₆ type carbide was out layered crystal A method for producing a high-strength Co-based alloy. After the solution treatment of the Co-based alloy having the composition of claim 1 or 2 at 900 to 1400 ° C., aging treatment at 500 to 900 ° C. f. c. c. Α phase and B2 type β-phase structure, L1 ₂ type gamma 'phase, wherein the D0 ₁₉ type precipitates and / or M ₂₃ and C ₆ type carbide to the lamellar structure of by stratified deposit A method for producing a high-strength Co-based alloy. The method for producing a high-strength Co-based alloy according to claim 3 or 4, wherein the Co-based alloy after the formation of the lamellar structure is subjected to cold working with a processing rate of 10% or more.

Images