WO2007114439A1 - Materiau ayant un tissu granulaire superfin et son procede de production - Google Patents

Materiau ayant un tissu granulaire superfin et son procede de production Download PDF

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Publication number
WO2007114439A1
WO2007114439A1 PCT/JP2007/057478 JP2007057478W WO2007114439A1 WO 2007114439 A1 WO2007114439 A1 WO 2007114439A1 JP 2007057478 W JP2007057478 W JP 2007057478W WO 2007114439 A1 WO2007114439 A1 WO 2007114439A1
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alloy
metal
rolling
twins
temperature
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PCT/JP2007/057478
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English (en)
Japanese (ja)
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Hiromi Miura
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National University Corporation The University Of Electro-Communications
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Priority to US12/295,640 priority Critical patent/US20090165903A1/en
Priority to JP2008508699A priority patent/JPWO2007114439A1/ja
Publication of WO2007114439A1 publication Critical patent/WO2007114439A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C9/00—Alloys based on copper
    • C22C9/04—Alloys based on copper with zinc as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon

Definitions

  • the present invention relates to a material having an ultrafine grain structure and a method for producing the same.
  • Crystal grain refinement also has another advantage of improved material processability. Therefore, various studies on crystal grain refinement have been conducted.
  • the most common grain refinement method is a so-called thermomechanical treatment method.
  • crystal grains are refined by heat-treating the processed material under various conditions. For example, a method of refining crystal grains by recrystallizing a hot-rolled copper alloy at a temperature of about 300 ° C to 400 ° C has been proposed (Patent Document Do, A method has been proposed in which a ferrous metal after rolling or cold rolling is annealed at a temperature of about 750 ° C. to refine crystal grains (Patent Document 2).
  • the crystal grain size obtained by this method is at least about 1 ⁇ m.
  • Typical examples of ultra-strong processing methods are ECAP (Equal Channel Angular Press) method and ARB (Accumulate Roll Bonding method).
  • the ECAP method is a method in which a metal material called a billet is inserted into an L-shaped mold and extruded from the opening, and the crystal grains are made ultrafine without changing the shape.
  • the ARB method is a method in which the plate material is rolled to about 50%, cut in half, two cut plates are stacked, and this is rolled again several times. Through a series of treatments, the crystal grains of the material can be made ultrafine.
  • Non-Patent Document 2 is a method in which the plate material is rolled to about 50%, cut in half, two cut plates are stacked, and this is rolled again several times. Through a series of treatments, the crystal grains of the material can be made ultrafine.
  • Patent Document 1 International Publication No. 2004Z022805 Pamphlet
  • Patent Document 2 Japanese Patent Laid-Open No. 62-182219
  • Non-patent literature 1 RZ Valiev, Islamic Galiev (RK Islamgaliev), Alexa Ndrov (IV Alexandrov), Material Science (Mat. Sci.), 45 ⁇ , 2000, p.103
  • Non-Patent Document 2 Shin Yabu, Iron and Steel, 2002, 88 ⁇ , p.359-369
  • the ECAP method described above is not suitable for industrial ultrafine grain processing because it requires a large number of processing steps and cannot produce a long material.
  • the ARB method described above in the thickness direction, crystal grains with a grain size of about 0.1 ⁇ m can be obtained. In the force rolling surface, the crystal grains become coarse and uniform in the in-plane direction. It is not possible to obtain an equiaxed ultrafine grained structure. Therefore, there may arise a problem that the strength distribution of the material becomes non-uniform or the material does not have a desired strength.
  • This method is also not suitable for industrial mass production with many processing steps. For this reason, there is a need for a crystal grain refinement technology that can form an equiaxed and uniform ultrafine grain structure more easily and increase the material strength.
  • the present invention has been made in view of such problems, and provides a material having a high-strength ultrafine grain structure and a method capable of easily manufacturing such a material. It is an issue to provide.
  • twin in the present application is a concept including a deformation twin.
  • a material having an ultrafine grain structure made of a metal or an alloy having a stacking fault energy of 50 mjZmm 2 or less and having a crystal grain size of 20 ⁇ A material characterized by having recrystallized grains in the range of ⁇ 600 nm is provided. By setting the material structure to such a characteristic recrystallized structure, a material having high strength and uniform ultrafine crystal grains can be obtained. [0010] Further, in the present invention, there is provided a method for producing a material having an ultrafine grain structure, the step of providing a metal or alloy having a stacking fault energy of 50 mjZmm 2 or less, and processing the metal or alloy. And introducing a deformation twin having a twin spacing of 200 nm or less into the metal or alloy structure.
  • the step of introducing the deformation twin may include a step of subjecting the metal or the alloy to a multiaxial forging process (hereinafter also referred to as “MDF processing”) at a temperature of room temperature or lower.
  • MDF processing multiaxial forging process
  • said step of multi-axis forging process 1 X 10- 4 Z seconds or strain rate, good have a step of forging the metal or alloy! ⁇ .
  • MDF processing at a high strain rate can increase the deformation resistance of the material, making it easier to introduce deformation twins into the material.
  • the temperature below room temperature is preferably an absolute temperature of 223 K or less.
  • the deformation resistance of the work material can be easily increased, so that the same effect as when the strain rate is increased can be obtained more easily. it can. Therefore, a material having an ultrafine grain structure can be provided more easily.
  • the forging process there may be a step of annealing the metal or alloy that has been subjected to the multi-axis forging process. Thereby, the material structure after forging can be made homogeneous.
  • the step of introducing the deformation twin may include a step of rolling the metal or alloy at a temperature of room temperature or lower.
  • this method it is possible to introduce high-density deformation twins into the material structure relatively easily as soon as cutting stress is applied to the material. Therefore, when this method is applied, the crystal grains can be made ultrafine more easily than the MDF processing method described above.
  • a step of annealing the rolled metal or alloy may be added. Thereby, the material structure after rolling can be homogenized.
  • the step of annealing after forging or rolling is performed by annealing the metal or alloy at a temperature of 0.5 X Tm or less, where Tm is the melting point of the metal or alloy. Prefer to have a step ⁇ . By performing the annealing treatment at such a temperature, it becomes possible to make the structure uniform without coarsening the ultrafine grains obtained after forging or rolling.
  • the step of rolling may include the step of rolling the metal or alloy at a rolling speed of 5 X 10-mZ seconds or more. Since the deformation resistance can be increased by increasing the rolling speed, a large number of deformation twins can be introduced into the material structure.
  • the step of rolling may include a step of rolling the metal or alloy so that a final reduction ratio is 20% or more. Since the deformation resistance can be increased by increasing the rolling reduction, a large number of deformation twins can be introduced into the material structure.
  • the rolling step includes a step of rolling the metal or alloy at an absolute temperature of 223K or lower.
  • the deformation resistance of the material can be increased. Therefore, a large number of deformation twins can be introduced without increasing the rolling speed and Z or the rolling reduction during rolling, and a material having an ultrafine grain structure can be provided more easily.
  • the first packet includes a layered twin group substantially oriented in the first direction
  • at least one of the twins in the first packet includes:
  • a second packet comprising a layered twin group substantially oriented in a second direction, wherein the first direction and the second direction include those forming an angle other than 60 degrees.
  • a material having an ultrafine grain structure is provided.
  • packet means a layered twin group oriented in the same crystal orientation as described later.
  • a first yarn and weaving including a first packet including a plurality of layered twin groups oriented substantially in the first direction in one crystal grain.
  • At least one of the twins has a first structure having a second packet comprising a twin group oriented in a second direction substantially different from the first direction; and the first packet And a third structure containing recrystallized grains formed of a plurality of layered twins oriented in substantially the same direction.
  • a material having an ultrafine grain structure is provided.
  • the material having such an ultrafine grain structure may be brass.
  • a high-strength material having an ultrafine grain structure is provided.
  • a material having such an ultrafine grain structure can be obtained relatively easily.
  • FIG. 1 is a diagram schematically showing an example of a structure diagram of a material having an ultrafine grain structure of the present invention.
  • FIG. 2 is a schematic explanatory diagram of an MDF cache processing method.
  • FIG. 3 is a stress strain curve of a copper 30 mass% zinc material manufactured by the ultrafine grain processing method (MDF processing method) of the present invention.
  • FIG. 5 A structure chart (OIM map) of a copper 30 mass% zinc alloy sample after annealing at 503 K for 8 hours after cryogenic rolling treatment using an orientation dispersion analyzer.
  • FIG. 6 is a diagram schematically showing an example of an apparatus configuration for carrying out the ultrafine grain processing method of the present invention.
  • FIG. 8 A graph showing changes in the Vickers hardness of a material when 60% of a copper 30mass% zinc alloy is rolled at 77K and then annealed at temperatures of 503K, 523mm and 543mm.
  • FIG. 9 A structural photograph of a copper 30mass% zinc alloy rolled 60% at 77% and annealed at 523K for 1000 seconds.
  • (B) is an enlarged view of (a).
  • FIG. 10 is a graph showing the relationship between the annealing time and the average grain size in the material structure when 60% of a 30 mass% zinc alloy is rolled at 77K and then annealed at both temperatures of 503K and 523K.
  • FIG. 11 is a diagram showing a stress-strain curve at room temperature of pure copper after performing MDF cache treatment at a cryogenic temperature of 77K and room temperature (300K).
  • a material having an ultrafine grain structure is produced by a method characterized by comprising:
  • the “ultrafine grain structure” means a structure having an “average crystal grain size” force of less than 1 ⁇ m.
  • the average crystal grain size is measured for the deformed structure from the transmission electron microscope (TEM) photograph using the linear crossing method, and for the annealed structure, the orientation dispersion analyzer (Orientation Imaging MicroscopyZOIM) ) In the crystal orientation distribution image obtained by the analysis, the structure having a boundary with an orientation difference of 3 degrees or more is taken as the crystal grain and calculated from the average grain area.
  • twins are considered not to contribute to the mechanical strength of materials, and it is considered important to exclude twins from crystal yarns and weaves in order to improve the mechanical strength of materials. It was done.
  • this twin is actively introduced into the material structure, It is characterized in that the grains are made finer, thereby improving the material strength.
  • a large number of deformation twins are introduced into the material structure by performing processing with large deformation on the workpiece material, and these deformation twins The crystal grains are made ultrafine by cutting. According to the study of the present inventor, by such processing
  • the mechanical strength of the material is remarkably improved when an ultrafine grain structure having a twinning force of deformation twins of not more than 00 is obtained.
  • twin spacing is included in the distance D of the arrow, that is, in one twin 110 in the ultrafine grain structure 100 having a plurality of twins 110 as shown in FIG. The interval between twin lines and the twin lines adjacent to them.
  • twin spacing cannot be measured with a normal optical microscope, in the present application, from a structural photograph obtained by observation at about 8000 to 80000 times with a transmission electron microscope, The twin spacing of twins contained in the ultrafine grain structure is measured.
  • the processing method for introducing a large number of such deformation twins into the material is not particularly limited, and various methods can be used.
  • MDF Multi-direction al forging
  • This method is also called a multi-axis forging method, and is a processing method that repeats compression by changing the forging direction of the work material so that the major axis direction becomes the compression direction for each forging process in one direction.
  • FIG. Figure 2 is a schematic illustration of the MDF processing method.
  • a bulk material with a rectangular aspect ratio as shown in Fig. 2 (1) is prepared.
  • the aspect ratio of the bulk material is determined by the compression ratio by forging from each axial direction shown in (2) to (4) (each forging is called a pass).
  • each forging is called a pass.
  • the aspect ratio of the bulk material can be changed according to the compression rate for each pass to be adopted. In the example in the figure, this corresponds to a case where the processing strain for one pass is 0.4. When one processing strain is increased, deformation resistance increases, and deformation twins are more likely to appear.
  • the strain that can be introduced into the material in one pass is 0.8 (in that case, the aspect ratio is 1.0: 1.49: 2.22), theoretically, the total strain should be 2.4 This means that 3 pass processing is required.
  • MDF cache treatment a large number of deformation twins can be introduced into the material. Further, the crystal grains are refined by the crossing of the introduced deformation twins.
  • MDF caloche processing multi-directional force materials are compressed, so that an equiaxed ultrafine grain structure can be obtained after processing.
  • this processing method can form a superfine grain structure in a material by a simple processing process of changing the compression axis and repeating forging, so mass production of a material with an ultrafine grain structure is easy. There is a feature that can be.
  • deformation resistance the resistance to deformation of the material
  • the MDF processing method when adopted as a processing method for introducing the deformation twins, it is preferable that the MDF processing is performed at a temperature of room temperature (300K) or less. As a result, the deformation resistance during processing can be further increased, and more deformation twins can be introduced at one time. Further, when the MDF mosquitoes ⁇ E processed in under "cryogenic" below 223 K (absolute temperature), the processing speed is selected so the strain rate of about 1 X 10- 4 Z seconds or more, Otherwise, it is preferable to select as the strain rate of about 5 X 10- 4 Z seconds. If a large strain rate is selected, the amount of deformation applied to the material for each pass can be increased, and the deformation resistance can be increased, so that the processing temperature is high (about room temperature). However, more deformation twins can be introduced into the material structure.
  • the major axis direction of the work material becomes the compression direction for each processing.
  • Such an operation can be easily performed by using, for example, an electric or mechanical work material position (or direction) control means such as a manipulator. This eliminates the hassle of changing the orientation of the material to be coated for each pass.
  • a material having an ultrafine grain structure 100 composed of a large number of twins 110 as schematically shown in FIG. 1 can be obtained.
  • the average grain size is at most in the range of about 500 nm to less than 1 ⁇ m, and the twin spacing is about 80 to 10 Onm.
  • Such deformed twins tend to appear parallel to one direction within one grain, but when the sample is changed in the direction of addition and forged again, deformed twins in another direction appear, and both As deformed twins cut into each other, they change into ultrafine crystal grains.
  • the two crystals sandwiching the twin plane have an orientation difference of about 60 degrees, and due to the appearance of the deformation twin, the formation of the deformation twin itself, as well as the crossing and cutting of them.
  • An ultrafine grain structure surrounded by high misorientation grain boundaries is easily generated.
  • the forged material may be annealed! ⁇ .
  • the annealing treatment is preferably performed at the lowest possible temperature. This is because if the processing temperature is increased, the growth of ultrafine crystal grains may be promoted.
  • the annealing temperature is preferably 0.5 Tm or less. For example, in the case of a copper-one 30 mass% zinc alloy, the melting point of this alloy is 1223K, so the processing temperature is 611K or less.
  • FIG. 3 shows an example of a stress strain curve at room temperature of a material having an ultrafine grain structure manufactured by the method of the present invention.
  • These test samples were produced by introducing strains of 0.4 (1 pass), 2.4 (6 passes) and 6.0 (15 passes) into a copper 30 mass% zinc alloy by the MDF processing described above. is there.
  • the upper figure shows the result of the sample manufactured by MDF force treatment at 77K, and the lower figure shows the result of the sample manufactured by MDF processing at room temperature (300K). Show me!
  • the maximum strength of this material, which has not been subjected to normal grain refinement, is about 500 MPa.
  • the maximum strength of the sample processed at MDF at 77K increased from 600MPa to 900MPa, and the introduced strain was 0.4 (1 pass) in the sample processed at MDF at 300K. Except for the sample, the maximum intensity increases from 700 MPa to 800 MPa!
  • FIG. 4 shows a structure photograph of the sample after the MDF processing. This sample was manufactured by introducing strain of 6.0 (15 passes) into a copper-30mass% zinc alloy by the MDF caloe process described above.
  • the photo (a) on the left shows the organization after the MDF cache treatment at 77K.
  • the middle photo (b) is after the MDF cache processing at 300K.
  • the right figure (c) shows an enlarged schematic view of a part of the central tissue photograph.
  • layered twins oriented in the same crystal orientation are formed in the crystal grains of the sample after the MDF cache treatment.
  • a layered twin group will be specifically referred to as “packet” (or packet 120).
  • packet 120 When the twins in the packet 120 are observed in more detail, a second packet having a smaller layered twin group is formed inside one twin. It can be seen that the twins included in the packet are oriented in the same crystal orientation.
  • Such a structure is considered to be caused by repeating the deformation process by MDF processing, so that the twins in the packet 120 are divided into smaller twin groups.
  • twins included in a twin group constituting one packet are divided into finer layered twin groups each time a deformation process is applied, whereby further fine packets are separated. As it is formed, the crystal grains are refined and an ultrafine grain structure is formed.
  • the difference in orientation between the twin groups is 60 degrees.
  • twins introduced by MDF processing by repeating the deformation process, the packet existing before the deformation process is deformed, and the twins constituting the packet are crystal rotated. Occurs. Therefore, the orientation of the twin group forming the first packet generated by the first deformation process and the twin group formed in the twin of the second packet generated by the second deformation process. The difference will be at an angle other than 60 degrees.
  • Another processing method for introducing a large number of deformation twins is a rolling method.
  • shear stress is applied to the material, and a high-density deformation twin can be introduced into the material structure relatively easily. Therefore, when this method is applied, it is possible to make the crystal grains ultra finer more easily than the MDF processing method described above.
  • the rolling method can be applied to a large-scale material such as a large-area plate material that is less restricted by the shape of the material to be processed.
  • the processing conditions for rolling the material include “very low temperature processing”, “low temperature high speed processing”, “low temperature high pressure processing” or “high speed high pressure processing”! I prefer to use one or the other.
  • “cryogenic treatment” is a method of rolling in a state where the material to be rolled is kept at an “extremely low temperature” of 223 K (absolute temperature) or less.
  • cryogenic treatment the material temperature is lowered to a cryogenic temperature of 223K or lower, and the rolling treatment is performed. Therefore, the deformation resistance can be increased regardless of other processing condition parameters. That is, under these conditions, the deformation resistance state sufficient to form a large number of deformation twins can be obtained simply by maintaining the material at a very low temperature. The feature is that detailed control of other parameters is unnecessary.
  • Low-temperature high-speed treatment and “low-temperature high-pressure treatment” are methods in which rolling is performed while the material to be rolled is maintained at a temperature of about 223 to 300K (room temperature). Only by rolling at such a temperature, it is difficult to introduce high-density deformation twins as in the “cryogenic treatment”. Therefore, under these processing conditions, high-density deformation twins are introduced into the material to be rolled, in combination with parameters that increase the amount of deformation that can be applied to the material at one time.
  • a large amount of deformation twins is introduced into the material to be rolled by adding strain to the material to be rolled at a high speed in order to increase the deformation resistance.
  • the rolling speed needs to be higher than that in the “cryogenic treatment”, and is preferably at least 5 ⁇ 10 ⁇ mZ seconds.
  • the reduction rate of the material to be rolled is reduced by treating the material to be rolled under high pressure rolling conditions by taking advantage of the fact that deformation twins are more likely to be generated as the amount of strain increases.
  • the final reduction ratio of the material is preferably 20% or more.
  • it is desirable that the final reduction ratio is 60% or more for the viewpoint power to uniformly disperse the deformation twins.
  • high-speed and high-pressure treatment refers to a rolling treatment on a material to be rolled in a non-low temperature region such as room temperature. This is a method of increasing the deformation resistance of the material to be rolled and introducing high-density deformation twins by combining high-speed processing and high-pressure processing. For example, in the case of general rolling at room temperature, deformed twins appear when the rolling speed is 5 ⁇ 10-mZ seconds or more and the rolling reduction is 70% or more.
  • the above-mentioned rolled material may be annealed.
  • the annealing treatment is preferably performed at the lowest possible temperature. This is because if the processing temperature is increased, the growth of ultrafine grains may be promoted.
  • the annealing temperature is preferably 0.5 Tm or less.
  • the melting point of this alloy is 1223K, so the processing temperature is 611K or less.
  • FIG. 5 is a map using an orientation dispersion analyzer (OIM) of a sample that was subjected to a cryogenic rolling process at 77K (rolling rate: 60%) and annealed for 8 hours at a temperature of 503K. .
  • OIM orientation dispersion analyzer
  • the ultrafine grain structure produced by the method of the present invention does not progress so much even after annealing as will be described later. This is thought to be because a large number of deformation twins with different orientations contained in the structure play a role of restraining the crystal grains and suppress the grain growth. Therefore, the material having the ultrafine grain structure obtained by the method of the present invention has a significant characteristic if it is excellent in thermal stability.
  • the twin spacing as shown in FIG. An ultrafine grain structure containing a large number of deformation twins tends to be obtained more easily with a metal or alloy having a lower stacking fault energy. This is because, for metals or alloys with large stacking fault energy, even if processing such as MDF cache treatment is performed, the dislocation density accumulated in the material is difficult to increase, and the critical stress for generating deformation twins is applied to the material. This is because it is difficult to apply more stress. Therefore, the present invention is preferably applied to a metal or alloy having a stacking fault energy of 50 mj / mm 2 or less.
  • examples of metals or alloys with low stacking fault energy include silver (stacking fault energy of about 22 mjZmm 2 ), copper (78 mjZmm 2 ), cobalt (15 mjZmm 2 ), nickel (128 mj / mm 2 ), brass. (About 20mj / mm 2 ) and stainless steel (211mjZmm 2 ).
  • brass means an alloy of copper and zinc and contains 20 mass% or more of zinc (the aforementioned stacking fault energy is the value of copper 30 mass% zinc alloy). Even when the stacking fault energy of the metal or alloy itself exceeds 50 mj / mm 2 , stacking fault energy is remarkably increased by adding one or more impurity elements to such metal or alloy.
  • the stacking fault energy decreases to 5 mj / mm 2 . Therefore, it should be noted that the above-described stacking fault energy can be included in the scope of the present invention by adding an impurity element even in a metal or alloy or other alloy having 50 mjZmm 2 or more.
  • Fig. 6 schematically shows an example of a rolling apparatus for carrying out the method of the present invention (rolling treatment under cryogenic treatment conditions).
  • the rolling device 10 includes a cryogenic bath 50, a transport device 30, and a rolling roll 20.
  • the conveying device 30 is used to guide the material 40 to be rolled toward the rolling tool 20.
  • the cryogenic bath 50 is used to cool the material to be rolled 40 in advance.
  • the temperature of the cryogenic bath 50 is 223 K or less, but is particularly preferably a liquid nitrogen temperature (77 K) or less.
  • the position of the cryogenic bath 50 may be changed or deleted.
  • the material to be rolled 40 is cooled to the above-mentioned temperature immediately before the material to be rolled 40 passes through the rolling roll 20.
  • a cooling tank is provided in the middle of the conveyance path, the material to be rolled 40 passes through the cooling tank before being conveyed to the rolling roll 20, and the rolling portion of the material to be rolled 40 is cooled to the temperature as described above. It is okay to configure the device as described.
  • the rolling apparatus 10 can introduce deformation twins into the material to be rolled 40 such as a copper 30 mass% zinc alloy by the following operation.
  • the material 40 to be rolled that has been pre-cooled in the cryogenic bath 50 is placed on the conveying device 30.
  • the conveying device 30 is operated, and the material 40 to be rolled moves in the direction of the rolling roll 20.
  • the feed speed (rolling speed) of the material to be rolled 40 is preferably about 1 ⁇ 10 ⁇ mZ seconds or more, but is not particularly limited thereto.
  • the rolling reduction of one pass is preferably about 10 to 20%.
  • the force is not particularly limited to this. This is because, as described above, in the case of the cryogenic treatment condition, the influence of the reduction rate and the feed rate itself on the generation density of deformation twins is not significant.
  • Such an operation is repeated as many times as necessary (pass), and a large number of deformation twins are introduced into the material. It is preferable that the material to be rolled 40 be recooled every time one pass of the rolling process of the material to be rolled 40 is completed. Prevents the temperature of the material to be rolled 40 from being raised by the rolling process, and the temperature of the material to be rolled 40 cannot be maintained in the extremely low temperature range suitable for deformation twinning when the material to be rolled 40 is re-rolled. It is to do.
  • the material 40 to be rolled is maintained in an appropriate cryogenic temperature range after one pass rolling (for example, when the entire rolling processing apparatus 10 is installed in a low temperature environment), the material to be rolled It is also possible to repeatedly perform rolling of 2 to several passes in a range where the temperature of 40 does not exceed a predetermined value.
  • the material to be rolled 40 is kept at a very low temperature and the deformation resistance is sufficiently high, so that a large number of deformation twins can be easily introduced. Further, after the treatment, a material having an ultrafine grain structure can be obtained.
  • Annealing treatment may be performed using the material rolled in this manner! As described above, the annealing treatment is preferably performed at the lowest possible temperature. For example, when the melting point of the material is Tm, an ultrafine grain structure having recrystallized grains having a crystal grain size in the range of 20 nm 600 can be obtained by annealing at a temperature of 0.5 X Tm or less.
  • Experiment 1 MDF processing was performed using the test material, and the strength of the obtained material was evaluated.
  • Figure 7 shows the temperature 77K, the TEM observation tissue copper 30mas s% zinc alloy after the MDF processed in the true strain rate 1 X 10- 3 Zeta seconds.
  • the number of passes of the MDF cache process that covers the material is six, and the cumulative strain introduced into the material is 2.4.
  • many deformation twins are introduced into the material by MDF processing, and an ultrafine grain structure with an average crystal grain size of 1 ⁇ m or less is formed by the cross-cutting of these deformation twins.
  • the halo ring (a phenomenon in which diffraction spots are connected and appear in a ring shape) appears in the 1 / zm region limited field diffraction image circled in the figure.
  • halo ring is caused by the close proximity of diffraction spots corresponding to each particle when there are many crystals with different orientations in the structure. Therefore, it can be seen from this result that the material structure obtained by this method contains a large number of ultrafine crystal grains.
  • Fig. 3 shows the stress-strain curve at room temperature of the specimen obtained by MDF processing at temperatures of 77K and 300K (room temperature).
  • the amount of strain introduced into the material was changed to 0.4 2.4 and 6.0 by changing the number of passes of the MDF Karoe treatment to the material to 1, 6, and 15, respectively.
  • the strain force increased from .4 to 6.0 as shown in the upper part of the figure.
  • the maximum strength changed to 600MPa force 900MPa. Elongation was about 20% in all specimens.
  • the maximum strength of the same material obtained by conventional thermomechanical processing is usually around 500 MPa.
  • Experiment 2 the same material (copper-30ma SS % zinc alloy) as in Experiment 1 was used, and the cryogenic rolling process was performed, and the state of the resulting structure and its stability were evaluated.
  • a cryogenic rolling process was performed using the apparatus shown in FIG.
  • the material temperature during rolling was 77K.
  • the rolling reduction for each pass during rolling was in the range of 10% force and 20%.
  • the structure of the material after 60% rolling was observed with a transmission electron microscope (TEM). As a result, it was found that a very fine grain structure with a grain strength of about 500 nm to less than l ⁇ m was developed, similar to the structure shown in Fig. 1.
  • TEM transmission electron microscope
  • FIG. 8 is a graph showing changes in the Vickers hardness of the material when the material is rolled at 77K by 60% and then annealed at temperatures of 503K, 523%, and 543%. From this figure, it can be seen that although it depends on the annealing temperature, the hardness decreases rapidly after 10 3 10 4 seconds, and static recrystallization occurs after this time.
  • Fig. 9 shows a TEM photograph of a sample that was annealed for 1000 seconds at a temperature of 523K after a 30 mass% copper alloy was cryogenically rolled at 77% (rolling rate 60%).
  • the photo on the right is a high magnification view of the photo on the left. From these photographs, at the stage of annealing at 523K for 1000 seconds, the “packets” generated by the deformation process still remain! However, some “packets” have been recrystallized and static recrystallization has occurred. I found out that has started. Furthermore, it was found that recrystallized grains formed of a plurality of layered twins with uniform orientation were formed in part of the crystal grains. Since the recrystallized grains have a grain size of about 20 nm, the twins contained in the recrystallized grains are considered to have a grain size much smaller than 20.
  • FIG. 10 shows the relationship between the annealing time and the average crystal grain size in the material structure when the material was rolled 60% at 77K and then annealed at both temperatures of 503K and 523K.
  • the average crystal grain size was calculated by the straight line crossing method using a transmission electron microscope as a crystal grain with a boundary structure.
  • the reason why the structure having the boundary is the crystal grain is that the deformation twin contained in the structure has a high orientation difference of 60 degrees or more, and therefore, these structures are surrounded by the high orientation boundary. This is because it is obvious that it is a crystal grain.
  • the fine deformation twins developed inside the crystal grains are not used in the calculation, and the actual crystal grain size is even smaller than the value shown in FIG. It can be seen from Fig. 10 that the crystal grains are not coarsened even by the annealing treatment and are about 0.6 / zm at the maximum.
  • Fig. 5 shows an example of the structure when 60% of a 30mass% copper alloy is rolled at 77K and then annealed at 503K for 8 hours.
  • Figure 11 shows the stress-strain curve of pure copper at room temperature after the MDF cache treatment at 77K cryogenic temperature and room temperature (300K).
  • the horizontal axis is cumulative strain.
  • the cumulative strain exceeds 2%, the maximum stress becomes 380 MPa, and the maximum stress does not change even after ultra-strong stress treatment up to cumulative strain 6 is performed. I got it.
  • almost no deformation twins occurred.
  • the maximum stress was 590 MPa at a cumulative strain of 2.
  • the microstructure of the specimen with strain up to cumulative strain 2 was observed, it was found that some deformation twins were partially formed. However, deformation twins were generated non-uniformly, and it was impossible to obtain a uniform ultra-fine grain structure on the entire surface, such as the aforementioned copper 30 mass% zinc alloy. This result shows that even if the deformation stress is large, it is difficult to obtain a deformation twin when the stacking fault energy of the material is large.

Abstract

La présente invention concerne un procédé de production d'un matériau ayant un tissu granulaire superfin. Le procédé comprend les étapes consistant à : fournir un métal ou un alliage ayant une énergie de défaut d'empilement inférieure ou égale à 50 mJ/mm2 ; et traiter le métal ou l'alliage de façon à introduire un bicristal déformé ayant un espacement interbicristallin inférieur ou égal à 200 nm dans le tissu du métal ou de l'alliage. Le procédé permet de proposer un matériau ayant un tissu granulaire superfin, le matériau étant caractérisé en ce qu'il contient un bicristal dans le tissu cristallin et en ce qu'il a un espacement interbicristallin dans le bicristal inférieur ou égal à 200 nm.
PCT/JP2007/057478 2006-04-03 2007-04-03 Materiau ayant un tissu granulaire superfin et son procede de production WO2007114439A1 (fr)

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