CN112126875A - A kind of multi-level heterostructure dual-phase alloy and hot rolling method thereof - Google Patents

Abstract

The invention discloses a multi-level heterostructure dual-phase alloy and a hot rolling method thereof, wherein a zirconium-niobium alloy is kept at a temperature of 700-beta transition temperature for 10-60 min under an argon atmosphere, then the alloy is subjected to rolling deformation with a single-pass reduction of 10-30%, and the alloy is kept at the temperature and the atmosphere for 1-10 min again after every 1-3 passes until the total rolling reduction rate reaches 60-100%. And annealing the rolled zirconium-niobium alloy at the temperature and in the atmosphere for 1-30 min, and cooling to room temperature at different rates. Finally, stress annealing is carried out on the annealed zirconium-niobium alloy at the temperature of 300-500 ℃ in an argon atmosphere for 0.5-2 h, and air cooling is carried out to room temperature; the multi-level heterostructure dual-phase zirconium-niobium alloy prepared by the method has high plasticity, the yield strength is not less than 658MPa, the tensile strength is not less than 880MPa, and the fracture elongation is not less than 17.6%.

Description

A kind of multi-level heterostructure dual-phase alloy and hot rolling method thereof

technical field

The invention belongs to the field of metal materials, in particular to a multi-level heterostructure dual-phase alloy and a hot rolling method thereof.

Background technique

Zirconium alloys are widely used in the cladding tubes of nuclear reactor fuel assemblies due to their low thermal neutron absorption cross-section, good high temperature water corrosion resistance, excellent comprehensive mechanical properties and high thermal conductivity. An irreplaceable key structural material for nuclear-powered ships. However, with the gradual extension of the nuclear fuel refueling cycle and the gradual increase of the operating power of the reactor in nuclear power plants and nuclear-powered ships, the service properties of the existing zirconium alloy cladding materials, especially the mechanical properties (<500MPa) can no longer meet the requirements. Therefore, the development of zirconium alloy materials with better mechanical properties has become one of the urgent problems to be solved in the nuclear industry.

Chinese invention patent CN102965605A introduces a method for preparing high-strength plastic nanostructured zirconium alloy material by liquid nitrogen low-temperature rolling, which has the advantages of high tensile strength (>836MPa) and good uniform elongation (>6%). But its disadvantage is that the process flow is long: the zirconium alloy sheet rolled in liquid nitrogen at low temperature needs to be pressed into a columnar sheet in boron nitride powder, and then put into a muffle furnace for drying; then the zirconium oxide powder and diluted water glass are mixed Press into columnar zirconium nitride sheets and put them into a muffle furnace to dry; finally, stack the dolomite sheets, the above-mentioned zirconium boron nitride sheets and zirconia sheets in the columnar holes of the pyrophyllite cube, and place them in a six-sided top press. medium and high pressure treatment.

Chinese invention patent CN110195199A introduces a three-dimensional layered structure zirconium alloy. This structure contains a large number of phase interfaces, which hinders the dislocation slip during the plastic deformation process of the zirconium alloy, and can improve the strength of the zirconium alloy. . But its disadvantage is that zirconium alloy needs to be compressed by 75% in a single pass, the deformation is huge, and the forging ability of mechanical equipment is very high; secondly, the α phase and β phase of the layered structure conform to the Burges relationship of crystallography, and the interface is in In the coherent or semi-coherent state, the hindering effect of dislocation slip in the plastic deformation process of zirconium alloy is weak, so the strength of zirconium alloy is improved slightly (≤693MPa).

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a multi-level heterostructure dual-phase alloy and a hot rolling method thereof. The method can reasonably utilize the hindering effect of various interfaces on dislocation slip, and improve the strength of the zirconium alloy. At the same time, the heterostructure is used to improve the strain strengthening ability of the alloy and maintain a high elongation at break. The hot rolling method is simple in process, short in process and low in equipment requirements.

The present invention is achieved through the following technical solutions:

A method for hot rolling of a multi-level heterostructure dual-phase alloy, comprising the following steps:

Step 1. In an argon atmosphere, keep the alloy in the α+β two-phase region between 700°C and β transformation temperature for 10 to 60 minutes to form an equiaxed α phase and an equiaxed β phase in the alloy;

Step 2. The alloy obtained in step 1 is subjected to rolling deformation with a single-pass reduction of 10-30%. After each 1-3 passes of rolling, the alloy is subjected to argon gas at a temperature of 700°C to β transformation. Re-insulation in the atmosphere for 1-10min, until the total rolling reduction rate of the alloy reaches 60-100%;

Step 3. The alloy obtained in step 2 is annealed at a temperature of 700°C to beta transition temperature and an argon atmosphere for 1 to 30 minutes, and then cooled to room temperature;

Step 4. The alloy obtained in step 3 is subjected to stress relief annealing at 300-500° C. in an argon atmosphere for 0.5-2 hours, and then air-cooled to room temperature to obtain a multi-level heterostructure dual-phase alloy.

Preferably, in step 2, after the alloy is rolled and deformed, it is returned to the furnace for heat preservation, and the time interval is less than 2 minutes.

Preferably, the cooling rate after annealing in step 3 is >25°C/s or <25°C/s.

Preferably, when the cooling rate is >25°C/s, the multi-level heterostructure dual-phase alloy prepared is as follows:

The alloy contains α and α' dual-phase structure, in which the α phase is a micron-scale equiaxed crystal structure, and the α' phase is a sub-micron-scale prism-shaped and lath-shaped lamellar structure, the The prismatic lamella structure contains nano-scale twinned lamellae, and the twinned lamellae are parallel to each other.

Preferably, the lamellar structure α' phase is transformed from the equiaxed β phase upon cooling at a rate of >25°C/s.

Preferably, when the cooling rate is <25°C/s, the prepared multi-level heterostructure dual-phase alloy is as follows:

The alloy contains α and β dual-phase structures, in which the α phase is a micron-scale equiaxed crystal structure and a sub-micron-scale lamellar structure, the β phase is a nano-scale lamellar structure, and the lamellae are The alpha phase of the structure and the beta phase of the lamellar structure are parallel to each other.

Preferably, the mutually parallel lamellar structure α phase and lamellar structure β phase are transformed from the equiaxed β phase when cooled at a speed of <25°C/s.

A multi-level heterostructure dual-phase alloy prepared by the hot rolling method, the alloy comprises α and α' dual-phase structures, the α phase is a micron-level equiaxed crystal structure, and the α' phase is sub-micron The prism-shaped and slat-shaped lamella structures of the first order, the prism-shaped lamella structures contain nano-scale twinned wafer layers, and the twinned wafer layers are parallel to each other;

Or contain α and β dual-phase structure, the α phase is a micron-scale equiaxed crystal structure and a sub-micron-scale lamellar structure, and the β-phase is a nano-scale lamellar structure, and the α-phase and lamellar structure of the lamellar structure are The β phases are parallel to each other.

Preferably, the volume fraction of the micron-scale equiaxed α phase is less than or equal to 80%, and not 0.

Preferably, the alloy is a zirconium alloy or a titanium alloy.

Compared with the prior art, the present invention has the following beneficial technical effects:

The hot rolling method of the multi-level heterostructure dual-phase alloy provided by the present invention is hot rolling and cooling in the α+β two-phase region, which not only retains a certain content of equiaxed α-phase, but also produces sub-micron and nano-scale α-phase. The fine lamellar structure phase, the coarse soft phase and the fine hard phase are not uniformly deformed during the plastic deformation process. In order to maintain the continuity of the deformation, dislocations will accumulate near the interface of the softer phase, and the accumulated dislocations will The backing of the hard phase reacts to the dislocation source. This microscopic internal stress is called back stress. When the back stress is large enough, the dislocation source can be stopped, and the back stress can improve the work hardening ability of the alloy at the same time. and strain strengthening ability, so that the alloy shows a good combination of strength and plasticity. At the same time, the α' phase formed during the cooling process contains high-density dislocations, and dislocation strengthening is also beneficial to the improvement of the alloy strength. Therefore, the α+α' dual-phase alloy has high strength. The grain size of the alloy prepared by this method is small, which can fully strengthen the back stress of the heterostructure alloy. At the same time, the stress distribution is uniform, avoiding local stress concentration and premature cracking, so that higher strength can be obtained while maintaining excellent plasticity. The hot rolling method is simple in process, short in process and low in equipment requirements.

The multi-level heterostructured dual-phase alloy provided by the present invention makes full use of the hindering effect of multi-scale and multi-morphological grain interfaces on dislocation slip, significantly improves the tensile strength of the alloy (>880MPa), and at the same time, soft and hard Different heterostructures can coordinate the deformation on both sides of the interface and avoid stress concentration, so the alloy also maintains a high elongation at break (>17.6%).

Description of drawings

FIG. 1 is an EBSD photograph of the microstructure of the zirconium-niobium alloy in Example 1 of the present invention.

2 is a transmission electron microscope photograph of the zirconium-niobium alloy structure of Example 1 of the present invention.

FIG. 3 is an engineering strain-engineering stress tensile curve diagram of the zirconium-niobium alloy in Example 1 of the present invention.

FIG. 4 is an EBSD photograph of the microstructure of the zirconium-niobium alloy in Example 2 of the present invention.

5 is a transmission electron microscope photograph of the zirconium-niobium alloy structure of Example 2 of the present invention.

FIG. 6 is an engineering strain-engineering stress tensile curve diagram of the zirconium-niobium alloy in Example 2 of the present invention.

7 is a transmission electron microscope photograph of the zirconium-niobium alloy structure of Example 4 of the present invention.

FIG. 8 is an engineering strain-engineering stress tensile curve diagram of the zirconium-niobium alloy in Example 4 of the present invention.

Figure 9 is a transmission electron microscope photograph of the zirconium-niobium alloy structure of the comparative example of the present invention.

FIG. 10 is an engineering strain-engineering stress tensile curve diagram of a zirconium-niobium alloy of a comparative example of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings, which are to explain rather than limit the present invention.

Example 1:

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. Keep a 7mm thick Zr-2.5Nb alloy plate at 815°C in a furnace with argon gas for 30min;

Step 2. Take it out for rolling, the reduction in a single pass is 20%, and after every two passes of rolling, the sample is re-insulated in a furnace with argon gas at 815 ° C for 1 min, and the total rolling reduction is 75 %.

Step 3. After rolling, the sample is annealed again at 815°C in a furnace with argon for 5 minutes, and after the annealing is completed, it is cooled to room temperature at a rate of 25°C/s.

Step 4. The deformed and annealed samples are subjected to stress relief annealing at 400° C. for 1 hour in a furnace filled with argon gas to obtain a dual-phase zirconium-niobium alloy with a multi-level heterostructure.

As shown in Figure 1, it can be seen from the figure that the tissue contains an equiaxed α phase of 2 to 5 μm and a flake α’ phase of 0.15 to 0.25 μm, and the volume fraction of the equiaxed α phase is 40%. Further magnified TEM photos show that the prism-shaped lamellar α' phase also contains twin layers with a thickness of 30-60 nm, as shown in Figure 2; the mechanical properties test shows that the yield strength of the zirconium-niobium alloy reaches 607MPa, and the tensile strength It reaches 808MPa, the elongation at break reaches 16%, and the tensile curve is shown in Figure 3.

Example 2:

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. Keep a 7mm thick Zr-2.5Nb alloy plate at 860°C for 30min in an argon furnace;

Step 2. Take it out for rolling, the reduction in a single pass is 20%, and after every two passes of rolling, the sample is re-insulated in a furnace with argon gas at 860 ° C for 1 min, and the total rolling reduction rate is 75 %.

Step 3. After rolling, the sample is annealed again at 860° C. in a furnace with argon gas for 5 min, and after the annealing is completed, it is cooled to room temperature at a rate of 25° C./s.

Step 4. The deformed and annealed samples were subjected to stress relief annealing at 400° C. for 1 h in a furnace with argon passing through them. The multi-level heterostructure dual-phase zirconium-niobium alloy can be obtained.

As shown in Figure 4, it can be seen from the figure that the tissue contains equiaxed α phase of 2 to 5 μm and flaky α’ phase of 0.17 to 0.32 μm, and the volume fraction of equiaxed α phase is 25%. Further magnified TEM images show that the prismatic lamellar α' phase also contains 30-60 nm thick twinned wafer layers, as shown in Figure 5. The mechanical property test shows that the multi-scale and multi-morphological heterostructure zirconium-niobium alloy has a yield strength of 658 MPa, a tensile strength of 880 MPa, and a fracture elongation of 17.6%. The tensile curve is shown in Figure 6.

Example 3:

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. The 7mm thick Zr-2.5Nb alloy plate was kept at 880°C for 30min in an argon furnace.

Step 2. Take it out for rolling, the reduction in a single pass is 20%, and after every two passes of rolling, the sample is re-insulated in a furnace with argon gas at 860 ° C for 1 min, and the total rolling reduction rate is 75 %.

Step 3. After rolling, the sample is annealed again at 880°C in a furnace with argon for 5 minutes, and after the annealing is completed, it is cooled to room temperature at a rate of 25°C/s.

Step 4. The deformed and annealed samples are subjected to stress relief annealing at 400° C. for 1 hour in a furnace filled with argon gas to obtain a dual-phase zirconium-niobium alloy with a multi-level heterostructure.

The structure of the dual-phase zirconium-niobium alloy includes an equiaxed α phase of 2 to 5 μm and a flake α’ phase of 0.17 to 0.32 μm, and the volume fraction of the equiaxed α phase is 12%. Further magnified TEM pictures show that the prism-shaped lamellar α' phase also contains 30-60 nm thick twinned wafer layers. The mechanical property test shows that the multi-scale and multi-morphological heterostructure zirconium-niobium alloy has a yield strength of 645 MPa, a tensile strength of 797 MPa, and a fracture elongation of 15.9%.

Example 4:

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. The 7mm thick Zr-2.5Nb alloy plate was kept at 910°C for 30min in a furnace with argon gas.

Step 2. Take it out for rolling, the reduction in a single pass is 20%, and after every two passes of rolling, the sample is re-insulated in a furnace with argon gas at 910 ° C for 1 min, and the total rolling reduction ratio is 75 %.

Step 3. After rolling, the sample is annealed again at 910°C in a furnace with argon for 2 minutes, and after the annealing is completed, it is cooled to room temperature at a rate of 3°C/s.

Step 4. The deformed and annealed samples are subjected to stress relief annealing at 400° C. for 1 hour in a furnace filled with argon gas to obtain a dual-phase zirconium-niobium alloy with a multi-level heterostructure.

As shown in Fig. 7, it can be seen from the figure that the tissue contains an equiaxed α phase with a thickness of 2-5 μm, a platelet-shaped α-phase with a thickness of 0.14-0.3 μm and a platelet-shaped β-phase with a thickness of 10-30 nm. Among them, the flaky α phase and the flaky β phase are parallel to each other. At this time, the total volume of the mesoaxial α phase in the sample was 1%. The mechanical properties test shows that the yield strength of the multi-level heterostructured dual-phase zirconium-niobium alloy reaches 605MPa, the tensile strength reaches 812MPa, and the elongation at break reaches 14.2%. The tensile curve is shown in Figure 8.

Example 5:

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. Keep a 7mm thick Zr-2.5Nb alloy plate at 700°C for 60min in an argon furnace,

Step 2. Take out for rolling, the single pass reduction is 30%, after every three passes, the sample is re-insulated at 700 ° C in a furnace with argon for 10 minutes, and the total rolling reduction is 100 %.

Step 3: After rolling, the sample is annealed again at 700°C in a furnace with argon gas for 30min, and after the annealing is completed, it is cooled to room temperature at a rate of 26°C/s.

Step 4. The deformed and annealed samples are subjected to stress relief annealing at 500° C. for 2 hours in a furnace filled with argon gas to obtain a dual-phase zirconium-niobium alloy with a multi-level heterostructure.

At this time, the structure contained an equiaxed α phase of 2 to 5 µm and a flaky α' phase of 0.13 to 0.22 µm, and the volume fraction of the equiaxed α phase was 79%. Further magnifying observation found that the prism-shaped lamellar α' phase also contained twin layers with a thickness of 30-60 nm; the mechanical properties test showed that the yield strength of the zirconium-niobium alloy reached 546 MPa, the tensile strength reached 725 MPa, and the elongation at break reached 21% , the stretching curve is shown in Figure 3.

Example 6:

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. Heat the 7mm thick Zr-2.5Nb alloy plate at 700°C for 10min in a furnace with argon.

Step 2. Take it out for rolling. The reduction in a single pass is 10%. After each pass of rolling, the sample is re-insulated in a furnace with argon gas at 700 ° C for 1 min, and the total rolling reduction is 60%. .

Step 3. After rolling, the sample was annealed again at 700°C in a furnace with argon for 1 min, and after the annealing was completed, it was cooled to room temperature at a rate of 24°C/s.

Step 4. The deformed and annealed samples are subjected to stress relief annealing at 300° C. for 0.5 h in a furnace filled with argon gas to obtain a dual-phase zirconium-niobium alloy with a multi-level heterostructure. Example 7:

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. Keep a 7mm thick Zr-2.5Nb alloy plate at 700°C for 60min in an argon furnace,

Step 2. Take it out for rolling, the reduction in a single pass is 10%, and after every three passes of rolling, the sample is re-insulated at 700 ° C in a furnace with argon gas for 1 min, and the total rolling reduction is 60 %.

Step 3. After rolling, the sample was annealed again at 700°C in a furnace with argon for 30min, and after the annealing was completed, it was cooled to room temperature at a rate of 1°C/s.

Step 4. The deformed and annealed samples are subjected to stress relief annealing at 300° C. for 0.5 h in a furnace filled with argon gas to obtain a dual-phase zirconium-niobium alloy with a multi-level heterostructure.

Comparative Example

This comparative example is basically the same as the method of the above-mentioned examples 1-7, except for the process parameters, especially the stress relief annealing temperature and time in step 4

A method for hot rolling of a multi-level heterostructure dual-phase zirconium-niobium alloy, comprising the following steps:

Step 1. The 7mm thick Zr-2.5Nb alloy plate was kept at 860°C for 30min in an argon furnace.

Step 2. Then take it out for rolling, and the single-pass reduction is 20%. After every two passes of rolling, the sample is re-insulated in a furnace with argon gas at 860 ° C for 1 min. The total rolling reduction is 75%.

Step 3. After rolling, the sample is annealed again at 860° C. in a furnace with argon gas for 5 min, and after the annealing is completed, it is cooled to room temperature at a rate of 25° C./s.

Step 4. The deformed and annealed samples are annealed at 580° C. for 10 hours in a furnace filled with argon gas to relieve stress to obtain a zirconium-niobium alloy with a coarse equiaxed structure.

As shown in Figure 9, the mechanical properties test shows that the yield strength of the zirconium-niobium alloy with this structure reaches 502MPa, the tensile strength reaches 575MPa, and the elongation at break reaches 42.5%. The tensile curve is shown in Figure 10.

The sample consists of only coarse equiaxed grains, the total area of the grain boundary of the coarse equiaxed grain sample is small, and the resistance to dislocation slip during the tensile deformation process is also small. At the same time, the coarser the grains, the fewer the number of grains with different orientations, and the fewer times the dislocation slip propagates from one grain to another grain with different orientations, that is, the greater the obstacle to dislocation slip. few. Therefore, the sample with only coarse equiaxed crystals has lower strength and larger tensile deformation. However, in the multi-level heterostructured dual-phase alloy, the content of sub-micron and nano-scale grains is large, the total area of grain boundaries is large, and the orientation of each grain is different, so the dislocation slip resistance during tensile deformation is large. The strength is higher, and at the same time, the stress concentration caused by dislocation accumulation can easily lead to local necking fracture of the alloy, because the plasticity is reduced.

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention all fall within the scope of the claims of the present invention. within the scope of protection.

Claims (10)

1. A hot rolling method of a multi-level heterostructure dual-phase alloy is characterized by comprising the following steps:

step 1, preserving the temperature of an alloy in an alpha + beta two-phase region between 700 and beta transition temperature for 10-60 min under an argon atmosphere to form an equiaxial alpha phase and an equiaxial beta phase in the alloy;

step 2, carrying out rolling deformation with the single-pass reduction of 10-30% on the alloy obtained in the step 1, and after each 1-3-pass rolling, preserving the heat of the alloy again for 1-10 min at the 700-beta transition temperature and in an argon atmosphere until the total rolling reduction rate of the alloy reaches 60-100%;

step 3, annealing the alloy obtained in the step 2 at 700-beta transition temperature and in an argon atmosphere for 1-30 min, and cooling to room temperature;

and 4, performing stress annealing on the alloy obtained in the step 3 at the temperature of 300-500 ℃ in an argon atmosphere for 0.5-2 h, and then performing air cooling to room temperature to obtain the multi-level heterostructure biphase alloy.

2. A hot rolling method of a multi-level heterostructure two-phase alloy according to claim 1, wherein in step 2, the alloy is kept warm for less than 2min after rolling deformation and after returning to the furnace.

3. A hot rolling process of a multi-level heterostructure dual phase alloy according to claim 1, characterized in that the cooling rate after annealing in step 3 is >25 ℃/s or <25 ℃/s.

4. A hot rolling process of a multi-level heterostructure dual phase alloy according to claim 3, characterized in that the multi-level heterostructure dual phase alloy is prepared with a cooling rate >25 ℃/s as follows:

the alloy comprises an alpha and alpha 'dual-phase structure, wherein the alpha phase in the dual-phase structure is a micron-sized isometric crystal structure, the alpha' phase is a submicron-sized prism-shaped lamellar structure and a lath-shaped lamellar structure, and the prism-shaped lamellar structure contains nanoscale twin crystal lamella which are parallel to each other.

5. A hot rolling process of a multi-level heterostructure dual phase alloy according to claim 4, wherein the lamellar structure α' phase is transformed from equiaxed β phase when cooled at a rate >25 ℃/s.

6. A hot rolling process of a multi-level heterostructure dual phase alloy according to claim 3, characterized in that the multi-level heterostructure dual phase alloy is prepared when the cooling rate is <25 ℃/s as follows:

the alloy comprises an alpha and beta double-phase structure, wherein the alpha phase in the double-phase structure is a micron-sized isometric crystal structure and a submicron-sized lamellar structure, the beta phase is a nanoscale lamellar structure, and the alpha phase of the lamellar structure and the beta phase of the lamellar structure are parallel to each other.

7. A hot rolling process of a multi-level heterostructure two-phase alloy according to claim 6, wherein the mutually parallel lamellar α and β phases are transformed from equiaxed β phases upon cooling at a rate <25 ℃/s.

8. A multi-level heterostructure two-phase alloy prepared by the hot rolling method according to claim 1, wherein the alloy comprises a and a 'two-phase structures, the a phase is a micron-sized equiaxed crystal structure, the a' phase is a submicron-sized prism-shaped lamellar structure and a lath-shaped lamellar structure, the prism-shaped lamellar structure comprises nanometer-sized twin crystal lamella, and the twin crystal lamella are parallel to each other;

or comprises alpha and beta double-phase structures, the alpha phase is a micron-sized isometric crystal structure and a submicron-sized lamellar structure, the beta phase is a nanoscale lamellar structure, and the alpha phase of the lamellar structure and the beta phase of the lamellar structure are mutually parallel.

9. The multi-level heterostructure dual phase alloy of claim 8, wherein the micron-sized equiaxed alpha phase has a volume fraction of 80% or less and is not 0.

10. The multi-level heterostructure dual-phase alloy of claim 8, wherein the alloy is a zirconium alloy or a titanium alloy.

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