Disclosure of Invention
Aiming at the problem that yield strength is improved and good plasticity is kept by NiCoCr medium entropy alloy, the invention provides the NiCoCr medium entropy alloy with excellent strength and plasticity matching and a preparation method thereof.
The invention is realized by the following technical scheme:
an excellent-strength plastic-matching NiCoCr-based medium entropy alloy comprises, by atomic percentage, 29-33% of Ni, 29-33% of Co, 29-33% of Cr, 4-8% of Al and 1.0-3.0% of Ta.
Preferably, the particle purity of the Ni, Co, Cr, Al and Ta is not less than 99.95%.
Preferably, the NiCoCr-based medium entropy alloy is of a single-phase fcc structure.
Preferably, in the single-phase fcc structure, the equiaxed grain size is 8 +/-2 microns, and the volume fraction of the annealed twin crystals is 42-48%.
Preferably, the tensile strength of the NiCoCr-based medium entropy alloy is greater than 950MPa, the yield strength is greater than 600MPa, and the fracture elongation is greater than 50%.
A preparation method of NiCoCr-based medium entropy alloy with excellent strength and plasticity matching comprises the following steps:
step 1, mixing 29-33% of Ni, 29-33% of Co, 29-33% of Cr, 4-8% of Al and 1.0-3.0% of Ta in atomic percentage, and forming an ingot with uniform components through vacuum arc melting;
step 2, carrying out homogenization treatment at the temperature of 1150-1250 ℃;
step 3, cold rolling at room temperature, wherein the deformation amount is controlled to be 50-80%;
and 4, recrystallizing at 1100-1200 ℃ and annealing to obtain the NiCoCr-AlTa medium-entropy alloy with the single-phase fcc structure.
Preferably, in the step 1, in the smelting process, the vacuum is firstly reduced to 5Pa, then high-purity argon is introduced, the vacuum pumping is carried out, the smelting induction current is 400-500A, electromagnetic stirring is adopted in the smelting process, the remelting is carried out repeatedly until the components are uniform, and finally, the ingot is obtained by cooling in a water-cooled copper crucible.
Preferably, the remelting is carried out more than 5 times in the smelting process.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention provides a NiCoCr-based medium entropy alloy with excellent strength and plasticity matching, which utilizes Al and Ta elements to carry out micro-alloying treatment, and the alloy can obtain excellent strength-plasticity combination after a simple deformation heat treatment process; generally, a coarse grain NiCoCr alloy has a plurality of slip systems due to the crystallographic characteristics of the fcc structure, and has a strong plastic deformability, but has a limited strength, and the yield strength thereof is generally 250 to 400 MPa. Thus, in order to obtain a good strength-plasticity combination, it is necessary to further increase the strength without seriously losing plasticity. According to the invention, through Al/Ta element alloying, not only is the grain size reduced and the twin content improved, but also a remarkable solid solution strengthening effect is generated, so that the lattice friction is greatly improved, but the alloy still keeps an fcc matrix, so that the alloy has good toughness while the strength is improved. The alloy has excellent room temperature mechanical property, improves the yield strength of the entropy alloy in NiCoCr by 106 to about 635MPa, improves the tensile strength by 35 to about 1000MPa, and simultaneously has 52 percent of tensile ductility. Based on the characteristics, the alloy has great competitive advantage in single-phase fcc high/medium entropy alloy and has great engineering application prospect.
The preparation method provided by the invention is simple, and the alloy can obtain excellent strength-plasticity matching after smelting, homogenizing treatment, cold rolling and annealing.
Detailed Description
The present invention will now be described in further detail with reference to the attached drawings, which are illustrative, but not limiting, of the present invention.
An NiCoCr-AlTa medium entropy alloy comprises, by atomic percentage (at.%), Ni 29-33%, Co 29-33%, Cr 29-33%, Al 4-8% and Ta 1.0-3.0%.
The raw materials are high-purity metal particles, and the purity is not lower than 99.95%;
the NiCoCr-based medium entropy alloy is of a single-phase fcc structure, wherein the equiaxed grain size is about 8 +/-2 mu m, and the volume fraction of annealing twin crystals is 42-48%.
The preparation method of the NiCoCr-AlTa intermediate entropy alloy comprises the following steps:
step 1, uniformly mixing 29-33% of Ni, 29-33% of Co, 29-33% of Cr, 4-8% of Al and 1.0-3.0% of Ta according to atomic percentage.
The weight of the raw materials is accurately 0.01g when the raw materials are weighed, and then the alloy is smelted by adopting a vacuum arc smelting method.
In the smelting process, firstly, vacuumizing to 5Pa, introducing high-purity argon, vacuumizing, repeatedly washing the furnace for three times to ensure a high-purity vacuum environment, smelting induction current of 400-500A, carrying out electromagnetic stirring in the alloy smelting process, repeatedly remelting for 5 times to ensure component uniformity, and finally cooling in a water-cooled copper crucible to obtain an ingot;
step 2, homogenizing the alloy ingot at 1150-1250 ℃;
step 3, cold rolling at room temperature, wherein the deformation amount is controlled to be 50-80%;
and 4, recrystallizing at 1100-1200 ℃ and annealing to obtain the single-phase fcc alloy.
Example 1
A preparation method of NiCoCr-AlTa medium entropy alloy comprises the following steps:
step 1, uniformly mixing metal particles of 29% of Ni, 31% of Co, 33% of Cr, 4% of Al and 3% of Ta in atomic percentage.
In the smelting process, firstly, vacuumizing to 5Pa, introducing high-purity argon, vacuumizing, repeatedly washing the furnace for three times to ensure a high-purity vacuum environment, smelting induced current of 400A, carrying out electromagnetic stirring in the alloy smelting process, repeatedly remelting for 5 times to ensure component uniformity, and finally cooling in a water-cooled copper crucible to obtain an ingot;
step 2, homogenizing the alloy ingot at 1150 ℃;
step 3, cold rolling at room temperature, wherein the deformation amount is controlled to be 50%;
and 4, carrying out recrystallization annealing treatment at 1100 ℃ to obtain the single-phase fcc alloy.
In the single-phase fcc structure, the equiaxed grain size is about 8 +/-2 microns (twin boundaries are included), the volume fraction of annealed twin crystals is as high as 46 percent, and the structure enables the alloy to have both high strength and excellent plasticity. According to the requirements of GB/T228.1-2010 standard, the mechanical properties of the alloy are measured as follows: tensile Strength σUTS1030MPa, yield strength sigmay660MPa, elongation at break ε T50%, the alloy has excellent strong plasticity.
Example 2
A preparation method of NiCoCr-AlTa medium entropy alloy comprises the following steps:
step 1, uniformly mixing metal particles of 31 percent of Ni, 29 percent of Co, 31 percent of Cr, 7 percent of Al and 2.0 percent of Ta in percentage by atom.
In the smelting process, firstly, vacuumizing to 5Pa, introducing high-purity argon, vacuumizing, repeatedly washing the furnace for three times to ensure a high-purity vacuum environment, smelting induction current of 450A, carrying out electromagnetic stirring in the alloy smelting process, repeatedly remelting for 6 times to ensure component uniformity, and finally cooling in a water-cooled copper crucible to obtain an ingot;
step 2, homogenizing the alloy ingot at 1200 ℃;
step 3, cold rolling at room temperature, wherein the deformation amount is controlled to be 65%;
and 4, carrying out recrystallization annealing treatment at 1150 ℃ to obtain the single-phase fcc alloy.
In the single-phase fcc structure, the equiaxed grain size is about 8 +/-2 microns (twin boundaries are included), the volume fraction of annealed twin crystals is up to 43 percent, and the structure enables the alloy to have both high strength and excellent plasticity. According to the requirements of GB/T228.1-2010 standard, the mechanical properties of the alloy are measured as follows: tensile Strength σUTS985MPa, yield strength sigmay625MPa, elongation at break εT56%, the alloy has excellent strong plasticity.
Example 3
A preparation method of NiCoCr-AlTa medium entropy alloy comprises the following steps:
step 1, uniformly mixing 33% of Ni, 33% of Co, 29% of Cr, 4% of Al and 1% of Ta according to atomic percentage.
In the smelting process, firstly, vacuumizing to 5Pa, introducing high-purity argon, vacuumizing, repeatedly washing the furnace for three times to ensure a high-purity vacuum environment, smelting induction current of 450A, carrying out electromagnetic stirring in the alloy smelting process, repeatedly remelting for 6 times to ensure component uniformity, and finally cooling in a water-cooled copper crucible to obtain an ingot;
step 2, homogenizing the alloy ingot at 1200 ℃;
step 3, cold rolling at room temperature, wherein the deformation amount is controlled to be 65%;
and 4, carrying out recrystallization annealing treatment at 1150 ℃ to obtain the single-phase fcc alloy.
In the single-phase fcc structure, the equiaxed grain size is about 8 μm (twin boundaries included), the volume fraction of annealed twin crystals is as high as 45%, and the structure enables the alloy to have both high strength and excellent plasticity. According to the requirements of GB/T228.1-2010 standard, the mechanical properties of the alloy are measured as follows: tensile Strength σUTS970MPa, yield strength sigmay605MPa, elongation at break εTAt 58%, the alloy has excellent strong plasticity.
Example 4
Preparation of a (NiCoCr)92Al6Ta2(at.%) while preparing the same method as the comparative example NiCoCr medium entropy alloy with equal atomic ratio, the preparation method is as follows:
step 1, uniformly mixing metal particles of 31% of Ni, 31% of Co, 30% of Cr, 6% of Al and 2% of Ta in atomic percentage, weighing the raw materials, wherein the weight is accurate to 0.01g, smelting the alloy by adopting a vacuum arc smelting method, firstly vacuumizing to 5Pa in the smelting process, then introducing high-purity argon, vacuumizing, repeating the steps for three times to ensure a high-purity vacuum environment, smelting induced current is 400-500A, carrying out electromagnetic stirring in the alloy smelting process, repeatedly remelting for 5 times to ensure component uniformity, and finally cooling in a water-cooled copper crucible to obtain an ingot; then the alloy ingot is subjected to homogenization treatment of heat preservation at 1225 ℃ for 24 hours and then water quenching. The homogenized sample was cut into sheets of about 6mm by wire cutting and then cold-rolled at room temperature to a strain (thickness direction) of 70%. And finally, carrying out annealing treatment of keeping the temperature of 1150 ℃ for 3min and then water quenching on the cold-rolled sheet to obtain a completely recrystallized structure.
(NiCoCr)92Al6Ta2(at.%) after the above-mentioned deformation heat treatment, the structure obtained is shown in fig. 1, and is a typical recrystallization structure of a low-stacking fault energy metal, and in a single-phase fcc structure, the equiaxed grain size is about 8 μm (including twin boundaries), and the annealed twin volume fraction is as high as 46%, and this structure enables the alloy to have both high strength and excellent plasticity. According to the GB/T228.1-2010 standard requirement, the alloy force is measuredThe chemical properties are as follows: tensile Strength σUTS998MPa, yield strength sigmay635MPa, elongation at break εT52%, the alloy has excellent strong plasticity.
Comparative example 1
An intermediate entropy alloy of NiCoCr comprises, by atom percentage, 32-34% of Ni, 32-34% of Co, 32-34% of Cr, a preparation method and (NiCoCr)92Al6Ta2(at.%) was prepared in the same manner.
The NiCoCr medium entropy alloy with equal atomic ratio is prepared to obtain a recrystallization structure, wherein in a single-phase fcc structure, the equiaxed grain size is about 18 mu m (including twin boundaries), and the volume fraction of annealed twin crystals is 22%. According to the requirements of the GB/T228.1-2010 standard, the measured mechanical properties of the alloy are shown as a curve 2 in figure 2: tensile Strength σUTS741MPa, yield strength sigmay309MPa, elongation at break εTAt 74%, the alloy has excellent plasticity but limited strength.
Comparative example 2
The NiCoCr-AlTa cold-rolled alloy prepared in the example 4 is subjected to annealing treatment of heat preservation at 1000 ℃ for 8min and then water quenching to obtain a completely recrystallized structure, and finally, mechanical property test is performed. The resulting structure was similar to the annealing treatment of example 4, which was held at 1150 ℃ for 3min and then water quenched, but the twinning density was relatively low and the grain size was small.
The mechanical properties of the alloy measured according to the requirements of GB/T228.1-2010 standard are shown in the curve 3 in figure 2, and the tensile strength sigma isUTS1050MPa, yield strength sigmay655MPa, elongation at break εTAt 19%, the strength of the alloy as a whole is significantly improved, but the elongation is severely reduced.
Comparative example 3
The NiCoCr-AlTa cold-rolled alloy prepared by the method in the embodiment 4 is subjected to annealing treatment of heat preservation at 1000 ℃ for 30min and then water quenching to obtain a completely recrystallized structure, and mechanical property test is performed. The resulting structure was similar to the fully recrystallized structure obtained by the annealing treatment of comparative example 2, which was heat-insulated at 1000 ℃ for 8min and then water-quenched.
According to the requirements of the GB/T228.1-2010 standard,the measured mechanical properties of the alloy are shown in FIG. 2, curve 4: tensile Strength σUTS1042MPa, yield strength sigmay644MPa, elongation at break εTAt 22%, the strength of the alloy as a whole is significantly improved, but the elongation is severely reduced.
FIG. 3 is a solid solution strengthening comparison graph of the entropy alloy of NiCoCr-AlTa system and other elements of the present invention, wherein (NiCoCr)100-xMx(at.%) M in the alloy represents a different solid solution strengthening element, it can be seen that the Al/Ta alloying contributes most to the strength.
FIG. 4 is a comparison graph of strength-plasticity of the entropy alloy in NiCoCr-AlTa system of the present invention and other single-phase fcc structure medium/high entropy alloys, wherein the comparison alloys are all single-phase fcc equiaxed crystal structures, and it can be seen that the entropy alloy in NiCoCr-AlTa system has excellent strength-plasticity matching.
The invention discloses a NiCoCr-based entropy alloy with excellent strength and plasticity matching and a preparation method thereof, wherein Al/Ta element alloying is carried out on a NiCoCr alloy with equal atomic ratio, a novel solid solution strengthening type NiCoCr-AlTa system entropy alloy is designed, the alloy can obtain excellent strength-plasticity matching after smelting, homogenization treatment, cold rolling and annealing, and compared with NiCoCr with equal atomic ratio prepared by the same process, the yield strength is improved mainly due to the addition of Al and Ta elements with large atomic radius, on one hand, crystal grains are refined due to the fact that the coarsening kinetics of the crystal grains are reduced, and the contribution of interface strengthening (grain boundary/twin boundary) is 48 MPa. On the other hand, the severe lattice distortion results in strong solid solution strengthening, the contribution of which is 278 MPa. Compared with NiCoCr medium entropy alloy, the yield strength is improved by 106% by interface strengthening and solid solution strengthening. The entropy alloy in the NiCoCr-AlTa system presents rich substructures in the deformation process, including dislocation plane slippage, a large number of network faults, high-density dislocation walls, micro-deformation zones and strong interaction of dislocation-twin boundaries, and the synergistic effect of the substructures enables the entropy alloy in the NiCoCr-AlTa system to have ultrahigh strain strengthening capability so as to remarkably improve tensile strength, and the substructures can effectively coordinate plastic deformation so as to ensure good plasticity. Based on the characteristics, the entropy alloy in the NiCoCr-AlTa system has excellent strength-plasticity matching. The Ni and Co elements selected in the alloy have good high-temperature stability, the Cr element improves the corrosion resistance/oxidation resistance, the Al element is beneficial to reducing the density and the cost of the alloy, and the Ta element improves the high-temperature creep resistance and the oxidation resistance, so the NiCoCr-AlTa entropy alloy has excellent comprehensive mechanical properties, has great potential in other properties, and has great engineering application prospect.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.