CN112725678B - Non-equal atomic ratio medium/high entropy alloy containing NiCoCr and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of medium/high entropy alloys, and in particular relates to a NiCoCr-containing medium/high entropy alloy with non-equiatomic ratio and a preparation method thereof. The composition of the medium/high entropy alloy includes Ni, Co, Cr, and M, and the atomic percentages of each element in the medium/entropy alloy are: Ni is 30% to 50%, Co is 20% to 40%, and Cr is 10% ～30%, M is 0%～12%; M is selected from 0～2 kinds of Al and Ti. The preparation method is as follows: putting high-purity metal block raw materials into a water-cooled copper mold crucible of an electric arc melting furnace in a certain proportion, and smelting under the protection of an argon atmosphere to obtain a cast product. The invention has reasonable component design, simple and controllable preparation process, and excellent performance of the obtained product.

Description

A kind of non-equiatomic ratio medium/high entropy alloy containing NiCoCr and preparation method thereof

technical field

The invention belongs to the field of medium/high entropy alloys, and in particular relates to a non-equiatomic ratio medium/high entropy alloy containing NiCoCr and a preparation method thereof, and has excellent mechanical properties at room temperature.

Background technique

Medium-entropy alloys (MEAs) or high-entropy alloys (HEAs) are potential structural materials in the future, and alloys with good strength and toughness are required in engineering applications. In many high-entropy alloy systems that pursue both strength and toughness, by adding alloying elements Al and Ti, precipitation in the high-plastic medium/high-entropy alloy matrix or directly introducing second phase particles can greatly improve the strength. On the basis of a greater degree of preservation of plasticity. The matrix composition of such precipitation-strengthened high-entropy alloys is generally a single-phase face-centered cubic (FCC) structure, which is mainly selected from the 3d transition group metal system dominated by three- to five-membered Co, Cr, Fe, Ni, Mn and other elements. , such as FeCoCrNiMn, FeCoCrNi, FeCoNi, NiCoCr, etc. At room temperature, the NiCoCr ternary alloy system has better plasticity than other ternary systems or even quaternary and quinary alloy systems. However, the NiCoCr ternary medium-entropy alloys with equal atomic ratio or the NiCoCr base with equal atomic ratio are mostly studied at present. High-entropy alloys, there are few reports on high-performance non-equiatomic NiCoCr ternary medium-entropy alloys or non-equiatomic NiCoCr-based high-entropy alloys, so the current high-performance non-equiatomic NiCoCr-based medium/high entropy alloys Alloys are yet to be developed.

SUMMARY OF THE INVENTION

The purpose of the invention is to prepare a non-equiatomic ratio NiCoCr medium/high entropy alloy with excellent room temperature mechanical properties, obtain excellent room temperature initial plasticity by adjusting the ratio of three components in NiCoCr, and then introduce alloying elements Al and/ Or Ti, and then obtain a high volume fraction of nano-precipitated phase to improve the strength of the alloy, thereby preparing an anisotomic NiCoCr-based high-entropy alloy with excellent room temperature mechanical properties.

The present invention tries for the first time a Ni, Co-rich NiCoCr medium-entropy alloy with non-equiatomic ratio NiCoCr, adding Al alone and simultaneously adding Al and Ti non-equiatomic ratio NiCoCr-based high-entropy alloy; the obtained product has excellent mechanical properties at room temperature and has industrial application value . At the same time, the design idea adopted by the present invention has a certain forward-looking.

The technical scheme adopted in the present invention is as follows:

A non-equiatomic ratio medium/high-entropy alloy containing NiCoCr; the medium/high-entropy alloy components include Ni, Co, Cr, M, and the atomic percentages of each element in the medium/high-entropy alloy are: Ni is 30% ～50%, Co is 20%～40%, Cr is 10%～30%, M is 0%～12%; M is selected from 0～2 kinds of Al and Ti.

As one of the preferred solutions; an unequal atomic ratio medium/high entropy alloy containing NiCoCr of the present invention; in the alloy, the atomic percentage of nickel is greater than the atomic percentage of cobalt, and the atomic percentage of cobalt is greater than the atomic percentage of Cr. content.

The present invention is an unequal atomic ratio medium/high entropy alloy containing NiCoCr; as one of the optimization schemes, in the medium entropy alloy, in atomic percentage, Ni is 40%-45%, and Co is 35%-40% , Cr is 15% to 20%.

The present invention is a non-equiatomic ratio medium/high entropy alloy containing NiCoCr; as a preferred solution, in the medium entropy alloy, in atomic ratio: Ni:Co:Cr=3.5:3:1.5.

The present invention is a non-equiatomic ratio medium/high entropy alloy containing NiCoCr; when the medium entropy alloy is Ni _3.5 Co ₃ Cr _1.5 medium entropy alloy, the room temperature tensile yield strength of the as-cast sample is 147 MPa, and the tensile strength It is 445MPa, the elongation at break is 78.8%, the Vickers hardness is 149HV, the microhardness is 2.81GPa, and the elastic modulus is 246GPa.

The present invention is an unequal atomic ratio medium/high entropy alloy containing NiCoCr; as a further optimization scheme, the M element is composed of Al, and the atomic percentages of each element are: Ni is 35% to 45%, and Co is 30% ~40%, Cr is 10%~20%, Al is 5~12%.

The present invention is a non-equiatomic ratio medium/high-entropy alloy containing NiCoCr; as a preferred solution, when the high-entropy alloy is (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₁₀ high-entropy alloy, the as-cast sample is stretched at room temperature The yield strength is 406MPa, the tensile strength is 646MPa, the elongation at break is 100.2%, the Vickers hardness is 269HV, the microhardness is 4.35GPa, and the elastic modulus is 220GPa.

The present invention is a non-equiatomic ratio medium/high entropy alloy containing NiCoCr; as a further optimization scheme, the M element is composed of Al and Ti, and the atomic percentage of each element is: Ni is 35% to 45%, Co It is 30% to 40%, Cr is 10% to 20%, Al is 0 to 10%, and Ti is 0 to 10%; when both Al and Ti are contained, (Al+Ti) is less than or equal to 12%.

The present invention is a non-equiatomic ratio medium/high-entropy alloy containing NiCoCr; as a preferred solution, when the high-entropy alloy is (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₅ Ti ₅ high-entropy alloy, the as-cast sample is room temperature The tensile yield strength is 792MPa, the tensile strength is 1004MPa, the elongation at break is 38.2%, the Vickers hardness is 429HV, the microhardness is 6.43GPa, and the elastic modulus is 268GPa.

The present invention is a kind of preparation method of the non-equiatomic ratio medium/high entropy alloy containing NiCoCr; comprises the following specific steps:

(1) use SiC sandpaper to remove the oxide layer on the surface of Ni, Co, Cr, M (Al, Ti) metal raw materials with a purity of > 99.99wt.%, then place it in an ultrasonic cleaner to clean with alcohol, and then take it out and dry it naturally;

(2) According to the designed atomic percentage, weigh the ingredients with an electronic precision balance;

(3) According to the order from low to high melting point of the metal raw materials, put the raw materials into the copper mold crucible of the vacuum arc melting furnace in turn, and feed high-purity argon in an environment where the vacuum degree is at least 3 × 10 ^-3 Pa;

(4) First, pure titanium is smelted to absorb the residual oxygen in the furnace cavity; then the alloy is smelted, and the arc holding time is 10-20 seconds when the sample is completely melted; after the alloy is cooled, it is turned over, and this is repeated more than 5 times; product.

In general, the advantages and positive effects of the present invention are as follows:

(1) The present invention prepares an unequal atomic ratio NiCoCr medium entropy alloy, and uses the characteristics and dosage of each element to obtain a single-phase FCC structure anisotomic NiCoCr medium entropy alloy, and the as-cast alloy without subsequent treatment It exhibits excellent room temperature elongation (~78.8%), which is higher than the room temperature elongation (~60%) of the equiatomic NiCoCr medium entropy alloy after homogenization annealing, cold rolling, and recrystallization annealing.

(2) Al (2.7g/cm ³ ) and Ti (4.5g/cm ³ ) used in the present invention are low-density elements, which can reduce the overall density of the alloy system, which is in line with the development trend of lightweight materials in the future. Al can form Ni ₃ Al intermetallic compound, which is a L1 ₂ (ordered FCC) tough phase that can maintain a coherent relationship with the NiCoCr matrix. By controlling the amount of Al to be less than or equal to 12%, a large amount of L1 ₂ phase can be precipitated Without the purpose of forming a dendrite structure or a hard and brittle phase. At the same time, there are also appropriate amounts of Co, Cr, and Ti in the present invention, which can promote the formation of (Ni, Co, Cr) ₃ (Al, Ti) multi-component intermetallic compounds, and have better strengthening effect, which is The necessary conditions are provided to obtain pentary high-entropy alloys with high strength, high hardness and high elongation.

(3) The present invention uses an unequal atomic ratio NiCoCr medium entropy alloy as a matrix, and after introducing appropriate amount of alloying elements Al and Ti, since Ni/Al>3, and the amount of Co > the amount of Cr, the unequal atomic ratio NiCoCr base The high-entropy alloy can form a multi-component L1 ₂ strengthening phase with a high volume fraction in the as-cast state, so in the preferred scheme, the strength and plasticity are improved after adding 10 at.% Al, adding 5 at.% Al and 5 at.% Al The strength of Ti is greatly improved (~5 times) and still retains a certain plasticity.

Description of drawings

1 is a metallographic microstructure diagram of the non-equiatomic NiCoCr medium/high entropy alloy obtained in the embodiment of the present invention and the comparative example.

Figure 2 is the TEM precipitation morphology of the NiCoCr-based high-entropy alloy with Al and Ti added in Example 3 of the present invention.

3 is a three-dimensional diagram of the tensile yield strength, tensile strength and elongation at break of as-cast anisoatomic NiCoCr medium/high-entropy alloys obtained in Examples and Comparative Examples of the present invention.

FIG. 4 is the nanoindentation load-displacement curve at room temperature of the as-cast NiCoCr medium/high entropy alloy obtained in the embodiment of the present invention.

5 is a graph showing the results of Vickers hardness testing of as-cast NiCoCr medium/high entropy alloys obtained in the embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments described herein are only used to explain the present invention and are not limited to the present invention. These technical solutions can be further improved by those skilled in the art without departing from the spirit and scope of the present invention.

In the following examples and comparative examples:

Vacuum arc melting furnace: WK series vacuum arc melting furnace produced by Beijing Wuke Photoelectric Co., Ltd.

Metallographic structure: LEICA DM 2007M metallographic microscope was used to observe the microscopic morphology of the medium/high entropy alloy prepared by the present invention.

Precipitation phase morphology: Tecnai G2 F20 field emission transmission electron microscope was used to observe the precipitation phase morphology of the non-equiatomic NiCoCr-based high-entropy alloy added with Al and Ti in the present invention, and the radius and proportion of nanoparticles were analyzed by ImageJ software. Statistical Analysis.

Vickers hardness test: use the HV-50 hardness tester of Jinan Fengzhi Testing Instrument Co., Ltd. for Vickers hardness test, the loading load is 300g (2.942N), the dwell time is 15s, and each sample is tested in different areas for 10 The mean and standard deviation were calculated for each measurement, and the standard deviation is indicated by error bars.

Room temperature tensile mechanical property test: The room temperature tensile test was carried out by using the American MTS landmark testing machine, the strain rate was 3×10 ^-3 s ^-1 , and the dimensions of the tensile sample were as follows: the gauge length was 8 mm, the width was 3.4 mm, and the thickness was 1mm.

Nanoindentation test: use an indentation tester (UNHT+MCT) to measure the microhardness and elastic modulus of the medium/high entropy alloy prepared by the present invention. The test parameters are as follows: the loading load is 30mN, and the loading rate is 1mN/ s, dwell time is 10s, and each sample is tested 5 times to make 5 indentations.

The embodiments and comparative examples of the non-equiatomic NiCoCr medium/high entropy alloy proposed by the present invention are described in detail as follows:

Example 1

Step 1: Use SiC sandpaper to remove the oxide layer on the surface of Ni, Co, Cr metal raw materials with a purity of > 99.99%, then place it in an ultrasonic cleaner to clean with alcohol, and then take it out and dry it naturally;

Step 2: Calculate and weigh out pure metal raw materials with a total mass of (50±0.1) g according to the atomic ratio Ni:Co:Cr=3.5:3:1.5;

Step 3: according to the order from low to high melting point of the metal raw materials, put the raw materials into the copper mold crucible of the vacuum arc melting furnace in turn, and pass high-purity argon in an environment with a vacuum degree of at least 3×10 ^-3 Pa;

Step 4: First, smelting pure titanium to absorb the residual oxygen in the furnace cavity; then smelting the alloy, the arc holding time is 10 to 20 seconds when the sample is completely melted; after the alloy is cooled, it is turned over, and this is repeated more than 5 times to obtain Anisotomic NiCoCr medium entropy alloy.

According to the metallographic structure diagram in Fig. 1, it can be seen that the Ni _3.5 Co ₃ Cr _1.5 medium entropy alloy has a coarse equiaxed grain structure, and the grain size ranges from 100 to 500 μm. According to Figures 3, 4 and 5, the room temperature tensile yield strength of the as-cast sample is 147MPa, the tensile strength is 445MPa, the elongation at break is 78.8%, the Vickers hardness is 149HV, the microhardness is 2.81GPa, and the elastic modulus is 149HV. is 246GPa.

Example 2

Step 1: Use SiC sandpaper to remove the oxide layer on the surface of Ni, Co, Cr, and Al metal raw materials with a purity of > 99.99%, then place it in an ultrasonic cleaner to clean with alcohol, and then take it out and dry it naturally;

Step 2: Calculate and weigh out pure metal raw materials with a total mass of (50±0.1) g according to the composition of (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₁₀ ;

Step 3: According to the order from low to high melting point of the metal raw materials, put the raw materials into the copper mold crucible of the vacuum arc melting furnace in turn, and pass high-purity argon in an environment with a vacuum degree of at least 3×10 ^-3 Pa;

Step 4: First, smelting pure titanium to absorb the residual oxygen in the furnace cavity; then smelting the alloy, the arc holding time is 10-20 seconds when the sample is completely melted; after the alloy is cooled, it is turned over, and this is repeated more than 5 times to obtain The composition is (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₁₀ anisotomic NiCoCr-based high-entropy alloy.

It can be seen from the metallographic microstructure in Fig. 1 that the (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₁₀ high-entropy alloy has an equiaxed or columnar structure, and the grain size ranges from 100 to 400 μm. According to Figures 3, 4 and 5, the room temperature tensile yield strength of the as-cast sample is 406MPa, the tensile strength is 646MPa, the elongation at break is 100.2%, the Vickers hardness is 269HV, the microhardness is 4.35GPa, and the elastic modulus is 220GPa. The grain boundary is a small-angle grain boundary, which is beneficial to the grain boundary slip and improves the plasticity, and the addition of Al promotes the production of precipitates and improves the strength.

Example 3

Step 1: Use SiC sandpaper to remove the oxide layer on the surface of Ni, Co, Cr, Al, Ti metal raw materials with a purity of > 99.99%, then place it in an ultrasonic cleaner to clean with alcohol, take it out and air dry it naturally;

Step 2: Calculate and weigh out pure metal raw materials with a total mass of (50±0.1) g according to the composition (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₅ Ti ₅ ;

Step 3: according to the order from low to high melting point of the metal raw materials, put the raw materials into the copper mold crucible of the vacuum arc melting furnace in turn, and pass high-purity argon gas in an environment where the vacuum degree is lower than 3×10 ^-3 Pa;

Step 4: First, smelting pure titanium to absorb the residual oxygen in the furnace cavity; then smelting the alloy, the arc holding time is 10-20 seconds when the sample is completely melted; after the alloy is cooled, it is turned over, and this is repeated more than 5 times to obtain (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₅ Ti ₅ high-entropy alloy.

It can be seen from the metallographic microstructure in Fig. 1 that the grains of the (Ni _3.5 Co ₃ Cr _1.5 ) ₉₀ Al ₅ Ti ₅ high-entropy alloy are not significantly refined relative to the NiCoCr matrix, and the grain size ranges from 100 to 500 μm. According to Fig. 2, high-density nano-precipitation phases are precipitated in the matrix, with an average size of about 92.6 nm, and the nano-precipitation phases account for about 66% of the total volume. According to Figures 3, 4 and 5, the room temperature tensile yield strength of the as-cast sample is 792MPa, the tensile strength is 1004MPa, the elongation at break is 38.2%, the Vickers hardness is 429HV, the microhardness is 6.45GPa, and the elastic modulus is 268GPa. The existence of a large number of precipitates improves the hardness and strength of the alloy, improves the elastic properties, and reduces the ductility.

Comparative Example 1

Step 1: Use SiC sandpaper to remove the oxide layer on the surface of Ni, Co, Cr, Al, Ti metal raw materials with a purity of > 99.99%, then place it in an ultrasonic cleaner to clean with alcohol, take it out and air dry it naturally;

Step 2: Calculate and weigh out pure metal raw materials with a total mass of (50±0.1) g according to the composition (Ni _3.5 Co ₃ Cr _1.5 ) ₈₀ Al ₁₀ Ti ₁₀ ;

Step 3: According to the order from low to high melting point of the metal raw materials, put the raw materials into the copper mold crucible of the vacuum arc melting furnace in turn, and pass high-purity argon in an environment with a vacuum degree of at least 3×10 ^-3 Pa;

Step 4: First, smelting pure titanium to absorb the residual oxygen in the furnace cavity; then smelting the alloy, the arc holding time is 10-20 seconds when the sample is completely melted; after the alloy is cooled, it is turned over, and this is repeated more than 5 times to obtain The composition is (Ni _3.5 Co ₃ Cr _1.5 ) ₈₀ Al ₁₀ Ti ₁₀ anisotomic ratio NiCoCr-based high-entropy alloy.

According to the metallographic structure diagram in Fig. 1, it can be seen that a large number of dendrites appear in the (Ni _3.5 Co ₃ Cr _1.5 ) ₈₀ Al ₁₀ Ti ₁₀ high-entropy alloy. According to Table 1 and Figure 3, the room temperature yield strength of the as-cast sample is 804MPa, the tensile strength is 1096MPa, the Vickers hardness is 560HV, and the elongation at break is only 3.6%. This shows that the excessive addition of Al and Ti increases the strength and hardness of the material, but a large number of dendrites greatly reduce the ductility, which is not conducive to practical engineering applications.

The present invention selects Al and Ti as alloying elements, adding a certain amount of Al alone can improve the strength and toughness of the material at the same time, adding an appropriate amount of Al and Ti can greatly improve the strength and retain a certain plasticity, but excessive addition of Al and Ti will lead to a serious decline in plasticity.

In summary, they are only specific embodiments of the invention. The protection scope of the present invention is not limited to this, and any modification or adjustment that can be made to the present invention by any person skilled in the art within the technical scope disclosed by the present invention shall be covered within the protection scope of the present invention.

Table 1 is a table of room temperature mechanical properties of the non-isoatomic NiCoCr medium/high entropy alloys obtained in Examples and Comparative Examples.

Table 1

Claims (1)

1. A non-equiatomic ratio medium/high entropy alloy containing NiCoCr is characterized in that:

the medium entropy alloy is Ni_3.5Co₃Cr_1.5The room-temperature tensile yield strength of an as-cast sample of the medium-entropy alloy is 147MPa, the tensile strength is 445MPa, the elongation at break is 78.8 percent, the Vickers hardness is 149HV, the microhardness is 2.81GPa, and the elastic modulus is 246 GPa;

the high-entropy alloy is (Ni)_3.5Co₃Cr_1.5)₉₀Al₁₀The high-entropy alloy has an as-cast sample tensile yield strength of 406MPa at room temperature, a tensile strength of 646MPa, an elongation at break of 100.2 percent, a Vickers hardness of 269HV, a microhardness of 4.35GPa and an elastic modulus of 220 GPa; or

The high-entropy alloy is (Ni)_3.5Co₃Cr_1.5)₉₀Al₅Ti₅The high-entropy alloy is an as-cast sample of which the room-temperature tensile yield strength is 792MPa, the tensile strength is 1004MPa, the elongation at break is 38.2 percent, the Vickers hardness is 429HV, the microhardness is 6.43GPa, and the elastic modulus is 268 GPa;

the non-equiatomic ratio medium/high entropy alloy containing NiCoCr is prepared by the following specific steps:

(1) when the alloy is Ni_3.5Co₃Cr_1.5During medium entropy alloying, SiC sand paper is used for removing oxide layers on the surfaces of Ni, Co and Cr metal raw materials with the purity of more than 99.99wt%, then the materials are placed in an ultrasonic cleaning instrument and cleaned by alcohol, and the materials are taken out and naturally dried;

when the alloy is (Ni)_3.5Co₃Cr_1.5)₉₀Al₁₀When the high-entropy alloy is used, SiC sand paper is used for removing oxide layers on the surfaces of Ni, Co, Cr and Al metal raw materials with the purity of more than 99.99wt%, then the materials are placed in an ultrasonic cleaning instrument and cleaned by alcohol, and the materials are taken out and naturally dried;

when the alloy is (Ni)_3.5Co₃Cr_1.5)₉₀Al₅Ti₅When the high-entropy alloy is used, SiC sand paper is used for removing oxide layers on the surfaces of Ni, Co, Cr, Al and Ti metal raw materials with the purity of more than 99.99wt%, then the metal raw materials are placed in an ultrasonic cleaning instrument and cleaned by alcohol, and the metal raw materials are taken out and naturally dried;

(2) weighing and proportioning by using an electronic precision balance according to the designed atomic percentage;

(3) sequentially putting the raw materials into a copper mold crucible of a vacuum arc melting furnace from low to high of the melting point of the metal raw materials in sequence, wherein the vacuum degree is at least 3 multiplied by 10^-3Introducing high-purity argon in a Pa environment;

(4) firstly, smelting pure titanium to absorb residual oxygen in a furnace chamber; then smelting the alloy, wherein the arc holding time is 10-20 seconds when the sample is completely molten; after the alloy is cooled, turning the alloy for smelting again, and repeating the process for more than 5 times; and (5) obtaining a product.

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