A grain boundary engineering treatment method for improving corrosion resistance of CoCrFeNiMn high-entropy alloy

Abstract

The application discloses a grain boundary engineering treatment method for improving corrosion resistance of CoCrFeNiMn high-entropy alloy. The CoCrFeNiMn high-entropy alloy raw material is subjected to solid solution treatment at 1100 DEG C for more than 10 hours, then is subjected to 50%-80% cold rolling deformation, and then is subjected to annealing treatment at 1010 DEG C-1070 DEG C for not less than 1.5 minutes, to obtain an initial sample; the initial sample is subjected to cold rolling treatment with a deformation of 4%-10%, and finally the alloy is subjected to annealing treatment at 1010 DEG C-1070 DEG C for not less than 3 minutes. The proportion of low Sigma CSL grain boundaries of the CoCrFeNiMn high-entropy alloy treated by the method is more than 70%, the proportion of Sigma 3 grain boundaries is more than 60%, and the proportion of coherent Sigma 3 grain boundaries in the Sigma 3 grain boundaries is more than 70%. The application not only improves the proportion of Sigma 3 grain boundaries, but also improves the proportion of coherent twin grain boundaries and {1 1 1} / {1 1 5} matched Sigma 9 grain boundaries, effectively improves the corrosion resistance of the CoCrFeNiMn high-entropy alloy, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of deformation and heat treatment processing of metal materials, and particularly relates to a grain boundary engineering treatment method for improving the corrosion resistance of a CoCrFeNiMn high-entropy alloy. BACKGROUND

[0002] The equiatomic CoCrFeMnNi high-entropy alloy (also known as Cantor alloy) has excellent strength and plasticity at low temperatures, and exhibits dynamic strain hardening and dynamic Hall-Petch effect caused by deformation twinning. Grain boundary engineering (GBE) is widely used to improve the performance of medium and low stacking fault energy (SFE) face-centered cubic (fcc) materials by increasing the proportion of CSL grain boundaries (Σ≤29) and blocking the connectivity of random grain boundaries in the grain boundary network. Grain boundary engineering has been proven to improve the plasticity, intergranular corrosion, hot corrosion, oxidation, creep and fatigue performance of many alloys (such as austenitic stainless steel, nickel-based superalloy, etc.). The Cantor alloy has a low SFE (30±5 mJ / m 2 ), which is suitable for grain boundary engineering treatment.

[0003] Researchers have carried out grain boundary engineering research on the Cantor alloy by the traditional three-parameter method, mainly by means of small deformation and long-time (1h-10h) annealing at medium temperature (800℃-1000℃) to increase the proportion of low-Σ CSL special grain boundaries, but this method requires a long annealing time, consumes a lot of energy in industrial production, and has a high cost, so a new grain boundary engineering method is needed. It is also necessary to pay attention to the fact that in medium and low stacking fault energy face-centered cubic metals, the energy of coherent ∑3 grain boundaries is lower than that of incoherent ∑3 grain boundaries, and the stability is better, which is more beneficial to improve the comprehensive performance of the material. And the Σ9 grain boundaries with {1 1 1} / {1 1 5} matching characteristics also have high structural order, low energy, good structural stability, and high grain boundary corrosion resistance. However, the traditional three-parameter grain boundary characterization method cannot distinguish between coherent ∑3 grain boundaries and incoherent ∑3 grain boundaries, nor can it accurately determine the proportion of coherent ∑3 grain boundaries and Σ9 grain boundaries with {1 1 1} / {1 1 5} matching characteristics. In recent years, the grain boundary interface matching characterization method provides key technical support for accurately determining the proportion of coherent Σ3 grain boundaries and {1 1 1} / {1 1 5} matching Σ9 grain boundaries in face-centered cubic metals. Therefore, in view of the deficiencies of the existing grain boundary engineering treatment method for the Cantor alloy, the application develops a new grain boundary engineering treatment method based on the grain boundary interface matching characterization method. SUMMARY

[0004] The application aims to provide a grain boundary engineering treatment method for improving the corrosion resistance of CoCrFeNiMn high-entropy alloy, which is based on the formation of annealing twins to improve the low Sigma CSL grain boundary proportion of such materials.

[0005] A grain boundary engineering treatment method for improving the corrosion resistance of CoCrFeNiMn high-entropy alloy, comprising the following steps:

[0006] 1) Original structure regulation

[0007] The CoCrFeNiMn high-entropy alloy raw material is solid-solution treated at 1100 DEG C for more than 10 hours, then the material is subjected to large deformation cold rolling with a deformation amount of 50%-80%, and then annealed at 1010 DEG C-1070 DEG C for not less than 1.5 min to obtain a pretreated material.

[0008] 2) Small deformation and high-temperature annealing:

[0009] The pretreated material is subjected to small deformation cold rolling with a deformation amount of 4%-10%, and the rolling force of the material is as uniform as possible, and then the material is recrystallized annealed at 1010 DEG C-1070 DEG C for not less than 3 min.

[0010] Before the solid-solution treatment and annealing treatment of steps 1) and 2), the surface of the material is polished, that is, 800 # , 1000 # and 2000 # sandpaper are used in sequence, and the material is cleaned by ultrasonic alcohol and dried to ensure that the sample surface is not contaminated before the solid-solution treatment and annealing treatment.

[0011] In step 1), the large deformation cold rolling is carried out by unidirectional rolling, and single-pass rolling or multi-pass rolling can be used. When multi-pass rolling is used, the rolling direction of each pass should be the same. Through unidirectional rolling, the grain of the CoCrFeNiMn alloy can be refined, and the dislocation density of the grain boundary can be increased.

[0012] In step 2), the small deformation cold rolling is carried out in the same rolling direction as step 1) and one-time forming, so that the deformation energy storage of the material is consistent, and the special grain boundary proportion of each region of the material tends to be consistent.

[0013] Compared with the prior art, the application has the following advantages:

[0014] 1. By the above process regulation, according to a more strict criterion, i.e. the angle deviation is set to ±2.5° (such as the orientation difference is <111> / 60°, which contains the orientation difference <111> / 57.5° to <111> / 62.5°), which is much smaller than the Brandon and Palumbo-Aust criterion, the proportion of Σ3 grain boundaries is more than 60%. On this basis, the proportion of coherent Σ3 grain boundaries in Σ3 grain boundaries is about 70% by the five-parameter method and the grain boundary interface matching quantitative characterization method.

[0015] 2. The present application adopts high temperature of 1010-1070 DEG C and short time annealing, which can effectively solve the problem of high cost caused by long annealing time in the prior art.

[0016] 3. The proportion of low ΣCSL grain boundaries of the material obtained after the method of the present application is more than 70%, the proportion of Σ3 grain boundaries is more than 60%, and the proportion of coherent Σ3 grain boundaries in Σ3 grain boundaries is more than 70%. The present application not only improves the proportion of Σ3 grain boundaries, but also improves the proportion of coherent twin boundaries and {111} / {115} matched Σ9 grain boundaries, effectively improves the corrosion resistance of CoCrFeNiMn high-entropy alloy, and has a wide application prospect.

[0017] 4. The equipment required in the process of the present application is the most conventional equipment in actual factory production, and has high controllability, strong reliability and easy factory actual production promotion. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The orientation imaging micrographs of CoCrFeNiMn alloy amorphous grain boundary engineering sample (A) and grain boundary engineering sample (B) obtained by EBSD; wherein (a) is the orientation imaging micrograph of sample A, (b) is the grain boundary network diagram (GNB) of sample A, (c) is the orientation imaging micrograph of sample B, and (d) is the grain boundary network diagram (GNB) of sample B.

[0019] Figure 2 (a) is a low ΣCSL grain boundary proportion statistical diagram of CoCrFeNiMn alloy sample A, and (b) is a low ΣCSL grain boundary proportion statistical diagram of CoCrFeNiMn alloy sample B. The proportion of low ΣCSL grain boundaries contained in sample A is 54%, and the proportion of low ΣCSL grain boundaries contained in sample B is 74%.

[0020] Figure 3 (a) is a Σ3 (<111> / 60°) grain boundary interface distribution diagram of sample B, and (b) is a Σ9 (<011> / 38.94°) grain boundary interface distribution diagram of sample B.

[0021] Figure 4(a) is a weighted average misorientation Gaussian distribution curve for sample BΣ3 (<111> / 60°); (b) is a weighted average misorientation Gaussian distribution curve for sample BΣ9 (<011> / 38.94°)

[0022] Figure 5 are potentiodynamic polarization curves obtained from electrochemical testing of Cantor alloy samples.

[0023] Figure 6 is a plot of corrosion current density for samples A, B, C, and D. DETAILED DESCRIPTION

[0024] The application will be further described below in conjunction with the accompanying drawings and specific examples.

[0025] Example 1

[0026] A grain boundary engineering treatment method for improving the corrosion resistance of a CoCrFeNiMn high-entropy alloy, comprising the following steps:

[0027] First step, control the original structure:

[0028] After solid solution treatment of the original CoCrFeNiMn alloy strip at 1100°C for 10h, use a Y132S-4 type test rolling mill with a roller diameter of 130mm, double roller drive, and a rotation speed of 33r / min. In the first rolling, the CoCrFeNiMn alloy strip with a size of 26mm x 10mm x 10mm is fed into the roller along the length direction in multiple passes, and rolled to 2.0mm thick, with a cross-section deformation of 80% (from 10mm to 2mm). A CoCrFeNiMn alloy strip with a size of 120mm x 14mm x 2.0mm is obtained, and a KSY-12-16 type box muffle furnace is used for vacuum annealing at 1010°C for 5min. The CoCrFeNiMn alloy strip obtains a uniform grain size structure.

[0029] Second step, small deformation cold rolling and high temperature annealing:

[0030] The CoCrFeNiMn alloy strip obtained in the first step is rolled to 1.96mm thick by one pass, with a cross-section deformation of 4%, obtaining a Cantor alloy strip with a size of 120mm x 14mm x 1.92mm. After annealing at 1010°C for 25min using a KSY-12-16 type box muffle furnace, the sample is taken out and water cooled. The grain boundary engineering treated sample is recorded as B.

[0031] Comparative Example 1: CoCrFeNiMn non-grain boundary engineering treated sample A

[0032] The sample obtained after the first step treatment of the CoCrFeNiMn alloy strip is denoted as A, i.e., sample A is subjected to original microstructure control and is not subjected to grain boundary engineering treatment.

[0033] Experimental test analysis: The CoCrFeNiMn alloy strips A and B obtained from Example 1 and Comparative Example were measured by electron backscatter diffraction (EBSD) method, and after analysis by HKL-Channel 5 software according to Palumbo-Aust standard, it was found that the proportion of low Σ CSL grain boundaries in sample B was 74%, which was not subjected to GBE process treatment, while the proportion of low Σ CSL grain boundaries in sample A treated by traditional process was 54%. See Figure 1 and Figure 2 .

[0034] The grain boundary data obtained above were filtered with fixed rotation axis and rotation angle. <1 1 1> and <0 11> were selected as the rotation axis, and the axis angle deviation was ±8°. Then the rotation angle filtering was performed, and the angle deviation was ±2.5°, which was more stringent than the angle of Palumbo-Aust criterion, to ensure the credibility and accuracy of the obtained data.

[0035] The previously screened grain boundaries with fixed misorientation were analyzed one by one by single section five-parameter analysis method (FPA), and the grain boundary plane distribution (GBPD) was counted to generate the grain boundary plane distribution map (usually projected on the (0 0 1) plane). The single section five-parameter analysis method is a method proposed by Rohrer et al. in 2004 based on stereology. This method takes into account the influence of preferred distribution, and under the condition of two-dimensional measurement, it corrects the true length of the grain boundary plane distribution on any crystal plane (h k l). The area distribution intensity of the grain boundary in the actual three-dimensional space is represented by the ratio of the corrected true length to the length of the randomly distributed grain boundary on the crystal plane (multiples of random distribution, MRD), i.e., the grain boundary plane distribution intensity.

[0036] After obtaining the grain boundary plane distribution of the grain boundaries with fixed misorientation, the "grain boundary interface matching" (GBIC) method was used to determine the interface matching type of the grain boundaries of the material.

[0037] The grain boundary interface matching type such as {h1 k1 l1} / {h2 k2 l2} is usually determined according to the grain boundary interface distribution map of the grain boundary. If {h1 k1 l1} and {h2 k2 l2} are both the strongest or the second strongest distribution in the grain boundary interface distribution map and satisfy the following formulas (1) and (2), it can be determined that the grain boundary interface matching feature of the group of grain boundaries is {h1 k1 l1} / {h2 k2 l2}, such as whether there is a {1 1 1} / {1 1 1} coherent twin grain boundary in a Σ3 (orientation difference is <1 1 1> / 60°) grain boundary, whether there is a {1 1 1} / {1 1 5} grain boundary in a Σ9 (orientation difference is <0 1 1> / 38.9°) grain boundary, and the like.

[0038]

[0039]

[0040] m cosθ, n = sinθ, the rotation axis [u, v, w] in formula (2) is normalized, that is, u 2 + v 2 + w 2 = 1.

[0041] The proportion of the grain boundary with the {h1 k1 l1} / {h2 k2 l2} interface matching feature in each group of grain boundaries with a fixed orientation difference in the total grain boundaries can be calculated by the following formula (3)

[0042] F = AP + B (PM / M) (3)

[0043] Wherein, A = 0.4888, B = 0.0393 are fitting parameters, P is the proportion of the fixed orientation difference grain boundary in the total grain boundary, W is the weighted average orientation difference Gaussian distribution curve half width, and M is the distribution intensity of {h1 k1 l1} or {h2 k2 l2} in the grain boundary interface distribution map.

[0044] Σ3 grain boundary P value calculation: for Σ3 grain boundary with an orientation difference of <1 1 1> / 60°, the <1 1 1> axis filtering length percentage is 62.11%, the proportion of the grain boundary filtered out by <1 1 1> / 60° angle (grain boundary with an orientation difference between <1 1 1> / 57.5° and <1 1 1> / 62.5°) in the grain boundary filtered out by <1 1 1> axis is 97.61%, then the proportion of Σ3 grain boundary, that is, the P value is 62.11% x 97.61% = 60.6%.

[0045] Result analysis: P = 60.6%; it can be known from the figure that the maximum value of MRD is 5.82: W = 0.58348.

[0046] By formula (3), the above obtained results are substituted into, F = 53.54% can be obtained, which is the proportion of Σ3 grain boundaries with {1 1 1} / {1 1 1} matching. The proportion of Σ3 grain boundaries is 60.6%, and the proportion of coherent twin grain boundaries in Σ3 grain boundaries is 88.3%.

[0047] Σ9 grain boundary P value calculation: for Σ9 grain boundary <0 1 1> / 38.94°, the percentage of <1 1 1> axis filtering length is 11.60%, the percentage of <1 1 1> / 60° angle filtering length is 64.27%, and the P value is the proportion of Σ9 grain boundaries (orientation difference is <1 1 1> / 57.5° to <1 1 1> / 62.5°).

[0048] Result analysis: P = 7.4%; it can be known from the figure that the maximum value of MRD is 1.40: W = 1.11674.

[0049] By formula (3), the above obtained results are substituted into, F = 53.54% can be obtained, which is the proportion of Σ3 grain boundaries with {1 1 1} / {1 1 1} matching. The proportion of Σ3 grain boundaries is 60.6%, and the proportion of coherent twin grain boundaries in Σ3 grain boundaries is 88.3%.

[0050] Example 2

[0051] Sample A: Comparative Example 1 product

[0052] Sample B: Example 1 product

[0053] Sensitization treatment sample C: sample A is kept at 780℃ for 50 hours and then cooled to room temperature in air, as sensitization treatment sample C.

[0054] Sensitization treatment sample D: sample B is kept at 780℃ for 50 hours and then cooled to room temperature in air, as sensitization treatment sample C.

[0055] Samples A, B, C, D are used in turn 400 # , 600 # , 800 # , 1000 # , 1500 # , 2000 # , 000 # , 000 #The metallographic sand paper is ground to remove the oxide skin, and then mechanical polishing is performed using a W2.5 diamond polishing paste, the residual polishing paste on the surface of the sample is first scrubbed using a cotton swab under water flow, and then ultrasonic cleaning is performed using alcohol, and an electric hair dryer is used for drying. Four samples are used for electrochemical testing using a CHI660E electrochemical workstation, a saturated calomel electrode (SCE) is used as a reference electrode, and a large platinum plate is used as a counter electrode. The solution used for testing is a 10% NH4Cl solution, and the remaining five surfaces of the sample to be tested, except for the working surface, are sealed with resin powder. Before testing, the sample is immersed in the solution for 2 hours to achieve pre-passivation treatment, and then an open circuit potential (OCP) test is performed for 1800 seconds to stabilize the system. The polarization curve of the sample is measured from -1 to 0.1 V at a scan rate of 0.5 mV / s.

[0056] The following is data processing and analysis:

[0057] The corrosion potential reflects the thermodynamic tendency of material corrosion, and the corrosion current density reflects the kinetic characteristics of material corrosion.

[0058] Figure 5 It can be seen that the corrosion potential of sample C is the smallest, and the corrosion potential of sample B is the largest, so it can be considered that sample C is most prone to corrosion, and sample B is most difficult to corrode. The corrosion current densities of samples A, B, C and D are calculated by fitting, and are shown in Table 1, respectively. Figure 6 -8 A / cm 2 , 4.547 x 10 -8 A / cm 2 , 2.661 x 10 -7 A / cm 2 , 5.615 x 10 - 8 A / cm 2 It can be seen that the corrosion current density of sample C is the largest, and the corrosion current density of sample B is the smallest. Therefore, it can be considered that the corrosion rate of sample C is the largest, and the corrosion rate of sample B is the smallest. In summary, it can be concluded that the corrosion resistance of sample B is the best, that is, the corrosion resistance of the CoCrFeNiMn alloy treated by the two steps of controlling the original structure, small deformation cold rolling and high temperature annealing is significantly improved.​

Claims

1. A grain boundary engineering treatment method for improving the corrosion resistance of a CoCrFeNiMn high-entropy alloy, characterized by, The method comprises the following steps: 1) original tissue regulation The CoCrFeNiMn high-entropy alloy raw material is solid-solved at 1100 DEG C for more than 10 h, then the material is cold-rolled with large deformation, the deformation amount is 50%-80%, and then the material is annealed at 1010 DEG C-1070 DEG C, the annealing time is not less than 1.5 min, and the pretreated material is obtained; 2) small deformation and high-temperature annealing The pretreated material is cold-rolled with small deformation, the deformation amount is 4%-10%, and then the material is recrystallized annealed at 1010 DEG C-1070 DEG C, the annealing time is not less than 3 min.

2. The grain boundary engineering treatment method for improving the corrosion resistance of CoCrFeNiMn high-entropy alloy according to claim 1, characterized in that, Before the solid-solution treatment and the annealing treatment in steps 1) and 2), the surface of the material is polished, and then the material is cleaned by ultrasonic cleaning with alcohol and dried.

3. The grain boundary engineering treatment method for improving the corrosion resistance of CoCrFeNiMn high-entropy alloy according to claim 1, characterized in that, When the large deformation cold rolling in step 1) is performed, single pass rolling is adopted.

4. The grain boundary engineering treatment method for improving the corrosion resistance of CoCrFeNiMn high-entropy alloy according to claim 1, characterized in that, When the large deformation cold rolling in step 1) is performed, multi-pass rolling is adopted and the rolling direction is the same each time.

5. The grain boundary engineering treatment method for improving the corrosion resistance of CoCrFeNiMn high-entropy alloy according to claim 1, characterized in that, When the small deformation cold rolling in step 2) is performed, the rolling direction is the same as that in step 1) and one-time forming is adopted.

6. The grain boundary engineering treatment method for improving the corrosion resistance of CoCrFeNiMn high-entropy alloy according to claim 1, characterized in that, The proportion of low Sigma CSL grain boundaries of the material obtained after step 2) is 74%, the proportion of Sigma 3 grain boundaries is 60.6%, and the proportion of coherent Sigma 3 grain boundaries in the Sigma 3 grain boundaries is 88.3%.

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