CN113802073A

CN113802073A - Preparation method of metal bar with wide-size gradual-evolution gradient nano structure

Info

Publication number: CN113802073A
Application number: CN202110935701.4A
Authority: CN
Inventors: 马新凯; 杨亮; 陈卓; 罗胜年
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2021-08-16
Filing date: 2021-08-16
Publication date: 2021-12-17

Abstract

The invention discloses a preparation method of a metal bar with a wide-size gradually-evolving gradient nano structure, which solves the technical problem that the gradient distribution of the grain size shows sharp change in the prior art. The technical scheme is as follows: the metal rod-shaped material is nickel, copper, aluminum or iron, and the grain size along the radial direction is continuously reduced from inside to outside, wherein the grain size of the core part is more than or equal to 1000nm, and the grain size of the surface layer is less than or equal to 100 nm. The blank has: the deformation part generates the metal material with the grain size continuously changing in a gradient manner after the deformation part generates shear strain, and the grain size of the core part is less than or equal to that of the blank; the clamping parts are positioned at two ends of the deformation part and are used for being matched with a clamp of the torsion equipment. The preparation method comprises the following steps: obtaining the blank; clamping the clamping parts at two ends of the blank body on a clamp of the twisting equipment; and controlling the clamp at one end or two ends to twist, and obtaining the metal rod-shaped material with the grain size changing continuously and gradiently after twisting.

Description

Preparation method of metal bar with wide-size gradual-evolution gradient nano structure

Technical Field

The invention relates to the technical field of gradient nano materials, in particular to a preparation method of a metal bar with a wide-size gradually-evolving gradient nano structure.

Background

Gradient nanostructure materials are generally composed of a nanostructure surface layer and a central coarse crystal layer with gradient grains distributed in the middle, and thus, the gradient nanostructure is a typical cross-scale particle hierarchical structure with a superior combination of strength and ductility. The gradient structure can form completely different grain sizes, different twin crystal intervals or the combination of micro-nano grains and twin crystals, so that the gradient nano structure has the potential of avoiding the trade-off problem of strength and ductility in material science.

The preparation methods of gradient nanostructure materials are generally divided into two categories: (1) top-down methods, including surface mechanical treatment methods such as cumulative rolling and laser shock peening; (2) bottom-up methods, including physical and chemical deposition techniques such as electrodeposition, magnetron sputtering, and 3D printing.

The surface mechanical treatment technology needs to repeatedly and mechanically grind the surface of a metal sample, and needs to repeatedly adjust a plurality of process parameters such as test indentation, rotation speed, horizontal feeding speed and the like according to the metal category, so that the process is very complex and the processing efficiency is low; or the strain can be controlled only by experience; different materials have obvious difference under the same process parameters, so that the design and control of a gradient structure are difficult to realize; the surface quality of the processed metal sample is obviously reduced compared with the initial state, and the success rate is low; generally, the thickness of the sample is thin, the interface between the nanocrystalline and the coarse crystal is clear, and no gradual gradient change is formed.

The material prepared by physical and chemical deposition techniques is composed of a plurality of granular layers with different grain sizes in the depth direction, the grain size in each granular layer is basically consistent, and the granular layers have obvious boundaries, so that although the microstructure of the material generates gradient distribution, the grain size and the microscopic defect gradient distribution of the gradient structure are changed rapidly and do not have continuous gradient span; the problem of weak bonding force between particle layers may exist; moreover, the processes have high difficulty and high cost, and the overall quality of the sample is difficult to ensure and the large-scale application is difficult.

Disclosure of Invention

In a first aspect, the present invention is directed to a metal rod material to solve the problem of the prior art that the material exhibits a sharp change in the grain size gradient distribution.

In a second aspect, the invention aims to provide a blank and a method for preparing the metal rod-shaped material, so as to solve the technical problems of the prior art that the grain size gradient distribution of the material shows a sharp change and the process is difficult to be applied on a large scale

In order to achieve the above object, according to a first aspect of the present invention, a metal bar-shaped material is provided. The technical scheme is as follows:

the metal rod-shaped material is nickel, copper, aluminum or iron, and the grain size along the radial direction is continuously reduced from inside to outside, wherein the grain size of the core part is more than or equal to 1000nm, and the grain size of the surface layer is less than or equal to 100 nm.

In order to achieve the above object, according to a second aspect of the present invention, a blank is first provided. The technical scheme is as follows:

a blank for producing the metal rod-like material of the first aspect, having: the deformation part generates the metal rod-shaped material with the grain size continuously changing in a gradient manner after the deformation part generates shear strain, and the grain size of the core part is less than or equal to that of the blank; the clamping parts are positioned at two ends of the deformation part and are used for being matched with a clamp of the torsion equipment.

Further, the length of the deformation part is 4-7 times of the diameter of the cross section; and/or the cross section diameter of the deformation part is 0.5-20 mm.

Further, the cross-sectional area of the deformation portion is smaller than the cross-sectional area of the clamping portion; and/or an arc part is further arranged between the deformation part and the clamping part, and the length of the arc part is preferably 5-15 mm.

In order to achieve the above object, according to a second aspect of the present invention, there is provided a method for producing a metal rod-like material. The technical scheme is as follows:

the method for preparing the metal rod-like material of the first aspect comprises the following steps: obtaining the blank; clamping the clamping parts at two ends of the blank body on a clamp of the twisting equipment; and controlling the clamp at one end or two ends to twist, and obtaining the metal rod-shaped material with the grain size changing continuously and gradiently after twisting.

Further, during the twisting process, the distance between the two clamps is constant; and/or the rotating shaft of the clamp is coaxial with the axis of the blank.

Further, the twisting rate is 2 to 10 DEG/sec.

Furthermore, the shear strain gamma generated by torsion is more than or equal to 7, gamma is r theta/L, wherein r is the cross section radius of the deformation part, L is the length of the deformation part, theta is the torsion angle, theta is 360 DEG n, and n is the number of torsion turns.

Further, a green body is obtained by turning; and/or, the method also comprises the step of pretreating the blank, wherein the pretreatment comprises annealing treatment and surface treatment.

Further, the annealing treatment is heat treatment for 1.5 to 3.5 hours at 700 to 800 ℃; the surface treatment comprises descaling treatment, deoiling treatment and polishing treatment.

The deformation mechanisms of metallic materials mainly include slip, twinning and phase transition. Therefore, the metal can be roughly divided into a metal based on the dislocation slip deformation mechanism and a metal based on the non-slip deformation mechanism by dividing the metal from the deformation mechanism. The invention can generate metal rod-shaped materials with continuous gradient change gradient nanostructures from metal materials (such as nickel, copper, aluminum and iron) mainly based on a dislocation slip deformation mechanism.

The metal rod-shaped material, the blank and the preparation method of the metal rod-shaped material have the following advantages:

(1) the grain size of the obtained metal rod-shaped material is continuously changed along the radial direction to form a gradient nano structure which evolves gradually, so that the continuous gradient distribution of the grain microstructure from inside to outside in a real sense is realized, and the problem that obvious sections exist between a gradient layer and an original coarse crystal layer and between a particle layer and the particle layer in the prior art is solved.

(2) Besides the microstructure with continuous gradient distribution of grain size, wide-size metal rod-shaped material with larger thickness size (namely the cross section diameter of the metal rod-shaped material) can be obtained, and the material strength is improved more obviously.

(3) The metal rod-shaped material with the advantages can be obtained through pure torsional deformation, and the processing efficiency is high.

(4) The pure torsional deformation is adopted, the initial surface quality is basically not influenced, and the surface quality of the prepared metal rod-shaped material is higher.

(5) By controlling the torsional deformation angle theta, the length L and the radius r of the blank, the shearing strain of the surface layer of the blank can be controlled, so that the gradient structure characteristics of the metal rod-shaped material are controlled, and the problems of complex and variable process parameters and low sample success rate are effectively solved.

The invention is further described with reference to the following figures and detailed description. Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to assist in understanding the invention, and are included to explain the invention and their equivalents and not limit it unduly. In the drawings:

fig. 1 is a schematic structural view of a first embodiment of a blank.

Fig. 2 is a schematic structural view of a second embodiment of the blank.

FIG. 3 is a cross-sectional structure view of the metal rod-like materials of examples 1 to 6.

FIG. 4 is a graph showing the hardness gradient distribution of the metal bar-shaped materials of examples 1 to 6.

Fig. 5 shows an IPF chart (left) and a stress distribution chart (right) of the core longitudinal section (0R) of PT2, an IPF chart (left) and a stress distribution chart (right) of the middle longitudinal section (0.5R), and an IPF chart (left) and a stress distribution chart (right) of the surface layer (1R).

Fig. 6 shows an IPF chart (left) and a stress distribution chart (right) of the core longitudinal section (0R) of PT6, an IPF chart (left) and a stress distribution chart (right) of the middle longitudinal section (0.5R), and an IPF chart (left) and a stress distribution chart (right) of the surface layer (1R).

The relevant references in the above figures are:

100-deformation, 200-grip, 300-arc.

Detailed Description

The invention will be described more fully hereinafter with reference to the accompanying drawings. Those skilled in the art will be able to implement the invention based on these teachings. Before the present invention is described in detail with reference to the accompanying drawings, it is to be noted that:

the technical solutions and features provided in the present invention in the respective sections including the following description may be combined with each other without conflict.

Moreover, the embodiments of the present invention described in the following description are generally only some embodiments of the present invention, and not all embodiments. Therefore, all other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort shall fall within the protection scope of the present invention.

With respect to terms and units in the present invention. The terms "comprising," "having," and any variations thereof in the description and claims of this invention and the related sections are intended to cover non-exclusive inclusions.

The preparation method of the metal rod-shaped material comprises the following steps:

(1) obtaining a blank body, specifically as follows:

fig. 1 is a schematic structural view of a first embodiment of a blank.

As shown in fig. 1, the blank has a deformation portion 100 and a clamping portion 200, the deformation portion 100 generates a metal rod-shaped material with a continuous gradient change of crystal grain size after being subjected to shear strain, the clamping portion 200 is positioned at two ends of the deformation portion 100, and the clamping portion 200 is used for matching with a clamp of a twisting device; the cross-sectional area of the deformation portion 100 is smaller than that of the grip portion 200; the cross-section of the deformation 100 is preferably circular, which helps to obtain a metal rod-like material with a uniform microstructure.

Fig. 2 is a schematic structural view of a second embodiment of the blank.

As shown in fig. 2, in addition to the first embodiment, the second embodiment of the blank further includes an arc portion 300 provided between the deforming portion 100 and the clamping portion 200, and the length of the arc portion 300 is preferably 5 to 15 mm.

In the blanks of the two embodiments, the arc-shaped part 300 of the second embodiment of the blank can reduce the shear stress concentration caused by the sudden diameter change of the deformation part 100 and the clamping part 200, and improve the overall quality of the metal rod-shaped material.

Preferably, the blank is obtained by lathing, that is, two ends of a cylindrical sample made of nickel, copper, aluminum or iron are clamped on lathing equipment, then the parts to be formed into the deformation part 100 and the arc part 300 are lathed, and the clamping part 200 is formed on the non-lathed parts, so that the blank is obtained. Generally, a blind hole connected with a turning device may be left inside the clamping portion 200 of the green body formed after turning.

(2) The method comprises the following steps of pretreating a blank, wherein the pretreatment comprises annealing treatment and surface treatment, the surface treatment comprises scale breaking treatment, deoiling treatment and polishing treatment, and the method comprises the following specific steps:

annealing treatment: heat treatment is carried out for 1.5 to 3.5 hours at the temperature of 700 to 800 ℃; the stress inside the blank can be removed by annealing treatment.

And (3) scale breaking treatment: soaking the annealed blank in a pickling solution for 0.5h at 30 ℃, wherein the pickling solution comprises 50% of hydrofluoric acid, 10% of sulfuric acid and the balance of water by mass; the oxide scale breaking treatment can remove impurities on the surface of the blank, and the surface quality of the product is improved.

Deoiling treatment: and (2) putting the blank subjected to scale breaking treatment into a degreasing agent to remove oil stains on the surface of the blank, wherein the degreasing agent comprises 10% of sodium hydroxide, 5% of Tween 80, 5% of octyl phenol polyoxyethylene ether, 5% of diethylene glycol monobutyl ether, 0.1% of benzotriazole and the balance of water by mass.

Polishing with abrasive paper: and sequentially grinding the surfaces of the blanks after the oil removal treatment by using 400#, 800#, 1200#, 1500# and 2000# sandpaper to reduce the surface roughness of the blanks.

In order to further reduce the surface roughness of the blank, one or any of the following polishing modes can be further adopted:

polishing treatment by using a polishing solution: using SiO₂Polishing the polishing solution and the velveteen polishing cloth for 15-30 min, wherein the rotating speed of the polishing machine is 300-600 r/min.

Electrolytic polishing treatment: the electrolyte consists of 12.5% of perchloric acid, 37.5% of glacial acetic acid and the balance of absolute ethyl alcohol by mass, the electrolytic polishing voltage is 15-18V, the current is 0.25-0.35A, the temperature is-15 to-25 ℃, and the electrolytic time is 30-50 min.

(3) The clamping portions 200 at both ends of the blank are clamped on the clamps of the twisting device, and in order to obtain the optimal twisting effect, the rotating shaft of the clamps needs to be coaxial with the axis of the blank.

(4) Controlling the clamp at one end or two ends to twist, and obtaining the metal rod-shaped material with the grain size changing continuously and gradiently after twisting; the method comprises the following specific steps:

in the twisting process, the distance between the two clamps is constant, so that the magnitude of the shear strain can be accurately controlled conveniently.

The torsion rate is 2-10 DEG/s; only when the torsion rate is in the numerical range, the blank can generate quasi-static torsion, so that the gradient nano structure with better gradient change can be obtained.

The shear strain gamma generated by torsion is more than or equal to 7, wherein gamma is r theta/L, wherein r is the cross section radius of the deformation part 100, L is the length of the deformation part 100, theta is the torsion angle, theta is 360 DEG n, and n is the number of torsion turns; it is verified that when the shear strain gamma is less than 7, it is difficult to make the surface layer of the blank nano.

The shear strain gamma increases with the increase of the cross-sectional radius r of the deformation part 100, that is, with the increase of the cross-sectional radius r of the deformation part 100, the torsion force required for preparing the gradient nanostructure increases, and therefore, in order to obtain a metal bar material with a wide size as much as possible, the cross-sectional diameter of the deformation part 100 is preferably 0.5-20 mm; while the shear strain γ decreases with increasing length L of the deformation 100, i.e. a longer deformation 100 can more easily obtain a gradient nanostructure under the same twisting force, the length L of the deformation 100 is preferably 4 to 7 times the cross-sectional diameter for ease of handling.

When a torsion mode that one end is fixed and the other end is twisted is adopted, theta is the rotation angle of the twisted end; when a twisting mode that two ends are simultaneously twisted is adopted, theta is the sum of the rotation angles of the two twisted ends.

In addition, the direction of torsion can be unidirectional or multidirectional; unidirectional means that the twisting end always rotates clockwise or counterclockwise; the multi-directional rotation means that the rotation is clockwise or anticlockwise.

The metal rod-shaped material prepared by the method is made of nickel, copper, aluminum or iron, and the grain size along the radial direction is continuously reduced from inside to outside, wherein the grain size of the core part is more than or equal to 1000nm and less than or equal to that of the blank, the grain size of the surface layer is less than or equal to 100nm, and the grains of the surface layer have a nano structure, so that the metal rod-shaped material has a gradually-evolving gradient nano structure.

The advantageous effects of the present invention are further illustrated by examples 1 to 6 below.

The preparation methods of the metal rod-shaped materials in examples 1 to 6 are different only in the number of turns, and specific process parameters are shown in Table 1. In table 1, the effective shear strain is an empirical value obtained from the shear strain, and can be basically considered as an actual measurement value.

The other parameters are the same, and specifically are as follows: the blank is made of metallic nickel, the length L of the deformation part 100 is 24mm, the diameter of the deformation part is 4mm, the length L1 of the clamping part 200 is 7mm, and the length L2 of the arc-shaped part 300 is 11 mm; the annealing temperature is 750 ℃, and the annealing time is 2 hours; the rate of twist was 5 °/second; a torsion mode that one end is fixed and the other end is twisted is adopted; the rotation direction is unidirectional.

TABLE 1

FIG. 3 is a cross-sectional structure of the metal rod-like materials of examples 1 to 6, which is observed with a microscope, wherein the left side of the drawing is a core part and the right side thereof is a surface layer.

As can be seen from FIG. 3, when the number of turns is less than or equal to 2, the surface layer grains are not obviously refined;

when the number of turns is 6, the grain size of the surface layer is obviously reduced;

when the number of the twisting turns is 12 and 16, the grain size of the surface layer is less than or equal to 100nm and reaches the nanometer level; the grain size refinement effect of the core part is not obvious, the grain size of the core part is almost the same as that of the blank, and the grain size of the core part is more than or equal to 1000 nm; the grain size between the core part and the surface layer is changed in a continuous gradient mode, and the section caused by the sudden change of the grain size is avoided.

The "continuous gradient change" is understood to mean: the length from the core part to the surface layer is taken as an X axis, the grain size is taken as a Y axis, and the variation curve of the grain size along with the length on the cross section from the core part to the surface layer is taken as a straight line.

FIG. 4 is a graph showing the gradient of Hardness of the metal bar-shaped materials of examples 1 to 6, wherein the abscissa "Distance" is the diameter of the cross section of the deformed portion 100 in mm and the ordinate "Hardness" is the Hardness in HV0.2, HV0.2 meaning that the Hardness load was measured at 200 g.

As can be seen from fig. 4, the hardness inside the material is substantially uniform when not twisted; after twisting, the hardness in the material shows continuous gradient change, and the change rate of the hardness along the diameter is basically consistent under different twisting turns, which shows that the grain size in the material is changed integrally along with the increase of the twisting turns.

Fig. 5 shows the IPF map (left) and the stress profile (right) of the longitudinal section (0R) of the core portion of PT2, the IPF map (left) and the stress profile (right) of the longitudinal section (0.5R) of the central portion, which is an intermediate position between the core portion and the surface layer, and the IPF map (left) and the stress profile (right) of the surface layer (1R).

As can be seen from fig. 5: when the core was twisted by 2 turns, the grain refinement from the core to the surface layer was not sufficiently significant, but the concentration of local strain was gradually increased as seen from the stress profile.

As can be seen from fig. 6: when the steel wire is twisted for 6 circles, the grain size from the core part to the surface layer is obviously reduced, the local strain concentration is more obvious, the strain is gradually increased from the core part to the surface layer and has an opposite trend with the change of the grain size, and the whole steel wire conforms to the strain rule of the prepared gradient structure.

The contents of the present invention have been explained above. Those skilled in the art will be able to implement the invention based on these teachings. All other embodiments, which can be derived by a person skilled in the art from the above description without inventive step, shall fall within the scope of protection of the present invention.

Claims

1. The metal rod-shaped material is nickel, copper, aluminum or iron, and is characterized in that: the grain size along the radial direction is continuously reduced from inside to outside, wherein the grain size of the core part is more than or equal to 1000nm, and the grain size of the surface layer is less than or equal to 100 nm.

2. A body for use in the production of a metal rod-like material according to claim 1, characterized in that: comprising:

the deformation part (100) generates the metal rod-shaped material with the continuously gradient change of the grain size after the shear strain is generated on the deformation part (100), and the grain size of the core part is less than or equal to that of the blank;

the clamping part (200), clamping part (200) are located the both ends of deformation portion (100), clamping part (200) are used for cooperating with the anchor clamps of torsion equipment.

3. The blank of claim 2, wherein: the length of the deformation part (100) is 4-7 times of the diameter of the cross section; and/or the cross section diameter of the deformation part (100) is 0.5-20 mm.

4. The blank of claim 2, wherein: the cross-sectional area of the deformation part (100) is smaller than that of the clamping part (200); and/or an arc part (300) is arranged between the deformation part (100) and the clamping part (200), and the length of the arc part (300) is preferably 5-15 mm.

5. A method for preparing a metal rod-like material according to claim 1, comprising the steps of:

obtaining a body according to any one of claims 2 to 4;

clamping the clamping parts (200) at the two ends of the blank body on a clamp of the twisting equipment;

and controlling the clamp at one end or two ends to twist, and obtaining the metal rod-shaped material with the grain size changing continuously and gradiently after twisting.

6. The method of claim 5, wherein: in the twisting process, the distance between the two clamps is constant; and/or the rotating shaft of the clamp is coaxial with the axis of the blank.

7. The method of claim 5, wherein: the twisting rate is 2 to 10 DEG/sec.

8. The method of claim 5, wherein: the shear strain gamma generated by torsion is more than or equal to 7, and gamma is r theta/L, wherein r is the cross section radius of the deformation part (100), L is the length of the deformation part (100), theta is the torsion angle, theta is 360 DEG n, and n is the number of torsion turns.

9. The method of claim 5, wherein: obtaining a green body by adopting turning; and/or, the method also comprises the step of pretreating the blank, wherein the pretreatment comprises annealing treatment and surface treatment.

10. The method of claim 9, wherein: the annealing treatment is heat treatment at 700-800 ℃ for 1.5-3.5 hours; the surface treatment comprises descaling treatment, deoiling treatment and polishing treatment.