阅读说明：本技术 一种制备具有确定孪晶取向的纳米孪晶金属试样的方法 (Method for preparing nano twin crystal metal sample with determined twin crystal orientation ) 是由 梁春园 张奕志 刘嘉斌 王宏涛 于 2019-02-25 设计创作，主要内容包括：本发明公开了一种制备具有确定孪晶取向的纳米孪晶金属试样的方法,包括以下步骤：选取层错能较低的材料,制成圆棒；剪切上述圆棒,得到纳米金属尖端,将此圆棒装入样品杆固定端,使断口端朝外；取另一圆棒,制备出金属针尖,剪切圆棒,后装入样品杆活动端,使金属针尖朝外；将样品杆插入透射电镜中,选择与所需形成的孪晶取向的纳米孪晶材料具有相同晶体取向的纳米金属尖端,使该纳米金属尖端处于正焦状态；使活动端针尖与该纳米金属尖端正对；在固定端和活动端间施加电压,活动端针尖与固定端纳米金属尖端相接触,发生熔化,形成纳米孪晶金属试样。本发明方法可以快捷地制备出一定孪晶取向的纳米孪晶材料。(The invention discloses a method for preparing a nanometer twin crystal metal sample with a determined twin crystal orientation, which comprises the following steps: selecting a material with lower stacking fault energy to prepare a round bar; shearing the round bar to obtain a nano metal tip, and loading the round bar into the fixed end of the sample rod to enable the fracture end to face outwards; taking another round bar, preparing a metal needle point, shearing the round bar, and then loading the round bar into the movable end of the sample rod to enable the metal needle point to face outwards; inserting a sample rod into a transmission electron microscope, and selecting a nano-metal tip with the same crystal orientation as a nano-twin material with the twin orientation to be formed so as to enable the nano-metal tip to be in a positive focal state; the needle point of the movable end is opposite to the nano metal tip; and applying voltage between the fixed end and the movable end, and melting the needle point of the movable end in contact with the nano metal tip of the fixed end to form the nano twin crystal metal sample. The method can quickly prepare the nanometer twin crystal material with certain twin crystal orientation.)

1. A method of preparing a nano twinned metal coupon having a defined twinning orientation, comprising the steps of:

(1) selecting a material with lower stacking fault energy, cutting the material into cuboids with the length, width and height of 30mm, 0.3mm and 0.3mm respectively, and polishing the cuboids into round rods with the diameter of 0.2-0.25 mm;

(2) shearing the round rod with the diameter of 0.2-0.25 mm obtained in the step (1), obtaining a nano metal tip at the fracture, and putting the sheared round rod into the fixed end of the sample rod to enable the fracture end of the round rod to be outward;

(3) taking another round bar which is processed in the step (1) and has the diameter of 0.2-0.25 mm, preparing a metal needle point by an electrochemical polishing method, cutting the round bar into the length of 3-5 mm, and then placing the round bar into the movable end of the sample rod to enable the metal needle point to face outwards;

(4) inserting the nanofactory sample rod into a transmission electron microscope, observing the nano metal tip on the fixed end, performing selective electron diffraction on the nano metal tip on the fixed end, and selecting the nano metal tip with the same crystal orientation as the nano twin crystal material to be formed so as to enable the nano metal tip to be in a positive focal state;

(5) adjusting the position of the needle point of the movable end to enable the needle point to be opposite to the nano metal tip selected in the step (4);

(6) and applying 3-5V voltage between the fixed end and the movable end, moving the needle point of the movable end to make the needle point contact with the nano metal tip of the fixed end, and melting the needle point of the movable end and the nano metal tip of the fixed end under the action of instantaneous joule heat to finally form the nano twin crystal metal sample.

2. The method for preparing a nano twin crystal metal specimen with definite twin crystal orientation as claimed in claim 1, wherein in step (1), the rectangular parallelepiped material is put between two pieces of sandpaper, and the sandpaper is rubbed back and forth to make the rectangular parallelepiped material generate rolling friction between the sandpaper, so that the rectangular parallelepiped material is ground into a round bar with a diameter of 0.2-0.25 mm.

3. The method for preparing a nano twin metal specimen with definite twin orientation as claimed in claim 1, wherein in the step (2), the method of shearing the round bar is: horizontally placing a round rod, enabling a jaw of the diagonal pliers to be vertical to the round rod, applying force to vertically cut the upper portion and the lower portion of the round rod into a depth h, wherein the relation between h and the diameter D of the round rod is 20% < h/D < 30%; and then, respectively applying axial force F to the left end and the right end of the round bar, and breaking the round bar along the fracture at the speed of about 0.5-5 mm/s, thereby obtaining the nano metal tip.

4. The method for preparing a nano twin crystal metal specimen with definite twin crystal orientation as claimed in claim 1, wherein the process of preparing the metal tip by electrochemical polishing in the step (3) is:

(1) preparing corrosive liquid, putting the corrosive liquid into a glass container, and placing a plastic bracket beside the glass container;

(2) connecting two leads with the tail ends connected with the copper sheet with two ends connected with two ends of a power supply, immersing the copper sheet connected with the negative electrode into corrosive liquid of a glass container, and fixing the copper sheet connected with the positive electrode on a bracket above the corrosive liquid;

(3) sleeving a round bar to be corroded on two plastic sleeves, wherein one end of the round bar is connected with a copper sheet fixed on a bracket; a small gap of 0.5-1.0 mm is exposed between the upper plastic sleeve and the lower plastic sleeve; the upper end of the upper plastic sleeve is positioned above the liquid level, and the lower end of the lower plastic sleeve is positioned below the lower end of the round rod;

(4) after the arrangement is finished, turning on a power supply, adjusting the voltage value to be 5-20V, and carrying out corrosion reaction;

(5) and (3) breaking the small seam between the two plastic sleeves, turning off the power supply after the lower end of the round rod falls into the corrosive liquid, taking out the falling round rod from the corrosive liquid, and taking out the plastic protective sleeve from the tail part of the round rod by using tweezers to obtain the nanoscale metal needle tip.

5. The method for preparing a nano twin metal specimen with definite twin orientation as claimed in claim 1 wherein in step (4), observation of the nano metal tip on the fixed end is performed at a multiple of 40k-100 k.

6. The method of claim 1, wherein in step (4), the nano-metal tip at the fixed end is subjected to selective electron diffraction by using a four-stage selective diaphragm.

7. The method for preparing a nano twin crystal metal specimen with definite twin crystal orientation as claimed in claim 1, wherein in the step (4), the nano metal tip is in positive focus state by adjusting the Z-axis height of the electron microscope.

8. The method for preparing a nano twin metal sample with definite twin orientation as claimed in claim 1, wherein in step (5), the number of times is adjusted to 40k-100k, and the height of the active end is adjusted to make the tip of the active end and the tip of the nano metal selected in step (4) be in the same focal plane; and (4) adjusting the left and right positions of the needle point of the movable end to enable the needle point to be opposite to the nano metal tip selected in the step (4).

Technical Field

The invention relates to a method for preparing a nanometer twin metal sample with determined twin orientation.

Background

The design and preparation of high-performance metal materials have been an important topic in the field of material science research. As two core properties of the metal material, strength and toughness determine the service performance of the metal material in the industrial application process, the research on the strengthening and toughening of the metal material has important significance for guiding the design of novel high-performance metal materials. The traditional method for improving the strength of a metal material to obtain an alloy with excellent performance mainly comprises fine grain strengthening, solid solution strengthening, aging strengthening, dispersion strengthening, phase change strengthening, cold work hardening and the like. Essentially, these strengthening means are all through the introduction of various point, line, surface defects such as second phase particles, strengthening phases, dislocations, grain boundaries, and the like. These defects increase the strength of the alloy by preventing the movement of dislocations, and thus have the inevitable disadvantage of achieving the purpose of increasing the strength of the material at the expense of plasticity. In the case of fine grain strengthening, since grain boundaries can serve as effective barriers to dislocation movement, making plastic deformation difficult, the strength of a material can be effectively improved by introducing a high density of grain boundaries into the material through grain refinement, and fine grain strengthening is also widely used to improve the strength of the material. However, it is worth noting that the existence of the grain boundary can hinder the movement of dislocation, so as to improve the strength of the material, and meanwhile, the movable dislocation density in the material is greatly reduced, so that the plasticity of the material is reduced. In addition, due to the non-coherence of the grain boundary interface, the capability of storing dislocation is limited, and when a large amount of dislocation is accumulated at the grain boundary, stress concentration at the grain boundary is caused to cause the stress at the grain boundary to reach fracture stress, and the material is cracked to cause fracture failure. In order to solve the contradictory problems of alloy strength and plasticity and obtain a metal material with higher strength and better plasticity, researchers try to introduce twin boundaries into the alloy and propose a new strengthening method.

The twin boundary is a special interface different from the boundary, and crystals on two sides of the twin boundary are mutually symmetrical planes to form a mirror symmetry relationship, and the energy of the twin boundary is far lower than that of the conventional boundary. The twin crystal has the capability of blocking and storing dislocation stronger than the grain boundary, and in the plastic deformation process, the dislocation forms high-density dislocation (Shockley incomplete dislocation, full dislocation, and the like) and immobile dislocation (Frank incomplete dislocation, compression bar dislocation, and the like) near the twin grain boundary, so that serious dislocation plugging products are formed around the twin grain boundary, and the strength of the metal is greatly enhanced, namely the introduction of the twin crystal can more effectively strengthen the alloy. Meanwhile, the twin crystal and the sliding system in the matrix have extremely high symmetry, and in order to eliminate stress concentration in the twin boundary and coordinate deformation, the twin boundary emits dislocation to the matrix or the twin crystal, so that the dislocation in the twin crystal material can still keep certain mobility under a higher strain level. In conclusion, the interaction of dislocations with twin boundaries is the key reason why twin boundaries can handle the contradiction between metal strength and plasticity well.

However, the interaction of dislocations with the twin boundaries is extremely complicated, and this complicated interaction is closely related to the microstructure of the twin (twin lamella thickness, twin boundary orientation, etc.). However, there is a great difficulty in directionally controlling the twinning growth orientation. How to understand the influence of twin boundary orientation on the deformation mechanism of the twin crystal material from the root and guide the toughness design of the material is a problem which needs to be solved urgently.

Disclosure of Invention

In order to solve the existing problems, the invention provides a method for preparing a nano twin metal sample with determined twin orientation.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method of preparing a nano twinned metal coupon having a defined twinning orientation, comprising the steps of:

(1) selecting a material with lower stacking fault energy, cutting the material into cuboids with the length, width and height of 30mm, 0.3mm and 0.3mm respectively, and polishing the cuboids into round rods with the diameter of 0.2-0.25 mm;

(2) shearing the round rod with the diameter of 0.2-0.25 mm obtained in the step (1), obtaining a nano metal tip at the fracture, and putting the sheared round rod into the fixed end of the sample rod to enable the fracture end of the round rod to be outward;

(3) taking another round bar which is processed in the step (1) and has the diameter of 0.2-0.25 mm, preparing a metal needle point by an electrochemical polishing method, cutting the round bar into the length of 3-5 mm, and then placing the round bar into the movable end of the sample rod to enable the metal needle point to face outwards;

(4) inserting the nanofactory sample rod into a transmission electron microscope, observing the nano metal tip on the fixed end, performing selective electron diffraction on the nano metal tip on the fixed end, and selecting the nano metal tip with the same crystal orientation as the nano twin crystal material to be formed so as to enable the nano metal tip to be in a positive focal state;

(5) adjusting the position of the needle point of the movable end to enable the needle point to be opposite to the nano metal tip selected in the step (4);

(6) and applying 3-5V voltage between the fixed end and the movable end, moving the needle point of the movable end to make the needle point contact with the nano metal tip of the fixed end, and melting the needle point of the movable end and the nano metal tip of the fixed end under the action of instantaneous joule heat to finally form the nano twin crystal metal sample.

Further, in the step (1), the cuboid material is placed between two pieces of abrasive paper, and the abrasive paper is rubbed back and forth to enable the cuboid material to generate rolling friction between the pieces of abrasive paper, so that the cuboid material is ground into a round rod with the diameter of 0.2-0.25 mm.

Further, in the step (2), the method for shearing the round bar comprises the following steps: horizontally placing a round rod, enabling a jaw of the diagonal pliers to be vertical to the round rod, applying force to vertically cut the upper portion and the lower portion of the round rod into a depth h, wherein the relation between h and the diameter D of the round rod is 20% < h/D < 30%; and then, respectively applying axial force F to the left end and the right end of the round bar, and breaking the round bar along the fracture at the speed of about 0.5-5 mm/s, thereby obtaining the nano metal tip.

Further, the process of preparing the metal tip by the electrochemical polishing method in the step (3) is as follows:

(1) preparing corrosive liquid, putting the corrosive liquid into a glass container, and placing a plastic bracket beside the glass container;

(2) connecting two leads with the tail ends connected with the copper sheet with two ends connected with two ends of a power supply, immersing the copper sheet connected with the negative electrode into corrosive liquid of a glass container, and fixing the copper sheet connected with the positive electrode on a bracket above the corrosive liquid;

(3) sleeving a round bar to be corroded on two plastic sleeves, wherein one end of the round bar is connected with a copper sheet fixed on a bracket; a small gap of 0.5-1.0 mm is exposed between the upper plastic sleeve and the lower plastic sleeve; the upper end of the upper plastic sleeve is positioned above the liquid level, and the lower end of the lower plastic sleeve is positioned below the lower end of the round rod;

(4) after the arrangement is finished, turning on a power supply, adjusting the voltage value to be 5-20V, and carrying out corrosion reaction;

(5) and (3) breaking the small seam between the two plastic sleeves, turning off the power supply after the lower end of the round rod falls into the corrosive liquid, taking out the falling round rod from the corrosive liquid, and taking out the plastic protective sleeve from the tail part of the round rod by using tweezers to obtain the nanoscale metal needle tip.

Further, in the step (4), the observation of the nanometal tip on the fixed end was performed at a multiple of 40k to 100 k.

Further, in the step (4), a fourth selective area diaphragm is applied to perform selective area electron diffraction on the nano metal tip on the fixed end.

Further, in the step (4), the nano metal tip is in a positive focal state by adjusting the Z-axis height of the electron microscope.

Further, in the step (5), the multiple is adjusted to 40k-100k, and the active end needle tip and the nano metal tip selected in the step (4) are positioned on the same focal plane by adjusting the height of the active end; and (4) adjusting the left and right positions of the needle point of the movable end to enable the needle point to be opposite to the nano metal tip selected in the step (4).

The invention has the beneficial effects that:

(1) in the traditional study on the twin crystal orientation to the deformation mechanism, a complex preparation method is often needed to prepare the metal twin crystal with determined orientation, and the nanometer twin crystal material with certain twin crystal orientation can be conveniently and quickly prepared by determining the orientation of the nanometer metal tip in advance.

(2) The method prepares the nano twin crystal material with the twin crystal orientation, can be used for carrying out in-situ mechanical experiments, and can understand the influence of the twin crystal boundary orientation in the nano twin crystal material on the deformation mechanism thereof from the root, thereby guiding the obdurability design of the material.

(3) The traditional metal material deformation mechanism research usually needs to consume a large amount of materials, but the invention saves materials, and can repeatedly research the deformation mechanism of the metal material by only needing a small amount of samples.

Drawings

FIG. 1 is a schematic structural diagram of a rectangular parallelepiped with a length, width and height of 30mm, 0.3mm and 0.3mm, respectively.

FIG. 2 is a schematic view of a nanofactory sample stage (right end is a fixed end, and left end is a movable end).

Fig. 3 is a schematic view showing a process of obtaining a nano-metal tip by shearing a round bar using a diagonal pliers (the lower end of the figure is a transmission electron microscope image of the nano-metal tip formed after shearing).

Fig. 4 is a schematic view of a metal tip fabricated by electrochemical polishing.

Fig. 5 is a transmission electron microscope image of a metal tip prepared by an electrochemical polishing method.

FIG. 6 is a transmission electron microscope image of the active end metal tip and the fixed end nano-metal tip in the facing position.

FIG. 7 is a transmission electron microscope image of a nano-twin metal specimen in which the direction of the formed twin boundary is parallel to the axial direction.

Detailed Description

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, and it should be noted that the detailed description is only for describing the present invention, and should not be construed as limiting the present invention.