WO2019227786A1 - 一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法 - Google Patents

一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法 Download PDF

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WO2019227786A1
WO2019227786A1 PCT/CN2018/106659 CN2018106659W WO2019227786A1 WO 2019227786 A1 WO2019227786 A1 WO 2019227786A1 CN 2018106659 W CN2018106659 W CN 2018106659W WO 2019227786 A1 WO2019227786 A1 WO 2019227786A1
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gradient
mechanical properties
twin
nano
metal material
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French (fr)
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卢磊
程钊
金帅
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中国科学院金属研究所
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Priority to JP2020566650A priority patent/JP7206301B2/ja
Priority to EP18920970.3A priority patent/EP3805431A4/en
Publication of WO2019227786A1 publication Critical patent/WO2019227786A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
    • C25C1/12—Electrolytic production, recovery or refining of metals by electrolysis of solutions of copper
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/06—Operating or servicing
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D21/00—Processes for servicing or operating cells for electrolytic coating
    • C25D21/12—Process control or regulation
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/615—Microstructure of the layers, e.g. mixed structure
    • C25D5/617—Crystalline layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/38—Electroplating: Baths therefor from solutions of copper
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the invention relates to the technical field of nano-structured metal materials, and in particular to a method for improving the mechanical properties of materials by changing the nano-twin structure of a metallic material gradient.
  • Metal materials are the earliest and most widely used materials by human beings. Since ancient times in China in the Shang and Zhou Dynasties, bronzes have been used to make bells and weapons, and iron tools have been used to make agricultural tools. So far, metal materials have been widely used in transportation, machinery, power electronics, petrochemicals, and energy fields because of their good strength, toughness, electrical conductivity, and ease of processing. They have become the structural materials on which humans depend.
  • the mechanical properties of metallic materials are determined by their microstructure.
  • Changing the grain size is a common method to improve the mechanical properties of metal materials. From decades of research, by deforming the original metal material, the grain size can be reduced, and the strength of the metal material can be greatly improved, but its plasticity is reduced. When the grain size is reduced to 200 nm, the strength of the metal material is extremely high, but it has almost no plastic deformation ability. Therefore, although changing the grain size can effectively control the strength and plasticity of metal materials, the strong inversion relationship of strong plasticity makes it difficult to achieve excellent overall performance of metal materials.
  • the direct-current electrolytic deposition technology can be used to prepare columnar nano-twin copper bulk materials. Its microstructure is composed of column-shaped micron-sized grains, and the nano-sized twin wafer layer structures are distributed inside the columnar grains.
  • the strength of the columnar nano-twin copper material is mainly determined by the thickness of the twin layer, and it increases as the thickness of the twin layer decreases; the plasticity is determined by the grain size, and it increases with the increase of the grain size. Therefore, the strength and plasticity of the columnar nano-twin copper material can be adjusted and improved by changing the thickness and grain size of the twin wafer layer.
  • the columnar nano-twin structure can improve the strong plastic inversion relationship of metallic materials.
  • the thickness of the twin layer of the columnar nano-twin copper has a positive correlation with the grain size, that is, when the twin layer decreases, the grain size also decreases. This causes the plasticity to decrease as the strength increases, and when the yield strength exceeds 440 MPa, the elongation at break is only 2%.
  • the gradient structure that has attracted much attention can also make metal materials obtain good toughening properties.
  • a gradient structure that gradually transitions from coarse crystals at the core to nanocrystals at the surface is obtained.
  • This structure realizes that the yield strength of the coarse-grained pure copper material is increased by two times, while its plasticity is hardly lost.
  • the mechanical properties of metallic materials can be adjusted by changing the volume percentage content of the gradient layer-as the percentage content of the gradient layer increases, the strength increases but the plasticity decreases. Therefore, although this method improves the strong plastic inversion relationship of the metal material, it is also difficult to maintain good plasticity when the metal material obtains high strength.
  • the present invention provides a method for improving the mechanical properties of a material by changing the gradient nano-twin structure of the metal material.
  • a method for improving the mechanical properties of a material by changing the gradient nano-twin structure of a metal material uses the law of the microstructure and mechanical properties of a metal material to improve the mechanical properties of the material.
  • the metal material has a gradient nano-twin structure.
  • the law of microstructure and mechanical properties of metal materials means that the mechanical properties of metal materials can be controlled by changing the gradient size of the nano-twin structure.
  • the gradient nano twin structure is formed by superposing N (N is a positive integer and N ⁇ 1) gradient layers; each gradient layer is composed of micron-level grains, and micron-level grains have nano-level twins,
  • N is a positive integer and N ⁇ 1 gradient layers; each gradient layer is composed of micron-level grains, and micron-level grains have nano-level twins,
  • the grain size ranges from 0.5-50 ⁇ m, and the thickness of the twin layer ranges from 1 nm to 1000 nm. Within each gradient layer, the grain size or the thickness of the twin layer also ranges from small to large (along the gradient direction).
  • the corresponding micro hardness in each gradient layer shows a gradual change from large to small or small to large from the bottom to the top, so the hardness within a unit distance along the gradient direction is used
  • the change is used to indicate how quickly the microstructure (grain size or twin layer) changes from bottom to top, and is defined as a structural gradient.
  • the structural gradient increases, the yield strength and the work hardening rate of the metal material increase simultaneously, and the elongation at break remains unchanged.
  • the use of the rules of the microstructure and mechanical properties of metallic materials to improve the mechanical properties of materials refers to increasing the structural gradient of the gradient nano-twin structure, thereby increasing the yield strength and work hardening rate of the metal bulk material, while maintaining the elongation at break. constant.
  • the invention integrates two strengthening methods of nano twin structure and gradient structure.
  • the thickness and width of the twin wafer layer can be changed along the gradient direction from large to small or from small to large. This is distinctly different from the microstructure that is uniformly distributed in conventional materials.
  • the mechanism of nano twinning strengthening is not inconsistent with the mechanism of gradient material strengthening, which can complement each other's advantages and can exert a stronger strengthening effect.
  • the present invention creatively discovers the law of the structure and mechanical properties of gradient nano twins in metallic materials; comprehensively improves the comprehensive mechanical properties of metallic materials by changing the size of the structural gradient, that is, by changing the grain size or the twin wafer layer along the gradient direction Change the speed to control the mechanical properties of metal materials such as strength, work hardening rate and plasticity.
  • the invention can improve the yield strength and work hardening rate of the metal material, while maintaining the elongation at break unchanged.
  • the pure copper material strengthened by this method has higher tensile strength at room temperature, its yield strength can be as high as 481 ⁇ 15 MPa, and it has an elongation at break of 12 ⁇ 1%. This property has broken through the limit of almost no plasticity when the DC electrolytically deposited nano twin copper has a yield strength greater than 440 MPa.
  • the invention has a wide application range.
  • metal materials with low fault energy such as copper, TWIP steel, and copper alloys
  • nano twin structures are extremely likely to occur during the deformation or growth process.
  • Gradient nano twins can be achieved only by performing non-isostatic strain treatment or design on these materials.
  • the laws of the structure and mechanical properties of the gradient nano twins are used to improve the mechanical properties of the corresponding materials.
  • FIG. 1 is a microstructure diagram of a gradient nano-twin copper material in a thickness direction under a scanning electron microscope of Example 1.
  • FIG. 1 is a microstructure diagram of a gradient nano-twin copper material in a thickness direction under a scanning electron microscope of Example 1.
  • FIG. 2 is a sample cross-section microhardness distribution of the gradient nano-twin copper material in the thickness direction of Example 1.
  • FIG. 4 is a microstructure diagram of the thickness direction of the gradient nano twin copper material under the scanning electron microscope of Example 2.
  • FIG. 5 is a sample cross-section microhardness distribution of the gradient nano-twin copper material of Example 2 along the thickness direction.
  • FIG. 5 is a microstructure diagram of the thickness direction of the gradient nano-twin copper material under the scanning electron microscope of Example 3.
  • FIG. 5 is a microstructure diagram of the thickness direction of the gradient nano-twin copper material under the scanning electron microscope of Example 3.
  • FIG. 7 is a sample cross-section microhardness distribution of the gradient nano-twin copper material in the thickness direction of Example 3.
  • Figure 8 shows the change in yield strength and tensile strength of a gradient nano-twin copper material with a structural gradient.
  • FIG. 9 shows the change of the work hardening rate of the gradient nano twin copper material with the structural gradient when the true strain is 1%.
  • Figure 10 shows the elongation at break of the gradient nano-twin copper material as a function of the structural gradient.
  • Electrolytic deposition equipment DC stabilized power supply
  • a 10 wt.% NaCl aqueous solution prepared with high-purity NaCl was added in an amount of 0.6 mL / L.
  • the cathode is a pure copper plate with a purity higher than 99.99%, and the cathode is a pure titanium plate.
  • Electrolysis process parameters current density is 30mA / cm 2 ; DC plating; distance between cathode and anode is 100mm, area ratio between cathode and anode is 15: 1, and cathode and anode are placed in parallel (center symmetrical).
  • the structural gradient of the pure copper material is controlled by controlling the change of the temperature of the electrolyte.
  • the method for controlling the temperature of the electrolytic solution refers to controlling the temperature of the electrolytic solution to gradually increase or decrease with time; the grain size of the obtained pure copper material in the direction perpendicular to the deposition surface (gradient direction) and the thickness of the twin wafer layer are also corresponding. Increase or decrease of the temperature; control the gradient of the structure of pure copper materials by controlling the rate of increase or decrease of the temperature of the electrolyte; during the deposition process, the temperature of the electrolyte ranges from 5 to 60 ° C and the electrolysis time is 0.1 to 500 hours.
  • Gradient nano-twin structure copper material with a total sample thickness of 400 ⁇ m.
  • the sample consisted of micron-sized columnar grains grown along the deposition direction.
  • the grains contained high-density twin boundaries, and most of the twin boundaries were parallel to the growth surface.
  • the pure copper material in this embodiment has a gradient layer, and the grain size and the thickness of the twin layer in the material show a monotonically increasing gradient along the thickness direction.
  • the average grain size gradually transitions from 2.5 ⁇ m to 15.8 ⁇ m.
  • the wafer layer thickness gradually transitioned from 29nm to 72nm, as shown in Figure 1.
  • the micro-hardness of the gradient nano-twin copper material gradually decreases along the thickness direction, from 1.5 GPa to 0.8 GPa, showing a gradient distribution, and the structural gradient is 1.75 GPa / mm, as shown in FIG. 2.
  • Curve 1 in FIG. 3 is the engineering stress-strain curve of the electrolytically-deposited gradient nano-twin copper sample of this embodiment at room temperature.
  • the tensile rate is 5 ⁇ 10 -3 s -1
  • the yield strength of the gradient nano twin copper is 364 ⁇ 12 MPa
  • the tensile strength is 397 ⁇ 11 MPa
  • the uniform elongation is 9.8 ⁇ 1.7%
  • the elongation at break is 12.9 ⁇ 1.9 %.
  • Embodiment 1 The difference from Embodiment 1 lies in:
  • the gradient nano-twin copper material has two gradient layers. In the thickness direction, the grain size of the material and the thickness of the twin layer both show a symmetric gradient change that increases first and then decreases, as shown in FIG. 4.
  • the cross-section hardness of the gradient nano-twin copper material first decreases and then increases along the thickness direction, and the structural gradient is 3.2 GPa / mm, as shown in FIG. 5.
  • the room temperature tensile of the gradient nano twin structure copper material when the tensile rate is 5 ⁇ 10 -3 s -1 , the yield strength is 437 ⁇ 19MPa, the tensile strength is 471 ⁇ 18MPa, and the uniform elongation is It is 9.2 ⁇ 1%, and the elongation at break is 14 ⁇ 1.9%, as shown by curve 2 in FIG. 4.
  • Embodiment 1 The difference from Embodiment 1 lies in:
  • the gradient nano-twin structure copper material has eight gradient layers. Along the thickness direction, the grain size and the thickness of the twin layer of the material show a four-cycle gradient change that first increases and then decreases.
  • the microstructure diagram is shown in FIG. 6.
  • the hardness of the gradient nano-twin structure copper material exhibits a four-cycle gradient change that decreases first and then increases along the thickness direction, and the structural gradient is 11.6 GPa / mm, as shown in FIG. 7.
  • the room temperature tensile of the gradient nano twin copper material when the tensile rate is 5 ⁇ 10 -3 s -1 , the yield strength is 481 ⁇ 15MPa, the tensile strength is 520 ⁇ 12MPa, and the uniform elongation is 7 ⁇ 0.5%, elongation at break was 11.7 ⁇ 1.3%. As shown by curve 3 in FIG. 4.
  • the structural gradient is increased from 1.75 GPa / mm to 11.6 GPa / mm
  • the yield strength of pure copper materials is increased from 364 ⁇ 12 MPa to 481 ⁇ 15 MPa
  • the elongation at break is basically maintained at 12-14%.
  • Figures 8, 9 and 10 respectively describe the effects of structural gradients on strength, work hardening rate, and elongation at break in pure copper materials, showing that as the structural gradient increases, the yield strength and tensile strength of pure copper materials The strength and work hardening rate increased significantly, and the elongation at break remained unchanged. This shows that changing the structural gradient can effectively regulate the mechanical properties of metal materials, so that metal materials have both high strength and good plasticity.
  • the ordinary annealed coarse-grained pure copper (grain size is about 25 ⁇ m) is stretched at room temperature, the yield strength is about 50 MPa, the tensile strength is about 200 MPa, and the elongation at break is about 50%. After cold rolling deformation, the yield strength and tensile strength of ordinary coarse-grained copper can be increased to 250 MPa and 290 MPa, respectively, and the elongation at break is about 8%.
  • the sample consisted of micron-sized columnar grains grown along the deposition direction.
  • the grains contained high-density twin boundaries, and most of the twin boundaries were parallel to the growth surface.
  • the tensile properties of this material depend on its microstructure (grain size and twin layer thickness).
  • the average twin layer thickness of the sample is 29 nm and the average grain size is 2.5 ⁇ m
  • the yield strength is 446 ⁇ 10 MPa
  • the tensile strength is 470 ⁇ 11 MPa
  • the elongation at break is only 2 ⁇ 1 %.
  • the average twin layer thickness of the sample (sample B in FIG. 4) is 95 nm and the average grain size is 18 ⁇ m, the yield strength is 223 ⁇ 9 MPa, the tensile strength is 272 ⁇ 4 MPa, and the elongation at break is 29 ⁇ 3%.
  • Lu Ke's research group at the Institute of Metal Research, Chinese Academy of Sciences uses a surface mechanical grinding technology to process pure copper rods with a diameter of 6 mm.
  • Nanocrystalline (grain size about 20nm) gradient nanocrystalline structure Within 150 ⁇ m of the surface of the material is a gradient nano-deformation layer, from 150 ⁇ m to 700 ⁇ m is a deformed coarse crystal layer, and the rest of the core is a coarse crystal matrix that is completely unaffected by deformation. The material was stretched at room temperature, the yield strength was 150 MPa, and the elongation at break was 50%.
  • the results of the above examples and comparative examples show that compared with the conventional strengthening methods (rolling deformation, severe plastic deformation, introduction of nano-twin structures, introduction of gradient structures), the method of using gradient nano-twin structures has obvious strengthening advantages.
  • the strengthening of the gradient nano-twin structure can obtain a material with higher strength and plasticity; compared with the nano-sheet structure obtained by severe plastic deformation, the gradient nano-twin structure can maintain higher Compared with the uniform nano-twin structure, the strength of the gradient nano-twin structure can exceed the strength of the strongest uniform nano-twin material A and has good plasticity, which overcomes the high Nano-twin materials with uniform strength have almost no plastic shortcomings, which highlights the advantages of the gradient structure.
  • the strength of the gradient nano-twin structure is almost 4 times higher and it has a certain degree of plasticity.
  • the shortcomings of better plastic gradient nanostructures and lower strengths highlight the advantages of nanotwinned structures.
  • the gradient nano-twin structure is a combination of the advantages of the nano-twin structure and the gradient structure, which can solve the problem that metal materials are difficult to balance high strength and good plasticity.
  • adjusting the structure gradient size of the gradient nano-twin structure can effectively regulate the metal material Mechanical properties.

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Abstract

一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，属于纳米结构金属材料技术领域。该方法是利用金属材料微观结构与力学性能的内在规律来提高材料力学性能；所述金属材料具有梯度纳米孪晶结构，所述金属材料微观结构与力学性能的规律是指通过改变纳米孪晶结构的梯度大小调控金属材料的力学性能。该方法综合了纳米孪晶强化和梯度结构两种强化方法，可显著提高金属材料的力学性能。利用电解沉积制备技术制备出的梯度纳米孪晶结构纯铜材料：屈服强度高达481±15MPa，抗拉强度高达520±12MPa，同时均匀延伸率可达到7±0.5％，断裂延伸率可达到11.7±1.3％％。

Description

一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法 技术领域
本发明涉及纳米结构金属材料技术领域，具体涉及一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法。
背景技术
金属材料是人类使用最早和应用最广泛的材料，我国从古代商周时期就开始大量使用青铜制作钟鼎和武器，及其使用铁器制作农具。迄今为止，金属材料因为具有良好的强度、韧性、导电性和易加工性，仍被广泛用于交通运输、机械、电力电子、石化及能源等领域，已经成为了人类赖以生存的结构材料。
金属材料大多数是通过金属矿石冶炼获得，初始组织中晶粒尺寸较大，强度普遍较低。为了提高金属材料的强度，材料科学家们经过几个世纪的努力，提出了固溶强化、变形强化、细化晶粒强化以及第二相强化等多种强化方法。这些强化方法可有效地提高材料的强度，扩大了金属材料的应用范围。但是这些方法在强化金属材料的同时，也降低了金属材料的塑性。这些高强低塑性金属材料在工业应用中受到很大的局限。
随着当代高度文明社会的发展，对金属材料的性能提出了更高的要求。金属材料的高强韧化和轻量化已成为金属材料发展的主题。例如快速发展的高速列车，对金属材料的综合强韧性要求越来越高；飞机的主体结构仍为金属材料，提高金属材料的强韧性，就可以达到即增加飞机可靠性又减轻飞机重量的效果；在精密仪器制造行业，要求材料具有极高的强度和一定的塑性，达到减小体积的目的。所以，如何在提高金属材料强度的同时又能保持其优异的塑性，这一问题变得越来越关键。
实际上，金属材料的力学性能是由其微观结构所决定的。改变晶粒大小是改善金属材料力学性能的常用方法。从几十年的研究来看，通过对原始金属材料进行变形处理，可以减小晶粒尺寸，从而大幅度提高金属材料的强度，但其塑性随之降低。当晶粒尺寸减小到200nm时，金属材料的强度极高，但几乎没有塑性变形能力。所以，改变晶粒尺寸大小虽然可以有效地控制金属材料的强度和塑性，但强烈的强塑性倒置关系难以使金属材料达到优异的综合性能。
最近的研究表明，在金属材料中引入纳米孪晶结构，可以获得极高的强度和良好的塑性，打破了高强度低塑性的矛盾。利用直流电解沉积技术可制备柱状纳米孪晶铜块体材料，其微观结构由柱状微米级晶粒组成，并且在柱状晶粒内部分布相互平行的纳米级孪晶片层结构。柱状纳米孪晶铜材料的强度主要由孪晶片层厚度决定，并随着孪晶片层厚度减小而增大；塑性是由晶粒尺寸决定，并随着晶粒尺寸的增加而增加。因此柱状纳米孪晶铜材料的强度和塑性可以通过改变孪晶片层厚度和晶粒尺寸得到调节和提高。研究结果表明柱状纳米孪晶结构可以改善金属材料的强塑性倒置关系。但是柱状纳米孪晶铜的孪晶片层厚度与晶粒尺寸成正相关变化，即当孪晶片层减小时晶粒尺寸也随之减小。这就造成强度提高时塑性也会降低，并且当屈服强度超过440MPa时，断裂延伸率仅有2％。
目前备受关注的梯度结构也可以使金属材料获得良好的强韧化性能。通过在棒状金属表面进行机械研磨或喷丸处理，从而得到一种从芯部粗晶逐渐过渡到表层纳米晶的梯度结构。这种结构实现了使粗晶纯铜材料屈服强度提高2倍的同时几乎不损失其塑性。并且可以通过改变梯度层的体积百分含量来调节金属材料的力学性能——随着梯度层百分含量的增加，强度增加但是塑性降低。所以，这种方法虽然改善了金属材料的强塑性倒置关系，但也难以使金属材料获得高强度时保持良好的塑性。
发明内容
为了解决现有技术中存在的金属材料难以兼具高强度和良好塑性的问题，本发明提供一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，借助纳米孪晶结构强化和梯度结构强化两种有效的强韧化方法，并利用梯度纳米孪晶结构与材料力学性能的规律，使金属材料获得更优异的强韧化性能。
为了实现上述目的，本发明所采用的技术方案如下：
一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，该方法是利用金属材料微观结构与力学性能的规律来提高材料力学性能；所述金属材料具有梯度纳米孪晶结构，所述金属材料微观结构与力学性能的规律是指通过改变纳米孪晶结构的梯度大小能够调控金属材料的力学性能。
所述梯度纳米孪晶结构由N(N为正整数且N≥1)个梯度层叠加而成；每个梯度层由微米级的晶粒组成，微米级晶粒内具有纳米级的孪晶，晶粒尺寸范围为0.5-50 μm，孪晶片层厚度范围为1nm-1000nm；在每个梯度层内晶粒尺寸或孪晶片层厚度由下到上(沿梯度方向)也呈现出由小到大或由大到小的逐渐变化；在每个梯度层内所对应的显微硬度由下到上呈现出由大到小或由小到大的逐渐变化，因此用沿梯度方向单位距离内硬度的变化来表示微观结构(晶粒尺寸或孪晶片层)从下到上变化的快慢，并定义为结构梯度。
所述金属材料微观结构与力学性能的规律中，结构梯度增加，金属材料的屈服强度和加工硬化率同时增加，断裂延伸率不变。
所述利用金属材料微观结构与力学性能的规律来提高材料力学性能是指：通过增加梯度纳米孪晶结构的结构梯度，从而提高金属块体材料的屈服强度和加工硬化率，同时保持断裂延伸率不变。
在室温和拉伸速率为5×10 -3s -1的条件下，当金属材料的结构梯度为1～50GPa/mm时，其屈服强度300～500MPa，抗拉强度为350～600MPa，均匀延伸率为5-15％，断裂延伸率为10～20％，真应变为1％时的加工硬化率为1～3GPa。
本发明具有如下优点：
1、具有独特的微观结构和强化机理：
本发明综合了纳米孪晶结构和梯度结构两种强化方法。使孪晶片层的厚度和宽度沿梯度方向呈现由大到小或由小到大的连续梯度变化。这明显不同于在常规材料中均匀分布的微观结构。纳米孪晶强化的机理与梯度材料强化的机理并不矛盾，可以优势互补，能够发挥出更强的强化效果。
2、本发明创造性的发现了金属材料中梯度纳米孪晶结构与力学性能的规律；通过改变结构梯度大小全面提高金属材料的综合力学性能，即，通过改变晶粒尺寸或孪晶片层沿梯度方向变化快慢来控制金属材料的强度、加工硬化率和塑性等力学性能。
3、高的强度和优异的(均匀)塑性匹配：
本发明通过增加梯度纳米孪晶结构的结构梯度，能够使金属材料的屈服强度和加工硬化率提高，同时保持断裂延伸率不变。经此方法强化的纯铜材料具有较高的室温拉伸强度，其屈服强度可高达481±15MPa，并且具有12±1％的断裂延伸率。该性能已经突破了直流电解沉积纳米孪晶铜屈服强度大于440MPa时几乎无塑性的限制。
4、应用范围广：
本发明的应用范围较广。对于低层错能的金属材料(如铜、TWIP钢、铜合金) 在变形或生长过程中极容易产生纳米孪晶结构，只需要对这些材料进行非等应变处理或设计即可实现梯度纳米孪晶结构，比如表面机械研磨的梯度变形处理、电解沉积或磁控溅射铜或其它合金工艺参数的梯度变化等。并进一步利用梯度纳米孪晶结构与力学性能的规律来提高相应材料的力学性能。
附图说明
图1为实施例1的扫描电子显微镜下梯度纳米孪晶铜材料厚度方向的微观结构图。
图2为实施例1的梯度纳米孪晶铜材料沿厚度方向的样品截面显微硬度分布。
图3为实施例1-3的梯度纳米孪晶铜材料与均匀纳米孪晶铜材料的工程应力-应变曲线。
图4为实施例2的扫描电子显微镜下梯度纳米孪晶铜材料厚度方向的微观结构图。
图5为实施例2的梯度纳米孪晶铜材料沿厚度方向的样品截面显微硬度分布。
图5为实施例3的扫描电子显微镜下梯度纳米孪晶铜材料厚度方向的微观结构图。
图7为实施例3的梯度纳米孪晶铜材料沿厚度方向的样品截面显微硬度分布。
图8为梯度纳米孪晶铜材料的屈服强度和抗拉强度随结构梯度的变化。
图9为梯度纳米孪晶铜材料的在真应变为1％时加工硬化率随结构梯度的变化。
图10为梯度纳米孪晶铜材料的断裂延伸率随结构梯度的变化。
具体实施方式
以下实施例是利用直流电解沉积技术制备梯度纳米孪晶铜材料，具体制备工艺过程与参数如下：
电解沉积设备：直流稳压稳流电源；
电解沉积所用电解液的要求：MOS级纯度CuSO 4溶液，严格控制电解液的金属杂质含量，配电解液所用水应为高纯度去离子水，使用分析纯H 2SO 4调解电解液pH值，电解液pH＝1。
在上述CuSO 4溶液中加入以下的添加剂：
采用分析纯明胶配制的浓度5wt.％的明胶水溶液，加入量为1mL/L；
采用高纯NaCl配制的浓度10wt.％的NaCl水溶液，加入量为0.6mL/L。
阴极、阳极要求：阴极为纯度高于99.99％的纯铜板，阴极为纯钛板。
电解工艺参数：电流密度为30mA/cm 2；直流方式电镀；阴极、阳极之间距离100mm，阴极、阳极面积比为15:1，阴极与阳极平行放置(中心对称)。
沉积过程中，通过控制电解液温度的变化方式来控制纯铜材料的结构梯度。所述控制电解液温度的变化方式是指控制电解液温度随时间逐渐升高或逐渐降低；所得纯铜材料在垂直于沉积面方向(梯度方向)上的晶粒尺寸和孪晶片层厚度也相应的增加或减小；通过控制电解液温度升高或降低的速率来控制纯铜材料结构梯度大小；沉积过程中，电解液温度范围为：5～60℃，电解时间为0.1～500小时。
下面结合附图和实施例详述本发明。
实施例1
梯度纳米孪晶结构铜材料，样品总厚度为400μm。样品由沿沉积方向生长的微米尺寸柱状晶粒构成，晶粒内含有高密度孪晶界，且大部分孪晶界平行于生长表面。本实施例纯铜材料具有1个梯度层，沿厚度方向该材料中的晶粒尺寸和孪晶片层厚度都呈现单调增加的梯度变化，平均晶粒尺寸由2.5μm逐渐过渡到15.8μm，平均孪晶片层厚度由29nm逐渐过渡到72nm，如图1所示。
本实施例中，梯度纳米孪晶铜材料的显微硬度沿厚度方向逐渐降低，由1.5GPa降低到0.8GPa，呈现梯度变化的分布，结构梯度为1.75GPa/mm，如图2所示。
本实施例中，梯度纳米孪晶铜材料的室温拉伸：图3中曲线1为本实施例电解沉积梯度纳米孪晶铜样品在室温下的工程应力-应变曲线。拉伸速率为5×10 -3s -1时，梯度纳米孪晶铜的屈服强度为364±12MPa，抗拉强度为397±11MPa，均匀延伸率9.8±1.7％，断裂延伸率为12.9±1.9％。
实施例2
与实施例1不同之处在于：
梯度纳米孪晶铜材料具有2个梯度层。沿厚度方向该材料的晶粒尺寸和孪晶片层厚度都呈现先增加后降低的对称梯度变化，如图4所示。
本实施例中，梯度纳米孪晶铜材料的截面硬度沿厚度方向先降低再增加，结构梯度为3.2GPa/mm，如图5所示。
本实施例中，梯度纳米孪晶结构铜材料的室温拉伸：当拉伸速率为5×10 -3s -1时，屈服强度为437±19MPa，抗拉强度为471±18MPa，均匀延伸率为9.2±1％，断裂延伸率为14±1.9％，如图4中曲线2所示。
实施例3
与实施例1不同之处在于：
梯度纳米孪晶结构铜材料具有8个梯度层。沿厚度方向该材料的晶粒尺寸和孪晶片层厚度都呈现先增加后降低的四周期梯度变化，其微观结构图如图6所示。
本实施例中，梯度纳米孪晶结构铜材料的硬度沿厚度方向呈现先降低后升高的四周期梯度变化，结构梯度为11.6GPa/mm，如图7所示。
本实施例中，梯度纳米孪晶铜材料的室温拉伸：当拉伸速率为5×10 -3s -1时，屈服强度为481±15MPa，抗拉强度为520±12MPa，均匀延伸率7±0.5％，断裂延伸率为11.7±1.3％。如图4中曲线3所示。
从以上实施例中可以看出，结构梯度由1.75GPa/mm增加到11.6GPa/mm，纯铜材料的屈服强度由364±12MPa增加到481±15MPa，断裂延伸率基本保持在12-14％。图8,、图9和图10分别描述了在纯铜材料中结构梯度对强度、加工硬化率和断裂延伸率的影响，表明了随着结构梯度的增加，纯铜材料的屈服强度、抗拉强度和加工硬化率明显增加，断裂延伸率保持不变。这说明改变结构梯度可有效调控金属材料的力学性能，从而实现金属材料同时具备高强度和良好的塑性。
比较例1
普通退火态粗晶纯铜(晶粒尺寸约为25μm)在室温下拉伸，屈服强度约为50MPa，抗拉强度约为200MPa，断裂延伸率约为50％。冷轧变形后，普通粗晶铜的屈服强度和抗拉强度分别可提高到250MPa和290MPa，断裂延伸率约为8％。
比较例2
澳大利亚科学家F.Dalla Torre等人利用等通道挤压(ECAP)严重塑性技术对纯铜进行处理，经过2道次的处理后，其微观组织演变为片层厚度约为200nm的均匀层片状结构。拉伸实验结果表明，其屈服强度约为440MPa，但断裂延伸率不足5％，均匀延伸率不足1％。
比较例3
国内中国科学院金属研究所卢磊研究组利用直流电解沉积制备的纳米孪晶铜样品。样品由沿沉积方向生长的微米尺寸柱状晶粒构成，晶粒内含有高密度孪晶界，且大部分孪晶界平行于生长表面。该材料的拉伸性能取决于其微观结构(晶粒尺寸和孪晶片层厚度)。当样品(图4中A样品)的平均孪晶片层厚度为29nm，平均晶粒尺寸为2.5μm时，屈服强度为446±10MPa，抗拉强度为470±11MPa，断裂延伸率仅为2±1％。当样品(图4中B样品)的平均孪晶片层厚度为95nm，平均晶粒尺寸为18μm时，屈服强度为223±9MPa，抗拉强度为272±4MPa，断裂延伸率为29±3％。
比较例4
国内中国科学院金属研究所卢柯研究组利用表面机械研磨技术处理对直径为6mm的纯铜棒材进行处理，得到的微观结构为芯部粗晶结构(晶粒尺寸约为25μm)逐渐过渡到表面纳米晶(晶粒尺寸约为20nm)的梯度纳米晶结构。该材料表面150μm内是梯度纳米变形层，从150μm到700μm是形变粗晶层，其余芯部则为完全未受变形影响的粗晶基体。该材料在室温下拉伸，屈服强度为150MPa，断裂延伸率为50％。
以上实施例和比较例结果表明，与常规的强化方法(轧制变形，严重塑性变形，引入纳米孪晶结构，引入梯度结构)相比，利用梯度纳米孪晶结构强化的方法具有明显的强化优势。比如，与轧制方法相比，梯度纳米孪晶结构强化可以得到强度更高和塑性更好的材料；与严重塑性变形得到的纳米片层结构相比，梯度纳米孪晶结构既可以保持较高的强度又能保持良好的塑性；与均匀纳米孪晶结构相比，梯度纳米孪晶结构强化后得到的强度可以超过最强均匀纳米孪晶材料A的强度同时具有较好的塑性，克服了高强度均匀纳米孪晶材料几乎无塑性的缺点，这凸显出了梯度结构的优势；与梯度纳米晶结构相比，梯度纳米孪晶结构的强度高出了近4倍左右同时具有一定的塑性，克服了较好塑性梯度纳米结构强度较低的缺点，这凸显出了纳米孪晶结构的优势。总之，梯度纳米孪晶结构是综合了纳米孪晶结构和梯度结构的优势，可以解决金属材料难以兼顾高强度和良好塑性的问题；同时调节梯度纳米孪晶结构的结构梯度大小可以有效调控金属材料的力学性能。

Claims (5)

  1. 一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，其特征在于：该方法是利用金属材料微观结构与力学性能的规律来提高材料力学性能；所述金属材料具有梯度纳米孪晶结构，所述金属材料微观结构与力学性能的规律是指通过改变纳米孪晶结构的梯度大小能够调控金属材料的力学性能。
  2. 按照权利要求1所述的通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，其特征在于：所述梯度纳米孪晶结构由N个梯度层叠加而成；每个梯度层由微米级的晶粒组成，微米级晶粒内具有纳米级的孪晶，晶粒尺寸范围为0.5-50μm，孪晶片层厚度范围为1nm-1000nm；在每个梯度层内晶粒尺寸或孪晶片层厚度由下到上呈现出由小到大或由大到小的逐渐变化；在每个梯度层内所对应的显微硬度由下到上也呈现出由大到小或由小到大的逐渐变化，因此用沿梯度方向单位距离内硬度的变化来表示微观结构(晶粒尺寸或孪晶片层)从下到上变化的快慢，并定义为结构梯度。
  3. 按照权利要求2所述的通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，其特征在于：所述金属材料微观结构与力学性能的规律中，结构梯度增加，金属材料的屈服强度和加工硬化率同时增加，断裂延伸率不变。
  4. 按照权利要求2所述的通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，其特征在于：所述利用金属材料微观结构与力学性能的规律来提高材料力学性能是指，通过增加梯度纳米孪晶结构的结构梯度，从而提高金属块体材料的屈服强度和加工硬化率，同时保持断裂延伸率不变。
  5. 按照权利要求1所述的通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法，其特征在于：在室温和拉伸速率为5×10 -3s -1的条件下，当纯铜材料的结构梯度为1～50GPa/mm时，其屈服强度300～500MPa，抗拉强度为350～600MPa，均匀延伸率为5-15％，断裂延伸率为10～20％，真应变为1％时的加工硬化率为1～3GPa。
PCT/CN2018/106659 2018-05-31 2018-09-20 一种通过改变金属材料梯度纳米孪晶结构提高材料力学性能的方法 WO2019227786A1 (zh)

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