Gradient layer mechanical property evaluation method of gradient nanomaterial
By inverting mechanical properties on gradient nanomaterial gradient layers through micron scratch testing, the problems of high time consumption and high cost of traditional methods are solved, and efficient and continuous mechanical property evaluation is achieved, which is applicable to high-end equipment manufacturing and aerospace fields.
Patent Information
- Application Number
- CN202511857458.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-03-20
AI Technical Summary
Existing technologies are insufficient to accurately characterize the changes in mechanical properties of gradient nanomaterial gradient layers. Traditional methods are time-consuming, costly, and unable to continuously reflect gradual performance changes.
The mechanical property changes of gradient materials are inverted by using micron scratch testing on the gradient layer. Parameters at different positions in the gradient direction are obtained through scratch testing, and the fracture toughness, nominal strength and scratch hardness are calculated to plot the law of mechanical property change.
It enables high-resolution, low-damage mechanical property testing, continuously reflects changes in material properties, improves testing efficiency, and shortens R&D screening time.
Smart Images
Figure CN121702824A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nanomaterials technology, and more specifically, this invention relates to a method for evaluating the mechanical properties of gradient layers in gradient nanomaterials. Background Technology
[0002] Gradient nanostructured materials (GNMs) represent a major breakthrough in materials science. In recent years, researchers, led by Academician Lu Ke's team at the Chinese Academy of Sciences, have developed the concept of structural gradient, which refers to the continuous and controllable gradual change in grain size or microstructure from the nanoscale to the macroscale within a single material. By preparing a structural layer on the material surface with grain sizes gradientd from the nanoscale to the micrometer scale, the surface can achieve near-nanocrystalline high strength and hardness, while the core retains the excellent plastic deformation capacity of coarse grains. Original technologies such as surface mechanical grinding (SMGT) and surface mechanical rolling (SMRT) have been developed. This perfect combination of properties makes gradient nanostructured materials demonstrate enormous application potential in high-end equipment manufacturing, aerospace, and precision components. Currently, companies such as Southwest Aluminum and Baosteel have successfully achieved controllable preparation and pilot production of gradient nanostructured layers on the surface of industrial-grade rollers using SMGT technology.
[0003] Despite the superior properties of gradient nanomaterials, their unique structure presents unprecedented challenges to the accurate characterization of their mechanical properties. The core of this challenge lies in the unique scale of their gradient layers: these layers are typically very thin, ranging from tens to hundreds of micrometers in thickness. However, mechanical properties (such as hardness, yield strength, and fracture toughness) can vary dramatically within this extremely thin layer. Traditional macroscopic mechanical property testing methods (such as standard tensile and compression tests) obtain the overall average properties of the material, completely failing to discern the gradient variation of properties with depth.
[0004] Currently, mainstream methods for measuring the mechanical properties of gradient layers in gradient nanomaterials heavily rely on microsample preparation and testing. The most common method involves using focused ion beam (FIB) to excavate micrometer-scale columnar samples (typically 1 μm × 1 μm × 2 μm) at specific depths within the gradient layer, followed by micropillar compression or nanoindentation testing. However, this method requires the preparation of numerous micropillars at different depths, a process that is extremely time-consuming and costly, yielding discrete data points that fail to continuously reflect gradual property changes and struggle to accurately determine the absolute depth of the micropillars within the gradient layer. Another method involves layer-by-layer electrolytic peeling followed by tensile testing. This method is limited by electrolytic precision, resulting in limited resolution along the gradient layer direction, making it difficult to accurately correspond to the properties of extremely shallow layers. Furthermore, it is a repetitive and destructive process, leading to low efficiency. Summary of the Invention
[0005] In view of this, this application provides a method for evaluating the mechanical properties of gradient layers of gradient nanomaterials, which is based on micron scratch testing to invert the changes in mechanical properties of gradient layers of gradient materials.
[0006] Specifically, the following technical solutions are included:
[0007] On the one hand, embodiments of this application provide a method for evaluating the mechanical properties of gradient layers in gradient nanomaterials, the method being as follows:
[0008] (1) Prepare specimens for evaluating the mechanical properties of gradient layers;
[0009] (2) Scratch test is performed along the gradient direction of the depth layer of the sample to obtain scratch parameters at different positions in the gradient direction;
[0010] (3) Determine the variation of mechanical properties of the gradient layer along the gradient direction based on the scratch parameters at different positions in the gradient direction.
[0011] Furthermore, the mechanical property parameters characterizing the mechanical properties of the gradient layer include: fracture toughness, nominal strength, and scratch hardness.
[0012] Furthermore, the specific formula for calculating fracture toughness is as follows:
[0013] ;
[0014] in, Indicates lateral force. This represents the perimeter of the projected area of the contact point between the probe and the test position in the yz plane. This represents the area of the projected region of the contact point between the probe and the test position on the yz plane.
[0015] Furthermore, the specific formula for calculating scratch hardness is as follows:
[0016] ;
[0017] in, Represents normal force, This represents the projected area of the contact point between the indenter and the test position on the xy plane.
[0018] Furthermore, the specific formula for calculating nominal strength is as follows:
[0019] ;
[0020] in, Indicates lateral force. This represents the area of the projected region of the contact point between the probe and the test position on the xy plane.
[0021] Furthermore, a scratch test was conducted using a Rockwell C diamond indenter. The specific scratch test procedure is as follows:
[0022] Pre-scan the test area;
[0023] After the pre-scan is completed, a scratch test is performed with a normal load of 5N and scratch data at different locations along the gradient direction is recorded.
[0024] After the scratching is completed, a post-scan is performed along the scratch groove with a post-scan load of 5mN.
[0025] Furthermore, a test area is selected within the cut surface, covering the entire gradient layer.
[0026] Furthermore, the mechanical property parameters at different locations along the gradient direction were calculated. The different locations along the gradient direction were plotted on the x-axis and the mechanical property parameters were plotted on the y-axis to obtain the variation law of the mechanical properties of the gradient nanomaterials in the gradient layer direction.
[0027] Furthermore, the sample preparation process is as follows:
[0028] (11) Cut the nanogradient material along the gradient direction of the gradient layer, put it into an acetone-alcohol solution and clean it with ultrasonic waves, and then dry it.
[0029] (12) Cold mounting of the sample at room temperature;
[0030] (13) Grind and polish the cut surfaces of the sample in sequence;
[0031] (14) After polishing, the test block is placed in acetone alcohol solution and ultrasonically cleaned. After drying, the sample is obtained.
[0032] The gradient layer mechanical property evaluation method for gradient nanomaterials provided by this invention has the following beneficial effects: (1) The scratch test can obtain a continuous mechanical response curve from the nanocrystalline surface to the coarse-grained matrix, which perfectly matches the continuous change characteristics of the gradient structure and provides high-resolution data; (2) The scratch test causes less damage to the material, especially under low load mode, which can more realistically reflect the near-surface properties of the material; (3) A single test is usually completed within a few minutes, which greatly improves the testing efficiency and speeds up the research and development screening. Attached Figure Description
[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0034] Figure 1 A flowchart of a method for evaluating the mechanical properties of gradient layers in gradient nanomaterials provided in an embodiment of the present invention;
[0035] Figure 2 A trend diagram of the gradient layer's mechanical properties provided in an embodiment of the present invention;
[0036] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation
[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0038] Unless otherwise defined, all technical terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art.
[0039] Figure 1 The flowchart of the gradient layer mechanical property evaluation method for gradient nanomaterials provided in this embodiment of the invention is as follows:
[0040] (1) Prepare specimens for evaluating the mechanical properties of gradient layers;
[0041] In this embodiment of the invention, the preparation of the sample includes the following steps:
[0042] (11) Use an electrical discharge wire cutter to cut the nanogradient material along the gradient direction of the gradient layer, put it in an acetone-alcohol solution and clean it with ultrasonic waves for 10 minutes, and then dry it.
[0043] (12) Use epoxy resin mounting powder to cold mount the sample at room temperature;
[0044] Mix epoxy resin and curing agent at a weight ratio of 2:1, and stir in one direction for 2-3 minutes with a stirring rod until the mixture is uniform in color. Place the sample face down into the mold, add the insert until it completely covers the sample, and remove it from the mold after it has solidified at room temperature.
[0045] (13) The cut surface of the sample was polished in sequence with 200 grit, 400 grit, 800 grit and 2000 grit sandpaper of metallographic polishing machine, and the cut surface was polished with diamond suspension polishing liquid on lint-free polishing cloth.
[0046] The sample was coarsely ground using 200-grit sandpaper on a metallographic grinder to remove the wire cutting damage layer. The sample was then finely ground using 400-grit, 800-grit, and 2000-grit sandpaper respectively, until no obvious directional scratches were visible under a single light source. Finally, the sample was polished using a silica suspension on a lint-free polishing cloth to obtain a scratch-free, deformation-free mirror surface.
[0047] (14) After polishing, the sample block is placed in acetone-alcohol solution and ultrasonically cleaned for 10 minutes. After drying with a hair dryer, the sample is obtained and sealed for storage.
[0048] (2) Perform micron scratch test on the cut surface of the sample along the gradient direction to obtain scratch parameters at different positions in the gradient direction. The scratch parameters include: indentation depth, friction normal force and lateral force, etc.
[0049] The test area is selected within the cut surface using the optical microscope that comes with the scratch instrument. The test area covers the entire gradient layer.
[0050] A Rockwell C diamond indenter with radius R = 100 μm and half-apex angle θ = 60 ° was selected to pre-scan the test area. The pre-scan parameters were: normal load 5 mN, loading speed 1 mm / min, loading distance 300 μm, and acquisition rate 30 Hz to obtain the initial surface profile.
[0051] After the pre-scan is completed, a scratch test is performed. The test parameters are: normal load 5N, loading speed 1mm / min, loading distance 300μm, acquisition rate 30 Hz, and real-time recording of scratch data at different positions in the gradient direction, such as indentation depth, frictional normal force and lateral force.
[0052] After the scratching is completed, a post-scan is performed along the scratch groove with a post-scan load of 5mN to obtain the residual depth and surface information of the groove, and to export the relevant scratch data, including: indentation depth, lateral force and normal force.
[0053] (3) Determine the change of mechanical properties of the gradient layer along the gradient direction based on the scratch parameters at different positions in the gradient direction. The mechanical property parameters characterizing the mechanical properties of the gradient layer include: fracture toughness, nominal strength, and scratch hardness.
[0054] In this embodiment of the invention, the formula for calculating fracture toughness is as follows:
[0055] (1)
[0056] in, Indicates lateral force. This represents the perimeter of the projected area of the contact point between the probe and the test position in the yz plane. This represents the area of the projected region of the contact point between the probe and the test position on the yz plane.
[0057] It should be noted that the probe movement direction is defined as the y-axis, the probe moves along the gradient direction of the gradient layer, the load applied to the probe is the z-axis, and the direction perpendicular to the yz plane is the x-axis.
[0058] In this embodiment of the invention, the formula for calculating scratch hardness is as follows:
[0059] (2)
[0060] in, Represents normal force, This represents the projected area of the contact point between the indenter and the test position on the xy plane.
[0061] In this embodiment of the invention, the formula for calculating nominal strength is as follows:
[0062] (3)
[0063] in, Indicates lateral force. This represents the area of the projected region of the contact point between the probe and the test position on the xy plane.
[0064] The perimeter of the projected area of the contact point between the probe and the test position in the xy plane. The area of the projected region of the contact point between the probe and the test position on the xy plane. and the projected area of the contact point between the indenter and the test position on the xz plane. It is determined based on the indentation depth obtained from the indenter size and scratch test.
[0065] The mechanical property parameters at different locations along the gradient direction are calculated using formulas (1) to (3) above. Using the different locations along the gradient direction as the abscissa and the mechanical property parameters as the ordinate, a graph is plotted using Origin software to obtain the variation law of the mechanical properties of the gradient nanomaterial along the gradient layer direction, such as... Figure 2 As shown, Figure 2 The surface in the model represents the xz plane. The mechanical properties of this gradient nanomaterial decrease sharply within the 0-75 μm range, decrease slowly within the 75-140 μm range, and then increase again within the 140-250 μm range, exhibiting slight oscillations in the matrix region. Using a Vickers hardness tester, the absolute hardness value was measured at 30 μm depths next to the scratch. Comparing these discrete, absolute data points with the continuous hardness curve obtained from the micron-level scratch test revealed a consistent pattern, fully validating the reliability of the micron-level scratch test.
[0066] The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials provided by this invention has the following advantages:
[0067] (1) The scratch test can obtain a continuous mechanical response curve from the nanocrystalline surface to the coarse-grained matrix, which perfectly matches the continuous change characteristics of the gradient structure and provides high-resolution data;
[0068] (2) The scratch test causes less damage to the material, especially under low load mode, and can more realistically reflect the near-surface properties of the material;
[0069] (3) A single test is usually completed within a few minutes, which greatly improves testing efficiency and speeds up the R&D screening process.
[0070] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only.
[0071] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.
Claims
1. A method for evaluating the mechanical properties of gradient layers in gradient nanomaterials, characterized in that, The method is as follows: (1) Prepare specimens for evaluating the mechanical properties of gradient layers; (2) Scratch test is performed along the gradient direction of the sample gradient layer to obtain scratch parameters at different positions along the gradient direction; (3) Determine the variation of mechanical properties of the gradient layer along the gradient direction based on the scratch parameters at different positions in the gradient direction.
2. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 1, characterized in that, The mechanical properties parameters characterizing the mechanical properties of the gradient layer include: fracture toughness, nominal strength, and scratch hardness.
3. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 2, characterized in that, The specific formula for calculating fracture toughness is as follows: ； in, Indicates lateral force. This represents the perimeter of the projected area of the contact point between the probe and the test position in the yz plane. This represents the area of the projected region of the contact point between the probe and the test position on the yz plane.
4. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 2, characterized in that, The formula for calculating scratch hardness is as follows: ； in, Represents normal force, This represents the projected area of the contact point between the indenter and the test position on the xy plane.
5. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 2, characterized in that, The formula for calculating nominal strength is as follows: ； in, Indicates lateral force. This represents the area of the projected region of the contact point between the probe and the test position on the xy plane.
6. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 1, characterized in that, A scratch test was conducted using a Rockwell C diamond indenter. The specific procedure for the scratch test is as follows: Pre-scan the test area; After the pre-scan is completed, a scratch test is performed with a normal load of 5N and scratch data at different locations along the gradient direction is recorded. After the scratching is completed, a post-scan is performed along the scratch groove with a post-scan load of 5mN.
7. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 6, characterized in that, Select the test area within the cut surface; the test area covers the entire gradient layer.
8. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 1, characterized in that, The mechanical property parameters at different locations along the gradient direction were calculated. The graph was plotted with the different locations along the gradient direction as the abscissa and the mechanical property parameters as the ordinate, thus obtaining the variation law of the mechanical properties of the gradient nanomaterial in the gradient layer direction.
9. The method for evaluating the mechanical properties of gradient layers in gradient nanomaterials as described in claim 1, characterized in that, The sample preparation process is as follows: (11) Cut the nanogradient material along the gradient direction of the gradient layer, put it into an acetone-alcohol solution and clean it with ultrasonic waves, and then dry it. (12) Cold mounting of the sample at room temperature; (13) Grind and polish the cut surfaces of the sample in sequence; (14) After polishing, the test block is placed in acetone alcohol solution and ultrasonically cleaned. After drying, the sample is obtained.