In-situ test method for microstructure evolution of metal 3D printing sample

Abstract

The invention relates to an in-situ test method for microstructure evolution of a metal 3D printing sample. The in-situ test method comprises the following steps: cutting two small test samples from a to-be-tested sample; respectively processing the two small test samples into a tensile sample and an embedded clamp; placing the tensile sample and the embedded clamp at corresponding positions of in-situ mechanical test equipment, and carrying out a tensile experiment; and observing the change condition of the microstructure of the tensile sample in the tensile process and the creep process. According to the invention, the to-be-tested sample is adopted to prepare the tensile sample and the embedded clamp, the tensile sample is relatively small in size, and the tensile sample is transitionally clamped by the embedded clamp, so that the clamping stability and constraint reliability of the tensile sample can be ensured, and infirm clamping caused by clamping the tensile sample by adopting a standard clamp is avoided; therefore, the in-situ test of microstructure evolution of the metal 3D printing sample can be facilitated, and the accuracy of a test result can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to an in-situ testing method for the microstructure evolution of a metal 3D printed sample. Background Art

[0002] Selective laser melting (SLM) is an important development direction of metal 3D printing technology. However, due to the characteristics of the SLM process, it is still difficult to produce 100% dense samples in the actual printing process. Under long-term high-temperature load conditions, the microstructure of the SLM sample will produce creep damage and creep cracks. Creep deformation is closely related to temperature. Generally, when the temperature T≥0.3~0.5Tm (Tm is the melting point, unit is K), the creep deformation is more significant. At present, due to the lack of in-situ creep experiments on the microscale, the grain boundary dynamics, dislocation dynamics and micro-damage mechanism of SLM samples during high-temperature creep are still unclear. Summary of the invention

[0003] The present invention relates to an in-situ testing method for the microstructure evolution of a metal 3D printed sample, which can at least solve some of the defects of the prior art.

[0004] The present invention relates to an in-situ testing method for the microstructure evolution of a metal 3D printed sample, the in-situ testing method comprising:

[0005] S1, cut two test samples from the sample to be tested;

[0006] S2, two test specimens are processed into tensile specimens and embedded fixtures respectively;

[0007] S3, placing the tensile specimen and the embedded fixture at corresponding positions of the in-situ mechanical testing equipment to perform a tensile test;

[0008] S4, observing the changes in the microstructure of the tensile specimen during the stretching process and the creep process. As one embodiment, the in-situ mechanical testing device is an in-situ TEM testing device, wherein the tensile specimen and the embedded fixture are respectively arranged at two ends of an in-situ mechanical measurement rod.

[0009] As one of the implementation modes, S2 includes:

[0010] S21, preparing two test samples into needle-shaped specimens respectively;

[0011] S22, performing graphic etching processing on the two needle-shaped specimens respectively to obtain the tensile specimen and the embedded fixture.

[0012] As one of the implementation modes, S21 specifically includes:

[0013] removing the cutting deformation layer of the test sample;

[0014] The test sample is prepared into a needle-shaped sample by a step-by-step etching process.

[0015] As one of the implementation modes, the cutting deformation layer is removed by electrolytic polishing, wherein an acidic electrolyte is used.

[0016] As one of the implementation methods, two needle-shaped samples are patterned and etched using a focused ion beam.

[0017] As one of the embodiments, the ion source used by the focused ion beam is gallium ions. In the patterning etching process, the ion beam energy is 20-40 keV and the beam current density is 3-5 A / cm 2 , the etching rate is 0.1μm / h~5μm / h. .

[0018] As one of the implementation modes, the tensile specimen includes a specimen body, one end of which is enlarged to form a bell head, and the embedded fixture matches a clamping cavity for accommodating the bell head and a clearance channel for the specimen body to pass through.

[0019] As one of the implementation modes, multiple tensile tests are performed to observe the microstructural changes of the tensile specimen in each tensile test;

[0020] During each tensile test, the tensile specimen is heated to a set temperature, kept at that temperature for a period of time, and then maintained under a set stress for a set time.

[0021] As one of the implementation modes, the test sample is a sheet metal thin sample.

[0022] The present invention has at least the following beneficial effects:

[0023] In the present invention, a tensile specimen and an embedded fixture are prepared using a sample to be tested. Since the size of the tensile specimen is small, the tensile specimen is transitionally clamped by the embedded fixture, which can ensure the clamping stability and constraint reliability of the tensile specimen, avoid the use of a standard fixture to clamp the tensile specimen, resulting in unreliable clamping, tensile specimen holding force, deformation, and even torsional fracture, etc., thereby facilitating in-situ testing of the evolution of the microstructure of metal 3D printed specimens and improving the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A schematic flow chart of an in-situ testing method provided by an embodiment of the present invention;

[0026] Figure 2 It is a schematic diagram of the coordination between the tensile specimen and the embedded specimen;

[0027] Figure 3 The structural images of the tensile specimen and the embedded specimen;

[0028] Figure 4 This is the structural image of the needle-shaped sample. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] like Figure 1 The embodiment of the present invention provides an in-situ testing method for the microstructure evolution of a metal 3D printed sample, the in-situ testing method comprising:

[0031] S1, cut two test samples from the sample to be tested;

[0032] S2, processing two test specimens into a tensile specimen 1 and an embedded fixture 2 respectively;

[0033] S3, placing the tensile specimen 1 and the embedded fixture 2 at corresponding positions of the in-situ mechanical testing equipment to perform a tensile test;

[0034] S4, observing the changes in the microstructure of the tensile specimen 1 during the tensile process and the creep process.

[0035] In one embodiment, the test sample is an SLM sample, that is, a 3D printed sample made based on the SLM process.

[0036] Optionally, a small test sample is cut from the sample to be tested using equipment such as a diamond wire saw.

[0037] The test sample includes but is not limited to a sheet metal sample. Optionally, the length of the test sample is in the range of 10 to 40 mm, the width of the test sample is in the range of 0.3 to 1 mm, and the thickness of the test sample is in the range of 0.3 to 1 mm; in a specific embodiment, the size of the test sample is 20 mm×0.5 mm×0.5 mm.

[0038] In one of the embodiments, the in-situ mechanical testing equipment is an in-situ TEM (Transmission Electron Microscope) testing equipment, which can reliably and accurately observe the microstructural evolution process of the 3D printed sample to understand the grain boundary dynamics, dislocation dynamics and microscopic damage mechanism of the 3D printed sample.

[0039] Wherein, the tensile specimen 1 and the embedded fixture 2 are respectively arranged at two ends of the in-situ mechanical measurement rod.

[0040] In one embodiment, S2 includes:

[0041] S21, preparing two test samples into needle-shaped test pieces 100 respectively;

[0042] S22, performing patterning and etching processing on the two needle-shaped specimens 100 respectively to obtain the tensile specimen 1 and the embedded fixture 2.

[0043] Preferably, S21 specifically includes:

[0044] removing the cutting deformation layer of the test sample;

[0045] The test sample is prepared into a needle-shaped sample 100 by a step-by-step etching process.

[0046] In one embodiment, the preparation process of the needle-shaped sample 100 specifically includes:

[0047] ① Rough cutting and positioning: Use a larger FIB beam to separate the rough outline of the needle-shaped sample 100 to be processed from the test sample through a specific pattern or direct cutting method, and determine the position and orientation of the cone; control the depth and range of the cutting to avoid excessive cutting that may damage the sample or lose the area of ​​interest;

[0048] ② Make a rough cone blank: Use an ion beam to gradually etch out the basic shape of the cone to form a relatively rough cone blank; the shape of the rough cone blank can be drawn in CAD software first, and then the CAD file can be imported into the control software of the FIB to etch according to the designed shape; during etching, the beam current and scanning speed of the ion beam are controlled to ensure the size and shape accuracy of the rough cone blank;

[0049] ③ Fine-tune the cone shape: Use a smaller ion beam current to further shape-trim and surface-polish the rough cone blank so that the size, shape and surface quality of the cone meet the requirements; during the trimming process, the beam current can be gradually reduced to avoid increasing the surface roughness of the sample or causing defects due to excessive beam intensity.

[0050] like Figure 4FIG. 1 is a prepared needle-shaped sample 100 .

[0051] In the above method, the needle-shaped sample 100 is prepared: ① It helps to reduce the imaging interference caused by uneven thickness when the electron beam passes through the sample; ② The conical shape helps to better adjust the position and angle of the sample in a limited space, so that the electron beam can accurately pass through the area of ​​interest of the sample, which is beneficial to the preparation of the tensile sample 1 and the embedded fixture 2.

[0052] The cutting deformation layer is formed in the process of cutting a test sample from the test sample in S1. By removing the cutting deformation layer, the accuracy of the in-situ test result can be ensured. The cutting deformation layer can be removed by electrolytic polishing, preferably using an acidic electrolyte, including but not limited to a phosphoric acid electrolyte, and the concentration is preferably controlled within the range of 0.8 to 2 mol / L (for example, controlled at about 1 mol / L).

[0053] Preferably, in S22, a focused ion beam is used to perform patterning etching on the two needle-shaped samples 100. Preferably, the ion source used by the focused ion beam is gallium ions, and more preferably, gallium ions under a high voltage of 20 to 40 kV (preferably controlled at about 30 kV) are used. Preferably, in the patterning etching process step, the ion beam energy is 20 to 40 keV, and the beam current density is 3 to 5 A / cm 2 , the etching rate is 0.1μm / h~5μm / h. .

[0054] In one embodiment, multiple tensile tests are performed to observe the microstructural changes of the tensile specimen 1 in each tensile test; wherein, during each tensile test, the tensile specimen 1 is heated to a set temperature, kept warm for a period of time, and held for a set time under a set stress. In this way, by observing the microstructural changes of the tensile specimen 1 at different set temperatures, the microstructural evolution mechanism of the metal 3D printed specimen can be more accurately understood.

[0055] In one embodiment, in multiple tensile tests, the set temperatures to which the tensile specimen 1 is heated are 400°C, 600°C, 800°C, 1000°C and 1200°C respectively; the load holding setting time can be 20min, 30min, 40min, etc.

[0056] like Figure 2 and Figure 3 In one embodiment, the tensile specimen 1 includes a specimen body 11, one end of the specimen body 11 is expanded to form a bell head 12, and the embedded fixture 2 matches and has a clamping cavity 21 for accommodating the bell head 12 and a clearance channel 22 for the specimen body 11 to pass through.

[0057] By cooperating between the bell head 12 and the clamping cavity 21 , the bell head 12 can be reliably clamped by the embedded clamp 2 as a stretching head, thereby ensuring the accuracy and reliability of the in-situ test results.

[0058] Among them, it is best that the size of the clearance channel 22 and the size of the sample body 11 form a clearance fit relationship between the two, for example: the sample body 11 is in the shape of a square rod, which is adapted to the clearance channel 22 in the thickness direction, and the width of the clearance channel 22 is designed to be slightly larger than the thickness of the sample body 11; or the sample body 11 is in the shape of a cylinder, and the width of the clearance channel 22 is designed to be slightly larger than the diameter of the sample body 11. Based on the above design, the embedded fixture 2 can have better restraint on the tensile specimen 1, thereby improving the accuracy of the test results.

[0059] Alternatively, if Figure 2 and Figure 3 The bell head 12 includes a gradually expanding section 121 and a constant cross-section section 122, the gradually expanding section 121 connects the sample body 11 and the constant cross-section section 122 respectively and gradually expands from the sample body 11 to the constant cross-section section 122; the clamping cavity 21 can matchably include a gradually expanding area and a constant cross-section area, the gradually expanding area connects the make way channel 22 and the constant cross-section area respectively and gradually expands from the make way channel 22 to the constant cross-section area, the gradual slope of the gradually expanding area matches the gradual slope of the gradually expanding section 121, so that the outer wall of the gradually expanding section 121 can fit the inner wall of the gradually expanding area.

[0060] The bell head 12 is defined as the first end of the tensile specimen 1, and the second end of the tensile specimen 1 needs to be clamped to facilitate the application of loads through the second end of the tensile specimen 1 and the embedded fixture 2. Figure 2 and Figure 3 The second end is enlarged relative to the specimen body 11, including but not limited to making the tensile specimen 1 dumbbell-shaped; the size of the second end can be larger than the bell head 12 to facilitate its clamping by the standard clamp of the in-situ mechanical testing equipment, and the tensile specimen 1 can accordingly be an asymmetric dumbbell-shaped.

[0061] It can be understood that the above-mentioned embedded fixture 2 can be clamped by a standard fixture of an in-situ mechanical testing device.

[0062] In this embodiment, the tensile specimen 1 is designed to be dumbbell-shaped, which has at least the following advantages:

[0063] ① During the stretching process, the stress in the middle part of the dumbbell-shaped specimen can be several times or even dozens of times higher than that in other parts. This clear stress concentration area facilitates the accurate observation of the microstructural changes of the material under high stress, such as the movement and proliferation of dislocations;

[0064] ②The geometric shape of the dumbbell-shaped specimen conforms to the basic assumptions of many material mechanics theoretical models, which can improve the accuracy of the test results;

[0065] ③ The tensile specimen 1 can be conveniently fixed on the in-situ TEM tensile device; during the stretching process, the tensile specimen 1 can maintain a relatively stable position, reducing the observation error caused by specimen shaking or position displacement.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An in-situ testing method for the microstructure evolution of a metal 3D printed sample, characterized in that: The in-situ testing method comprises: S1, cut two test samples from the sample to be tested; S2, two test specimens are processed into tensile specimens and embedded fixtures respectively; S3, placing the tensile specimen and the embedded fixture at corresponding positions of the in-situ mechanical testing equipment to perform a tensile test; S4, observing the changes in the microstructure of the tensile specimen during the tensile process and the creep process.

2. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 1, characterized in that: The in-situ mechanical testing equipment is an in-situ TEM testing equipment, wherein the tensile specimen and the embedded fixture are respectively arranged at two ends of an in-situ mechanical measuring rod.

3. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 1, characterized in that S2 include: S21, preparing two test samples into needle-shaped specimens respectively; S22, performing graphic etching processing on the two needle-shaped specimens respectively to obtain the tensile specimen and the embedded fixture.

4. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 3, characterized in that: S21 specifically includes: removing the cutting deformation layer of the test sample; The test sample is prepared into a needle-shaped sample by a step-by-step etching process.

5. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 4, characterized in that: The cutting deformation layer is removed by electrolytic polishing, wherein an acidic electrolyte is used.

6. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 3, characterized in that: The two needle-shaped samples were patterned and etched using a focused ion beam.

7. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 6, characterized in that: The ion source used by the focused ion beam is gallium ions. In the patterning etching process, the ion beam energy is 20-40 keV and the beam current density is 3-5 A / cm 2 , the etching rate is 0.1μm / h~5μm / h.

8. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to any one of claims 1 to 7, characterized in that: The tensile specimen comprises a specimen body, one end of which is expanded to form a bell head, and the embedded clamp is matched with a clamping cavity for accommodating the bell head and a clearance channel for the specimen body to pass through.

9. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 1, characterized in that: Conducting multiple tensile tests to observe changes in the microstructure of the tensile specimen in each tensile test; During each tensile test, the tensile specimen is heated to a set temperature, kept at that temperature for a period of time, and then held for a set time under a set stress.

10. The in-situ testing method for the microstructure evolution of a metal 3D printed sample according to claim 1, characterized in that: The test sample is a sheet-shaped metal thin sample.

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