A non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar

Abstract

The present invention relates to a non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar. The reconstructed image is subjected to filtering and noise reduction processing by Avizo image processing software, and then interactive threshold segmentation is performed to obtain the test bar contour image, and the gray-scale image of the sample with closed internal holes is obtained; the gray-scale image is subtracted from the test bar contour image to obtain a gray-scale image containing only holes; by setting a gray-scale threshold greater than the standard deviation of the gray-scale of the sample material in the image, gray-scale difference operation is performed on the gray-scale image containing only holes to remove noise, and a binary image is obtained. The present invention proposes a method for detecting the internal porosity of an additive manufacturing titanium alloy test bar by using micro-focus industrial CT, which overcomes the disadvantage that conventional ray detection cannot detect the internal micro-defects of an additive manufacturing titanium alloy test bar, detects and counts the geometric characteristics of the pores, and realizes the non-destructive evaluation of the internal micro-defects of an additive manufacturing titanium alloy test bar.

Description

Technical Field

[0001] The present invention relates to the technical field of nondestructive testing, and specifically to a method for nondestructively evaluating the internal pores of an additive manufacturing titanium alloy test bar. Background Art

[0002] Additive manufacturing technology is a revolutionary breakthrough in manufacturing technology. Starting from a three-dimensional model, it can directly manufacture parts near net shape, and can manufacture complex structures that cannot be processed by traditional methods. This technology has begun to be applied in the fields of aircraft and aeroengines, and shows a rapid growth trend. Due to the special nature of the additive manufacturing process, the additive manufacturing parts have characteristics different from traditional metal parts. Their internal typical defects are pores, lack of fusion, etc., with sizes only in the micron range, and the distribution has characteristics such as randomness and dispersion. It is difficult to detect using conventional methods, and the internal quality cannot be evaluated by conventional nondestructive testing methods.

[0003] The principle of industrial CT technology is based on the fact that substances with different densities have different X-ray attenuation coefficients. After reconstruction, materials with different densities show different gray levels on the CT image, with intuitive display, and can simultaneously obtain characteristic information such as the location, distribution, and morphology of defects. It is an advanced technical means for detecting the internal quality of parts. Summary of the Invention

[0004] The purpose of the present invention is: In view of the above problems, the present invention designs a method for nondestructively evaluating the internal pores of an additive manufacturing titanium alloy test bar, a microfocus industrial CT detection device and an image processing software Avizo, for evaluating the internal quality of the additive manufacturing titanium alloy test bar.

[0005] The technical solution of the present invention is:

[0006] Provide a method for nondestructively evaluating the internal pores of an additive manufacturing titanium alloy test bar, including the following steps:

[0007] Step 1: Process the material sample into a cylindrical test bar;

[0008] Step 2: Fix the cylindrical test bar at the center position of the turntable of the industrial CT system; the industrial CT system is installed with the Avizo image processing software;

[0009] Step 3: Determine the height range of CT scanning according to the DR imaging of the industrial CT system. The calculation formula for the scanning height range is: the imaging height of the specimen in DR imaging × the pixel size of DR imaging, and the imaging height is the difference between the upper and lower boundary coordinate height values of the imaging; set the industrial CT scanning process parameters according to the image gray level distribution histogram in the DR image;

[0010] Step 4: Calibrate the detector of the industrial CT system; set the number of projections of the industrial CT system to the threshold value; select the type of filter plate and perform adaptation; obtain a sinogram by scanning the specimen with the industrial CT system;

[0011] Step 5: Use the image reconstruction software of the industrial CT system to perform image reconstruction, including rotation center correction and beam hardening calibration during the process;

[0012] Step 6: Perform filtering and noise reduction processing on the reconstructed image through Avizo image processing software, then perform interactive threshold segmentation to obtain the test bar contour image, perform a Close operation on the test bar contour image to obtain a closed internal hole specimen gray-scale image; perform a difference operation between the gray-scale image and the test bar contour image to obtain a gray-scale image containing only holes; perform a gray-scale difference operation on the gray-scale image containing only holes to remove noise by setting a gray-scale threshold greater than the standard deviation of the specimen material gray-scale in the image, assign the gray-scale value of the voxels where the holes are located in the current image to 1, and assign the remaining voxels to 0 to obtain a binary image;

[0013] Step 7: Analyze the binary image through the three-dimensional information statistical analysis function of Avizo image processing software to obtain the sum of the volumes of all holes V 孔 in the test bar, analyze the test bar contour of the test bar contour image obtained by the interactive threshold segmentation to obtain the specimen volume V 试样 , calculate to obtain the porosity P of the test bar = V 孔 / V 试样 .

[0014] Further, the industrial CT scanning process parameters include a voltage of 120 kV, a current of 200 μA, and an integration time of 500 ms.

[0015] Further, the filter plate is a 1-mm copper filter plate

[0016] Further, the threshold value of the number of projections of the industrial CT system is 1000 or 1500.

[0017] Further, the diameter of the cylindrical test bar is Ф10 mm - Ф16 mm.

[0018] Further, the length of the cylindrical test bar is 60 mm - 80 mm.

[0019] Further, the cylindrical test bar is laser additive manufactured TC4

[0020] Further, the cylindrical test bar is fixed by means of gluing and / or bundling.

[0021] The advantages of the present invention are as follows: The present invention develops a non-destructive evaluation method for internal pores of additively manufactured titanium alloy test bars, overcomes the drawback that conventional ray detection cannot detect tiny internal defects of additively manufactured titanium alloy test bars, detects and statistically analyzes the geometric characteristics of the pores, and realizes the non-destructive evaluation of the internal quality of additively manufactured titanium alloy test bars. Detailed implementation manners

[0022] In fact, many different examples can be described and these examples should not be construed as limited to the examples set forth herein. On the contrary, these examples are described so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0023] The detailed embodiment provides a non-destructive evaluation method for internal pores of additively manufactured titanium alloy test bars, including the following steps:

[0024] Step 1: Process the material sample into a cylindrical test bar;

[0025] Step 2: Fix the cylindrical test bar at the center position of the turntable of the industrial CT system; the Avizo image processing software is installed in the industrial CT system;

[0026] Step 3: Determine the height range of CT scanning according to the DR imaging of the industrial CT system. The calculation formula for the scanning height range is: the imaging height of the specimen in DR imaging × the pixel size of DR imaging, and the imaging height is the difference between the upper and lower boundary coordinate height values of the imaging; set the industrial CT scanning process parameters according to the image gray level distribution histogram in the DR image;

[0027] Step 4: Calibrate the detector of the industrial CT system; set the projection number of the industrial CT system to a threshold value; select the type of filter slice and perform adaptation; obtain a sinogram by scanning the specimen through the industrial CT system;

[0028] Step 5: Use the image reconstruction software of the industrial CT system to perform image reconstruction, including rotation center correction and beam hardening calibration during the process;

[0029] Step 6: Perform filtering and noise reduction processing on the reconstructed image through the Avizo image processing software, then perform interactive threshold segmentation to obtain the test bar contour image, perform a Close operation on the test bar contour image to obtain a closed internal hole specimen gray level image; perform a subtraction operation on the gray level image and the test bar contour image to obtain a gray level image containing only holes; perform a gray level difference operation on the gray level image containing only holes to remove noise by setting a gray level threshold greater than the standard deviation of the gray level of the specimen material in the image, assign the gray level of the voxel where the hole is located in the current image to 1, and assign the remaining voxels to 0 to obtain a binary image;

[0030] Step 7: Analyze the binary image through the three-dimensional information statistical analysis function of Avizo image processing software to obtain the sum V of the volumes of all holes in the test bar, analyze the test bar contour of the test bar contour image obtained by the interactive threshold segmentation to obtain the sample volume V, calculate and obtain the porosity P of the test bar = V / V. 孔 Perform analysis on the test bar contour of the test bar contour image obtained by the interactive threshold segmentation to obtain the sample volume V. 试样 Calculate and obtain the porosity P of the test bar = V 孔 / V 试样 .

[0031] Example 1

[0032] For the working section of the original test bar of the high-cycle fatigue performance of TC4 manufactured by laser additive with a diameter of Ф15mm, the porosity detection method is as follows:

[0033] The steps of this method are as follows:

[0034] 1.1 Sample requirements and placement

[0035] The sample is a cylindrical test bar with a diameter of Ф15mm and a length of 60mm, and the length of the working section is about 30mm.

[0036] 1.2 Sample clamping and geometric arrangement

[0037] Fix the sample on the low-density acrylic extension bar tooling by gluing and bundling, and place it near the center position of the turntable of the industrial CT system to ensure no shaking during rotation.

[0038] 1.3 DR imaging

[0039] Determine the height range of CT scanning according to the DR imaging of the industrial CT system. The calculation formula for the height range of the scanning is: the imaging height of the sample in DR imaging × the pixel size of DR imaging. The imaging height is the difference between the upper and lower boundary coordinate height values of the imaging. The scanning magnification ratio is 13.3, and the pixel size is about 15μm. Accordingly, the scanning range includes the 30mm working section. Determine the industrial CT scanning process parameters according to the image gray distribution histogram in the DR image, with a voltage of 120kV, a current of 200μA, and an integration time of 500ms.

[0040] 1.4 CT scanning

[0041] Calibrate the detector of the industrial CT system; set the projection number of the industrial CT system as the threshold; select the type of filter plate and perform adaptation; obtain the sinogram by scanning the sample through the industrial CT system; determine the rotation projection number, and the projection number is selected as 1.5 times the number of pixel points covered horizontally by the sample projection during the 360-degree rotation. Select a filter plate to reduce beam hardening artifacts. The number of projection images is 1000, and a 1mm copper filter plate is selected.

[0042] 1.5 Image reconstruction

[0043] Image reconstruction is performed using the image reconstruction software of the industrial CT system, including rotation center correction and beam hardening calibration during the process. The deviation within 100 pixels from the center position of the X-axis can be compensated through the rotation center correction module, and the beam hardening calibration value BHC is adjusted to 6. To improve the dimensional measurement accuracy, the reconstruction range is the smallest area containing the region of interest.

[0044] 1.6 Hole defect extraction

[0045] The reconstructed image is processed by Avizo image processing software for filtering and noise reduction, and then interactive threshold segmentation is performed to obtain the test bar contour image. A Close operation is performed on the test bar contour image to obtain a closed internal hole sample gray image; the difference operation is performed between the gray image and the test bar contour image to obtain a gray image containing only holes; by setting a gray threshold greater than the standard deviation of the gray level of the sample material in the image, the gray difference operation is performed on the gray image containing only holes to remove noise, and the gray value of the voxels where the holes are located in the current image is assigned 1, and the other voxels are assigned 0 to obtain a binary image.

[0046] 1.7 Porosity calculation

[0047] The binary image is analyzed through the three-dimensional information statistical analysis function of Avizo image processing software to obtain the sum V of the volumes of all holes in the test bar 孔 , the test bar contour obtained by the interactive threshold segmentation is analyzed to obtain the sample volume V 试样 , and the porosity P of the test bar is calculated as P = V 孔 / V 试样 .

[0048] Example 2

[0049] For the working section of a machined test bar of laser additive manufactured TC4 with high-cycle fatigue performance having a diameter of Ф10mm, the porosity detection method is as follows:

[0050] The steps of this method are:

[0051] 1.1 Sample requirements and placement

[0052] The sample is a machined test bar with a diameter of Ф10mm cylinder, a length of 60mm, and a working section length of about 30mm.

[0053] 1.2 Sample clamping and geometric arrangement

[0054] The sample is fixed on the low-density acrylic extension bar tooling by gluing and bundling, and placed near the center position of the turntable of the industrial CT system to ensure no shaking during rotation.

[0055] 1.3 DR imaging

[0056] Determine the height range of CT scanning based on the DR imaging of the industrial CT system. The calculation formula for the scanning height range is: the imaging height of the specimen in DR imaging × the pixel size of DR imaging. The imaging height is the difference between the upper and lower boundary coordinate height values of the imaging. The scanning magnification ratio is 13.3, and the pixel size is about 15 μm. Accordingly, the scanning range includes a 30-mm working section. Determine the industrial CT scanning process parameters according to the image gray distribution histogram in the DR image: voltage 120 kV, current 200 μA, and integration time 500 ms.

[0057] 1.4 CT Scanning

[0058] Calibrate the detector of the industrial CT system; set the number of projections of the industrial CT system to a threshold value; select the type of filter slice and perform adaptation; obtain a sinogram by scanning the specimen through the industrial CT system; determine the number of rotational projections. The number of projections is selected as 1.5 times the number of pixel points covered horizontally by the sample projections during a 360-degree rotation. Select a filter slice to reduce beam hardening artifacts. The number of projection images is 1000, and a 1-mm copper filter slice is selected.

[0059] 1.5 Image Reconstruction

[0060] Perform image reconstruction using the image reconstruction software of the industrial CT system. The process includes rotation center correction and beam hardening calibration; through the rotation center correction module, compensate for the deviation within 100 pixels from the center position of the X-axis, and adjust the beam hardening calibration value BHC to 6. To improve the dimensional measurement accuracy, the reconstruction range is the smallest area containing the region of interest.

[0061] 1.6 Hole Defect Extraction

[0062] Perform filtering and noise reduction processing on the reconstructed image through Avizo image processing software, then perform interactive threshold segmentation to obtain the test bar contour image, perform a Close operation on the test bar contour image to obtain a closed internal hole specimen gray image; perform a subtraction operation on the gray image and the test bar contour image to obtain a gray image containing only holes; perform a gray difference operation on the gray image containing only holes to remove noise by setting a gray threshold greater than the standard deviation of the gray level of the specimen material in the image. Assign the gray level of the voxels where the holes are located in the current image to 1, and assign the remaining voxels to 0 to obtain a binary image.

[0063] 1.7 Porosity Calculation

[0064] Analyze the binary image through the three-dimensional information statistical analysis function of Avizo image processing software to obtain the sum of the volumes of all holes V 孔 , analyze the test bar contour of the test bar contour image obtained by the interactive threshold segmentation to obtain the specimen volume V 试样, the porosity P of the test bar is calculated to be P = V 孔 / V 试样 .

[0065] Descriptions of different advantageous arrangements have been presented for purposes of illustration and description, but the description is not intended to be exclusive or limited to examples of the disclosed forms. Many modifications and variations will be obvious to those of ordinary skill in the art. Additionally, different advantageous examples may describe different advantages compared to other advantageous examples. The selected example or examples are chosen and described in order to best illustrate the principles of the examples, the practical application, and to enable those of ordinary skill in the art to understand the disclosure with various examples that have been modified to be suitable for the particular use contemplated.

Claims

1. A non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar, characterized in that, It includes the following steps: Step 1, process the material sample into a cylindrical test bar; Step 2, fix the cylindrical test bar at the central position of the turntable of the industrial CT system; the Avizo image processing software is installed in the industrial CT system; Step 3, determine the height range of CT scanning according to the DR imaging of the industrial CT system. The calculation formula for the scanning height range is: the imaging height of the specimen in DR imaging × the pixel size of DR imaging. The imaging height is the difference between the upper and lower boundary coordinate height values of the imaging; set the industrial CT scanning process parameters according to the image gray distribution histogram in the DR image; Step 4, calibrate the detector of the industrial CT system; set the projection number of the industrial CT system to a threshold value; select the type of filter plate and perform adaptation; obtain a sinogram by scanning the specimen through the industrial CT system; Step 5, perform image reconstruction using the image reconstruction software of the industrial CT system, including rotation center correction and beam hardening calibration during the process; Step 6, perform filtering and noise reduction processing on the reconstructed image through the Avizo image processing software, then perform interactive threshold segmentation to obtain the test bar contour image, perform a Close operation on the test bar contour image to obtain a closed internal hole specimen gray image; perform a subtraction operation on the gray image and the test bar contour image to obtain a gray image containing only holes; By setting a gray threshold greater than the standard deviation of the specimen material gray level in the image, perform a gray difference operation on the gray image containing only holes to remove noise, assign the gray level of the voxels where the holes are located in the current image to 1, and assign the remaining voxels to 0 to obtain a binary image; Step 7: Analyze the binary image through the three-dimensional information statistical analysis function of Avizo image processing software to obtain the sum of the volumes of all holes in the test bar, V 孔 , analyze the test bar contour of the test bar contour image obtained by the interactive threshold segmentation to obtain the sample volume, V 试样 , calculate to obtain the porosity of the test bar, P = V 孔 / V 试样 .

2. The non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar according to claim 1, wherein: The industrial CT scanning process parameters include a voltage of 120 kV, a current of 200 μA, and an integration time of 500 ms.

3. The non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar according to claim 1, characterized in that: The filter plate is a 1 mm copper filter plate.

4. The non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar according to claim 1, characterized in that: The threshold value of the projection number of the industrial CT system is 1000 or 1500.

5. The non-destructive evaluation method for internal pores of an additively manufactured titanium alloy test bar according to claim 1, characterized in that: The diameter of the cylindrical test bar is Ф10 mm - Ф16 mm.

6. The non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar according to claim 1, characterized in that: The length of the cylindrical test bar is 60 mm - 80 mm.

7. The non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar according to claim 1, wherein: The cylindrical test bar is laser additive manufactured TC4.

8. The non-destructive evaluation method for internal pores of an additive manufacturing titanium alloy test bar according to claim 1, characterized in that: The cylindrical test bar is fixed by means of bonding and / or bundling.