A method for preparing a sample for metallographic corrosion by differentiating the XY section and the XZ section of a selective laser melting printed part

Abstract

The application discloses a kind of selective laser melting printing piece XY section and XZ section differentiation metallographic sample preparation corrosion method, this method obtains XY section sample and XZ section sample from the same selective laser melting printing component respectively, two groups of samples are embedded in the same sample carrier, synchronous completion polishing, polishing pretreatment procedure;Two target sections are respectively subjected to corrosion treatment using different corrosion liquid component distribution ratio, corrosion process parameters and corrosion operation mode;After corrosion, execute termination corrosion, washing, dehydration and air drying treatment, finally obtain qualified metallographic sample that can be used for metallographic microscope, scanning electron microscope observation.The application solves the existing SLM sample metallographic sample preparation using uniform corrosion process, XY section fish scale shape molten pool profile, equiaxed crystal organization and XZ section columnar crystal, layer band fusion organization along deposition direction can be clearly shown simultaneously, greatly improve the accuracy of metallographic structure observation, quantitative statistical analysis.

Description

Technical Field

[0001] This invention belongs to the field of metallographic sample preparation technology in metal additive manufacturing, specifically relating to a selective laser melting method for differential metallographic sample preparation and etching of XY and XZ sections of printed parts. Background Technology

[0002] Selective laser melting (SLM) is a mainstream metal additive manufacturing process that relies on a high-energy laser beam to scan and melt metal powder layer by layer, stacking them to form a component. Due to the process characteristics of layer-by-layer melting and rapid solidification, SLM-formed metal components exhibit significant microstructural anisotropy. In the XY section perpendicular to the laser deposition direction, the melt pool exhibits a nearly circular fish-scale stacked morphology, with equiaxed and fine-grained grains as the main structure and relatively uniform grain boundary distribution. In the XZ section parallel to the laser deposition direction, the melt pool shows an elongated semi-ellipsoidal shape along the printing direction, with a large number of columnar grains growing directionally along the heat conduction direction. There are fusion bands between layers, and the XZ section also shows more obvious micro-elemental segregation and substructure gradient changes along the deposition direction. The grain boundary ratio, second-phase distribution, and electrochemical corrosion and dissolution behavior of the two orientation sections are significantly different.

[0003] Current industry-standard SLM metallographic etching processes follow the traditional approach to preparing homogeneous forged and cast metal materials. They prepare XY and XZ section specimens separately, or mount them together and then use the same etching solution formula and time-temperature parameters for uniform etching treatment. Existing technologies have four main significant drawbacks:

[0004] First, it is difficult to adapt the uniform corrosion parameters to the electrochemical corrosion behavior of two cross sections simultaneously. If the corrosion process is set according to the requirements of the XY cross section, the corrosion rate of the columnar grain boundaries in the XZ cross section is faster, which easily leads to over-corrosion, resulting in a large number of pitting and concave defects, and the columnar grain outline is eroded and destroyed. If the corrosion process is set according to the requirements of the XZ cross section, the corrosion degree of the XY cross section is insufficient, the boundaries of the fish-scale molten pool are blurred, the grain boundaries cannot be exposed, and quantitative metallographic statistics cannot be carried out.

[0005] Second, the separate mounting and separate sample preparation scheme means that the two samples have undergone completely different grinding, polishing and corrosion histories. The degree of grinding and polishing damage and corrosion are inconsistent, which will introduce human sample preparation errors when comparing and observing, and is not conducive to the lateral comparative analysis of the XY and XZ cross-sections.

[0006] Third, the few current sample preparation improvement schemes for SLM samples only optimize the etching solution formula and do not implement differentiated etching for the anisotropy of the two cross sections; they still use the overall immersion etching method, with both cross sections being etched simultaneously, which cannot solve the inherent contradiction of the mismatch between the two cross sections' etching rates.

[0007] Fourth, there is a lack of multi-dimensional methods for determining corrosion termination. Most rely solely on fixed corrosion time. SLM samples are affected by fluctuations in the printing process, and there are batch-to-batch differences in the microstructure. Simply relying on a fixed time can easily lead to unstable sample quality between batches. Inadequate control of the post-corrosion processing can easily result in water stains and surface oxidation, further reducing the quality of metallographic images.

[0008] In summary, the existing technology lacks a complete sample preparation method for co-embedding synchronous grinding and polishing + segmented differential etching of the XY and XZ sections of SLM printed parts, which makes it difficult to ensure that two sections with different orientations can obtain high-quality metallographic morphology at the same time, thus limiting the accuracy of microstructure evaluation of additively manufactured components. Summary of the Invention

[0009] To address the problems raised in the background art, the purpose of this invention is to provide a method for differential metallographic sample preparation and etching of XY and XZ sections of selective laser melting printed parts. This invention solves the problem of using a uniform etching process for metallographic sample preparation in existing SLM samples, and can simultaneously and clearly expose the fish-scale molten pool outline and equiaxed crystal structure of the XY section, as well as the columnar crystals and layered fusion structure extending along the deposition direction of the XZ section, greatly improving the accuracy of metallographic observation and quantitative statistical analysis.

[0010] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0011] A selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part includes the following steps:

[0012] S1 was taken from the same selective laser melting printed component, and XY section sample and XZ section sample were obtained respectively. The XY section sample and XZ section sample were jointly embedded in the same mounting carrier, so that the XY section and XZ section were exposed outwards and the two sections to be etched were at the same plane height.

[0013] S2 performs grinding and polishing on the entire inlay carrier after the inlay is completed, and simultaneously grinds and polishes the XY and XZ sections to obtain a mirror-like surface to be etched without processing damage;

[0014] Based on the anisotropic differences in the microstructure of the XY and XZ sections of the selective laser melting printed parts, S3 matches the corresponding etching solution formula, etching process parameters and etching operation mode to separately etch the XY and XZ sections.

[0015] When any cross section reaches the preset corrosion termination condition, the corrosion reaction of that cross section is immediately terminated. The rinsing, dehydration, and cold air drying operations are performed in sequence to complete the metallographic sample preparation and obtain a finished metallographic sample that can be observed under a microscope.

[0016] Further specifying, step S1 includes the following sub-steps:

[0017] S11 involves cutting and sampling from the same selective laser melting printed component. The XY section is perpendicular to the laser deposition printing direction of the component, and the XZ section is parallel to the laser deposition printing direction of the component. The cutting process uses a low-speed diamond cutter for water-cooled cutting, and the edges of the sample are chamfered and deburred after cutting.

[0018] S12 Place the processed XY section specimen and XZ section specimen inside the specimen mounting mold cavity, and adjust the specimen placement posture to ensure that the XY section to be observed and the XZ section to be observed are flush upwards.

[0019] Encapsulation is performed using hot-mounted resin or cold-mounted epoxy resin to form an integrated mounting carrier; after mounting, the height difference between the two sections to be corroded is checked, and the height difference is controlled within the range of 0-0.2mm.

[0020] Further specifying, step S2 includes the following sub-steps:

[0021] S21 clamps the sample carrier on the metallographic polishing machine fixture and wet-grinds it step by step with silicon carbide wet sandpaper from coarse to fine grit. Each time the sandpaper is changed, the sample carrier is rotated 90° for polishing until the polishing scratches produced by the previous sandpaper are completely eliminated.

[0022] After S22 grinding is completed, switch to mechanical polishing process. Coarse, medium and fine diamond polishing suspensions are used in sequence on the velvet polishing cloth for polishing. Water cooling is continuously circulated during the polishing process to control the polishing pressure. After polishing, the XY and XZ sections reach a mirror finish.

[0023] Further specifying, in the S3 cross-section differentiated corrosion treatment, the differentiated corrosion process includes differentiated corrosion liquid composition ratios, with a first corrosion liquid with strong corrosion activity configured for the XY cross section and a second corrosion liquid with mild corrosion activity configured for the XZ cross section.

[0024] For titanium alloy SLM printed parts, the first etching solution is a mixed solution of hydrofluoric acid, nitric acid and deionized water, and the second etching solution is a mixed solution of hydrofluoric acid, nitric acid and deionized water with a reduced relative proportion of hydrofluoric acid.

[0025] For aluminum alloy SLM printed parts, the first etching solution is a hydrofluoric acid-hydrochloric acid-water system, and the second etching solution reduces the proportion of hydrofluoric acid added.

[0026] For nickel-based alloy SLM printed parts, the first etching solution uses an aqua regia dilution system, and the second etching solution reduces the volume percentage of highly corrosive acid components.

[0027] Furthermore, the S3 cross-sectional differentiated corrosion treatment also includes differentiated corrosion time settings and differentiated corrosion environment temperature settings; the XY cross section is set with a shorter corrosion time, and the XZ cross section is set with a longer corrosion time.

[0028] The corrosion environment temperature for the XY section is set to room temperature or slightly below room temperature, while the corrosion temperature for the XZ section is selected based on the material properties, either at room temperature or slightly increased.

[0029] Further specifying, the S3 cross-sectional differentiated corrosion treatment uses either a local wiping corrosion mode or a local isolation immersion corrosion mode as the corrosion operation mode; the local wiping corrosion mode uses a dust-free cotton swab soaked in corrosion liquid to perform point wiping corrosion on the XY and XZ cross sections respectively, and controls the degree of corrosion by controlling the number of wipings and the wiping pressure;

[0030] The local isolation immersion mode uses an acid and alkali resistant rubber water-blocking sleeve to seal and isolate one section, exposing only a single target section to be immersed in the corresponding corrosive liquid. After the corrosion of that section is completed, the sealed and protected object is replaced, and the corrosive liquid is switched to treat another section.

[0031] Further specifying, the S3 cross-sectional differentiated corrosion treatment includes corrosion termination criteria; these criteria include three determination methods, which can be used individually or in combination:

[0032] The first method is a preset time threshold determination, which pre-calibrates the maximum allowable corrosion time for the XY and XZ sections based on the material grade, and terminates corrosion immediately upon reaching the time threshold. The second method is in-situ microscopic real-time observation determination, which uses a low-magnification metallographic microscope to observe the surface of the section in situ, and terminates corrosion of the corresponding section immediately when the outline of the molten pool and the grain boundary lines are clearly visible. The third method is surface color grayscale determination, which relies on the grayscale changes in the metallographic image, and triggers corrosion termination when the grayscale difference between the grain boundary and the matrix reaches a preset threshold.

[0033] Further specifying, step S4 includes the following sub-steps:

[0034] Once the corrosion termination condition of a certain section is met, the sample is immediately removed from the corrosion system and rinsed with a large amount of flowing deionized water to quickly dilute and remove the residual corrosive agent on the surface of the section, thus blocking the continued corrosion chemical reaction.

[0035] After S42 completes the water rinsing, the entire sample carrier is immersed in anhydrous ethanol for ultrasonic rinsing or soaking rinsing to replace the residual moisture in the gaps on the sample surface.

[0036] S43 Remove the sample and use clean compressed cold air to dry the two sections of the sample to be observed; after drying, seal and store.

[0037] Further specifying, the material of the selective laser melting printed component is any one of titanium alloy, aluminum-silicon alloy, nickel-based high-temperature alloy, and cobalt-chromium alloy.

[0038] Further specifying, after sample preparation is completed in S4, a sample quality re-inspection sub-step is also included, in which the XY and XZ sections are observed using a metallographic microscope, and the quality re-inspection indicators include:

[0039] The molten pool boundary is completely and continuously exposed, the grain boundary is clearly distinguishable, and the cross section has no obvious over-corrosion pits, pitting, or water stains. If any cross section does not meet the re-inspection criteria, the grinding, polishing, and differential etching processes are repeated until both cross sections simultaneously meet the metallographic observation quality criteria.

[0040] The beneficial effects of this invention are:

[0041] This invention co-embeds and simultaneously polishes XY and XZ samples of the same component, eliminating human error caused by the polishing process. Addressing the differences in molten pool, grain size, and elemental segregation between the two sections, it employs multi-dimensional differentiated etching based on etchant ratio, time, and temperature. This allows for the simultaneous and clear exposure of the fish-scale molten pool and equiaxed crystals in the XY section, as well as the elongated molten pool and columnar crystal structure in the XZ section, avoiding insufficient or excessive etching defects in a single section. Furthermore, this invention provides two differentiated operation modes: localized wiping etching and localized isolation etching. It supports multiple etching termination criteria, including time thresholds, in-situ microscopic observation, and grayscale recognition, overcoming sample instability caused by batch-wise microstructure fluctuations in SLM printing and significantly improving sample yield.

[0042] By polishing XY and XZ samples within the same mounting medium, maintaining a consistent thickness of the polished damage layer, and differentiating only the etching steps, the metallographic results of the two sections can be directly compared laterally, improving the reliability of experimental data for grain size and molten pool size statistics. The overall process of this invention is universal; only the etching solution ratio and etching parameters need to be adjusted to adapt to various mainstream SLM-printed metal materials, including titanium alloys, aluminum-silicon-aluminum alloys, nickel-based superalloys, and cobalt-chromium alloys.

[0043] This invention employs a standardized post-processing procedure, including corrosion, rapid termination, water rinsing, ethanol dehydration, and cold air drying, and adds a post-sample quality re-inspection step to avoid secondary defects such as water stains, surface oxidation, and pitting. The prepared samples can be used for observation under a conventional metallographic microscope and also meet the sample preparation requirements for scanning electron microscopy. Attached Figure Description

[0044] The present invention can be further illustrated by the non-limiting embodiments given in the accompanying drawings;

[0045] Figure 1This is a flowchart illustrating the steps of an embodiment of the selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to the present invention. Detailed Implementation

[0046] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0047] like Figure 1 As shown, the present invention provides a selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a printed part, comprising the following steps:

[0048] S1 was taken from the same selective laser melting printed component, and XY section sample and XZ section sample were obtained respectively. The XY section sample and XZ section sample were jointly embedded in the same mounting carrier, so that the XY section and XZ section were exposed outwards and the two sections to be etched were at the same plane height.

[0049] S2 performs grinding and polishing on the entire inlay carrier after the inlay is completed, and simultaneously grinds and polishes the XY and XZ sections to obtain a mirror-like surface to be etched without processing damage;

[0050] Based on the anisotropic differences in the microstructure of the XY and XZ sections of the selective laser melting printed parts, S3 matches the corresponding etching solution formula, etching process parameters and etching operation mode to separately etch the XY and XZ sections.

[0051] When any cross section reaches the preset corrosion termination condition, the corrosion reaction of that cross section is immediately terminated. The rinsing, dehydration, and cold air drying operations are performed in sequence to complete the metallographic sample preparation and obtain a finished metallographic sample that can be observed under a microscope.

[0052] In practical applications of this embodiment, step S1 includes the following sub-steps:

[0053] S11 involves cutting and sampling from the same selective laser melting printed component. The XY section is perpendicular to the laser deposition printing direction of the component, and the XZ section is parallel to the laser deposition printing direction of the component. The cutting process uses a low-speed diamond cutter for water-cooled cutting, and the edges of the sample are chamfered and deburred after cutting.

[0054] S12 Place the processed XY section specimen and XZ section specimen inside the specimen mounting mold cavity, and adjust the specimen placement posture to ensure that the XY section to be observed and the XZ section to be observed are flush upwards.

[0055] Encapsulation is performed using hot-mounted resin or cold-mounted epoxy resin to form an integrated mounting carrier; after mounting, the height difference between the two sections to be corroded is checked, and the height difference is controlled within the range of 0-0.2mm.

[0056] In practical applications of this embodiment, step S2 includes the following sub-steps:

[0057] S21 clamps the sample carrier on the metallographic polishing machine fixture and wet-grinds it step by step with silicon carbide wet sandpaper from coarse to fine grit. Each time the sandpaper is changed, the sample carrier is rotated 90° for polishing until the polishing scratches produced by the previous sandpaper are completely eliminated.

[0058] After S22 grinding is completed, switch to mechanical polishing process. Coarse, medium and fine diamond polishing suspensions are used in sequence on the velvet polishing cloth for polishing. Water cooling is continuously circulated during the polishing process to control the polishing pressure. After polishing, the XY and XZ sections reach a mirror finish.

[0059] In the practical application of this embodiment, the S3 cross-sectional differential corrosion treatment includes differential corrosion liquid composition ratio, with a first corrosion liquid with strong corrosion activity configured for the XY cross section and a second corrosion liquid with mild corrosion activity configured for the XZ cross section.

[0060] For titanium alloy SLM printed parts, the first etching solution is a mixed solution of hydrofluoric acid, nitric acid and deionized water, and the second etching solution is a mixed solution of hydrofluoric acid, nitric acid and deionized water with a reduced relative proportion of hydrofluoric acid.

[0061] For aluminum alloy SLM printed parts, the first etching solution is a hydrofluoric acid-hydrochloric acid-water system, and the second etching solution reduces the proportion of hydrofluoric acid added.

[0062] For nickel-based alloy SLM printed parts, the first etching solution uses an aqua regia dilution system, and the second etching solution reduces the volume percentage of highly corrosive acid components.

[0063] In the practical application of this embodiment, the S3 cross-sectional differential corrosion treatment also includes differential corrosion time settings and differential corrosion environment temperature settings; the XY cross section is set with a shorter corrosion time, and the XZ cross section is set with a longer corrosion time.

[0064] The corrosion environment temperature for the XY section is set to room temperature or slightly below room temperature, while the corrosion temperature for the XZ section is selected based on the material properties, either at room temperature or slightly increased.

[0065] In the practical application of this embodiment, the S3 cross-sectional differentiated corrosion treatment uses either a local wiping corrosion mode or a local isolation immersion corrosion mode. The local wiping corrosion mode uses dust-free cotton swabs soaked in corrosion liquid to perform point wiping corrosion on the XY and XZ cross sections respectively, and controls the degree of corrosion by controlling the number of wipings and the wiping pressure.

[0066] The local isolation immersion mode uses an acid and alkali resistant rubber water-blocking sleeve to seal and isolate one section, exposing only a single target section to be immersed in the corresponding corrosive liquid. After the corrosion of that section is completed, the sealed and protected object is replaced, and the corrosive liquid is switched to treat another section.

[0067] In the practical application of this embodiment, the S3 cross-sectional differentiated corrosion treatment sets corrosion termination criteria; the corrosion termination criteria include three determination methods, which can be used individually or in combination:

[0068] The first method is a preset time threshold determination, which pre-determines the maximum allowable corrosion time for the XY and XZ sections based on the material grade, and terminates corrosion immediately upon reaching the time threshold. The second method is in-situ microscopic real-time observation determination, which uses a low-magnification metallographic microscope to observe the surface of the section in situ, and terminates corrosion of the corresponding section immediately when the outline of the molten pool and the grain boundary lines are clearly visible. The third method is surface color grayscale determination, which relies on the grayscale changes in the metallographic image, and triggers corrosion termination when the grayscale difference between the grain boundary and the matrix reaches a preset threshold.

[0069] In practical applications of this embodiment, step S4 includes the following sub-steps:

[0070] Once the corrosion termination condition of a certain section is met, the sample is immediately removed from the corrosion system and rinsed with a large amount of flowing deionized water to quickly dilute and remove the residual corrosive agent on the surface of the section, thus blocking the continued corrosion chemical reaction.

[0071] After S42 completes the water rinsing, the entire sample carrier is immersed in anhydrous ethanol for ultrasonic rinsing or soaking rinsing to replace the residual moisture in the gaps on the sample surface.

[0072] S43 Remove the sample and use clean compressed cold air to dry the two sections of the sample to be observed; after drying, seal and store.

[0073] In the practical application of this embodiment, the material of the selective laser melting printed component is any one of titanium alloy, aluminum-silicon alloy, nickel-based high-temperature alloy, and cobalt-chromium alloy.

[0074] In the practical application of this embodiment, after sample preparation is completed in S4, a sample quality re-inspection sub-step is also included, in which the XY and XZ sections are observed using a metallographic microscope. The quality re-inspection indicators include:

[0075] The molten pool boundary is completely and continuously exposed, the grain boundary is clearly distinguishable, and the cross section has no obvious over-corrosion pits, pitting, or water stains. If any cross section does not meet the re-inspection criteria, the grinding, polishing, and differential etching processes are repeated until both cross sections simultaneously meet the metallographic observation quality criteria.

[0076] Working principle of the invention:

[0077] Because the XY and XZ sections of selective laser melting (SLM) printed parts differ under different solidification conditions, there are significant differences in the number of grain boundaries, the precipitation of second phases, and the degree of micro-element segregation. Therefore, the electrochemical corrosion dissolution rates of the grain boundaries and matrix in the two sections are inconsistent. This invention embeds two test samples taken from the same component together and performs simultaneous grinding and polishing to ensure that the surface processing damage states of the two sections are completely consistent. Instead of using a uniform corrosion mode of complete immersion, different active corrosion reagents are applied to the XY and XZ sections, along with differentiated corrosion time and temperature parameters to match the preferential corrosion dissolution rate of the grain boundaries in each section. Multiple corrosion termination conditions are set; when the grain boundary-matrix contrast of a certain section reaches the observation requirements, the corrosion of that section is immediately terminated to avoid over-etching. Subsequent standardized rinsing, dehydration, and air drying eliminate water stains and secondary oxidation damage, ultimately achieving metallographic samples with suitable contrast and no defects from both oriented sections simultaneously.

[0078] Example 1: Differential metallographic etching of XY and XZ sections of SLM-TC4 titanium alloy printed parts

[0079] S1 selects TC4 titanium alloy components for SLM printing, and samples are taken using a water-cooled low-speed diamond cutter; XY section samples perpendicular to the printing direction and XZ section samples parallel to the printing deposition direction are cut; the sample size is 10mm×10mm×5mm, and the sample edges are chamfered and deburred.

[0080] Two samples were placed in a thermal mounting mold with the two sections to be observed facing upwards, and thermal mounting was performed using bakelite thermal mounting powder; after mounting, the height difference of the test sections was 0.1 mm, which met the co-mounting requirements.

[0081] S2 clamps the sample block in a metallographic polishing machine; wet polishing is performed sequentially using 240#, 400#, 800#, 1200#, and 2000# silicon carbide wet sandpaper, rotating 90° each time the sandpaper is changed; after polishing, mechanical polishing is performed sequentially using W3.5 and W1.5 diamond suspension polishing cloth, with water cooling during the polishing process; after polishing, both cross-sections reach a mirror finish without scratches.

[0082] S3 employs a localized isolation etching mode, using an acid and alkali resistant rubber sleeve to seal and protect the XZ section, exposing only the XY section. The XY section uses the first etching solution with a volume ratio of HF:HNO3:H2O = 1:3:16, at room temperature.

[0083] In-situ low-magnification metallographic microscopy was used as the primary termination criterion, with a maximum corrosion time of 20 seconds set as an auxiliary factor. The fish-scale molten pool outline and grain boundaries were observed, and the corrosion of the XY section was terminated immediately after 14 seconds.

[0084] Replace the rubber sealing sleeve to isolate and protect the XY section that has been completely corroded, exposing only the XZ section; use a second etchant for the XZ section with a volume ratio of HF:HNO3:H2O=1:4:20 at room temperature; observe under an in-situ microscope, and the columnar grain boundaries and fusion zones are clearly visible, taking 24 seconds, and then terminate the corrosion of the XZ section.

[0085] After removing the S4 sample, rinse it with plenty of flowing deionized water; immerse it in anhydrous ethanol for 1 minute to replace the water; dry the sample surface with clean cold air and store it in a sealed container.

[0086] Sample re-inspection: Metallographic microscopy showed that the fish-scale molten pool boundary of the XY section was continuous and the equiaxed grain boundaries were clear; the columnar crystals and layered fusion zones along the deposition direction were completely exposed in the XZ section; there were no over-corrosion pits or water stains in either section, which met the requirements for quantitative metallographic analysis.

[0087] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for selective laser melting printing of XY and XZ sections of a part using differential metallographic etching, characterized in that, Includes the following steps: S1 was taken from the same selective laser melting printed component, and XY section sample and XZ section sample were obtained respectively. The XY section sample and XZ section sample were jointly embedded in the same mounting carrier, so that the XY section and XZ section were exposed outwards and the two sections to be etched were at the same plane height. S2 performs grinding and polishing on the entire inlay carrier after the inlay is completed, and simultaneously grinds and polishes the XY and XZ sections to obtain a mirror-like surface to be etched without processing damage; Based on the anisotropic differences in the microstructure of the XY and XZ sections of the selective laser melting printed parts, S3 matches the corresponding etching solution formula, etching process parameters and etching operation mode to separately etch the XY and XZ sections. When any cross section reaches the preset corrosion termination condition, the corrosion reaction of that cross section is immediately terminated. The rinsing, dehydration, and cold air drying operations are performed in sequence to complete the metallographic sample preparation and obtain a finished metallographic sample that can be observed under a microscope.

2. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 1, characterized in that, S1 includes the following sub-steps: S11 involves cutting and sampling from the same selective laser melting printed component. The XY section is perpendicular to the laser deposition printing direction of the component, and the XZ section is parallel to the laser deposition printing direction of the component. The cutting process uses a low-speed diamond cutter for water-cooled cutting, and the edges of the sample are chamfered and deburred after cutting. S12 Place the processed XY section specimen and XZ section specimen inside the specimen mounting mold cavity, and adjust the specimen placement posture to ensure that the XY section to be observed and the XZ section to be observed are flush upwards. Encapsulation is performed using hot-mounted resin or cold-mounted epoxy resin to form an integrated mounting carrier; after mounting, the height difference between the two sections to be corroded is checked, and the height difference is controlled within the range of 0-0.2mm.

3. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 1, characterized in that, S2 includes the following sub-steps: S21 clamps the sample carrier on the metallographic polishing machine fixture and wet-grinds it step by step with silicon carbide wet sandpaper from coarse to fine grit. Each time the sandpaper is changed, the sample carrier is rotated 90° for polishing until the polishing scratches produced by the previous sandpaper are completely eliminated. After S22 grinding is completed, switch to mechanical polishing process. Coarse, medium and fine diamond polishing suspensions are used in sequence on the velvet polishing cloth for polishing. Water cooling is continuously circulated during the polishing process to control the polishing pressure. After polishing, the XY and XZ sections reach a mirror finish.

4. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 1, characterized in that, In the S3 cross-section differentiated corrosion treatment, the differentiated corrosion process includes differentiated corrosion liquid composition ratios: the XY cross section is configured with a first corrosion liquid with strong corrosion activity, and the XZ cross section is configured with a second corrosion liquid with mild corrosion activity.

5. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 4, characterized in that, The S3 cross-section differentiated corrosion treatment also includes differentiated corrosion time settings and differentiated corrosion environment temperature settings; the XY cross section is set with a shorter corrosion time, and the XZ cross section is set with a longer corrosion time. The corrosion environment temperature for the XY section is set to room temperature or slightly below room temperature, while the corrosion temperature for the XZ section is selected based on the material properties, either at room temperature or slightly increased.

6. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 5, characterized in that, The S3 cross-sectional differentiated corrosion treatment uses either a local wiping corrosion mode or a local isolation immersion corrosion mode. The local wiping corrosion mode uses a dust-free cotton swab soaked in corrosion liquid to perform point wiping corrosion on the XY and XZ cross sections respectively, and controls the degree of corrosion by controlling the number of wipings and the wiping pressure. The local isolation immersion mode uses an acid and alkali resistant rubber water-blocking sleeve to seal and isolate one section, exposing only a single target section to be immersed in the corresponding corrosive liquid. After the corrosion of that section is completed, the sealed and protected object is replaced, and the corrosive liquid is switched to treat another section.

7. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 1, characterized in that, The S3 cross-sectional differentiated corrosion treatment sets corrosion termination criteria; the corrosion termination criteria include three determination methods, which can be used individually or in combination: The first method is a preset time threshold determination, which pre-calibrates the maximum allowable corrosion time for the XY and XZ sections based on the material grade, and terminates corrosion immediately upon reaching the time threshold. The second method is in-situ microscopic real-time observation determination, which uses a low-magnification metallographic microscope to observe the surface of the section in situ, and terminates corrosion of the corresponding section immediately when the outline of the molten pool and the grain boundary lines are clearly visible. The third method is surface color grayscale determination, which relies on the grayscale changes in the metallographic image, and triggers corrosion termination when the grayscale difference between the grain boundary and the matrix reaches a preset threshold.

8. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 1, characterized in that, S4 includes the following sub-steps: Once the corrosion termination condition of a certain section is met, the sample is immediately removed from the corrosion system and rinsed with a large amount of flowing deionized water to quickly dilute and remove the residual corrosive agent on the surface of the section, thus blocking the continued corrosion chemical reaction. After S42 completes the water rinsing, the entire sample carrier is immersed in anhydrous ethanol for ultrasonic rinsing or soaking rinsing to replace the residual moisture in the gaps on the sample surface. S43 Remove the sample and use clean compressed cold air to dry the two sections of the sample to be observed; after drying, seal and store.

9. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to any one of claims 1-8, characterized in that, The material of the selective laser melting printed component is any one of titanium alloy, aluminum-silicon alloy, nickel-based high-temperature alloy, and cobalt-chromium alloy.

10. The selective laser melting printing method for differential metallographic sample preparation and etching of XY and XZ sections of a part according to claim 9, characterized in that, After sample preparation is completed in S4, the process also includes a sample quality re-inspection sub-step. The XY and XZ sections are observed using a metallographic microscope, and the quality re-inspection indicators include: The molten pool boundary is completely and continuously exposed, the grain boundary is clearly distinguishable, and the cross section has no obvious over-corrosion pits, pitting, or water stains. If any cross section does not meet the re-inspection criteria, the grinding, polishing, and differential etching processes are repeated until both cross sections simultaneously meet the metallographic observation quality criteria.

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