Method for detecting hydrogen embrittlement sensitivity based on tubular copper alloy grain boundary bubble characteristics

Abstract

The application discloses a hydrogen embrittlement sensitivity detection method based on tubular copper alloy grain boundary bubble characteristics, which comprises sample positioning, multi-stage deoxidation pretreatment, weak hydrogen atmosphere precise gas washing, hydrogen permeation pre-stabilization treatment, directional hydrogen embrittlement induction, atmosphere safety shutdown, in-situ grain boundary defect shaping, targeted sample preparation and 360-degree global judgment observation. The application creatively adds 350 DEG C hydrogen permeation pre-stabilization treatment, realizes uniform shallow hydrogen atom penetration, solves the problems of uneven hydrogen penetration and unstable bubble generation caused by traditional direct high-temperature heating, and simultaneously adopts inert atmosphere ≥ 30 DEG C / min rapid cooling for in-situ grain boundary defect shaping, and truly retains the hydrogen-induced defect morphology at high temperature. Through three-point support, double-cycle deoxidation, three-stage soaking, partition quadrant corrosion and quantitative judgment, the application realizes precise, stable and repeatable detection of hydrogen embrittlement of tubular copper alloy, and is suitable for hydrogen embrittlement sensitivity evaluation of thin-walled copper pipes under high-temperature hydrogen-containing working conditions.

Description

Technical Field

[0001] This invention belongs to the field of copper alloy testing technology, and particularly relates to a method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys. Background Technology

[0002] In aerospace, electronics, and refrigeration equipment, tubular copper alloys are commonly used in hydrogen-containing environments such as high-temperature sintering and brazing. During use, hydrogen atom infiltration can easily cause grain boundary hydrogen embrittlement, leading to premature component failure. Current methods for detecting hydrogen embrittlement in copper alloys mostly employ the conventional process of direct high-temperature heating followed by natural cooling, which has significant technical limitations.

[0003] Existing methods directly and rapidly heat the sample from room temperature to high temperature, lacking a low-temperature pre-permeation step. At high temperatures, hydrogen atoms diffuse rapidly and the permeation rate is uncontrollable, which can easily lead to a significant difference in the hydrogen distribution gradient along the tube wall thickness, random nucleation sites of grain boundary bubbles, and large fluctuations in the number of bubbles. Ultimately, this results in uneven hydrogen permeation, unstable bubble formation, and large deviations in detection and judgment.

[0004] After high-temperature induction, the sample was cooled naturally without defects in situ for shaping and protection. During the slow cooling process, hydrogen-induced bubbles are prone to internal hydrogen escape, bubble merging and shrinking, or even complete annihilation. The grain boundary separation morphology will also be distorted due to high-temperature recovery. It is impossible to retain the hydrogen embrittlement characteristics that are actually formed at high temperature, and it is difficult to objectively reflect the actual hydrogen embrittlement sensitivity of the material.

[0005] Meanwhile, traditional methods do not construct a precise characterization system for partitioned corrosion and full-domain scanning of the annular cross-section of tubular samples, which further exacerbates the unreliability and non-reproducibility of the detection results. Summary of the Invention

[0006] The purpose of this invention is to provide a method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys, so as to solve the problems mentioned in the background art.

[0007] In view of this, the present invention provides a method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys, comprising the following steps:

[0008] (1) Sample positioning: Take a tubular copper alloy sample with a length of 40 mm, fix it in the graphite frame positioning groove with the axis perpendicular to the airflow direction, put it into the quartz tube of the tubular sintering furnace and seal the flange.

[0009] (2) Multi-stage deoxygenation pretreatment: First, purge with high-purity nitrogen, then evacuate to an absolute pressure ≤2Pa, and maintain pressure to check for leaks;

[0010] (3) Precise gas scrubbing in a weak hydrogen atmosphere: A nitrogen-hydrogen mixture with a volume fraction of 10% is introduced and scrubbed at a constant flow rate until the oxygen content in the furnace is below 10 ppm.

[0011] (4) Hydrogen permeation pre-stabilization treatment: Before heating, the furnace temperature is raised to 350℃ and kept for 10 minutes to allow hydrogen atoms to form a uniform pre-permeation layer in the shallow layer of the tube wall;

[0012] (5) Directional hydrogen embrittlement: The temperature is increased to 850℃ at 15℃ / min and held radially uniformly for 30min to allow hydrogen atoms to penetrate deeply along the wall thickness direction and accumulate at the grain boundaries;

[0013] (6) Atmosphere safety shutdown: shut off the nitrogen-hydrogen mixture, seal and allow to cool naturally to below 200°C before removing the sample;

[0014] (7) In-situ shaping of grain boundary defects: The sample is rapidly cooled to room temperature under inert gas protection to suppress the merging or disappearance of hydrogen-induced bubbles during the cooling stage;

[0015] (8) Targeted sample preparation for grain boundary defects: After cutting an annular section, embedding, grinding and polishing, the sample is etched in sections at time using a preset grain boundary etchant;

[0016] (9) Full-area judgment observation: Observe the full area along the annular section in 360° under a metallographic microscope, and use the number of grain boundary bubbles and the grain boundary separation length as the basis for judging hydrogen embrittlement sensitivity.

[0017] In this invention, the graphite frame positioning groove in step (1) further includes a three-point elastic support mechanism evenly arranged along the circumference. The support mechanism forms a uniform air gap of 0.5 mm between the outer wall of the tubular sample and the positioning groove, which is used to ensure uniform airflow and eliminate local overheating and temperature field distortion of the sample.

[0018] In this invention, further, the multi-stage deoxygenation pretreatment in step (2) specifically includes two complete cycles of alternating high-purity nitrogen purging and vacuum extraction, and micro-heating desorption is performed simultaneously in the vacuum stage to reduce the residual oxygen and adsorbed water vapor in the furnace to below the experimental interference threshold.

[0019] In this invention, further, the precise gas washing in the weak hydrogen atmosphere in step (3) specifically includes real-time online monitoring of oxygen content and hydrogen concentration in the furnace during the gas washing process. Only when the oxygen content is stably below 10 ppm and the hydrogen concentration fluctuation is less than ±0.2% and maintained for more than 1 minute can the subsequent heating step be entered.

[0020] In this invention, further, the hydrogen permeation prestabilization treatment in step (4) specifically includes maintaining a weak hydrogen atmosphere in the 350°C heat preservation stage, so that hydrogen atoms form a uniform gradient shallow permeation distribution in the copper tube wall thickness direction, providing a stable initial state for subsequent high-temperature hydrogen embrittlement.

[0021] In this invention, the radial uniform heat preservation in step (5) specifically adopts a three-stage heat control mode: first, heat preservation at 850℃ for 15 minutes, then slightly increase to 852℃ for 10 minutes, and finally drop back to 850℃ for 5 minutes, so as to promote the stable nucleation and controllable growth of hydrogen-induced grain boundary defects and improve the clarity of characterization.

[0022] In this invention, further, the in-situ shaping of grain boundary defects in step (7) specifically includes placing the sample in a high-purity nitrogen atmosphere and rapidly cooling it at a rate of ≥30℃ / min, so that hydrogen-induced bubbles and microcracks at the grain boundaries remain in a high-temperature generation state without annihilation, merging or morphological changes.

[0023] In this invention, the pre-set grain boundary etchant in step (8) is specifically prepared by phosphoric acid, anhydrous ethanol and deionized water in a volume ratio of 2:3:5, with the corrosion temperature controlled at 22±2℃ and the corrosion time precisely 45±5s, so as to achieve selective highlighting of grain boundary defects without damaging the matrix structure.

[0024] In this invention, further, the partitioned timed corrosion in step (8) specifically includes dividing the annular cross section into four quadrant regions at 0°, 90°, 180° and 270°, with each quadrant independently controlling corrosion parameters, and setting a 0.2mm non-corrosion isolation zone between adjacent regions to avoid over-corrosion at the edges leading to tissue distortion.

[0025] In this invention, further, the global determination observation in step (9) specifically includes using a fixed magnification of 200 times, a step distance of 0.2 mm for line-by-line scanning imaging and automatic stitching of the global spectrum; when ≥3 hydrogen-induced bubbles or a grain boundary separation length ≥0.5 mm appear at any continuous 1 mm grain boundary within the 360° range of the cross section, the sample is determined to have hydrogen embrittlement sensitivity.

[0026] The beneficial effects of this invention are:

[0027] 1. By employing hydrogen permeation pre-stabilization treatment, uniform hydrogen atom infiltration and stable bubble formation are achieved. This invention adds a 350°C low-temperature hydrogen permeation pre-stabilization step before high-temperature induction. This first allows hydrogen atoms to form a uniformly distributed pre-permeation layer in the shallow layer of the pipe wall, constructing a stable initial hydrogen concentration field. Then, the temperature is increased to 850°C at a set rate for deep induction. This fundamentally avoids the runaway hydrogen diffusion problem caused by direct high-temperature heating, ensuring that hydrogen atoms infiltrate uniformly along the pipe wall thickness direction and accumulate orderly at the grain boundaries. This guarantees consistent nucleation, uniform size, and stable distribution of bubbles at the grain boundaries, significantly improving the reliability and accuracy of hydrogen embrittlement induction.

[0028] 2. By in-situ shaping of grain boundary defects, the original morphology of high-temperature hydrogen embrittlement is truly preserved. During the cooling stage, a rapid cooling in-situ shaping step under inert atmosphere protection is introduced. The sample is rapidly cooled to room temperature at a rate of ≥30℃ / min, which forcibly locks the morphology of hydrogen-induced bubbles generated at high temperature and grain boundaries, inhibits bubble annihilation, merging, deformation and microstructure recovery, and ensures that the observed defect characteristics are consistent with the real state under high-temperature conditions. This solves the problem of defect distortion caused by traditional natural cooling and realizes a true, objective and repeatable evaluation of the hydrogen embrittlement sensitivity of tubular copper alloys.

[0029] 3. The overall scheme has a high degree of standardization and significantly improved detection accuracy and repeatability. Combined with constraints such as three-point support, dual-cycle deoxidation, online atmosphere monitoring, three-stage homogenization, quadrant corrosion, and 360° full-domain quantitative judgment, this method achieves precise control of the entire process from clamping, atmosphere, temperature, sample preparation to observation. It can stably trigger and clearly characterize grain boundary hydrogen embrittlement of tubular copper alloys, and the repeatability error of the detection results is ≤5%, providing a reliable evaluation method for the safe application of thin-walled copper tubes under high-temperature hydrogen-containing conditions. Attached Figure Description

[0030] Figure 1 This is a flowchart of the steps of the hydrogen embrittlement sensitivity detection method based on the characteristics of grain boundary bubbles in tubular copper alloys according to the present invention.

[0031] Figure 2 This is a logic block diagram for precise gas scrubbing in a weak hydrogen atmosphere. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0033] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, charcoal adsorption comparison verification methods and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, charcoal adsorption comparison verification methods and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items, and therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0034] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class, without limiting the number of objects; for example, the first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0035] It should be noted that in the description of this application, the directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0036] It should be noted that in this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, charcoal adsorption comparison verification method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, charcoal adsorption comparison verification method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, charcoal adsorption comparison verification method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the charcoal adsorption comparison verification method and apparatus in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described charcoal adsorption comparison verification method may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0037] This embodiment provides a method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys, including the following steps:

[0038] (1) Sample positioning: Select tubular copper alloy raw materials with consistent specifications and uniform structure, and use precision cutting equipment to cut standard samples with a length of 40mm. The cutting process adopts low-speed precision cutting to ensure that the end face of the sample is strictly perpendicular to the axis, without burrs, deformation, or heat damage layer; use anhydrous ethanol to ultrasonically clean the inner and outer walls of the sample for 5min to 10min, and dry to remove surface oil, oxide scale and dust impurities; fix the pretreated sample in a special positioning groove made of high-purity graphite material with the axis strictly perpendicular to the axial airflow direction inside the tubular sintering furnace, so that the sample is in the core area of ​​uniform heating and uniform gas in the high-temperature atmosphere field, and avoids the phenomenon of uneven hydrogen permeation caused by local airflow scouring and local high / low temperature due to clamping eccentricity or tilt.

[0039] The graphite frame containing the sample was smoothly moved into the quartz tube of the tubular sintering furnace, ensuring that the sample was completely within ±5mm of the center of the axial constant temperature zone of the tubular furnace, minimizing the interference of temperature field fluctuations on the hydrogen embrittlement induced process. Finally, the quartz tube was sealed and tightened to the stainless steel flange, and a flexible graphite sealing ring was used to ensure that there was no leakage or release of impurities on the sealing surface, providing a closed and stable cavity environment for subsequent experiments.

[0040] The graphite frame positioning groove mentioned in step (1) specifically includes a three-point elastic support mechanism evenly arranged along the circumference. The support mechanism is formed by isostatic pressing high-purity graphite, which is resistant to high temperature ≥1000℃ and does not release impurity gas. The support points are evenly distributed at 120° angles along the circumference of the sample. The top of the support is a rounded blunt curved surface structure to avoid sharp edges causing mechanical scratches, stress concentration or local indentation defects on the outer wall of the copper tube. The extension length of the support pin is uniformly set to 0.3mm, so that a 0.5mm uniform air gap channel is formed between the outer wall of the tubular sample and the inner wall of the positioning groove. This channel can ensure that the weak hydrogen atmosphere is evenly covered and flows smoothly along the outer wall of the sample in all directions of 360°, eliminating problems such as local atmosphere stagnation, local overheating and local high hydrogen concentration. From the perspective of the clamping structure, it ensures the uniform penetration of hydrogen atoms in the entire circumference of the tube wall, providing structural guarantee for the stable generation of hydrogen-induced grain boundary defects in the future.

[0041] (2) Multi-stage deoxygenation pretreatment: First, high-purity nitrogen with a purity of ≥99.999% is introduced into the sealed quartz tube cavity to force purge the cavity with a set flow rate, quickly replacing the air, free oxygen, floating dust and water vapor in the tube, and significantly reducing the initial oxygen content; after purging, the inlet valve is closed, and the rotary vane vacuum pump + Roots vacuum pump unit is started to perform staged vacuum treatment inside the quartz tube. The pump is continuously pumped until the absolute pressure inside the quartz tube is stable at ≤2Pa. The vacuum pump valve is closed and the pressure holding state is entered. The pressure is held for 3 minutes and the pressure display value is observed to have no obvious rebound. It is confirmed that there is no leakage in the flange, pipeline and quartz tube as a whole, so as to build an ultra-low oxygen, ultra-low humidity and high purity closed reaction environment for subsequent weak hydrogen atmosphere high temperature experiment.

[0042] In this invention, further, the multi-stage deoxidation pretreatment in step (2) specifically includes two complete cycles of alternating high-purity nitrogen purging and high-vacuum extraction. Through the repeated coupling effect of "gas replacement - vacuum removal", the physically adsorbed oxygen, chemically adsorbed oxygen and bound water molecules on the inner wall of the quartz tube, the sample surface and the graphite frame surface are deeply removed. During the vacuum extraction stage, the outer wall of the quartz tube is simultaneously subjected to low-temperature auxiliary heating of 40℃~50℃. The slight temperature rise is used to enhance the thermal motion of the adsorbed gas molecules, promote the full desorption of adsorbed oxygen and water vapor and discharge them by the vacuum pump, so that the residual oxygen concentration in the furnace is reduced to below 10ppm and the water vapor partial pressure is reduced to below 5Pa. This completely eliminates the problems of oxygen competing with hydrogen atoms for adsorption at high temperature, oxide film hindering hydrogen permeation, and water vapor interfering with the formation of grain boundary defects. It ensures that hydrogen atoms only interact with the copper alloy grain boundaries, significantly improving the authenticity, stability and repeatability of the experimental results.

[0043] (3) Precise gas washing in a weak hydrogen atmosphere: A nitrogen-hydrogen standard mixed gas with a volume fraction of 10% is introduced into the quartz tube that has undergone vacuum pretreatment. The gas passes through a drying and filtration module to remove trace impurities and moisture. The gas washes and replaces the furnace cavity at a constant mass flow rate of 0.9 L / min, continuously discharging residual air, leaked gas and impurity components, and gradually establishing a weak reducing atmosphere system with stable composition, uniform concentration and low oxygen cleanliness. The gas washing process continues until the oxygen content in the furnace is stably lower than 10 ppm, meeting the atmospheric environment requirements induced by high-temperature hydrogen embrittlement.

[0044] The precise gas washing with a weak hydrogen atmosphere described in step (3) specifically includes real-time online monitoring of the furnace atmosphere throughout the gas washing process using an online zirconia oxygen analyzer and a thermal conductivity hydrogen concentration sensor. This involves collecting oxygen content and hydrogen concentration data in real time and determining the dynamic fluctuation range. Only when the oxygen content is consistently below 10 ppm, the hydrogen concentration fluctuation is less than ±0.2%, and the above indicators remain consistently stable for more than 1 minute without sudden changes, is the atmosphere system considered to have reached a thermodynamically stable equilibrium state, allowing subsequent heating steps to proceed. By controlling the atmosphere stability threshold, problems such as abnormal hydrogen permeation behavior, uncontrollable grain boundary bubble nucleation, and distorted defect morphology caused by atmosphere fluctuations, unstable hydrogen concentration, and residual oxygen interference are avoided, ensuring the consistency of the experimental process and the reliability of the detection results from the source.

[0045] (4) Hydrogen permeation pre-stabilization treatment: Before directly heating to high temperature to induce the hydrogen permeation, a hydrogen permeation pre-stabilization treatment step is added. The specific implementation method is as follows: the tubular sintering furnace is slowly heated from room temperature to 350℃ at a gentle heating rate of 5℃ / min to 8℃ / min, and held at 350℃ for 10min. In this low temperature range, the hydrogen atom diffusion coefficient is moderate and the diffusion rate is gentle and controllable. Under the premise of not inducing violent grain boundary diffusion and not producing local hydrogen enrichment, hydrogen atoms can be uniformly introduced into the interior of the surface grains and grain boundary regions of the copper tube. A hydrogen pre-permeation layer with a gradient continuity, uniform distribution and stable concentration is formed within the shallow thickness range of the tube wall. This fundamentally avoids the problems of uncontrolled hydrogen diffusion, uneven penetration, local hydrogen supersaturation and chaotic bubble nucleation caused by the traditional method of directly heating from room temperature to high temperature.

[0046] The hydrogen permeation pre-stabilization treatment in step (4) specifically includes maintaining a 10% nitrogen-hydrogen mixture at a continuous and stable flow rate of 0.9 L / min throughout the entire heat treatment at 350℃. This ensures high stability in atmosphere composition, pressure, and flow rate, allowing hydrogen atoms to diffuse slowly from the surface to the interior along the copper tube wall thickness at a controllable rate, forming a shallow hydrogen distribution state with uniform surface concentration and gentle gradient changes. This pre-permeation layer can provide a stable initial concentration field and diffusion starting point for the deep diffusion of hydrogen atoms in the subsequent high-temperature heating stage, avoiding problems such as sudden and violent diffusion of hydrogen atoms at high temperatures, resulting in abrupt changes in grain boundary stress, excessive local hydrogen enrichment, disordered bubble nucleation, and large dispersion of defect size distribution. Its function is that 350℃ is a mild permeation temperature range for hydrogen atoms in copper alloys, which can achieve effective solid solution of hydrogen without triggering hydrogen-induced defect nucleation and growth. This is achieved through "mild pre-permeation followed by high-temperature deep induction". The two-stage hydrogen introduction mechanism enables the uniform penetration of hydrogen atoms along the thickness of the tube wall and the enrichment of ordered grain boundaries, completely solving the technical problems of uneven hydrogen penetration, unstable grain boundary bubble formation, and large detection and judgment deviation caused by direct high temperature heating.

[0047] Traditional methods involve rapidly heating to high temperatures, causing hydrogen atoms to diffuse violently and instantly under intense thermal activation. This can lead to excessive hydrogen accumulation on the surface of the tube wall and at local grain boundaries, resulting in excessive local hydrogen embrittlement, abnormal defect growth, stress concentration cracking, and extremely uneven hydrogen distribution along the wall thickness. This causes significant differences in defect characteristics between samples from different locations and batches, ultimately leading to large fluctuations in test results, high judgment bias, and unreproducible data.

[0048] By adding a 350℃ pre-stabilization step, hydrogen atoms first complete shallow and uniform pre-permeation at a gentle rate, establishing a continuous and gradual hydrogen concentration field and a stable diffusion starting point, thus preventing sudden uncontrolled hydrogen diffusion at high temperatures. During subsequent heating and holding processes, hydrogen atoms migrate uniformly, synchronously, and controllably towards the internal grain boundaries along the wall thickness direction, eliminating local supersaturation and stress abrupt changes. This ensures that the degree of hydrogen-induced defect formation is consistent, the distribution is uniform, and the characteristics are stable throughout the entire pipe and cross-section. Simultaneously, it effectively suppresses permeation anomalies caused by oxide film interference and atmospheric fluctuations.

[0049] (5) Directional hydrogen embrittlement induction: After the hydrogen permeation prestabilization treatment is completed, the tubular sintering furnace is uniformly heated from 350℃ to 850℃ at a constant heating rate of 15℃ / min, and radially uniformly held at 850℃ for 30min. During this high temperature stage, hydrogen atoms diffuse from the shallow pre-permeation layer of the tube wall to the inner depth under the thermal activation effect, selectively segregating in the region with higher energy of the copper alloy grain boundary, reducing the grain boundary binding energy and promoting the nucleation, growth and expansion of hydrogen-induced bubbles at the grain boundary, ultimately achieving directional, uniform and repeatable induction of hydrogen embrittlement defects, providing a stable and clear defect structure for subsequent metallographic characterization.

[0050] The radial uniform heat preservation described in step (5) specifically adopts a three-stage precise heat control mode: the first stage is to keep the temperature at 850℃ for 15 minutes to complete the deep penetration of hydrogen atoms and the stable nucleation of grain boundary bubbles; the second stage is to precisely and slightly raise the furnace temperature to 852℃ and keep it for 10 minutes, using the slight temperature rise to increase the driving force of hydrogen atom diffusion, promote hydrogen to further agglomerate towards the grain boundary, and promote the stable growth of bubbles and the initial formation of grain boundary separation; the third stage is to precisely lower the furnace temperature back to 850℃ and keep it for 5 minutes, so that the morphology, size and distribution of defects tend to be in a thermodynamically stable state, and avoid abnormal growth, merging or annihilation of defects caused by drastic temperature fluctuations; this three-stage temperature control system can promote the stable nucleation, controllable growth and uniform distribution of hydrogen-induced grain boundary defects, significantly improve the characterization clarity and observation identification of defect structures, and make hydrogen embrittlement characteristics easier to accurately determine.

[0051] (6) Atmosphere safety shutdown: After the high temperature holding stage is over, immediately close the nitrogen-hydrogen mixture inlet valve to quickly and completely cut off the hydrogen source, so as to avoid the continuous hydrogen supply at high temperature causing the sample to become too embrittled, the defects to grow abnormally, or the degree of hydrogen embrittlement to exceed the evaluation range; keep the quartz tube flange sealed, so that the sample can be naturally cooled to below 200°C in a hydrogen-free, sealed, and oxygen-free environment, and then slowly open the furnace body to take out the sample, so as to prevent the high temperature sample from being directly exposed to the air and causing severe oxidation and ablation, while avoiding the sample from thermal stress cracking due to excessive cooling, and protecting the hydrogen-induced defect structure formed at high temperature from being destroyed.

[0052] (7) In-situ shaping of grain boundary defects: The specific implementation method is as follows: the tubular sample cooled to below 200°C in the furnace is quickly transferred to a rapid cooling chamber protected by high-purity nitrogen within 10s. Forced rapid cooling shaping is carried out in a closed environment that is completely isolated from air, oxidation, hydrogen emission, and external interference. The defects such as hydrogen-induced bubbles, grain boundary separation, and microcracks that are actually formed at high temperature are instantly "frozen" and preserved in situ. From the physical mechanism, the phenomena such as internal hydrogen desorption, bubble merging and shrinkage, bubble annihilation, grain boundary recovery, and defect morphology distortion that occur during the slow cooling process of hydrogen-induced bubbles are suppressed. This ensures that the observed defect structure is completely consistent with the real state under high temperature hydrogen-containing conditions.

[0053] The in-situ shaping of grain boundary defects in step (7) specifically includes placing the sample in a continuously flowing high-purity nitrogen atmosphere (purity ≥99.999%), and using a forced air cooling + high thermal conductivity graphite base coupling rapid cooling method to accurately achieve ≥30℃ / min. The high cooling rate rapidly reduces the sample temperature from 200°C to room temperature (below 25°C) in a very short time. Its core function is that the stability of hydrogen-induced bubbles is highly temperature-dependent. At high temperatures, the hydrogen partial pressure inside the bubbles is high and the morphology is stable. Slow cooling at low temperatures causes hydrogen atoms to diffuse out from the grain boundaries, and the pressure inside the bubbles decreases, leading to collapse, merging, or disappearance. This invention "locks" hydrogen atoms at grain boundaries, phase boundaries, and defects in place through an ultra-high cooling rate, so that the hydrogen-induced bubbles, grain boundary separation, micropores, and other features formed at high temperatures completely maintain their original morphology, size, quantity, and distribution, without annihilation, merging, deformation, disappearance, or tissue restoration. This step fundamentally solves the technical pain points of hydrogen-induced defect distortion, morphological changes, and deviations from the true value in judgment results caused by traditional natural cooling processes, and achieves true restoration, objective characterization, and accurate evaluation of the high-temperature hydrogen embrittlement characteristics of tubular copper alloys.

[0054] (8) Targeted sample preparation for grain boundary defects: The tubular sample with in-situ grain boundary defects is cut into a standard annular cross-section with a thickness of 2mm to 3mm in the radial vertical direction using a low-speed precision cutting machine. The cutting process is free from thermal damage and mechanical stress. The cross-section sample is then cold-mounted and cured. The mounting material is a low-stress epoxy resin system to avoid stress and deformation caused by hot mounting. After mounting, the sample is prepared by a four-stage sample preparation process of coarse grinding, fine grinding, mechanical polishing, and chemical polishing to achieve the ideal state of mirror smoothness, no scratches, no deformation layer, and no stress layer on the annular cross-section. Then, a special pre-set grain boundary etchant is used to perform precise etching of the polished cross-section in sections at timed intervals to selectively highlight the hydrogen-induced defect structure at the grain boundary, while keeping the matrix grain structure from being over-etched.

[0055] The pre-prepared grain boundary etchant mentioned in step (8) is specifically prepared by phosphoric acid, anhydrous ethanol, and deionized water in a volume ratio of 2:3:5. The etchant is prepared and used immediately and kept at a constant temperature to avoid the volatilization of components and uneven concentration affecting the consistency of corrosion. The corrosion process is strictly controlled in a constant temperature environment of 22±2℃ and the corrosion time is precisely set to 45±5s. This can achieve high selectivity, high contrast, and high clarity corrosion of copper alloy grain boundaries, clearly highlighting the defect characteristics such as hydrogen-induced bubbles, micropores, and grain boundary separation at the grain boundaries, while not damaging the matrix grains or producing over-corrosion pits, ensuring the accuracy and authenticity of defect observation.

[0056] The partitioned timed corrosion described in step (8) further includes dividing the annular cross section into four quadrants with equal area and clear boundaries at four directions: 0°, 90°, 180°, and 270°. Each quadrant is isolated by a mask to implement independent corrosion time control and independent corrosion degree regulation, effectively overcoming the problem of over-corrosion at the edges and insufficient corrosion at the center caused by the edge effect of the annular cross section. A non-corrosion isolation zone with a width of 0.2 mm is set between adjacent quadrants to prevent the corrosion liquid from penetrating and spreading laterally along the grain boundaries, avoiding cross-interference and structural distortion, and ensuring that the grain boundary defects are displayed uniformly, clearly, observably, and quantifiable within the 360° range of the entire cross section.

[0057] (9) Full-area judgment observation: After the annular cross-section sample that has been corroded is cleaned and dried with anhydrous ethanol, it is placed on the stage of a fully automatic metallographic microscope and continuously scanned along the annular cross-section of the tubular sample with no dead angles. The focus is on identifying, counting and recording the number, size, distribution state of hydrogen-induced bubbles at the grain boundaries, as well as the grain boundary separation length and morphology and other typical hydrogen embrittlement characteristics. The number of grain boundary bubbles and the grain boundary separation length are used as the core quantitative judgment basis for hydrogen embrittlement sensitivity, so as to achieve an objective, accurate, standardized and repeatable evaluation of the hydrogen embrittlement sensitivity of tubular copper alloys.

[0058] The full-area judgment observation described in step (9) also includes using a fixed magnification of 200 times for unified standard observation, continuously scanning and acquiring full-section metallographic images with a precision step distance of 0.2 mm, and automatically generating a complete annular cross-section full-area high-definition map through dedicated image stitching software to achieve defect-free, blind-angle, and full-coverage capture; the quantitative judgment standard is: within a 360° range along the cross-section, if ≥3 independent hydrogen-induced bubbles appear on any continuous 1 mm length grain boundary, or if the total length of grain boundary separation is ≥0.5 mm, the tubular copper alloy material is judged to have hydrogen embrittlement sensitivity; this judgment method is intuitive and clear, quantitatively controllable, and standardized, which can effectively avoid subjective errors of manual observation and provide high-precision and high-reliability data support for material quality evaluation, process optimization, and engineering applications.

[0059] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys, characterized in that, Includes the following steps: (1) Sample positioning: Take a tubular copper alloy sample with a length of 40 mm, fix it in the graphite frame positioning groove with the axis perpendicular to the airflow direction, put it into the quartz tube of the tubular sintering furnace and seal the flange. (2) Multi-stage deoxygenation pretreatment: First, purge with high-purity nitrogen, then evacuate to an absolute pressure ≤2Pa, and maintain pressure to check for leaks; (3) Precise gas scrubbing in a weak hydrogen atmosphere: A nitrogen-hydrogen mixture with a volume fraction of 10% is introduced and scrubbed at a constant flow rate until the oxygen content in the furnace is below 10 ppm. (4) Hydrogen permeation pre-stabilization treatment: Before heating, the furnace temperature is raised to 350℃ and kept for 10 minutes to allow hydrogen atoms to form a uniform pre-permeation layer in the shallow layer of the tube wall; (5) Directional hydrogen embrittlement: The temperature is increased to 850℃ at 15℃ / min and held radially uniformly for 30min to allow hydrogen atoms to penetrate deeply along the wall thickness direction and accumulate at the grain boundaries; (6) Atmosphere safety shutdown: shut off the nitrogen-hydrogen mixture, seal and allow to cool naturally to below 200°C before removing the sample; (7) In-situ shaping of grain boundary defects: The sample is rapidly cooled to room temperature under inert gas protection to suppress the merging or disappearance of hydrogen-induced bubbles during the cooling stage; (8) Targeted sample preparation for grain boundary defects: After cutting an annular section, embedding, grinding and polishing, the sample is etched in sections at time using a preset grain boundary etchant; (9) Full-area judgment observation: Observe the full area along the annular section in 360° under a metallographic microscope, and use the number of grain boundary bubbles and the grain boundary separation length as the basis for judging hydrogen embrittlement sensitivity.

2. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The graphite frame positioning groove in step (1) specifically includes a three-point elastic support mechanism evenly arranged along the circumference. The support mechanism forms a uniform air gap of 0.5 mm between the outer wall of the tubular sample and the positioning groove, which is used to ensure uniform airflow and eliminate local overheating and temperature field distortion of the sample.

3. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The multi-stage deoxygenation pretreatment in step (2) specifically includes two complete cycles of alternating high-purity nitrogen purging and vacuum extraction, and micro-heating desorption during the vacuum stage, so that the residual oxygen and adsorbed water vapor in the furnace are reduced to below the experimental interference threshold.

4. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The precise gas washing in the weak hydrogen atmosphere mentioned in step (3) also includes real-time online monitoring of oxygen content and hydrogen concentration in the furnace during the gas washing process. Only when the oxygen content is stably below 10 ppm and the hydrogen concentration fluctuation is less than ±0.2% and maintained for more than 1 minute can the subsequent heating step be carried out.

5. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The hydrogen permeation prestabilization treatment in step (4) specifically includes maintaining a weak hydrogen atmosphere in the 350℃ heat preservation stage, so that hydrogen atoms form a uniform gradient shallow permeation distribution in the copper tube wall thickness direction, providing a stable initial state for subsequent high-temperature hydrogen embrittlement.

6. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The radial uniform heat preservation in step (5) specifically adopts a three-stage heat control mode: first, heat preservation at 850℃ for 15 minutes, then slightly increase to 852℃ for 10 minutes, and finally drop back to 850℃ for 5 minutes, so as to promote the stable nucleation and controllable growth of hydrogen-induced grain boundary defects and improve the clarity of characterization.

7. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The in-situ shaping of grain boundary defects in step (7) specifically includes placing the sample in a high-purity nitrogen atmosphere and rapidly cooling it at a rate of ≥30℃ / min, so that hydrogen-induced bubbles and microcracks at the grain boundaries remain in a high-temperature generation state without annihilation, merging, or morphological changes.

8. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The pre-set grain boundary etchant mentioned in step (8) is specifically prepared by phosphoric acid, anhydrous ethanol and deionized water in a volume ratio of 2:3:

5. The corrosion temperature is controlled at 22±2℃ and the corrosion time is precisely 45±5s, so as to achieve selective highlighting of grain boundary defects without damaging the matrix structure.

9. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The partitioned timed corrosion described in step (8) further includes dividing the annular cross section into four quadrants at 0°, 90°, 180°, and 270°. Corrosion parameters are controlled independently in each quadrant, and a 0.2 mm non-corrosion isolation zone is set between adjacent areas to avoid over-corrosion at the edges, which could lead to tissue distortion.

10. The method for detecting hydrogen embrittlement sensitivity based on the characteristics of grain boundary bubbles in tubular copper alloys according to claim 1, characterized in that, The full-domain determination observation in step (9) specifically includes using a fixed magnification of 200x, a step distance of 0.2mm for line-by-line scanning imaging and automatic stitching of the full-domain spectrum; when ≥3 hydrogen-induced bubbles or a grain boundary separation length ≥0.5mm appear at any continuous 1mm grain boundary within the 360° range of the cross section, the sample is determined to have hydrogen embrittlement sensitivity.

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