Observation method for water jet stripping treatment of ultra-high molecular weight polyethylene wear surface plastic deformation layer

Abstract

The invention relates to an observation method for stripping a plastic deformation layer on an ultra-high molecular weight polyethylene worn surface by water jet, which comprises the following steps of: on a friction testing machine, taking a GCr15 steel pin as the sample, carrying out a friction experiment on the UHMWPE sample through a rotating module to form a worn surface, fixing the UHMWPE sample with the worn surface at the bottom of a water tank through a clamp, and placing the water tank at the bottom of the water tank; adjusting the height from the spray head to the sample, filling water to completely immerse the test piece and the spray head, adjusting the pressure of a water jet outlet of the spray head to carry out water jet treatment on the surface of the sample, taking out and air-drying after water jet treatment, and then carrying out metal spraying treatment and observation to obtain the morphology of the ultra-high molecular weight polyethylene worn surface plastic deformation layer. According to the method, complex procedures of a traditional method are avoided, thermal damage caused by mechanical polishing is avoided, the internal structure of the plastic deformation layer is directly exposed through the peeled peeling interface after peeling, and subsurface microcosmic evidence is provided for studying a friction failure mechanism.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polymer material characterization, and particularly relates to a method for observing plastic deformation layer of wear surface of ultra-high molecular weight polyethylene treated by water jet peeling. BACKGROUND

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is widely used in key friction components such as ship tail shaft bushings and artificial joints due to its excellent wear resistance and impact resistance. The plastic deformation layer formed on the surface of UHMWPE during friction service directly affects the wear life and failure mechanism of the material. However, the current characterization technology for the deformation layer has significant limitations.

[0003] Currently, the industry relies heavily on destructive section analysis techniques to evaluate the plastic deformation layer on the surface of UHMWPE. This method requires cutting the sample along a specific section, and after complex sample preparation processes such as embedding, grinding, and polishing, the local cross-sectional structure is observed by electron microscope or optical instrument. This process not only completely destroys the structural integrity of the sample, making it impossible to use for subsequent tribological performance review or long-term service behavior research, but also significantly distorts the true topographic features of the plastic deformation layer due to stress concentration during mechanical cutting and heat production effects during polishing.

[0004] More fundamentally, the untreated UHMWPE friction surface has an observation blind area: the plastic deformation layer and the substrate are highly consistent in chemical composition and crystal structure, and are transparent and tightly bonded to the ground, making it difficult for conventional surface analysis methods (such as white light interferometer, low-power optical electron microscope) to directly observe the geometric shape and distribution state of the plastic deformation layer. Even if a high-resolution microscope is used to directly observe the original surface, the plastic deformation layer is hidden in the subsurface area and cannot be directly identified by conventional topographic features (such as scratches, wear marks) to determine its boundary, thickness, and distribution state, resulting in a lack of key microscopic evidence for analyzing the material wear mechanism. After water jet treatment, the plastic deformation layer on the surface of UHMWPE is peeled off from the substrate, forming micron-scale peeling layers, warping or curling features, which can be directly observed, and the internal structure of the deformation layer is exposed, providing a non-destructive observation window for studying the subsurface features such as crystal defects and micro-cracks in the deformation layer. SUMMARY

[0005] Since the plastic deformation layer in the metamorphic layer of the worn surface is thin and transparent, and is tightly bonded with the base material, when the worn surface is observed, the sample needs to be cut and observed after polishing, which completely destroys the sample and cannot be reused, and only partial cross-sectional information can be obtained, and the global range of the plastic deformation layer cannot be evaluated. After the water jet stripping treatment of the application, the plastic deformation layer is directly exposed through the surface stripping phenomenon, and the sample does not need to be completely destroyed to be observed; and by quantifying the area of the stripping region, the range of the surface plastic deformation layer can be objectively evaluated. At the same time, the interface between the plastic deformation layer and the substrate is directly exposed after the water jet stripping, and the microstructure characteristics (such as grain deformation, micro-pore distribution, crack propagation path, etc.) inside the deformation layer can be further observed by scanning electron microscopy or atomic force microscopy, which provides more comprehensive data support for studying the material failure mechanism in the friction process. The method uses the water jet to impact the surface of the UHMWPE treated by friction, and uses the instantaneous shock wave generated when the cavitation bubbles formed by the water jet collapse to selectively excite the plastic deformation layer to warp and directly expose its distribution pattern. The morphology and distribution range of the warped plastic deformation layer are observed, and the morphology, structure and spatial stacking state of the plastic deformation layer are evaluated. The basic morphology and distribution state of the plastic deformation layer of the UHMWPE worn surface are observed by using the water jet treatment, To solve the above technical problems, the application adopts the following technical solutions: (1) A wear test is performed on the smooth surface of the UHMWPE sample, and during the friction process, the UHMWPE surface material flows plastically and forms a plastic deformation layer which is tightly stacked along the friction direction and tightly adheres to the base material, thereby obtaining the worn UHMWPE sample.

[0006] (2) The worn UHMWPE sample obtained in step (1) is fixed on a water jet platform, the height of the nozzle from the surface of the sample is adjusted to 30 mm, and the outlet pressure of the water jet is 20 MPa. When the high-pressure water flow impacts the surface, cavitation bubbles will be generated on the surface of the UHMWPE sample, and the bubbles will instantaneously collapse at the interface between the plastic deformation layer and the substrate, causing a local micro-explosion shock wave. The energy generated by the shock wave acts on the weakly bonded plastic deformation layer, causing it to separate from the substrate and form micron-scale peeling, warping or curling features, thereby obtaining the water jet stripped UHMWPE sample.

[0007] (3) The water jet stripped UHMWPE sample obtained in step (2) is taken out, dried and then subjected to gold spraying treatment to obtain a gold-plated sample, and the SEM morphology of the plastic deformation layer is observed by using a scanning electron microscope.

[0008] According to an aspect of the present application, there is provided a method for observing plastic deformation layer of an abrasion surface of ultra-high molecular weight polyethylene (UHMWPE) treated by water jet, the method comprising the following steps: Step 1, sample pretreatment: on a friction testing machine, using the sample GCr15 steel pin, the UHMWPE sample is subjected to friction experiment by a rotating module to form an abrasion surface, and a pretreated UHMWPE sample is obtained; Step 2, water jet treatment: the pretreated UHMWPE sample obtained in step 1 is fixed on the bottom of a water tank by a clamp, the height of the nozzle from the pretreated UHMWPE sample is adjusted, the water tank is filled with water and the sample and the nozzle are completely immersed, the water jet outlet pressure of the nozzle is adjusted to treat the surface of the pretreated UHMWPE sample by water jet, and a water jet treated UHMWPE sample is obtained; Step 3, gold plating treatment: the water jet treated UHMWPE sample obtained in step 2 is taken out and air dried, and the air dried UHMWPE sample is subjected to gold plating treatment by using a SC7620 magnetron sputtering coating instrument, and a gold plated UHMWPE sample is obtained; Step 4, observation: the gold plated UHMWPE sample obtained in step 3 is installed on a scanning electron microscope sample stage for observation, and the morphology of the plastic deformation layer of the abrasion surface of the UHMWPE is obtained.

[0009] Further, the diameter of the GCr15 steel pin in step 1 is 3 mm, and the surface hardness is HRC63±3; The conditions of the friction experiment in step 1 are as follows: The rotation speed of the friction experiment is 100-400 r / min, preferably 400 r / min; The normal pressure of the friction experiment is 10-40 N, preferably 20 N; The time of the friction experiment is 50-80 min, preferably 60 min.

[0010] Further, the height of the nozzle from the pretreated UHMWPE sample in step 2 is 30 mm.

[0011] Further, the conditions of the water jet treatment in step 2 are as follows: The water jet outlet pressure of the nozzle is 20-50 Mpa, preferably 20 Mpa; The time of the water jet treatment is 10-30 min, preferably 30 min.

[0012] Further, the water jet treated UHMWPE sample in step 2 has a characteristic sheet-like warping or curling structure.

[0013] Further, the conditions of the air drying in step 3 are as follows: The temperature of the air drying is 30-60℃, preferably 40℃; The time of the air drying is 4-8h, preferably 6h.

[0014] Further, the observation in step 4 is specifically: the gold-plated UHMWPE sample obtained in step 3 is installed on a scanning electron microscope sample stage, the position of the gold-plated UHMWPE sample is adjusted so that the buckling area is in the observation center, the full surface is scanned in a low magnification mode, the plastic deformation layer buckling distribution area is located, a typical curling / buckling area is selected, and the high magnification mode is switched to for observation, and the morphology of the plastic deformation layer of the ultra-high molecular weight polyethylene wear surface is observed.

[0015] Further, the magnification of the low magnification mode in step 4 is 100-500 times.

[0016] Further, the magnification of the high magnification mode in step 4 is 1000-2000 times.

[0017] Compared with the prior art, the beneficial effects of the present application are: (1) The traditional method needs to destroy the structural integrity by cutting the sample to obtain the cross-sectional information, while the technical scheme disclosed by the present application uses high-pressure water jet to precisely impact the UHMWPE surface treated by friction, uses the micro-explosion force generated by the collapse of cavitation bubbles away from the surface to selectively excite the peeling of the plastic deformation layer and the substrate, and only the micron-level deformation area of the surface layer is peeled off, and the main body structure of the sample is kept intact (as shown in Figure 3 ), completely avoiding destructive operations such as cutting, inlaying, and polishing, and directly exposing the three-dimensional morphology and spatial distribution characteristics of the plastic deformation layer on the original surface.

[0018] (2) The peeling phenomenon induced by the cavitation effect of the water jet generated by the technical scheme disclosed by the present application converts the transparent and tightly stacked plastic deformation state into a buckled single-layer structure, so that the three-dimensional morphology, bonding parameters, and stacking state of the buckled plastic deformation layer can be directly observed.

[0019] (3) Compared with the traditional detection method which can only observe the cross section, the technical scheme disclosed by the present application can detect the plastic deformation layer on the whole surface of the sample, overcoming the shortcomings of the traditional cross-section observation method that needs to destroy the sample and the lack of observable points.

[0020] (4) The technical scheme disclosed by the present application is simple to operate, only needs to fix the sample and use water jet treatment, avoids the complex procedures of traditional methods, and avoids the thermal damage introduced by mechanical polishing, and can directly expose the internal structure (such as lattice distortion and micro-crack network) of the plastic deformation layer through the peeling interface, providing sub-surface micro-evidence for the study of the friction failure mechanism. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The schematic diagram of the wear test process described in the embodiment of the present application (wherein 1 is a friction pin, and 2 is a UHMWPE sample); Figure 2 The water jet stripping treatment device diagram described in the embodiment of the present application (wherein 1 is a water jet nozzle, 2 is a clamp, 3 is a pretreated UHMWPE sample, 4 is a PVC pipe, 5 is a high-pressure pump, and 6 is distilled water); Figure 3 The SEM morphology of the plastic deformation layer of the UHMWPE wear sample surface after water jet stripping treatment described in the embodiment 1 of the present application (the magnification is 500 times); Figure 4 The SEM morphology of the plastic deformation layer of the UHMWPE wear sample surface after water jet stripping treatment described in the embodiment 1 of the present application (the magnification is 2000 times); Figure 5 The SEM morphology of the UHMWPE wear sample surface without water jet treatment described in the comparative example 1 of the present application. DETAILED DESCRIPTION

[0022] The present application will be further described in conjunction with specific embodiments, but in no way limits the present application.

[0023] The UHMWPE sample used in the embodiment and the comparative example of the present application is purchased from Beijing Tongyitai Technology Co., Ltd.

[0024] According to the present application, a method for observing the plastic deformation layer of the wear surface of the ultra-high molecular weight polyethylene treated by water jet stripping is provided in the specific embodiment part, and the specific steps are as follows: Step 1, install the UHMWPE sample on the rotating workbench of the Rtec MFT-5000 type friction and wear tester, and the upper sample of the friction pair with the UHMWPE sample is a GCr15 steel pin (diameter of 3 mm, surface hardness of HRC63±3), set the constant rotating speed to 400 r / min, apply a normal pressure of 20 N through a hydraulic servo system, and continuously run for 60 minutes under dry friction conditions. During the friction process, the UHMWPE surface first forms a wear surface, then forms a wear metamorphic layer, and then forms a stable plastic deformation layer, to obtain a pretreated UHMWPE sample, and the friction coefficient of the plastic deformation layer is 0.154 (the friction coefficient is stable).

[0025] Step 2, the pretreated UHMWPE sample obtained in step (1) is transferred to a 304 stainless steel water tank (volume 50 L) of a high-pressure water jet platform, the sample is fixed by clamp 2 (four-jaw hydraulic clamp) to ensure that the wear surface of the sample faces upward. The nozzle position is adjusted by a three-degree-of-freedom moving stage, and the jet axis is strictly locked to coincide with the central axis of the sample, with a vertical distance control of 30 mm. This positioning accuracy ensures that the cavitation bubble collapse energy is focused on the surface of the wear area of the sample, avoiding the overflow of the jet core area to cause unintended damage to the substrate. Distilled water 6 is filled in the water tank, and the pretreated UHMWPE sample 3 and the water jet nozzle 1 are fully immersed. The high-pressure pump 5 is started, and the high-pressure water flow is transmitted to the water jet nozzle 1 through the PVC pipe 4. The water jet pressure is controlled at 20 MPa, which impacts the surface of the pretreated UHMWPE sample 3 to form a turbulent state jet impact surface, and the treatment is continued for 10-30 min. Cavitation nuclei are induced in the near-wall low-pressure area, and the bubbles are driven by pressure to migrate and accumulate to the plastic deformation layer-substrate interface. Bubble collapse occurs at the interface, producing local high pressure, causing the plastic deformation layer and the substrate to interface delaminate, forming a characteristic sheet warping or curling structure. The transient pressure generated by cavitation causes the plastic deformation layer to be excited to the skin, and the water jet treated UHMWPE sample is obtained.

[0026] Step 3, the water jet treated UHMWPE sample obtained in step 2 is taken out and thoroughly air dried. Gold spraying treatment is performed using a Quorum SC7620 magnetron sputter coater. The gold-plated sample is installed on the scanning electron microscope sample stage, and the edges of the sample are fixed using conductive glue. The sample stage is adjusted so that the warped area of the gold-plated sample is in the center of observation. First, the entire surface is scanned in low magnification mode (500x) to locate the plastic deformation layer warping distribution area, and then the typical curling / warping area is selected for observation in high magnification mode (2000x).

[0027] Example 1 Step 1, sample pretreatment: on a friction tester, the upper test piece of the friction pair consisting of the UHMWPE sample is a GCr15 steel pin (diameter 3 mm, surface hardness HRC63±3), and the friction experiment is performed on the UHMWPE sample under the friction conditions of a rotating module at a speed of 400 r / min and a normal pressure of 20 N for 1 h to form a wear surface. At this time, the closely attached plastic deformation layer in the wear metamorphic layer of the wear surface is the evaluation object, and the pretreated UHMWPE sample 3 is obtained, with a friction coefficient of 0.154; Step 2, water jet treatment: the pretreated UHMWPE sample 3 obtained in step 1 was fixed on the bottom of a stainless steel water tank (volume 50 L) by a clamp 2, the height of the water jet nozzle 1 from the friction surface of the pretreated UHMWPE sample 3 was adjusted to 30 mm, the water tank was filled with water and the pretreated UHMWPE sample 3 and the water jet nozzle 1 were completely immersed (50 L of the volume of the water tank), the outlet pressure Fn of the water jet nozzle 1 was adjusted to 20 MPa (fluctuation <±0.5 MPa) to treat the surface of the pretreated UHMWPE sample 3 with water jet for 30 min, and the water jet treated UHMWPE sample was obtained.

[0028] Step 3, gold plating treatment and observation: the water jet treated UHMWPE sample obtained in step 2 was taken out and air-dried at 40℃ for 6 h, and then gold plating treatment was performed by using an SC7620 magnetron sputtering film coater, and the gold plated UHMWPE sample was obtained. The gold plated UHMWPE sample was installed on a scanning electron microscope sample stage, and the edges of the sample were fixed by using conductive glue; the sample stage was adjusted so that the buckling area was in the center of observation, the whole surface was scanned in a low magnification mode (100-500 times) to locate the buckling distribution area of the plastic deformation layer, and a typical curling / buckling area was selected, and the surface of the gold plated UHMWPE sample was observed in a high magnification mode (1000-2000 times), and the specific observation results are shown in Figure 3 、 4 It can be observed that the buckling structure of the plastic deformation layer is obvious.

[0029] Comparative Example 1 The difference from Example 1 is that the water jet treatment in step 2 is not performed, and the gold plating treatment is directly performed, and the other steps remain the same as those in Example 1, and the surface of the gold plated UHMWPE sample was observed, and the specific observation results are shown in Figure 5 It is shown that the surface morphology of the UHMWPE wear sample without water jet treatment cannot be directly observed.

[0030] The above is only a few embodiments of the present application, and does not limit the present application in any form, although the present application is disclosed as above with preferred embodiments, however, it is not intended to limit the present application, any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications by using the above disclosed technical content, which is equivalent to the equivalent embodiment, and belongs to the scope of the technical solution.

Claims

1. A method for observing the plastic deformation layer on the worn surface of ultra-high molecular weight polyethylene treated by water jet stripping, characterized in that: The observation method comprises the following steps: Step 1, sample pretreatment: On a friction tester, the above sample is a GCr15 steel pin, and a friction test is performed on the UHMWPE sample through a rotating module to form a wear surface, thereby obtaining a pretreated UHMWPE sample; Step 2, water jet treatment: The pretreated UHMWPE sample obtained in step 1 is fixed to the bottom of a water tank by a clamp, the height of the nozzle from the pretreated UHMWPE sample is adjusted, the water tank is filled with water and the sample and the nozzle are completely immersed, and the water jet outlet pressure of the nozzle is adjusted to perform water jet treatment on the surface of the pretreated UHMWPE sample to obtain a water-jet-treated UHMWPE sample; Step 3, gold plating: The UHMWPE sample after the water spray treatment obtained in step 2 is taken out and air-dried, and the air-dried UHMWPE sample is subjected to gold spraying treatment using an SC7620 magnetron sputtering coater to obtain a gold-plated UHMWPE sample; Step 4, observation: The gold-plated UHMWPE sample obtained in step 3 is mounted on a scanning electron microscope sample stage for observation to obtain the morphology of the plastic deformation layer on the worn surface of the ultra-high molecular weight polyethylene.

2. The observation method according to claim 1, characterized in that The diameter of the GCr15 steel pin in step 1 is 3 mm and the surface hardness is HRC63±3; The conditions for the friction test described in step 1 are as follows: The rotation speed of the friction test is 100-400 r / min, preferably 400 r / min; The normal pressure of the friction test is 10-40N, preferably 20N; The friction test time is 50 to 80 minutes, preferably 60 minutes.

3. The observation method according to claim 1, wherein: The height between the nozzle and the pretreated UHMWPE sample in step 2 is 30 mm.

4. The observation method according to claim 1, wherein: The conditions for the water jet treatment in step 2 are as follows: The water jet outlet pressure of the nozzle is 20-50 MPa, preferably 20 MPa; The water jet treatment time is 15 to 30 minutes.

5. The observation method according to claim 1, characterized in that: The UHMWPE sample after the water jet treatment in step 2 exhibits a characteristic sheet-like warping or curling structure.

6. The observation method according to claim 1, characterized in that: The air-drying conditions in step 3 are as follows: The air-drying temperature is 30-60°C, preferably 40°C; The air-drying time is 4 to 8 hours, preferably 6 hours.

7. The observation method according to claim 1, characterized in that: The observation described in step 4 is specifically as follows: the gold-plated UHMWPE sample obtained in step 3 is mounted on the scanning electron microscope sample stage, the position of the gold-plated UHMWPE sample is adjusted so that the warping area is at the observation center, the entire surface is scanned in low-magnification mode, the warping distribution area of ​​the plastic deformation layer is located, a typical curling / warping area is selected, and the high-magnification mode is switched to observe to observe the morphology of the plastic deformation layer on the worn surface of the ultra-high molecular weight polyethylene.

8. The observation method according to claim 7, characterized in that: The low magnification mode in step 4 uses a magnification of 100 to 500 times.

9. The observation method according to claim 7, characterized in that: The high magnification mode in step 4 uses a magnification of 1000 to 2000 times.

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