Preparation method of high-density low-pore zirconia precision water jet plunger

Abstract

The application discloses a preparation method of a high-density low-pore zirconia precision water jet plunger, and belongs to the technical field of precision structure ceramics and high-pressure fluid machinery accessory preparation. In view of the technical pain points that micro-pores, closed pores and loose structures exist in the existing zirconia water jet plunger, water seepage, washing and peeling, fatigue cracking and short service life occur under super-high pressure working conditions, fine-grained 3Y-TZP nano powder is used as a matrix, an alumina grain refining system and a trace amount of a composite sintering additive are used, slurry vacuum negative pressure degassing, super-high cold isostatic compaction densification forming, segmented slow degreasing gradient sintering, high-temperature argon gas thermal isostatic pressure micro-pore filling, multi-stage ultra-precision mirror polishing and full-dimension nondestructive testing are carried out, and finally, the low-pore high-density zirconia plunger is obtained. The plunger prepared by the application can stably resist 300-600MPA super-high pressure reciprocating impact and abrasive water flow washing for a long time, and can be widely applied to the fields of super-high pressure water jet high-pressure pumps, high-pressure reciprocating fluid pumps and other precision high-pressure equipment.

Description

Technical Field

[0001] This invention belongs to the field of precision structural ceramics and high-pressure fluid machinery component preparation technology, specifically relating to a method for preparing a high-density, low-porosity zirconia precision waterjet plunger. Background Technology

[0002] Ultra-high pressure waterjet cutting equipment relies on ultra-high water pressure to achieve precision cold cutting, and is widely used in the processing of metals, stone, composite materials, and aerospace special materials. The plunger, as the core reciprocating component of the waterjet high-pressure pump, withstands long-term ultra-high pressure water of 300–600 MPa, high-frequency reciprocating impact, continuous scouring of water containing trace abrasives, and frequent alternating hot and cold loads. This places extremely high demands on the material's density, toughness, surface integrity, impermeability, and erosion resistance.

[0003] Currently, commercially available zirconia waterjet plungers generally suffer from fatal flaws: traditional manufacturing processes rely solely on conventional ball milling, ordinary pressure forming, and conventional isothermal sintering. This results in the incomplete removal of air bubbles trapped within the powder slurry, and the presence of intergranular pores and lamination pores in the green body. During sintering, the rapid volatilization of the binder easily creates interconnected pores and residual micropores, and the sintered green body generally contains nanoscale closed micropores. These microscopic porosity defects, under ultra-high pressure conditions, can lead to high-pressure water seepage, surface pitting, grain spalling, and rapid propagation of microcracks, ultimately causing plunger scoring, leakage, and fracture failure. This results in equipment pressure drop, high failure rates, and frequent replacements, severely restricting the continuous and stable operation capability of ultra-high pressure waterjet equipment.

[0004] Most existing technologies only optimize material hardness and conventional wear resistance, without systematically eliminating core defects such as micropores, closed pores, and intergranular porosity. This makes it impossible to achieve a truly high-density, low-porosity structure, which is insufficient to meet the long-term stable operation requirements of ultra-high pressure systems at 400 MPa. Therefore, developing a method for preparing zirconia precision plungers that achieves high density, low porosity, and is suitable for extreme high-pressure scouring conditions is a pressing technical challenge in this field. Summary of the Invention

[0005] Purpose of the invention

[0006] This invention aims to overcome the defects of existing zirconia waterjet plungers, such as numerous primary air bubbles, forming pores, sintered micropores, and closed-cell residues, which lead to high-pressure leakage, erosion spalling, fatigue cracking, and short lifespan. It provides a method for preparing a high-density, low-porosity zirconia precision waterjet plunger, achieving a plunger with a highly dense, low-porosity, high-precision, and high-impact and erosion-resistant microstructure, suitable for long-term stable operation under extreme conditions of ultra-high-pressure waterjet systems.

[0007] Technical solution

[0008] To achieve the above objectives, the present invention provides a method for preparing a high-density, low-porosity zirconia precision waterjet plunger, comprising the following steps:

[0009] (1) Preparation of low-bubble, high-dispersion slurry: High-purity nano 3Y-TZP zirconia powder was used as the matrix, combined with alumina refiner and TiO2-MgO composite sintering aid. The powder was strictly screened to remove large particles and agglomerates. Deionized water was used as the medium and high-purity, low-viscosity dispersant was used for long-term wet ball milling. After ball milling, the slurry was degassed by constant temperature stirring under a vacuum negative pressure of -0.09MPa for 30-45 minutes to remove microbubbles wrapped in the slurry. Finally, low-speed uniform spray drying was used for granulation to obtain solid spherical dense powder with internal hollow and gas-like defects removed.

[0010] (2) Ultra-precision dense molding: The dense spherical powder is evenly layered and distributed. First, 20MPa bidirectional pre-pressing is used to eliminate loose accumulation gaps. Then, 300-320MPa ultra-high pressure cold isostatic pressing is used to hold the pressure for 10 minutes, forcing the powder particles to fit tightly and plastically together, eliminating the interlayer pores and particle gaps of the green blank, and obtaining a green blank with uniform density throughout the entire area.

[0011] (3) Segmented debinding gradient densification sintering: The slow segmented heating process is adopted. The temperature is raised to 500℃ at 2℃ / min and held for 2.5h to remove all additives and binders at low temperature and uniform speed to avoid rapid gas volatilization and pore formation. Then, the temperature is raised to 1100℃ at 4℃ / min to complete the crystal preheating and stabilization. The temperature is then raised to 1530~1550℃ at 3℃ / min and sintered at a constant temperature for 4h to achieve uniform grain growth and full grain boundary closure. Finally, the temperature is slowly reduced in a gradient for annealing to eliminate residual internal stress in sintering.

[0012] (4) Fully close micropores in hot isostatic pressing: The sintered green body is placed in a hot isostatic pressing equipment and kept at 1480℃ and 180MPa high-purity argon atmosphere for 2 hours. By utilizing the high temperature and high pressure coupling effect, the residual nanoscale closed micropores inside the green body are fully collapsed, healed and closed, so that the green body is free of open pores, closed pores and intercrystalline pores.

[0013] (5) Multi-stage ultra-precision mirror polishing: The surface loose layer is removed by coarse grinding, the dimensional accuracy and roundness are corrected by fine grinding and ultra-fine grinding, and finally the mirror polishing is performed by nano-silica polishing liquid to eliminate grinding micropores and surface micro defects, and obtain an ultra-dense smooth surface.

[0014] (6) Full-dimensional non-destructive testing and sorting: The finished products are subjected to ultrasonic internal flaw detection, metallographic cross-section micropore detection, and 350MPa high pressure holding leakage test to screen out qualified precision plunger finished products without visible or detectable pore defects.

[0015] Further, in step (1), the raw material powder is composed of the following by weight percentage: 90.3-91.5% nano-3Y-TZP zirconium oxide, 4.8-5.2% yttrium oxide, 3.0-4.0% ultrafine alumina, and 0.2-0.5% TiO2-MgO composite additive; the nano-3Y-TZP zirconium oxide powder has a D50 of 0.2-0.4 μm and a total mass fraction of ZrO2, HfO2, and Y2O3 ≥ 99.9%.

[0016] Furthermore, in step (1), the wet ball milling speed is 450-500 r / min, the ball milling time is 8-10 h, the ball milling medium is high-purity zirconia balls, and the vacuum degassing environment temperature is constant at 20-25℃.

[0017] Furthermore, in step (4), the argon purity is ≥99.99%, and the heating, pressurization, cooling and depressurization are all controlled at a uniform and slow speed to prevent parameter fluctuations from causing microscopic defects.

[0018] Furthermore, in step (5), the rough grinding single-sided allowance is 0.2 mm, the cylindricity of the finished plunger is ≤0.003 mm, and the surface roughness Ra is ≤0.02 μm.

[0019] Furthermore, the prepared zirconia plunger has a volumetric porosity ≤0.05%, an overall density ≥99.95%, a flexural strength ≥1300MPa, and a fracture toughness ≥7.0MPa·m. 1 / 2 It can withstand ultra-high pressure conditions of 300-600MPa for a long time.

[0020] Beneficial effects

[0021] Compared with the prior art, the present invention has the following outstanding innovations and beneficial effects:

[0022] 1. This invention systematically blocks the formation of pores from the source. It eliminates the original encapsulated air bubbles by vacuum negative pressure degassing of the slurry, completely eliminates the forming gap pores and lamination pores by ultra-high pressure cold isostatic pressing, prevents volatilization and pore formation by slow segmental degreasing, and achieves full filling of nano-closed pores by high temperature hot isostatic pressing. It solves the defects of multi-level pores in traditional processes and realizes the material with truly ultra-low porosity and ultra-dense structure.

[0023] 2. This invention uses a fine-grained composite modification formula combined with a gradient sintering process, resulting in uniform grain growth, dense and continuous grain boundaries, and reduced porosity and defects in near-granular spaces. This significantly improves the material's mechanical properties, thermal shock resistance, and fatigue resistance, and prevents the initiation and propagation of microcracks under high-pressure impact.

[0024] 3. This invention is equipped with a multi-stage ultra-precision mirror polishing process to eliminate micropores and loose layers in the surface grinding, resulting in an extremely dense and smooth plunger surface with low frictional resistance, no abrasive residue, no water seepage, and no pressure leakage, thus completely solving the problems of high-pressure leakage, pressure attenuation, and erosion peeling of water jet plungers.

[0025] 4. The process of this invention has strong stability, can be mass-produced, and has high consistency. The service life of the finished product is 2.5 to 3 times that of ordinary zirconia plungers, which greatly reduces the failure rate and maintenance cost of ultra-high pressure water jet equipment and has extremely high industrialization and promotion value. Detailed Implementation

[0026] Example 1

[0027] A method for preparing a high-density, low-porosity zirconia precision waterjet plunger, wherein the raw materials are as follows by weight percentage: 91.0% nano 3Y-TZP zirconia, 5.0% yttrium oxide, 3.6% ultrafine alumina, and 0.4% TiO2-MgO composite additive.

[0028] The preparation steps are as follows:

[0029] 1. Slurry preparation and vacuum degassing: Powder was sieved to remove agglomerates, and ball-milled for 9 hours at 480 r / min using a deionized water + high-purity dispersant system; degassed at 22℃ under vacuum at -0.09 MPa for 40 minutes; and spray-dried at a uniform speed to obtain solid, dense spherical powder.

[0030] 2. Molding: 20MPa bidirectional pre-pressing, 310MPa cold isostatic pressing for 10 minutes to obtain a high-density, non-porous green blank.

[0031] 3. Segmented sintering: Heat to 500℃ at 2℃ / min and hold for 2.5h, heat to 1100℃ at 4℃ / min and hold for 2h, heat to 1540℃ at 3℃ / min and hold for 4h, followed by gradient cooling annealing.

[0032] 4. HIP hot isostatic pressing: heat treatment in a 1480℃, 180MPa high-purity argon atmosphere for 2 hours to fully seal the micropores.

[0033] 5. Precision machining: rough grinding leaves a 0.2mm allowance, followed by fine grinding and nano-silica mirror polishing to ensure Ra≤0.02μm and cylindricity≤0.003mm.

[0034] 6. Non-destructive testing: Ultrasonic testing shows no defects, metallographic examination shows no micropores, and pressure holding at 350MPa shows no leakage.

[0035] The finished product in this embodiment has the following characteristics: volumetric porosity of 0.04%, overall density of 99.96%, flexural strength of 1360 MPa, and fracture toughness of 7.3 MPa·m. 1 / 2 Continuous service life ≥7800h.

[0036] Example 2

[0037] Raw material ratio: 90.7% nano 3Y-TZP zirconium oxide, 5.2% yttrium oxide, 3.8% ultrafine alumina, and 0.3% composite additives. The preparation process parameters are the same as in Example 1. The volume porosity of the finished product is ≤0.05%, the overall density is ≥99.95%, and all properties meet the requirements of ultra-high pressure water jet operation.

[0038] Example 3

[0039] Raw material ratio: 91.5% nano 3Y-TZP zirconium oxide, 4.8% yttrium oxide, 3.2% ultrafine alumina, and 0.5% composite additives. The preparation process parameters are the same as in Example 1. The finished product has low porosity, no leakage, and excellent erosion resistance.

[0040] Comparative example (common commercial zirconia plunger)

[0041] Prepared using conventional ball milling, vacuum degassing, ordinary isostatic pressing, conventional constant temperature sintering, and no HIP treatment process, the finished product contains many micropores and closed pores, with a volume porosity of 0.35%. Under high pressure conditions, it is prone to water seepage and peeling, and its service life is only about 2600 hours.

Claims

1. A method for preparing a high-density, low-porosity zirconia precision waterjet plunger, characterized in that, Includes the following steps: (1) Preparation of low-bubble, high-dispersion slurry: Nano 3Y-TZP zirconia powder is used as the matrix, combined with alumina refiner and TiO2-MgO composite sintering aid. The powder is screened to remove large agglomerated particles. Wet ball milling is carried out using deionized water and high-purity, low-viscosity dispersant as the medium. After ball milling, the slurry is degassed by constant temperature stirring under a vacuum of -0.09MPa for 30-45 minutes to remove microbubbles. The slurry is then spray-dried and granulated to obtain solid, dense spherical powder. (2) Ultra-precision dense molding: The spherical powder is evenly layered and distributed, and the loose gaps are eliminated by bidirectional pre-pressing at 20MPa. Then, it is subjected to ultra-high pressure cold isostatic pressing at 300-320MPa for 10 minutes to obtain a high-density uniform blank that can avoid interlayer pores and particle gap pores generated during the molding stage. (3) Segmented degreasing and gradient densification sintering: slowly degrease at 2℃ / min to 500℃ and hold for 2.5h, preheat crystal form at 4℃ / min to 1100℃, sinter at 3℃ / min to 1530~1550℃ for 4h, and then anneal at gradient cooling to eliminate sintering internal stress. (4) Hot isostatic pressing micropores are fully closed: The sintered green body is kept at 1480℃ and 180MPa high-purity argon atmosphere for 2h to cause the internal nanoscale closed micropores to collapse, heal and close. (5) Multi-stage ultra-precision mirror polishing: The dimensions are corrected by coarse grinding, fine grinding and ultra-fine grinding in sequence, and mirror polishing is carried out by nano-silica polishing liquid to eliminate surface grinding micropores and micro defects; (6) Non-destructive testing and sorting: Through ultrasonic flaw detection, metallographic micropore detection and 350MPa high pressure holding test, workpieces with visible and detectable pore defects are screened out to obtain qualified precision plunger products.

2. The method for preparing a high-density, low-porosity zirconia precision waterjet plunger according to claim 1, characterized in that, In step (1), the raw material powder is composed of the following weight percentages: 90.3-91.5% nano-3Y-TZP zirconium oxide, 4.8-5.2% yttrium oxide, 3.0-4.0% ultrafine alumina, and 0.2-0.5% TiO2-MgO composite sintering aid. The nano-3Y-TZP zirconium oxide powder has a D50 of 0.2-0.4 μm and a total mass fraction of ZrO2, HfO2, and Y2O3 of ≥99.9%.

3. The method for preparing a high-density, low-porosity zirconia precision waterjet plunger according to claim 1, characterized in that, In step (1), the wet ball milling speed is 450-500 r / min, the ball milling time is 8-10 h, the ball milling medium is high-purity zirconia balls, and the vacuum degassing constant temperature is 20-25℃.

4. The method for preparing a high-density, low-porosity zirconia precision waterjet plunger according to claim 1, characterized in that, In step (4), the argon purity is ≥99.99%. During the hot isostatic pressing process, the heating, pressurizing, cooling and depressurizing processes are controlled to avoid sudden changes in temperature and pressure.

5. The method for preparing a high-density, low-porosity zirconia precision waterjet plunger according to claim 1, characterized in that, In step (5), the single-sided machining allowance for rough grinding is 0.2 mm, the cylindricity of the finished plunger is ≤0.003 mm, and the surface roughness Ra is ≤0.02 μm.

6. The method for preparing a high-density, low-porosity zirconia precision waterjet plunger according to claim 1, characterized in that, The prepared zirconia plunger has a volumetric porosity ≤0.05%, an overall density ≥99.95%, a flexural strength ≥1300MPa, and a fracture toughness ≥7.0MPa·m. 1 / 2 .

7. The method for preparing a high-density, low-porosity zirconia precision waterjet plunger according to claim 1, characterized in that, The zirconia plunger is used in the reciprocating motion components of a 300-600MPa ultra-high pressure water jet pump.