Ceramic projectile and its preparation method and application

Abstract

This invention relates to a ceramic projectile, its preparation method, and its application, belonging to the field of special ceramic preparation technology. The chemical composition of the ceramic projectile is: 78-82 wt% zirconium oxide, 15-17 wt% cerium oxide, 1-2 wt% yttrium oxide, 0.5-2.5 wt% lanthanum oxide, and 0-2 wt% other oxides; the other oxides are at least one of aluminum oxide, manganese oxide, and titanium dioxide; the D50 of the ceramic projectile raw material is 0.4-0.6 μm. This invention also provides a method for preparing the ceramic projectile, resulting in a ceramic projectile based on a "cerium-yttrium-lanthanum multi-element co-stabilization" structure, exhibiting high density, high hardness, and high toughness; a smooth surface, eliminating the need for subsequent mechanical polishing, and its surface finish directly meets the requirements for shot peening strengthening of precision parts, simplifying the production process and reducing costs.

Description

Technical Field

[0001] This invention belongs to the field of special ceramics preparation technology, and particularly relates to a ceramic projectile, its preparation method and application. Background Technology

[0002] Shot peening, as an important surface cold working process, introduces a residual compressive stress layer by impacting the workpiece surface with a high-speed shot stream, significantly improving the fatigue strength, wear resistance, and stress corrosion resistance of components. Based on this, this technology is widely used in fields with extremely high component reliability requirements, such as aerospace, automotive manufacturing, and precision medical devices. Ceramic shot, in particular, has unique advantages in shot peening applications in high-end fields such as aerospace because it does not cause metal contamination on the component surface.

[0003] Methods for preparing ceramic shot mainly include spray granulation, melt blowing, flame spraying, and rolling spheroidization, but these methods generally suffer from problems such as poor sphericity, wide size distribution, low surface finish, and insufficient density and hardness. In terms of material systems, zirconium oxide, alumina, and silicon oxide are predominantly used, but the density and hardness of their sintered bodies are insufficient to meet the strengthening requirements of modern high-strength materials (such as turbine disks, blades, and landing gear for aero-engines). Therefore, shot needs higher kinetic energy to generate a deeper residual compressive stress layer and achieve the specified coverage in a shorter time. Traditional ceramic shot peening suffers from low density and low hardness, failing to meet the process requirements of high-strength materials, which require higher Alman strength and a deeper residual compressive stress layer. Therefore, based on the above shortcomings, proposing a method for preparing ceramic shot that can precisely control shot size, improve yield, and simultaneously improve shot density, toughness, and hardness has become a pressing technical problem to be solved in the current technology. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a ceramic projectile, its preparation method and application, which solves the technical problems of excessive internal pores and insufficient intrinsic strength and hardness of existing ceramic projectiles.

[0006] (II) Technical Solution

[0007] This invention proposes a ceramic projectile, its preparation method, and its application.

[0008] One objective of this invention is to provide a ceramic projectile, wherein the chemical composition of the ceramic projectile is: 78-82 wt% zirconium oxide, 15-17 wt% cerium oxide, 1-2 wt% yttrium oxide, 0.5-2.5 wt% lanthanum oxide, and 0-2 wt% other oxides; wherein the other oxides are at least one of aluminum oxide, manganese oxide, and titanium dioxide; and the D50 of the ceramic projectile raw material is 0.4-0.6 μm.

[0009] The second objective of this invention is to provide a method for preparing ceramic projectiles, comprising the following steps:

[0010] S1. Prepare an organic monomer premix containing acrylamide and methylenebisacrylamide, add ceramic powder to the organic monomer premix, control the solid content of the slurry, add polyacrylamide dispersant, and obtain a high solid content and low viscosity slurry by ball milling and degassing.

[0011] The ceramic powder is composed of: 78-82 wt% zirconium oxide, 15-17 wt% cerium oxide, 1-2 wt% yttrium oxide, 0.5-2.5 wt% lanthanum oxide, and 0-2 wt% other oxides.

[0012] The other oxides are at least one of aluminum oxide, manganese oxide, and titanium dioxide;

[0013] S2. The high-solids-content, low-viscosity slurry is dropped into an alkaline coagulation bath containing a redox initiator in the form of droplets. At the moment the droplets fall into the alkaline coagulation bath, the organic monomers on the surface of the droplets undergo a polymerization reaction, causing the droplets to become spherical under the action of surface tension and solidify to obtain gel microspheres. The gel microspheres are then soaked in the alkaline coagulation bath for aging and cleaned to remove residual chemical reagents from the surface, resulting in cleaned gel microspheres.

[0014] S3. Place the cleaned gel microbeads in a dry environment and perform a multi-stage humidity reduction step drying process to obtain dried gel microbeads.

[0015] S4. The dried gel microspheres are degreased and sintered to obtain ceramic pellets.

[0016] The ceramic pellets prepared by this method exhibit significantly better sphericity than those produced by spray granulation or rolling spheroidization, with the diameter standard deviation controllable within 0.01 mm, achieving precise dimensional control. The entire preparation process has clearly defined parameters and strong controllability, and each step from slurry preparation to sintering is easily standardized, facilitating large-scale stable production and achieving a high yield.

[0017] Furthermore, in S1, the D of the ceramic pellet raw material 50 The thickness is 0.4~0.6μm.

[0018] Further, the mass ratio of acrylamide to methylenebisacrylamide is 10-30:1; the total concentration of the organic monomer premix is ​​8-12%; the solid content of the high-solids-content, low-viscosity slurry is 55-70 wt%; the amount of polyacrylamide dispersant added is 0.5-2.0% of the mass of the ceramic powder; the ball milling time is 6-12 h; and the viscosity of the high-solids-content, low-viscosity slurry at 25°C is 1000-3000 mPa·s. The high-solids-content, low-viscosity slurry with a viscosity of 1000-3000 mPa·s at 25°C prepared by this method is uniform and stable. The acrylamide system is used for gel curing, resulting in a rapid and uniform reaction, and the formed three-dimensional network structure endows the gel microspheres with high green strength.

[0019] Further, in S2, the temperature of the alkaline coagulation bath is 60~90℃; the alkaline coagulation bath contains 0.1~0.5mol / L of redox initiator and 0.1~1mol / L of tetramethylethylenediamine, and its pH value is 8.5-12; the redox initiator is selected from at least one of ammonium persulfate, potassium persulfate, sodium bisulfite, and sodium bromate.

[0020] Furthermore, the gel microspheres are soaked and aged in the coagulation bath for 0.5 to 2 hours; and the deionized water is used for 3 to 5 washes.

[0021] Furthermore, the alkaline coagulation bath also contains polyvinylpyrrolidone and / or sodium chloride; wherein the concentration of polyvinylpyrrolidone in the alkaline coagulation bath is 0.5~1.5wt%; and the concentration of sodium chloride in the alkaline coagulation bath is 1~5wt%, to increase surface tension and prevent adhesion between microbeads.

[0022] Furthermore, in step S2, the alkaline coagulation bath is also supplemented with a pH adjuster and a pH buffer; the pH adjuster is selected from inorganic bases, including sodium carbonate or sodium hydroxide. The pH buffer is selected from at least one of ethanolamine and triethanolamine, used to stabilize the pH of the system.

[0023] Furthermore, in S3, the multi-stage humidity-decreasing step drying process includes: a first stage, temperature 23~27℃, humidity 86-94%, time 12h; a second stage, temperature 23~27℃, humidity 67-73%, time 12h; and a third stage, temperature 28~32℃, humidity 48-52%, time 12h.

[0024] Furthermore, in S4, the degreasing conditions are: heating to 600℃ at a rate of 0.5~1℃ / min and holding for 2 hours; the sintering conditions are: heating to 1450~1550℃ at a rate of 3-5℃ / min and holding for 2~4 hours, followed by furnace cooling.

[0025] A third objective of this invention is to provide an application of ceramic projectiles in the manufacture of aerospace, automotive, or precision medical devices.

[0026] (III) Beneficial Effects

[0027] The ceramic projectiles prepared by this invention, based on a cerium-yttrium-lanthanum multi-element synergistic structure, exhibit high density, high hardness, and high toughness. The gel titration instant curing technology employed in this invention, combined with the excellent flowability of a high-solids-content, low-viscosity slurry, ensures, in principle, a near-perfect spherical shape for the projectiles. The prepared ceramic projectiles have a smooth surface, eliminating the need for subsequent mechanical polishing. Their surface finish directly meets the requirements for shot peening of precision components, simplifying the production process and reducing costs.

[0028] Furthermore, this invention employs a cerium-yttrium-lanthanum multi-element co-stabilized zirconia system, utilizing the synergistic solid solution strengthening and grain boundary optimization effects of ions with different radii to overcome the bottlenecks in density and hardness of traditional yttrium-stabilized zirconia, achieving excellent properties such as a density greater than 6.20 g / cm³ and a Vickers hardness greater than 1300 HV. Benefiting from the inherent high phase transformation toughening characteristics of cerium-stabilized zirconia, the ceramic projectiles prepared by this invention possess both ultra-high hardness and excellent fracture toughness, exhibiting a significantly lower breakage rate than traditional ceramic projectiles in stringent shot peening tests, thus extending the projectile's service life and preventing workpiece surface contamination. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the preparation process of the ceramic projectiles of this invention.

[0030] Figure 2 The image shows an enlarged view of the ceramic projectile prepared according to the present invention, with a diameter of 0.15-0.2 mm. Detailed Implementation

[0031] To better explain and facilitate understanding of the present invention, it will be described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0032] Example 1:

[0033] This embodiment describes the preparation of ceramic pellets in a coagulation bath using ammonium persulfate as an initiator, tetramethylethylenediamine as a catalyst, and an inorganic base to maintain the pH value of the coagulation bath.

[0034] Step 1: Slurry preparation

[0035] Weigh out 80g of zirconium oxide, 16g of cerium oxide, 1.5g of yttrium oxide, 1.5g of lanthanum oxide, and 1g of aluminum oxide, mix and grind to 0.5μm to obtain ceramic powder. Prepare 67g of a 10% concentration premixed solution of acrylamide and methylenebisacrylamide at a mass ratio of 20:1. Add the ceramic powder to the premixed solution, the slurry solid content is 60%, and ball mill for 6 hours.

[0036] Step 2: Titration and Shaping

[0037] The slurry was dropped into a coagulation bath containing 0.3 mol / L ammonium persulfate and 0.5 mol / L tetramethylethylenediamine. The pH was adjusted to 9 with sodium carbonate, and the temperature was controlled at 70°C. After the droplets solidified, they were aged in the coagulation bath for 2 hours, and then rinsed 5 times with deionized water.

[0038] Step 3: Slow drying in stages

[0039] The cleaned gel microbeads were placed in a dry environment and dried according to the following procedure: First stage: temperature 25℃, humidity 90%, time 12h; Second stage: temperature 25℃, humidity 70%, time 12h; Third stage: temperature 30℃, humidity 50%, time 12h.

[0040] Step 4: Degreasing and Sintering

[0041] The dried gel microspheres were degreased and sintered. Degreasing procedure: heating to 600℃ at a rate of 0.5℃ / min and holding for 2 hours. Sintering procedure: heating to 1500℃ at a rate of 5℃ / min and holding for 3 hours, followed by furnace cooling.

[0042] Example 2:

[0043] This embodiment is the same as Embodiment 1, except that the ammonium persulfate in the coagulation bath is replaced with 0.3 mol / L potassium persulfate.

[0044] Example 3:

[0045] This embodiment is the same as Embodiment 1, except that a pH buffer, ethanolamine / triethanolamine, is added to the coagulation bath to adjust the pH to 9 together with sodium carbonate. The molar concentration ratio of sodium carbonate to ethanolamine / triethanolamine is 1:1.

[0046] Example 4:

[0047] This embodiment is the same as Embodiment 1, except that 1g of polyvinylpyrrolidone (PVP-K30) is added to the coagulation bath.

[0048] Example 5:

[0049] This embodiment is the same as Embodiment 1, except that 3% NaCl is added to the coagulation bath.

[0050] Example 6:

[0051] This embodiment is the same as Embodiment 1, except that the composition ratio of the ceramic powder is different. Zirconia is 78.5g, cerium oxide is 15g, yttrium oxide is 2g, lanthanum oxide is 2.5g, and other oxides are 2g.

[0052] Example 7:

[0053] This embodiment is the same as Embodiment 3, except that the composition ratio of the ceramic powder is different. In this embodiment, zirconium oxide is 78.5g, cerium oxide is 15g, yttrium oxide is 2g, lanthanum oxide is 2.5g, and other oxides are 2g.

[0054] Example 8:

[0055] This embodiment is the same as Embodiment 4, except that the composition ratio of the ceramic powder is different. In this embodiment, zirconium oxide is 82g, cerium oxide is 16g, yttrium oxide is 1g, lanthanum oxide is 0.5g, and other oxides are 0.5g.

[0056] Example 9:

[0057] This embodiment is the same as Embodiment 5, except that the composition ratio of the ceramic powder is different. The composition ratio of the ceramic powder is the same as that in Embodiment 8.

[0058] Example 10:

[0059] This embodiment is the same as Embodiment 6, except that the solid content of the slurry is slightly reduced to 55%.

[0060] Example 11:

[0061] This embodiment is the same as Embodiment 6, except that the solid content of the slurry is slightly increased to 70%.

[0062] Example 12:

[0063] This embodiment is the same as Embodiment 3, except that 1g of polyvinylpyrrolidone (PVP-K30) is added to the coagulation bath.

[0064] Comparative Example 1:

[0065] This comparative example is the same as Example 1, except that calcium oxide is added to the ceramic powder. The amount of zirconium oxide is 80g, cerium oxide is 16g, yttrium oxide is 1.5g, lanthanum oxide is 1.5g, and calcium oxide is 1g.

[0066] Comparative Example 2:

[0067] This comparative example is the same as Example 1, except that the composition ratio of the ceramic powder is different, wherein zirconium oxide is 75g, cerium oxide is 12g, yttrium oxide is 4g, lanthanum oxide is 5g and aluminum oxide is 4g.

[0068] Comparative Example 3:

[0069] This comparative example is the same as Example 1, except that the solid content is reduced to 50%.

[0070] Comparative Example 4:

[0071] This comparative example is the same as Example 1, except that the measured slurry viscosity is 3200 mPa·s.

[0072] Comparative Example 5:

[0073] This comparative example is the same as Example 1, except that the drying process uses a fixed humidity rapid drying method, a fixed temperature of 30°C, a humidity of 50%, and a drying time of 36 hours.

[0074] Table 1: Comparison Results of Parameters between Embodiments of the Invention and Comparative Examples

[0075]

[0076] Experimental results (see Table 1) show that the obtained ceramic pellets have a smooth surface and good sphericity. Two hundred microspheres were randomly selected and their diameters were measured using an optical microscope; the average diameter was 0.302 mm, and the standard deviation was 0.008 mm. The sintering density was 6.25 g / cm³. 3 The Vickers hardness is 1350 HV. This invention is based on the solid solution strengthening effect of CeO2 to form a stable cerium-stabilized zirconium oxide phase, which effectively improves the intrinsic strength and hardness of the material. Y2O3 and La2O3, as auxiliary stabilizers, have a synergistic effect, which can optimize the grain boundary structure, promote sintering densification, reduce internal porosity, and effectively improve density and hardness. La2O3 can also inhibit abnormal grain growth at high temperatures, producing a fine-grain strengthening effect.

[0077] Furthermore, this invention selects sodium carbonate and ethanolamine / triethanolamine to adjust the pH value, instead of the commonly used ammonia, which results in a more uniform ceramic pellet structure, fewer defects, and superior performance. The buffer system constructed with ethanolamine / triethanolamine provides a continuously stable alkaline environment, maintaining the pH value within an optimal narrow range, making the reaction process more gentle, effectively stabilizing metal ions, slowing down the reaction rate, and enabling more uniform and fully spherical droplet structures. In contrast, the volatility of ammonia leads to unstable and continuously decreasing pH values, while strong alkalis have no buffering capacity, and even slight disturbances in pH value will cause drastic changes. The volatility of ammonia also easily leads to pH instability. Furthermore, this buffer system enables the gel reaction to have higher gel kinetics and structural uniformity, while ammonia, as a rapid gelling agent, causes the droplet surface to solidify instantly, forming a hard shell, hindering internal ion exchange and reactions, resulting in a loose internal structure, uneven density, and easy cracking during drying. Furthermore, the nitrogen and hydroxyl groups in ethanolamine / triethanolamine can be adsorbed onto the surface of ceramic particles, preventing particle agglomeration through steric hindrance and electrostatic repulsion, thus making the slurry more stable and with better flowability. The resulting ceramic pellets exhibit higher sintering density, more uniform microstructure, and more consistent mechanical properties.

[0078] Furthermore, the present invention uses polyvinylpyrrolidone as a dispersant or adds 3% NaCl, which can effectively improve the uniformity of the solidification process, improve the performance of ceramic shot products, and obtain ceramic shot products with higher sintering density and Vickers hardness, and more uniform and flat shape.

[0079] Furthermore, the present invention employs a multi-stage, progressively decreasing humidity drying process, which can precisely match the needs of the shot components at different drying stages, significantly improving the final performance of the ceramic shot and enabling the shot product to achieve better sphericity, more uniform size, higher sintering density, and Vickers hardness.

[0080] In summary, this invention, based on gel titration instant curing technology and combined with the good fluidity of high-solids-content, low-viscosity slurry, ensures that the sphericity and roundness of the projectiles are close to 1. Its sphericity is significantly better than products obtained by spray granulation or rolling spheroidization, and the standard deviation of the diameter can be controlled within 0.01 mm, achieving precise and controllable dimensions. Furthermore, the ceramic projectiles are gel-cured based on an acrylamide system, resulting in a rapid and uniform reaction. The resulting three-dimensional network structure gives the gel microspheres high green strength. Furthermore, the ceramic projectiles prepared by this invention have a smooth surface, eliminating the need for subsequent mechanical polishing. Their surface finish directly meets the requirements for shot peening strengthening of precision parts, simplifying the production process and reducing costs. Furthermore, the preparation process of the ceramic projectiles is well-defined and highly controllable. Each step, from slurry preparation to sintering, is easily standardized, facilitating large-scale stable production with a high yield. Furthermore, the ceramic projectile, based on a cerium-yttrium-lanthanum multi-element co-stabilized zirconia system, utilizes the synergistic solid solution strengthening and grain boundary optimization effects of ions with different radii to overcome the limitations of traditional yttrium-stabilized zirconia in terms of density and hardness, achieving excellent properties such as a density greater than 6.20 g / cm³ and a Vickers hardness greater than 1300 HV. Moreover, based on the inherent high phase transformation toughening characteristics of cerium-stabilized zirconia, the ceramic projectile prepared by this invention possesses both ultra-high hardness and excellent fracture toughness, exhibiting a significantly lower breakage rate than traditional ceramic projectiles in stringent shot peening tests, thus extending the projectile's service life and preventing workpiece surface contamination.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ceramic projectile, characterized in that, The chemical composition of the ceramic projectile is as follows: 78-82 wt% zirconium oxide, 15-17 wt% cerium oxide, 1-2 wt% yttrium oxide, 0.5-2.5 wt% lanthanum oxide, and 0-2 wt% other oxides; The other oxides are at least one of aluminum oxide, manganese oxide, and titanium dioxide; The method for preparing the ceramic projectile includes the following steps: S1. Prepare an organic monomer premix containing acrylamide and methylenebisacrylamide, add ceramic powder to the organic monomer premix, control the solid content of the slurry, add polyacrylamide dispersant, and obtain a high solid content and low viscosity slurry by ball milling and degassing. The ceramic powder is composed of: 78-82 wt% zirconium oxide, 15-17 wt% cerium oxide, 1-2 wt% yttrium oxide, 0.5-2.5 wt% lanthanum oxide, and 0-2 wt% other oxides. The D50 of the ceramic shot raw material is 0.4~0.6μm; The other oxides are at least one of aluminum oxide, manganese oxide, and titanium dioxide; The solid content of the high-solids, low-viscosity slurry is 55-70 wt%. The viscosity of the high-solids-content, low-viscosity slurry at 25°C is 1000~3000 mPa·s; S2. The high-solids-content, low-viscosity slurry is dropped into an alkaline coagulation bath containing a redox initiator in the form of droplets. At the moment the droplets fall into the alkaline coagulation bath, the organic monomers on the surface of the droplets undergo a polymerization reaction, causing the droplets to become spherical under the action of surface tension and solidify to obtain gel microspheres. The gel microspheres are then soaked in the alkaline coagulation bath for aging and cleaned to remove residual chemical reagents from the surface, resulting in cleaned gel microspheres. The alkaline coagulation bath also contains a pH adjuster and a pH buffer. The pH adjuster is sodium carbonate; The pH buffer is selected from at least one of ethanolamine and triethanolamine; S3. Place the cleaned gel microbeads in a dry environment and perform a multi-stage humidity reduction step drying process to obtain dried gel microbeads. S4. The dried gel microspheres are degreased and sintered to obtain ceramic pellets.

2. The ceramic projectile according to claim 1, characterized in that, In S1, the mass ratio of acrylamide to methylenebisacrylamide is 10~30:1; The total concentration of the organic monomer premix is ​​8-12%; The amount of polyacrylamide dispersant added is 0.5~2.0% of the mass of the ceramic powder; The ball milling time is 6~12 hours.

3. The ceramic projectile according to claim 1, characterized in that, In S2, the temperature of the alkaline coagulation bath is 60~90°C; The alkaline coagulation bath contains 0.1-0.5 mol / L of redox initiator and 0.1-1 mol / L of tetramethylethylenediamine, and has a pH of 8.5-12; the redox initiator is selected from at least one of ammonium persulfate, ferric persulfate, sodium bisulfite, and sodium bromate.

4. The ceramic projectile according to claim 3, characterized in that, The alkaline coagulation bath also contains polyvinylpyrrolidone and / or sodium chloride; The concentration of polyvinylpyrrolidone in the alkaline coagulation bath is 0.5~1.5wt%; the concentration of sodium chloride in the alkaline coagulation bath is 1~5wt%.

5. The ceramic projectile according to any one of claims 1-4, characterized in that, In S3, the multi-stage humidity-decreasing step drying process includes: The first stage, with a temperature of 23-27℃ and a humidity of 86-94%, lasts for 12 hours. The second stage, with a temperature of 23-27℃, a humidity of 67-73%, and a duration of 12 hours; The third stage involves a temperature of 28-32℃, a humidity of 48-52%, and a duration of 12 hours.

6. The ceramic projectile according to claim 1, characterized in that, In S4, the degreasing conditions are: heating to 600℃ at a rate of 0.5~1℃ / min and holding for 2 hours; The sintering conditions are as follows: heat up to 1450~1550℃ at a rate of 3-5℃ / min, hold for 2~4 hours, and then cool with the furnace.

7. The application of the ceramic projectile as described in any one of claims 1-6 in the manufacture of aerospace, automotive, or precision medical devices.

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