A method for strengthening laser additive manufacturing zirconia ceramic based on grain refinement

Abstract

The application discloses a laser additive forming zirconia ceramic strengthening method based on grain refinement. First, 5-7 wt% of alumina ceramic powder and 93-95 wt% of zirconia ceramic powder are weighed according to the weight percentage; second, the weighed zirconia ceramic powder and alumina ceramic powder are mixed for more than 5 hours, and then the mixed powder is dried at 100-200 DEG C for 2-4 hours to obtain dry raw powder for standby; finally, the additive forming of the zirconia ceramic is carried out by using the directional energy deposition technology, the preparation of the strengthened zirconia ceramic based on grain refinement is completed; a small amount of alumina solute component is added in the zirconia ceramic raw powder, the solidification interface front in the forming is promoted to form a component undercooling zone, the existing nucleation particles in the zone are activated, the microstructure after the forming is changed from coarse columnar crystal organization to uniform and small equiaxed crystal organization, and then the microstructure is strengthened and homogenized, finally, the crack inhibition and mechanical property improvement of the additive forming zirconia ceramic are realized, and the problems of many defects and poor performance of the zirconia ceramic in the laser additive manufacturing are solved.

Description

Technical Field

[0001] This invention relates to the field of laser additive manufacturing technology for zirconia ceramic materials, and specifically proposes a laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement. Background Technology

[0002] Zirconia ceramics possess excellent mechanical properties, chemical stability, corrosion resistance, and biocompatibility, making them promising candidates for applications in aerospace, biomedicine, energy, and environmental fields. However, existing manufacturing processes struggle to meet the growing demand for high-performance, complex-shaped zirconia ceramic components. Traditional ceramic manufacturing processes, such as dry pressing, isostatic pressing, injection molding, and slurry casting, offer low forming complexity and are ill-suited for manufacturing complex ceramic parts. Furthermore, these processes require solid-state sintering to densify the ceramic body, resulting in long sintering times, high energy consumption, and significant shrinkage and deformation in the finished ceramic product, affecting dimensional accuracy and quality. Subsequent processing of sintered zirconia ceramic parts also presents numerous challenges. Traditional machining easily causes cracking, chipping, and other damage to the ceramic parts, reducing yield. Simultaneously, machining zirconia ceramics requires high-hardness, wear-resistant tools, and the process is time-consuming, leading to high processing costs and severe tool wear.

[0003] The increasing maturity of laser additive manufacturing technologies (such as selective laser melting and directional energy deposition) has provided an opportunity to solve the aforementioned problems. This type of technology is based on the principle of layered manufacturing, using a high-energy laser beam as a heat source to completely melt ceramic powder, directly forming three-dimensional solid parts through a bottom-up, layer-by-layer accumulation process. Compared to traditional forming processes, laser additive manufacturing technology has significant advantages such as high design freedom, simple process, short production cycle, no need for molds, and near-net-shape forming, enabling low-energy, high-efficiency manufacturing of complex ceramic structural parts. However, due to the inherent brittleness of ceramics and the extremely high temperature gradient and thermal stress in laser additive forming, microcracks and micropores are easily formed inside zirconia ceramic additive-formed parts, leading to performance degradation or forming failure, which is detrimental to the widespread use of additive-manufactured zirconia ceramic components.

[0004] Regarding defect suppression and performance improvement in laser additive manufacturing of zirconia ceramics, the literature "Ferrage L, Bertrand G, Lenormand P. 2018. Dense yttria-stabilized zirconia obtained by direct selective laser sintering. Addit. Manuf. 21, 472–478." found that the coarse columnar crystal structure formed inside the zirconia ceramic after additive manufacturing is an important factor in defect formation and performance degradation. This is because cracks generated under thermal stress are prone to propagate along the weak regions of the columnar crystal boundaries, eventually forming dense crack defects inside the zirconia ceramic sample. The literature "Fan Z, Zhao Y, Lu M, Huang H. 2019. Yttria stabilized zirconia (YSZ) thin wall structures fabricated using laser engineered net" further supports this finding. “Shaping (LENS). Int. J. Adv. Manuf. Technol. 105, 4491–4498.” In the process of laser additive manufacturing of zirconia ceramics, an attempt was made to optimize the forming quality by optimizing process parameters. It was found that appropriately increasing the laser power can reduce the thermal stress during the forming process and thus reduce the number of defects. However, the study also showed that the defect suppression effect of the forming parameter optimization method is relatively limited, and a small number of microcracks still exist inside the sample. The literature “Liu Q, Danlos Y, Song B, Zhang B, Yin S, Liao H. 2015. Effect of high-temperature preheating on the selective laser melting of yttria-stabilized zirconia ceramic. J. Mater. Process. Technol. 222, 61–74.” Zirconia ceramic samples were prepared by laser preheating-assisted laser additive manufacturing technology, and the effect of preheating temperature on defect formation was analyzed. The results showed that when the preheating temperature is above 2000℃, vertical periodic cracks in ceramic components can be eliminated, but a large number of short cracks in random directions still exist inside the sample.Furthermore, the use of laser preheating-assisted technology also suffers from limitations in part size, poor surface quality, and high cost of laser preheating equipment. The literature "Urruth G, Maury D, Voisin C, Baylac V, Grossin D. 2022. Powder bed selective laser processing (sintering / melting) of Yttrium Stabilized Zirconia using carbon-based material (TiC) as absorbance enhancer. J. Eur. Ceram. Soc. 42, 2381–2390." investigated the effect of TiC particle doping on the forming quality of zirconia ceramics. The study showed that while adding an appropriate amount of TiC particles increased the density of the finished zirconia ceramic, it did not significantly inhibit internal crack defects in the formed parts. In summary, there is currently no effective method to achieve defect suppression and performance improvement in additively formed zirconia ceramics, which severely restricts the future development of laser additive manufacturing technology in the field of ceramic forming. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, the present invention aims to provide a laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement. Based on the classical solidification theory in metal casting, a small amount of alumina solute is added to the zirconia ceramic raw material powder to promote the formation of a compositionally supercooled zone at the solidification interface front during molding. This activates nucleation points in the region, transforming the microstructure after molding from coarse columnar crystals to uniform fine equiaxed crystals. This strengthens and homogenizes the microstructure, ultimately achieving crack suppression and improved mechanical properties in additively manufactured zirconia ceramics. This method solves the problems of numerous defects and poor performance currently faced by zirconia ceramics in laser additive manufacturing.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A grain-refined reinforced zirconia ceramic, the raw materials of which, by weight percentage, include 5-7 wt% alumina ceramic powder and 93-95 wt% yttrium-stabilized zirconia ceramic powder.

[0008] In the yttrium oxide-stabilized zirconia ceramic powder, the sum of the contents of yttrium oxide and zirconia is 99.9 wt%-99.99 wt%, of which the yttrium oxide content accounts for 5 wt%-11 wt% of the sum of the contents of yttrium oxide and zirconia.

[0009] The alumina purity in the alumina ceramic powder is 99.9wt%-99.99wt%.

[0010] The particle size of the yttrium-stabilized zirconia ceramic powder and the alumina ceramic powder is 50-120 μm.

[0011] A laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement includes the following steps:

[0012] Step 1: Weigh 5-7 wt% alumina ceramic powder and 93-95 wt% yttrium oxide-stabilized zirconia ceramic powder by weight percentage, wherein the yttrium oxide content accounts for 5 wt%-11 wt% of the sum of the yttrium oxide and zirconia contents.

[0013] Step 2: Mix the weighed yttrium-stabilized zirconia ceramic powder and alumina ceramic powder thoroughly for more than 5 hours, and then dry the mixed powder at 100-200℃ for 2-4 hours to obtain dried raw material powder for later use.

[0014] Step 3: Use directional energy deposition technology to perform additive manufacturing of zirconia ceramics, and complete the preparation of reinforced zirconia ceramics based on grain refinement.

[0015] The specific steps of step 3 are as follows:

[0016] 3.1) Polish the Ti6Al4V substrate until a distinct metallic luster appears on the surface of the Ti6Al4V substrate, and then clean it with alcohol to remove the oxide film on the surface of the Ti6Al4V substrate.

[0017] 3.2) Place the polished Ti6Al4V substrate into the additive molding cavity, and place a layer of fireproof cotton under the Ti6Al4V substrate to reduce the thermal diffusion rate of the Ti6Al4V substrate.

[0018] 3.3) The surface of the Ti6Al4V substrate was pre-scanned multiple times using a laser heat source;

[0019] 3.4) Set the additive manufacturing process parameters for the additive manufacturing equipment, and preset the movement trajectory of the laser nozzle of the additive manufacturing equipment and the number of ceramic layers to be prepared;

[0020] 3.5) Starting from the current position of the laser head of the additive manufacturing equipment, start the laser and powder feeding device of the additive manufacturing equipment; the laser beam is output through the laser head and irradiates the surface of the Ti6Al4V substrate, while the dried raw material powder is transported to the Ti6Al4V surface through a coaxial powder feeding method. The laser heats the raw material powder to above 2700℃ (zirconia melting point), forming a stable molten pool on the Ti6Al4V surface, which gradually extends as the laser head moves along the preset trajectory; after completing the preset trajectory, the laser beam irradiation is stopped, the temperature of the melt in the molten pool drops below 2700℃ and solidifies, forming the first layer of reinforced zirconia ceramic;

[0021] 3.6) Repeat step 3.5) according to the set number of layers until a reinforced zirconia ceramic product with the preset number of layers is prepared.

[0022] The additive manufacturing process parameters set for the additive manufacturing equipment in step 3.4) include: laser power of 300-500W, laser scanning speed of 350-600mm / min, single layer thickness of 0.3-0.5mm, and powder feeding rate of 0.8-1.2rpm.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. This invention promotes grain refinement by adding a small amount of a specific solute (5-7 wt% alumina ceramic powder) to yttrium-stabilized zirconia ceramic powder, thereby generating compositional supercooling. The stronger the solute segregation ability, the larger the compositional supercooled zone and the better the grain refinement effect. Alumina ceramic powder has extremely low solid solubility in zirconia ceramics. During solidification, it segregates at the solid-liquid interface of the zirconia ceramic, resulting in compositional supercooling. Consequently, during zirconia grain growth, it is almost completely expelled to the solid-liquid interface, forming a large-scale supercooled zone in the melt, which greatly promotes heterogeneous nucleation. This, in turn, promotes the formation of fine equiaxed crystal structures.

[0025] 2. Compared with traditional ceramic forming technology and indirect additive manufacturing technology, the directional energy deposition technology used in this invention uses a high-energy laser beam to rapidly melt and solidify ceramic powder, eliminating the need for post-processing sintering, and can efficiently achieve near-net-shape forming of zirconia ceramic parts; by reasonably controlling the additive manufacturing process parameters and scanning path, it is possible to prepare complex structure zirconia ceramic parts; laser additive manufacturing technology does not require molds, which can reduce manufacturing costs; in addition, compared with indirect additive manufacturing technology, the directional energy deposition technology used in this invention does not require debinding, which can effectively reduce environmental pollution.

[0026] 3. Compared with zirconia ceramic parts prepared by conventional laser additive manufacturing, the zirconia ceramic components prepared by this invention eliminate the coarse columnar crystal structure and form a fine equiaxed crystal structure. The added alumina solute is continuously discharged into the melt during solidification, thus uniformly distributing at the grain boundaries of the equiaxed zirconia crystals after forming, thereby achieving grain boundary strengthening. Therefore, this invention can effectively improve the forming quality of zirconia ceramics, enhance the mechanical properties of ceramic parts, and reduce the anisotropy of the material.

[0027] 4. Compared with previous methods, the method for suppressing molding defects by grain refinement proposed in this invention is more convenient to operate, lower in cost, and uses simpler raw materials. It only requires mixing a small amount of second-phase solute particles into the raw material powder, and does not require expensive preheating auxiliary equipment. At the same time, the defect suppression effect of this invention is very obvious, effectively suppressing the formation and propagation of cracks by refining grains and strengthening grain boundary regions. Attached Figure Description

[0028] Figure 1 This is a microscopic SEM image of the ceramic powder raw material after thorough mechanical mixing.

[0029] Figure 2 This is a schematic diagram of the working principle of a direct energy deposition additive manufacturing equipment for zirconia ceramics.

[0030] Figure 3 This is a macroscopic morphology image of a zirconia ceramic sample.

[0031] Figure 4 The images show a comparison of the cross-sections of additively formed zirconia ceramics before and after the addition of alumina solute; among them, Figure 4 (a) is pure zirconium oxide ceramic; Figure 4 (b) is doped with 5 wt% alumina.

[0032] Figure 5 SEM image of the microstructure of additively formed zirconia ceramics after the addition of alumina solute. Detailed Implementation

[0033] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0034] A grain-refined reinforced zirconia ceramic, the raw materials of which, by weight percentage, include 5-7 wt% alumina ceramic powder and 93-95 wt% yttrium-stabilized zirconia ceramic powder.

[0035] In the yttrium oxide-stabilized zirconia ceramic powder, the sum of the contents of yttrium oxide and zirconia is 99.9 wt%-99.99 wt%, of which the yttrium oxide content accounts for 5 wt%-11 wt% of the sum of the contents of yttrium oxide and zirconia.

[0036] The alumina purity in the alumina ceramic powder is 99.9wt%-99.99wt%.

[0037] The particle size of the yttrium-stabilized zirconia ceramic powder and the alumina ceramic powder is 50-120 μm.

[0038] A laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement includes the following steps:

[0039] Step 1: Weigh 5-7 wt% alumina ceramic powder and 93-95 wt% yttrium oxide-stabilized zirconia ceramic powder by weight percentage, wherein the yttrium oxide content accounts for 5 wt%-11 wt% of the sum of the yttrium oxide and zirconia contents.

[0040] Step 2: Mix the weighed yttrium-stabilized zirconia ceramic powder and alumina ceramic powder thoroughly for more than 5 hours, and then dry the mixed powder at 100-200℃ for 2-4 hours to obtain dried raw material powder for later use.

[0041] Step 3: Use directional energy deposition technology to perform additive manufacturing of zirconia ceramics, and complete the preparation of reinforced zirconia ceramics based on grain refinement.

[0042] The specific steps of step 3 are as follows:

[0043] 3.1) Polish the Ti6Al4V substrate until a distinct metallic luster appears on the surface of the Ti6Al4V substrate, and then clean it with alcohol to remove the oxide film on the surface of the Ti6Al4V substrate.

[0044] 3.2) Place the polished Ti6Al4V substrate into the additive molding cavity, and place a layer of fireproof cotton under the Ti6Al4V substrate to reduce the thermal diffusion rate of the Ti6Al4V substrate.

[0045] 3.3) The surface of the Ti6Al4V substrate was pre-scanned multiple times using a laser heat source;

[0046] 3.4) Set the additive manufacturing process parameters for the additive manufacturing equipment, and preset the movement trajectory of the laser nozzle of the additive manufacturing equipment and the number of ceramic layers to be prepared;

[0047] 3.5) Starting from the current position of the laser head of the additive manufacturing equipment, start the laser and powder feeding device of the additive manufacturing equipment; the laser beam is output through the laser head and irradiates the surface of the Ti6Al4V substrate, while the dried raw material powder is transported to the Ti6Al4V surface through a coaxial powder feeding method. The laser heats the raw material powder to above 2700℃ (zirconia melting point), forming a stable molten pool on the Ti6Al4V surface, which gradually extends as the laser head moves along the preset trajectory; after completing the preset trajectory, the laser beam irradiation is stopped, the temperature of the melt in the molten pool drops below 2700℃ and solidifies, forming the first layer of reinforced zirconia ceramic;

[0048] 3.6) Repeat step 3.5) according to the set number of layers until a reinforced zirconia ceramic product with the preset number of layers is prepared.

[0049] The additive manufacturing process parameters set for the additive manufacturing equipment in step 3.4) include: laser power of 300-500W, laser scanning speed of 350-600mm / min, single layer thickness of 0.3-0.5mm, and powder feeding rate of 0.8-1.2rpm.

[0050] Example 1

[0051] A laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement includes the following steps:

[0052] Step 1: Weigh out 7 wt% alumina ceramic powder and 93 wt% yttrium oxide-stabilized zirconia ceramic powder (where the yttrium oxide content accounts for 5.6 wt% of the sum of the yttrium oxide and zirconia contents) by weight percentage.

[0053] Step 2: Mix the weighed yttrium-stabilized zirconia ceramic powder and alumina ceramic powder thoroughly for more than 6 hours. Then, place the mixed powder in a drying oven and dry it at 100°C for 4 hours to obtain dried raw material powder, which is then placed in the powder feeding device of the additive molding equipment for later use.

[0054] Step 3: Additively shape zirconia ceramics using directional energy deposition technology to complete the preparation of grain-refined reinforced zirconia ceramics, as detailed below:

[0055] 3.1) Polish the Ti6Al4V substrate until a distinct metallic luster appears on the surface of the Ti6Al4V substrate, then clean it with alcohol to remove the oxide film on the surface of the Ti6Al4V substrate, while improving the coupling efficiency between the Ti6Al4V substrate material and the laser.

[0056] 3.2) Place the polished Ti6Al4V substrate into the additive molding cavity, and place fireproof cotton under the Ti6Al4V substrate to reduce the thermal diffusion rate of the Ti6Al4V substrate.

[0057] 3.3) Use a laser heat source to perform multiple pre-scans on the surface of the Ti6Al4V substrate to increase the substrate temperature, thereby reducing the thermal stress during the zirconia forming process;

[0058] 3.4) Set the additive manufacturing process parameters for the additive manufacturing equipment, and preset the moving trajectory of the laser nozzle of the additive manufacturing equipment and the number of ceramic layers to be prepared; the process parameters include laser power, laser scanning speed, layer thickness, and powder feeding tray rotation speed, including: laser power of 350W, laser scanning speed of 500mm / min, single layer thickness of 0.3mm, and powder feeding rate of 0.8rpm;

[0059] 3.5) Starting from the current position of the laser head of the additive manufacturing equipment, start the laser and powder feeding device of the additive manufacturing equipment; the laser beam is output through the laser head and irradiates the surface of the Ti6Al4V substrate, while the dried raw material powder is transported to the Ti6Al4V surface through a coaxial powder feeding method. The laser heats the raw material powder to above 2700℃ (zirconia melting point), forming a stable molten pool on the Ti6Al4V surface, which gradually extends as the laser head moves along the preset trajectory; after completing the preset trajectory, the laser beam irradiation is stopped, the temperature of the melt in the molten pool drops below 2700℃ and solidifies, forming the first layer of reinforced zirconia ceramic;

[0060] 3.6) Repeat step 3.5) according to the set number of layers until a reinforced zirconia ceramic product with the preset number of layers is prepared.

[0061] Example 2

[0062] A laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement includes the following steps:

[0063] Step 1: Weigh 6 wt% alumina ceramic powder and 94 wt% yttrium oxide-stabilized zirconia ceramic powder (the yttrium oxide content accounts for 7.4 wt% of the sum of the yttrium oxide and zirconia contents) by weight percentage.

[0064] Step 2: Mix the weighed yttrium-stabilized zirconia ceramic powder and alumina ceramic powder thoroughly for more than 7 hours. Then, place the mixed powder in a drying oven and dry it at 150°C for 3 hours to obtain dried raw material powder, which is then placed in the powder feeding device of the additive molding equipment for later use.

[0065] Step 3: Additively shape zirconia ceramics using directional energy deposition technology to complete the preparation of grain-refined reinforced zirconia ceramics, as detailed below:

[0066] 3.1) Polish the Ti6Al4V substrate until a distinct metallic luster appears on the surface of the Ti6Al4V substrate, then clean it with alcohol to remove the oxide film on the surface of the Ti6Al4V substrate, while improving the coupling efficiency between the Ti6Al4V substrate material and the laser.

[0067] 3.2) Place the polished Ti6Al4V substrate into the additive molding cavity, and place fireproof cotton under the Ti6Al4V substrate to reduce the thermal diffusion rate of the Ti6Al4V substrate.

[0068] 3.3) Use a laser heat source to perform multiple pre-scans on the surface of the Ti6Al4V substrate to increase the substrate temperature, thereby reducing the thermal stress during the zirconia forming process;

[0069] 3.4) Set the additive manufacturing process parameters for the additive manufacturing equipment, and preset the moving trajectory of the laser nozzle of the additive manufacturing equipment and the number of ceramic layers to be prepared; the process parameters include laser power, laser scanning speed, layer thickness, and powder feeding tray rotation speed, including: laser power of 400W, laser scanning speed of 500mm / min, single layer thickness of 0.4mm, and powder feeding rate of 1.0rpm;

[0070] 3.5) Starting from the current position of the laser head of the additive manufacturing equipment, start the laser and powder feeding device of the additive manufacturing equipment; the laser beam is output through the laser head and irradiates the surface of the Ti6Al4V substrate, while the dried raw material powder is transported to the Ti6Al4V surface through a coaxial powder feeding method. The laser heats the raw material powder to above 2700℃ (zirconia melting point), forming a stable molten pool on the Ti6Al4V surface, which gradually extends as the laser head moves along the preset trajectory; after completing the preset trajectory, the laser beam irradiation is stopped, the temperature of the melt in the molten pool drops below 2700℃ and solidifies, forming the first layer of reinforced zirconia ceramic;

[0071] 3.6) Repeat step 3.5) according to the set number of layers until a reinforced zirconia ceramic product with the preset number of layers is prepared.

[0072] Example 3

[0073] A laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement includes the following steps:

[0074] Step 1: Weigh out 5 wt% alumina ceramic powder and 95 wt% yttrium oxide-stabilized zirconia ceramic powder (the yttrium oxide content accounts for 10.8 wt% of the sum of the yttrium oxide and zirconia contents) by weight percentage.

[0075] Step 2: Mix the weighed yttrium-stabilized zirconia ceramic powder and alumina ceramic powder thoroughly for more than 8 hours. Then, place the mixed powder in a drying oven and dry it at 200°C for 2 hours to obtain dried raw material powder, which is then placed in the powder feeding device of the additive molding equipment for later use.

[0076] Step 3: Additively shape zirconia ceramics using directional energy deposition technology to complete the preparation of grain-refined reinforced zirconia ceramics, as detailed below:

[0077] 3.1) Polish the Ti6Al4V substrate until a distinct metallic luster appears on the surface of the Ti6Al4V substrate, then clean it with alcohol to remove the oxide film on the surface of the Ti6Al4V substrate, while improving the coupling efficiency between the Ti6Al4V substrate material and the laser.

[0078] 3.2) Place the polished Ti6Al4V substrate into the additive molding cavity, and place fireproof cotton under the Ti6Al4V substrate to reduce the thermal diffusion rate of the Ti6Al4V substrate.

[0079] 3.3) Use a laser heat source to perform multiple pre-scans on the surface of the Ti6Al4V substrate to increase the substrate temperature, thereby reducing the thermal stress during the zirconia forming process;

[0080] 3.4) Set the additive manufacturing process parameters for the additive manufacturing equipment, and preset the moving trajectory of the laser nozzle of the additive manufacturing equipment and the number of ceramic layers to be prepared; the process parameters include laser power, laser scanning speed, layer thickness, and powder feeding tray rotation speed, including: laser power of 450W, laser scanning speed of 600mm / min, single layer thickness of 0.5mm, and powder feeding rate of 1.2rpm;

[0081] 3.5) Starting from the current position of the laser head of the additive manufacturing equipment, start the laser and powder feeding device of the additive manufacturing equipment; the laser beam is output through the laser head and irradiates the surface of the Ti6Al4V substrate, while the dried raw material powder is transported to the Ti6Al4V surface through a coaxial powder feeding method. The laser heats the raw material powder to above 2700℃ (zirconia melting point), forming a stable molten pool on the Ti6Al4V surface, which gradually extends as the laser head moves along the preset trajectory; after completing the preset trajectory, the laser beam irradiation is stopped, the temperature of the melt in the molten pool drops below 2700℃ and solidifies, forming the first layer of reinforced zirconia ceramic;

[0082] 3.6) Repeat step 3.5) according to the set number of layers until a reinforced zirconia ceramic product with the preset number of layers is prepared.

[0083] By selecting the above-mentioned laser additive manufacturing forming parameters, it is possible to ensure that the powder ceramic raw material is completely melted, while the forming accuracy of zirconia ceramic is good.

[0084] Figure 4 The cross-sectional morphology of the example (with 5 wt% alumina addition) and pure zirconia ceramics manufactured by laser additive manufacturing were compared using optical microscopy. It was found that the pure zirconia ceramic sample contained coarse columnar crystals with an average grain size of approximately 110 μm. Microcracks induced by thermal stress easily propagated along the printing direction at the grain boundaries of these columnar crystals, eventually forming through-cracks. Adding 5 wt% alumina solute to the zirconia ceramic during re-forming resulted in the complete disappearance of these through-cracks. Therefore, the addition of alumina solute has a significant defect suppression effect.

[0085] Figure 5Using SEM microscopy, it was found that the microstructure of the ceramic sample in the example (5wt% alumina added) was a fine equiaxed crystal structure with an average grain size of about 15μm. Therefore, the addition of alumina solute has a significant grain refining effect.

[0086] Furthermore, the hardness and fracture toughness of the example (5 wt% alumina addition) and the laser additive manufacturing of pure zirconia ceramics were tested using a microindenter. By obtaining the average values ​​from multiple measurements, it was found that the addition of alumina solute improved the mechanical properties; specifically, the average hardness increased from 13.47 GPa to 14.33 GPa, and the fracture toughness increased from 2.88 MPa. 1 / 2 Increased to 4.07 MPa.m 1 / 2 Therefore, adding alumina solute has a significant performance-enhancing effect.

[0087] In summary, the embodiments demonstrate that the grain refinement method proposed in this invention can effectively suppress defect formation in laser additively formed zirconia and improve its mechanical properties.

[0088] 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 therein. Such modifications or substitutions 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 laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement, characterized in that, The specific steps include: Step 1: Weigh 5-7 wt% alumina ceramic powder and 93-95 wt% yttrium oxide-stabilized zirconia ceramic powder by weight percentage, wherein the yttrium oxide content accounts for 5-11 wt% of the sum of the yttrium oxide and zirconia contents, and the particle size of the yttrium oxide-stabilized zirconia ceramic powder and the alumina ceramic powder are both 50-120 μm. Step 2: Mix the weighed yttrium-stabilized zirconia ceramic powder and alumina ceramic powder thoroughly for more than 5 hours, and then dry the mixed powder at 100-200℃ for 2-4 hours to obtain dried raw material powder for later use. Step 3: Laser additive manufacturing of zirconia ceramics using directional energy deposition (OED) technology, specifically including: polishing the Ti6Al4V substrate until a distinct metallic luster appears on the surface, then cleaning with alcohol to remove the oxide film on the Ti6Al4V substrate surface; placing the polished Ti6Al4V substrate into the additive manufacturing cavity, and placing a layer of fireproof cotton under the Ti6Al4V substrate to reduce the thermal diffusion rate of the Ti6Al4V substrate; performing multiple pre-scans on the surface of the Ti6Al4V substrate using a laser heat source; setting the additive manufacturing process parameters for the additive manufacturing equipment, and preset the movement trajectory of the laser nozzle of the additive manufacturing equipment and the number of ceramic layers to be prepared; from the additive manufacturing process... Starting from the current position of the laser head in the forming equipment, the laser and powder feeding device of the additive manufacturing equipment are activated. The laser beam is output through the laser head and irradiates the surface of the Ti6Al4V substrate. At the same time, the dried raw material powder is transported to the Ti6Al4V surface through a coaxial powder feeding method. The laser heats the raw material powder to above 2700°C, forming a stable molten pool on the Ti6Al4V surface. As the laser head moves along the preset trajectory, the molten pool gradually extends. After completing the preset trajectory, the laser beam irradiation is stopped, and the temperature of the melt in the molten pool drops below 2700°C and solidifies, forming the first layer of reinforced zirconia ceramic. The above process is repeated according to the set number of layers until a reinforced zirconia ceramic product with the preset number of layers is produced. The additive manufacturing process parameters include: laser power of 300-500 W, laser scanning speed of 350-600 mm / min, single-layer thickness of 0.3-0.5 mm, and powder feeding rate of 0.8-1.2 rpm.

2. The laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement according to claim 1, characterized in that, In the yttrium oxide-stabilized zirconia ceramic powder, the sum of the contents of yttrium oxide and zirconia is 99.9 wt%-99.99 wt%.

3. The laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement according to claim 1, characterized in that, The alumina purity in the alumina ceramic powder is 99.9 wt%-99.99 wt%.

4. The laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement according to claim 1, characterized in that, In step 1, 5 wt% alumina ceramic powder and 95 wt% yttrium oxide-stabilized zirconia ceramic powder are weighed.

5. The laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement according to claim 1, characterized in that, In step 2, the yttrium-stabilized zirconia ceramic powder and alumina ceramic powder are thoroughly mixed for more than 8 hours and then dried at 200°C for 2 hours.

6. The laser additive manufacturing method for strengthening zirconia ceramics based on grain refinement according to claim 1, characterized in that, The laser power is 450 W, the laser scanning speed is 600 mm / min, the single-layer thickness is 0.5 mm, and the powder feeding rate is 1.2 rpm.

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