Gradient silicon nitride ceramic femoral head prosthesis and preparation method

Abstract

This invention provides a gradient silicon nitride ceramic femoral head prosthesis and its preparation method, relating to the technical fields of clinical medicine and biomaterials. The femoral head prosthesis is prepared from 88-94 parts of silicon nitride powder, 4-12 parts of sintering aid, 5-20 parts of tungsten carbide titanium, and 0-30 parts of pore-forming agent, wherein the pore-forming agent cannot be 0 parts. The gradient silicon nitride ceramic femoral head prosthesis of this invention retains the advantages of silicon nitride ceramics—low wear, low friction, high strength, high fracture toughness, and good chemical stability—at the interface between the femoral head prosthesis and the liner, while reducing wear on the titanium alloy femoral stem cone caused by the large hardness difference between the femoral head prosthesis and the liner. This reduces the incidence of organ toxicity, periprosthetic osteolysis, and aseptic loosening caused by metal wear debris, improves the survival rate of the femoral head prosthesis and the femoral stem cone, reduces the revision rate of replacement surgery, and saves patients' treatment costs.

Description

Technical Field

[0001] This invention relates to the technical field of clinical medicine and biomaterials, and in particular to a gradient silicon nitride ceramic femoral head prosthesis and its preparation method, for use in artificial hip replacement surgery. Background Technology

[0002] Total hip arthroplasty is widely recognized as one of the most successful surgical interventions to date, and over the past 100 years, artificial hip prostheses have undergone continuous development and advancement. Initially, the first and second generation femoral head prostheses were integrated with the stem. With the invention of the "Mohr's taper," starting with the third generation of femoral head prostheses, the femoral head and femoral stem taper were assembled separately. Since then, the taper press-fit fixation design has become the mainstream design for artificial prostheses. This design effectively solves the problems of large surgical incisions, difficult prosthesis installation, long operation time, and significant blood loss in total hip arthroplasty. Moreover, surgeons can choose different materials and sizes of femurs during the operation according to the patient's actual condition.

[0003] In addition, the materials of femoral head prostheses have been continuously improved and developed, from metal ball heads to silicon nitride ceramic ball heads. The hardness of femoral head prostheses has been continuously improved, the coefficient of friction has been continuously reduced, significantly reducing postoperative complications and lowering the revision rate.

[0004] Although the tapered press-fit design of the femoral head and prosthesis stem is very successful, some potential problems still exist. Among these, fretting and corrosion at the tapered connection are the most serious. During walking and activity, the femoral head and prosthesis connection bear enormous, cyclical loads, leading to extremely small relative movements between them. This fretting constantly rubs and damages the protective layer of the metal surface, producing metal debris. The wear between the ceramic ball head and the metal femoral stem, two materials with a significant difference in hardness, is particularly noticeable. Furthermore, the femoral prosthesis is constantly exposed to corrosive bodily fluids, inevitably generating metal ions and corrosion particles. This causes local tissue reactions and systemic metal ion toxicity, leading to periprosthetic osteolysis, inflammatory pseudotumor formation, and ultimately, pain and prosthesis loosening.

[0005] Chinese patent CN118459229A discloses a method for preparing orthopedic silicon nitride ceramics. This method creatively introduces one or more sintering aids and a second reinforcing phase, selected from Y2O3, MgO, Al2O3, Yb2O3, Nd2O3, Eu2O3, La2O3, Sm2O3, and CeO, into silicon nitride. Through a preparation process including photocuring, low-temperature debinding, and high-temperature sintering, a reinforcement is formed that is strengthened in three dimensions: point, line, and surface, promoting a complete phase transformation of silicon nitride grains. However, the prepared ceramics have low density, high cost of rare earth oxides, and uneven distribution of the reinforcing phase in the ceramics, resulting in uneven wear performance on the ceramic surface and failing to overcome the technical defects caused by wear problems.

[0006] Chinese patent CN118271072A discloses a method for preparing ceramic artificial hip joints, the main component of which is alumina instead of silicon nitride, and the ground alumina powder includes nano-alumina, nano-zirconia, alumina plate crystals, and strontium aluminate plate crystals. Obviously, the composition is relatively complex, and the control of crystal structure and its size and morphology is costly and inefficient. Furthermore, the subsequent addition of activators and binders for cold pressing and sintering cannot synergistically improve the density and wear resistance of the product.

[0007] Chinese patent CN115196973A discloses a multilayer silicon nitride ceramic implant and its manufacturing method, which includes a core and a shell surrounding the core. Obviously, it does not consider the intermediate layer structure between the core and the shell and its function; and the only difference between the core and the shell is the choice of additives. From its technical solution, the hardness of the first additive in the shell is generally lower than that of the second additive in the core. If applied to artificial hip replacement surgery, it does not meet the wear performance requirements of femoral head prostheses. Summary of the Invention

[0008] The main objective of this invention is to provide a graded silicon nitride ceramic femoral head prosthesis and its preparation method for total hip replacement surgery, in order to solve the unavoidable wear and metal debris generation between current silicon nitride ceramic femoral head prostheses and metal femoral stem prostheses, thereby reducing the incidence of systemic toxicity, local inflammatory reactions, periprosthetic osteolysis and aseptic loosening caused by metal ions, and thus improving the survival rate of the prosthesis.

[0009] A gradient silicon nitride ceramic femoral head prosthesis is prepared from the following raw materials in parts by weight: 88-94 parts of silicon nitride powder, 4-12 parts of sintering aid, 5-20 parts of tungsten carbide titanium, and 0-30 parts of pore-forming agent, wherein the pore-forming agent cannot be 0 parts.

[0010] Optionally, the sintering aid is selected from two or a combination of alumina, yttrium oxide, magnesium oxide, cerium oxide, silicon oxide, lanthanum oxide, and calcium oxide.

[0011] Optionally, the pore-forming agent is selected from one or a combination of polystyrene (PS), polymethyl methacrylate (PMMA), soluble starch, toner, graphite, ammonium carbonate, and ammonium bicarbonate.

[0012] A method for preparing a gradient silicon nitride ceramic femoral head prosthesis, comprising the following steps:

[0013] S1. Raw material weighing: Weigh 88-94 parts of silicon nitride powder, 4-12 parts of sintering aid, 5-20 parts of tungsten titanium carbide and 0-30 parts of pore-forming agent according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0014] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 3 to 4 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0015] S3. Green body preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a special hemispherical mold by distributing the 3 to 4 layers of powder of S2 layer by layer according to their hardness, using a pre-forming core mold to obtain a mold containing silicon nitride ceramic green body.

[0016] S4. Cold isostatic pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and isotropic pressure is applied through a liquid medium to obtain a silicon nitride ceramic preform with relatively dense structure and certain strength.

[0017] S5, Gas pressure sintering + hot isostatic pressing sintering: The silicon nitride ceramic preform of S4 is densified by gas pressure sintering and hot isostatic pressing sintering in sequence to obtain a porous silicon nitride ceramic material with a regular pore structure with multiple gradients.

[0018] Optionally, the particle size distribution of the silicon nitride powder in S1 ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.4-0.7μm, the particle size of tungsten carbide titanium is controlled in the range of 0.6-1.5μm, and the particle size of the pore-forming agent is controlled in the range of 10-120μm.

[0019] Optionally, in S2, the stirring speed for mixing is 250-500 r / min, and the stirring time is 2-5 h; the grinding balls in the ball mill are made of silicon nitride with a diameter of 3-8 mm, the ball-to-material ratio is 2:1-4:1, the ball milling speed is 150-350 r / min, and the ball milling time is 10-24 h; the drying temperature is 65-80℃, and the drying time is 6-10 h; the sieve mesh size is 100-300 μm, and the average particle size of the silicon nitride ceramic composite powder is 50-100 μm.

[0020] Optionally, in S2, the three layers are an outer composite powder, a middle composite powder, and an inner composite powder, and the four layers are an outer composite powder, a second outer composite powder, a second inner composite powder, and an inner composite powder. The outer composite powder is composed of silicon nitride powder, sintering aid, and tungsten carbide titanium. The second outer composite powder, the second inner composite powder, and the inner composite powder, or the middle composite powder and the inner composite powder, are composed of silicon nitride powder, sintering aid, and pore-forming agent, with the content of pore-forming agent increasing towards the inner layer. In S3, the size of the hemispherical mold is 26-45mm, and the density of the silicon nitride ceramic green body is 45-65%.

[0021] Optionally, the hardness of the 3 to 4 layers of powder in S3 is distributed layer by layer in a special hemispherical mold for preliminary shaping. Specifically, in the special hemispherical mold, the outer layer of composite powder is first filled in, flattened, and a certain pressure is applied with the pre-formed core mold to make the composite powder initially shaped. Then, the core mold is carefully removed, and the above steps are repeated to fill in the second outer layer, the second inner layer and the inner layer of composite powder in sequence.

[0022] Optionally, the isotropic pressure in S4 is 50-300 MPa, the density of the silicon nitride ceramic preform is 55-80%, and the strength is 15-40 MPa.

[0023] Optionally, in S5, gas pressure sintering uses an Ar or N2 atmosphere of 0.5-1 MPa, a heating rate of 0.5-2℃ / min, a sintering temperature of 1650-1840℃, and a holding time of 10-360 min; hot isostatic pressing sintering uses an Ar or N2 atmosphere of 150-200 MPa or a mixture of the two, a heating rate of 1-4℃ / min, a sintering temperature of 1600-1700℃, and a holding time of 2-3 h.

[0024] Optionally, the gas pressure sintering in S5 is divided into three stages with different heating rates, and the heating rate gradually increases as the stages progress.

[0025] Optionally, the porous silicon nitride ceramic material with a regular pore structure having multiple gradients in S5 is subjected to one or a combination of the following post-processing operations: confirming gradient integrity, identifying internal defects, roughing, precision grinding, polishing, cleaning, and inspection.

[0026] Optionally, when the spur of the porous silicon nitride ceramic material with a regular pore structure of three layers in S5 is located in the outer layer, the hardness is 1500-1632 HV, the density is 97-99%, the porosity is 1-3%, the flexural strength is 1100-1250 MPa, and the fracture toughness is 7-8 MPa·m. 1 / 2 The coefficient of friction is 0.02-0.05, and the wear rate is 1.5-3mm. 3 / N·m; When the prosthesis is located in the intermediate layer, the hardness is 600-900 HV, the density is 70-90%, the porosity is 10-30%, the flexural strength is 500-700 MPa, and the fracture toughness is 4.5-6 MPa·m. 1 / 2 When the implant is located in the inner layer, the hardness is 200-500 HV, the density is 60-75%, the porosity is 25-40%, the flexural strength is 180-350 MPa, and the fracture toughness is 3.5-4 MPa·m. 1 / 2 ;

[0027] When the spur is located in the outer layer of a porous silicon nitride ceramic material with a regular pore structure exhibiting a four-layer gradient, the hardness is 1500-1632 HV, the density is 97-99%, the porosity is 1-3%, the flexural strength is 1100-1250 MPa, and the fracture toughness is 7-8 MPa·m. 1 / 2 The coefficient of friction is 0.02-0.05, and the wear rate is 1.5-3mm. 3 / N·m; When the prosthesis is located in the subouter layer, the hardness is 1000-1200 HV, the density is 85-91%, the porosity is 9-15%, the flexural strength is 800-1000 MPa, and the fracture toughness is 6-7 MPa·m. 1 / 2 When the implant is located in the subinner layer, the hardness is 500-700 HV, the density is 70-82%, the porosity is 18-30%, the flexural strength is 400-600 MPa, and the fracture toughness is 4-6.5 MPa·m. 1 / 2 When the implant is located in the inner layer, the hardness is 200-500 HV, the density is 60-75%, the porosity is 25-40%, the flexural strength is 180-350 MPa, and the fracture toughness is 3.5-4 MPa·m. 1 / 2 .

[0028] Technical principle of the invention:

[0029] Gradient silicon nitride ceramic femoral head prostheses have two contact interfaces: a "hard-to-hard" external friction interface between the femoral head prosthesis and the liner, and a "soft-to-soft" internal friction interface between the femoral head prosthesis and the titanium alloy femoral stem prosthesis. Since hip joint movement primarily occurs between the femoral head prosthesis and the liner, this interface needs to possess characteristics of low friction, low wear, and high hardness. A silicon nitride ceramic material with a Vickers hardness of 1326-1632 HV is used at the contact interface between the femoral head prosthesis and the liner to achieve a "hard-to-hard" external friction interface. The Vickers hardness of the titanium alloy femoral stem is 200-500 HV, while the hardness of ceramic is much greater than that of the titanium alloy femoral stem. Therefore, a silicon nitride ceramic material with a Vickers hardness of 200-500 HV is designed at the contact interface between the femoral head prosthesis and the titanium alloy femoral stem prosthesis, matching or slightly lowering its hardness to achieve a "soft-to-soft" internal friction interface, thereby reducing wear on the titanium alloy femoral stem. The hardness of silicon nitride ceramic femoral head prostheses decreases gradually from the outside to the inside.

[0030] By using dry pressing and lamination techniques, the proportions of the manufacturing materials are gradually and proportionally changed from the outside to the inside. This mainly involves gradually reducing the proportions of yttrium oxide, alumina, and titanium tungsten carbide as the depth increases, while increasing the proportion of nitriding. This achieves a gradient decrease in the contact voltage of the silicon nitride ceramic femoral head prosthesis from 1326-1632 HV at the interface with the liner to 200-500 HV at the interface with the titanium alloy femoral stem prosthesis.

[0031] The above technical solution has at least the following advantages compared with the existing technology:

[0032] The present invention proposes a gradient silicon nitride ceramic femoral head prosthesis and its preparation method, which can solve the technical problems existing in the prior art, such as unavoidable wear and metal debris generation between silicon nitride ceramic femoral head prostheses and metal femoral stem prostheses, systemic toxicity caused by metal ions, local inflammatory reactions, periprosthetic osteolysis, and aseptic loosening.

[0033] This invention utilizes a gradient hardness structure design for the femoral head prosthesis, formed using silicon nitride powder, sintering aids, tungsten titanium carbide, and pore-forming agents. This results in a gradient silicon nitride ceramic femoral head prosthesis that retains the advantages of silicon nitride ceramics—low wear, low friction, high strength, high fracture toughness, and good chemical stability—at the interface between the femoral head prosthesis and the liner, while reducing wear on the titanium alloy femoral stem cone caused by the significant hardness difference between the femoral head prosthesis and the liner.

[0034] This invention involves initially forming a silicon nitride ceramic green body by distributing 3 to 4 layers of powder with progressively varying hardness in a dedicated hemispherical mold. This mold provides physical support and shape protection for the green body before it gains sufficient strength, ensuring that the multi-layered gradient structure does not shift or deform during handling, cold isostatic pressing, and the initial stage of sintering. Simultaneously, the mold acts as a pressure transmission medium, ensuring that isotropic pressure is applied uniformly to the green body during cold isostatic pressing, resulting in a preform with uniform density and good interlayer bonding. This provides a guarantee for the subsequent sintering preparation of a structurally complete and gradually changing graded silicon nitride ceramic femoral head prosthesis.

[0035] This invention applies isotropic pressure through a liquid medium to obtain a relatively dense silicon nitride ceramic preform with a certain strength, enabling the obtained silicon nitride ceramic preform to have uniformly increased density and mechanical strength. The core beneficial effects of this step are: First, it eliminates the internal density gradient of the green body caused by differences in powder characteristics and multilayer structure, providing a high-quality green body with uniform shrinkage and low defect rate for subsequent sintering; second, it significantly enhances the 'green body strength' of the green body, ensuring the structural integrity of the green body during the debinding and early sintering stages; finally, the uniform and dense preform structure lays an ideal foundation for subsequent gas pressure sintering and hot isostatic pressing sintering, allowing the outer layer to achieve near-full densification to obtain ultra-high hardness and wear resistance, while the inner layer can form a porous structure with controllable pore size and distribution supported by a dense ceramic skeleton, thereby synergistically ensuring the reliability and reproducibility of the overall performance of the gradient silicon nitride ceramic femoral head prosthesis.

[0036] This invention enables the complete densification and microstructure optimization of gradient silicon nitride ceramic preforms through gas pressure sintering and hot isostatic pressing. Specifically, gas pressure sintering, while suppressing silicon nitride decomposition, utilizes a liquid phase sintering aid to densify the material matrix and initially form a porous layer framework structure. Subsequent hot isostatic pressing eliminates all residual closed pores under ultra-high pressure, achieving near-theoretical density in the outer layer, thus obtaining a friction surface with ultra-high hardness and ultra-low wear rate. Simultaneously, hot isostatic pressing strengthens the porous inner layer ceramic framework under high temperature and pressure, significantly improving the toughness and load-bearing strength of the porous structure while maintaining its designed porosity to match the hardness of the metal shank cone. The synergistic effect of the two sintering processes ultimately ensures a continuous gradual change in hardness from the outside to the inside of the gradient prosthesis, strong interlayer bonding, and a synergistic improvement in overall mechanical properties and service reliability.

[0037] Therefore, this invention utilizes dry pressing and lamination technology to achieve a gradient decrease in hardness of the silicon nitride ceramic ball head from the outside to the inside by gradually changing the ratio of additives in the silicon nitride ceramic, thereby manufacturing a gradient silicon nitride ceramic femoral head prosthesis for artificial hip replacement surgery.

[0038] In summary, compared with traditional femoral head prosthesis technology, the method of this invention prepares a gradient silicon nitride ceramic femoral head prosthesis through the preparation of multi-layer silicon nitride ceramic composite powder, a mold containing silicon nitride ceramic green bodies, and cold isostatic pressing and gas pressure sintering + hot isostatic pressing under liquid medium. The resulting gradient silicon nitride ceramic femoral head prosthesis exhibits synergistic improvements in density, hardness, flexural strength, fracture toughness, and wear resistance, achieving a shift from "hard against soft" to "soft against soft." This reduces the incidence of organ toxicity, periprosthetic osteolysis, and aseptic loosening caused by metal wear debris, improves the survival rate of silicon nitride ceramic femoral head prostheses and femoral stem cones, reduces the revision rate of total hip arthroplasty, saves patients' treatment costs, and facilitates large-scale industrial production and application. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the hardness gradient of a gradient silicon nitride ceramic femoral head prosthesis according to the present invention. Detailed Implementation

[0041] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0042] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0043] In the embodiments of the present invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction is not emphasized, their intended meanings are consistent.

[0044] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0045] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0046] A gradient silicon nitride ceramic femoral head prosthesis is prepared from the following raw materials in parts by weight: 88-94 parts of silicon nitride powder, 4-12 parts of sintering aid, 5-20 parts of tungsten carbide titanium, and 0-30 parts of pore-forming agent, wherein the pore-forming agent cannot be 0 parts.

[0047] Specifically, the sintering aid is selected from two or a combination of alumina, yttrium oxide, magnesium oxide, cerium oxide, silicon oxide, lanthanum oxide, and calcium oxide.

[0048] Specifically, the pore-forming agent is selected from one or a combination of polystyrene (PS), polymethyl methacrylate (PMMA), soluble starch, toner, graphite, ammonium carbonate, and ammonium bicarbonate.

[0049] A method for preparing a gradient silicon nitride ceramic femoral head prosthesis, comprising the following steps:

[0050] S1. Raw material weighing: Weigh 88-94 parts of silicon nitride powder, 4-12 parts of sintering aid, 5-20 parts of tungsten titanium carbide and 0-30 parts of pore-forming agent according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0051] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 3 to 4 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0052] S3. Green body preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a special hemispherical mold by distributing the 3 to 4 layers of powder of S2 layer by layer according to their hardness, using a pre-forming core mold to obtain a mold containing silicon nitride ceramic green body.

[0053] S4. Cold isostatic pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and isotropic pressure is applied through a liquid medium to obtain a silicon nitride ceramic preform with relatively dense structure and certain strength.

[0054] S5. Gas pressure sintering + hot isostatic pressing: The silicon nitride ceramic preform of S4 is densified by sequential gas pressure sintering and hot isostatic pressing, resulting in a porous silicon nitride ceramic material with a multi-layered gradient regular pore structure. The hardness gradient distribution of the gradient silicon nitride ceramic femoral head prosthesis is as follows: Figure 1 As shown.

[0055] Specifically, the particle size distribution of silicon nitride powder in S1 ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.4-0.7μm, the particle size of tungsten carbide titanium is controlled in the range of 0.6-1.5μm, and the particle size of the pore-forming agent is controlled in the range of 10-120μm.

[0056] Specifically, in S2, the stirring speed for mixing is 250-500 r / min, and the stirring time is 2-5 h; the grinding balls in the ball mill are made of silicon nitride with a diameter of 3-8 mm, the ball-to-material ratio is 2:1-4:1, the ball milling speed is 150-350 r / min, and the ball milling time is 10-24 h; the drying temperature is 65-80℃, and the drying time is 6-10 h; the sieve mesh size is 100-300 μm, and the average particle size of the silicon nitride ceramic composite powder is 50-100 μm.

[0057] Specifically, in S2, the three layers are an outer composite powder, a middle composite powder, and an inner composite powder, while the four layers are an outer composite powder, a second outer composite powder, a second inner composite powder, and an inner composite powder. The outer composite powder is composed of silicon nitride powder, sintering aid, and tungsten titanium carbide. The second outer composite powder, the second inner composite powder, and the inner composite powder, or the middle composite powder and the inner composite powder, are composed of silicon nitride powder, sintering aid, and pore-forming agent, with the content of pore-forming agent increasing towards the inner layer. In S3, the size of the hemispherical mold is 26-45mm, and the density of the silicon nitride ceramic green body is 45-65%.

[0058] Specifically, the initial forming of the 3 to 4 layers of powder in S3, with the hardness gradually distributed layer by layer, is carried out in a special hemispherical mold as follows: In the special hemispherical mold, the outer layer of composite powder is first filled in, flattened, and a certain pressure is applied with the pre-formed core mold to make the composite powder initially shaped; then the core mold is carefully removed, and the above steps are repeated to fill in the secondary outer layer, secondary inner layer and inner layer of composite powder in sequence.

[0059] Specifically, the isotropic pressure in S4 is 50-300 MPa, the density of the silicon nitride ceramic preform is 55-80%, and the strength is 15-40 MPa.

[0060] Specifically, in S5, gas pressure sintering uses an atmosphere of 0.5-1 MPa of Ar or N2 or a mixture of both, with a heating rate of 0.5-2℃ / min, a sintering temperature of 1650-1840℃, and a holding time of 10-360 min; hot isostatic pressing sintering uses an atmosphere of 150-200 MPa of Ar or N2, with a heating rate of 1-4℃ / min, a sintering temperature of 1600-1700℃, and a holding time of 2-3 h.

[0061] Specifically, in S5, the gas pressure sintering is divided into three stages with different heating rates. As the stages progress, the heating rate gradually increases.

[0062] Specifically, porous silicon nitride ceramic materials with a regular pore structure and multiple gradients in S5 undergo one or a combination of the following post-processing operations: confirming gradient integrity, identifying internal defects, roughing, precision grinding, polishing, cleaning, and inspection.

[0063] Specifically, in S5, when the spur of the porous silicon nitride ceramic material with a regular pore structure having a three-layer gradient is located in the outer layer, the hardness is 1500-1632 HV, the density is 97-99%, the porosity is 1-3%, the flexural strength is 1100-1250 MPa, and the fracture toughness is 7-8 MPa·m. 1 / 2 The coefficient of friction is 0.02-0.05, and the wear rate is 1.5-3mm. 3 / N·m; When the prosthesis is located in the intermediate layer, the hardness is 600-900 HV, the density is 70-90%, the porosity is 10-30%, the flexural strength is 500-700 MPa, and the fracture toughness is 4.5-6 MPa·m. 1 / 2 When the implant is located in the inner layer, the hardness is 200-500 HV, the density is 60-75%, the porosity is 25-40%, the flexural strength is 180-350 MPa, and the fracture toughness is 3.5-4 MPa·m. 1 / 2 ;

[0064] When the spur is located in the outer layer of a porous silicon nitride ceramic material with a regular pore structure exhibiting a four-layer gradient, the hardness is 1500-1632 HV, the density is 97-99%, the porosity is 1-3%, the flexural strength is 1100-1250 MPa, and the fracture toughness is 7-8 MPa·m. 1 / 2 The coefficient of friction is 0.02-0.05, and the wear rate is 1.5-3mm. 3 / N·m; When the prosthesis is located in the subouter layer, the hardness is 1000-1200 HV, the density is 85-91%, the porosity is 9-15%, the flexural strength is 800-1000 MPa, and the fracture toughness is 6-7 MPa·m. 1 / 2 When the implant is located in the subinner layer, the hardness is 500-700 HV, the density is 70-82%, the porosity is 18-30%, the flexural strength is 400-600 MPa, and the fracture toughness is 4-6.5 MPa·m. 1 / 2 When the implant is located in the inner layer, the hardness is 200-500 HV, the density is 60-75%, the porosity is 25-40%, the flexural strength is 180-350 MPa, and the fracture toughness is 3.5-4 MPa·m. 1 / 2 .

[0065] Example 1

[0066] This embodiment provides a method for preparing a gradient silicon nitride ceramic femoral head prosthesis, the specific steps of which are as follows:

[0067] S1. Raw material weighing: Weigh 91 parts of silicon nitride powder, 7 parts of sintering aid, 8 parts of tungsten carbide titanium and 18 parts of pore-forming agent (polymethyl methacrylate PMMA) according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0068] The particle size distribution of silicon nitride powder ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the specific surface area was measured to be 5.5 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.5-1.2μm, the particle size of tungsten carbide titanium is controlled in the range of 0.8-1.6μm, and the pore-forming agent PMMA is spherical micro powder with a particle size controlled in the range of 80-150μm.

[0069] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 4 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0070] The specific process parameters are as follows: the stirring speed for mixing is 350 r / min, and the stirring time is 2.5 h; the grinding balls for ball milling are silicon nitride grinding balls with a diameter of 5 mm, the ball-to-material ratio is 3:1, the ball milling speed is 220 r / min, and the ball milling time is 24 h; the drying temperature is 75℃, and the drying time is 10 h; the sieve mesh size is 200 μm, and the average particle size of the silicon nitride ceramic composite powder is 74 μm.

[0071] The four gradient components, from the outside to the inside, are as follows:

[0072] ① The outer layer is premixed with 87.5 wt% silicon nitride powder, 7.5 wt% sintering aid and 5 wt% tungsten carbide titanium, wherein the sintering aid is selected from a ternary composite system of 4.5 wt% alumina and 3 wt% yttrium oxide;

[0073] ② The outermost layer is premixed with 85 wt% silicon nitride powder, 8.5 wt% sintering aid and 6.5 wt% PMMA. The sintering aid is selected from a ternary composite system of 3.5 wt% alumina and 5 wt% yttrium oxide.

[0074] ③ The inner layer is premixed with 78 wt% silicon nitride powder, 7 wt% sintering aid and 15 wt% PMMA. The sintering aid is selected from a ternary composite system of 4 wt% alumina and 3 wt% yttrium oxide.

[0075] ④ The inner layer is premixed with 68 wt% silicon nitride powder, 6 wt% sintering aid and 26 wt% PMMA. The sintering aid is selected from a ternary composite system of 3.5 wt% alumina and 2.5 wt% yttrium oxide.

[0076] S3. Green Body Preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a dedicated hemispherical mold by distributing the four layers of powder of S2 layer by layer according to their hardness using a pre-formed core mold. First, the outer layer composite powder is filled in and leveled. A certain pressure is applied using the pre-formed core mold to initially shape the composite powder. Then, the core mold is carefully removed, and the above steps are repeated to fill in the second outer layer, second inner layer, and inner layer composite powder in sequence to obtain a mold containing a silicon nitride ceramic green body. The diameter of the hemispherical mold is 32 mm, and the density of the silicon nitride ceramic green body is 45%.

[0077] S4. Cold Isostatic Pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and an isotropic pressure of 180 MPa is applied through a liquid medium to uniformly compress each layer of powder, resulting in a relatively dense silicon nitride ceramic preform with a certain strength; the density of the silicon nitride ceramic preform is 65%, and the strength is 15 MPa.

[0078] S5. Gas Pressure Sintering + Hot Isostatic Pressing (HIP): The silicon nitride ceramic preform of S4 was densified by gas pressure sintering and hot isostatic pressing sequentially. Gas pressure sintering was carried out in a 0.8 MPa N2 atmosphere with a heating rate of 0.5 °C / min from 300 °C to 600 °C, and held for 4 hours to ensure that the pore-forming agent PMMA had sufficient time to decompose and be discharged, thus avoiding cracking or blistering of the preform. The heating rate was 1 °C / min from 600 °C to 1680 °C. Hot isostatic pressing was carried out in a 180 MPa Ar and N2 mixed atmosphere with a heating rate of 2 °C / min, a sintering temperature of 1700 °C, and a holding time of 3 hours to obtain a porous silicon nitride ceramic material with a regular pore structure of 4 layers.

[0079] The porous silicon nitride ceramic material with a regular pore structure and a four-layer gradient prepared in this embodiment, when the spur is located in the outer layer, has a hardness of 1632 HV, a density of 99.2%, a porosity of 0.8%, a flexural strength of 1150 MPa, and a fracture toughness of 7.2 MPa·m. 1 / 2 The coefficient of friction is 0.06, and the wear rate is 1.8 × 10⁻⁶. -7 mm 3 / N·m; When the prosthesis is located in the subouter layer, the hardness is 1065HV, the density is 92.5%, the porosity is 7.5%, the flexural strength is 780MPa, and the fracture toughness is 6.3MPa·m. 1 / 2When the prosthesis is located in the subinner layer, the hardness is 563 HV, the density is 81%, the porosity is 19%, the flexural strength is 480 MPa, and the fracture toughness is 5.5 MPa·m. 1 / 2 When the prosthesis is located in the inner layer, the hardness is 238 HV, the density is 68.5%, the porosity is 31.5%, the flexural strength is 220 MPa, and the fracture toughness is 4.0 MPa·m. 1 / 2 .

[0080] Example 2

[0081] This embodiment provides a method for preparing a gradient silicon nitride ceramic femoral head prosthesis, the specific steps of which are as follows:

[0082] S1. Raw material weighing: Weigh 90 parts of silicon nitride powder, 8 parts of sintering aid, 2 parts of tungsten carbide titanium and 20 parts of pore-forming agent (polymethyl methacrylate PMMA) according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0083] The particle size distribution of silicon nitride powder ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.5-1.2μm, the particle size of tungsten carbide titanium is controlled in the range of 0.8-1.6μm, and the pore-forming agent PMMA is spherical micro powder with a particle size controlled in the range of 80-150μm.

[0084] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 4 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0085] The specific process parameters are as follows: the stirring speed for mixing is 350 r / min, and the stirring time is 2.5 h; the grinding balls for ball milling are silicon nitride grinding balls with a diameter of 5 mm, the ball-to-material ratio is 3:1, the ball milling speed is 220 r / min, and the ball milling time is 24 h; the drying temperature is 75℃, and the drying time is 10 h; the sieve mesh size is 200 μm, and the average particle size of the silicon nitride ceramic composite powder is 74 μm.

[0086] The four gradient components, from the outside to the inside, are as follows:

[0087] ①The outer layer is premixed with 90.wt% silicon nitride powder, 8wt% sintering aid and 2wt% tungsten carbide titanium, wherein the sintering aid is selected from a ternary composite system of 5wt% alumina and 3wt% yttrium oxide;

[0088] ② The outermost layer is premixed with 83.5 wt% silicon nitride powder, 6.5 wt% sintering aid and 10 wt% PMMA. The sintering aid is selected from a ternary composite system of 4.5 wt% alumina and 2 wt% yttrium oxide.

[0089] ③ The inner layer is premixed with 77 wt% silicon nitride powder, 6 wt% sintering aid and 17 wt% PMMA. The sintering aid is selected from a ternary composite system of 4 wt% alumina and 2 wt% yttrium oxide.

[0090] ④ The inner layer is premixed with 67wt% silicon nitride powder, 5wt% sintering aid and 28wt% PMMA. The sintering aid is selected from a ternary composite system of 3.5wt% alumina and 1.5wt% yttrium oxide.

[0091] S3. Green Body Preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a dedicated hemispherical mold by distributing the four layers of powder of S2 layer by layer according to their hardness using a pre-formed core mold. First, the outer layer composite powder is filled in and leveled. A certain pressure is applied using the pre-formed core mold to initially shape the composite powder. Then, the core mold is carefully removed, and the above steps are repeated to fill in the second outer layer, second inner layer, and inner layer composite powder in sequence to obtain a mold containing a silicon nitride ceramic green body. The hemispherical mold has a diameter of 32 mm, and the density of the silicon nitride ceramic green body is approximately 45%.

[0092] S4. Cold Isostatic Pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and an isotropic pressure of 180 MPa is applied through a liquid medium to uniformly compress each layer of powder, resulting in a relatively dense silicon nitride ceramic preform with a certain strength; the density of the silicon nitride ceramic preform is 65%, and the strength is 15 MPa.

[0093] S5. Gas Pressure Sintering + Hot Isostatic Pressing (HIP): The silicon nitride ceramic preform of S4 was densified by gas pressure sintering and hot isostatic pressing sequentially. Gas pressure sintering was carried out in a 0.8 MPa N2 atmosphere with a heating rate of 0.6 °C / min from 350 °C to 800 °C, and held for 6 hours to ensure that the pore-forming agent PMMA had sufficient time to decompose and be discharged, thus avoiding cracking or blistering of the preform. The temperature was then increased from 800 °C to 1770 °C at a heating rate of 2 °C / min. Hot isostatic pressing was carried out in a 200 MPa Ar and N2 mixed atmosphere with a heating rate of 2 °C / min, a sintering temperature of 1670 °C, and a holding time of 4 hours to obtain a porous silicon nitride ceramic material with a regular pore structure of 4 layers.

[0094] The porous silicon nitride ceramic material with a regular pore structure and a four-layer gradient prepared in this embodiment, when the spur is located in the outer layer, has a hardness of 1608 HV, a density of 98.8%, a porosity of 1.2%, a flexural strength of 1180 MPa, and a fracture toughness of 7.5 MPa·m. 1 / 2 The coefficient of friction is 0.05, and the wear rate is 1.5 × 10⁻⁶. -7 mm 3 / N·m; When the prosthesis is located in the subouter layer, the hardness is 1171HV, the density is 91%, the porosity is 9%, the flexural strength is 850MPa, and the fracture toughness is 6.8MPa·m. 1 / 2 When the prosthesis is located in the subinner layer, the hardness is 684 HV, the density is 83.5%, the porosity is 16.5%, the flexural strength is 600 MPa, and the fracture toughness is 6.0 MPa·m. 1 / 2 When the prosthesis is located in the inner layer, the hardness is 352 HV, the density is 71%, the porosity is 29%, the flexural strength is 320 MPa, and the fracture toughness is 4.8 MPa·m. 1 / 2 .

[0095] Example 3

[0096] This embodiment provides a method for preparing a gradient silicon nitride ceramic femoral head prosthesis, the specific steps of which are as follows:

[0097] S1. Raw material weighing: Weigh 92 parts of silicon nitride powder, 6 parts of sintering aid, 2 parts of tungsten carbide titanium and 22 parts of pore-forming agent (polymethyl methacrylate PMMA) according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0098] The particle size distribution of silicon nitride powder ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.5-1.2μm, the particle size of tungsten carbide titanium is controlled in the range of 0.8-1.6μm, and the pore-forming agent PMMA is spherical micro powder with a particle size controlled in the range of 80-150μm.

[0099] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 4 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0100] The specific process parameters are as follows: the stirring speed for mixing is 350 r / min, and the stirring time is 2.5 h; the grinding balls for ball milling are silicon nitride grinding balls with a diameter of 5 mm, the ball-to-material ratio is 3:1, the ball milling speed is 220 r / min, and the ball milling time is 24 h; the drying temperature is 75℃, and the drying time is 10 h; the sieve mesh size is 200 μm, and the average particle size of the silicon nitride ceramic composite powder is 74 μm.

[0101] The four gradient components, from the outside to the inside, are as follows:

[0102] ①The outer layer is premixed with 92.wt% silicon nitride powder, 6wt% sintering aid and 2wt% tungsten carbide titanium, wherein the sintering aid is selected from a ternary composite system of 3wt% alumina and 3wt% yttrium oxide;

[0103] ② The outermost layer is premixed with 86 wt% silicon nitride powder, 9 wt% sintering aid and 5 wt% PMMA. The sintering aid is selected from a ternary composite system of 5.5 wt% alumina and 3.5 wt% yttrium oxide.

[0104] ③ The inner layer is premixed with 79 wt% silicon nitride powder, 7 wt% sintering aid and 14 wt% PMMA. The sintering aid is selected from a ternary composite system of 4.5 wt% alumina and 2.5 wt% yttrium oxide.

[0105] ④ The inner layer is premixed with 69 wt% silicon nitride powder, 6 wt% sintering aid and 25 wt% PMMA. The sintering aid is selected from a ternary composite system of 4 wt% alumina and 2 wt% yttrium oxide.

[0106] S3. Green Body Preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a dedicated hemispherical mold by distributing the four layers of powder of S2 layer by layer according to their hardness using a pre-formed core mold. First, the outer layer composite powder is filled in and leveled. A certain pressure is applied using the pre-formed core mold to initially shape the composite powder. Then, the core mold is carefully removed, and the above steps are repeated to fill in the second outer layer, second inner layer, and inner layer composite powder in sequence to obtain a mold containing a silicon nitride ceramic green body. The hemispherical mold has a diameter of 40 mm, and the density of the silicon nitride ceramic green body is 47%.

[0107] S4. Cold Isostatic Pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and an isotropic pressure of 160 MPa is applied through a liquid medium to uniformly compress each layer of powder, resulting in a relatively dense silicon nitride ceramic preform with a certain strength; the density of the silicon nitride ceramic preform is 66%, and the strength is 16 MPa.

[0108] S5. Gas Pressure Sintering + Hot Isostatic Pressing (HIP): The silicon nitride ceramic preform of S4 was densified by gas pressure sintering and hot isostatic pressing sequentially. Gas pressure sintering was carried out in a 0.9 MPa N2 atmosphere with a heating rate of 0.4 °C / min from 320 °C to 650 °C, and held for 4 hours to ensure that the pore-forming agent PMMA had sufficient time to decompose and be discharged, thus avoiding cracking or blistering of the preform. The heating rate was 2 °C / min from 650 °C to 1710 °C. Hot isostatic pressing was carried out in a 200 MPa Ar and N2 mixed atmosphere with a heating rate of 3 °C / min, a sintering temperature of 1620 °C, and a holding time of 3 hours to obtain a porous silicon nitride ceramic material with a regular pore structure of 4 layers.

[0109] The porous silicon nitride ceramic material with a regular pore structure and a four-layer gradient prepared in this embodiment, when the spur is located in the outer layer, has a hardness of 1508 HV, a density of 98.5%, a porosity of 1.5%, a flexural strength of 1050 MPa, and a fracture toughness of 6.8 MPa·m. 1 / 2 The coefficient of friction is 0.07, and the wear rate is 2.2 × 10⁻⁶. -7 mm 3 / N·m; When the prosthesis is located in the subouter layer, the hardness is 1371 HV, the density is 94%, the porosity is 6%, the flexural strength is 920 MPa, and the fracture toughness is 6.5 MPa·m. 1 / 2 When the prosthesis is located in the subinner layer, the hardness is 647 HV, the density is 82%, the porosity is 18%, the flexural strength is 580 MPa, and the fracture toughness is 5.8 MPa·m. 1 / 2 When the prosthesis is located in the inner layer, the hardness is 210 HV, the density is 66%, the porosity is 34%, the flexural strength is 200 MPa, and the fracture toughness is 3.8 MPa·m. 1 / 2 .

[0110] Example 4

[0111] This embodiment provides a method for preparing a gradient silicon nitride ceramic femoral head prosthesis, the specific steps of which are as follows:

[0112] S1. Raw material weighing: Weigh 89 parts of silicon nitride powder, 9 parts of sintering aid, 4 parts of tungsten carbide titanium and 25 parts of pore-forming agent (soluble starch) according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0113] The particle size distribution of silicon nitride powder ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.5-1.2μm, the particle size of tungsten carbide titanium is controlled in the range of 0.8-1.6μm, and the particle size of the pore-forming agent soluble starch is controlled in the range of 50-120μm.

[0114] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 3 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0115] The specific process parameters are as follows: the stirring speed for mixing is 450 r / min, and the stirring time is 2 h; the grinding balls for ball milling are silicon nitride grinding balls with a diameter of 5 mm, the ball-to-material ratio is 2:1, the ball milling speed is 300 r / min, and the ball milling time is 18 h; the drying temperature is 75℃, and the drying time is 10 h; the sieve mesh size is 200 μm, and the average particle size of the silicon nitride ceramic composite powder is 74 μm;

[0116] The three gradient components, from the outside to the inside, are as follows:

[0117] ①The outer layer is premixed with 88.wt% silicon nitride powder, 8wt% sintering aid and 4wt% tungsten carbide titanium, wherein the sintering aid is selected from a ternary composite system of 5wt% alumina and 3wt% yttrium oxide;

[0118] ②The intermediate layer is made by premixing 80wt% of silicon nitride powder, 8wt% of sintering aid and 12wt% of PMMA. The sintering aid is selected from a ternary composite system of 5wt% alumina and 3wt% yttrium oxide.

[0119] ③ The inner layer is premixed with 68 wt% silicon nitride powder, 5 wt% sintering aid and 27 wt% PMMA. The sintering aid is selected from a ternary composite system of 1 wt% alumina and 4 wt% yttrium oxide.

[0120] S3. Green Body Preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a dedicated hemispherical mold by distributing the three layers of powder of S2 layer by layer according to their hardness using a pre-formed core mold. First, the outer layer composite powder is filled in and flattened. A certain pressure is applied using the pre-formed core mold to initially shape the composite powder. Then, the core mold is carefully removed, and the above steps are repeated to fill in the second outer layer, second inner layer, and inner layer composite powder in sequence to obtain a mold containing a silicon nitride ceramic green body. The hemispherical mold has a diameter of 28 mm, and the density of the silicon nitride ceramic green body is 42%.

[0121] S4. Cold Isostatic Pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and an isotropic pressure of 220 MPa is applied through a liquid medium to uniformly compress each layer of powder, resulting in a relatively dense silicon nitride ceramic preform with a certain strength; the density of the silicon nitride ceramic preform is 70%, and the strength is 20 MPa.

[0122] S5. Gas Pressure Sintering + Hot Isostatic Pressing (HIP): The silicon nitride ceramic preform of S4 was densified by gas pressure sintering and hot isostatic pressing sequentially. Gas pressure sintering was carried out in a 0.6 MPa N2 atmosphere with a heating rate of 0.5 °C / min from 290 °C to 750 °C, and then at a heating rate of 0.7 °C / min. The temperature was held for 5 hours to ensure that the pore-forming agent PMMA had sufficient time to decompose and be discharged, avoiding cracking or blistering of the preform. The temperature was then increased from 750 °C to 1760 °C at a heating rate of 1 °C / min. Hot isostatic pressing was carried out in a 180 MPa Ar and N2 mixed atmosphere with a heating rate of 2.5 °C / min, a sintering temperature of 1620 °C, and a holding time of 4 hours to obtain a porous silicon nitride ceramic material with a regular pore structure with three layers.

[0123] The porous silicon nitride ceramic material with a regular pore structure and a three-layer gradient prepared in this embodiment, when the spur is located in the outer layer, has a hardness of 1271 HV, a density of 97%, a porosity of 3%, a flexural strength of 1007 MPa, and a fracture toughness of 6.0 MPa·m. 1 / 2 The coefficient of friction is 0.09, and the wear rate is 3.5 × 10⁻⁶. -7 mm 3 / N·m; When the prosthesis is located in the intermediate layer, the hardness is 586HV, the density is 78%, the porosity is 22%, the flexural strength is 520MPa, and the fracture toughness is 5.0MPa·m. 1 / 2 When the prosthesis is located in the inner layer, the hardness is 190 HV, the density is 60%, the porosity is 40%, the flexural strength is 180 MPa, and the fracture toughness is 3.5 MPa·m. 1 / 2 .

[0124] Example 5

[0125] This embodiment provides a method for preparing a gradient silicon nitride ceramic femoral head prosthesis, the specific steps of which are as follows:

[0126] S1. Raw material weighing: Weigh 91 parts of silicon nitride powder, 8 parts of sintering aid, 8 parts of tungsten carbide titanium and 15 parts of pore-forming agent (soluble starch) according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0127] The particle size distribution of silicon nitride powder ranges from 0.4 to 1.5 μm, D50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.3-0.8μm, the particle size of tungsten carbide titanium is controlled in the range of 0.8-1.5μm, and the particle size of the pore-forming agent soluble starch is controlled in the range of 50-150μm.

[0128] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 3 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0129] The specific process parameters are as follows: the stirring speed for mixing is 400 r / min, and the stirring time is 2 h; the grinding balls for ball milling are silicon nitride grinding balls with a diameter of 5 mm, the ball-to-material ratio is 3:1, the ball milling speed is 200 r / min, and the ball milling time is 20 h; the drying temperature is 75℃, and the drying time is 8 h; the sieve mesh size is 200 μm, and the average particle size of the silicon nitride ceramic composite powder is 80 μm;

[0130] S3. Green body preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a special hemispherical mold according to the hardness of the three layers of powder of S2, using a pre-forming core mold to obtain a mold containing silicon nitride ceramic green bodies; the diameter of the hemispherical mold is 36mm, and the density of the silicon nitride ceramic green body is about 52%;

[0131] The three layers consist of an outer composite powder, a second outer composite powder, a second inner composite powder, and an inner composite powder. The outer composite powder is composed of silicon nitride powder, sintering aid, and tungsten titanium carbide. The second outer composite powder, the second inner composite powder, and the inner composite powder, or the middle composite powder and the inner composite powder, are composed of silicon nitride powder, sintering aid, and pore-forming agent, with the content of pore-forming agent increasing towards the inner layer.

[0132] S4. Cold isostatic pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and an isotropic pressure of 180 MPa is applied through a liquid medium to obtain a relatively dense silicon nitride ceramic preform with a certain strength; the density of the silicon nitride ceramic preform is 68%, and the strength is 18 MPa.

[0133] S5. Gas pressure sintering + hot isostatic pressing (HIP): The silicon nitride ceramic preform of S4 was densified by gas pressure sintering and hot isostatic pressing sequentially. Gas pressure sintering was carried out in an Ar or N2 atmosphere of 0.8 MPa, with a heating rate of 0.6 °C / min before 300 °C, 0.9 °C / min for 3 h at 300–700 °C, and 1.5 °C / min for 90 h at 700–1750 °C. Hot isostatic pressing was carried out in an Ar or N2 atmosphere of 180 MPa, with a heating rate of 3 °C / min, a sintering temperature of 1650 °C, and a holding time of 2.5 h, resulting in a porous silicon nitride ceramic material with a regular pore structure of 3 layers.

[0134] The porous silicon nitride ceramic material with a regular pore structure and a three-layer gradient prepared in this embodiment, when the spur is located in the outer layer, has a hardness of 1520 HV, a density of 96.5%, a porosity of 3.5%, a flexural strength of 1120 MPa, and a fracture toughness of 7.1 MPa·m. 1 / 2 The coefficient of friction is 0.065, and the wear rate is 1.9 × 10⁻⁶. -7 mm 3 / N·m; When the prosthesis is located in the intermediate layer, the hardness is 720HV, the density is 86%, the porosity is 14%, the flexural strength is 620MPa, and the fracture toughness is 5.8MPa·m. 1 / 2 When the prosthesis is located in the inner layer, the hardness is 310 HV, the density is 72%, the porosity is 28%, the flexural strength is 260 MPa, and the fracture toughness is 4.3 MPa·m. 1 / 2 .

[0135] Example 6

[0136] This embodiment provides a method for preparing a gradient silicon nitride ceramic femoral head prosthesis, the specific steps of which are as follows:

[0137] S1. Raw material weighing: Weigh 93 parts of silicon nitride powder, 5 parts of sintering aid, 7 parts of tungsten titanium carbide and 15 parts of pore-forming agent (ammonium bicarbonate) according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis.

[0138] The particle size distribution of silicon nitride powder ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.2-0.7μm, the particle size of tungsten carbide titanium is controlled in the range of 1.0-2.0μm, and the pore-forming agent ammonium bicarbonate is an irregular particle with a particle size controlled in the range of 100-250μm.

[0139] S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 4 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder.

[0140] The specific process parameters are as follows: the stirring speed for mixing is 400 r / min, and the stirring time is 2 h; the grinding balls for ball milling are silicon nitride grinding balls with a diameter of 5 mm, the ball-to-material ratio is 2.5:1, the ball milling speed is 230 r / min, and the ball milling time is 18 h; the drying temperature is 60℃, and the drying time is 12 h; the sieve mesh size is 250 μm, and the average particle size of the silicon nitride ceramic composite powder is 85 μm;

[0141] S3. Green body preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a special hemispherical mold according to the hardness of the four layers of powder of S2, using a pre-forming core mold to obtain a mold containing silicon nitride ceramic green body; the size of the hemispherical mold is 34mm in diameter, and the density of the silicon nitride ceramic green body is 44%;

[0142] The four layers consist of an outer composite powder, a second outer composite powder, a second inner composite powder, and an inner composite powder. The outer composite powder is composed of silicon nitride powder, sintering aid, and tungsten titanium carbide. The second outer composite powder, the second inner composite powder, and the inner composite powder, or the middle composite powder and the inner composite powder, are composed of silicon nitride powder, sintering aid, and pore-forming agent, with the content of pore-forming agent increasing towards the inner layer.

[0143] S4. Cold isostatic pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and an isotropic pressure of 230 MPa is applied through a liquid medium to obtain a relatively dense silicon nitride ceramic preform with a certain strength; the density of the silicon nitride ceramic preform is 62%, and the strength is 12 MPa.

[0144] S5. Gas pressure sintering + hot isostatic pressing (HIP): The silicon nitride ceramic preform of S4 was densified by gas pressure sintering and hot isostatic pressing sequentially. Gas pressure sintering was carried out in an Ar atmosphere of 0.5 MPa, with a heating rate of 0.8 °C / min, a sintering temperature of 1720 °C, and a holding time of 90 min. Hot isostatic pressing was carried out in an N2 atmosphere of 160 MPa, with a heating rate of 1.5 °C / min, a sintering temperature of 1650 °C, and a holding time of 2.5 h, resulting in a porous silicon nitride ceramic material with a regular pore structure of 4 layers.

[0145] The porous silicon nitride ceramic material with a regular pore structure and a four-layer gradient prepared in this embodiment, when the spur is located in the outer layer, has a hardness of 1550 HV, a density of 98.5%, a porosity of 1.5%, a flexural strength of 1100 MPa, and a fracture toughness of 7 MPa·m.1 / 2 The coefficient of friction is 0.065, and the wear rate is 2.0 × 10⁻⁶. -7 mm 3 / N·m; When the prosthesis is located in the subouter layer, the hardness is 980HV, the density is 90%, the porosity is 10%, the flexural strength is 720MPa, and the fracture toughness is 6MPa·m. 1 / 2 When the prosthesis is located in the subinner layer, the hardness is 520 HV, the density is 78%, the porosity is 22%, the flexural strength is 450 MPa, and the fracture toughness is 5.2 MPa·m. 1 / 2 When the prosthesis is located in the inner layer, the hardness is 265 HV, the density is 64%, the porosity is 36%, the flexural strength is 250 MPa, and the fracture toughness is 4.2 MPa·m. 1 / 2 .

[0146] The present invention proposes a gradient silicon nitride ceramic femoral head prosthesis and its preparation method, which can solve the technical problems existing in the prior art, such as unavoidable wear and metal debris generation between silicon nitride ceramic femoral head prostheses and metal femoral stem prostheses, systemic toxicity caused by metal ions, local inflammatory reactions, periprosthetic osteolysis, and aseptic loosening.

[0147] This invention utilizes a gradient hardness structure design for the femoral head prosthesis, formed using silicon nitride powder, sintering aids, tungsten titanium carbide, and pore-forming agents. This results in a gradient silicon nitride ceramic femoral head prosthesis that retains the advantages of silicon nitride ceramics—low wear, low friction, high strength, high fracture toughness, and good chemical stability—at the interface between the femoral head prosthesis and the liner, while reducing wear on the titanium alloy femoral stem cone caused by the significant hardness difference between the femoral head prosthesis and the liner.

[0148] This invention involves initially forming a silicon nitride ceramic green body by distributing 3 to 4 layers of powder with progressively varying hardness in a dedicated hemispherical mold. This mold provides physical support and shape protection for the green body before it gains sufficient strength, ensuring that the multi-layered gradient structure does not shift or deform during handling, cold isostatic pressing, and the initial stage of sintering. Simultaneously, the mold acts as a pressure transmission medium, ensuring that isotropic pressure is applied uniformly to the green body during cold isostatic pressing, resulting in a preform with uniform density and good interlayer bonding. This provides a guarantee for the subsequent sintering preparation of a structurally complete and gradually changing graded silicon nitride ceramic femoral head prosthesis.

[0149] This invention applies isotropic pressure through a liquid medium to obtain a relatively dense silicon nitride ceramic preform with a certain strength, enabling the obtained silicon nitride ceramic preform to have uniformly increased density and mechanical strength. The core beneficial effects of this step are: First, it eliminates the internal density gradient of the green body caused by differences in powder characteristics and multilayer structure, providing a high-quality green body with uniform shrinkage and low defect rate for subsequent sintering; second, it significantly enhances the 'green body strength' of the green body, ensuring the structural integrity of the green body during the debinding and early sintering stages; finally, the uniform and dense preform structure lays an ideal foundation for subsequent gas pressure sintering and hot isostatic pressing sintering, allowing the outer layer to achieve near-full densification to obtain ultra-high hardness and wear resistance, while the inner layer can form a porous structure with controllable pore size and distribution supported by a dense ceramic skeleton, thereby synergistically ensuring the reliability and reproducibility of the overall performance of the gradient silicon nitride ceramic femoral head prosthesis.

[0150] This invention enables the complete densification and microstructure optimization of gradient silicon nitride ceramic preforms through gas pressure sintering and hot isostatic pressing. Specifically, gas pressure sintering, while suppressing silicon nitride decomposition, utilizes a liquid phase sintering aid to densify the material matrix and initially form a porous layer framework structure. Subsequent hot isostatic pressing eliminates all residual closed pores under ultra-high pressure, achieving near-theoretical density in the outer layer, thus obtaining a friction surface with ultra-high hardness and ultra-low wear rate. Simultaneously, hot isostatic pressing strengthens the porous inner layer ceramic framework under high temperature and pressure, significantly improving the toughness and load-bearing strength of the porous structure while maintaining its designed porosity to match the hardness of the metal shank cone. The synergistic effect of the two sintering processes ultimately ensures a continuous gradual change in hardness from the outside to the inside of the gradient prosthesis, strong interlayer bonding, and a synergistic improvement in overall mechanical properties and service reliability.

[0151] Therefore, this invention utilizes dry pressing and lamination technology to achieve a gradient decrease in hardness of the silicon nitride ceramic ball head from the outside to the inside by gradually changing the ratio of additives in the silicon nitride ceramic, thereby manufacturing a gradient silicon nitride ceramic femoral head prosthesis for artificial hip replacement surgery.

[0152] In summary, compared with traditional femoral head prosthesis technology, the method of this invention prepares a gradient silicon nitride ceramic femoral head prosthesis through the preparation of multi-layer silicon nitride ceramic composite powder, a mold containing silicon nitride ceramic green bodies, and cold isostatic pressing and gas pressure sintering + hot isostatic pressing under liquid medium. The resulting gradient silicon nitride ceramic femoral head prosthesis exhibits synergistic improvements in density, hardness, flexural strength, fracture toughness, and wear resistance, achieving a shift from "hard against soft" to "soft against soft." This reduces the incidence of organ toxicity, periprosthetic osteolysis, and aseptic loosening caused by metal wear debris, improves the survival rate of silicon nitride ceramic femoral head prostheses and femoral stem cones, reduces the revision rate of total hip arthroplasty, saves patients' treatment costs, and facilitates large-scale industrial production and application.

[0153] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0154] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0155] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0156] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A gradient silicon nitride ceramic femoral head prosthesis, characterized in that, The gradient silicon nitride ceramic femoral head prosthesis is prepared from the following raw materials in parts by weight: 88-94 parts silicon nitride powder, 4-12 parts sintering aid, 5-20 parts tungsten carbide titanium, and 0-30 parts pore-forming agent, wherein the pore-forming agent cannot be 0 parts.

2. The gradient silicon nitride ceramic femoral head prosthesis according to claim 1, characterized in that, The sintering aid is selected from two or a combination of alumina, yttrium oxide, magnesium oxide, cerium oxide, silicon oxide, lanthanum oxide, and calcium oxide.

3. The gradient silicon nitride ceramic femoral head prosthesis according to claim 1, characterized in that, The pore-forming agent is selected from one or a combination of polystyrene (PS), polymethyl methacrylate (PMMA), soluble starch, toner, graphite, ammonium carbonate, and ammonium bicarbonate.

4. A method for preparing a gradient silicon nitride ceramic femoral head prosthesis according to claim 1, characterized in that, The specific steps for preparing the gradient silicon nitride ceramic femoral head prosthesis are as follows: S1. Raw material weighing: Weigh 88-94 parts of silicon nitride powder, 4-12 parts of sintering aid, 5-20 parts of tungsten titanium carbide and 0-30 parts of pore-forming agent according to the ratio of the silicon nitride ceramic femoral head prosthesis to obtain the raw material of the femoral head prosthesis. S2, Raw material mixing: The femoral head prosthesis raw material of S1 is successively stirred, mixed, ball-milled, dried and sieved, and divided into 3 to 4 layers according to the hardness gradient from large to small to obtain multilayer silicon nitride ceramic composite powder. S3. Green body preparation: The multilayer silicon nitride ceramic composite powder of S2 is initially formed in a special hemispherical mold by distributing the 3 to 4 layers of powder of S2 layer by layer according to their hardness, using a pre-forming core mold to obtain a mold containing silicon nitride ceramic green body. S4. Cold isostatic pressing: The mold containing the silicon nitride ceramic green body from S3 is placed into a cold isostatic press, and isotropic pressure is applied through a liquid medium to obtain a silicon nitride ceramic preform with relatively dense structure and certain strength. S5, Gas pressure sintering + hot isostatic pressing sintering: The silicon nitride ceramic preform of S4 is densified by gas pressure sintering and hot isostatic pressing sintering in sequence to obtain a porous silicon nitride ceramic material with a regular pore structure with multiple gradients.

5. The method for preparing a gradient silicon nitride ceramic femoral head prosthesis according to claim 4, characterized in that, The particle size distribution of silicon nitride powder in S1 ranges from 0.4 to 1.5 μm, D 50 The median particle size was controlled within the range of 0.2-0.6 μm, and the measured specific surface area was less than 6 m². 2 / g, the α phase crystal structure accounts for more than 92%; the particle size of the sintering aid is controlled in the range of 0.4-0.7μm, the particle size of tungsten carbide titanium is controlled in the range of 0.6-1.5μm, and the particle size of the pore-forming agent is controlled in the range of 10-120μm.

6. The method for preparing a gradient silicon nitride ceramic femoral head prosthesis according to claim 4, characterized in that, In S2, the stirring speed for mixing is 250-500 r / min, and the stirring time is 2-5 h; the grinding balls in the ball mill are made of silicon nitride with a diameter of 3-8 mm, the ball-to-material ratio is 2:1-4:1, the ball milling speed is 150-350 r / min, and the ball milling time is 10-24 h; the drying temperature is 65-80℃, and the drying time is 6-10 h; the sieve mesh size is 100-300 μm, and the average particle size of the silicon nitride ceramic composite powder is 50-100 μm.

7. The method for preparing a gradient silicon nitride ceramic femoral head prosthesis according to claim 4, characterized in that, In S2, there are three layers: an outer composite powder, a middle composite powder, and an inner composite powder. In S3, there are four layers: an outer composite powder, a second outer composite powder, a second inner composite powder, and an inner composite powder. The outer composite powder consists of silicon nitride powder, sintering aids, and tungsten titanium carbide. The second outer composite powder, the second inner composite powder, and the inner composite powder, or the middle composite powder and the inner composite powder, consist of silicon nitride powder, sintering aids, and pore-forming agents, with the content of pore-forming agents increasing towards the inner layers. In S3, the size of the hemispherical mold is 26-45mm, and the density of the silicon nitride ceramic green body is 45-65%.

8. The method for preparing a gradient silicon nitride ceramic femoral head prosthesis according to claim 4, characterized in that, The isotropic pressure in S4 is 50-300 MPa, the density of the silicon nitride ceramic preform is 55-80%, and the strength is 15-40 MPa.

9. The method for preparing a gradient silicon nitride ceramic femoral head prosthesis according to claim 4, characterized in that, In S5, gas pressure sintering uses an Ar or N2 atmosphere of 0.5-1 MPa, a heating rate of 0.5-2℃ / min, a sintering temperature of 1650-1840℃, and a holding time of 10-360 min; hot isostatic pressing sintering uses an Ar or N2 atmosphere or a mixture of the two at 150-200 MPa, a heating rate of 1-4℃ / min, a sintering temperature of 1600-1700℃, and a holding time of 2-3 h.

10. The method for preparing a gradient silicon nitride ceramic femoral head prosthesis according to claim 4, characterized in that, For porous silicon nitride ceramic materials with a regular pore structure and multiple gradients in S5, one or a combination of the following post-processing operations are performed: confirming gradient integrity, identifying internal defects, roughing, precision grinding, polishing, cleaning, and inspection.

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