Cermet composite gradient orthopedic implant material and preparation process thereof

Abstract

This invention discloses a metal-ceramic composite gradient orthopedic implant material and its preparation process. This orthopedic implant material, obtained through gradient structure design, includes a specific intermediate layer thickness and interface structure: Ti matrix → Ti-Al-Si diffusion layer → Al alloy buffer layer → Al2O3 ceramic layer, effectively alleviating contact stress and preventing ceramic layer brittleness. The preparation process involves cladding a silicon-aluminum alloy onto the surface of a titanium alloy Ti-6Al-4V / TC4 using cold metal transfer (CMT) technology. After controlling the layer thickness through precision machining, a dense alumina ceramic layer is grown in situ using micro-arc oxidation (MAO). Finally, a mirror-finish composite gradient material is achieved through ultra-precision grinding. This preparation process solves the problems of easy peeling and poor wear resistance of existing coatings, addressing the clinical challenges of poor wear resistance, insufficient adhesion of ceramic coatings, and easy peeling in traditional titanium alloy implants. It constructs an integrated gradient structure with a "tough titanium alloy matrix – metallurgically bonded transition layer – high-hardness ceramic functional layer."

Description

Technical Field

[0001] This invention relates to the field of biomedical material surface modification and high-end medical device manufacturing technology, specifically to a metal-ceramic composite gradient orthopedic implant material and its preparation process. Background Technology

[0002] I. Clinical Challenges and Current Status of Orthopedic Implant Materials With the increasing aging of the global population, the demand for total hip arthroplasty (THA) and total knee arthroplasty (TKA) is experiencing explosive growth. Titanium alloys (especially Ti-6Al-4V, TC4), considered the "gold standard" material for implants, dominate the orthopedic field due to their excellent biocompatibility, high specific strength, and low elastic modulus close to cortical bone (approximately 110 GPa, compared to 210 GPa for stainless steel and 240 GPa for cobalt-chromium-molybdenum alloys, significantly reducing bone resorption caused by the "stress shielding" effect). However, titanium alloys have a fatal tribological defect as joint friction pair materials: Low hardness and high coefficient of friction: The surface hardness of titanium alloys is usually only HV 300-350, and the coefficient of friction is relatively high (>0.5).

[0003] Oxide film instability: The passivation film (TiO2) that forms naturally on its surface is extremely thin and has weak bonding force. It is very easy to break during high-load shearing motion of the joint, resulting in the exposure of the substrate.

[0004] Severe adhesive wear: Titanium alloys have high chemical activity and are prone to severe adhesive wear with mating materials (such as ultra-high molecular weight polyethylene, UHMWPE), generating a large number of wear particles.

[0005] Osteolysis and aseptic loosening: Micron- and nano-sized titanium / titanium oxide particles generated by wear can induce macrophage activation, releasing inflammatory mediators (IL-1, IL-6, TNF-α), which in turn activate osteoclasts, leading to periprosthetic osteolysis, and ultimately causing aseptic loosening of the prosthesis and surgical failure.

[0006] II. Limitations of Existing Surface Modification Technologies To overcome the wear resistance problem of titanium alloys, the industry has developed a variety of surface modification technologies, but all of them have significant limitations: Physical vapor deposition (PVD) / chemical vapor deposition (CVD): Although it can prepare hard coatings such as TiN and DLC, the coatings are usually extremely thin (<5μm), and due to the large difference in the coefficient of linear expansion between the coating and the substrate, fatigue delamination is prone to occur under long-term cyclic contact stress. Once the coating delaminates locally, the resulting hard fragments become "third-body abrasive particles," accelerating joint wear.

[0007] Plasma spraying: This is currently the mainstream industrial method for preparing hydroxyapatite (HA) or ceramic coatings. However, the coating layer and the substrate mainly rely on mechanical interlocking, resulting in low bonding strength (typically <50 MPa), and the coating has high porosity and uneven structure. Under high shear forces at the joint surfaces, the coating-substrate interface is a typical failure source.

[0008] Ion implantation and nitriding / carburizing: Although they can improve surface hardness, the modified layer depth is limited (usually only 0.1-0.3 μm), which cannot withstand long-term wear and tear, and cannot fundamentally change the tribochemical properties of the titanium alloy surface.

[0009] All-ceramic materials (Zirconia / Alumina): Although they have excellent wear resistance, they are at risk of brittle fracture (catastrophic failure) and require extremely high processing precision. Once squaking occurs, it will greatly affect the patient's quality of life.

[0010] III. Technical Bottlenecks in Titanium-Aluminum Composites and In-situ Ceramicization In recent years, leveraging the ease with which aluminum alloys can be anodized to form hard alumina (Al2O3), constructing an aluminum coating on the surface of titanium alloys and then performing micro-arc oxidation (MAO / PEO) has become a research hotspot. This technical approach theoretically combines the toughness of titanium with the hardness of alumina ceramics. However, realizing this approach faces significant metallurgical challenges: The challenge of welding dissimilar metals: Titanium (Ti) and aluminum (Al) have vastly different physicochemical properties (melting points: Ti 1668°C vs Al 660°C). During high-temperature fusion bonding, violent interfacial reactions easily occur, forming a series of brittle intermetallic compounds (IMCs), such as TiAl3 and TiAl. If the IMC layer is too thick (>10 μm), the interface becomes extremely brittle, causing the coating to peel off even under minor loads.

[0011] Heat input control: Traditional MIG / TIG welding has excessive heat input, resulting in high dilution rate and a large amount of titanium mixed into the aluminum layer. This not only deteriorates the film quality of subsequent micro-arc oxidation (forming low-hardness titanium oxide), but also causes the rampant growth of brittle phases at the interface.

[0012] Ceramic layer quality: Ordinary micro-arc oxidation process tends to form a loose and porous layer on the coating surface with high roughness (Ra> 1-2μm). If used directly as a joint surface, it will wear down the mating surface like sandpaper.

[0013] Therefore, there is an urgent need for a comprehensive manufacturing process that can precisely control heat input to suppress the growth of brittle interfaces, regulate the thickness of intermediate layers to alleviate stress, and produce mirror-finish dense ceramic layers. This invention proposes a complete solution based on the low heat input characteristics of cold metal transfer (CMT) technology and the interface modification mechanism of silicon-aluminum alloys, combined with "soft spark" micro-arc oxidation and ultra-precision grinding. Summary of the Invention

[0014] The purpose of this invention is to provide an orthopedic implant material with a specific intermediate layer thickness and interface structure. Through a gradient structure design (Ti matrix -> Ti-Al-Si diffusion layer -> Al alloy buffer layer -> Al2O3 ceramic layer), contact stress is effectively relieved and the ceramic layer is prevented from becoming brittle. Another objective of this invention is to provide a process for preparing a gradient coating with high adhesion, high hardness, and low friction coefficient on a titanium alloy surface, solving the problems of easy peeling and poor wear resistance of existing coatings.

[0015] The technical solution of the present invention is as follows: a metal-ceramic composite gradient orthopedic implant material, which, from the inside out, consists of: a titanium alloy matrix region, a metallurgical bonding interface region containing Ti5Si3 phase, an aluminum alloy buffer transition region, and an Al2O3 ceramic functional region.

[0016] Furthermore, the orthopedic implant material, from the inside out, consists of: a medical titanium alloy matrix region, a metallurgical bonding interface region (containing Ti5Si3 phase) with a thickness of 1-5 μm, an aluminum alloy buffer transition region with a thickness of 10-150 μm, and a dense α-Al2O3 ceramic functional region with a thickness of 20-60 μm.

[0017] Furthermore, the Vickers hardness of the ceramic functional area is ≥ HV1500, and the bonding strength between the coating and the substrate is ≥ 60MPa.

[0018] This invention provides a process for preparing a titanium alloy surface gradient orthopedic implant material, comprising the following steps: Step 1: Matrix Pretreatment Medical-grade titanium alloy (Ti-6Al-4V) was selected as the substrate and subjected to surface sandblasting, degreasing, and chemical micro-corrosion treatment to remove the surface oxide scale and activate the surface, thereby increasing the wettability of the molten metal.

[0019] Step 2: Cold Metal Transfer (CMT) Cladding of Silicon-Aluminum Alloy Using a CMT welding machine and an automated robot system, ER4047 (Al-12Si) aluminum-silicon alloy welding wire is clad onto the surface of titanium alloy.

[0020] Material selection: ER4047 was chosen instead of pure aluminum (ER1100) or aluminum-magnesium (ER5356) because Si can preferentially react with Ti to form the Ti5Si3 phase. This phase acts as a diffusion barrier layer, which can effectively inhibit the excessive growth of the brittle TiAl3 phase and significantly improve the interfacial bonding toughness.

[0021] Heat input control: CMT technology reduces heat input to extremely low levels (more than 30% lower than traditional MIG) through mechanical droplet transfer by wire retraction, achieving "cold" bonding, controlling the substrate dilution rate to below 5%, and controlling the interface IMC layer thickness to 1-5μm.

[0022] Step 3: Precision Grinding and Thickness Control (The "Gradient" Enabler) Precision machining (turning or grinding) is performed on the rough surface after cladding.

[0023] Key indicator: The thickness of the aluminum alloy layer retained after processing must be strictly controlled between 10μm and 150μm.

[0024] Principle: If the thickness is <10μm, the MAO process can easily penetrate the aluminum layer and damage the titanium substrate; if the thickness is >150μm, because the elastic modulus of aluminum alloy (~70GPa) is much lower than that of the ceramic layer, it will produce large deformation under the high contact stress of the joint, causing the hard and brittle surface ceramic layer to lack support and resulting in the "egg-shell effect" and breakage. The thickness range of 10-150μm is the balance point for achieving the best mechanical support and stress buffering.

[0025] Step 4: Micro-arc oxidation (MAO) in-situ ceramization In a specially designed aluminate-tungstate electrolyte system, a bipolar pulse power supply is used to perform plasma electrolytic oxidation on the aluminum alloy layer.

[0026] Electrolyte: NaAlO2 is used as the main salt to provide sufficient Al source, and Na2WO4 (sodium tungstate) is added as a densifying agent. The participation of tungstate ions in film formation can improve the breakdown voltage, promote the conversion of γ-Al2O3 to high-hardness α-Al2O3, and improve the toughness of the film.

[0027] Soft Sparking Mode: By adjusting the negative voltage and duty cycle, the discharge is induced to enter the "Soft Sparking" mode, eliminating large pores on the surface and generating a dense, low-defect ceramic layer.

[0028] Step 5: Ultra-precision grinding and polishing The surface of the MAO coating naturally contains a loose, porous outer layer, which must be removed.

[0029] Process: Use diamond abrasives to grind away the loose layer of 10-30μm on the surface to expose the dense inner functional layer, followed by chemical mechanical polishing (CMP).

[0030] Objective: The final surface roughness Ra ≤ 0.05 μm, reaching the optical mirror level, and meeting the tribological requirements of the ISO standard for artificial joints.

[0031] Compared with the prior art, the beneficial effects of the present invention are: Metallurgical bonding, eliminating delamination: Ti-Al bonding achieved through CMT technology is an atomic diffusion metallurgical bond with a shear strength >150MPa, far exceeding the mechanical bonding of plasma spraying (~30-50MPa), completely eliminating the risk of coating delamination. Gradient structure, impact resistance: A four-level gradient structure is formed, consisting of "Ti matrix (tough) -> Ti-Si-Al interface layer (strong) -> Al alloy residual layer (buffer) -> Al2O3 ceramic layer (hard)," which effectively alleviates the thermal expansion and elastic modulus mismatch between ceramic and metal.

[0032] Ultra-high wear resistance: The surface layer is corundum phase (α-Al2O3), with a Vickers hardness of HV1500-2000. Its wear resistance is comparable to that of bulk ceramics, and there is no risk of brittle fracture.

[0033] Interface toughening with Si: The Ti5Si3 phase generated by introducing Si refines the interface grains, avoids the formation of continuous network brittle TiAl3, and significantly improves the fatigue life of the joint.

[0034] Low coefficient of friction: Combined with ultra-precision polishing and the unique hydrodynamic lubrication retention capability of ceramic surfaces, the generation of wear particles is significantly reduced. Detailed Implementation

[0035] To make the technical solution of the present invention clearer, it will be described in detail below with reference to specific process parameters, principle analysis and embodiments.

[0036] Selection and mechanism of core raw materials Matrix material: Medical-grade titanium alloy Ti-6Al-4V ELI (Extra Low Interstitial), conforming to ASTM F136 standard.

[0037] Cladding material: ER4047 aluminum-silicon alloy welding wire. Composition (wt%): Si 11.0-13.0, Fe < 0.8, Cu <0.3, Mn < 0.15, Mg < 0.1, Zn < 0.2, Al balance.

[0038] Reasons for selection: Compared to ER5356 (Al-Mg), ER4047 has a lower melting point (approximately 577°C) and better fluidity. More importantly, Si plays a crucial role in the Ti / Al interfacial reaction. Thermodynamic calculations show that Ti has a stronger affinity for Si than for Al, preferentially forming Ti5Si3. These dispersed silicides hinder excessive diffusion of Ti atoms to the Al side, thereby suppressing the formation of thick, brittle TiAl3 plate-like phases and keeping the reaction layer thickness within a safe range (<5 μm).

[0039] Detailed process steps and parameters Step 1: Matrix Pretreatment Mechanical polishing: Use 400#-800# SiC sandpaper to polish the TC4 surface step by step to remove macroscopic defects and natural oxide film, and obtain a uniform surface roughness (Ra 0.4-0.8μm).

[0040] Chemical cleaning: Soak in acetone and anhydrous ethanol for 15 minutes each, then ultrasonically clean to remove oil stains.

[0041] Pickling and activation: Immerse in a solution with a volume ratio of HF:HNO3:H2O=3:15:82 for 30-60 seconds to expose the fresh metal substrate, then immediately rinse with deionized water and dry to prevent secondary oxidation.

[0042] Step 2: CMT Cold Metal Transfer Cladding A six-axis industrial robot equipped with a Fronius CMT Advanced power supply was used for cladding. For spherical joint surfaces (such as the femoral head), a positioner was used in conjunction with a helical scanning path; for planar or irregular surfaces, a reciprocating scanning path was used.

[0043] Preferred process parameter range: Parameter Range Preferred value Mechanism of action explanation Welding current 60 - 150 A 90 - 120 A Excessive current leads to increased dilution and thickening of the IMC layer; insufficient current results in incomplete fusion. Welding voltage 10 - 16 V 12 - 14 V Control the arc length in conjunction with CMT waveform Web feed speed (WFS) 4.0 - 7.5 m / min 5.5 m / min Determines the cladding layer height and deposition rate Welding speed (Travel Speed) 0.3 - 1.0 m / min 0.5 - 0.6 m / min The faster the speed, the lower the heat input, which helps to suppress IMC growth. Shielding Gas 99.999% Ar 15 - 20 L / min Argon gas flow can effectively cool the molten pool and prevent high-temperature oxidation. Dilution rate < 10% < 5% Extremely low dilution rate ensures the purity of the aluminum layer and prevents Ti from entering the aluminum layer and interfering with subsequent MAO film formation. CMT waveform control: Employs a typical CMT cycle – arc ignition (droplet formation) – short circuit (wire insertion) – retraction (mechanical arc termination / droplet transfer). This process achieves an alternation of "hot-cold-hot-cold," significantly reducing cumulative heat input.

[0044] Step 3: Mechanical thinning and thickness control (key step) The original aluminum layer after cladding is typically 1-3 mm thick and has a relatively large surface ripple. Precision machining is required.

[0045] Rough machining: Use PCD (polycrystalline diamond) tools to turn or mill to remove most of the excess material from the surface.

[0046] Finishing: Precision grinding is used, along with in-situ measurement using an ultrasonic thickness gauge or an eddy current thickness gauge.

[0047] Target thickness: 10 μm-150 μm.

[0048] Reason for upper limit: According to Hertzian contact stress analysis, when the soft interlayer is too thick, plastic deformation will occur under the high contact pressure of the joint (up to 10-20MPa), causing the hard and brittle ceramic layer on the surface to lose support and crack (Egg-shell effect).

[0049] Reason for the lower limit: The MAO process consumes aluminum substrate. Typically, 0.6-0.8 μm of aluminum substrate is required to form 1 μm of ceramic layer. If the allowance is too thin, the discharge channel will break down into the titanium substrate, forming a loose TiO2 hybrid layer and destroying the bonding force.

[0050] Step 4: Micro-arc oxidation (MAO) ceramization The workpiece is used as the anode, and the stainless steel plate is used as the cathode, and the workpiece is immersed in an electrolytic cell equipped with a stirring and cooling system.

[0051] Electrolyte Formula: Main salt: Sodium aluminate (NaAlO2): 10-25 g / L. Provides AlO2. - Ions are the main source of material for the growth of ceramic layers.

[0052] Densifying agent: Sodium tungstate (Na2WO4): 2-8 g / L. Tungstate ions participate in film formation, significantly improving the film breakdown voltage, promoting the sintering and densification of molten oxides, and giving the coating a dark appearance to facilitate radiative heat dissipation.

[0053] Stabilizer: Potassium hydroxide (KOH): 1-3 g / L. Adjust the pH to 11-13 to maintain the conductivity of the electrolyte.

[0054] Functional additives (optional): Graphene oxide (GO) 0.5-1.0 g / L or nano-MoS2. These are deposited into the micropores using electrophoretic deposition to provide self-lubricating properties.

[0055] Electrical parameters (process parameters): Power supply mode: Bipolar pulsed power supply. Compared to DC, bipolar pulsed power supply can use negative voltage to eliminate the polarization layer, extinguish large electric arcs, and achieve "soft spark".

[0056] Forward voltage: 450 - 550 V.

[0057] Negative voltage: 100 - 150 V.

[0058] Frequency: 500 - 1000 Hz. High frequencies are beneficial for generating fine, high-density sparks and reducing pore size.

[0059] Duty cycle: 15% - 25%. The low duty cycle gives the coating sufficient "thermal relaxation" time, preventing localized overheating and burn-off.

[0060] Processing time: 30 - 60 min.

[0061] Endpoint control: Stop when the current density decays to 10-20% of the initial value or reaches the predetermined time.

[0062] Step 5: Ultra-precision post-processing MAO coatings typically have a loose, porous layer of 10-20 μm, with low hardness and a rough surface.

[0063] Coarse polishing: Grinding is performed using a diamond grinding disc with a grit size of 10-20μm to remove the loose layer.

[0064] Fine polishing: Mechanical polishing is performed using diamond polishing paste with a particle size of 1-3μm.

[0065] CMP (Chemical Mechanical Polishing): Final polishing is performed using an alkaline polishing solution containing nano-SiO2 or Al2O3 (particle size 50-100 nm).

[0066] Final specifications: Surface roughness Ra < 0.05 μm, and the exposed surface is a dense α-Al2O3 layer. Example

[0067] Example 1: Preparation and Properties of TC4 Ball Head Surface Matrix: Φ28mm TC4 ball head.

[0068] CMT: Current 90A, voltage 12.5V, speed 60 cm / min, argon gas 18 L / min. Cladding ER4047.

[0069] Grinding: Retain an aluminum layer thickness of 60μm.

[0070] MAO: NaAlO2 (18 g / L) + Na2WO4 (5 g / L) + KOH (2 g / L). 500V / 600Hz / 20%. Treatment time: 40 minutes.

[0071] Polishing: Removed 15μm of surface layer, Ra decreased to 0.03μm.

[0072] result: Cross-sectional structure: Ti matrix / 2μm IMC layer / 35μm Al alloy layer / 25μm dense ceramic layer.

[0073] Hardness: Surface hardness HV 1750.

[0074] Bonding force: Critical load L in scratch test c >60N, tensile bond strength >70MPa.

[0075] Phase composition: XRD shows that the main phase is α-Al2O3 and a small amount of γ-Al2O3, and no Al-Si elemental was detected (it was completely oxidized or encapsulated).

[0076] Example 2: The Influence of Parameters on the Interface (Comparative Experiment) Control group A: Using ER5356 (Al-Mg) welding wire. Results showed that a continuous TiAl3 layer up to 12 μm thick was formed at the interface, with a shear strength of only 45 MPa, and fracture occurred in the IMC layer. This demonstrates that Si is crucial for controlling IMC growth.

[0077] Control group B: The aluminum layer thickness was maintained at 200 μm. Results showed that the ceramic layer cracked during the reciprocating friction experiment. This demonstrates that a thickness upper limit of 150 μm is necessary.

[0078] Control group C: CMT current 180A. The results showed a dilution rate of 15%, with a large amount of TiO2 appearing in the MAO film, and a hardness of only HV 800. This demonstrates the importance of low heat input in maintaining the purity of the aluminum source.

[0079] Example 3: The Influence of Electrolyte Composition Adding 2 g / L sodium tungstate to the base formulation resulted in a decrease in coating porosity from 12% to 4% and an increase in hardness of approximately 300 HV compared to the unadded group. This demonstrates the crucial role of tungstate in promoting densification and the "soft spark" transition.

[0080] Performance Testing and Mechanism Analysis 1) Bonding mechanism: gradient metallurgical bonding

[0081] The adhesion of the coating prepared by this invention originates from controlled atomic diffusion during the CMT process. During the ER4047 cladding process, Si atoms preferentially occupy the interstitial spaces of the Ti lattice, forming a Ti5Si3 pinned phase, which blocks the rapid pathways of Al atoms. This not only limits the thickness of the brittle TiAl3 phase (<5 μm) but also forms a micro-serrated metallurgical interlocking interface. Compared to the van der Waals force / mechanical interlocking bonding of plasma spraying, the metallurgical bonding strength of this invention is increased by 2-3 times, fully meeting the ISO 13779 requirements for implant coating bonding strength.

[0082] 2) Wear-resistant mechanism: corundum phase and mirror effect The high hardness of the micro-arc oxide layer originates from α-Al₂O₃ (corundum) generated by high-temperature plasma sintering. Typically, MAO layers contain more metastable γ-Al₂O₃ and have lower hardness. This invention promotes the γ-to-α phase transformation by adding sodium tungstate and optimizing thermal parameters. Furthermore, ultra-precision grinding (Ra < 0.05 μm) removes the porous surface structure. According to Stribeck curve theory, extremely low roughness facilitates the formation of a hydrodynamic lubricating film in the synovial fluid, transforming friction from "boundary lubrication" to "mixed lubrication" or even "fluid lubrication," thereby significantly reducing the wear rate.

[0083] 3) Biosafety Although aluminum ions have potential neurotoxicity, this process ensures safety through two lines of defense: Dense ceramic barrier: The α-Al2O3 formed by MAO is one of the most chemically inert ceramics, almost insoluble in physiological saline and body fluids, completely sealing the underlying aluminum alloy.

[0084] 4) Gradient structural integrity: Extremely high adhesion and reasonable thickness design prevent the coating from cracking during use, avoiding direct exposure of the aluminum alloy substrate. In vitro cytotoxicity experiments (MC3T3-E1 osteoblasts) showed that the cells spread well on the surface of the coating after cleaning and sterilization, with no obvious toxic reaction.

[0085] This process utilizes mature industrial robots and welding power sources, combined with standard CNC machining and micro-arc oxidation equipment, facilitating automated mass production. Compared to expensive electron beam melting (EBM) or vacuum plasma spraying (VPS), this process offers lower equipment costs, cheaper and more environmentally friendly raw materials (welding wire, chemical reagents) (water-based electrolyte). This technology is not only suitable for the load-bearing friction surfaces of artificial hip and knee joints, but can also be applied to orthopedic implants such as bone plates and intramedullary nails that require high wear resistance and anti-adhesion properties, demonstrating significant clinical translational value and market potential.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A metal-ceramic composite gradient orthopedic implant material, characterized in that, The material, from the inside out, consists of: a titanium alloy matrix region, a metallurgical bonding interface region containing Ti5Si3 phase, an aluminum alloy buffer transition region, and an Al2O3 ceramic functional region.

2. The metal-ceramic composite gradient orthopedic implant material according to claim 1, characterized in that, The material, from the inside out, consists of: a titanium alloy matrix region, a 1-5 μm thick metallurgical bonding interface region containing Ti5Si3 phase, a 10-150 μm thick aluminum alloy buffer transition region, and a 20-60 μm thick α-Al2O3 ceramic functional region.

3. A process for preparing the titanium alloy surface gradient orthopedic implant material as described in claim 1 or 2, characterized in that, Includes the following steps: 1) Substrate pretreatment: The titanium alloy substrate is cleaned, sandblasted, and chemically etched for activation; 2) CMT Precision Cladding: Using cold metal transfer technology, a layer of silicon-containing aluminum alloy is clad onto the surface of a titanium alloy substrate. By controlling the welding heat input, a diffusion layer containing Ti-Si compounds with a thickness of 1-5 μm is formed at the titanium / aluminum interface, and the substrate dilution rate is less than 5%. 3) Thickness-controlled grinding: Precision machining is performed on the clad aluminum alloy layer to remove irregular parts on the surface, and the thickness of the aluminum alloy layer retained on the titanium alloy substrate is strictly controlled to be between 10μm and 150μm. 4) Micro-arc oxidation ceramization: The processed workpiece is placed in an alkaline electrolyte containing sodium aluminate (NaAlO2) and sodium tungstate (Na2WO4), and a bipolar pulse voltage is applied for micro-arc oxidation treatment to grow a dense alumina ceramic layer in situ. 5) Ultra-precision post-processing: Grinding and polishing the micro-arc oxidation ceramic layer to remove the loose surface layer and obtain a mirror-like functional surface with a surface roughness Ra≤0.05μm.

4. The preparation process according to claim 3, characterized in that, The silicon-containing aluminum alloy welding wire mentioned in step 2) has a silicon content of 11wt% - 13wt%.

5. The preparation process according to claim 3, characterized in that, The process parameters for CMT cladding described in step 2) are: welding current 60 A - 150 A, welding voltage 10 V - 16 V, wire feed speed 4.0 - 7.5 m / min, welding speed 20 - 60 cm / min, and shielding gas is pure argon with a flow rate of 15 - 20 L / min.

6. The preparation process according to claim 3, characterized in that, The electrolyte composition in step 4) is: sodium aluminate 10-25 g / L, potassium hydroxide 1-3 g / L, sodium tungstate 2-8 g / L; the electrical parameters of the micro-arc oxidation treatment are: positive peak voltage 450-550 V, negative voltage 100-150 V, frequency 500-1000 Hz, and duty cycle 15%-25%.

7. The preparation process according to claim 6, characterized in that, The electrolyte also contains graphene oxide (GO) or molybdenum disulfide (MoS2) particles at a concentration of 0.5-2.0 g / L to impart self-lubricating properties to the coating.

8. The preparation process according to claim 3, characterized in that, The thickness of the aluminum alloy layer retained in step 3) is preferably 40μm-80μm.

9. The preparation process according to claim 3, characterized in that, The ultra-precision post-processing described in step 5) includes removing a loose surface layer of 10-30 μm using a diamond grinding wheel, followed by chemical mechanical polishing.

10. The use of the gradient orthopedic implant material according to claim 1 or 2 in the preparation of artificial hip joint acetabular cups and femoral heads, knee joint femoral condyles or tibial supports.