Dental cobalt-chromium alloy restoration 3D printing process capable of reducing ceramic cracking rate

Abstract

The invention aims to provide a dental cobalt-chromium alloy restoration 3D printing process capable of reducing the ceramic cracking rate, and cobalt-chromium alloy powder comprises the following components in percentage by weight: 58-64wt% of Co; 25 to 31 wt% of Cr; 5 to 6 wt% of Mo; 2 to 3 wt% of W; 0.8 to 1.2 wt% of Si; mn: 0.5 to 1.0 wt%; and 0.1 to 0.3 wt% of rare earth oxide. The printing technology comprises the steps that the cobalt-chromium alloy powder is adopted for preheating, 3D printing is conducted, in the printing process, after a core area, a transition area and a surface area are printed through dynamic energy density modulation, a restoration printed piece is obtained, and the cobalt-chromium alloy printed piece is subjected to aftertreatment to obtain the cobalt-chromium alloy restoration. According to the method, the powder material, the 3D printing technology and the post-treatment element doping technology are combined in a breakthrough mode, the gold and ceramic binding force is remarkably improved, progressive connection of metal and ceramic is achieved, and the interface mismatch problem is essentially solved.

Description

Technical Field

[0001] This application belongs to the field of metal additive manufacturing technology, specifically relating to a 3D printing process for dental cobalt-chromium alloy restorations that reduces the rate of porcelain cracking. Background Technology

[0002] Porcelain cracking is a common technical complication in dental restorations, referring to the cracking or even peeling of the porcelain layer on the surface of porcelain crowns or bridges. The cracking rate of traditional cast cobalt-chromium alloy porcelain restorations is as high as 8-15%, mainly due to factors such as the mismatch in thermal expansion coefficients between the metal substrate and the porcelain layer, insufficient metal-ceramic bonding strength, improper metal surface treatment, and internal micropore defects. Although 3D printing technology has brought a revolution in precision to the manufacture of cobalt-chromium alloy dentures, it is still difficult to fundamentally solve this clinical problem without specific optimization for addressing porcelain cracking. Currently, conventional cobalt-chromium alloy 3D printing often uses laser powder bed fusion (L-PBF / SLM) technology. While printed parts have a higher 0.2% specified non-proportional tensile strength and Vickers hardness than cast products (cast parts are approximately 300-350 HV, while 3D printed parts can reach 350-400 HV), there is still room for improvement in the stability of the metal-ceramic interface. Studies show that the surface morphology and microstructure of 3D-printed cobalt-chromium alloys have a decisive impact on the metal-ceramic bonding performance; unoptimized printing parameters can lead to a 20-30% decrease in metal-ceramic layer adhesion. Existing solutions mostly focus on adjusting powder thickness (20-50 μm) or surface roughening, which have significant limitations. I. Insufficient powder coating leads to low production efficiency (single crown printing time ≥ 3 hours).

[0003] II. Sandblasting can introduce surface cracks (10-20μm deep), which become crack sources.

[0004] III. Intermediate coatings (such as GoldBond) have issues with clear interfaces and abrupt changes in thermal expansion. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a 3D printing process for dental cobalt-chromium alloy restorations that reduces the rate of porcelain cracking. This invention innovatively combines powder materials, 3D printing technology and post-processing element doping technology to significantly improve the bonding force between metal and ceramic, achieve a progressive connection between metal and ceramic, and fundamentally solve the problem of interface mismatch.

[0006] This invention provides a cobalt-chromium alloy powder, wherein the cobalt-chromium alloy powder comprises the following components by weight percentage: Co: 58-64wt%; Cr: 25-31 wt%; Mo: 5-6 wt%; W: 2-3 wt%% Si: 0.8-1.2 wt%; Mn: 0.5-1.0 wt%; Rare earth oxides: 0.1-0.3 wt%.

[0007] The second aspect of the present invention provides a 3D printing process for dental cobalt-chromium alloy restorations that reduces the rate of porcelain cracking. The printing process includes: using cobalt-chromium alloy powder as described in the present invention for 3D printing; printing the core area, transition area and surface area separately by dynamic energy density modulation during the printing process to obtain a restoration print; and post-processing the cobalt-chromium alloy print to obtain a cobalt-chromium alloy restoration.

[0008] A third aspect of the present invention provides a cobalt-chromium alloy restoration, which is prepared using the 3D printing process for dental cobalt-chromium alloy restorations with reduced porcelain cracking rate as described in the present invention.

[0009] The technical solution of this invention is: By adopting the aforementioned technical solution, the beneficial effects of the present invention are: 1. Breakthrough in material system: Special alloy formulations balance high strength and good doping activity (traditional alloys have poor doping uniformity), and rare earth oxides stabilize grain boundaries, thus limiting grain growth during high-temperature processing.

[0010] 2. Precise control of molten pool solidification is achieved by substrate preheating, gradient energy input, and interlayer laser annealing, which eliminates element segregation and cracks, reduces thermal stress, and balances the mechanical properties of the restoration with the bonding strength between the metal and ceramic.

[0011] 3. The micro-nano anchoring structure improves mechanical bonding force and further strengthens the bond between metal and ceramic.

[0012] 4. Element doping innovation: A chemical bonding network is constructed at the interface through a Si / Al / Sn / Ce / Zr multi-component system, with a bonding strength exceeding 40 MPa; 5. Thermochemical gradient doping process achieves gradient thermal expansion properties, from 14.5 × 10⁻⁶ on the metal side. -6 / ℃ gradually changes to 13.0×10 on the ceramic side -6 / ℃, effectively buffering thermal stress. The metallurgical bond between the transition layer and the substrate avoids the problem of easy peeling of traditional coatings, and the shear strength reaches over 300MPa. Attached Figure Description

[0013] Figure 1 This invention demonstrates the technical approach for 3D printing cobalt-chromium alloy repair bodies. Figure 2 The diagram shows the structure of the cobalt-chromium alloy repair body of the present invention combined with ceramic. Detailed Implementation

[0014] The following describes in detail the implementation of the 3D printing process for dental cobalt-chromium alloy restorations that reduces the rate of porcelain cracking provided by the present invention.

[0015] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0016] Cobalt-chromium alloy powder This invention provides a cobalt-chromium alloy powder. The cobalt-chromium alloy powder designed by this invention has a unique composition system, providing a foundation for subsequent elemental doping. The cobalt-chromium alloy powder comprises the following components by weight percentage: Co: 58-64wt%; optional 58-60wt% or 60-64wt%; ensure matrix toughness.

[0017] Cr: 25-31 wt%; optional 25-26 wt% or 26-31 wt%; corrosion resistant.

[0018] Mo: 5-6 wt%; optional 5-5.5 wt% or 5.5-6 wt%; can refine grain size.

[0019] W: 2-3 wt%; optional 2-2.5 wt% or 2.5-3 wt%; exhibits high temperature stability.

[0020] Si: 0.8-1.2 wt%; optional: 0.8-1.1 wt% or 1.1-1.2 wt%; can lower the melting point.

[0021] Mn: 0.5-1.0 wt%; optional: 0.5-0.8 wt% or 0.8-1.0 wt%; used as a deoxidizer.

[0022] Rare earth oxides: 0.1-0.3 wt%, optionally 0.1-0.2 wt% or 0.2-0.3 wt%, used for grain boundary strengthening. The rare earth oxides are selected from yttrium oxide (Y₂O₃) and lanthanum oxide (La₂O₃).

[0023] It also includes other components, the remainder being other components. The other components are boron (B) and / or gallium (Ga), with a total content of 0.01 ~ 1.0 wt%, used to improve printing processability.

[0024] The cobalt-chromium alloy powder provided by the present invention has a particle size distribution of 15-45 μm, which can be selected as 15-30 μm, 30-45 μm, 15-25 μm, 25-35 μm, or 35-45 μm.

[0025] The cobalt-chromium alloy powder provided by the present invention has a D50 of 30±3μm, which can be selected as 30±1μm, 30±2μm, etc.

[0026] The cobalt-chromium alloy powder provided by this invention is prepared by plasma rotating electrode method (PREP) and has a sphericity ≥98%.

[0027] The cobalt-chromium alloy powder provided by this invention has the following flowability: ≤30s / 50g (Hall flow meter test), meeting the requirements for high-precision powder spreading. Oxygen content: ≤0.08wt%, avoiding excessive oxidation that could affect the doping effect.

[0028] The formulation of the cobalt-chromium alloy powder of this invention is strengthened by the dispersion of rare earth oxides, so that the hardness of the printed parts reaches HV400-500, while maintaining an elongation of ≥8%, which is superior to conventional cobalt-chromium alloys (HV300-350, elongation of 5-6%).

[0029] [3D Printing Technology for Cobalt-Chromium Alloy Dental Restorations to Reduce Porcelain Cracking Rate] This invention also provides a 3D printing process for dental cobalt-chromium alloy restorations that reduces the rate of porcelain cracking. The printing process includes: using cobalt-chromium alloy powder as described in this invention for 3D printing; printing the core area, transition area and surface area separately through dynamic energy density modulation during the printing process to obtain the restoration print; and post-processing the cobalt-chromium alloy print to obtain the cobalt-chromium alloy restoration.

[0030] The cobalt-chromium alloy restoration 3D printing process provided in this invention proposes Dynamic Energy Density Modulation (DEDM) technology, which optimizes the molten pool characteristics by adjusting laser parameters in real time. Core area printing: power of 190-210W (high power), scanning speed of 900-1100mm / s (high-speed scanning), energy density of 65-80J / mm³, forming a dense equiaxed crystal structure with a porosity of <0.05%. The power can be selected as 190-200W or 200-210W. The scanning speed can be selected as 900-1000mm / s or 1000-1100mm / s. The energy density can be selected as 65-70J / mm³ or 70-80J / mm³.

[0031] Transition zone printing: Power is reduced to 170-190W, scanning speed is adjusted to 700-900mm / s, and energy density is 85-100J / mm³, generating a mixed structure of columnar and equiaxed crystals. The elastic modulus of this mixed structure is 18-25GPa, which is close to that of natural teeth. Specifically, the power can be selected as 170-180W or 180-190W, the scanning speed as 700-800mm / s or 800-900mm / s, and the energy density as 85-90J / mm³ or 90-100J / mm³.

[0032] Surface area printing: A micro-vibration scanning strategy is employed, with a laser power of 160-175W (selectable from 160-170W or 100-175W), a scanning speed of 500-700mm / s (selectable from 500-600mm / s or 600-700mm / s), and superimposed with 100-200Hz high-frequency vibration (selectable from 100-150Hz or 150-200Hz), resulting in an energy density of 110-130J / mm³ (selectable from 110-120J / mm³ or 120-130J / mm³), forming a nanocrystalline surface layer. The grain size of the nanocrystalline surface layer is 50-100nm (selectable from 50-80nm, 80-100nm, 50-70nm, 70-90nm, or 90-100nm). The surface roughness Ra of the nanocrystalline surface layer is stable at 3.5-4.0 μm, and can be selected as 3.5-3.8 μm or 3.8-4.0 μm. This provides an ideal mechanical interlocking basis for the ceramic layer.

[0033] Table 1. Gradient Energy Density 3D Printing Parameter Design

[0034] The process of this invention enables the restoration to exhibit a gradual change in performance from the inside out through the energy density gradient distribution: high strength in the core area (tensile strength ≥950MPa), moderate elastic modulus in the transition area, and optimized metal-ceramic bonding interface in the surface area.

[0035] In the 3D printing process of the cobalt-chromium alloy repair provided by this invention, the substrate is preheated at 400±20℃ to reduce residual stress.

[0036] In the 3D printing process for cobalt-chromium alloy restorations provided by this invention, online annealing is performed: local laser annealing is carried out every 5 layers printed, where "local" refers to the boundary area scanned by a laser spot with a diameter of 0.1-0.3 mm. The power is 40-80W, selectable as 40-60W or 60-80W, effectively reducing thermal stress.

[0037] In the 3D printing process of cobalt-chromium alloy repairs provided by this invention, a micro-nano-level anchoring structure is used: periodic inverted conical micropores are designed in the contour layer, with a diameter of 20-60μm, which can be selected as 20-40μm or 40-60μm; a depth of 10-50μm, which can be selected as 10-30μm or 30-50μm; and a spacing of 20-100μm, which can be selected as 20-60μm, 60-100μm, 20-40μm, 40-60μm, 60-70μm, or 80-100μm, increasing the mechanical bonding area of ​​ceramic powder by 40%.

[0038] In the 3D printing process for cobalt-chromium alloy repairs provided by this invention, the post-processing includes the following steps: 1) Surface activation treatment: The printed restoration is ultrasonically cleaned with an acidic solution containing ammonium fluoride to remove the surface oxide layer and form nanoscale pits on the surface of the printed restoration. 2) Solid element diffusion: The ultrasonically cleaned restoration print and doped powder from step 1) are heated in a hydrogen atmosphere, allowing the doped elements to penetrate into the restoration print. 3) In-situ oxidation treatment: The doped restoration printed part in step 2) is oxidized in-situ to obtain a composite oxide layer, and finally a cobalt-chromium alloy restoration is obtained.

[0039] This patent constructs a transition layer, namely a composite oxide layer, through a three-step process.

[0040] In the cobalt-chromium alloy restoration 3D printing process provided by the present invention, step 1) is surface activation treatment: the restoration printing part is ultrasonically cleaned with an acidic solution containing ammonium fluoride to remove the surface oxide layer and form nanoscale pits on the surface of the restoration printing part.

[0041] In step 1) of the present invention, the pH value of the acidic solution containing ammonium fluoride is 2.5-3.0, which can be selected as 2.5-2.8 or 2.8-3.0.

[0042] In step 1) of this invention, the cleaning time of the printed restoration is 5-8 minutes, which can be 5-6 minutes or 6-8 minutes.

[0043] In step 1) of the present invention, the diameter of the nanoscale pit is 50-100nm, which can be selected as 50-80nm or 80-100nm, and the depth is 20-50nm, which can be selected as 20-40nm or 40-50nm.

[0044] In one specific embodiment, the printed restoration is ultrasonically cleaned for 5-8 minutes with an acidic solution containing ammonium fluoride (NH4F) (pH=2.5-3.0) to remove the surface oxide layer (thickness reduced from 1.2μm to 0.3μm), exposing fresh metal to form nanoscale pits (diameter 50-100nm, depth 20-50nm), thereby increasing the specific surface area.

[0045] In the cobalt-chromium alloy restoration 3D printing process provided by this invention, step 2) solid element diffusion: the restoration printout after ultrasonic cleaning in step 1) and the dopant powder are heated in a hydrogen atmosphere, allowing the dopant elements to penetrate into the restoration printout. Specifically: In step 2) of this invention, the temperature is raised to 950-1000℃, which can be selected as 950-980℃ or 980-1000℃. The holding time is 2-3 hours, which can be selected as 2-2.5 hours or 2.5-3 hours.

[0046] In step 2) of this invention, the doped powder includes Si, Al, Zr, Sn, and Ce; the doping elements Si, Al, Zr, Sn, and Ce permeate to a depth of 30-50 μm; the concentration gradient changes as follows: Surface area 0.1-10μm: Si 5-8at%, Al 3-5at%, Zr 2-3at%, Sn 0-3at%, Ce0-3at%; Transition region 10-40 μm: elemental concentration decreases linearly; specifically, the overall concentration range in the transition region is Si 0-5 at%, Al 0-3 at%, Zr 0-2 at%, Sn 0-3 at%, Ce 0-3 at%; Core region (>40μm): Maintains the original composition of the powder, i.e., cobalt-chromium alloy powder, without any doped powder.

[0047] Doping elements have a synergistic effect: Si / Al enhances chemical bonding strength, Sn optimizes wettability, Ce strengthens interfacial toughness, and Zr forms an active oxide film, improving the stability and density of the oxide layer. This multi-component system enables the gold-ceramic bonding strength to be >40MPa (ISO 9693 standard ≥25MPa).

[0048] In the 3D printing process of cobalt-chromium alloy restorations provided by this invention, step 3) in-situ oxidation treatment: the doped restoration print from step 2) is subjected to in-situ oxidation to obtain a composite oxide layer, ultimately yielding the cobalt-chromium alloy restoration. Specifically: In step 3) of this invention, the temperature of the in-situ oxidation treatment is 1080-1120℃; it can be selected as 1080-1100℃ or 1100-1120℃.

[0049] In step 3) of this invention, the H2:H2O ratio in the wet hydrogen atmosphere is (1~3):1, which can be (1~2):1 or (2~3):1.

[0050] In step 3) of this invention, the composite oxide layer is formed by surface oxidation treatment.

[0051] In one specific embodiment, controlled oxidation is performed by treating the composite oxide layer for 1 hour in a humid hydrogen atmosphere (H2 / H2O=3 / 1) at 650°C.

[0052] Table 2: Three-step post-processing parameters and effects

[0053]

[0054] This composite oxide layer exhibits unique gradient thermal expansion properties, from 14.5 × 10⁻⁶ on the metal side. -6 / ℃ gradually changes to 13.0×10 on the ceramic side -6 / ℃, effectively buffering thermal stress. The metallurgical bond between the transition layer and the substrate avoids the problem of easy peeling of traditional coatings, and the shear strength reaches over 300MPa.

[0055] Methods for forming a ceramic layer on cobalt-chromium alloy restorations include the following: Phase 1: Pretreatment of Metal-Based Coronation This is the most critical step in ensuring that the ceramic adheres firmly to the cobalt-chromium alloy. Improper handling can lead to the ceramic layer peeling off (ceramic chipping).

[0056] 1. Cleaning: Objective: To remove residual grease, impurities and oxides from the alloy surface during casting, grinding and sandblasting processes.

[0057] Method: Place the thoroughly sandblasted and cleaned metal substrate crown into a ceramic furnace and heat it to approximately 950°C - 1050°C in air or vacuum, maintaining this temperature for a period of time (according to the furnace and material instructions). This allows surface impurities to burn and volatilize completely.

[0058] 2. Oxidation: Objective: To form a thin, dense chromium oxide (Cr2O3) film on a clean alloy surface. This oxide film serves as a bridge for the chemical bonding between ceramics and metals.

[0059] Method: The oxidation process is usually completed simultaneously with the cleaning step. At high temperatures, chromium in the cobalt-chromium alloy reacts with oxygen in the air to form Cr2O3. Temperature and time must be strictly controlled; excessive oxidation will produce an overly thick oxide layer, which becomes a weak point and leads to a decrease in bonding strength.

[0060] Phase Two: Construction and Sintering of Porcelain Powder Porcelain powder is typically constructed and sintered in several layers, each with its specific function. Modern porcelain powder is mostly vacuum sintered to eliminate air bubbles and obtain a dense structure.

[0061] Step 1: Sintering the Opaque Layer Purpose: To cover the color of the metal, providing a bright background for the subsequent aesthetic ceramic layer; at the same time, it forms a major chemical bond with the oxide film on the metal surface.

[0062] method: 1. Mix the opaque porcelain powder (containing a large amount of color-masking oxides, such as SnO2, TiO2, ZrO2) with distilled water or a special liquid to form a paste.

[0063] 2. Use a fine brush to evenly coat a thin layer (about 0.1-0.2mm) on the metal surface.

[0064] 3. Gently shake to absorb water and allow it to dry initially.

[0065] 4. Place the ceramic powder in a ceramic furnace and sinter under vacuum. The sintering temperature is usually 900°C - 950°C (strictly follow the sintering procedure provided by the ceramic powder supplier). The furnace chamber will first be evacuated, then the vacuum will be released at a specific temperature during the heating process to remove air bubbles, and finally the vacuum will be restored until sintering is complete.

[0066] Step Two: Construction and Sintering of Body / Dentin Porcelain and Enamel Porcelain Objective: To sculpt the anatomical shape and main color of the tooth crown, simulating the layered texture of natural teeth.

[0067] method: 1. Cut-back: First, make the complete shape of the crown on the model with wax or resin, and then evenly remove a layer (about 1.0-1.5mm) to leave space for porcelain powder.

[0068] 2. Construction: Neck porcelain: Darker porcelain powder is piled up on the neck.

[0069] Body porcelain: The main body of the dentin, forming its color and basic shape.

[0070] Incisal porcelain: A translucent glaze porcelain is built up at the incisal edge to imitate the transparency of the natural incisal edge of a tooth.

[0071] Transparent porcelain: A layer of highly transparent porcelain powder is piled on the outermost layer to increase the sense of depth and gloss.

[0072] 3. Condensation: After each layer is piled up, excess moisture is removed by tapping, shaking, absorbing water, and brushing, so that the porcelain powder particles are tightly packed together, reducing shrinkage during sintering.

[0073] 4. Pre-drying: The molded crowns are thoroughly dried in the furnace opening or dryer to prevent them from cracking due to excessive moisture evaporation when placed in the furnace.

[0074] 5. Sintering: Place the porcelain in a porcelain furnace and sinter according to the precise program provided by the porcelain powder manufacturer. The sintering temperature for body porcelain and glazed porcelain is usually lower than that for opaque porcelain, approximately 850°C - 900°C. Vacuuming is also required to obtain a dense, bubble-free porcelain layer. This process may be completed in 2-3 stages, with gradual building up and sintering to achieve the optimal shape and color.

[0075] Third stage: Shaping and glazing 1. Adjustment: After sintering, the restoration will shrink and deform to some extent. It needs to be tried on on a model and the occlusion and adjoint relationship adjusted with diamond burs.

[0076] 2. Glazing: Objective: To restore the surface gloss lost due to grinding, to form a smooth, easy-to-clean surface, and to seal micropores.

[0077] method: Self-glazing: After thoroughly cleaning the restoration, place it directly into a porcelain kiln and heat it under atmospheric pressure (not vacuum) to a temperature slightly lower than the sintering temperature of the porcelain body (about 20-30°C lower than the sintering temperature), so that the surface melts slightly and forms a gloss.

[0078] Add glaze powder: Coat the surface with a layer of transparent glaze powder paste, and then sinter it.

[0079] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0080] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0081] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0082] In the following embodiments, unless otherwise specified, all the raw materials of the present invention are commercially available or prepared according to conventional methods in the art.

[0083] Example 1: This invention provides a 3D printing process for reducing the occurrence of porcelain cracking in cobalt-chromium alloy restorations. An example of using this invention to fabricate anterior all-ceramic crowns is as follows: The cobalt-chromium alloy powder raw material is prepared using the plasma rotating electrode method (PREP). The specific steps include: Step 1: Pretreatment - Electrode Rod Preparation 1. Alloy smelting and casting: First, cobalt, chromium, molybdenum, tungsten, silicon, manganese, and boron metal raw materials that meet dental standards, yttrium oxide, and lanthanum oxide are smelted in a vacuum induction furnace according to the proportions in Table 3.

[0084] 2. Casting and Machining: The molten alloy is cast into round ingots, and then processed into precisely sized consumable electrode rods through machining methods such as forging, turning, or grinding. The electrode rods have a diameter of 80 mm and a length of up to several hundred millimeters, and their surfaces need to be smooth to ensure the stability of the process.

[0085] Step 2: Core Technology - Plasma Rotating Electrode Atomization 1. Clamping and Rotation: Precisely clamp one end of the prepared cobalt-chromium alloy electrode rod onto the high-speed rotating spindle (anode) inside the chamber. The spindle speed is 30,000 RPM.

[0086] 2. Arc Ignition and Melting: One or more plasma torches (cathodes) are installed near the end face of the electrode rod. After the working gas (such as argon) is introduced, a high-temperature plasma arc (temperature can reach 10,000℃) is generated between the plasma torch and the end face of the electrode rod. The plasma arc instantly melts the end face of the rotating electrode locally.

[0087] 3. Liquid Film Formation and Atomization: Under strong centrifugal force, the molten liquid metal will not drip, but will form an extremely thin liquid film covering the electrode end face. When the centrifugal force exceeds the surface tension of the liquid metal, the molten metal film will be ejected from the electrode edge in the form of extremely fine droplets.

[0088] 4. Flight and Solidification: As these ejected high-temperature droplets fly towards the cabin wall, they rapidly solidify into spherical particles under the cooling effect of the inert gas. Due to surface tension and the absence of collisions during flight, the resulting powder particles have extremely high sphericity (typically >98%), smooth surfaces, and minimal satellite dust.

[0089] The third step is post-processing - powder treatment and classification. 1. Collection: The solidified powder particles will settle into the collection tank at the bottom of the process chamber.

[0090] 2. Sieving: The collected raw powder has a wide particle size distribution (potentially ranging from a few micrometers to hundreds of micrometers). The powder is sieved to the desired specific particle size distribution using an ultrasonic vibrating sieve or an air classifier system. For dental SLM printing, the target size is typically 53 μm.

[0091] 3. Batch Combining and Packaging: Different batches of sieved, qualified powder are mixed (batch combining) to ensure uniform composition and performance of the large batch of powder. Finally, the powder is vacuum-sealed under inert gas protection to prevent oxidation and contamination during storage.

[0092] The composition and properties of cobalt-chromium alloy powder are shown in the table below: Table 3: Composition of Cobalt-Chromium Alloy Powder

[0093] Table 4: Properties of Cobalt-Chromium Alloy Powder Particle size distribution Loose packing density Tap density Hall flow rate 15-45μm 5.2 g / cm³ 5.8 g / cm³ 16 s / 50g 3D printing uses the following process route: 1. Preheat the substrate to 420℃ for 30 minutes; 2. Scan the surface area; 3. Scan the transition region; 4. Scan the core area; The scanning parameter settings are shown in Table 5. During printing, the junction area was scanned with a 0.1 mm diameter, 60 W power laser spot every 5 layers for laser annealing. Periodic inverted conical micropores with a diameter of 30 μm, a depth of 20 μm, and a spacing of 80 μm were printed on the surface of the restoration.

[0094] Table 5: Printing Parameter Settings

[0095] After printing, the restoration was ultrasonically cleaned for 8 minutes with an acidic solution containing ammonium fluoride (NH4F) (pH=2.5). Then, the restoration and doped powder (containing Si, Al, Zr, Sn, and Ce elements) were placed together in a sealed container and heated to 1000℃ in a hydrogen atmosphere for 3 hours. Finally, it was treated in a humid hydrogen atmosphere (H2 / H2O=3 / 1) at 650℃ for 1 hour to generate a composite oxide layer. The improvement in restoration performance compared to traditional 3D printed parts is shown in Table 6.

[0096] Comparative Example 1 Traditional 3D Printing: Phase 1: Pre-printing Preparation

[0097] 1. 3D model design Using CAD software (such as SolidWorks, CATIA) or acquiring data through a 3D scanner, a three-dimensional digital model of the part to be printed is designed. In the dental field, this is typically based on the design of crowns, bridges, frameworks, etc., based on the patient's oral scan data.

[0098] Model slicing and generation support STL file conversion: Convert CAD models into STL format files that are compatible with 3D printing equipment.

[0099] Adding Support Structures: Since the metal printing process requires supporting the suspended portions of the current layer, aiding in heat dissipation, and preventing deformation, delicate support structures must be added to the model automatically or manually. This is a crucial step in dental printing, and the support design directly impacts the success rate. Slicing: Specialized software "slices" the 3D model along the Z-axis (height direction) into thousands of extremely thin two-dimensional cross-sectional layers (dental layer thickness is commonly 20-30μm), and generates laser scanning path codes (G-code) for each layer.

[0100] 3. Equipment and Material Preparation Clean the forming cylinder: Ensure the substrate of the printing platform is clean and flat.

[0101] Powder loading: Fill the printing equipment's powder supply cylinder with sealed metal powder (such as cobalt-chromium alloy powder).

[0102] Inert atmosphere protection: After closing the chamber door, the printing chamber is evacuated and filled with high-purity inert gas (usually argon) to reduce the oxygen content inside the chamber to an extremely low level (usually <1000 ppm) to prevent the metal from oxidizing at high temperatures.

[0103] Phase Two: Printing Process This is a layered, cyclical process, carried out entirely under the protection of an inert atmosphere: 4. Spread powder The powder supply cylinder rises to a certain height, and a scraper or roller spreads a thin layer of metal powder (with the same thickness as the slice layer) evenly on the printing substrate or the previous formed layer.

[0104] 5. Laser scanning melting A high-power precision fiber laser (typically 200-500W) scans and irradiates the powder bed according to the slice data of the current layer, following a preset path, power, and speed (see Table 5).

[0105] The metal powder at the focal point of the laser beam absorbs energy instantly, completely melts (rather than sinters), and achieves metallurgical bonding with the underlying solidified metal.

[0106] Laser scanning paths (strategies) are carefully designed (such as stripe scanning and checkerboard scanning) to distribute heat and reduce stress and deformation.

[0107] 6. Platform descent and cycle After scanning one layer, the forming cylinder descends 100μm.

[0108] The powder supply cylinder rises, and the scraper spreads powder again.

[0109] The laser begins scanning the next layer.

[0110] This process is repeated until the entire part is completely printed. At this point, the part is completely encased in unmelted metal powder.

[0111] Phase 3: Post-printing processing The printed parts cannot be used directly; they must undergo a series of post-processing steps, which is crucial for dental restorations.

[0112] 7. Powder recovery and parts removal After printing is complete, you need to wait for the forming cylinder to cool down to a safe temperature.

[0113] Carefully remove the forming cylinder from the equipment and brush away or use a powder suction machine to collect the unmelted powder coating the parts. Most of this powder can be reused after sieving.

[0114] The substrate with the printed parts is moved to the worktable.

[0115] 8. Wire cutting excision Electrical discharge machining (EDM) is used to cut the printed parts off the substrate. This is standard practice because direct physical cutting would damage both the parts and the substrate.

[0116] 9. Remove the supporting structure. The support structure added during printing is carefully removed by cutting with pliers, vibrating, or sanding. This is a process that requires extremely delicate handling.

[0117] 10. Heat Treatment The printed parts have huge residual stress and uneven structure.

[0118] Hot isostatic pressing (HIP) or annealing in a protective atmosphere must be performed to eliminate internal stress, reduce defects (such as porosity), homogenize chemical composition, and optimize microstructure, thereby improving the mechanical properties and durability of the parts.

[0119] 11. Surface Treatment Sandblasting: Using tiny glass beads or alumina particles to sandblast parts removes residual powder and impurities from the surface and obtains a uniform matte surface.

[0120] Polishing: Dental restorations need to be highly polished to a mirror finish to prevent plaque buildup and improve aesthetics and comfort.

[0121] Other: For certain performance requirements, electropolishing may also be performed.

[0122] Table 6: Improvement effect of thermochemical post-treatment in Example 1 and Comparative Example 1

[0123] (i) Test method for metal-ceramic bond strength ISO 9693:2019; "Dental Science: Test method for metal-ceramic bond strength of restorations"

[0124] 1. Sample preparation Metal substrate: Cobalt-chromium alloy is typically cast or printed into disc-shaped specimens with a diameter of 10-15 mm and a thickness of 2-3 mm. Its surface requires the same treatments as in clinical applications, including sandblasting, cleaning, and sintering of an oxide layer.

[0125] Ceramic layer sintering: A cylindrical ceramic block with a diameter of 3-5 mm and a height of 2-3 mm is deposited and sintered in the center of a metal substrate using a specialized mold. The sintering process must strictly follow the instructions of the ceramic powder manufacturer.

[0126] 2. Testing apparatus The prepared sample is fixed on the universal testing machine.

[0127] Using a special clamp (or hard metal rod), apply a shear force parallel to the metal substrate to the top of the ceramic column at a crosshead speed of 0.5-1.0 mm / min.

[0128] The direction of the force should be as close as possible (distance <0.1mm) to the metal-ceramic bonding interface.

[0129] 3. Data Processing Record the maximum load value F_max (unit: N) at the time of failure.

[0130] Calculate the bond strength: σ = F_max / A σ represents the shear bond strength (unit: MPa or N / mm²). A is the base area of ​​the ceramic column (unit: mm²). A = π * r² (r is the radius of the ceramic column)

[0131] 4. Failure Mode Analysis (Crucial) After testing, the failed surface must be observed under a microscope to determine the type of failure. This is more informative than the strength value itself. A. Adhesive Failure: Failure occurs entirely at the metal-ceramic interface. This indicates poor bonding strength and is the least desirable failure mode.

[0132] B. Cohesive Failure: Cohesive failure in ceramics: Failure occurs inside the ceramic. This indicates that the bond strength between the metal and ceramic is higher than the strength of the ceramic itself, which is the ideal result and proves that the bond is very strong.

[0133] Cohesive failure of metals: Failure occurs inside the metal oxide layer.

[0134] C. Mixed Failure: This type of failure encompasses multiple modes mentioned above. It is the most common outcome. The report should indicate the approximate proportion of each mode.

[0135] (ii) Test method for porcelain chipping rate under thermal shock cycle ISO 9693:2019 "Dental science, metal-ceramic restorations, test method for the strength of the metal-ceramic bond", the standard specifies thermal shock cycle as part of the metal-ceramic bond performance test (usually performed before mechanical performance test).

[0136] Sample preparation: Prepare specimens identical to those used in the gold-ceramic bond strength test (usually disc-shaped specimens with sintered ceramic pillars on a metal substrate).

[0137] Number of samples: at least 15 per group to ensure statistical significance.

[0138] Circulating medium: Deionized water is typically used as the medium to avoid the effects of scale buildup. Some studies have also used media such as silicone oil, but water is the most commonly used due to its high specific heat capacity and ubiquity.

[0139] Temperature setting: High-temperature bath: 60 ± 2 ℃ (simulates hot food, such as drinking coffee) Low-temperature bath: 5 ± 2 ℃ (simulates cold food, such as eating ice cream and drinking ice water) Temperature difference: A temperature difference of 55°C is key to generating significant thermal stress.

[0140] Loop parameters: Dwelling Time: The soaking time in each tank is 30 seconds. This time is sufficient for the entire sample to reach the tank temperature.

[0141] Transfer Time: The time it takes for the sample to move between the two tanks should be as short as possible, with the standard requirement being no more than 2 seconds. Rapid transfer is key to generating "thermal shock".

[0142] Number of Cycles: 10,000 or 20,000. This depends on the research objectives and standard requirements.

[0143] 10,000 cycles are roughly equivalent to 2-5 years of clinical use.

[0144] A cycle of 20,000 times simulates a longer usage time.

[0145] Test process: 1. Place the sample in the sample basket.

[0146] 2. Start the equipment, and the robotic arm will automatically move the sample back and forth between the high-temperature bath and the low-temperature bath.

[0147] 3. Each complete "hot-cold" or "cold-hot" process is counted as one cycle.

[0148] 4. Continue until the preset number of cycles is reached.

[0149] (III) Interfacial Shear Strength Test Method ISO 9693:2019, "Dental science, metal-ceramic restorations, test method for the strength of the metal-ceramic bond," defines the interface shear strength test as the most fundamental and commonly used method for evaluating the performance of the metal-ceramic bond. It aims to quantify the stress required for the ceramic layer to peel off from the metal substrate.

[0150] Specimen Preparation This is the first and crucial step in ensuring the accuracy of the results.

[0151] Metal substrate: Material: The cobalt-chromium alloy to be tested (which may be cast or 3D printed).

[0152] Shape and size: Typically disc-shaped, with a diameter ≥ 10 mm and a thickness ≥ 2 mm. The size must be large enough to avoid overall deformation during testing.

[0153] Surface treatment: One plane of the metal substrate needs to undergo the same treatment process as in clinical applications: sandblasting (usually with 110μm alumina) → ultrasonic cleaning → drying → sintering oxide layer (if necessary).

[0154] Porcelain layer sintering: Ceramic powder is deposited in the center of a metal substrate using a stainless steel mold (typically with an inner diameter of 3.0 mm or 3.5 mm and a height of 2.0 mm or 3.0 mm).

[0155] The processes of slab compaction, sintering, and sintering of ceramic powder must be strictly followed in accordance with the manufacturer's instructions (including preheating, sintering temperature, vacuum level, cooling rate, etc.).

[0156] After sintering, the ceramic column should form a regular cylinder.

[0157] 2. Test Setup Equipment: Universal testing machine.

[0158] Shearing fixture: This is the core component. The fixture should have a notched base for securing the metal base, and a loading rod.

[0159] Key requirement: The cutting edge of the loading rod must be very close to the metal-ceramic interface (distance should be <0.1 mm) to ensure that pure shear force, rather than bending moment, is generated. Excessive distance will result in an excessively long lever arm, generating a significant torque and leading to inaccurate test results.

[0160] Loading rate: A constant displacement rate of 0.5 mm / min or 1.0 mm / min is applied. This rate simulates quasi-static failure and more realistically reflects material properties.

[0161] 3. Data Recording Record the load-displacement curve in real time.

[0162] Record the maximum load value F_max (unit: Newtons, N) at the time of failure.

[0163] 4. Calculate the shear strength. Shear strength (σ) is calculated using the following formula: σ = F_max / A

[0164] σ: Shear strength, measured in megapascals (MPa) or N / mm².

[0165] F_max: The maximum load at failure, in Newtons (N).

[0166] A: The cross-sectional area of ​​the ceramic column, measured in square millimeters (mm²). A = π * r² (where r is the radius of the ceramic column).

[0167] 5. Failure Mode Analysis - Crucial After testing, the failure surface must be observed under a stereomicroscope or scanning electron microscope (SEM) to determine the type of failure. This is more important for interpreting the results than the intensity value itself.

[0168] A. Adhesive Failure: Failure occurs at the metal-ceramic interface. This indicates poor bonding strength and is the least desirable mode.

[0169] B. Cohesive Failure: Cohesive failure in ceramics: Failure occurs inside the ceramic. This indicates that the bond strength between the metal and ceramic is higher than the strength of the ceramic itself, which is the ideal result and proves that the bond is very strong.

[0170] Cohesive failure of metals: Failure occurs inside the metal oxide layer.

[0171] C. Mixed Failure: This type of failure includes multiple modes mentioned above and is the most common outcome. The report should indicate the approximate proportion of each mode.

[0172] An excellent result is: high shear strength (far exceeding the standard) + failure mode dominated by ceramic cohesive failure.

[0173] Furthermore, the ISO 9693 standard requires... According to ISO 9693:2019, for precious metals and cobalt-chromium alloys, the strength of their metal-ceramic bond must meet the following minimum requirement: ≥ 25 MPa.

[0174] Excellent modern cobalt-chromium alloy systems typically require shear strengths of 35-60 MPa or even higher.

[0175] Example 2 Compared with Example 1, the difference is that the repair body and the doped powder (containing Si, Al, Zr, Sn and Ce elements) are placed together in a sealed container and heated to 1000°C in a hydrogen atmosphere for 2 hours.

[0176] Table 7. Thermochemical post-treatment improvement effects of Example 2 and Comparative Example 1

[0177] Example 3 Compared with Example 1, the difference is that the repair body and the doped powder (containing Si, Al, Zr, Sn and Ce elements) are placed together in a sealed container and heated to 1000°C in a hydrogen atmosphere for 6 hours.

[0178] Table 8. Thermochemical post-treatment improvement effects of Example 3 and Comparative Example 1

[0179] Example 4 Compared with Example 1, the difference is that the repair body and the doped powder (containing Si, Al, Zr, Sn and Ce elements) are placed together in a sealed container and heated to 1000°C in a hydrogen atmosphere for 0.5 hours.

[0180] Table 9. Thermochemical post-treatment improvement effects of Example 4 and Comparative Example 1

[0181] In summary, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0182] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A cobalt-chromium alloy powder, characterized in that, The cobalt-chromium alloy powder comprises the following components by weight percentage: Co: 58-64wt%; Cr: 25-31 wt%; Mo: 5-6 wt%; W: 2-3 wt%% Si: 0.8-1.2 wt%; Mn: 0.5-1.0 wt%; Rare earth oxides: 0.1-0.3 wt%.

2. The cobalt-chromium alloy powder according to claim 1, characterized in that, It also includes one or more of the following conditions: A1) The particle size distribution of the cobalt-chromium alloy powder is 15-45 μm; A2) The D50 of the cobalt-chromium alloy powder is 30±3μm; A3) Prepared using the plasma rotating electrode method, with a sphericity ≥98%; A4) Flowability of cobalt-chromium alloy powder: ≤30s / 50g; Oxygen content: ≤0.08wt%; A5) The rare earth oxides are selected from yttrium oxide and lanthanum oxide; A6) The cobalt-chromium alloy powder also includes other components, namely boron and / or gallium, with a total content of 0.01 to 1.0 wt%.

3. A 3D printing process for dental cobalt-chromium alloy restorations that reduces porcelain cracking rate, characterized in that, The printing process includes: using cobalt-chromium alloy powder as described in any one of claims 1 to 2 for 3D printing; printing the core area, transition area and surface area separately by dynamic energy density modulation during the printing process to obtain the repair body print; and post-processing the cobalt-chromium alloy print to obtain the cobalt-chromium alloy repair body.

4. The 3D printing process for dental cobalt-chromium alloy restorations with reduced porcelain cracking rate according to claim 3, characterized in that, It also includes one or more of the following conditions: B1) The core area printing: power is 190-210W, scanning speed is 900-1100mm / s, energy density is 65-80J / mm³, forming a dense equiaxed crystal structure; B2) Printing of the transition zone: power reduced to 170-190W, scanning speed adjusted to 700-900mm / s, energy density 85-100J / mm³, to generate a mixed structure of columnar and equiaxed crystals; B3) Surface area printing: laser power 160-175W, scanning speed 500-700mm / s, superimposed 100-200Hz high frequency vibration, energy density 110-130J / mm³, forming a nanocrystalline surface layer.

5. The 3D printing process for dental cobalt-chromium alloy restorations with reduced porcelain cracking rate according to claim 4, characterized in that, It also includes one or more of the following conditions: B11) In feature B1), the porosity of the dense equiaxed crystal structure is <0.05%; B21) In feature B2), the elastic modulus of the mixed columnar and equiaxed crystal structure is 18-25 GPa; B31) In feature B3), the grain size of the nanocrystalline surface layer is 50-100 nm; B32) In feature B3), the surface roughness Ra of the nanocrystalline surface layer is stable at 3.5-4.0 μm.

6. The 3D printing process for dental cobalt-chromium alloy restorations with reduced porcelain cracking rate according to claim 3, characterized in that, It also includes one or more of the following conditions: C1) The substrate is preheated at 400±20℃; C2) Online annealing: Local laser annealing is performed every 5 layers printed, with a power of 40-80W; C3) Micro-nano-scale anchoring structure: Periodic inverted conical micropores are designed in the contour layer.

7. The 3D printing process for dental cobalt-chromium alloy restorations with reduced porcelain cracking rate according to claim 3, characterized in that, It also includes one or more of the following conditions: In feature C2), the local area is the boundary region of the light spot scan with a diameter of 0.1-0.3 mm; C31) In feature C3), each of the periodic inverted conical micropores has a diameter of 20-60 μm, a depth of 10-50 μm, and a spacing of 20-100 μm between adjacent periodic inverted conical micropores.

8. The 3D printing process for dental cobalt-chromium alloy restorations with reduced porcelain cracking rate according to claim 3, characterized in that, The post-processing includes the following steps: Surface activation treatment: The printed restoration is ultrasonically cleaned with an acidic solution containing ammonium fluoride to remove the surface oxide layer and form nanoscale pits on the surface of the printed restoration. Solid element diffusion: The ultrasonically cleaned restoration printout after step 1) is heated with doped powder in a hydrogen atmosphere, so that the doped elements penetrate into the restoration printout; In-situ oxidation treatment: The doped restoration printed part in step 2) is oxidized in-situ to obtain a composite oxide layer, and finally a cobalt-chromium alloy restoration is obtained.

9. The 3D printing process for dental cobalt-chromium alloy restorations with reduced porcelain cracking rate according to claim 8, characterized in that, It also includes one or more of the following conditions: D1) In step 1), the pH value of the acidic solution containing ammonium fluoride is 2.5-3.0; In step 1) of D2), the cleaning time for the printed restoration is 5-8 minutes; In step 1) of D3), the diameter of the nanoscale pit is 50-100nm and the depth is 20-50nm; In step 2) of D4, heat to 950-1000℃; In step 2) of D5, the heat preservation time is 2-3 hours; In step 2) of D6), the doped powder includes Si, Al, Zr, Sn, and Ce; the dopant elements Si, Al, Zr, Sn, and Ce permeate to a depth of 30-50 μm; the concentration gradient changes as follows: Surface area 0.1-10μm: Si 5-8at%, Al 3-5at%, Zr 2-3at%, Sn 0-3at%, Ce0-3at%; Transition region 10-40μm: The concentrations of doping elements Si, Al, Zr, Sn, and Ce decrease linearly; Core area >40μm: Maintains the original powder composition; In step 3) of D7), the temperature for in-situ oxidation treatment is 1080-1120℃; In step 3) of D8, the ratio of H2:H2O in the wet hydrogen atmosphere is 1-3:

1.

10. A cobalt-chromium alloy restoration, characterized in that, The dental cobalt-chromium alloy restoration was prepared using a 3D printing process for reducing porcelain cracking rate as described in any one of claims 3 to 9.

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