Ultra-fine grain gradient hard alloy cutter and preparation method thereof

Abstract

The invention relates to the technical field of hard alloy machining, and particularly discloses an ultra-fine grain gradient hard alloy cutter which comprises a hard alloy matrix and a coating deposited on the surface of the hard alloy matrix, and the hard alloy matrix comprises the following raw materials of, by mass, 10-12% of Co, 0.5-0.7% of VC, smaller than or equal to 0.6% of TaC, smaller than or equal to 0.8% of NbC, 0.5-0.6% of Cr3C2, 0.8-1.0% of Ti (C, N), 0.5-0.8% of TiN, 0.3-0.5% of Ni and the balance WC; the coating comprises a TiN bottom layer, a TiCN transition layer, an amorphous Al2O3 nucleating layer, an alpha-Al2O3 layer and a columnar crystal TiN top layer which are sequentially arranged from inside to outside. A preparation method of an ultra-fine grain gradient hard alloy cutter comprises the following steps that firstly, raw materials are weighed according to the proportion; secondly, WC powder is subjected to vacuum dehydration and then sieved; step 3, ion-assisted ball milling; fourthly, a green body is obtained through compression molding, gradient sintering is conducted on the green body, and a hard alloy matrix is obtained; 5, scanning on the surface of the hard alloy matrix by adopting a laser, then carrying out sand blasting to remove an oxide layer, and then carrying out ultrasonic cleaning; and 6, sequentially depositing coatings by adopting CVD (Chemical Vapor Deposition) equipment. According to the scheme, the grain size D50 is smaller than or equal to 0.5 mu m, coarse grain aggregation is avoided, and the adaptability of a matrix gradient layer and the thermal expansion coefficient of a coating is improved.

Description

Technical Field

[0001] The invention relates to the technical field of cemented carbide processing, in particular to an ultrafine-grained gradient cemented carbide tool and a preparation method thereof. Background Art

[0002] Since their introduction in the mid-20th century, cemented carbide cutting tools have become a core cutting tool in modern manufacturing, thanks to their high hardness, wear resistance, and chemical stability. With the advancement of precision machining technology, ultrafine-grained cemented carbide cutting tools (grain size ≤ 0.5 μm) have gained widespread application in aerospace, precision molds, and other fields due to their higher strength (flexural strength ≥ 4000 MPa) and wear resistance. However, WC-Co-based cemented carbide produced using traditional processes still faces two major technical bottlenecks.

[0003] Existing ultrafine-grained cemented carbide preparation technology (such as patent CN117684036B) suppresses abnormal grain growth during sintering by adding grain inhibitors such as VC and Cr3C2. However, it has the following key defects in industrial applications: First, powder dispersion defects: ultrafine tungsten carbide powder (D 50 ≤0.5μm) is prone to form agglomerates with a size of >3μm due to the cold welding effect during the mechanical ball milling process. Literature shows that after 30 hours of conventional ball milling, 1.2-3.5% of coarse particles (>1μm) still remain, resulting in abnormal local grain growth after sintering. Although patent CN117684036B uses a staged ball milling strategy (coarse grinding → ion-assisted fine grinding) to increase the bending strength to 4330MPa, the coarse grain aggregation phenomenon has not been fundamentally solved. The core reasons include: First, the uneven distribution of inhibitors: Cubic carbides such as TaC / NbC have a low diffusion coefficient (D=1.2×10 at 800℃) -14 m² / s), it is difficult to achieve atomic-level dispersion with traditional ball milling process, and it is easy to form a diffusion barrier at the WC grain boundary; secondly, the oxygen content is out of control: the ultrafine powder has a large specific surface area (≥3.5 m 2 / g), the oxygen content is likely to rise to 800-1200ppm during ball milling, causing the sintering density to drop below 99.2%.

[0004] Second, gradient structure failure: Existing coated tools (such as patent CN111826655A) use TiN / TiCN / Al2O3 structure, but due to the matrix (CTE = 5.5×10 -6 / K) and electroplated Al2O3 coating (CTE is about 8.3×10 -6 The mismatch in thermal expansion coefficients (K) between the two materials leads to thermal stress spalling during high-temperature cutting. This patent improves bonding by adding a TiAlYN transition layer, but the hardness of the electroplated oxide layer is only 1500 HV, which is difficult to meet the processing requirements of hardened steel. Summary of the Invention

[0005] The present invention is intended to provide an ultrafine-grained gradient cemented carbide tool and a preparation method thereof, and is intended to simultaneously achieve a grain size D 50 ≤0.5μm and no coarse crystal aggregation, and improve the adaptability of the thermal expansion coefficient of the substrate gradient layer and the coating.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: An ultrafine-grained gradient cemented carbide tool comprises a cemented carbide substrate and a coating deposited on the surface of the cemented carbide substrate, wherein the cemented carbide substrate comprises the following raw materials in percentage by mass: Co 10-12%, VC 0.5-0.7%, TaC ≤ 0.6%, NbC ≤ 0.8%, Cr3C2 0.5-0.6%, Ti(C,N) 0.8-1.0%, TiN 0.5-0.8%, Ni 0.3-0.5%, and the balance WC; The coating includes a TiN bottom layer, a TiCN transition layer, an amorphous Al2O3 nucleation layer, an α-Al2O3 layer, and a columnar TiN top layer, which are arranged from the inside to the outside. The thickness of the bottom TiN layer is 0.5-1.0μm, the TiCN transition layer is 2.0-5.0μm, the thickness of the amorphous Al2O3 nucleation layer is 0.1-0.3μm, the thickness of the α-Al2O3 layer is 4.0-5.0μm, and the thickness of the columnar TiN top layer is 1.0-1.5μm.

[0007] Preferably, as an improvement, the TiCN transition layer has a structure that gradually changes from columnar crystals to equiaxed crystals, so that the thermal expansion coefficient is more matched with the inner and outer layers.

[0008] Preferably, as an improvement, the aspect ratio of the columnar TiN top layer is ≥3.

[0009] The present invention also provides a method for preparing an ultrafine-grained gradient cemented carbide tool, comprising the following steps: Step 1: weigh the raw materials according to the ratio of claim 1; Step 2: WC powder is vacuum dehydrated and then sieved; Step 3: ion-assisted ball milling; Step 4: pressing and molding to obtain a green body, and gradient sintering the green body to obtain a cemented carbide matrix; Step 5: Use laser to scan the surface of cemented carbide substrate, then sandblast to remove the oxide layer, and then ultrasonically clean; Step 6: Use CVD equipment to deposit TiN bottom layer - TiCN transition layer - amorphous Al2O3 nucleation layer - α-Al2O3 layer - columnar crystal TiN top layer in sequence.

[0010] Preferably, as an improvement, the ion-assisted ball milling includes the following three stages: Initial stage: put WC, Co, VC powder into the ball mill, and mill at 350±10rpm under argon protection until the powder D 90 ≤1.0μm; Mid-term ball milling: Add TaC and NbC powders, turn on the pulse bias, tilt the ball mill tank 30°, and mill for 2.5-3.5 hours; Later ball milling: add Cr3C2, TiN, Ti(C,N) powders, spray into 0.1% zinc stearate ethanol solution, and ball mill at 250±10rpm until the powder D 50 =0.30μm (±0.05μm), oxygen content ≤500ppm.

[0011] This scheme achieves uniform dispersion by sequential feeding in the ball milling stage (first high energy crushing of basic components → mid-term electric field dispersion of high density phase → late protective mixing of brittle phase). 50 ≤0.5μm and no coarse grains >1μm, ensuring the flexural strength after sintering ≥4500MPa.

[0012] Preferably, as an improvement, the gradient sintering steps are as follows: First, the temperature was raised to 1150°C and kept for 30 minutes, then cooled to 800°C, then raised to 1380°C and kept for 60 minutes, then cooled to 1100°C and kept for 20 minutes, and finally slowly cooled to room temperature.

[0013] In this scheme, pre-sintering at 1150°C is intended to allow TiN / Ti(C,N) to initially diffuse and position in a metastable state, followed by cooling to prevent overreaction. 800°C is the cobalt phase transition point (HCP→FCC), and keeping at this temperature can reorganize the cobalt distribution and eliminate lattice distortion. Finally, full densification is achieved at 1380°C. This scheme breaks the unidirectional heating and densification method of the conventional sintering process and adopts an "up-down-up" oscillating temperature control method, thereby achieving the effect of precise control of the gradient layer thickness and zero microcracks in the substrate.

[0014] Preferably, as an improvement, the CVD device deposits the coating in the following steps: A: TiN bottom layer: 850±10℃ deposition 0.5-1.0μm; B: TiCN transition layer: 2.0-3.0 μm was deposited at 900±10℃, and the CH3CN / TiCl4 molar ratio was gradually controlled from 0.8 to 0.3 during the deposition process; C: amorphous Al2O3 nucleation layer: 0.1-0.3 μm deposited at 600±10℃; D: α-Al2O3 layer: 4.0-5.0 μm deposition at 980±10℃, with H2S / H2=0.005; E: Columnar TiN top layer: 1-1.5 μm deposited by magnetron sputtering at 500±10℃.

[0015] In this scheme, the CH3CN / TiCl4 molar ratio is gradually controlled from 0.8 to 0.3 during the deposition of the TiCN transition layer, thereby forming columnar crystals in a carbon-rich environment with a high proportion of CH3CN, thereby enhancing toughness. In the subsequent gradual reduction, the compositional mutation that causes internal stress concentration can be avoided. The amorphous Al2O3 nucleation layer (0.1-0.3μm) is deposited at a low temperature of 600℃ to prevent thermal damage to the substrate, and the Co-rich gradient layer (CTE = 7.2×10 -6 / K) greatly improves the coating adhesion.

[0016] Preferably, as an improvement, before the amorphous Al2O3 nucleation layer is deposited, the TiCN transition layer is etched by hydrogen plasma at 900°C.

[0017] Preferably, as an improvement, when there is a time difference between ball milling and pressing, the metal powder obtained by ball milling is coated with zinc stearate and then temporarily stored. Preferably, as an improvement, the temporary storage method is as follows: zinc stearate powder is added to the powder obtained by ball milling by dry method and stirred evenly, then dried, and finally stored in a packaging bag containing an oxygen absorber.

[0018] In the preparation of traditional cemented carbide tools, the raw material powder has a coarse particle size, a small specific surface area, a low activity, a slow oxidation rate, and the effect of oxygen content on sintering performance is relatively controllable. Therefore, in the traditional process, the powder after ball milling can be directly pressed into shape without the need for strict oxygen control during storage. However, in the case of ultrafine-grained cemented carbide tools, especially this solution, the metal powder can be ball milled to D 50 =0.30μm (±0.05μm), the specific surface area increases sharply. If the metal powder is directly pressed without oxygen control, the greatly increased specific surface area will increase oxygen adsorption, which will lead to grain coarsening during sintering. In addition, a low-oxygen environment is a prerequisite for the free migration of the Co liquid phase. Excessive oxygen content will hinder the formation of a Co-rich layer on the surface. This solution uses zinc stearate coating to physically isolate oxygen, uses oxygen absorbers for chemical deoxidation, and uses packaging bags for oxygen isolation to ensure the oxygen content of the metal powder when it is pressed and used.

[0019] The technical principles and advantages of the present invention are: First, the core of the present invention lies in the coupling effect of the TiN / Ti(C,N) cooperative diffusion system and the triple inhibitor: Diffusion mechanism: TiN decomposes during pre-sintering at 1150℃ (TiN→Ti+N), and the released N atoms react with the surface WC to form WN (WC+2N→WN+C), consuming W atoms to form a W-poor region; the C / N elements in Ti(C,N) form a low-melting-point eutectic phase (Co-WCN) with Co, which drives Co to migrate to the W-poor region during liquid phase sintering at 1380℃, forming a 8-10μm thick Co-rich layer, which reduces the CTE of the substrate surface from 5.5×10 -6 / K increased to 7.2×10 -6 / K.

[0020] Inhibition system: ① VC (0.5-0.7%) pins the WC grain boundary and inhibits grain boundary migration; ② Then Cr3C2 (0.5-0.6%) coats the WC particles to block contact; ③ TaC / NbC stabilizes the grain boundary, and the three work together to 50 The particle size is controlled at ≤0.5μm. Adding Ni (0.3-0.5%) lowers the melting point of the Co phase and increases the density to 99.8%.

[0021] Secondly, to address the grain coarsening problem, the triple inhibitor (VC+ Cr3C2+TaC / NbC) is uniformly dispersed in the ball milling stage by sequentially feeding (first high-energy crushing of basic components → mid-term electric field dispersion of high-density phase → late protective mixed brittle phase). 50 ≤0.5μm and no coarse grains >1μm, flexural strength ≥4500MPa. To prevent coating peeling, the amorphous Al2O3 nucleation layer (0.1-0.3μm) is deposited at 600℃ in the five-step deposition process to block thermal damage to the substrate, combined with the Co-rich gradient layer (CTE = 7.2×10 -6 / K) greatly improves the coating adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic cross-sectional view of an ultrafine-grained gradient cemented carbide tool according to an embodiment of the present invention.

[0023] The reference numerals in the drawings of the specification include: Co-rich layer 1, TiN bottom layer 2, TiCN transition layer 3, amorphous Al2O3 nucleation layer 4, α-Al2O3 layer 5, columnar crystal TiN top layer 6. DETAILED DESCRIPTION

[0024] The following is further described in detail through specific implementation methods: Example An ultrafine-grained gradient cemented carbide tool comprises a cemented carbide substrate and a coating deposited on the surface of the cemented carbide substrate, wherein the cemented carbide substrate comprises the following raw materials in percentage by mass: Co 10%, VC 0.5%, TaC 0.4%, NbC 0.7%, Cr3C20.5%, Ti(C,N) 0.8%, TiN 0.5%, Ni 0.5%, and the balance is WC; The coating includes a TiN bottom layer, a TiCN transition layer, an amorphous Al2O3 nucleation layer, an α-Al2O3 layer, and a columnar TiN top layer, which are arranged from the inside to the outside. The thickness of the bottom TiN layer is 0.5-1.0μm, the TiCN transition layer is 2.0-5.0μm, the thickness of the amorphous Al2O3 nucleation layer is 0.1-0.3μm, the thickness of the α-Al2O3 layer is 4.0-5.0μm, and the thickness of the columnar TiN top layer is 1.0-1.5μm.

[0025] The preparation method of ultrafine-grained gradient cemented carbide cutting tools comprises the following steps: S1: Weigh each component according to the raw materials of the cemented carbide substrate mentioned above.

[0026] S2: Spread the WC powder evenly on an alumina crucible (thickness ≤ 20 mm), place it in a vacuum drying oven, set at 120°C × 2 h for vacuum dehydration (vacuum degree ≤ 10 Pa) until the residual moisture content is ≤ 0.05%; then use a 400 mesh (38 μm) ultrasonic vibrating screen with an amplitude of 0.5 mm and a frequency of 28 kHz. The proportion of the sieve (agglomerates) is ≤ 0.3%, otherwise repeat the crushing and sieving.

[0027] S3: Ion-assisted ball milling, as follows: S31: Put tungsten carbide, cobalt powder and vanadium carbide into a WC-Co lined ball mill, add yttria stabilized zirconia grinding balls (Φ5mm / Φ10mm=1:2), with a ball-to-material ratio of 8:1, and mill at 350rpm under argon protection until the powder D 90 ≤1.0μm; S32: mid-term: add tantalum carbide and niobium carbide, turn on pulse bias (-60V, 20kHz, duty cycle 20%), tilt the tank 30°, and ball mill for 3 hours; S33: Late stage: Add chromium carbide, titanium nitride, and titanium carbonitride, spray in 0.1% zinc stearate ethanol solution (5 ml / kg powder), reduce the speed to 250 rpm, and ball mill for 2 hours. End point powder D 50 =(0.3±0.02)μm, oxygen content 500ppm.

[0028] S4: Zinc stearate coated ball-milled metal powder, which is then stored in an intelligent oxygen-controlled manner; details are as follows: S41: Zinc stearate powder (0.1 wt%) was added to the ball-milled powder by dry method, and then stirred for 20 minutes using a mixer; S42: The mixture was vacuum dried at 60°C for 2 hours, then placed in an aluminum-plastic composite bag containing a zirconium iron vanadium oxygen absorber (2g / kg), and vacuum heat-sealed with a nylon bag on the outer layer; S43: The vacuum-sealed mixture is stored in an intelligent nitrogen cabinet (O2 ≤ 100ppm, RH ≤ 10%), where it is monitored in real time using an RFID tag. The intelligent nitrogen cabinet, which is kept at room temperature, has an electrochemical sensor for sensing oxygen concentration. When the oxygen content exceeds a set value, the cabinet issues an alarm.

[0029] S5: After the green body is pressed and formed, it undergoes gradient sintering (pre-sintering at 1150°C → final sintering at 1380°C → stress release at 1100°C). The gradient sintering process is as follows: heating to 1150°C at 10°C / min and holding for 30 minutes, cooling to 800°C with the furnace, heating to 1380°C at 5°C / min and holding for 60 minutes, cooling to 1100°C at 15°C / min and holding for 20 minutes, and cooling to room temperature at 5°C / min. The resulting cemented carbide substrate is free of microcracks, and the gradient layer thickness is 8-10μm.

[0030] S6: First, use laser to process micro-pits, then sandblast, and finally ultrasonic cleaning; the details are as follows: S61: Fiber laser (1064 nm) processing micro-pits: 50 μm diameter, 15 μm depth, 100 μm pitch hexagonal array; S62: 120 mesh white corundum sand blasting: pressure 0.3MPa, spraying at an angle of 45°, surface roughness Ra = 0.82μm; S63: Cleaning: Acetone ultrasonic treatment for 10 minutes → rinsing with deionized water → vacuum drying at 80°C.

[0031] S7: Hydrogen plasma etching: 900°C with H2 300 sccm for 5 minutes.

[0032] S8: Gradient CVD deposition coating, as follows: S81: TiN bottom layer: 850℃, TiCl4:N2:H2=1:3:10, depositing 1μm equiaxed TiN; S82: TiCN transition layer: 900°C, control the CH3CN / TiCl4 molar ratio from 0.8 to 0.3, and deposit a 5μm columnar-equiaxed gradient structure; specifically, CH3CN / TiCl4=0.8 in the first hour, and then reduce to CH3CN / TiCl4=0.3 within the next 2 hours; S83: Low-pressure deposition (2.0-3.0 kPa) of an amorphous Al2O3 nucleation layer at 600°C using a 1:2:15 ratio of AlCl3:CO2:H2 to deposit a 0.2 μm amorphous layer. During deposition at 600°C, the amorphous Al2O3 nucleation layer penetrates the micropores on the surface of the TiCN transition layer, forming a "nano-rivet" structure. During subsequent crystallization at 980°C, this interface layer in situ transforms into α-Al2O3 facets, epitaxially matching the TiCN surfaces. S84: α-Al2O3 layer: 980℃, H2S addition (H2S / H2=0.005), depositing 4.5μm pure α phase; The core advantages of the α-Al2O3 layer lie in its extreme high-temperature stability, chemical inertness, and high hardness. As the workhorse of the coating system, it maintains ultra-high red hardness even at the high temperatures generated by high-speed cutting (>800°C), effectively resisting abrasive wear. It also possesses top-notch resistance to crater wear (extremely low affinity for iron) and acts as an anti-oxidation / anti-diffusion barrier, significantly enhancing tool life and reliability in demanding conditions such as dry or high-speed machining of steel.

[0033] S85: Columnar TiN top layer: Magnetron sputtering at 500°C, bias voltage -100V, depositing 1μm columnar crystals with an aspect ratio ≥3; the columnar TiN top layer is used for drills and milling cutters, which can significantly improve wear resistance and cutting accuracy. The columnar TiN top layer has a low friction coefficient, which is conducive to chip flow and reduces the formation and adhesion of built-up edge; in addition, as the outermost layer of the coating, because the columnar TiN top layer has its own color different from the α-Al2O3 layer, it is convenient to know the wear condition of the tool directly through the color change during the cutting process.

[0034] The ball milling endpoint obtained in the embodiment of the present invention: D 50 =(0.3±0.02)μm, oxygen content 500ppm; the gradient layer thickness after sintering is 8-10um; the final high temperature hardness at 1100℃ is 1970HV30, thermal shock resistance is 25 times, and after sintering, D 50 ≤0.5μm and no coarse grains >1μm, the obtained flexural strength is 4580MPa.

[0035] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. Ultrafine-grained gradient carbide cutting tools, characterized by: The invention comprises a cemented carbide substrate and a coating deposited on the surface of the cemented carbide substrate, wherein the cemented carbide substrate comprises the following raw materials in mass percentage: Co is 10-12%, VC is 0.5-0.7%, TaC≤0.6%, NbC≤0.8%, Cr3C2 is 0.5-0.6%, Ti(C,N) is 0.8-1.0%, TiN is 0.5-0.8%, Ni is 0.3-0.5%, and the balance is WC; The coating includes a TiN bottom layer, a TiCN transition layer, an amorphous Al2O3 nucleation layer, an α-Al2O3 layer, and a columnar TiN top layer, which are arranged from the inside to the outside. The thickness of the bottom TiN layer is 0.5-1.0μm, the TiCN transition layer is 2.0-5.0μm, the thickness of the amorphous Al2O3 nucleation layer is 0.1-0.3μm, the thickness of the α-Al2O3 layer is 4.0-5.0μm, and the thickness of the columnar TiN top layer is 1.0-1.5μm.

2. The ultrafine-grained gradient carbide tool according to claim 1, characterized in that: The TiCN transition layer has a structure in which columnar crystals gradually change to equiaxed crystals.

3. The ultrafine-grained gradient carbide tool according to claim 2, characterized in that: The aspect ratio of the columnar TiN top layer is ≥3.

4. A method for preparing an ultrafine-grained gradient cemented carbide tool, characterized in that: The steps include: Step 1: weigh the raw materials according to the ratio of claim 1; Step 2: WC powder is vacuum dehydrated and then sieved; Step 3: ion-assisted ball milling; Step 4: pressing and molding to obtain a green body, and gradient sintering the green body to obtain a cemented carbide matrix; Step 5: Use laser to scan the surface of cemented carbide substrate, then sandblast to remove the oxide layer, and then ultrasonically clean; Step 6: Use CVD equipment to deposit TiN bottom layer - TiCN transition layer - amorphous Al2O3 nucleation layer - α-Al2O3 layer - columnar crystal TiN top layer in sequence.

5. The method for preparing an ultrafine-grained gradient cemented carbide tool according to claim 4, wherein: The ion-assisted ball milling includes the following three stages: Initial stage: put WC, Co, VC powder into the ball mill, and mill at 350±10rpm under argon protection until the powder D 90 ≤1.0μm; Mid-term ball milling: Add TaC and NbC powders, turn on the pulse bias, tilt the ball mill tank 30°, and mill for 2.5-3.5 hours; Later ball milling: add Cr3C2, TiN, Ti(C,N) powders, spray into 0.1% zinc stearate ethanol solution, and ball mill at 250±10rpm until the powder D 50 =0.30μm (±0.05μm), oxygen content ≤500ppm.

6. The method for preparing an ultrafine-grained gradient cemented carbide tool according to claim 4, wherein: The specific steps of the gradient sintering are as follows: First, the temperature was raised to 1150°C and kept for 30 minutes, then cooled to 800°C, then raised to 1380°C and kept for 60 minutes, then cooled to 1100°C and kept for 20 minutes, and finally slowly cooled to room temperature.

7. The method for preparing an ultrafine-grained gradient cemented carbide tool according to claim 4, wherein: The steps of depositing the coating using the CVD equipment are as follows: A: TiN bottom layer: 850±10℃ deposition 0.5-1.0μm; B: TiCN transition layer: 2.0-3.0 μm was deposited at 900±10℃, and the CH3CN / TiCl4 molar ratio was gradually changed from 0.8 to 0.3 during the deposition process; C: amorphous Al2O3 nucleation layer: 0.1-0.3 μm deposited at 600±10℃; D: α-Al2O3 layer: 4.0-5.0 μm deposition at 980±10℃, with H2S / H2=0.005; E: Columnar TiN top layer: 1-1.5 μm deposited by magnetron sputtering at 500±10℃.

8. The method for preparing an ultrafine-grained gradient cemented carbide tool according to claim 7, wherein: Before the deposition of the amorphous Al2O3 nucleation layer, the TiCN transition layer was etched by hydrogen plasma at 900℃.

9. The method for preparing an ultrafine-grained gradient cemented carbide tool according to any one of claims 4 to 8, characterized in that: The method also includes coating the metal powder obtained by ball milling with zinc stearate and then temporarily storing the metal powder when there is a time difference between ball milling and pressing.

10. The method for preparing an ultrafine-grained gradient cemented carbide tool according to claim 9, wherein: The temporary storage method is as follows: zinc stearate powder is added to the powder obtained by ball milling by dry method and stirred evenly, then dried, and finally stored in a packaging bag containing an oxygen absorber.

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