Cobalt-free high-corrosion-resistance hard alloy containing rare earth purification and preparation method thereof

Abstract

The invention discloses a cobalt-free high-corrosion-resistance hard alloy containing rare earth purification and a preparation method of the cobalt-free high-corrosion-resistance hard alloy. The cobalt-free high-corrosion-resistance hard alloy comprises the following raw materials in percentage: a hard phase, Fe, Ni, Cr, Mo, W, P, B, Y and La. According to the prepared cobalt-free high-corrosion-resistance hard alloy, a Fe-Ni-Cr-Mo-W high-entropy multi-element system is adopted as a cobalt-free binding phase, a nanoscale intermetallic compound dispersed phase is formed in the liquid phase sintering process through trace P and B elements, binding phase strengthening and structure refinement are achieved, meanwhile, rare earth Y and La elements are introduced, interface purification and grain boundary stabilization are achieved, and the cobalt-free high-corrosion-resistance hard alloy is obtained. And grain boundary segregation and binding phase corrosion are effectively inhibited, and the corrosion resistance and high-temperature hardness of the material are remarkably improved while high compactness and good toughness are kept through the design.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cemented carbide preparation, and particularly relates to a cobalt-free high-corrosion-resistance cemented carbide containing rare earth and a preparation method thereof. BACKGROUND

[0002] Traditional cemented carbide takes cobalt (Co) as a main binding phase, has excellent high-temperature strength and toughness, but has the following problems: 1. Insufficient corrosion resistance: cobalt is prone to electrochemical corrosion in a chlorine ion-containing environment, leading to preferential dissolution of the binding phase and reduction of the service life of the material; 2. Poor high-temperature stability: under a working condition of 700 DEG C or above, the cobalt-based binding phase is obviously softened, resulting in reduction of hardness and bending strength.

[0003] In addition, in recent years, researchers have tried to replace cobalt with elements such as Fe, Ni, Cr, Mo and W, but the conventional Fe-Ni system binding phase has problems such as organization coarsening, grain boundary segregation and insufficient hot hardness, and it is difficult to balance strength, corrosion resistance and stability. In view of the above, the present application provides a cobalt-free high-corrosion-resistance cemented carbide containing rare earth and a preparation method thereof. SUMMARY

[0004] Based on the technical problems in the background art, the present application provides a cobalt-free high-corrosion-resistance cemented carbide containing rare earth and a preparation method thereof.

[0005] The cobalt-free high-corrosion-resistance cemented carbide containing rare earth provided by the present application comprises the following raw material percentages: hard phase 70-90%, Fe 2-8%, Ni 2-6%, Cr 1-4%, Mo 1-3%, W 0.5-3%, P 0.05-0.25%, B 0.05-0.25%, Y 0.05-0.3% and La 0.05-0.3%.

[0006] Preferably, the following raw material percentages are included: hard phase 76%, Fe 8%, Ni 6%, Cr 4%, Mo 3%, W 2.3%, P 0.05%, B 0.05%, Y 0.3% and La 0.3%.

[0007] Preferably, the following raw material percentages are included: hard phase 79%, Fe 6%, Ni 5%, Cr 4%, Mo 2%, W 3%, P 0.25%, B 0.25%, Y 0.3% and La 0.3%.

[0008] Preferably, the following raw material percentages are included: hard phase 90%, Fe 2%, Ni 3%, Cr 1.4%, Mo 1.5%, W 0.5%, P 0.25%, B 0.25%, Y 0.05% and La 0.05%.

[0009] Preferably, the hard phase includes tungsten carbide, titanium carbide, tantalum carbide and niobium carbide, the tungsten carbide is the main body of the hard phase, has the characteristics of high hardness and wear resistance, is the basic framework of the hard alloy, the titanium carbide is used for improving high-temperature hardness and oxidation resistance, improving the compatibility of the alloy and the cutting material, the tantalum carbide is used for improving high-temperature strength and thermal stability, inhibiting grain growth, and the niobium carbide is used for improving toughness and thermal cracking resistance and enhancing overall thermal shock stability of the alloy;

[0010] The Ni has the advantages of improving the toughness and corrosion resistance of the bonding phase and stabilizing the high-temperature structure; the Cr is used for forming a passivation film, improving corrosion resistance and enhancing high-temperature oxidation resistance; the Mo is used for enhancing hardness and improving corrosion resistance and bonding phase strength; the W is used for increasing high-temperature strength and hardness and forming stable carbides with carbon to prevent grain growth; the P reacts with Fe and Ni to form intermetallic compounds and form a nano-dispersed phase in liquid phase sintering; the B forms different intermetallic compounds with metals and is used for enhancing wear resistance and high-temperature performance; the Y forms stable compounds with oxygen, sulfur and impurities, purifies grain boundaries and carbide interfaces, and improves the purity and bonding strength of the bonding phase; and the La is used for improving liquid phase fluidity, refining grains, purifying the structure, and enhancing corrosion resistance and crack resistance.

[0011] The application further provides a preparation method of the cobalt-free high-corrosion-resistant hard alloy containing rare earth purification.

[0012] S1: raw material preparation: weighing tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, 2-8% of Fe, 2-6% of Ni, 1-4% of Cr, 1-3% of Mo, 0.5-3% of W, 0.05-0.25% of P, 0.05-0.25% of B, 0.05-0.3% of Y and 0.05-0.3% of La, and the total amount of the weighed tungsten carbide, titanium carbide, tantalum carbide and niobium carbide is 70-90%, and the weighed raw materials are put into a vacuum ball mill for uniform grinding and mixing;

[0013] S2: drying and sieving: the mixed raw material powder after grinding in S1 is put into a vacuum drying box at 80-100 DEG C for 8-12h of drying, cooled at room temperature after drying, and sieved by using a 200-mesh sieve to obtain uniformly mixed powder;

[0014] S3: forming: the mixed powder in S2 is cold-pressed by using a cold press with a pressure of 100-200 MPa to form a green body;

[0015] S4: Liquid phase sintering: the green body obtained in S3 is sintered in a vacuum atmosphere, heated to 1380-1460°C, and kept for 30-90 min after sintering. During sintering, Fe, Ni, Cr, Mo and W form a high-entropy multi-element liquid phase, P and B elements promote the dispersion of intermetallic compounds between Fe and Ni, rare earth Y and La migrate to the interface, purifying the grain boundary and carbide interface;

[0016] S5: Cooling and post-treatment: after sintering, cool to room temperature, then perform HIP hot isostatic pressing treatment to further densify, thereby obtaining a rare earth-purified cobalt-free hard alloy with high corrosion resistance.

[0017] Preferably, in S1, the ball-to-material ratio of the vacuum ball mill is 5:1-10:1, and the ball milling time is 12-24 h. Ethanol is used as the medium during ball milling.

[0018] Preferably, the specific logical steps of S2 are as follows:

[0019] S201: Pour the mixed slurry after ball milling in S1 from the ball mill jar, remove the ethanol using a vacuum filtration device, and use a stainless steel tray to receive the wet powder during filtration to ensure that no external impurities are mixed in;

[0020] S202: Lay the wet powder after filtration in S201 on a heat-resistant tray, control the thickness to be 5-10 mm, adjust the temperature of the vacuum drying box with a vacuum degree ≤-0.08 MPa to 80-100°C, and place the entire tray with wet powder into the vacuum drying box. Dry for 8-12 h to remove residual ethanol, moisture and ball milling medium;

[0021] S203: After drying, naturally cool to room temperature 25-35°C under vacuum, take out the dry powder and gently knock it apart after cooling to avoid agglomerated blocks affecting the uniformity of screening;

[0022] S204: Put the dry powder into a screening machine equipped with a 200-mesh stainless steel screen, screen for 3-5 min to ensure that all the powder can pass through the screen, and use a jade pestle to lightly press the agglomerated particles that do not pass through the screen and then screen again to obtain uniformly mixed powder.

[0023] Preferably, the specific logical steps of S4 are as follows:

[0024] S401: Put the alloy green body formed by pressing in S3 into a graphite boat of a high-temperature vacuum sintering furnace, keep a distance of at least 5 mm between the green bodies, and vacuum the high-temperature vacuum sintering furnace to ≤5×10-3Pa a Protective atmosphere sintering is performed. The atmosphere is cycled and vacuumed three times before sintering to completely remove oxygen and water vapor to prevent oxidation.

[0025] S402: using a high-temperature vacuum sintering furnace to perform solid-phase sintering on the green body, from room temperature to 800-1000 DEG C, in the preliminary solid-phase sintering process, the contact points between the particles expand to form necks, the rare earth elements Y and La start to react with oxygen and sulfur impurities to generate Y2O3 and La2O3 purification products, and the green body is preliminarily densified by keeping warm for 20-40 min;

[0026] S403: continue to heat to 1380-1460 DEG C, when the temperature reaches about 1350 DEG C or above, the Fe-Ni-Cr-Mo-W system starts to partially melt to form a high-entropy multi-element liquid phase, the high-entropy liquid phase has high diffusion capacity, can rapidly fill the pores and wet the carbide particles, and realizes liquid-phase assisted densification, at this time, the P and B elements are activated and diffused in the liquid phase;

[0027] S404: keeping warm at the target temperature of 1380-1460 DEG C for 30-90 min, during the keeping warm process, the P and B elements react with Fe and Ni to generate nanoscale intermetallic compounds, which are uniformly precipitated in the bonding phase to form nanoscale dispersion strengthening phases with a particle size of about 10-50 nm, and meanwhile, the multi-element Fe, Ni, Cr, Mo and W fully interdiffuse in the liquid phase to form a high-entropy multi-element solid solution bonding phase, the rare earth elements Y and La migrate to the interfaces of WC, TiC and other carbide particles to form a thin layer of rare earth oxides and rare earth carbon oxides, and remove the interface impurities.

[0028] Preferably, the specific logic steps of S5 are as follows:

[0029] S501: after the keeping warm of step S404 is completed, the furnace is cooled to 800 DEG C, and then cooled to room temperature, during the cooling process, the liquid phase gradually solidifies to form a fine high-entropy bonding phase matrix, the dispersion phases are uniformly distributed, and the carbides maintain stable grain structures, so that a high-density sintered body with uniform structure, continuous bonding phase and clean interface is obtained;

[0030] S502: the green body cooled in S501 is taken out of the furnace, and appearance inspection is performed, if there is a slight oxide skin or color difference on the sintered surface, thin layer polishing or grinding is performed, and the removed surface is degreased, ultrasonically cleaned and dried;

[0031] S503: the sintered body is loaded into a HIP steel tank or directly loaded into a HIP chamber for hot isostatic pressing treatment, the temperature is adjusted to 1150-1250 DEG C, the pressure is adjusted to 80-120 MPa, and the pressure holding time is 1-2 h, so as to further improve the densification of the green body, thereby obtaining a rare earth-containing and cobalt-free high-corrosion-resistant hard alloy.

[0032] Compared with the prior art, the beneficial effects of the present application are:

[0033] The prepared cobalt-free high corrosion-resistant hard alloy adopts Fe-Ni-Cr-Mo-W high-entropy multi-element system as a cobalt-free binder phase, and through trace P and B elements, a nanoscale intermetallic compound dispersion phase is formed in the liquid phase sintering process, so that the binder phase strengthening and organization refinement are realized, and the interface purification and grain boundary stabilization are realized by introducing rare earth Y and La elements, so that the grain boundary segregation and binder phase corrosion are effectively inhibited, while the high density and good toughness are maintained, the corrosion resistance and high temperature hardness of the material are significantly improved, so that the alloy can still realize the effects of small hardness attenuation rate and large transverse fracture strength in the chlorine-containing cutting fluid and 700 DEG C high temperature environment, and has excellent comprehensive performance. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A flow chart of a preparation method of the cobalt-free high corrosion-resistant hard alloy containing rare earth purification is provided. DETAILED DESCRIPTION

[0035] The application will be further described below in combination with specific examples.

[0036] Example 1

[0037] Reference Figure 1 The present embodiment provides a cobalt-free high corrosion-resistant hard alloy containing rare earth purification, which comprises the following raw material percentages: hard phase 76%, Fe 8%, Ni 6%, Cr 4%, Mo 3%, W 2.3%, P 0.05%, B 0.05%, Y 0.3%, and La 0.3%.

[0038] The hard phase includes tungsten carbide, titanium carbide, tantalum carbide and niobium carbide, tungsten carbide is the main body of the hard phase, has the characteristics of high hardness and wear resistance, and is the basic framework of the hard alloy, titanium carbide is used to improve the high temperature hardness and oxidation resistance, and improve the compatibility of the alloy and the cutting material, tantalum carbide is used to improve the high temperature strength and thermal stability, and inhibit the grain growth, and niobium carbide is used to improve the toughness and thermal cracking resistance, and enhance the overall thermal shock stability of the alloy.

[0039] Ni has the effects of improving the toughness and corrosion resistance of the binder phase, and stabilizing the high temperature structure; Cr is used to form a passivation film, improve the corrosion resistance, and enhance the high temperature oxidation resistance; Mo is used to enhance the hardness, and improve the corrosion resistance and binder phase strength; W is used to increase the high temperature strength and hardness, and form stable carbides with carbon to prevent grain growth; P reacts with Fe and Ni to form intermetallic compounds in the liquid phase sintering process to form a nanodispersion phase; B forms different intermetallic compounds with metals to improve wear resistance and high temperature performance; Y forms stable compounds with oxygen, sulfur and impurities to purify the grain boundary and carbide interface, and improve the purity and bonding strength of the binder phase; La is used to improve the liquid flowability, refine the grains, purify the structure, and improve the corrosion resistance and crack resistance;

[0040] The preparation method comprises the following steps:

[0041] S1: raw material preparation: weigh tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, 5% of Fe, 6% of Ni, 4% of Cr, 3% of Mo, 2.3% of W, 0.05% of P, 0.05% of B, 0.3% of Y and 0.3% of La, and the total amount of tungsten carbide, titanium carbide, tantalum carbide and niobium carbide is 76%, and the weighed raw materials are put into a vacuum ball mill for uniform grinding and mixing;

[0042] wherein the ball-to-material ratio of the vacuum ball mill is 5:1, the ball milling time is 12h, and ethanol is used as the medium during ball milling;

[0043] S2: drying and sieving: the mixed powder after grinding in S1 is put into a vacuum drying box at 80℃ for 8h, cooled at room temperature after drying, and sieved using a 200-mesh sieve to obtain a uniformly mixed powder;

[0044] The specific logic steps are as follows:

[0045] S201: the mixed slurry after ball milling in S1 is poured out from the ball mill tank, and ethanol is removed using a vacuum filtration device, and a stainless steel tray is used to receive the wet powder during filtration to ensure that no external impurities are mixed in;

[0046] S202: the wet powder after filtration in S201 is laid flat on a heat-resistant tray with a thickness of 5mm, and the temperature of the vacuum drying box with a vacuum degree ≤-0.08MPa is adjusted to 80℃, and the entire tray with wet powder is placed in the vacuum drying box, and the drying time is 8h to remove residual ethanol, moisture and ball milling medium;

[0047] S203: after drying, it is naturally cooled to room temperature 25℃ under vacuum, and the dry powder is taken out and gently knocked apart after cooling to avoid agglomerated blocks affecting the uniformity of sieving;

[0048] S204: the dry powder is put into a sieving machine with a 200-mesh stainless steel sieve, and sieved for 3min to ensure that all the powder can pass through the sieve, and the agglomerated particles that do not pass through are lightly pressed with an agate pestle and sieved again to obtain a uniformly mixed powder;

[0049] S3: forming: the mixed powder in S2 is cold pressed into a green body using a cold press with a pressure of 100MPa;

[0050] S4: Liquid phase sintering: The green body obtained in S3 is sintered in a vacuum atmosphere and heated to 1380℃. After sintering, it is held at the temperature for 30 min. During the sintering process, Fe, Ni, Cr, Mo and W form a high-entropy multi-component liquid phase. P and B elements promote the dispersion and precipitation of intermetallic compounds between Fe and Ni. Rare earth Y and La migrate to the interface and purify the grain boundary and carbide interface.

[0051] The specific logical steps are as follows:

[0052] S401: The alloy billet pressed in S3 is placed into the graphite boat of the high-temperature vacuum sintering furnace, with a minimum spacing of 5 mm between the billets. The high-temperature vacuum sintering furnace is evacuated to ≤5×10-3 Pa for protective atmosphere sintering. Before sintering, the atmosphere is circulated and evacuated three times to completely remove oxygen and water vapor and prevent oxidation.

[0053] S402: The green body is solid-state sintered in a high-temperature vacuum sintering furnace. The temperature is raised from room temperature to 800℃. During the initial solid-state sintering process, the contact points between particles expand to form a neck. Rare earth elements Y and La begin to react with oxygen and sulfur impurities to generate Y2O3 and La2O3 purification products. The temperature is then maintained for 20 minutes to make the green body initially denser.

[0054] S403: Continue heating to 1380℃. When the temperature reaches about 1350℃ or above, the Fe-Ni-Cr-Mo-W system begins to partially melt, forming a high-entropy multi-component liquid phase. This high-entropy liquid phase has a high diffusion capacity, which can quickly fill the pores and wet the carbide particles, achieving liquid-assisted densification. At this time, P and B elements are activated and diffused in the liquid phase.

[0055] S404: After holding at the target temperature of 1380℃ for 30 min, P and B elements react with Fe and Ni to generate nano-intermetallic compounds. These compounds are uniformly precipitated in the bonding phase to form a nano-scale dispersed strengthening phase with a particle size of about 10 nm. At the same time, Fe, Ni, Cr, Mo and W multi-element elements fully interdiffused in the liquid phase to form a high-entropy multi-element solid solution bonding phase. Rare earth elements Y and La migrate to the interface of WC, TiC and other carbide particles to form a thin layer of rare earth oxides and rare earth carbon oxides, removing interface impurities.

[0056] S5: Cooling post-treatment: After sintering, cool to room temperature, and then perform HIP hot isostatic pressing to further densify, thereby obtaining a cobalt-free high corrosion-resistant cemented carbide containing rare earth purification.

[0057] The specific logical steps are as follows:

[0058] S501: After the holding of step S404, the furnace is cooled to 800℃, and then to room temperature. During the cooling process, the liquid phase gradually solidifies to form a fine high-entropy binding phase matrix, the dispersed phase is uniformly distributed, and the carbide maintains a stable grain structure, thereby obtaining a high-density sintered body with uniform structure, continuous binding phase, and clean interface;

[0059] S502: The sintered body after cooling in S501 is taken out of the furnace and subjected to appearance inspection. If there is a slight oxide scale or color difference on the sintered surface, thin layer polishing or grinding is performed, and the removed surface is degreased, ultrasonically cleaned, and dried;

[0060] S503: The sintered body is loaded into a HIP steel tank or directly into a HIP chamber for hot isostatic pressing treatment. The temperature is adjusted to 1150℃, the pressure is adjusted to 80MPa, and the pressure holding time is 1h, so as to further improve the densification of the blank, thereby obtaining a rare earth purified cobalt-free high corrosion resistant hard alloy.

[0061] Example Two

[0062] Reference Figure 1 The present embodiment proposes a rare earth purified cobalt-free high corrosion resistant hard alloy, which comprises the following raw materials in percentage: hard phase 79%, Fe 6%, Ni 5%, Cr 4%, Mo 2%, W 3%, P 0.25%, B 0.25%, Y 0.3%, La 0.3%;

[0063] The hard phase includes tungsten carbide, titanium carbide, tantalum carbide, and niobium carbide. Tungsten carbide is the main body of the hard phase, has the characteristics of high hardness and wear resistance, and is the basic framework of the hard alloy. Titanium carbide is used to improve high temperature hardness and oxidation resistance, and to improve the compatibility of the alloy and cutting materials. Tantalum carbide is used to improve high temperature strength and thermal stability, and to inhibit grain growth. Niobium carbide is used to improve toughness and thermal cracking resistance, and to enhance the overall thermal shock stability of the alloy.

[0064] Ni improves the toughness and corrosion resistance of the binding phase, and stabilizes the high temperature structure. Cr is used to form a passivation film, improve corrosion resistance, and enhance high temperature oxidation resistance. Mo is used to enhance hardness, and at the same time improve corrosion resistance and binding phase strength. W is used to increase high temperature strength and hardness, and form stable carbides with carbon to prevent grain growth. P reacts with Fe and Ni to form intermetallic compounds and form nanometer dispersed phase in liquid phase sintering. B forms different intermetallic compounds with metals to enhance wear resistance and high temperature performance. Y forms stable compounds with oxygen, sulfur, and impurities to purify the grain boundary and carbide interface, and to improve the purity and bonding strength of the binding phase. La is used to improve liquid flowability, refine grains, purify the structure, and at the same time to enhance corrosion resistance and crack resistance.

[0065] The preparation method comprises the following steps:

[0066] S1: raw material preparation: weigh tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, 6% Fe, 5% Ni, 4% Cr, 2% Mo, 3% W, 0.25% P, 0.25% B, 0.3% Y and 0.3% La, and the total amount of tungsten carbide, titanium carbide, tantalum carbide and niobium carbide is 79%, and the weighed raw materials are put into a vacuum ball mill for uniform grinding and mixing;

[0067] Wherein the ball-to-material ratio of the vacuum ball mill is 8:1, the ball milling time is 20h, and ethanol is used as the medium during ball milling;

[0068] S2: drying and sieving: the mixed raw material powder after grinding in S1 is put into a vacuum drying oven at 90℃ for 10h, cooled at room temperature after drying, and sieved using a 200 mesh screen to obtain a uniformly mixed powder;

[0069] The specific logic steps are as follows:

[0070] S201: pour the mixed slurry after ball milling in S1 from the ball mill jar, remove the ethanol using a vacuum filtration device, and use a stainless steel tray to receive the wet powder during filtration to ensure that no external impurities are mixed in;

[0071] S202: spread the wet powder after filtration in S201 on a heat-resistant tray with a thickness of 8mm, adjust the temperature of the vacuum drying oven with a vacuum degree ≤-0.08MPa to 80-100℃, and put the entire tray with wet powder into the vacuum drying oven, dry for 10h to remove residual ethanol, moisture and ball milling medium;

[0072] S203: after drying, naturally cool to room temperature 30℃ under vacuum, take out the dry powder and gently knock it apart after cooling to avoid agglomeration affecting the uniformity of sieving;

[0073] S204: put the dry powder into a sieving machine with a 200 mesh stainless steel screen, sieve for 4min to ensure that all the powder can pass through the screen, and for the agglomerated particles that do not pass through, use a jade pestle to lightly press and sieve again to obtain a uniformly mixed powder;

[0074] S3: forming: the mixed powder in S2 is cold pressed into a green body using a cold press with a pressure of 150MPa;

[0075] S4: liquid phase sintering: the green body obtained in S3 is sintered in a vacuum atmosphere, heated to 1420℃, and held for 75min after sintering. During sintering, Fe, Ni, Cr, Mo and W form a high-entropy multi-element liquid phase, P and B elements promote the dispersion of intermetallic compounds between Fe and Ni, rare earth Y and La migrate to the interface, and the interface is purified;

[0076] The specific logic steps are as follows:

[0077] S401: Put the alloy blank formed by compression molding in S3 into a graphite boat of a high-temperature vacuum sintering furnace, keep a distance of at least 5 mm between the blanks, and vacuumize the high-temperature vacuum sintering furnace to ≤5×10-3Pa a Protective atmosphere sintering is performed, and the atmosphere is cyclically vacuumized three times before sintering to completely remove oxygen and water vapor and prevent oxidation;

[0078] S402: Perform solid-phase sintering on the blank using the high-temperature vacuum sintering furnace, from room temperature to 900℃, during the initial solid-phase sintering process, the contact points between the particles expand to form necks, and the rare earth elements Y and La start to react with oxygen and sulfur impurities to generate Y2O3 and La2O3 purification products, and keep warm for 30 min to preliminarily densify the blank;

[0079] S403: Continue to heat to 1420℃, when the temperature reaches about 1350℃ or above, the Fe-Ni-Cr-Mo-W system starts to partially melt to form a high-entropy multi-element liquid phase, which has high diffusion capacity and can quickly fill pores and wet carbide particles to achieve liquid-phase-assisted densification, at this time, P and B elements are activated and diffuse in the liquid phase;

[0080] S404: Keep warm at the target temperature of 1420℃ for 75 min, during which P and B elements react with Fe and Ni to generate nanoscale intermetallic compounds, which are uniformly precipitated in the bonding phase to form nanoscale dispersion strengthening phases with a particle size of about 35 nm, while Fe, Ni, Cr, Mo, and W multi-element elements fully interdiffuse in the liquid phase to form a high-entropy multi-element solid solution bonding phase, and rare earth elements Y and La migrate to the interfaces of WC, TiC, and other carbide particles to form a thin layer of rare earth oxides and rare earth carbon oxides, removing interfacial impurities;

[0081] S5: Cooling treatment: after sintering, cool to room temperature, and then perform HIP hot isostatic pressing treatment to further densify, thereby obtaining a rare earth-purified cobalt-free hard alloy with high corrosion resistance;

[0082] The specific logic steps are as follows:

[0083] S501: After the temperature of the furnace cools to 800℃, and then to room temperature, the liquid phase gradually solidifies to form a fine high-entropy bonding phase matrix, the dispersion phase is uniformly distributed, and the carbide maintains a stable grain structure, resulting in a high-density sintered body with uniform organization, continuous bonding phase, and clean interface;

[0084] S502: The cooled blank in S501 is taken out of the furnace for appearance inspection. If there is a slight oxide scale or color difference on the sintered surface, thin layer polishing or grinding is performed, and the removed surface is degreased, ultrasonically cleaned and dried;

[0085] S503: The sintered body is loaded into a HIP steel tank or directly into a HIP chamber for hot isostatic pressing treatment. The temperature is adjusted to 1200℃, the pressure is adjusted to 100MPa, and the pressure holding time is 1.5h to further improve the densification of the blank, thereby obtaining a rare earth purified cobalt-free high corrosion resistant hard alloy.

[0086] Example Three

[0087] Reference Figure 1 The present embodiment proposes a rare earth purified cobalt-free high corrosion resistant hard alloy, comprising the following raw material percentages: hard phase 90%, Fe 2%, Ni 3%, Cr 1.4%, Mo 1.5%, W 0.5%, P 0.25%, B 0.25%, Y 0.05%, La 0.05%;

[0088] The hard phase includes tungsten carbide, titanium carbide, tantalum carbide and niobium carbide. Tungsten carbide is the main body of the hard phase, with high hardness and wear resistance, and is the basic framework of hard alloy. Titanium carbide is used to improve high temperature hardness and oxidation resistance, and to improve the compatibility of the alloy and cutting materials. Tantalum carbide is used to improve high temperature strength and thermal stability, and to inhibit grain growth. Niobium carbide is used to improve toughness and thermal cracking resistance, and to enhance the overall thermal shock stability of the alloy.

[0089] Ni improves the toughness and corrosion resistance of the bonding phase and stabilizes the high temperature structure. Cr is used to form a passivation film to improve corrosion resistance and enhance high temperature oxidation resistance. Mo is used to enhance hardness while improving corrosion resistance and bonding phase strength. W is used to increase high temperature strength and hardness, and to form stable carbides with carbon to prevent grain growth. P reacts with Fe and Ni to form intermetallic compounds in liquid phase sintering, forming a nanodispersion phase. B forms different intermetallic compounds with metals to enhance wear resistance and high temperature performance. Y forms stable compounds with oxygen, sulfur and impurities to purify grain boundaries and carbide interfaces, improving the purity and bonding strength of the bonding phase. La is used to improve liquid flowability, refine grains, purify the structure, and also to enhance corrosion resistance and crack resistance.

[0090] The preparation method comprises the following steps:

[0091] S1: raw material preparation: weigh tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, 2% Fe, 3% Ni, 1.4% Cr, 1.5% Mo, 0.5% W, 0.05% P, 0.25% B, 0.05% Y and 0.05% La, and the total amount of tungsten carbide, titanium carbide, tantalum carbide and niobium carbide is 90%, and the weighed raw materials are put into a vacuum ball mill for uniform grinding and mixing;

[0092] Wherein the ball-to-material ratio of the vacuum ball mill is 10:1, the ball milling time is 24h, and ethanol is used as the medium during ball milling;

[0093] S2: drying and sieving: the mixed powder after grinding in S1 is put into a vacuum drying oven at 100℃ for 12h, cooled at room temperature after drying, and sieved using a 200 mesh screen to obtain a uniformly mixed powder;

[0094] The specific logic steps are as follows:

[0095] S201: pour the mixed slurry after ball milling in S1 from the ball mill jar, remove the ethanol using a vacuum filtration device, and use a stainless steel tray to receive the wet powder during filtration to ensure that no external impurities are mixed in;

[0096] S202: spread the wet powder after filtration in S201 on a heat-resistant tray with a thickness of 10mm, adjust the temperature of the vacuum drying oven with a vacuum degree ≤-0.08MPa to 100℃, and put the entire tray with wet powder into the vacuum drying oven, dry for 12h to remove residual ethanol, moisture and ball milling medium;

[0097] S203: after drying, naturally cool to room temperature 35℃ under vacuum, take out the dry powder and gently knock it apart after cooling to avoid agglomeration affecting the uniformity of sieving;

[0098] S204: put the dry powder into a sieving machine equipped with a 200 mesh stainless steel screen, sieve for 5min to ensure that all the powder can pass through the screen, and for the agglomerated particles that do not pass through, use a jade pestle to lightly press and sieve again to obtain a uniformly mixed powder;

[0099] S3: forming: the mixed powder in S2 is cold pressed into a green body using a cold press with a pressure of 200MPa;

[0100] S4: liquid phase sintering: the green body obtained in S3 is sintered in a vacuum atmosphere, heated to 1460℃, and held for 90min after sintering. During sintering, Fe, Ni, Cr, Mo and W form a high-entropy multi-element liquid phase, P and B elements promote the dispersion of intermetallic compounds between Fe and Ni, rare earth Y and La migrate to the interface, and the crystal boundary and carbide interface are purified;

[0101] The specific logical steps are as follows:

[0102] S401: Put the alloy blanks pressed in S3 into the graphite boat of the high-temperature vacuum sintering furnace, keep a distance of at least 5 mm between the blanks, and vacuumize the high-temperature vacuum sintering furnace to ≤5×10-3Pa a Protective atmosphere sintering is performed, and the atmosphere is cyclically vacuumized three times before sintering to completely remove oxygen and water vapor to prevent oxidation;

[0103] S402: Perform solid-phase sintering on the blanks using the high-temperature vacuum sintering furnace, from room temperature to 1000℃, during the initial solid-phase sintering process, the contact points between the particles expand to form necks, and the rare earth elements Y and La start to react with oxygen and sulfur impurities to generate Y2O3 and La2O3 purification products, and keep the temperature for 20-40 min to preliminarily densify the blanks;

[0104] S403: Continue to heat to 1460℃, when the temperature reaches about 1350℃ or above, the Fe-Ni-Cr-Mo-W system starts to partially melt to form a high-entropy multi-element liquid phase, which has high diffusion capacity and can quickly fill pores and wet carbide particles to achieve liquid-phase-assisted densification, at this time, P and B elements are activated and diffuse in the liquid phase;

[0105] S404: Keep the temperature at the target temperature of 1460℃ for 90 min, during which P and B elements react with Fe and Ni to generate nanoscale intermetallic compounds, which are uniformly precipitated in the bonding phase to form nanoscale dispersion strengthening phases with a particle size of about 50 nm, while Fe, Ni, Cr, Mo, and W multi-element elements fully interdiffuse in the liquid phase to form a high-entropy multi-element solid solution bonding phase, and rare earth elements Y and La migrate to the interfaces of WC, TiC, and other carbide particles to form a thin layer of rare earth oxides and rare earth carbon oxides to remove interfacial impurities;

[0106] S5: Cooling and processing: after sintering, cool to room temperature, and then perform HIP hot isostatic pressing to further densify, thereby obtaining a rare earth-purified cobalt-free hard alloy with high corrosion resistance;

[0107] The specific logical steps are as follows:

[0108] S501: After the temperature of the furnace cools to 800℃, and then to room temperature, the liquid phase gradually solidifies to form a fine high-entropy bonding phase matrix, the dispersion phase is uniformly distributed, and the carbide maintains a stable grain structure, resulting in a high-density sintered body with uniform organization, continuous bonding phase, and clean interface;

[0109] S502: the blank cooled in S501 is taken out from the furnace, appearance inspection is carried out, if there is slight oxide scale or color difference on the sintering surface, thin layer polishing or grinding is carried out, and the surface after removal is degreased, ultrasonic cleaned and dried;

[0110] S503: the sintered body is loaded into a HIP steel tank or directly loaded into a HIP chamber for hot isostatic pressing treatment, the temperature is adjusted to 1250 DEG C, the pressure is adjusted to 120 MPa, and the pressure holding time is 2h, so as to further improve the densification of the blank, thereby obtaining a cobalt-free high corrosion-resistant hard alloy containing rare earth purification.

[0111] The cobalt-free high corrosion-resistant hard alloy prepared in examples one to three is compared with conventional hard alloy, and the experimental data are shown in the following table:

[0112]

[0113] From the above table, it can be seen that the corrosion resistance, high temperature stability and high temperature hardness of the cobalt-free high corrosion-resistant hard alloy prepared by the present application are obviously improved, and example two is the best embodiment. The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A cobalt-free, high corrosion-resistant cemented carbide containing rare earth elements, characterized in that, The composition includes the following percentages of raw materials: hard phase 70-90%, Fe 2-8%, Ni 2-6%, Cr 1-4%, Mo 1-3%, W 0.5-3%, P 0.05-0.25%, B 0.05-0.25%, Y 0.05-0.3%, and La 0.05-0.3%.

2. The cobalt-free, high corrosion-resistant cemented carbide containing rare earth purification according to claim 1, characterized in that, The composition includes the following percentages of raw materials: hard phase 76%, Fe 8%, Ni 6%, Cr 4%, Mo 3%, W 2.3%, P 0.05%, B 0.05%, Y 0.3%, and La 0.3%.

3. The cobalt-free, high corrosion-resistant cemented carbide containing rare earth purification according to claim 1, characterized in that, The composition includes the following percentages of raw materials: hard phase 79%, Fe 6%, Ni 5%, Cr 4%, Mo 2%, W 3%, P 0.25%, B 0.25%, Y 0.3%, and La 0.3%.

4. The cobalt-free, high corrosion-resistant cemented carbide containing rare earth elements and purified according to claim 1, characterized in that, The composition includes the following percentages of raw materials: hard phase 90%, Fe 2%, Ni 3%, Cr 1.4%, Mo 1.5%, W 0.5%, P 0.25%, B 0.25%, Y 0.05%, and La 0.05%.

5. The cobalt-free, high corrosion-resistant cemented carbide containing rare earth purification according to claim 1, characterized in that, The hard phase includes tungsten carbide, titanium carbide, tantalum carbide, and niobium carbide. Tungsten carbide is the main body of the hard phase, which has the characteristics of high hardness and wear resistance and is the basic skeleton of cemented carbide. Titanium carbide is used to improve high-temperature hardness and oxidation resistance, and improve the compatibility of the alloy with cutting materials. Tantalum carbide is used to improve high-temperature strength and thermal stability and inhibit grain growth. Niobium carbide is used to improve toughness and resistance to hot cracking and enhance the overall thermal shock stability of the alloy. The Ni improves the toughness and corrosion resistance of the bonding phase and stabilizes the high-temperature structure; Cr forms a passivation film, improves corrosion resistance, and enhances high-temperature oxidation resistance; Mo enhances hardness, while also improving corrosion resistance and bonding phase strength; W increases high-temperature strength and hardness, and forms stable carbides with carbon to prevent grain growth; P reacts with Fe and Ni in liquid-phase sintering to form intermetallic compounds, creating a nano-dispersed phase; B forms different intermetallic compounds with metals to enhance wear resistance and high-temperature performance; Y forms stable compounds with oxygen, sulfur, and impurities, purifying grain boundaries and carbide interfaces, and improving the purity and bonding strength of the bonding phase; La improves liquid-phase fluidity, refines grains, purifies the structure, and also enhances corrosion resistance and crack resistance.

6. A method for preparing a cobalt-free, high-corrosion-resistant cemented carbide containing rare-earth purification, used to achieve the cobalt-free, high-corrosion-resistant cemented carbide according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Raw material preparation: Weigh tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, 2-8% Fe, 2-6% Ni, 1-4% Cr, 1-3% Mo, 0.5-3% W, 0.05-0.25% P, 0.05-0.25% B, 0.05-0.3% Y and 0.05-0.3% La, and the total amount of tungsten carbide, titanium carbide, tantalum carbide and niobium carbide should be 70-90%. Put the weighed raw materials into a vacuum ball mill for uniform grinding and mixing. S2: Drying and sieving: Place the raw material powder after grinding and mixing in S1 into a vacuum drying oven at 80–100℃ and dry for 8–12 hours. After drying, cool to room temperature and sieve using a 200-mesh sieve to obtain a uniformly mixed powder. S3: Molding: The mixed powder in S2 is cold-pressed using a cold press with a pressure of 100–200 MPa to obtain a blank; S4: Liquid phase sintering: The green body obtained in S3 is sintered in a vacuum atmosphere and heated to 1380-1460℃. After sintering, it is held at the temperature for 30-90 min. During the sintering process, Fe, Ni, Cr, Mo and W form a high-entropy multi-component liquid phase. P and B elements promote the dispersion and precipitation of intermetallic compounds between Fe and Ni. Rare earth Y and La migrate to the interface and purify the grain boundary and carbide interface. S5: Cooling and post-treatment: After sintering, cool to room temperature and then perform HIP hot isostatic pressing to further densify, thereby obtaining a cobalt-free, high corrosion-resistant cemented carbide containing rare earth purification.

7. The method for preparing a cobalt-free, high-corrosion-resistant cemented carbide containing rare earth purification according to claim 6, characterized in that, In S1, the ball-to-material ratio of the vacuum ball mill is 5:1–10:1, the ball milling time is 12–24 hours, and ethanol is used as the medium during the ball milling process.

8. The method for preparing a cobalt-free, high-corrosion-resistant cemented carbide containing rare earth purification according to claim 6, characterized in that, The specific logical steps of S2 are as follows: S201: Pour the mixed slurry after ball milling in S1 out of the ball mill jar, remove ethanol using a vacuum filter, and use a stainless steel tray to receive wet powder during the filtration process to ensure that no external impurities are mixed in. S202: Spread the wet powder filtered in S201 on a heat-resistant tray with a thickness of 5–10 mm. Adjust the temperature of the vacuum drying oven with a vacuum degree ≤ -0.08 MPa to 80–100℃. Place the entire tray with the wet powder in the vacuum drying oven and dry for 8–12 hours to remove residual ethanol, moisture and ball milling media. S203: After drying, keep the dry powder under vacuum and let it cool naturally to room temperature of 25–35°C. After cooling, take out the dry powder and gently break it up to avoid agglomeration that would affect the uniformity of sieving. S204: Place the dry powder into a sieve equipped with a 200-mesh stainless steel sieve and sieve for 3–5 minutes to ensure that all powder can pass through the sieve. For any agglomerated particles that do not pass through, use an agate pestle to gently press and sieve again to obtain a uniformly mixed powder.

9. The method for preparing a cobalt-free, high-corrosion-resistant cemented carbide containing rare earth purification according to claim 6, characterized in that, The specific logical steps of S4 are as follows: S401: The alloy billets pressed in S3 are loaded into the graphite boat of the high-temperature vacuum sintering furnace, maintaining a minimum spacing of 5 mm between the billets, and the high-temperature vacuum sintering furnace is evacuated to ≤5×10-3P. a Sintering is carried out under a protective atmosphere. Before sintering, the atmosphere is circulated and vacuumed three times to completely remove oxygen and moisture and prevent oxidation. S402: The green body is solid-state sintered in a high-temperature vacuum sintering furnace. The temperature is raised from room temperature to 800–1000℃. During the initial solid-state sintering process, the contact points between particles expand to form a neck. Rare earth elements Y and La begin to react with oxygen and sulfur impurities to generate Y2O3 and La2O3 purification products. The temperature is then maintained for 20–40 minutes to initially densify the green body. S403: Continue heating to 1380–1460℃. When the temperature reaches about 1350℃ or above, the Fe-Ni-Cr-Mo-W system begins to partially melt, forming a high-entropy multi-component liquid phase. This high-entropy liquid phase has a high diffusion capacity, which can quickly fill the pores and wet the carbide particles, achieving liquid-phase assisted densification. At this time, P and B elements are activated and diffused in the liquid phase. S404: Hold at the target temperature of 1380–1460℃ for 30–90 min. During the holding process, P and B elements react with Fe and Ni to form nano-intermetallic compounds. These compounds are uniformly precipitated in the bonding phase to form a nano-scale dispersed strengthening phase with a particle size of about 10–50 nm. At the same time, Fe, Ni, Cr, Mo and W multi-element elements fully interdiffused in the liquid phase to form a high-entropy multi-element solid solution bonding phase. Rare earth elements Y and La migrate to the interface of WC, TiC and other carbide particles to form a thin layer of rare earth oxides and rare earth carbon oxides, removing interface impurities.

10. The method for preparing a cobalt-free, high-corrosion-resistant cemented carbide containing rare earth purification according to claim 9, characterized in that, The specific logical steps of S5 are as follows: S501: After the heat preservation in step S404 is completed, the furnace is cooled to 800°C and then cooled to room temperature. During the cooling process, the liquid phase gradually solidifies to form a fine high-entropy bound phase matrix, the dispersed phase is evenly distributed, and the carbide maintains a stable grain structure, resulting in a high-density sintered body with uniform structure, continuous bound phase, and clean interface. S502: Take the cooled billet from the furnace in S501 and inspect its appearance. If there is slight oxide scale or color difference on the sintered surface, perform thin-layer grinding or polishing, and degrease, ultrasonically clean and dry the removed surface. S503: The sintered body is loaded into a HIP steel tank or directly into a HIP chamber for hot static pressing. The temperature is adjusted to 1150–1250℃, the pressure is adjusted to 80–120MPa, and the holding time is 1–2h to further improve the densification of the billet, thereby obtaining a cobalt-free, high corrosion-resistant cemented carbide containing rare earth purification.

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