TWI790133B - Preparation method of superfine wc-base hard alloy - Google Patents

Abstract

The invention discloses a preparation method of a superfine WC-base hard alloy with a molecular formula WC-T-HEA, wherein T is at least one of a carbide, an oxide or a boride, HEA is a high-entropy alloy. The high-entropy alloy ingot is prepared by smelting and casting the raw material of the high-entropy alloy. Under the protection of inert atmosphere, the high-entropy alloy ingot is crushed by a mechanical crushing method to obtain the high-entropy alloy coarse powder. The submicron WC powder, T Powder and the high-entropy alloy coarse powder are added into the air flow mill in proportion to the ultrafine WC hard alloy components, and then are subjected to air flow grinding and crushing in an inert atmosphere without the classification steps, and 1 μm or less powder originally separated is mixed in the grinding powder to obtain mixed fine powder. The method can solve the problem of too high oxygen content in the superfine WC hard alloy preparation process, improves the processing performance of the ultrafine WC-base hard alloy, and can meet the requirement of the optical level surface through machining.

Description

A kind of preparation method of superfine WC cemented carbide

The invention relates to a preparation method of WC-based hard alloy, in particular to a preparation method of superfine WC hard alloy without Co and Ni binding phase.

Compared with the traditional WC-Co cemented carbide, Co and Ni-free cemented carbide has higher hardness, elastic modulus, corrosion resistance and wear resistance have also been greatly improved, and is gradually used in precision optical molds , Sandblasting nozzles, nuclear industry seals and other fields that require high precision, high hardness, high elastic modulus, and high corrosion resistance.

Chinese invention patent application CN1827817A discloses a cemented carbide sintered with a high-entropy alloy binder and composite carbide and its production method. The metal powder of the composite carbide and the binder phase is weighed and mixed in a ball mill, and then the ball mill Put it into the ball mill for at least 10 hours of high-energy ball milling, then add 1-2wt% paraffin wax as a wetting agent and binder to the ball mill cylinder, and then carry out at least 5 hours of low-energy ball milling, unloading and drying, then press into a round billet , followed by deesterification and sintering, and finally the finished product is obtained, but this method is not suitable for the preparation of superfine tungsten carbide cemented carbide without Co and Ni binder phase.

At present, the preparation method of superfine WC cemented carbide without Co and Ni binder phase, one is to first prepare submicron WC powder by high energy ball milling method to improve the surface energy of the powder, and then prepare superfine WC cemented carbide without binder phase by spark plasma sintering technology. WC cemented carbide, this preparation method is easy to introduce impurities during the preparation process. In addition, the submicron WC powder is very easy to absorb oxygen, resulting in too high oxygen content. Sample processing performance.

The purpose of the present invention is to provide a preparation method of WC-based cemented carbide, which can overcome the problem of excessive oxygen content in the preparation process of ultrafine WC cemented carbide, improve the processing performance of ultrafine WC cemented carbide, and can achieve optical grade surface requirements through processing.

The technical scheme provided by the present invention is as follows: a method for preparing ultrafine WC cemented carbide, the molecular formula of the ultrafine WC cemented carbide is WC-T-HEA, wherein T is at least one of carbide, oxide or boride, The T contains B elements, and HEA is a high-entropy alloy; the HEA is selected from Al, Nb, Ti, Zr, Ge, Si, V, Ta, Cr, Mn, Ce, Mo, W, and Hf at least Five types; the T contains element B, and the preparation method includes: step a, putting the raw material of the high-entropy alloy into a vacuum melting furnace for melting, and casting the molten liquid obtained by melting to obtain a high-entropy alloy alloy ingot; step b, under the protection of an inert atmosphere, crush the high-entropy alloy ingot by mechanical crushing to obtain high-entropy alloy coarse powder; step c, submicron WC powder, T powder and the high-entropy alloy Coarse alloy powder is added to the jet mill according to the ultrafine WC cemented carbide composition ratio, and the jet mill is pulverized under an inert atmosphere. powder; the superfine WC cemented carbide composition comprises: the HEA of 0.5wt%-5wt%, the T below 35wt%, the B of 0.1wt%-3wt%, the surplus is WC and unavoidable impurity; Step d: will The mixed fine powder is pressed into shape and sintered to obtain the superfine WC hard alloy.

10nm。 In the present invention, by adding the high-entropy alloy in the form of alloy powder, compared with adding each element of the high-entropy alloy in the form of metal elemental powder, it can effectively avoid the oxidation of some active elements of the high-entropy alloy, which is beneficial to reduce the oxygen content. The low-oxygen preparation process can avoid the absorption of oxygen by the submicron WC powder in the preparation process, and improve the processing performance of the ultra-fine WC cemented carbide. After processing, the surface roughness of the ultra-fine WC cemented carbide is Ra

10nm.

72W/m˙K，密度

12g˙cm^-3，硬度HRA

70，斷裂韌性

10MPa˙M^1/2，抗彎強度

1600N˙mm^-2，氧化增重

1.16mg˙cm^-2，加工後表面粗糙度Ra

10nm。 On the other hand, the superfine WC cemented carbide of the present invention introduces high-entropy alloys and fully exerts the effect of the B element. In the alloy system, HEA and B play a synergistic role, so that the ultrafine WC cemented carbide of the present invention as a whole has excellent strength and Toughness, high thermal conductivity and thermal stability, high density, can meet the requirements of optical molds: thermal conductivity

72W/m˙K, density

12g˙cm ^-3 , hardness HRA

70, fracture toughness

10MPa˙M ^1/2 , bending strength

1600N˙mm ^-2 , oxidation weight gain

1.16mg˙cm ^-2 , surface roughness Ra after processing

10nm.

The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In a recommended implementation, when the vacuum induction melting furnace is evacuated to a vacuum degree of 4Pa-9Pa, argon gas is filled into the melting chamber to bring the pressure in the furnace to 0.03MPa-0.06MPa before melting.

In a recommended implementation, the mechanical crushing adopts two closed jaw crushers connected in series, and under the protection of an inert atmosphere, the high-entropy alloy ingot is crushed to a coarse powder of 1mm-3mm. The mechanical crushing method is not limited to the jaw crusher, and a combination of turning and high-speed crushing or other crushing methods can also be used. The inert atmosphere may be an atmosphere containing inert gas or nitrogen conventional in the art.

In a recommended implementation, the pressure of the crushing chamber of the jet mill is 5MPa-11MPa, and the rotation speed of the sorting wheel is 3500rpm-4300rpm.

In a recommended implementation, the average particle size of the WC powder is 0.2 μm-0.8 μm, and the average particle size of the T powder is 0.5 μm-1 μm.

In a recommended implementation, the step of removing classification is to add a screening program in the cyclone separator of the jet mill to the compressor of the jet mill through a pipeline, and to screen The program is set to block the passage of ultrafine powder, so that the powder below 1 μm is not separated in the cyclone separator and mixed in the pulverized powder.

In a recommended implementation, in the step d, place the pressed body in a spark plasma sintering furnace and vacuumize it, adjust the sintering pressure to 35MPa-60MPa, raise the temperature to 750-800°C, and keep it warm for 1min-2min , continue to heat up to 1500°C-1700°C, and keep warm for 5min-30min.

In a preferred embodiment, the HEA has a melting point below 1850°C.

In a recommended embodiment, the T is Al ₄ C ₃ , HfC, TiC, Cr ₃ C ₂ , VC, ZrC, NbC, TaC, SiC, Mn ₃ C, MoC, CuC, Mg ₂ C ₃ , W ₂ At least two of C, CeO ₂ , La ₂ O ₃ , MgO, ZrO ₂ , Al ₂ O ₃ , ZrB ₂ , CrB ₂ , TiB ₂ or MnB ₂ ; in a preferred embodiment, preferred B is a transition metal Borides exist in the form of ZrB ₂ , CrB ₂ , TiB ₂ or MnB ₂ .

In a recommended embodiment, the high-entropy alloy HEA is selected from the group consisting of the molecular formulas Al _0.4 Hf _0.6 NbTaTiZr, AlMo _0.5 NbTa _0.5 TiZr, AlNbTaTiV, AlNb _1.5 Ta _0.5 Ti _1.5 Zr _0.5 , AlCr ₂ Mo ₂ Nb ₂ Ti ₂ Zr, At least one of HfMoNbTiZr, HfNbTaTiZr, HfNbTiVZr, CrNbTiVZr, CrMo _0.5 NbTa _0.5 TiZr, TiZrHfNbCr, TiNbMoTaW, TiVNbMoTaW, HfMoTaTiZr or HfMoNbTaTiZr. The above molecular formula contains a metal element with a slightly larger atomic radius and other elements with a similar atomic radius, which is beneficial to the formation of HEA, in which the metal element with a slightly larger atomic radius enters the lattice and promotes the distortion of the lattice, from face-centered cubic Phase to body-centered cubic phase transformation; the selected elements are more likely to combine between atoms during the sintering process to form an ordered solid solution; at the same time, the selected HEA is more beneficial to improve the thermal conductivity and thermal stability of WC-based cemented carbide.

It should be noted that all numerical ranges disclosed in the present invention include all point values within this range.

Oxygen content evaluation process in the sintered body: the oxygen content in the sintered body was detected by an EMGA-620W oxygen and nitrogen analyzer from Japan HORIBA Company.

Hardness test: refer to GB/T 7997-2014 "Cemented Carbide Vickers Hardness Test Method".

Bending strength and compressive strength: measured by CMT5305 microcomputer-controlled universal testing machine, referring to GB/T 3851-2015 "Measurement Method for Transverse Fracture Strength of Cemented Carbide", GB/T 23370-2009 "Cemented Carbide Compression Test Method".

Toughness test: refer to GB/T 33819-2017 "Barcol Toughness Test of Cemented Carbide".

Thermal conductivity: German NETZSCH LFA457 laser thermal conductivity meter is used, referring to the standard GB/T 22588-2008.

Density: measured by American Mike AccuPyc II 1340 true density analyzer.

Oxidation resistance: Refer to GB/T 13303-1991 "Method for Determination of Oxidation Resistance of Steel".

Surface roughness: It is measured by the method of shape retention, referring to GB/T 15056-2017 "Evaluation Method for Surface Roughness of Casting".

The present invention is described in further detail below in conjunction with embodiment.

Embodiment one

The preparation method of the superfine WC cemented carbide of embodiment one comprises the steps:

(1) Vacuum melting

According to the high-entropy alloy HEA molecular formula AlNb _1.5 Ta _0.5 Ti _1.5 Zr _0.5 , prepare five metal elemental powders (Al, Nb, Ta, Ti, Zr) that constitute HEA, and put the five metal elemental powders into the vacuum induction melting furnace , when the vacuum is evacuated to 5Pa, argon gas is filled into the melting chamber to make the pressure in the furnace reach 0.05MPa, and then melting and pouring are carried out to obtain high-entropy alloy ingots.

(2) Coarse crushing

Under the protection of an inert atmosphere, two jaw crushers are connected in closed series, and under the protection of high-purity nitrogen (99.99%), the high-entropy alloy ingot is crushed to a coarse powder of 1mm-3mm to obtain a high-entropy alloy coarse powder.

(3) fine crushing and mixing

Add the WC powder with an average particle size of 0.8 μm, the T powder with an average particle size of 0.5 μm, and the high-entropy alloy coarse powder into the jet mill according to the ultrafine WC cemented carbide composition ratio in Table 1, and under a nitrogen atmosphere, Under the condition that the pressure of the pulverizing chamber is 10MPa and the rotating speed of the sorting wheel is 3500rpm, carry out jet mill pulverization, and add a screening in the cyclone separator of the jet mill pulverizer through pipelines connected with the compressor of the jet mill pulverizer program, and set the screening program to block the ultrafine powder from passing through, so that the powder below 1 μm will not be separated in the cyclone separator, and the mixed fine powder will be obtained.

(4) suppression

The mixed fine powder was compressed under a pressure of 180 MPa for a holding time of 120 s to obtain a green body.

(5) Sintering

Put the green body in a discharge plasma sintering furnace and vacuumize it, adjust the sintering pressure to 50MPa, raise the temperature to 800°C, keep it for 1min, continue to raise the temperature to 1500°C, keep it for 10min, and get ultra-fine WC cemented carbide after cooling, and use nanometer Grade diamond abrasive paste for surface polishing.

The cemented carbides of each embodiment and comparative examples were subjected to performance tests, and the results are shown in Table 2.

72W/m˙K，密度

12g˙cm^-3，硬度

70，斷裂韌性

10MPa˙M^1/2，抗彎強度

1600N˙mm^-2，氧化增重

1.16mg˙cm^-2，合金的氧含量 均小於50ppm，各實施例的硬質合金拋光後的表面粗糙度Ra

10nm，均符合用於製造光學鏡片的合金模具的要求。 In the above-mentioned examples 1-7, the superfine WC-based cemented carbide components are combined with the low-oxygen preparation process, and the thermal conductivity of the alloy in each example is

72W/m˙K, density

12g˙cm ^-3 , hardness

70, fracture toughness

10MPa˙M ^1/2 , bending strength

1600N˙mm ^-2 , oxidation weight gain

1.16mg˙cm ^-2 , the oxygen content of the alloy is less than 50ppm, the surface roughness Ra of the cemented carbide of each embodiment after polishing

10nm, all meet the requirements of alloy molds used to manufacture optical lenses.

In Examples 1-7, when the amount of HEA added is 0.5wt%-5wt% and the amount of B added is 0.1wt%-3wt%, the added HEA increases, and the hardness and flexural strength of the alloy decrease. The thermal conductivity and fracture toughness have been improved, while the oxidation weight has increased slightly, that is, the oxidation resistance has decreased slightly; and the addition of other elements such as Ta, Al, etc., can properly enhance the strength of the alloy, such as hardness and flexural strength. .

Compared with Example 1, Comparative Example 1 has an alloy hardness lower than 70 and an oxidation weight gain higher than 1.16 mg due to HEA being higher than 5wt%. cm ^-2 , the surface roughness Ra of the prepared alloy after polishing is higher than 10nm, which obviously does not meet the requirements of alloy molds for optical lenses.

Compared with Example 4, Comparative Example 2 has a fracture toughness of less than 10MPa because B is higher than 3wt%. M ^1/2 , oxidation increase greater than 1.16mg. cm ^-2 , the surface roughness Ra of the alloy after polishing is higher than 10nm, which obviously does not meet the requirements of alloy molds for optical lenses.

Compared with Example 1 with 5wt% HEA added, Comparative Example 3 did not add HEA, resulting in alloy fracture toughness lower than 10MPa. M ^1/2 , and the oxidative weight gain was significantly higher than 1.16mg. cm ^-2 , the surface roughness Ra of the alloy after polishing is significantly higher than 10nm, which obviously does not meet the requirements of alloy molds for optical lenses; compared with Example 1, B is not added in Comparative Example 4, resulting in the hardness of the alloy Less than 70, while the oxidative weight gain is higher than 1.16mg. cm ^-2 , the surface roughness Ra of the alloy after polishing is higher than 10nm, which obviously does not meet the requirements of alloy molds for optical lenses.

Embodiment two

The difference between the preparation of ultrafine WC cemented carbide composed of Examples 8-12 and Example 1 is that the molecular formula of HEA powder in the raw material is not completely the same, and the composition of ultrafine WC-based cemented carbide is shown in Table 3 .

The cemented carbide of each embodiment was tested for performance, and the results are shown in Table 4.

72W/m˙K，密度

12g˙cm^-3，硬度HRA

70，斷裂韌性

10MPa˙M^1/2，抗彎強度

1600N˙mm^-2，氧化增重

1.16mg˙cm^-2。 In Examples 8-12, the superfine WC-based cemented carbide components are combined with the low-oxygen preparation process, and the oxygen content of the alloys in each example is less than 50ppm. The thermal conductivity, density, hardness, fracture toughness, and flexural strength of each alloy and oxidation weight gain are in line with the requirements of alloy molds for optical lenses: thermal conductivity

72W/m˙K, density

12g˙cm ^-3 , hardness HRA

70, fracture toughness

10MPa˙M ^1/2 , bending strength

1600N˙mm ^-2 , oxidation weight gain

1.16 mg˙cm ^-2 .

Comparative example one

The preparation method of the superfine WC cemented carbide of comparative example one comprises the steps:

(1) Raw material preparation

WC powder with an average particle size of 0.8 μm; five metal elemental powders (Al, Nb, Ta, Ti, Zr) that constitute HEA, all with a particle size of 0.5 μm; composed of boron carbide, titanium carbide, tantalum carbide or alumina Ceramic powder T with a particle size of 0.5 μm.

(2) ball mill

a. High-energy ball milling the elemental powder that constitutes HEA, the ball-to-material ratio is 15:1, the rotation speed is 400r/min, the ball milling medium is cemented carbide balls, and the time is 24 hours to obtain HEA alloy powder; b. Add WC powder and the ceramic powder T , Ball milling, the ratio of ball to material is 5:1, the speed is 100r/min, and the time is 40h.

(3) suppression

After being pressed under a pressure of 180 MPa and held for 120 s, a green body was obtained.

(4) Sintering

Place the green body above in a sintering furnace with a vacuum degree higher than 10 Pa, conduct discharge plasma sintering at a temperature of 1600° C. and a sintering pressure of 60 MPa for 30 minutes, and obtain a WC-based cemented carbide after cooling.

The cemented carbides of each embodiment and comparative examples were subjected to performance tests, and the results are shown in Table 6.

Compared with Example 1, Comparative Example 5 is easy to introduce too much oxygen because there is no inert gas protection in the preparation process, and it is easy to react with free carbon to form a carbon-deficient phase during the sintering process, and the oxygen content of the alloy suddenly increases by more than 100ppm, resulting in the hardness of the final alloy , oxidation weight gain, and surface roughness after processing have not reached the requirements of optical lens molds; compared with Example 2, Comparative Example 6 is easy to introduce too much oxygen because there is no inert gas protection in the preparation process, and it is easy to mix with free in the sintering process. Carbon reacts to form a carbon-deficient phase, and the oxygen content of the alloy suddenly increases to more than 100ppm, resulting in the final alloy oxidation weight gain and surface roughness not meeting the requirements of the optical lens mold.

Embodiment three

The ultra-fine WC-based cemented carbide obtained in Examples 1, 4, 9, 10, 12 and Comparative Examples 1-6 is applied to a mold for processing polycarbonate optical glass, and after the surface of the mold is coated, the coated mold is used for compression molding Optical lens, place the optical lens 3 cm below the square hole in front of the light source, and slightly tilt the lens for inspection. The light source is a 20W fluorescent lamp or a 100W light bulb, and the front, top, bottom, left and right of the testing environment are required to be black. For non-reflective objects, use a magnifying glass (4 times) to check the scars below #60 or #60: the optical glass made by the ultra-fine WC hard alloy mold of Examples 1, 4, 9, 10, and 12 has a good appearance; The optical lens produced by the mold made of the material of Comparative Examples 1-6 had a bad appearance and was unqualified.

The above-mentioned examples are only used to further illustrate several specific implementation modes of the present invention, but the present invention is not limited to the examples, any simple modifications, equivalent changes and modifications made to the above-mentioned examples according to the technical essence of the present invention , all fall within the scope of protection of the technical solution of the present invention.

Claims (10)

A preparation method of ultra-fine WC hard alloy, characterized in that the ultra-fine WC hard alloy has no Co, Ni binder phase, and the molecular formula of the ultra-fine WC hard alloy is WC-T-HEA, wherein T is carbide , at least one of oxides or borides, the T contains B elements, the B exists in the form of transition metal borides, HEA is a high-entropy alloy; the HEA is selected from Al, Nb, Ti, Zr, Ge , Si, V, Ta, Cr, Mn, Ce, Mo, W, Hf at least five elements; the preparation method includes: step a, the raw material of the high-entropy alloy is put into a vacuum melting furnace for melting , casting the molten liquid obtained by smelting to obtain a high-entropy alloy ingot; step b, under the protection of an inert atmosphere, crushing the high-entropy alloy ingot by mechanical crushing to obtain a high-entropy alloy coarse powder; step c , the submicron WC powder, T powder and the high-entropy alloy coarse powder are added to the jet mill pulverizer according to the ultrafine WC cemented carbide composition ratio, and the jet mill is pulverized under an inert atmosphere, and the classification step is removed to make the original separated The powder below 1 μm is mixed in the pulverized powder to obtain a mixed fine powder; the ultrafine WC cemented carbide composition includes: 0.5wt%-5wt% HEA, 35wt% or less T, 0.1wt%-3wt% B, The balance is WC and unavoidable impurities; step d: press-forming and sintering the mixed fine powder to obtain the ultra-fine WC cemented carbide. The preparation method of ultra-fine WC cemented carbide as claimed in claim 1, in step a, when the vacuum induction melting furnace is evacuated to a vacuum degree of 4Pa-9Pa, argon gas is filled into the melting chamber to make the furnace pressure Melting is carried out after reaching 0.03MPa-0.06MPa. The preparation method of ultra-fine WC cemented carbide as claimed in item 1, in step b, the mechanical crushing adopts two closed jaw crushers connected in series, and under the protection of an inert atmosphere, the high-entropy alloy The ingot is crushed to a coarse powder of 1mm-3mm. The preparation method of ultrafine WC cemented carbide as claimed in item 1, in step c, the crushing chamber pressure of the jet mill pulverizer is 5MPa-11MPa, and the rotating speed of the sorting wheel is 3500rpm-4300rpm. The preparation method of ultrafine WC cemented carbide as claimed in item 1, in step c, the average particle diameter of the submicron WC powder is 0.2 μm-0.8 μm, and the average particle diameter of the T powder is 0.5 μm -1 μm. The preparation method of ultra-fine WC cemented carbide as claimed in claim 5, in step c, the step of removing and classifying is to add a passage through the pipeline and the jet milling powder in the cyclone separator of the jet mill powder mill The screening program connected to the compressor of the machine, and the screening program is set to block the passage of ultrafine powder, so that the powder below 1 μm will not be separated in the cyclone separator and mixed in the pulverized powder. The preparation method of ultra-fine WC cemented carbide as claimed in item 1, in said step d, place the pressed body in a spark plasma sintering furnace and vacuumize it, adjust the sintering pressure to 35MPa-60MPa, and raise the temperature Heat to 750-800°C, keep warm for 1min-2min, continue to heat up to 1500°C-1700°C, keep warm for 5min-30min. The method for preparing ultra-fine WC cemented carbide according to claim 1, wherein the melting point of the HEA is below 1850°C. The preparation method of ultrafine WC cemented carbide as claimed in item 1, wherein said T is Al ₄ C ₃ , HfC, TiC, Cr ₃ C ₂ , VC, ZrC, NbC, TaC, SiC, Mn ₃ C, MoC , CuC, Mg ₂ C ₃ , W ₂ C, CeO ₂ , La ₂ O ₃ , MgO, ZrO ₂ , Al ₂ O ₃ , ZrB ₂ , CrB ₂ , TiB ₂ or MnB ₂ at least two. The preparation method of ultrafine WC cemented carbide as claimed in item 1, wherein the high-entropy alloy HEA is selected from the group consisting of molecular formulas of Al _0.4 Hf _0.6 NbTaTiZr, AlMo _0.5 NbTa _0.5 TiZr, AlNbTaTiV, AlNb _1.5 Ta _0.5 Ti _1.5 Zr _0.5 , At least one of AlCr ₂ Mo ₂ Nb ₂ Ti ₂ Zr, HfMoNbTiZr, HfNbTaTiZr, HfNbTiVZr, CrNbTiVZr, CrMo _0.5 NbTa _0.5 TiZr, TiZrHfNbCr, TiNbMoTaW, TiVNbMoTaW, HfMoTaTiZr or HfMoNbTaTiZr.