Gradient hard alloy and preparation method thereof

Abstract

The invention belongs to the technical field of powder metallurgy, and particularly relates to a gradient hardness alloy and a preparation method thereof, different mixtures are prepared, the mixtures are subjected to ball milling, drying granulation and compression molding to obtain different compacts, and the compacts are subjected to one-time pressure sintering treatment to obtain hard alloys with different cobalt contents and particle sizes. After a certain surface of the hard alloy is ground and planed, the hard alloy is spliced at the ground and planed surface, combined by a spraying boat, pressed and positioned by a heavy object and then subjected to secondary pressure sintering treatment, so that the gradient hard alloy is obtained, the method is easy to control, the problems of alloy deformation and the like are avoided, and the required gradient hard alloy can be stably and freely combined.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to a gradient cemented carbide and a preparation method thereof. Background Art

[0002] Cemented carbide is an alloy material made of hard compounds of refractory metals and bonding metals through powder metallurgy. It generally uses high-hardness refractory metal carbide powder as the hard phase and metals such as Co and Ni as the bonding phase. Cemented carbide has a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance, and corrosion resistance. Cemented carbide is known as the "teeth of industry" and is used to manufacture cutting tools, knives, drilling tools, and wear-resistant parts. It is widely used in military industry, aerospace, mechanical processing, metallurgy, oil drilling, mining tools, electronic communications, construction and other fields.

[0003] With the continuous development of modern industrial technology, the use scenarios of cemented carbide are also constantly changing and upgrading. Different working parts often have different performance requirements. The particle size and bonding phase of cemented carbide manufactured by traditional processes are uniform, which is a bit exhausted in the face of such scene requirements. In the properties of cemented carbide, hardness and toughness are a pair of contradictions. Increasing its hardness will inevitably reduce its toughness. In order to solve this difficulty, industry experts continue to study gradient materials.

[0004] There are many methods for preparing gradient cemented carbide. Among them, gas carburizing method, liquid infiltration method, etc. change the content of carbon and activator inside the product to form different distributions of cobalt and particle size. Such methods are complicated in process, easily affected by the environment, and difficult to control the gradient; while layered pressing molding method, etc. achieves the gradient effect by controlling the raw materials of the pressed blanks. Such methods are prone to homogenization and it is difficult to form a gradient. At the same time, it increases the difficulty of pressing, and the alloy is also prone to deformation. There is an urgent need for breakthroughs and improvements in the above-mentioned problems existing in the preparation process of gradient cemented carbide. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a gradient cemented carbide and a preparation method thereof.

[0006] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0007] A method for preparing a gradient cemented carbide comprises the following steps:

[0008] S1. Prepare two mixtures with different proportions of bonding metal, WC powder and inhibitor;

[0009] S2, the two mixed materials are respectively subjected to ball milling and spray drying for granulation, and then pressed into a compact;

[0010] S3, the two types of pressed green sheets are subjected to pressure sintering treatment respectively to obtain two types of alloys;

[0011] S4, grinding and polishing a flat surface of the two alloys, splicing the ground and polished surfaces of the two alloys to obtain a spliced ​​alloy, placing the spliced ​​alloy on a spray boat, and covering it with another spray boat, and then pressing a heavy object on the top of the spray boat;

[0012] S5. The spray boat, the assembled alloy and the weight after step S4 are put into a sintering furnace for secondary pressure sintering to obtain the hard gradient alloy.

[0013] As a preferred embodiment of the method for preparing a gradient cemented carbide according to the present invention, in step S1, the bonding metal accounts for 3-25wt% of the mixture, the inhibitor accounts for 0-0.5wt%, and the remainder is WC powder, and the carbon points of the WC powder are 6.07-6.13wt%.

[0014] As a preferred embodiment of the method for preparing a gradient cemented carbide according to the present invention, the bonding metal is Co, the inhibitor is carbide of titanium, tantalum, niobium and chromium, and the particle size range of WC powder Fsss is 0.8 to 10 μm.

[0015] As a preferred embodiment of the method for preparing a gradient cemented carbide described in the present invention, wherein: in the step S2, refined paraffin and oleic acid are added before ball milling, the amount of refined paraffin added is 2-2.5% of the mass of the mixture, the liquid-solid ratio of oleic acid to the mixture is 1-2mL:1kg, the ball milling time is 20-60h, and the ball-to-material ratio is 3-5:1.

[0016] As a preferred embodiment of the method for preparing a gradient cemented carbide according to the present invention, in step S2, the ball milling medium is alcohol with a volume concentration of 94-96%.

[0017] As a preferred embodiment of the preparation method of a gradient cemented carbide described in the present invention, wherein: in the step S3, the one-time pressure sintering treatment includes: dewaxing: dewaxing in an inert gas atmosphere at a negative pressure of -2.5 to 0 kPa at 20 to 600°C, the inert gas flow rate is 8 to 10 L / min, and the dewaxing time is 600 to 720 min; vacuum sintering: temperature 600 to 1350°C, sintering time is 300 to 400 min; partial pressure sintering: temperature 1350°C to final temperature, furnace pressure 5 kPa, sintering time is 30 to 50 min, wherein the final temperature is 1410 to 1470°C; heat and pressure holding: sintering at the final temperature for 85 to 105 min, and the furnace pressure is 5 to 9 MPa.

[0018] As a preferred embodiment of the method for preparing a gradient cemented carbide according to the present invention, in step S3, the inert gas is one of argon, nitrogen and helium.

[0019] As a preferred embodiment of the method for preparing a gradient cemented carbide according to the present invention, in said step S4, the coating composition of the spray boat is yttria or zirconium oxide, and the weight is ≥10kg.

[0020] As a preferred embodiment of the preparation method of a gradient cemented carbide described in the present invention, wherein: in the step S5, the secondary pressure sintering treatment includes: vacuum sintering: temperature 20-1280°C, sintering time 300-400min; partial pressure sintering: temperature 1280°C-final temperature, furnace pressure 5kPa, sintering time 100-150min, wherein the final temperature is 1390-1410°C; heat preservation and pressure preservation: sintering at the final temperature for 30-50min, and the furnace pressure is 5-9MPa.

[0021] To solve the above technical problem, according to another aspect of the present invention, the present invention provides the following technical solution:

[0022] A gradient cemented carbide is prepared by adopting the above-mentioned method for preparing the gradient cemented carbide.

[0023] The beneficial effects of the present invention are as follows:

[0024] The present invention provides a gradient cemented carbide and a preparation method thereof. The ingredients are prepared according to the cemented carbide formula to obtain a mixture, the mixture is precisely pressed into shape and then sintered once to prepare cemented carbide with different cobalt contents and particle sizes, a certain surface of the mixture is grinded, the cemented carbide is spliced ​​at the grinded surface, and after being pressed and positioned with a heavy object, the mixture is put into a sintering furnace for secondary sintering, thereby obtaining a gradient cemented carbide. This method is easy to control, avoids problems such as alloy deformation, and can stably and freely combine into the required gradient cemented carbide. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0026] Figure 1 This is the metallographic phase diagram of the gradient hardness alloy BC prepared in Example 1 of the present invention.

[0027] Figure 2 This is the metallographic image of the gradient hardness alloy CD prepared in Example 2 of the present invention.

[0028] Figure 3 This is the metallographic image of the gradient hardness alloy AE prepared in Example 3 of the present invention.

[0029] Figure 4 This is the metallographic image of the fused alloy BB prepared in Comparative Example 2 of the present invention.

[0030] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0031] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] According to one aspect of the present invention, the present invention provides the following technical solution:

[0033] A method for preparing a gradient cemented carbide comprises the following steps:

[0034] S1. Prepare two mixtures with different proportions of bonding metal, WC powder and inhibitor;

[0035] S2, the two mixed materials are respectively subjected to ball milling and spray drying for granulation, and then pressed into a compact;

[0036] S3, the two types of pressed green sheets are subjected to pressure sintering treatment respectively to obtain two types of alloys;

[0037] S4, grinding and polishing a flat surface of the two alloys, splicing the ground and polished surfaces of the two alloys to obtain a spliced ​​alloy, placing the spliced ​​alloy on a spray boat, and covering it with another spray boat, and then pressing a heavy object on the top of the spray boat;

[0038] S5, performing secondary pressure sintering on the assembled alloy processed in step S4 to obtain the hard gradient alloy.

[0039] The invention obtains mixed materials of different compositions by batching, and performs one sintering after the mixed materials are precisely pressed into shape to prepare cemented carbides with different cobalt contents and particle sizes. After a certain surface of the mixed materials is grinded, the cemented carbides are spliced ​​at the grinded surface, and after being pressed and positioned by a heavy object, the mixed materials are put into a sintering furnace for secondary sintering. The gradient cemented carbide is obtained by liquefying and fusing the bonding phases of two cemented carbides. Since the cobalt contents and particle sizes of the two cemented carbides are different, the obtained gradient alloy has an obvious boundary line when observed under an optical microscope, and the metallographic performance at the boundary line is A02B00C00E00 without holes.

[0040] Preferably, in step S1, the proportion of the binder metal in the mixture is 3-25wt%, the proportion of the inhibitor is 0-0.5wt%, and the balance is WC powder, and the carbon point of the WC powder is 6.07-6.13wt%. Specifically, the proportion of the binder metal can be, for example, any one of 3wt%, 4wt%, 6wt%, 10wt%, 12wt%, 15wt%, 17wt%, 20wt%, 22wt%, 25wt%, or any range between two of them, and the proportion of the inhibitor can be, for example, any one of 0, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, or any range between two of them.

[0041] Preferably, in step S1, the bonding metal is Co, the inhibitor can be carbides of metals such as titanium, tantalum, niobium, and chromium, and the particle size range of WC powder Fsss is 0.8 to 10.0 μm. Specifically, the inhibitor can be TaC, Cr 3 C 2 The particle size of the WC powder may be any one of 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, 5.0 μm, 8.0 μm, 9.0 μm, 10.0 μm or a range between any two of them.

[0042] Preferably, in step S2, refined paraffin and oleic acid are added before ball milling, the amount of refined paraffin added is 2-2.5% of the mass of the mixture, the liquid-solid ratio of oleic acid to the mixture is 1-2 mL:1 kg, the ball milling time is 20-60 h, and the ball-to-material ratio is 3-5:1.

[0043] Preferably, the ball milling medium is alcohol with a concentration of 94-96%.

[0044] Preferably, in step S3, the one-time pressure sintering treatment includes: dewaxing: dewaxing at 20-600°C in an inert gas atmosphere at a negative pressure of -2.5-0kPa, the inert gas flow rate is 8-10L / min, and the dewaxing time is 600-720min; vacuum sintering: temperature 600-1350°C, sintering time is 300-400min; partial pressure sintering: temperature 1350°C-final temperature, furnace pressure 5kPa, sintering time is 30-50min, wherein the final temperature is 1410-1470°C; heat and pressure holding: sintering at the final temperature for 85-105min, and the furnace pressure is 5-9MPa.

[0045] Preferably, in step S3, the inert gas is one of argon, nitrogen and helium.

[0046] Preferably, in step S4, the coating composition of the spray boat is yttria or zirconium oxide, and the weight of the weight is ≥10 kg.

[0047] Preferably, in step S5, the secondary pressure sintering treatment includes: vacuum sintering: temperature 20-1280°C, sintering time 300-400min; partial pressure sintering: temperature 1280°C-final temperature, furnace pressure 5kPa, sintering time 100-150min, wherein the final temperature is 1390-1410°C; heat and pressure keeping: sintering at the final temperature for 30-50min, and the furnace pressure is 5-9MPa.

[0048] According to another aspect of the present invention, the present invention provides the following technical solution:

[0049] A gradient cemented carbide is prepared by adopting the above-mentioned method for preparing the gradient cemented carbide.

[0050] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0051] In terms of mixture preparation: take any cemented carbide formula with WC particle size ranging from WC08 to WC100, Co content between 3 and 25wt%, inhibitor between 0 and 0.5wt%, and WC powder carbon point C / WC=6.07-6.13wt% to obtain mixtures with different particle sizes and cobalt contents. The following examples illustrate several mixture formulas (not all combinations are represented):

[0052] Mixture a: 96.8wt% WC30, 3.2wt% Co;

[0053] Mixture b: 93.5wt% WC10, 6wt% Co, 0.5wt% TaC;

[0054] Mix c: 89.5wt% WC08, 10wt% Co, 0.5wt% Cr 3C 2 ;

[0055] Mixture d: 90wt% WC100, 10wt% Co;

[0056] Mixture e: 75wt% WC90, 25wt% Co.

[0057] Specific examples are described with different combinations of the above mixtures:

[0058] Example 1

[0059] A method for preparing a gradient cemented carbide comprises the following steps:

[0060] S1, prepare mixed materials b and c;

[0061] S2, respectively ball milling and spray drying granulation, and then pressing into a specific shape of compact by a precision press, adding 2.2% refined paraffin and oleic acid before ball milling: ingredient amount = 1.5mL: 1kg oleic acid, ball milling time is 20-60h, ball-to-material ratio is 4:1, and the ball milling medium is 95% alcohol;

[0062] S3, subjecting both compacts to a pressure sintering treatment to obtain alloys B and C:

[0063] The treatment process is as follows: dewaxing stage (20-600°C): Ar gas negative pressure dewaxing, where the Ar flow rate is 10L / min and the dewaxing time is 680min;

[0064] Vacuum sintering (600-1350°C): sintering time is 360 minutes;

[0065] Partial pressure sintering (1350℃~final temperature): the internal pressure of the furnace is 5kPa, the sintering time is 40min, and the final temperature is 1430℃;

[0066] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 6MPa, and the sintering time is 85min;

[0067] S4, grinding and planing a plane part of alloys B and C (using a 60-mesh grinding disc for grinding) until the B1 / C1 surface is completely exposed to light, and the B1 / C1 surface is spliced ​​to obtain a spliced ​​alloy BC, which is placed on a spray boat, and then another spray boat is used to cover the spliced ​​alloy BC, and then a 10 kg weight is placed on the top of the spray boat to press it down; wherein the main component of the spray boat coating is yttrium oxide;

[0068] S5, placing the spray boat, the assembled alloy BC and the weight assembled in step S4 into a sintering furnace for secondary pressure sintering to obtain a gradient alloy BC;

[0069] The processing flow is: vacuum sintering (20-1280°C): sintering time is 360 min;

[0070] Partial pressure sintering (1280℃~final temperature): the internal pressure of the furnace is 5kPa, the sintering time is 120min, and the final temperature is 1400℃;

[0071] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 5MPa and the sintering time is 30min.

[0072] The metallographic properties of the gradient alloy BC prepared in this example are shown in Table 1. Figure 1 As shown, there is a clear dividing line in the metallographic structure at the splicing and fusion point.

[0073] Example 2

[0074] A method for preparing a gradient cemented carbide comprises the following steps:

[0075] S1, prepare mixed materials c and d;

[0076] S2, respectively ball milling and spray drying granulation, and then pressing into a specific shape of compact by a precision press, adding 2.3% refined paraffin and oleic acid before ball milling: ingredient amount = 1.5ml:1kg oleic acid, ball milling time is 20-60h, ball-to-material ratio is 4:1, and the ball milling medium is 96% alcohol;

[0077] S3, subjecting both compacts to a pressure sintering treatment to obtain alloys C and D:

[0078] The treatment process is as follows: dewaxing stage (20-600°C): Ar gas negative pressure dewaxing, where the Ar flow rate is 10L / min and the dewaxing time is 680min;

[0079] Vacuum sintering (600-1350°C): sintering time is 360 minutes;

[0080] Partial pressure sintering (1350℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 40min, and the final temperature is 1430℃;

[0081] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 6Mpa, and the sintering time is 85min;

[0082] S4, grinding and planing a plane part of alloys C and D until the C1 / D1 surface is completely exposed to light, splicing the C1 / D1 surface to obtain a spliced ​​alloy CD, placing it on a spray boat, and then using another spray boat to cover the spliced ​​alloy CD, and then placing a 10kg weight on the top of the spray boat to press it down; wherein the main component of the spray boat coating is yttrium oxide;

[0083] S5, placing the spray boat, the assembled alloy CD, and the heavy object assembled in step S4 into a sintering furnace for secondary pressure sintering to obtain a gradient alloy CD;

[0084] The processing flow is: vacuum sintering (20-1280°C): sintering time is 360 min;

[0085] Partial pressure sintering (1280℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 120min, and the final temperature is 1400℃;

[0086] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 5Mpa and the sintering time is 30min.

[0087] The metallographic properties of the gradient alloy CD prepared in this example are shown in Table 1. Figure 2 As shown, there is a clear dividing line in the metallographic structure at the splicing and fusion point.

[0088] Example 3

[0089] A method for preparing a gradient cemented carbide comprises the following steps:

[0090] S1, prepare mixed materials a, e;

[0091] S2, respectively ball milling and spray drying granulation, and then pressing into a specific shape of compact by a precision press, adding 2.2% refined paraffin and oleic acid before ball milling: ingredient amount = 1.2ml: 1kg oleic acid, ball milling time is 20-60h, ball-to-material ratio is 4:1, and the ball milling medium is 95% alcohol;

[0092] S3, subjecting both compacts to a pressure sintering treatment to obtain alloys A and E:

[0093] The treatment process is as follows: dewaxing stage (20-600°C): Ar gas negative pressure dewaxing, where the Ar flow rate is 10L / min and the dewaxing time is 680min;

[0094] Vacuum sintering (600-1350°C): sintering time is 360 minutes;

[0095] Partial pressure sintering (1350℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 40min, and the final temperature is 1440℃;

[0096] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 6Mpa, and the sintering time is 85min;

[0097] S4, grinding and planing a plane part of alloys A and E until the A1 / E1 surface is completely exposed to light, splicing the A1 / E1 surface to obtain a spliced ​​alloy AE, placing it on a spray boat, and then using another spray boat to cover the spliced ​​alloy AE, and then placing a 10kg weight on the top of the spray boat to press it down; wherein the main component of the spray boat coating is yttrium oxide;

[0098] S5, placing the spray boat, the assembled alloy AE and the weight assembled in step S4 into a sintering furnace for secondary pressure sintering to obtain a gradient alloy AE;

[0099] The processing flow is: vacuum sintering (20-1280°C): sintering time is 360min;

[0100] Partial pressure sintering (1280℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 120min, and the final temperature is 1400℃;

[0101] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 5Mpa and the sintering time is 30min.

[0102] The metallographic properties of the gradient alloy AE prepared in this example are shown in Table 1. Figure 3 As shown, there is a clear dividing line in the metallographic structure at the splicing and fusion point.

[0103] Example 4

[0104] A method for preparing a gradient cemented carbide comprises the following steps:

[0105] S1, prepare mixed materials a, c;

[0106] S2, respectively ball milling and spray drying granulation, and then pressing into a specific shape of compact by a precision press, adding 2.3% refined paraffin and oleic acid before ball milling: ingredient amount = 1.5ml:1kg oleic acid, ball milling time is 20-60h, ball-to-material ratio is 4:1, and the ball milling medium is 95% alcohol;

[0107] S3, subjecting both compacts to a pressure sintering treatment to obtain alloys A and C:

[0108] The treatment process is as follows: dewaxing stage (20-600°C): Ar gas negative pressure dewaxing, where the Ar flow rate is 10L / min and the dewaxing time is 680min;

[0109] Vacuum sintering (600-1350°C): sintering time is 360 minutes;

[0110] Partial pressure sintering (1350℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 40min, and the final temperature is 1440℃;

[0111] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 6Mpa, and the sintering time is 85min;

[0112] S4, grinding and planing a plane part of alloys A and C until the A1 / C1 surface is completely exposed to light, splicing the A1 / C1 surface to obtain a spliced ​​alloy AC, placing it on a spray boat, and then using another spray boat to cover the spliced ​​alloy AC, and then placing a 10kg weight on the top of the spray boat to press it down; wherein the main component of the spray boat coating is yttrium oxide;

[0113] S5, placing the spray boat, the assembled alloy AC, and the weight assembled in step S4 into a sintering furnace for secondary pressure sintering to obtain a gradient alloy AC;

[0114] The processing flow is: vacuum sintering (20-1280°C): sintering time is 360min;

[0115] Partial pressure sintering (1280℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 120min, and the final temperature is 1400℃;

[0116] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 5Mpa and the sintering time is 30min.

[0117] The metallographic properties of the gradient alloy AC prepared in this example are shown in Table 1. There is an obvious boundary line in the metallographic structure at the splicing and fusion point.

[0118] Example 5

[0119] A method for preparing a gradient cemented carbide comprises the following steps:

[0120] S1, prepare mixed materials b and d;

[0121] S2, respectively ball milling and spray drying granulation, and then pressing into a specific shape of compact by a precision press, adding 2.2% refined paraffin and oleic acid before ball milling: ingredient amount = 1.2ml: 1kg oleic acid, ball milling time is 20-60h, ball-to-material ratio is 4:1, and the ball milling medium is 95% alcohol;

[0122] S3, subjecting both compacts to a pressure sintering treatment to obtain alloys B and D:

[0123] The treatment process is as follows: dewaxing stage (20-600°C): Ar gas negative pressure dewaxing, where the Ar flow rate is 10L / min and the dewaxing time is 680min;

[0124] Vacuum sintering (600-1350°C): sintering time is 360 minutes;

[0125] Partial pressure sintering (1350℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 40min, and the final temperature is 1430℃;

[0126] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 7Mpa, and the sintering time is 85min;

[0127] S4, grinding and planing a plane part of alloys B and D until the B1 / D1 surface is completely exposed to light, splicing the B1 / D1 surface to obtain a spliced ​​alloy BD, placing it on a spray boat, and then using another spray boat to cover the spliced ​​alloy BD, and then placing a 10kg weight on the top of the spray boat to press it down; wherein the main component of the spray boat coating is yttrium oxide;

[0128] S5, placing the spray boat, the assembled alloy BD, and the heavy object assembled in step S4 into a sintering furnace for secondary pressure sintering to obtain a gradient alloy BD;

[0129] The processing flow is: vacuum sintering (20-1280°C): sintering time is 360min;

[0130] Partial pressure sintering (1280℃~final temperature): the internal pressure of the furnace is 5KPa, the sintering time is 120min, and the final temperature is 1400℃;

[0131] Heat preservation and pressure maintenance (final temperature): the pressure in the furnace is 5Mpa and the sintering time is 30min.

[0132] The metallographic properties of the gradient alloy BD prepared in this example are shown in Table 1, and there is an obvious boundary line in the metallographic structure at the splicing and fusion point.

[0133] Comparative Example 1

[0134] Two portions of mixed materials a were prepared and processed in the same manner as in the subsequent steps S2-S5 of Example 1 to obtain fused alloy AA.

[0135] Comparative Example 2

[0136] Two portions of mixed materials b were prepared and processed in the same manner as in the subsequent steps S2-S5 of Example 1 to obtain fused alloy BB.

[0137] Comparative Example 3

[0138] Two mixed materials c were prepared and processed in the same manner as in the subsequent steps S2-S5 of Example 1 to obtain fused alloy CC.

[0139] Comparative Example 4

[0140] Two mixed materials d were prepared and processed in the same manner as in the subsequent steps S2-S5 of Example 1 to obtain a fused alloy DD.

[0141] Comparative Example 5

[0142] Two mixed materials e were prepared and processed in the same manner as in the subsequent steps S2-S5 of Example 1 to obtain a fused alloy EE.

[0143] The metallographic properties of the fusion alloys AA, BB, CC, DD, and EE obtained in Comparative Examples 1-5 are shown in Table 1; the metallographic picture of the fusion alloy BB is shown in Figure 4 There is no obvious dividing line in the metallographic structure of the splicing and fusion.

[0144] Comparative Example 6

[0145] Mixed materials b and c were prepared and processed according to the same process as the subsequent steps S2-S5 of Example 1 (the difference from Example 1 is that the joint surface was not ground), to obtain a gradient alloy BC; the metallographic properties of the gradient alloy BC prepared in this comparative example are shown in Table 1, and there is an obvious boundary line at the gradient fusion point, and the metallographic properties of the boundary line are A06B02C00E00 without holes.

[0146] Comparative Example 7

[0147] Mixtures b and c were prepared and processed in the same process as in the subsequent steps S2-S5 of Example 1 (the difference from Example 1 is that another spray boat was not used to cover the joint alloy and press it with a heavy object), to obtain gradient alloy BC; the metallographic properties of the gradient alloy BC prepared in this comparative example are shown in Table 1, and there is an obvious boundary line at the gradient fusion, and the metallographic properties of the boundary line A02B04C00E00 have holes. .

[0148] Comparative Example 8

[0149] Mixtures b and c were prepared and processed in the same process as in the subsequent steps S2-S5 of Example 1 (the difference from Example 1 was that they were placed on a brushed paint boat, and another brushed paint boat was used to cover the jointed alloy), to obtain gradient alloy BC; the metallographic properties of the gradient alloy BC prepared in this comparative example are shown in Table 1, and there is an obvious boundary line at the gradient fusion, and the metallographic properties of the boundary line are A02B00C02E00 without holes. .

[0150] Comparative Example 9

[0151] Mixed materials b and c were prepared and processed according to the same process as the subsequent steps S2-S5 of Example 1 (the difference from Example 1 is that the final temperature of the secondary pressure sintering is 1450°C) to obtain a gradient alloy BC; the metallographic properties of the gradient alloy BC prepared in this comparative example are shown in Table 1, and there is an obvious dividing line in the metallographic structure at the gradient fusion point. The metallographic properties of the dividing line are A02B00C00E00, with no holes and a large number of coarse grains.

[0152] Comparative Example 10

[0153] Mixed materials b and c were prepared and processed according to the same process as the subsequent steps S2-S5 of Example 1 (the difference from Example 1 is that the furnace pressure in the secondary pressurized sintering and heat preservation stage is 2 MPa) to obtain a gradient alloy BC; the metallographic properties of the gradient alloy BC prepared in this comparative example are shown in Table 1, and there is an obvious dividing line in the metallographic structure at the gradient fusion point, and the metallographic properties of the dividing line are A04B00C00E00 without holes.

[0154] The metallographic properties of the alloys prepared in the above examples and comparative examples are shown in Table 1.

[0155] Table 1

[0156]

[0157]

[0158] As can be seen from the above embodiments and comparative examples, Table 1, different mixtures are ball-milled, dried and granulated, pressed, and sintered under pressure once to prepare cemented carbides with different cobalt contents and particle sizes. After surface grinding and planing, the cemented carbides are spliced ​​at the planed surface, and the spray boat combination and heavy objects are used to press and position the cemented carbides and then put them into the sintering furnace for secondary pressure sintering to obtain gradient cemented carbides. There is a clear metallographic boundary at the splicing and fusion, and the metallographic performance at the boundary is A02B00C00E00 without holes. The same mixture (Comparative Examples 1 to 5) produces alloys with no obvious boundary at the interface after splicing, and the metallographic performance is A02B00C00E00 without holes. The same metallographic performance proves that this method has a good effect on the fusion of alloys, which not only ensures the original performance of the spliced ​​alloy, but also forms a gradient alloy. Moreover, the setting of the process parameters of this method will also affect the performance of the metallographic phase of the fusion interface. The changes in the process parameters of Comparative Examples 6 to 10 will cause the alloy performance to deteriorate.

[0159] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a gradient cemented carbide, characterized in that: The steps include: S1. Prepare two mixtures with different proportions of bonding metal, WC powder and inhibitor; S2, the two mixed materials are respectively subjected to ball milling and spray drying for granulation, and then pressed into a compact; S3, the two types of pressed green sheets are subjected to pressure sintering treatment respectively to obtain two types of alloys; S4, grinding and polishing a flat surface of the two alloys, splicing the ground and polished surfaces of the two alloys to obtain a spliced ​​alloy, placing the spliced ​​alloy on a spray boat, and covering it with another spray boat, and then pressing a heavy object on the top of the spray boat; S5, placing the spray boat, the assembled alloy, and the weight assembled in step S4 into a sintering furnace for secondary pressure sintering to obtain the hard gradient alloy.

2. The method for preparing a gradient cemented carbide according to claim 1, characterized in that: In the step S1, the binder metal accounts for 3-25wt% of the mixture, the inhibitor accounts for 0-0.5wt%, and the remainder is WC powder, and the carbon points of the WC powder are 6.07-6.13wt%.

3. The method for preparing a gradient cemented carbide according to claim 2, characterized in that: In the step S1, the bonding metal is Co, the inhibitor is carbide of titanium, tantalum, niobium, and chromium, and the particle size range of the WC powder Fsss is 0.8 to 10 μm.

4. The method for preparing a gradient cemented carbide according to claim 1, characterized in that: In the step S2, refined paraffin and oleic acid are added before ball milling, the amount of refined paraffin added is 2-2.5% of the mass of the mixture, the liquid-solid ratio of oleic acid to the mixture is 1-2 mL:1 kg, the ball milling time is 20-60 h, and the ball-to-material ratio is 3-5:

1.

5. The method for preparing a gradient cemented carbide according to claim 4, characterized in that: In the step S2, the ball milling medium is alcohol with a volume concentration of 94-96%.

6. The method for preparing a gradient cemented carbide according to claim 1, characterized in that: In the step S3, the one-time pressure sintering treatment includes: dewaxing: dewaxing at 20-600°C in an inert gas atmosphere with a negative pressure of -2.5-0kPa, an inert gas flow rate of 8-10L / min, and a dewaxing time of 600-720min; vacuum sintering: temperature of 600-1350°C, and sintering time of 300-400min; partial pressure sintering: temperature of 1350°C to final temperature, furnace pressure of 5kPa, sintering time of 30-50min, wherein the final temperature is 1410-1470°C; heat preservation and pressure preservation: sintering at the final temperature for 85-105min, and the furnace pressure is 5-9MPa.

7. The method for preparing a gradient cemented carbide according to claim 6, characterized in that: In step S3, the inert gas is one of argon, nitrogen and helium.

8. The method for preparing a gradient cemented carbide according to claim 1, characterized in that: In the step S4, the coating composition of the spray boat is yttria or zirconium oxide, and the weight is ≥10kg.

9. The method for preparing a gradient cemented carbide according to claim 1, characterized in that: In the step S5, the secondary pressure sintering treatment includes: vacuum sintering: temperature 20-1280°C, sintering time 300-400min; partial pressure sintering: temperature 1280°C-final temperature, furnace pressure 5kPa, sintering time 100-150min, wherein the final temperature is 1390-1410°C; heat preservation and pressure preservation: sintering at the final temperature for 30-50min, and the furnace pressure is 5-9MPa.

10. A gradient cemented carbide, characterized in that: The gradient cemented carbide is prepared by the preparation method of any one of claims 1 to 9.

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