Background
The tungsten-copper composite material serving as a typical pseudo alloy has the high melting point and high hardness of tungsten and the excellent electrical conductivity and thermal conductivity of copper, and is widely applied to the fields of aerospace, military, electronics, vacuum high-voltage switches and the like. With the rapid development of the technical fields, the tungsten-copper composite material prepared by the traditional process is difficult to meet the performance requirements.
The refinement of microstructure and the doping modification by adding elements or compounds are the main research directions for improving the performance of the tungsten-copper composite material at present. On one hand, when the particle size is reduced to submicron or nanometer, the hardness and the strength of the material are obviously increased, and the toughness is also greatly improved; the nano-sized powder can significantly reduce sintering activation energy to promote sinterability and effectively improve uniform distribution of components to obtain a uniform structure. On the other hand, by adding a small amount of refractory, high-temperature resistant, high-strength doping materials, such as rare earth metals and their oxides (La, Ce, Y and their corresponding oxides), hard particles (B, WC, Al)2O3TiC, etc.) to improve the arc ablation resistance, high temperature strength, wear resistance, etc. of the material.
Chinese patent application CN201510425112.6 discloses a powder composition for copper alloy material, a composite material layer, an electrical contact and a preparation method thereof, wherein a high-frequency induction heating fusion welding mode is adopted, and Cu-W-WC-CeO is firstly adopted2The mixed material layer is arranged on the surface of the Cu-Cr alloy, and after high-frequency induction heating fusion welding treatment, the W-Cu composite material coated Cu-Cr alloy integral contact material is obtained through solid solution and aging treatment. The method prepares Cu-W-WC-CeO by using a V-shaped mixer2When powder is mixed, due to the fact that specific gravity difference among the powder is large, segregation of the powder is prone to occur in the mixing process, uniformity of the mixed powder is difficult to control, and problems of segregation and growth of doped particles can occur in the subsequent tungsten-copper alloy preparation process to affect component uniformity and service performance.
Chinese patent application CN201710294314.02 discloses a preparation method of a carbon nano tube reinforced tungsten-copper composite material, wherein high-energy ball milling is adopted to mix W powder and Cu powderAnd uniformly mixing the CNTs to obtain WCu mixed powder with the CNTs in dispersed distribution, and then pressing and sintering to obtain the CNTs and the in-situ synthesized WC hybrid reinforced tungsten-copper composite material thereof. However, during the in-situ reaction of CNTs and W particles, the uneven distribution of CNTs relative to W particles causes uneven carbonization on the surfaces of the W particles, which leads to brittle phase W2And C is generated. Meanwhile, in the high-temperature liquid phase sintering process, the structure of the CNTs is damaged, the original strengthening effect of the CNTs on the Cu matrix cannot be realized, and the manufacturing cost is increased.
The refinement of the microstructure is accompanied by an increase in the tungsten-copper interface, which further amplifies the interface bonding problem caused by poor wettability between tungsten and copper. The ideal interface should provide good adhesion, and in order to further improve the interface, the inventors research finds that the mechanical property of the tungsten-copper composite material can be improved by introducing an interface connection strengthening layer to improve the bonding strength between tungsten and copper.
Disclosure of Invention
The invention provides a preparation method of a W/WC composite grain reinforced tungsten-copper composite material, which comprises the following steps:
the preparation method comprises the steps of adding water-soluble tungsten salt, copper salt and an organic carbon source into water according to a preset proportion to obtain a precursor solution;
drying and pyrolyzing the precursor solution in a spray pyrolysis furnace to prepare tungsten copper oxide powder containing carbon;
performing ball milling on the tungsten-copper oxide powder containing carbon;
after ball milling, carrying out reduction carbonization on the tungsten-copper oxide powder containing carbon in a hydrogen furnace to obtain W/WC-Cu composite powder; wherein, the W/WC has a core-shell structure with W as a core and WC as a shell;
and fifthly, pressing the W/WC-Cu composite powder into a green compact and sintering to obtain the W/WC composite grain reinforced tungsten-copper composite material.
WC has a melting point and a linear expansion coefficient similar to those of W, and the high-temperature performance of WC is obviously superior to that of W, so that the WC is a superior tungsten-copper composite material doped material. In the preparation method, the organic carbon source is added in a solution form, so that the W, C element is more uniformly distributed; the precursor solution is dried and pyrolyzed to obtain molecular-grade blended tungsten-copper oxide powder, and a cracking carbon source is introduced to carry out in-situ synthesis of WC, so that the distribution uniformity of WC in the material is improved, and compared with a method for adding WC from the outside, the method avoids the harmful influence on the material performance caused by the problems of WC particle aggregation, weak bonding between WC and Cu and the like.
In the preparation method of the invention, the cracking carbon activity of the organic carbon source at high temperature is higher, so that the organic carbon source can react with W at lower temperature to generate WC. During reduction and carbonization, on one hand, the carbonization process of W is that C diffuses and reacts in W particles to generate WC, thereby forming W/WC composite crystal grains with W as a core and WC as a shell; on the other hand, copper with a lower melting point is melted at a high temperature and is precipitated on the surface of the W/WC composite crystal grain under the capillary action, so that WC becomes an interface connection strengthening layer between a W phase and a Cu phase, the interface thermal resistance is reduced, the interface combination is strengthened, and the performances of the material such as density, wear resistance, high-temperature strength and the like are improved. In addition, the wetting angle between WC and Cu as the interface bonding strengthening layer is far smaller than that between W and Cu, WC is in contact with Cu, the wetting effect is greatly improved, the driving force required by particle rearrangement in the liquid phase sintering process of the tungsten-copper composite material is smaller, the sintering temperature is reduced, and the production energy consumption is reduced.
In the preparation method embodiment of the invention, the tungsten salt can be ammonium metatungstate and/or ammonium paratungstate.
In the embodiment of the preparation method of the present invention, the copper salt may be at least one selected from the group consisting of copper nitrate, copper sulfate, copper acetate and copper chloride.
In the embodiment of the manufacturing method of the present invention, the organic carbon source may be at least one selected from the group consisting of glucose, sucrose and starch.
Preferably, the temperature of a feed inlet of the spray pyrolysis furnace is controlled to be 220-260 ℃, the pyrolysis temperature is 500-700 ℃, and the pyrolysis atmosphere is nitrogen atmosphere.
Preferably, in the step three, a planetary ball mill is used for ball milling, the ball milling time is 4-8 hours, the ball-material ratio is 5-10: 1, and the ball milling rotating speed is 100-150 rpm.
Preferably, in the step four, the reduction carbonization temperature is controlled to be 850-950 ℃, and the heat preservation time is 1-3 hours.
Preferably, the green body is obtained by adopting a bidirectional die pressing or cold isostatic pressing mode in the step fifthly, the pressing pressure is 50-500 MPa, the pressing time is 15-25 s, and the pressure maintaining time is 10-30 s.
Preferably, the sintering temperature is controlled to be 1150-1350 ℃, the heating rate is 5-10 ℃/min, the heat preservation time is 1-3 h, and the sintering atmosphere is hydrogen.
The second aspect of the invention provides a W/WC composite grain reinforced tungsten-copper composite material, which is formed by pressing W/WC-Cu composite powder into a green body and then sintering the green body; the proportion of Cu in the W/WC-Cu composite powder is 5-50 wt%, and the atomic molar ratio of W to C is 30: 1-320: 1; wherein, the W/WC has a core-shell structure with W as a core and WC as a shell. Preferably, the particle size distribution of the W/WC-Cu composite powder is between 100nm and 400 nm; the size distribution of the W/WC composite crystal grains after sintering is 0.5-1 mu m.
The tungsten-copper composite material (alloy) is formed by pressing W/WC-Cu composite powder into a green body and then sintering, wherein the W/WC composite crystal grain has a core-shell structure with W as a core and WC as a shell, and the WC is used as an interface connection strengthening layer between a W phase and a Cu phase, so that the interface thermal resistance is reduced, the interface combination is strengthened, and the performances of the material such as density, wear resistance, high-temperature strength and the like are improved. The wetting angle between WC and Cu existing in the form of the interface bonding strengthening layer is far smaller than that between W and Cu, so that the driving force required by particle rearrangement in the liquid phase sintering process of the tungsten-copper composite material is smaller, the sintering temperature is reduced, and the production energy consumption is reduced.
To more clearly illustrate the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the accompanying drawings and detailed description.
Detailed Description
The embodiment of the invention provides a W/WC composite grain reinforced tungsten-copper composite material, which is formed by pressing W/WC-Cu composite powder into a green body and then sintering the green body; wherein the proportion of Cu in the W/WC-Cu composite powder is 5-50 wt%, and the atomic molar ratio of W to C is 30: 1-320: 1; W/WC has a core-shell structure with W as the core and WC as the shell. The preparation method of the W/WC composite grain reinforced tungsten-copper composite material can comprise the following steps:
adding water-soluble tungsten salt, copper salt and an organic carbon source into water according to a predetermined proportion, and uniformly stirring to obtain a precursor solution; preferably, the pH of the precursor solution is adjusted to 3-4, and an appropriate amount of dispersant (such as citric acid, polyethylene glycol, stearic acid, etc.) is added thereto, and the addition amount of the dispersant may be 0.5-2 wt%, such as 1 wt%, of the precursor solution. Wherein the tungsten salt may be ammonium metatungstate and/or ammonium paratungstate, the copper salt may be at least one selected from the group consisting of copper nitrate, copper sulfate, copper acetate and copper chloride, and the organic carbon source may be at least one selected from the group consisting of glucose, sucrose and starch.
Drying and pyrolyzing the precursor solution in a spray pyrolysis furnace to prepare tungsten copper oxide powder containing carbon; preferably, the temperature of a feed inlet of the spray pyrolysis furnace is controlled to be 220-260 ℃, the pyrolysis temperature is controlled to be 500-700 ℃, the pyrolysis atmosphere is a nitrogen atmosphere, and the nitrogen flow is 1-3L/min.
Performing ball milling on the tungsten-copper oxide powder containing carbon; preferably, a planetary ball mill is used for ball milling, the ball milling time is 4-8 h, the ball-material ratio is 5-10: 1, and the ball milling rotation speed is 100-150 rpm.
After ball milling, carrying out reduction carbonization on the tungsten-copper oxide powder containing carbon in a hydrogen furnace to obtain W/WC-Cu composite powder, wherein the particle size of the W/WC-Cu composite powder is distributed between 100nm and 400 nm; wherein, the W/WC has a core-shell structure with W as a core and WC as a shell; preferably, the reduction carbonization temperature is controlled to be 850-950 ℃, the heat preservation time is 1-3 h, and the hydrogen flow is 0.5-3L/min.
And fifthly, pressing the W/WC-Cu composite powder into a green compact, and sintering to obtain the W/WC composite grain reinforced tungsten-copper composite material (alloy), wherein the size distribution of the W/WC composite grains after sintering is 0.5-1 mu m. Wherein the green body can be obtained by adopting a bidirectional die pressing or cold isostatic pressing mode, the pressing pressure is 50-500 MPa, the pressing time (time from no pressure to maximum pressure) is 15-25 s, and the pressure maintaining time (time for keeping under the maximum pressure) is 10-30 s; preferably, the sintering temperature is controlled to be 1150-1350 ℃, the heating rate is 5-10 ℃/min, the heat preservation time is 1-3 h, the sintering atmosphere is a hydrogen atmosphere, and the hydrogen flow is 0.5-2L/min.
Example 1
The tungsten-copper composite material of example 1 was prepared by pressing a W/WC-25Cu composite powder having a Cu content of 25 wt% into a green compact and sintering the green compact, wherein the W/WC had a core-shell structure in which W was the core and WC was the shell, the atomic molar ratio of W to C was 67:1, and the WC content was 1.19% of the total mass fraction of the material. The preparation method comprises the following steps:
weighing 166g of ammonium metatungstate, 102g of copper sulfate and 6g of glucose, dissolving in 1096ml of deionized water, and preparing into a precursor solution with the concentration of 20 wt%; that is, the atomic molar ratio of W to C in the raw materials actually weighed was controlled to 67:20 in consideration of the glucose loss.
Drying and pyrolyzing the precursor solution on a spray pyrolysis furnace to prepare W-25Cu oxide powder containing C, wherein the C exists in the W-25Cu oxide powder in the form of amorphous carbon; wherein the feeding rate is controlled to be 3ml/min, the temperature of a feeding hole is controlled to be 230 ℃, the pyrolysis temperature is controlled to be 650 ℃, the pyrolysis atmosphere is nitrogen atmosphere, and the nitrogen flow is controlled to be 2L/min;
thirdly, ball-milling the W-25Cu oxide powder containing C on a planetary ball mill for 5 hours at a ball-material ratio of 10:1 and a ball-milling rotation speed of 120 rpm;
putting the ball-milled W-25Cu oxide powder into a hydrogen furnace for continuous reduction carbonization to obtain W/WC-25Cu composite powder, wherein W/WC composite crystal grains in the powder have a core-shell structure with W as a core and WC as a shell; wherein the reduction carbonization temperature is 900 ℃, the heat preservation time is 2h, and the hydrogen flow is 1.5L/min;
pressing the W/WC-25Cu composite powder into a green compact and sintering to obtain a W/WC-25Cu composite material; wherein the pressing mode is cold isostatic pressing, the pressing pressure is 160MPa, the pressing time is 20s, and the pressure maintaining time is 20 s; the sintering temperature is 1200 ℃, the heating rate is 5 ℃/min, the heat preservation time is 2h, the sintering atmosphere is hydrogen atmosphere, and the hydrogen flow is 1L/min.
Fig. 1 is an XRD pattern of the W/WC-25Cu composite powder obtained in step four, from which the existence of a WC phase is clearly seen; FIG. 2 is an SEM image of the W/WC-25Cu composite powder, which shows that the particle size distribution of the W/WC-25Cu composite powder is between 100nm and 400 nm; FIG. 3 is an SEM image of the W/WC-25Cu composite material (surface Cu is etched after polishing), and it can be seen that the W/WC composite grains have a size distribution of 0.5 to 1 μm, and are typical fine-grained tungsten-copper composite materials.
Comparative example 1
The tungsten-copper composite material of comparative example 1 is prepared by pressing a W-25Cu composite powder with a Cu content of 25 wt% into a green compact and sintering the green compact, and the preparation method comprises the following steps:
weighing 166g of ammonium metatungstate and 102g of copper sulfate, dissolving in 1072ml of deionized water, and preparing into a precursor solution with the concentration of 20 wt%;
drying and pyrolyzing the precursor solution in a spray pyrolysis furnace to prepare tungsten-copper oxide powder; wherein the feeding rate of spray pyrolysis is 3ml/min, the temperature of a feeding hole is 230 ℃, the pyrolysis temperature is 650 ℃, the pyrolysis atmosphere is nitrogen atmosphere, and the nitrogen flow is 2L/min;
ball-milling tungsten-copper oxide powder on a planetary ball mill for 5 hours at a ball-material ratio of 10:1 and a ball-milling rotation speed of 120 rpm;
placing the tungsten-copper oxide powder subjected to ball milling in a hydrogen furnace for reduction to obtain W-25Cu composite powder; wherein the reduction carbonization temperature is 900 ℃, the heat preservation time is 2h, and the hydrogen flow is 1.5L/min;
pressing the W-25Cu composite powder obtained by hydrogen reduction into a green compact and sintering to obtain a W-25Cu composite material; the pressing mode is cold isostatic pressing, the pressing pressure is 160MPa, the pressing time is 20s, and the pressure maintaining time is 20 s; the sintering temperature is 1250 ℃, the heating rate is 5 ℃/min, the heat preservation time is 2h, the sintering atmosphere is hydrogen atmosphere, and the hydrogen flow is 1L/min.
The performance parameters of hardness, conductivity, density and the like of the W/WC-25Cu composite material prepared in example 1 and the W-25Cu composite material prepared in comparative example 1 were measured, and the results are shown in the following Table 1:
table 1: comparison of W/WC-25Cu composite and W-25Cu composite Performance
As can be seen from Table 1 above, the W/WC-25Cu composite material prepared in example 1 has higher density and obviously enhanced hardness. The W/WC composite grain reinforced tungsten-copper composite material has higher density and hardness, on one hand, because the W/WC composite grain has smaller size (the size after sintering is distributed between 0.5 mu m and 1 mu m), and on the other hand, because the W/WC composite grain has a core-shell structure with W as a core and WC as a shell, the WC becomes an interface connection strengthening layer between a W phase and a Cu phase, the interface thermal resistance is reduced, and the interface combination is strengthened.
Example 2
The tungsten-copper composite material of example 2 was prepared by pressing a W/WC-10Cu composite powder having a Cu content of 10 wt% into a green compact and sintering the green compact, wherein the W/WC had a core-shell structure in which W was the core and WC was the shell, the atomic molar ratio of W to C was 320:1, and the WC content was 0.29% of the total mass fraction of the material. The preparation method comprises the following steps:
dissolving ammonium metatungstate 397g, copper nitrate 98g and glucose 3g in 1992ml of deionized water to prepare a solution with the concentration of 20 wt%; wherein the atomic molar ratio of W and C in the raw materials is controlled to be 16:1 by actual weighing in consideration of the glucose loss.
Drying and pyrolyzing the precursor solution on a spray pyrolysis furnace to prepare W-10Cu oxide powder containing C, wherein the C exists in the W-10Cu oxide powder in the form of amorphous carbon; wherein the feeding rate is controlled to be 3ml/min, the temperature of a feeding hole is controlled to be 250 ℃, the pyrolysis temperature is controlled to be 650 ℃, the pyrolysis atmosphere is nitrogen atmosphere, and the nitrogen flow is 1L/min;
thirdly, ball-milling the W-10Cu oxide powder containing C on a planetary ball mill for 4 hours at a ball-to-material ratio of 10:1 and a ball-milling rotation speed of 120 rpm;
fourthly, placing the ball-milled W-10Cu oxide powder into a hydrogen furnace for continuous reduction carbonization to prepare W/WC-10Cu composite powder, wherein W/WC composite crystal grains in the powder have a core-shell structure with W as a core and WC as a shell; wherein the reduction carbonization temperature is 930 ℃, the heat preservation time is 2 hours, and the hydrogen flow is 1.5L/min;
pressing the W/WC-10Cu composite powder into a green compact and sintering to obtain a W/WC-10Cu composite material; wherein the pressing mode is cold isostatic pressing, the pressing pressure is 200MPa, the pressing time is 20s, and the pressure maintaining time is 20 s; the sintering temperature is 1330 ℃, the heating rate is 8 ℃/min, the heat preservation time is 3h, the sintering atmosphere is hydrogen atmosphere, and the hydrogen flow is 1L/min.
Example 3
The tungsten-copper composite material of example 3 was prepared by pressing a W/WC-50Cu composite powder having a Cu content of 50 wt% into a green compact and sintering the green compact, wherein the W/WC had a core-shell structure in which W was the core and WC was the shell, the atomic molar ratio of W to C was 56:1, and the WC content was 0.9% of the total mass fraction of the material. The preparation method comprises the following steps:
firstly, 70g of ammonium metatungstate, 128g of copper sulfate and 3g of glucose are weighed and dissolved in 804ml of deionized water to prepare a solution with the concentration of 20 wt%; namely, the glucose loss is calculated, and the molar ratio of W, C atoms which are actually weighed is controlled to be 14: 5.
Drying and pyrolyzing the precursor solution on a spray pyrolysis furnace to prepare W-50Cu oxide powder containing C, wherein the C exists in the W-50Cu oxide powder in the form of amorphous carbon; wherein the feeding rate is controlled to be 5ml/min, the temperature of a feeding hole is controlled to be 150 ℃, the pyrolysis temperature is controlled to be 580 ℃, the pyrolysis atmosphere is nitrogen atmosphere, and the nitrogen flow is controlled to be 3L/min;
thirdly, ball-milling the W-50Cu oxide powder containing C on a planetary ball mill for 5 hours at a ball-material ratio of 10:1 and a ball-milling rotating speed of 120 rpm;
fourthly, placing the ball-milled W-50Cu oxide powder into a hydrogen furnace for continuous reduction carbonization to prepare W/WC-50Cu composite powder, wherein W/WC composite crystal grains in the powder have a core-shell structure with W as a core and WC as a shell; wherein the reduction carbonization temperature is 850 ℃, the heat preservation time is 2 hours, and the hydrogen flow is 1.5L/min;
pressing the W/WC-50Cu composite powder into a green compact and sintering to obtain a W/WC-50Cu composite material; wherein the pressing mode is cold isostatic pressing, the pressing pressure is 120MPa, the pressing time is 20s, and the pressure maintaining time is 20 s; the sintering temperature is 1120 ℃, the heating rate is 8 ℃/min, the heat preservation time is 1.5h, the sintering atmosphere is hydrogen atmosphere, and the hydrogen flow is 1L/min.
Although the present invention has been described in terms of the above embodiments, it should be understood that equivalent modifications made in accordance with the present invention are intended to be included within the scope of the present invention as those skilled in the art would recognize without departing from the scope of the present invention.