CN111644599B - Three-dimensional continuous network structure graphite/cast steel composite material and preparation method thereof - Google Patents
Three-dimensional continuous network structure graphite/cast steel composite material and preparation method thereof Download PDFInfo
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- CN111644599B CN111644599B CN202010522120.3A CN202010522120A CN111644599B CN 111644599 B CN111644599 B CN 111644599B CN 202010522120 A CN202010522120 A CN 202010522120A CN 111644599 B CN111644599 B CN 111644599B
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Abstract
The invention provides a graphite/cast steel composite material with good antifriction property, shock absorption property, heat conductivity, electric conductivity, strength and toughness and lower density and thermal expansibility and a normal-pressure preparation method with low cost. The composite material is composed of interconnected network structure graphite and cast steel which are communicated with each other in three-dimensional space, and respective advantages of the graphite and the cast steel are combined, wherein the volume percentage of the graphite is 10% -50%. The preparation method comprises the following steps: (1) preparing a three-dimensional network graphite preform by adopting a polyurethane foam precursor slurry coating process and a chemical bonding heating curing method; (2) carrying out metallization treatment on the surface of the graphite preform; (3) and pouring molten steel into the graphite preform by adopting a normal-pressure casting infiltration method, and cooling and solidifying to obtain the graphite/cast steel composite material with the three-dimensional continuous network structure. The invention can be used as materials for self-lubricating antifriction, vibration reduction/sound insulation, heat conduction, electric conduction, electronic packaging and the like and applied to the fields of machinery, metallurgy, environmental protection, aerospace, electronics and the like.
Description
Technical Field
The invention relates to the field of metal matrix composite materials, in particular to a graphite/cast steel composite material with a three-dimensional continuous network structure and a normal-pressure preparation method thereof.
Background
Three-dimensional continuous Network structure Metal Matrix Composite (or Interpenetrating Network Metal Matrix Composite, may be abbreviated as INMMC material) is a new type of Composite research field that has been paid more and more attention by material researchers at home and abroad in recent years. The composite material has a completely different space topological structure form from the traditional composite material, namely, the metal matrix phase and the composite phase (or called modified phase) are continuous (communicated) in three-dimensional space and are in an interlaced network structure. The two phases are in a topological structure form of mutual entanglement and coiling, mutual penetration and infiltration in a three-dimensional space, and the composite material is a brand new composite modified structure form in the field of synthetic materials. The structural form enables the material to have more unique strength performance, antifriction/wear resistance, vibration reduction/sound insulation performance, thermodynamic performance, electromagnetic performance, chemical performance and the like, has isotropy of performance, is used as antifriction/wear resistance material, high-damping vibration reduction/sound insulation material, high-efficiency heat conduction/electric conduction material, high-temperature resistance structural material, electronic packaging material and the like in the industries of mechanical equipment, environmental protection, aerospace, electronic communication and the like, has good technical feasibility, and has extremely wide development prospect.
In the field of mechanical equipment, gray cast iron is generally used as a material for manufacturing important parts such as various machine bodies, guide rails and the like at present, because the gray cast iron has good wear resistance, vibration damping property, casting property and low notch sensitivity, and has good cutting processability, simple melting and proportioning and low cost. However, various important and important mechanical equipment is subjected to increasingly large and complex dynamic loads, and related parts generate increasingly severe vibration, fatigue and abrasion. To further reduce these hazards, it is necessary to use materials having high strength, high damping, and high wear resistance.
In order to solve the problems, a silicon carbide/gray cast iron composite material with a three-dimensional network structure is developed at home and abroad, and the silicon carbide/gray cast iron composite material is expected to have high strength, excellent wear resistance, good vibration damping performance and other performances and be used for replacing gray cast iron to manufacture important castings such as machine beds, guide rails and the like. A polyurethane foam precursor slurry coating forming method and a high-temperature sintering process are adopted, a silicon carbide foam prefabricated body with a uniform and mutual through hole structure is prepared, surface metallization is carried out on the silicon carbide foam prefabricated body, and then a normal-pressure casting infiltration forming process is adopted to prepare the silicon carbide/gray cast iron composite material with the three-dimensional network structure. The relative wear resistance of the composite material is 4.7-7.9 times that of gray cast iron, the average friction coefficient is 46-89% of that of the gray cast iron, the amplitude attenuation is quicker than that of the gray cast iron, the vibration reduction effect is obvious, but the tensile strength is not as good as the gray cast iron, and the performance requirements of increasingly advanced and heavy mechanical equipment are difficult to meet.
The recently developed nodular cast steel at home and abroad is also a new material with better antifriction/wear resistance and shock absorption, the strength of the nodular cast steel is higher than that of gray cast iron, but the antifriction/wear resistance and the shock absorption are lower than those of cast iron. The abrasion resistance is attributed to the supporting skeleton action of carbide, and the antifriction property is benefited by the self-lubricating capability of graphite phase. If graphite is added, the friction reduction/wear resistance is improved, but carbide is excessive, the graphite in molten steel is also floated during smelting and casting to cause uneven distribution of the graphite, so that the toughness and the strength are obviously reduced, therefore, the graphite content of the nodular cast steel cannot exceed 1.8 percent generally, and the performance improvement space is limited.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the three-dimensional continuous network structure graphite/cast steel composite material which simultaneously has good antifriction property, shock absorption/sound insulation property, strength, toughness, electric/thermal conductivity and lower density and thermal expansibility and the normal pressure preparation method thereof, and the preparation method has simple process and low cost.
The technical scheme of the three-dimensional continuous network structure graphite/cast steel composite material is that the composite material is composed of interconnected network structure graphite and cast steel which are communicated in a three-dimensional space, wherein the volume ratio of the graphite is 10-50%.
The composite material combines the advantages of graphite and cast steel, and has unique strength performance, friction reducing performance, vibration reducing/sound insulating performance, electric/heat conducting performance and the like.
Furthermore, the interconnected network structure graphite is prepared by soaking a polyurethane foam precursor in water-based graphite slurry, extruding redundant slurry, drying, heating and curing.
The preparation method of the three-dimensional continuous network structure graphite/cast steel composite material adopts the technical scheme that the method comprises the following steps:
(1) preparing a three-dimensional network graphite preform by adopting a polyurethane foam precursor slurry coating forming process and a chemical bonding heating curing method;
(2) carrying out metallization treatment on the surface of the three-dimensional network graphite preform to improve the wettability between graphite and steel;
(3) and pouring molten steel into the three-dimensional network graphite preform communicated with the pores by adopting a normal-pressure casting infiltration method, and cooling, solidifying and forming to obtain the graphite/cast steel composite material with the three-dimensional continuous network structure.
The invention takes cast steel as a metal matrix phase, takes graphite (flake graphite powder is adopted in the invention) as a composite phase (modified phase), and adopts a normal pressure casting process to prepare the graphite/cast steel composite material with a three-dimensional continuous network structure; the novel composite material obtained by the invention can simultaneously have good friction/wear resistance, shock absorption/sound insulation, strength, toughness, electric/thermal conductivity and lower density and thermal expansibility, has simple production process and lower production cost, and can replace gray cast iron, nodular cast steel and silicon carbide/gray cast iron composite material with a three-dimensional network structure to be used for manufacturing various important parts such as machine bodies, guide rails and the like.
Further, the specific steps of the step (1) are as follows:
a. cutting 5-25 ppi (namely the number of holes per inch of length) of polyurethane foam material into blocks according to the shape and size requirements, and carrying out surface modification treatment on the obtained polyurethane foam material block to obtain a polyurethane foam precursor;
b. preparing water-based graphite slurry;
c. fully soaking the polyurethane foam precursor obtained in the step a in the water-based graphite slurry prepared in the step b, extruding redundant slurry in the polyurethane foam precursor, recovering the polyurethane foam precursor to the original shape by virtue of the elasticity of the polyurethane foam precursor after the extrusion force is removed, and uniformly wrapping a layer of graphite slurry layer on the framework of the polyurethane foam precursor;
d. and naturally drying the polyurethane foam precursor wrapped with the graphite slurry at normal temperature, and heating at a proper temperature to perform chemical bonding and curing to obtain the graphite preform with the required strength and the three-dimensional network structure.
Still further, in the step a, the surface modification treatment of the polyurethane foam material block comprises the following specific steps: the preparation method comprises the steps of adopting a polymeric flocculant aqueous solution for dipping treatment, and then naturally drying for later use. By carrying out surface modification treatment on the polyurethane foam material block, the subsequent polyurethane foam precursor slurry coating forming process can be carried out more smoothly, and the slurry coating quality is easy to ensure.
Still further, the concrete steps of preparing the water-based graphite slurry in the step b are as follows: respectively weighing graphite powder, a binder, a rheological agent, a defoaming agent and a wetting agent according to the mass percentage for later use; wetting a rheological agent by using tap water of which the volume is 3-10 times that of the rheological agent, stirring and activating the rheological agent, and storing the rheological agent for later use after 24 hours; adding graphite powder into the prepared rheological agent slurry, and simultaneously adding a proper amount of tap water for stirring; then, sequentially adding a binder, a wetting agent, a defoaming agent and a proper amount of tap water, and fully stirring for 30-60 min; finally processing for more than 3 min by using a colloid mill; and standing and aging the processed slurry for more than 24 hours for later use.
Further, the water-based graphite slurry comprises the following components in percentage by mass: 100% of graphite powder, 5-14% of binder, 1.7-3.8% of rheological agent, 0.01-0.05% of defoaming agent, 0.2-0.5% of wetting agent and tap water, wherein the addition amount of the tap water is added according to the viscosity requirement of the graphite slurry; the binder is silica sol and water-soluble phenolic resin; the rheological agent comprises sodium-based rectorite powder and sodium carboxymethylcellulose, and the mass fractions of the rheological agent include 1.5-3% of the sodium-based rectorite powder, 0.2-0.8% of the sodium carboxymethylcellulose, 3-8% of silica sol and 2-6% of water-soluble phenolic resin; the defoaming agent is n-butyl alcohol; the wetting agent is fatty alcohol polyvinyl chloride ether. In the scheme, the binder is used for obtaining high strength; the function of the rheological agent is to enable the slurry to have better fluidity and thixotropy, enable the slurry to be in a solidification state when the slurry is static, and restore the fluidity when the slurry is stressed; the wetting agent is added to improve the wetting performance of the polyurethane foam precursor and the slurry, so that the slurry hanging amount of the slurry on the foam is increased, and the volume density of the polyurethane foam precursor is increased along with the increase of the slurry hanging amount of the slurry on the polyurethane foam precursor, so that the strength of the prepared graphite preform with the three-dimensional network structure is increased.
In addition, in the step d, the polyurethane foam precursor wrapped with the water-based graphite slurry is naturally dried at normal temperature, and is heated at a proper temperature to be chemically bonded and cured, and the specific steps are as follows: after the polyurethane foam precursor is subjected to slurry dipping and molding, the polyurethane foam precursor is naturally dried for more than 1 day, then the polyurethane foam precursor is put into a heating furnace to be heated to 350-450 ℃, the temperature is kept for 2-3 h, and after 3h, the polyurethane foam precursor is taken out of the furnace to be naturally cooled to normal temperature, so that the graphite preform with the three-dimensional network structure can be obtained.
In the scheme, when the polyurethane foam precursor is heated and cured, the temperature needs to be raised slowly, so that organic matters are fully volatilized and removed, otherwise, the organic matters and structural water in the polyurethane foam precursor are volatilized too fast, and a foam graphite blank body is easy to generate larger stress to cause damage; the heating temperature should not be too high, which would otherwise ablate the polyurethane foam precursor and reduce the strength and plasticity of the preform.
Further, the step (2) of performing metallization treatment on the surface of the three-dimensional network graphite preform includes the specific steps of: cleaning a three-dimensional network graphite preform by using absolute ethyl alcohol, drying and storing for later use, preparing alloy powder into metal slurry by using an ethanol solution containing polyvinyl butyral and phenolic resin, dip-coating the slurry on the surface of the cleaned three-dimensional network graphite preform, then placing the three-dimensional network graphite preform into a constant-temperature constant-humidity drying oven at 100 ℃, drying and storing for later use, wherein the alloy powder is a Cu-Cr-Ti mixture, the addition amounts of Ti and Cr are respectively 6-16%, the balance is Cu, the addition amounts of polyvinyl butyral and phenolic resin are respectively 1-3% of the alloy powder mixture, and the viscosity of the metal slurry is adjusted to be (3-7) x 10 by using ethanol-3 Pa.s。
By the method, a layer of Cu-Cr-Ti metal film is coated on the surface of the network graphite, and can replace direct contact between metal and graphite, so that the wettability of a graphite/metal interface is improved, the subsequent smooth compounding between the graphite and the metal is facilitated, the surface oxidation of the graphite when the graphite is contacted with high-temperature molten metal is avoided, and the mechanical property of the composite material is improved.
Further, the specific steps of the step (3) are as follows: fixing the three-dimensional network graphite preform in a prepared resin sand cavity, pouring molten steel into the three-dimensional network graphite preform by utilizing static pressure and dynamic pressure of the molten steel under the action of natural gravity under the condition of atmospheric pressure, cooling, solidifying and forming to obtain the graphite/cast steel composite material with the three-dimensional continuous network structure, coating a layer of alcohol-based zircon powder coating or corundum powder coating on the inner surface of the resin sand cavity when preparing a resin sand mold, immediately igniting and burning to dry the coating, and preventing the surface of the composite material from generating casting defects.
The scheme shows that the normal pressure casting infiltration forming process of the three-dimensional continuous network structure graphite/cast steel composite material is simple, and the preparation cost is low; and a layer of alcohol-based zircon powder coating or corundum powder coating is coated on the inner surface of the resin sand cavity, so that the surface roughness of the composite material can be prevented, and casting defects such as sand washing, sand inclusion, sand sticking and the like can be avoided.
Drawings
FIG. 1 is a macro-topographic map of the three-dimensional network graphite preform;
FIG. 2 is a comparison of a three-dimensional continuous network structure graphite/cast steel composite material prepared by the present invention with a gray cast iron material.
Detailed Description
The present invention will be described in detail with reference to specific examples.
The composite material is composed of interconnected network structure graphite and cast steel which are communicated in a three-dimensional space, wherein the volume ratio of the graphite is 10-50%. In this example, the volume ratio of graphite was specifically 18%, and flake graphite having excellent lubricating properties was used. The interconnected network structure graphite is prepared by adopting a polyurethane foam precursor to be soaked in water-based graphite slurry, extruding redundant slurry, drying, heating and curing.
The preparation method of the composite material comprises the following steps:
(1) preparing a three-dimensional network graphite preform by adopting a polyurethane foam precursor slurry coating forming process and a chemical bonding heating curing method;
(2) carrying out metallization treatment on the surface of the three-dimensional network graphite preform to improve the wettability between graphite and steel;
(3) and pouring molten steel into the three-dimensional network graphite preform communicated with the pores by adopting a normal-pressure casting infiltration method, and cooling, solidifying and forming to obtain the graphite/cast steel composite material with the three-dimensional continuous network structure.
Specifically, the preparation of the three-dimensional network graphite preform by adopting a polyurethane foam precursor slurry-coating forming process and a chemical bonding heating curing method is specifically shown as the following four steps a, b, c and d.
a. And cutting the polyurethane foam material with the required pore specification into blocks according to the shape and size requirements, and carrying out surface modification treatment on the obtained polyurethane foam material blocks to obtain the polyurethane foam precursor.
In this step, the pore size of the polyurethane foam precursor substantially determines the pore size of the final finished foam, and the polyurethane foam precursor should have a certain hydrophilicity and sufficient resilience to readily adsorb the water-based graphite slurry and ensure a rapid recovery of shape after excess slurry is extruded. Based on the above, the soft polyurethane foam plastic with the three-dimensional network skeleton structure is suitable for preparing the polyurethane foam precursor, and the material has the advantages of strong hydrophilicity, good pore uniformity, high rebound resilience, strong adsorbability, high tensile strength, high through porosity, less inter-network films, no tearing during slurry impregnation, resilience after slurry impregnation, and avoidance of collapse and hole plugging. Specifically, the polyurethane foam precursor with a pore size of 8ppi is selected in this embodiment. In order to facilitate the subsequent slurry-coating forming process of the polyurethane foam precursor, the polyurethane foam precursor needs to be subjected to surface modification treatment in advance before graphite slurry is impregnated. The surface modification treatment of the polyurethane foam material block comprises the following specific steps: and (3) soaking the polyurethane foam material block by adopting a high-molecular flocculant aqueous solution with a certain mass concentration, and then naturally drying for later use to obtain the polyurethane foam precursor. In this embodiment, the polymeric flocculant aqueous solution may be a Polyethyleneimine (PEI) aqueous solution, and the concentration of the polyethyleneimine aqueous solution is 15 to 20%; or a Polyacrylamide (PAA) aqueous solution with the concentration of 15-25%.
b. And preparing water-based graphite slurry.
The method comprises the following steps: weighing scale graphite powder, a binder, a rheological agent, a defoaming agent and a wetting agent according to the mass percentage for later use; wetting a rheological agent by using tap water of which the volume is 3-10 times that of the rheological agent, stirring and activating the rheological agent, and storing the rheological agent for later use after 24 hours; adding graphite powder into the prepared rheological agent slurry, and simultaneously adding a proper amount of tap water for stirring; then, sequentially adding a binder, a wetting agent, a defoaming agent and a proper amount of tap water, and fully stirring for 30-60 min; and finally, processing the graphite slurry by using a colloid mill for more than 3 min, and standing and aging the processed slurry for more than 24h for later use to prepare the water-based graphite slurry. Herein, 325 mesh or fine flake graphite powder (325 mesh or fine, carbon content is more than or equal to 97%, spherical particles are preferred) is selected, and tap water is used as solvent. Specifically, the water-based graphite slurry comprises the following components in percentage by mass: 100% of flake graphite powder, 5-14% of binder, 1.7-3.8% of rheological agent, 0.01-0.05% of defoaming agent, 0.2-0.5% of wetting agent and tap water, wherein the addition amount of the tap water is added according to the viscosity requirement of the graphite slurry. In the invention, the viscosity of the water-based graphite slurry is controlled to be 0.01-0.05 Pa for s. More specifically, the binder is silica sol and water-soluble phenolic resin, the rheological agent comprises sodium-based rectorite powder (sodium-based LT powder) and sodium carboxymethylcellulose (CMC), and the mass fractions of the sodium-based rectorite powder (sodium-based LT powder) and the sodium carboxymethylcellulose (CMC) are 1.5-3%, the sodium carboxymethylcellulose (CMC) 0.2-0.8%, the silica sol 3-8%, the water-soluble phenolic resin 2-6%, the defoaming agent is n-butyl alcohol, and the wetting agent is fatty alcohol polyvinyl chloride ether. The function of the rheological agent is to enable the slurry to have better fluidity and thixotropy, enable the slurry to be in a solidification state when the slurry is static, and restore the fluidity when the slurry is stressed; the wetting agent is added to improve the wetting performance of the polyurethane foam precursor and the slurry, so that the slurry hanging amount of the slurry on the foam is increased, and the volume density of the polyurethane foam precursor is increased along with the increase of the slurry hanging amount of the slurry on the polyurethane foam precursor, so that the strength of the prepared graphite preform with the three-dimensional network structure is increased. Before the precursor slurry coating process is carried out after the graphite slurry is prepared, the viscosity of the slurry is measured by a rotary viscometer, and the viscosity of the slurry is controlled to be 0.01-0.05 Pa for being beneficial to coating and slurry coating and not to influence the through hole rate due to hole blocking.
c. And c, fully soaking the polyurethane foam precursor obtained in the step a in the water-based graphite slurry prepared in the step b, extruding redundant slurry in the polyurethane foam precursor, recovering the polyurethane foam precursor to the original shape by virtue of the elasticity of the polyurethane foam precursor after the extrusion force is removed, and uniformly wrapping a layer of graphite slurry layer on the framework of the polyurethane foam precursor. In this embodiment, the thickness of the graphite slurry layer depends on the pore size specification of the polyurethane foam precursor, and the larger the precursor pore size, the larger the graphite slurry layer thickness may be. For 8ppi polyurethane foam precursor, the thickness of the graphite slurry layer is 0.2-0.4 mm. The graphite slurry layer is wrapped on the framework of the precursor, and the thickness of the graphite slurry layer is increased to a certain extent, so that the strength of the precursor is enhanced, the through-hole rate and the adsorptive tensile strength of the precursor are guaranteed to be good, the whole precursor is guaranteed not to be torn when the slurry is soaked, the slurry can be quickly rebounded after being soaked, and the situation that the hole is blocked due to collapse is avoided.
In step c, it is noted that the pre-treated polyurethane foam precursor is repeatedly squeezed to remove air before being impregnated with the slurry. The slurry needs to be kept uniform and consistent during impregnation, so that the local insufficient infiltration is avoided. Repeatedly kneading after dipping to ensure that the slurry is uniformly attached to the pore ribs of the polyurethane foam precursor with the three-dimensional reticular structure, and simultaneously extruding the redundant slurry to ensure that the material has higher through-hole rate. The product should be uniformly transparent when viewed under light. The aperture of the prepared polyurethane foam precursor is basically consistent.
The specific dipping forming process comprises the following steps:
1) tools (an enamel plate, a hand-push roller, a balance scale and the like) required by the slurry hanging operation are placed at the designated position of a workbench;
2) wearing medical rubber gloves on the left hand;
3) pouring the slurry into a porcelain basin;
4) immersing the polyurethane foam precursor into the slurry, and slightly pinching the polyurethane foam material by hands;
5) putting the polyurethane foam precursor attached with the graphite slurry into an enamel basin, and repeatedly rolling and beating for a plurality of times by using a manual roller;
6) observing under light, the product should be transparent, and the opaque person uses the roller to beat or roll lightly;
7) weighing the product by using balance, and adjusting the weight of the product according to the technical requirements;
8) after the shaping, the product was neatly placed on an aluminum plate on which tissue paper was laid.
d. And naturally drying the polyurethane foam precursor wrapped with the graphite slurry at normal temperature, and heating at a proper temperature to perform chemical bonding and curing to obtain the graphite preform with the required strength and the three-dimensional network structure.
This step is performed after the dip forming process. After the polyurethane foam precursor is subjected to slurry dipping and molding, the polyurethane foam precursor is naturally dried for more than 1 day, then the polyurethane foam precursor is put into a heating furnace to be heated to 350-450 ℃, the temperature is kept for 2-3 h, and after 3h, the polyurethane foam precursor is taken out of the furnace to be naturally cooled to normal temperature, so that the graphite preform with the three-dimensional network structure can be obtained.
The key of the heating curing is to control the heating temperature and speed. The temperature needs to be raised slowly, so that organic matters are fully volatilized and removed, otherwise, the organic matters and structural water in the foam graphite body volatilize too fast, and the foam graphite body is easy to generate larger stress to cause damage; the heating temperature should not be too high, which would otherwise ablate the polyurethane foam precursor and reduce the strength and plasticity of the preform.
The physical properties of the prepared three-dimensional network graphite preform are shown in the following table.
After the preparation of the graphite preform with the three-dimensional network structure is completed, the surface of the graphite preform needs to be modified so as to improve the wettability between graphite and steel and enhance the wetting and casting infiltration capacity of metal to graphite, thereby improving the mechanical property of the composite material. The invention adopts a metallization treatment process to modify the surface of a graphite material, coats a layer of Cu-Cr-Ti metal film on the surface of the network graphite, and can replace the direct contact between metal and graphite, thereby improving the wettability of a graphite/metal interface, facilitating the subsequent smooth compounding between the graphite and the metal, simultaneously avoiding the surface oxidation of the graphite when the graphite is contacted with high-temperature molten metal, and improving the mechanical property of the composite material.
The method comprises the following specific steps of carrying out metallization treatment on the surface of the three-dimensional network graphite preform: cleaning a three-dimensional network graphite preform by using absolute ethyl alcohol, drying and storing for later use, preparing alloy powder into metal slurry by using an ethanol solution containing polyvinyl butyral and phenolic resin, dip-coating the slurry on the surface of the cleaned three-dimensional network graphite preform, then placing the three-dimensional network graphite preform into a constant-temperature constant-humidity drying oven at 100 ℃, drying and storing for later use, wherein the alloy powder is a Cu-Cr-Ti mixture, the addition amounts of Ti and Cr are respectively 6-16%, the balance is Cu, the addition amounts of polyvinyl butyral and phenolic resin are respectively 1-3% of the alloy powder mixture, and the viscosity of the metal slurry is adjusted to be (3-7) x 10 by using ethanol-3 Pa.s。
Here, when copper is bonded to a material having a different coefficient of expansion at a high temperature, stress generated at the bonding interface is relaxed, and the copper melts and then wets graphite or permeates graphite to enhance the bonding force between graphite and copper. The addition of a proper amount (12-16%) of Ti and Cr to Cu can reduce the wetting angle of Cu and C at 1100 deg.C from 140 deg. to 23 deg. to promote interface combination.
After the preparation of the three-dimensional network graphite preform in the step (1) is completed and the surface of the three-dimensional network graphite preform is metallized in the step (2), the preparation of the three-dimensional continuous network structure graphite/cast steel composite material in the step (3) is carried out: and pouring molten steel into the prefabricated three-dimensional network graphite preform with communicated pores by adopting a normal-pressure casting infiltration method under the atmospheric pressure condition to prepare the graphite/cast steel composite material with the three-dimensional continuous network structure.
The specific process comprises the following steps: pre-fixing the three-dimensional continuous network structure graphite preform in a resin sand cavity, pouring molten steel into the three-dimensional network structure graphite preform under the atmospheric pressure condition by only utilizing static pressure and dynamic pressure of the molten steel under the action of natural gravity, and cooling, solidifying and forming to obtain the three-dimensional continuous network structure graphite/cast steel composite material.
In the process flow, the adopted materials comprise a three-dimensional network graphite preform subjected to metallization treatment, silica sand, furan resin, an organic sulfonic acid solution curing agent, a sample model, an alcohol-based zircon powder or corundum powder coating, a sand box, a metal furnace charge and the like. The specific flow is as follows.
(1) Molding method
The sand mold is made of furan resin self-hardening sand.
The proportions (mass ratio) of silica sand, furan resin and organic sulfonic acid solution curing agent are shown in the following table.
The mixing process comprises the following steps: a batch type sand mixer is adopted, silica sand and an organic sulfonic acid solution curing agent are mixed for 2 min, and then a resin binder is added into the mixture to be continuously mixed for 1 min, and then sand is immediately discharged.
The molding process comprises the following steps: and filling the uniformly mixed resin self-hardening sand into a sand box, and demolding after curing and forming.
(2) Casting process
In order to increase the static pressure and the dynamic pressure of molten iron and to enable the pouring position to be beneficial to molten steel mold filling and casting feeding, top pouring is adopted. The inner pouring channel and the whole sample cavity are completely arranged in the lower box, the straight pouring channel is positioned in the upper mould, and the heights of the upper mould and the pouring cup are increased as much as possible, so that the pouring system can fully play a feeding role during liquid shrinkage. A larger cross section area of an inner pouring gate is selected, pouring is performed as fast as possible, and a closed pouring system is adopted, namely Sigma F direct, Sigma F transverse and Sigma F internal. The height of the pressure head is not less than 240 mm.
(3) Coating material
In order to obtain a casting with a smooth surface and avoid casting defects such as sand washing, sand inclusion, sand sticking and the like, a layer of alcohol-based zircon powder coating or corundum powder coating is coated on the inner surface of a cavity, and the alcohol-based zircon powder coating or corundum powder coating is ignited and combusted immediately to dry the coating.
(4) Melting of molten steel
Casting carbon steel with ZG200-400 and above is selected.
(5) Pouring temperature
In order to improve the filling capacity of molten steel and the wettability of the molten steel and the surface of the three-dimensional network graphite preform, the pouring temperature should be as high as possible, and is about 1480 ℃. At a certain temperature, the surface energy of the liquid metal linearly decreases with the increase of the temperature, and the wetting angle of the metal and the graphite decreases with the increase of the temperature.
(6) Time of opening box
In order to reduce the thermal stresses due to the uneven wall thickness during cooling, it is required that the casting be carried out for 5 hours before opening the box, so that the graphite/cast steel composite material with a three-dimensional continuous network structure is obtained, as shown in the upper part of fig. 2 (the lower part of fig. 2 is gray cast iron).
The obtained graphite/cast steel composite material with the three-dimensional continuous network structure is subjected to line cutting and section morphology observation, and the graphite skeleton is found to be uniformly distributed in a metal matrix, the graphite/cast steel interface is clear, no obvious reaction layer is seen, no obvious casting defects such as holes and air holes are seen, and the casting infiltration effect is ideal. Tests prove that the three-dimensional network structure graphite/cast steel composite material prepared by the invention has the following main properties:
the volume density is less than or equal to 6.8g/cm3The content of the cast iron is reduced by more than 6 percent compared with that of gray cast iron;
the tensile strength is more than or equal to 230MPa and is improved by more than 50 percent compared with gray cast iron;
the relative wear resistance is more than 6.5 times of that of the gray cast iron;
the average friction coefficient is less than 74 percent of that of the gray cast iron;
the damping ratio is more than 2.1 times of that of the gray cast iron.
Therefore, the novel composite material prepared by the method has the advantages of obviously improved antifriction/wear resistance and shock absorption/sound insulation performance compared with gray cast iron, lower density, basically reaching the level of gray cast iron in strength, simpler normal pressure casting production process and lower production cost, can replace gray cast iron and nodular cast steel to be used for manufacturing important parts such as machine bodies, guide rails and the like of various important and major mechanical equipment, and obtains better use effect.
The invention can be used as an anti-friction/anti-friction material, a high-damping vibration damping/sound insulation material, a high-efficiency conductive/heat conductive material, a high-temperature resistant structural material, an electronic packaging material and the like to be applied to the industries of mechanical equipment, environmental protection, aerospace, electronic communication and the like.
Claims (6)
1. A preparation method of a three-dimensional continuous network structure graphite/cast steel composite material is characterized in that the composite material is composed of network structure graphite and cast steel which are communicated in a three-dimensional space, wherein the volume ratio of the graphite is 10-50%; the network structure graphite is prepared by dipping a polyurethane foam precursor into water-based graphite slurry, extruding redundant slurry, drying and heating for curing, and the method comprises the following steps:
(1) preparing a three-dimensional network graphite preform by adopting a polyurethane foam precursor slurry coating forming process and a chemical bonding heating curing method;
(2) carrying out metallization treatment on the surface of the three-dimensional network graphite preform to improve the wettability between graphite and steel;
(3) pouring molten steel into the three-dimensional network graphite preform communicated with the pores by adopting a normal-pressure casting infiltration method, and cooling, solidifying and forming to prepare a graphite/cast steel composite material with a three-dimensional continuous network structure; the cast steel is cast carbon steel with ZG200-400 and above;
the specific steps of the step (1) are as follows:
a. cutting 5-25 ppi of soft polyurethane foam material with a three-dimensional network skeleton structure into blocks according to shape and size requirements, and carrying out surface modification treatment on the obtained polyurethane foam material blocks to obtain a polyurethane foam precursor, wherein ppi is the number of holes per inch of length;
b. preparing water-based graphite slurry;
c. fully soaking the polyurethane foam precursor obtained in the step a in the water-based graphite slurry prepared in the step b, extruding redundant slurry in the polyurethane foam precursor, recovering the polyurethane foam precursor to the original shape by virtue of the elasticity of the polyurethane foam precursor after the extrusion force is removed, and uniformly wrapping a layer of graphite slurry layer on the framework of the polyurethane foam precursor;
d. naturally drying the polyurethane foam precursor wrapped with the graphite slurry at normal temperature, and heating at 350-450 ℃ to perform chemical bonding and curing to obtain a three-dimensional network structure graphite preform with required strength;
the step (2) of carrying out metallization treatment on the surface of the three-dimensional network graphite preform comprises the following specific steps: cleaning a three-dimensional network graphite preform by using absolute ethyl alcohol, drying and storing for later use, preparing alloy powder into metal slurry by using an ethanol solution containing polyvinyl butyral and phenolic resin, dip-coating the slurry on the surface of the cleaned three-dimensional network graphite preform, then placing the three-dimensional network graphite preform into a constant-temperature constant-humidity drying oven at 100 ℃ for drying and storing for later use, wherein the alloy powder is a Cu-Cr-Ti mixture, the addition amounts of Ti and Cr are respectively 6-16%, the balance is Cu, the addition amounts of polyvinyl butyral and phenolic resin are respectively 1-3% of the alloy powder mixture, and the viscosity of the metal slurry is adjusted to (3-7) x 10-3 Pa.s by using ethanol.
2. The method for preparing the three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 1, wherein the step a of performing surface modification treatment on the polyurethane foam material block comprises the following specific steps: and (2) carrying out dipping treatment by adopting a polymeric flocculant aqueous solution, and then naturally drying for later use, wherein the polymeric flocculant is a polyethyleneimine aqueous solution with the concentration of 15-20% or a polyacrylamide aqueous solution with the concentration of 15-25%.
3. The method for preparing the three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 1, wherein the step b of preparing the water-based graphite slurry comprises the following specific steps: respectively weighing graphite powder, a binder, a rheological agent, a defoaming agent and a wetting agent according to the mass percentage for later use; wetting a rheological agent by using tap water of which the volume is 3-10 times that of the rheological agent, stirring and activating the rheological agent, and storing the rheological agent for later use after 24 hours; adding graphite powder into the prepared rheological agent slurry, and simultaneously adding a proper amount of tap water for stirring; then, sequentially adding a binder, a wetting agent, a defoaming agent and a proper amount of tap water, and fully stirring for 30-60 min; finally processing for more than 3 min by using a colloid mill; and standing and aging the processed slurry for more than 24 hours for later use.
4. The method for preparing a three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 3, wherein the water-based graphite slurry comprises the following components by mass fraction: 100% of graphite powder, 5-14% of binder, 1.7-3.8% of rheological agent, 0.01-0.05% of defoaming agent, 0.2-0.5% of wetting agent and tap water, wherein the addition amount of the tap water is added according to the viscosity requirement of the graphite slurry; the binder is silica sol and water-soluble phenolic resin; the rheological agent comprises sodium-based rectorite powder and sodium carboxymethylcellulose, and the mass fractions of the rheological agent include 1.5-3% of the sodium-based rectorite powder, 0.2-0.8% of the sodium carboxymethylcellulose, 3-8% of silica sol and 2-6% of water-soluble phenolic resin; the defoaming agent is n-butyl alcohol, and the wetting agent is fatty alcohol polyvinyl chloride ether.
5. The method for preparing the graphite/cast steel composite material with the three-dimensional continuous network structure as claimed in claim 1, wherein the step d of naturally drying the polyurethane foam precursor wrapped with the water-based graphite slurry at normal temperature and heating at a proper temperature to cause chemical bonding and solidification comprises the following specific steps: after the polyurethane foam precursor is subjected to slurry dipping and molding, the polyurethane foam precursor is naturally dried for more than 1 day, then the polyurethane foam precursor is put into a heating furnace to be heated to 350-450 ℃, the temperature is kept for 2-3 h, and after 3h, the polyurethane foam precursor is taken out of the furnace to be naturally cooled to normal temperature, so that the graphite preform with the three-dimensional network structure can be obtained.
6. The method for preparing the three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 1, wherein the step (3) comprises the following specific steps: fixing the three-dimensional network graphite preform in a prepared resin sand cavity, pouring molten steel into the three-dimensional network graphite preform by utilizing static pressure and dynamic pressure of the molten steel under the action of natural gravity under the condition of atmospheric pressure, and cooling, solidifying and forming to obtain the graphite/cast steel composite material with the three-dimensional continuous network structure; when the resin sand mold is prepared, a layer of alcohol-based zircon powder coating or corundum powder coating is coated on the inner surface of a resin sand mold cavity, and ignition and combustion are immediately carried out, so that the coating is dried, and casting defects on the surface of the composite material are prevented.
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