CN116426860B - Preparation method of wide-temperature-range self-lubricating coating for hard seal control valve based on hBN - Google Patents
Preparation method of wide-temperature-range self-lubricating coating for hard seal control valve based on hBN Download PDFInfo
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Abstract
The invention discloses a preparation method of a wide-temperature-range self-lubricating coating for a hard sealing control valve based on hBN, which relates to the technical fields of new materials, surface engineering and control valves, and is characterized in that cBN/hBN complex-phase compact particles are formed through prepressing molding and crushing granulation, mn-C containing face-centered cubic high-entropy alloy is prepared to serve as a bonding phase, volume expansion is generated from cBN to hBN at high temperature to eliminate gaps generated by bridging between flaky hBN, residual pores can be eliminated from stress-induced austenite to martensite in the bonding phase, and coating compactness and wide-temperature-range service capability are improved. The invention solves the problems of large friction coefficient, wear resistance, compactness, small use temperature range and the like of the coating prepared by the prior art, has the maximum working pressure of 45MPa, the working temperature range of-196-660 ℃, the hardness of 950-160 HV and the bonding strength of 80-95 MPa, and can be used in the fields of petrochemical industry, silicon industry, metallurgy, hydropower and the like.
Description
Technical Field
The invention relates to the technical fields of new materials, surface engineering and control valves, in particular to a preparation method of a wide-temperature-range self-lubricating coating for a hard seal control valve based on hBN.
Background
The metal hard seal control valve is often used in severe working conditions such as high temperature, abrasion, corrosion and abrasion, and the like, and has been widely applied in many fields such as petrochemical industry, polysilicon, metallurgy, hydropower, and the like. In order to improve the wear resistance of the sealing surface, cr is generally thermally sprayed 3 C 2 The surface hardening is carried out on the coating such as NiCr, WC-Co and the like to improve the abrasion resistance and corrosion resistance of the coating, but the existing coating material still has the problems of high friction coefficient, large porosity, low density and the like, the early abrasion easily occurs in the opening/closing process of the hard sealing control valve to cause the coating to fall off, the hard sealing control valve is seized and the like, and the production safety is seriously threatened. CN111218638A provides an abrasion-resistant composite protective coating for a hard sealing surface of a ball valve, which comprises the following steps of sequentially preparing Cr on the surface of a metal matrix 3 C 2 -a NiCr coating, a Cr-Cr/C/WC dual mode transition layer and a WC/a-C nano multi-layer film, the composite protective coating having a lower coefficient of friction, good load carrying capacity and abrasion resistance. However, the method requires spraying and unbalanced magnetron sputtering deposition, and the control is relatively complex. On the one hand, the introduction of the solid lubricant can naturally improve the lubricating property of the coating, but because of the lamellar structure of the solid lubricant, lamellar objects are bridged with each other to form pores, so that a compact coating is difficult to obtain, and the high porosity easily causes the coating to be easily peeled off under the condition of being pressed and to lose efficacy early. On the other hand, the service temperature range of the hard seal control valve spans a large extent, and at extremely high and extremely low service temperatures, the self-lubricating action of many solid lubricants fails, which also reduces the service temperature range thereof. The high compactness and wide temperature range service capability are achieved while the friction coefficient of the coating is reduced, so that the requirement of the coating on service in severe working conditions is met.
Disclosure of Invention
The problems that the friction coefficient of a hardening coating on the surface of the existing hard sealing control valve is large, the hard sealing control valve is easy to wear, the coating is not compact and the using temperature range is small are solved. The invention provides a method for forming a face-centered cubic structure FCC high-entropy alloy containing a Mn-C element by pre-pressing, forming, crushing and granulating to form a cBN/hBN complex-phase compact particle, and preparing the face-centered cubic structure FCC high-entropy alloy containing the Mn-C element as a binding phase, and the densification and self-lubrication of a coating are realized by utilizing phase change volume expansion. On one hand, the volume expansion generated by the conversion of cBN to hBN at high temperature is utilized to eliminate gaps between flaky hBN caused by bridging to realize densification, and on the other hand, the stress-induced conversion of austenite to martensite in a bonding phase is utilized to eliminate residual pores, so that the compactness of the coating is improved, and the service capacity of the coating in a wide temperature range is improved; thereby successfully preparing the hard seal control valve surface wide temperature range self-lubricating coating based on the hBN.
The preparation method of the wide-temperature-range self-lubricating coating for the hard sealing control valve based on the hBN is characterized by sequentially comprising the following steps of:
(1) Preparation of cBN-containing hBN complex phase compact particles: firstly, mixing hexagonal boron nitride (hBN) and cubic boron nitride (cBN) powder in a three-dimensional mixer according to a weight ratio of 4:1, wherein the granularity of the hBN is 1-2 mu m, the cBN consists of three kinds of powder with granularity of 200-250 nm, 300-350 nm and 400-450 nm, and the mass ratio is 1:1:1; pressing the mixed powder into compact sheets with the thickness of 0.5-1 mm under the high pressure of 500-600 MPa, so that nano-scale cBN particles are filled in the pores among the hBN micro sheets; then, 60-mesh screen is adopted for grating and sieving, and then 2000-mesh screen is adopted for sieving, so as to obtain hBN complex-phase compact particles containing cBN;
(2) Preparing FCC high-entropy alloy binding phase powder with Mn-C element and face-centered cubic structure: weighing Co, cr, ni, fe, mn, C raw material powder according to the atomic percentage of Co, cr, ni, fe, mn, C=1:1:1:1, (0.7-0.8): (0.1-0.15), performing planetary ball milling on the weighed raw material powder at the ball milling rotating speed of 300-400 r/min, wherein the ball-to-material ratio of ball milling is 10:1, and adopting Si with the diameter of 5mm 3 N 4 Ceramic grinding balls are subjected to ball milling for 12-24 hours, and after ball milling, filtering, drying and sieving are carried out to prepare FCC high-entropy alloy binding phase powder containing Mn-C elements;
(3) Preparation of a powder feed containing a self-lubricating phase: weighing raw material powder for proportioning, and mixing according to the mass percentage of WC or Cr 3 C 2 65-85% of hard phase, 5-10% of hBN complex phase compact particles containing cBN, and the center of the face containing Mn-C element10-25% of cubic high-entropy alloy binding phase powder, and mixing the three raw material powders in a three-dimensional mixer for 12-24 hours; then adding an absolute ethyl alcohol mixed solution containing 2wt.% of paraffin into the powder, wherein the mass ratio of the addition of the absolute ethyl alcohol mixed solution to the raw material powder is 0.25-0.35:1, the temperature of the mixed solution is 50-60 ℃, the mixed solution is continuously mixed for 10min and then subjected to spray drying, then sintering is carried out in a vacuum sintering furnace for 1-2 h at 1150-1250 ℃, cBN and hBN keep stable and do not generate phase transition at the sintering temperature, and after the sintering is completed, crushing and gas flow classification are carried out, so that the powder feed containing the self-lubricating phase, wherein the phase composition is hard phase+self-lubricating phase+cBN+FCC binding phase CoCrNiFeMnC, the particle size is 55-70 mu m, and the particle sphericity is 0.8-0.9, is prepared, and the hard phase is WC or Cr 3 C 2 The self-lubricating phase is hBN;
(4) Thermal spray coating and cBN phase transition densification: carrying out supersonic flame spraying on the surfaces of a ball body and a valve seat of a hard seal control valve on a powder feed containing a self-lubricating phase, wherein the oxygen flow is 900-950L/min, the kerosene flow is 22-24L/h, the spraying distance is 300-350 mm, and the powder feeding rate is 65-75 g/min; the thickness of the coating after spraying is 250-350 mu m, cBN particles are converted into onion-shaped hexagonal boron nitride oBN in the coating process, the original cBN particles undergo volume expansion in the conversion process to fill gaps between flaky hBN particles due to bridging so as to densify the coating, the porosity of the coating is 0.5-1.0%, the phase composition of the coating is hard phase + self-lubricating phase + FCC binding phase CoCrNiFeMnC, wherein the hard phase is WC or Cr 3 C 2 The self-lubricating phase is hBN+ oBN;
(5) High-frequency start-stop stress induced martensitic transformation densification of self-lubricating coating: the ball body and the valve seat after the thermal spraying coating are subjected to fine grinding and lapping, the surface roughness of the valve ball and the valve seat after lapping is Ra0.2-0.4 mu m, the valve ball and the valve seat are well assembled with a valve body, a valve rod, a spring and a bearing which are matched, and then the valve ball and the valve seat are continuously opened and closed for 1000-2000 times, in the opening and closing process of the hard sealing control valve, the FCC bonding phase in the surface coating of the ball body and the valve seat generates martensitic transformation due to contact stress, the FCC phase is converted into a BCC body-centered cubic structure, the volume expansion is caused by the martensitic transformation, the pores in a matrix are reduced to further densify, and the coating porosity is 01-0.5%; the phase composition of the coating is hard phase, self-lubricating phase and BCC binding phase CoCrNiFeMnC, wherein the hard phase is WC or Cr 3 C 2 The self-lubricating phase is hBN+ oBN; the friction coefficient of the coating is 0.07-0.12; the working temperature range of the coating is-196-660 ℃, the maximum working pressure is 45MPa, the hardness of the coating is 950-160 HV, and the bonding strength of the coating is 70-95 MPa; thus preparing the wide-temperature-range self-lubricating coating for the hard sealing control valve based on the hBN.
The preparation method of the wide-temperature-range self-lubricating coating for the hard sealing control valve based on the hBN is further characterized by comprising the following steps of:
(1) When the hBN complex-phase compact particles containing the cBN are prepared, the rotating speed of the three-dimensional mixer is 15-25 r/min;
(2) When preparing Mn-C element-containing high-entropy alloy binding phase powder with face-centered cubic structure, adding absolute ethyl alcohol as a ball milling medium, wherein the adding amount is 22% of the total weight of the binding phase powder, charging 0.03MPa argon for protection in the ball milling process, filtering by a 400-mesh screen after ball milling, drying at 90-95 ℃, and sieving by a 100-mesh screen;
(3) When the powder feed containing the self-lubricating phase is prepared, the rotating speed of the three-dimensional mixer is 15-25 r/min; the rotation speed of an atomizing disc is 5000-6000 r/min during spray drying, and the drying temperature is 110-120 ℃; in the vacuum sintering process of the powder after spray drying, the heating speed is 10 ℃/min; the vacuum degree is 1-5 Pa;
(4) Before supersonic flame spraying, grinding the surfaces of a ball body and a valve seat of the hard seal control valve until the roughness is Ra0.4-0.8mu m;
(5) When the high-frequency opening and closing stress induces the densification of the martensitic transformation, the frequency of the high-frequency opening and closing of the hard sealing control valve is 5-10 times/min.
The invention has the advantages that:
(1) According to the invention, cBN nano particles are introduced into the hBN, and the hBN complex-phase compact particles containing the cBN are formed through high-pressure compaction, the cBN particles are converted into onion-shaped hexagonal boron nitride (oBN) at high temperature in the thermal spraying process, and gaps formed by bridging between flaky hBN are filled by volume expansion in the conversion process, so that the problems that a coating layer is easy to generate pores, not compact and easily flaking after the self-lubricating phase of the hBN is introduced are solved.
(2) The binding phase component is designed into a high-entropy alloy with a face-centered cubic structure containing Mn-C element, the face-centered cubic structure is kept stable in the thermal spraying process, then the high-frequency start-stop is carried out, the martensite phase is induced under the action of high stress, the FCC phase is converted into the BCC phase, the volume expansion is carried out, the pores after the thermal spraying are further eliminated, and the coating is compact.
(3) The densification of the coating is realized based on correlation in the preparation of the coating, does not depend on laser remelting and other treatments, does not need to introduce hole sealing agents, has simple process and does not introduce foreign substances, and the influence on the performance is avoided.
(4) The hard sealing control valve surface coating based on the hBN has the characteristics of self-lubrication, high density and wide adaptability, and the solid lubrication phase can meet the use requirement of a wide temperature range.
Drawings
FIG. 1 is a schematic diagram of a method for preparing a wide-temperature-range self-lubricating coating for a hard seal control valve based on hBN;
Detailed Description
Example 1:
as shown in fig. 1, a wide temperature range self-lubricating coating for hBN-based hard seal control valves was prepared as follows:
(1) Preparation of cBN-containing hBN complex phase compact particles: firstly, mixing hexagonal boron nitride (hBN) and cubic boron nitride (cBN) powder in a three-dimensional mixer according to a weight ratio of 4:1, wherein the granularity of the hBN is 1 mu m, the cBN consists of three kinds of powder with granularity of 200nm and 300,400nm, and the mass ratio is 1:1:1; the rotating speed of the three-dimensional mixer is 15r/min; pressing the mixed powder into compact sheets with the thickness of 0.6mm under the high pressure of 500MPa, so that nano-scale cBN particles are filled in the pores among the hBN micro sheets; then 60 mesh screen is adopted for grating and sieving, and 2000 mesh screen is adopted for sieving, so as to obtain the hBN complex phase compact particles containing cBN.
(2) Preparing FCC high-entropy alloy binding phase powder with Mn-C element and face-centered cubic structure: in atomic percent, co, cr, ni, fe, mn, C=1:1:1:0.7:0.1, weighing Co, cr, ni, fe, mn, C raw material powder, performing planetary ball milling on the weighed raw material powder at a ball milling rotating speed of 300r/min, wherein the ball-to-material ratio of ball milling is 10:1, and Si with the diameter of 5mm is adopted 3 N 4 Adding absolute ethyl alcohol as a ball milling medium into ceramic grinding balls for 12 hours, wherein the adding amount of the absolute ethyl alcohol is 22% of the total weight of binder phase powder, and filling 0.03MPa of argon for protection in the ball milling process; filtering by adopting a 400-mesh screen after ball milling, drying at 90 ℃, and sieving by adopting a 100-mesh screen to prepare the FCC high-entropy alloy binding phase powder containing Mn-C elements.
(3) Preparation of a powder feed containing a self-lubricating phase: weighing raw material powder for proportioning, wherein the weight percentage of WC hard phase is 83%, the weight percentage of hBN complex phase compact particles containing cBN is 5%, the weight percentage of face-centered cubic structure high-entropy alloy binding phase powder containing Mn-C element is 12%, the three raw material powder are mixed in a three-dimensional mixer for 12 hours, and the rotating speed of the three-dimensional mixer is 16r/min; then adding an absolute ethyl alcohol mixed solution containing 2wt.% of paraffin into the powder, wherein the mass ratio of the added absolute ethyl alcohol mixed solution to the raw material powder is 0.25:1, the temperature of the mixed solution is 52 ℃, and the mixed solution is continuously mixed for 10min and then subjected to spray drying, and the rotating speed of an atomizing disc is 5200r/min during the spray drying, and the drying temperature is 110 ℃; and then sintering for 1h at 1150 ℃ in a vacuum sintering furnace, wherein the heating speed is 10 ℃/min in the vacuum sintering process, the vacuum degree is 2Pa, cBN and hBN are kept stable and do not generate phase transition at the sintering temperature, and after the sintering is completed, the powder feed containing the self-lubricating phase, wherein the phase composition of the powder feed is hard phase WC+self-lubricating phase hBN+cBN+CoCrNiFeMnC binding phase FCC, the granularity of the powder feed is 60 mu m, and the granularity of the powder feed is 0.84, is prepared through crushing and air flow classification.
(4) Thermal spray coating and cBN phase transition densification: carrying out supersonic flame spraying on the surfaces of a ball body and a valve seat of a hard sealing control valve by powder feed containing a self-lubricating phase, and grinding the surfaces of the ball body and the valve seat of the hard sealing control valve to have roughness of Ra0.4mu m before the supersonic flame spraying; oxygen flow rate 910L/min, kerosene flow rate 22L/h, spray distance 320mm and powder feeding rate 66g/min during spraying; the thickness of the coating after spraying is 280 mu m, cBN particles are converted into onion-shaped hexagonal boron nitride oBN in the coating process, and because the theoretical density of the cBN is larger than oBN, the original cBN particles undergo volume expansion in the conversion process to fill gaps between flaky hBN particles due to bridging so as to densify the coating, the porosity of the coating is 0.53%, and the phase composition of the coating is a hard phase WC+a self-lubricating phase (hBN+ oBN) +CoCrNiFeMnC binding phase FCC.
(5) High-frequency start-stop stress induced martensitic transformation densification of self-lubricating coating: the ball body and the valve seat after the thermal spraying coating are subjected to fine grinding and lapping, the surface roughness of the valve ball and the valve seat after lapping is Ra0.2μm, the valve ball and the valve seat are well assembled with a valve body, a valve rod, a spring and a bearing which are matched with each other, then the valve is continuously opened and closed for 1200 times, the high-frequency opening and closing frequency of a hard sealing control valve is 6 times/min, the FCC bonding phase in the surface coating of the ball body and the valve seat generates martensitic transformation due to contact stress in the opening and closing process of the hard sealing control valve, the FCC phase is converted into a BCC structure, the volume expansion is generated to reduce the pores in a matrix to further densify, and the porosity of the coating is 0.39%; the phase composition of the coating is hard phase WC+self-lubricating phase (hBN+ oBN) +CoCrNiFeMnC binding phase BCC; the coefficient of friction of the coating is 0.079; the working temperature range of the coating is-196-660 ℃, the maximum working pressure is 45MPa, the hardness of the coating is 1480HV, and the bonding strength of the coating is 81MPa; thus preparing the wide-temperature-range self-lubricating coating for the hard sealing control valve based on the hBN.
Example 2:
as shown in fig. 1, a wide temperature range self-lubricating coating for hBN-based hard seal control valves was prepared as follows:
(1) Preparation of cBN-containing hBN complex phase compact particles: firstly, mixing hexagonal boron nitride (hBN) and cubic boron nitride (cBN) powder in a three-dimensional mixer according to a weight ratio of 4:1, wherein the granularity of the hBN is 1.5 mu m, and the cBN consists of three kinds of powder with granularity of 240nm and 350nm and 430nm, and the mass ratio is 1:1:1; the rotating speed of the three-dimensional mixer is 21r/min; pressing the mixed powder into compact sheets with the thickness of 0.9mm under the high pressure of 580MPa, so that nano-scale cBN particles are filled in the pores among the hBN micro sheets; then 60 mesh screen is adopted for grating and sieving, and 2000 mesh screen is adopted for sieving, so as to obtain the hBN complex phase compact particles containing cBN.
(2) Preparing FCC high-entropy alloy binding phase powder with Mn-C element and face-centered cubic structure: pressing the buttonWeighing Co, cr, ni, fe, mn, C raw material powder according to atomic percentage of Co, cr, ni, fe, mn and C=1:1:1:1:0.8:0.12, performing planetary ball milling on the weighed raw material powder at a ball milling rotating speed of 380r/min, wherein the ball-to-material ratio of ball milling is 10:1, and adopting Si with a diameter of 5mm 3 N 4 Adding absolute ethyl alcohol as a ball milling medium into ceramic grinding balls for 20 hours, wherein the adding amount of the absolute ethyl alcohol is 22% of the total weight of binder phase powder, and filling 0.03MPa of argon for protection in the ball milling process; filtering by adopting a 400-mesh screen after ball milling, drying at 93 ℃, and sieving by adopting a 100-mesh screen to prepare the FCC high-entropy alloy binding phase powder containing Mn-C elements.
(3) Preparation of a powder feed containing a self-lubricating phase: weighing raw material powder for proportioning, and mixing according to the mass percentage of Cr 3 C 2 73% of hard phase, 7% of hBN complex phase compact particles containing cBN, 20% of face-centered cubic structure high-entropy alloy binding phase powder containing Mn-C element, and mixing the three raw material powders in a three-dimensional mixer for 20 hours, wherein the rotating speed of the three-dimensional mixer is 15-25 r/min; then adding an absolute ethyl alcohol mixed solution containing 2wt.% of paraffin into the powder, wherein the mass ratio of the added absolute ethyl alcohol mixed solution to the raw material powder is 0.30:1, the temperature of the mixed solution is 58 ℃, the mixed solution is continuously mixed for 10min and then is subjected to spray drying, and the rotating speed of an atomizing disc is 5800r/min during the spray drying, and the drying temperature is 115 ℃; sintering for 1.5h at 1200 ℃ in a vacuum sintering furnace, wherein the temperature rising speed is 10 ℃/min in the vacuum sintering process, the vacuum degree is 5Pa, cBN and hBN keep stable and do not generate phase transition at the sintering temperature, and after sintering, the phase composition of the obtained product is hard phase Cr through crushing and air current classification 3 C 2 +self-lubricating phase hbn+cbn+cocrnifemnc binder phase FCC, particle size 58 μm, particle sphericity 0.87.
(4) Thermal spray coating and cBN phase transition densification: carrying out supersonic flame spraying on the surfaces of a ball body and a valve seat of a hard sealing control valve by powder feed containing a self-lubricating phase, and grinding the surfaces of the ball body and the valve seat of the hard sealing control valve to have roughness of Ra0.8μm before the supersonic flame spraying; the oxygen flow rate during spraying is 940L/min, the kerosene flow rate is 24L/h, the spraying distance is 330mm, and the powder feeding rate is 70g/min; the thickness of the coating after spraying is 340 mu m, and the coating processThe cBN particles are converted into onion-shaped hexagonal boron nitride oBN, and because the theoretical density of the cBN is larger than oBN, the original cBN particles undergo volume expansion in the conversion process to fill gaps between flaky hBN particles caused by bridging, so that the coating is densified, the porosity of the coating is 0.67%, and the phase composition of the coating is a hard phase Cr 3 C 2 +self-lubricating phase (hbn+ oBN) +cocrnifemnc binder phase FCC.
(5) High-frequency start-stop stress induced martensitic transformation densification of self-lubricating coating: the ball body and the valve seat after the thermal spraying coating are subjected to fine grinding and lapping, the surface roughness of the valve ball and the valve seat after lapping is Ra0.4μm, the valve ball and the valve seat are well assembled with a valve body, a valve rod, a spring and a bearing which are matched with each other, then the valve is continuously opened and closed for 2000 times, the high-frequency opening and closing frequency of a hard sealing control valve is 7 times/min, the FCC bonding phase in the surface coating of the ball body and the valve seat generates martensitic transformation due to contact stress in the opening and closing process of the hard sealing control valve, the FCC phase is converted into a BCC structure, the volume expansion is generated to reduce the pores in a matrix to further densify, and the porosity of the coating is 0.46%; the phase composition of the coating is hard phase Cr 3 C 2 +self-lubricating phase (hbn+ oBN) +cocrnifemnc binder phase BCC; the friction coefficient of the coating is 0.07-0.12; the working temperature range of the coating is-196-660 ℃, the maximum working pressure is 45MPa, the coating hardness is 980HV, and the coating bonding strength is 70MPa; thus, the hard seal control valve surface wide temperature range self-lubricating coating based on the hBN is prepared.
Claims (2)
1. The preparation method of the wide-temperature-range self-lubricating coating for the hard sealing control valve based on the hBN is characterized by comprising the following steps in sequence:
(1) Preparation of cBN-containing hBN complex phase compact particles: firstly, mixing hexagonal boron nitride (hBN) and cubic boron nitride (cBN) powder in a three-dimensional mixer according to a weight ratio of 4:1, wherein the granularity of the hBN is 1-2 mu m, the cBN consists of three kinds of powder with granularity of 200-250 nm, 300-350 nm and 400-450 nm, and the mass ratio is 1:1:1; pressing the mixed powder into compact sheets with the thickness of 0.5-1 mm under the high pressure of 500-600 MPa, so that nano-scale cBN particles are filled in the pores among the hBN micro sheets; then, 60-mesh screen is adopted for grating and sieving, and then 2000-mesh screen is adopted for sieving, so as to obtain hBN complex-phase compact particles containing cBN;
(2) Preparing FCC high-entropy alloy binding phase powder with Mn-C element and face-centered cubic structure: weighing Co, cr, ni, fe, mn, C raw material powder according to the atomic percentage of Co, cr, ni, fe, mn, C=1:1:1:1, (0.7-0.8): (0.1-0.15), performing planetary ball milling on the weighed raw material powder at the ball milling rotating speed of 300-400 r/min, wherein the ball-to-material ratio of ball milling is 10:1, and adopting Si with the diameter of 5mm 3 N 4 Ceramic grinding balls are subjected to ball milling for 12-24 hours, and after ball milling, filtering, drying and sieving are carried out to prepare FCC high-entropy alloy binding phase powder containing Mn-C elements;
(3) Preparation of a powder feed containing a self-lubricating phase: weighing raw material powder for proportioning, and mixing according to the mass percentage of WC or Cr 3 C 2 65-85% of hard phase, 5-10% of hBN complex phase compact particles containing cBN, 10-25% of face-centered cubic structure high-entropy alloy binding phase powder containing Mn-C element, and mixing the three raw material powders in a three-dimensional mixer for 12-24 h; then adding an absolute ethyl alcohol mixed solution containing 2wt.% of paraffin into the powder, wherein the mass ratio of the addition of the absolute ethyl alcohol mixed solution to the raw material powder is 0.25-0.35:1, the temperature of the mixed solution is 50-60 ℃, the mixed solution is continuously mixed for 10min and then subjected to spray drying, then sintering is carried out in a vacuum sintering furnace for 1-2 h at 1150-1250 ℃, cBN and hBN keep stable and do not generate phase transition at the sintering temperature, and after the sintering is completed, crushing and gas flow classification are carried out, so that the powder feed containing the self-lubricating phase, wherein the phase composition is hard phase+self-lubricating phase+cBN+FCC binding phase CoCrNiFeMnC, the particle size is 55-70 mu m, and the particle sphericity is 0.8-0.9, is prepared, and the hard phase is WC or Cr 3 C 2 The self-lubricating phase is hBN;
(4) Thermal spray coating and cBN phase transition densification: carrying out supersonic flame spraying on the surfaces of a ball body and a valve seat of a hard seal control valve on a powder feed containing a self-lubricating phase, wherein the oxygen flow is 900-950L/min, the kerosene flow is 22-24L/h, the spraying distance is 300-350 mm, and the powder feeding rate is 65-75 g/min; the thickness of the sprayed coating is 250-350 mu m, cBN particles are converted into onion-shaped hexagonal boron nitride oBN in the coating process, and the original cBN particles undergo volume expansion in the conversion process to fill gaps between flaky hBN particles caused by bridging because the theoretical density of the cBN is larger than oBNThe gaps densify the coating, the porosity of the coating is 0.5-1.0%, the phase composition of the coating is hard phase, self-lubricating phase and FCC binding phase CoCrNiFeMnC, wherein the hard phase is WC or Cr 3 C 2 The self-lubricating phase is hBN+ oBN;
(5) High-frequency start-stop stress induced martensitic transformation densification of wide-temperature-range self-lubricating coating: the ball body and the valve seat after the thermal spraying coating are subjected to fine grinding and lapping, the surface roughness of the valve ball and the valve seat after lapping is Ra0.2-0.4 mu m, the valve ball and the valve seat are well assembled with a valve body, a valve rod, a spring and a bearing which are matched with each other, and then the valve ball and the valve seat are continuously opened and closed for 1000-2000 times, wherein in the opening and closing process of the hard sealing control valve, the FCC bonding phase of the ball body and the surface coating of the valve seat generates martensitic transformation due to contact stress, the FCC phase is converted into a BCC structure, and the volume expansion is caused by the martensitic transformation, so that the pores in a matrix are reduced to be further densified, and the porosity of the coating is 0.1-0.5%; the phase composition of the coating is hard phase, self-lubricating phase and BCC binding phase CoCrNiFeMnC, wherein the hard phase is WC or Cr 3 C 2 The self-lubricating phase is hBN+ oBN; the friction coefficient of the coating is 0.07-0.12; the working temperature range of the coating is-196-660 ℃, the maximum working pressure is 45MPa, the hardness of the coating is 950-160 HV, and the bonding strength of the coating is 70-95 MPa; thus preparing the wide-temperature-range self-lubricating coating for the hard sealing control valve based on the hBN.
2. The method for preparing the wide-temperature-range self-lubricating coating for the hard sealing control valve based on the hBN, as claimed in claim 1, is characterized in that:
(1) When the hBN complex-phase compact particles containing the cBN are prepared, the rotating speed of the three-dimensional mixer is 15-25 r/min;
(2) When preparing Mn-C element-containing high-entropy alloy binding phase powder with face-centered cubic structure, adding absolute ethyl alcohol as a ball milling medium, wherein the adding amount is 22% of the total weight of the binding phase powder, charging 0.03MPa argon for protection in the ball milling process, filtering by a 400-mesh screen after ball milling, drying at 90-95 ℃, and sieving by a 100-mesh screen;
(3) When the powder feed containing the self-lubricating phase is prepared, the rotating speed of the three-dimensional mixer is 15-25 r/min; the rotation speed of an atomizing disc is 5000-6000 r/min during spray drying, and the drying temperature is 110-120 ℃; in the vacuum sintering process of the powder after spray drying, the heating speed is 10 ℃/min; the vacuum degree is 1-5 Pa;
(4) Before supersonic flame spraying, grinding the surfaces of a ball body and a valve seat of the hard seal control valve until the roughness is Ra0.4-0.8mu m;
(5) When the high-frequency opening and closing stress induces the densification of the martensitic transformation, the frequency of the high-frequency opening and closing of the hard sealing control valve is 5-10 times/min.
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