CN1757793A - Spray coating technology for preparing high melting point coramic coating layer - Google Patents

Abstract

A process for preparing the high-smelting-point ceramic layer or ceramic-metal layer on the surface of substrate includes such steps as conventional pre-treating on the surface of substrate, charging the powder material to be sprayed in the cavity of spray gun, applying a high shock current to electrodes, electric explosion for preheating and pushing said ceramic powder to the inlet of stage-2 spray gun, breaking through its electrode for generating high current and forming a plasma channel, heating and pushing the powder to move forward at high speed, and colliding with the surface of said substrate to form said ceramic layer.

Description

The spraying coating process of preparation high-melting-point ceramic coating

Technical field:

The present invention relates to a kind of powder coating process, be meant a kind of spraying coating process that the high-melting-point ceramic powder can be sprayed on the matrix especially.

Background technology:

Hot-spraying techniques promptly utilizes spraying method to prepare certain thickness coated material at workpiece surface, thereby obtain performance and function that base material does not possess and expects to have, it can significantly improve corrosion-resistant, high temperature resistant, anti-oxidant, the wear resisting property of material surface, thereby significantly improves the work-ing life of parts.

Wearing and tearing, fracture and corrosion are three kinds of principal modes of material damage.The financial loss that is caused by wearing and tearing also is huge.The loss that brings in the annual wearing and tearing of industrial country accounts for 2～8% of gross national product, wherein only the loss that causes of abrasive wear accounts for 1～4% of gross national product, according to relevant research, the expense of the maintenance and repair of equipment accounts for 30～50% of machine expense.The technological process of top coat technology is divided into four classes according to the state of sediment-filled phase at present: vapour deposition, liquid deposition, fusion deposits mutually, solid precipitation, these conventional top coat technology all have benefit and limitation separately, and the performance of the coating of making differs greatly.Improve coating and high base strength, aspect the abradability that improves material, have great significance.

Traditional powder thermospraying technology such as technology such as plasma spraying and HVOF HVOF (High Velocity Oxygen Fuel) are present proven technique, are used widely in engineering.But these technology also have some limitation, and are specific as follows: (1) is difficult to prepare the ceramic coating (or coating performance is not high) of some high-melting-points (2800-3830 ℃), as HfC, NbC, TaC, ZrC, ZrB, TiC, TiB ₂, B ₄C etc. (these high-melting-point coatings have crucial meaning for prolong some component lifes of working under 800-1500 ℃ of high temperature, corrosive environment).(2) traditional powder thermospraying technology mostly utilizes gas thermokinetics principle to promote the powder motion, and powder speed generally is lower than 1000m/s, and coating and matrix are mainly mechanical bond, and coating and high base strength are lower, are generally tens of MPa; For example use plasma spraying B ₄C coating (coating that is used for nuclear reactor first wall material), its bonding strength is 10～20MPa, and porosity is higher, is difficult to satisfy requirement of engineering.Other has is exactly to utilize the electrical explosion technology with the electrical explosion of metal or alloy silk under the effect of big electric current, make the collision of metal-powder and matrix and form coating, therefore how this method can't make non-metallic material as coating material, and non-metallic material and matrix can be reached the good binding coating is a present technical barrier.

Summary of the invention:

Goal of the invention of the present invention is to disclose a kind ofly can prepare wear-resisting, the corrosion-resistant and oxidation resistant high-melting-point ceramic coating of high bond strength or the processing method of ceramic-metal compound coating at substrate material surface.

Realize that technology settlement steps to deal of the present invention is as follows:

A. to the surface to be sprayed of matrix remove contamination, antirust, the conventional pre-treatment of oil removing;

B. material powder to be sprayed is sent in the cavity of close electrode of spray gun of an end band pair of discharge electrodes, according to experimental result and calculating, the required electrical condenser energy storage of one-level spray gun is 15-25kJ;

C. apply a heavy impulse current to electrode, the electrode puncture also produces transient high-current between electrode, at spray gun inner chamber generation electrical explosion, high temperature, high pressure plasma that electrical explosion produces carry out preheating to ceramic powder, and promote the other end motion of ceramic powder to the cavity of spray gun;

D. when the ceramic powder of high-speed motion arrives the secondary spray gun ingress that is connected with spray gun, make the electrode puncture of secondary spray gun and produce big electric current by trigger device, formation comprises the plasma body conductive channel of the ceramic powder of componental movement, or be called plasma armature, on, lower electrode and plasma armature are subjected to the effect of electric power and Lorentz (Lorentz) power respectively, under the effect of electromagnetic force, plasma body travels forward at a high speed, high temperature, high pressure plasma is in high-speed motion forward, heating also promotes ceramic powder high-speed motion forward, according to calculating and experimental result, the total energy storage of the required electrical condenser of secondary spray gun is 20-30kJ;

E. the ceramic powder of high-speed motion forms spray-on coating with the to be sprayed surperficial high velocity impact of the matrix that places secondary spray gun exit.

Described discharge electrode be the two negative plate mid-ways of relatively extending for anodal, be insulating material between the positive and negative electrode, certain tip-shape of positive and negative electrode end tool.

Described secondary spray gun is the non-conducting material that there is a spacing two centres of two planar electrode clampings, intermediate formation one strip passage.

Can carry out the high velocity impact spraying of once above high velocity powder to the surface of base material, repeatedly spraying can increase the thickness of coating, improves performances such as wear-resisting, corrosion-resistant, improves work-ing life.

The pulse powder conveyer that utilization of the present invention can repeat powder feeding is sent material powder to be sprayed in the spray gun through hole appropriate location (utilizing pulsed pressurized gas powder conveyer that powder disperse in spray gun is distributed) near discharge electrode, trigger high-current generation device by delay control circuit subsequently, on the two poles of the earth of discharge electrode, apply a high-voltage, interelectrode air dielectric is punctured the formation short-circuit condition, by an instantaneous big electric current, between electrode, form the discharge of moment, produce the plasma area of a High Temperature High Pressure, the plasma body of this High Temperature High Pressure heats the ceramic powder that is preset in the spray gun, and the promotion powder travels forward, according to experimental result, in spray gun, there is the ceramic powder of certain degree to reach temperature more than the fusing point, and according to theoretical calculate and experiment measuring, ceramic powder can reach 1000～2000m/s in the velocity of discharge of one-level spray gun exit end.When powder moves to the secondary spray gun, make the switch connection that connects the secondary spray gun by activation time delayed device, behind the switch conduction, two electrodes of secondary spray gun are breakdown by point discharge, and produce big electric current, formation comprises the plasma body conductive channel of the ceramic powder of componental movement, or be called plasma armature, on, lower electrode and plasma armature are subjected to the effect of electric power and Lorentz (Lorentz) power respectively, under the effect of electromagnetic force, plasma body travels forward at a high speed, high temperature, high pressure plasma is in high-speed motion forward, and heating also promotes ceramic powder high-speed motion forward.The discharge high-current generation device is sophisticated prior art at present, and structure of the present invention is quite simple, and the ceramic powder of the high-speed motion of generation and matrix surface to be coated collision produce atmospheric pressure more than several ten thousand at the collision interface of particulate and matrix.This pressure is considerably beyond the yield strength of any material, body material and microparticle material all can be considered high-velocity fluid under above-mentioned pressure, cause body material and microparticle material to form metallurgical binding, bonding strength greatly improves, and particularly can carry out high-intensity coating to the ceramic-like non-metallic material.

Description of drawings:

Fig. 1 is a systematic schematic diagram of the present invention.

Fig. 2 is the structural representation of the spray equipment realizing the present invention relates to.

Fig. 3 is the A-A cross-sectional view of Fig. 1.

Fig. 4 is the B-B cross-sectional view of Fig. 1.

Label 11 wherein is a current-limiting resistance.

Label 12 wherein is a step-up transformer.

Label 13 wherein is a high-voltage pulse charge and discharge capacitance device group.

Label 14 wherein is a gap switch.

Label 15 wherein is a trigger device.

Label 16 wherein is a current measuring device.

Label 17 wherein is a voltage measuring apparatus.

Embodiment:

Please be simultaneously with reference to Fig. 1～Fig. 4, the processing step of specific embodiments of the invention is as follows:

A. to the surface to be sprayed of matrix remove contamination, antirust, the conventional pre-treatment of oil removing;

B. material powder 9 to be sprayed is placed in the cavity of close electrode of spray gun 5 of an end band pair of discharge electrodes (one-level spray gun), one-level spray gun total length is in 150～250mm scope, and cross-sectional area is at 2～3cm ²Scope;

C. apply a heavy impulse current to electrode, the electrode puncture also produces transient high-current between electrode, at spray gun 5 inner chamber generation electrical explosions, high temperature, high pressure plasma that electrical explosion produces carry out preheating to ceramic powder 9, and promote the other end motion of ceramic powder 9 to the cavity of spray gun 5;

D. when the ceramic powder 9 of high-speed motion arrives secondary spray gun 6 ingress that are connected with spray gun 5, make the electrode puncture of secondary spray gun 6 and produce big electric current by trigger device 8, formation comprises the plasma body conductive channel of the ceramic powder of componental movement, or be called plasma armature, on, lower electrode and plasma armature are subjected to the effect of electric power and Lorentz (Lorentz) power respectively, under the effect of electromagnetic force, plasma body travels forward at a high speed, high temperature, high pressure plasma is in high-speed motion forward, heating also promotes ceramic powder high-speed motion forward, the length of secondary spray gun is in 300～500mm scope, and cross-sectional area is at 2～3cm ²Scope;

E. the ceramic powder of high-speed motion forms spray-on coating with the to be sprayed surperficial high velocity impact of the matrix that places secondary spray gun 6 exits.

Described discharge electrode is two negative plate 3 mid-ways of relatively extending for anodal 4, is insulating material between the positive and negative electrode, certain tip-shape of positive and negative electrode end tool.

Described secondary spray gun 6 is the non-conducting material 7 that there is a spacing two centres of two planar electrode clampings, intermediate formation one strip passage.

Can carry out the high velocity impact spraying of once above high velocity powder to the surface of base material, repeatedly spraying can increase the thickness of coating, improves performances such as wear-resisting, corrosion-resistant, improves work-ing life.

Can be simultaneously in conjunction with the given spray equipment of Fig. 1～Fig. 3, describe particular content of the present invention in detail, spray equipment of the present invention comprises the pilot circuit of high-current generation device 1 and the discharge of control high-current generation device, this part is a prior art, there is sophisticated circuit available, key is the discharge electrode that high-current generation device 1 connects spray gun 5 through holes one end, the nearly blind end of spray gun 5 has a pay-off 2, this pay-off can make ceramic powder to be sprayed 9 insert the appropriate location of spray gun 5, pay-off 2 has a feedhole and can open or cut out the mechanism in this hole on spray gun 5 walls exactly in fact, after powder 9 is inserted spray gun 5, close this feedhole, the other end of spray gun 5 is the opening shape; During actual the use, earlier ceramic powder 9 is inserted in spray gun 5 through holes, triggering circuit make high-current generation device 1 produce high pressure at the positive and negative electrode of electrode, and make to puncture between the positive and negative electrode of electrode and be the short circuit shape, and there is big electric current to pass through positive and negative electrode, this essence is exactly to produce big electric arc, also can be described as electrical explosion, then the blind end at spray gun 5 produces high temperature and high speed expansible plasma body, powder before the drive electrode travels forward, simultaneously powder is heated, according to Theoretical Calculation and measuring, powder can accelerate to 1000～2000m/s, and the powder direct impact of high temperature and high speed places the matrix surface of spray gun opening end, high velocity impact produces High Temperature High Pressure again, makes powder and matrix surface form high-intensity metallurgical binding.

The structure of above-mentioned discharge electrode is that negative plate 3 mid-ways that tool two extends relatively are anodal 4, it between the positive and negative electrode insulating material, positive and negative extreme tool tip, owing to be symmetry shape between the positive and negative electrode, and intermediary positive pole 4 is in the shaft core position of spray gun 5 through holes substantially, then the electrical explosion of Chan Shenging is substantially for symmetrically, can protect the promotion that allows to powder is the driving of an almost plane, the electrical explosion of spray gun 5 ends can be thought satisfy unidimensional piston motion model, the V-bar that then can get powder as calculated is about 1000～2000m/s.

Above-mentioned spray gun 5 is a non-conducting material, and the center is a through hole, and an end is removable fixedlying connected with the negative plate 3 of discharge electrode; Because discharge electrode can produce ablation to a certain degree after discharging through the several times high-voltage great-current, can make the precision of coating produce certain variation, detachable between electrode and the spray gun, then can change discharge electrode according to the ablation situation, the realization of this removable connection is prior art fully, for example buckle-connected type or screw connected all can, then can guarantee the precision that repeatedly applies.

The high-pressure side of the electrical condenser group of above-mentioned high-current generation device 1 is connected with an electrode of discharge electrode by three pole switch, and low pressure end directly is connected with another electrode of discharge electrode.

The opening end of above-mentioned spray gun 5 horizontal extensions (being made up of the non-conductive ceramic material) connects secondary spray gun 6, the structure of this secondary spray gun 6 is the non-conducting material 7 (as aluminium sesquioxide) that there is a spacing two centres of two flat electrode clampings, the through hole 10 of intermediate formation one strip, two plate electrodes connect another independently high-current generation device 8, and pilot circuit is sent out in high-current generation device 8 contacts; The high-pressure side of the electrical condenser group of high-current generation device 8 contacts with an electrode of secondary spray gun 6 by three electrode switch, and low pressure end directly is connected with another electrode of secondary spray gun; When heated powder in spray gun 5 moves to the junction of spray gun 5 and secondary spray gun 6, two electrodes that pilot circuit triggers 8 pairs of secondary spray guns 6 of high-current generation device apply high-voltage and puncture and pass through a big electric current, form the plasma conductive channel (also claiming plasma armature) that comprises part ceramic powder and travel forward.Upper/lower electrode and plasma armature are subjected to the effect of electric power and Lorentz power respectively, under the effect of electromagnetic force, and the accelerated motion forward of plasma armature.The plasma body of High Temperature High Pressure shape is in high-speed motion forward, rapid heating wherein ceramic powder and promote its strip passage (being through hole 10) high-speed motion in the secondary spray gun 6, according to Theoretical Calculation, ceramic powder is reached more than the 3000m/s in the speed in secondary spray gun 6 exits.

Though powder can obtain higher speed in one-level spray gun 5,, in one-level spray gun 5, only have to be less than 50% powder and to reach molten state because powder is shorter in the time of one-level spray gun heating.Therefore, powder also need enter in the secondary spray gun 6, continues to be heated and to quicken.

Secondary spray gun 6 can be analyzed the translational speed of plasma body by plasma armature motion model, and the current equation of establishing the loop is

I(t)＝I ₀e ^-βtsinωt

As calculated, it is as follows to promote the plasma arc speed formula of particle motion at last:

$v=\frac{C_2}{4C_1\mathrm{\β}}(1-e^{-2\mathrm{\βt}})-\frac{C_2\mathrm{\β}}{4C_1({\mathrm{\β}}^2+{\mathrm{\ω}}^2)}[1-(\cos 2\mathrm{\ωt}-\frac{\mathrm{\ω}}{\mathrm{\β}}\sin 2\mathrm{\ωt})e^{-2\mathrm{\βt}}]$

Its tripping speed $v^{*}=\frac{C_2}{4C_1\mathrm{\β}}=4.69\×{10}^{3}m/s$

Calculated examples:

Get d ₀=2cm=0.02m, b=2cm=0.02m;

$I\left(t\right)=8.3e^{-1.47\×{10}^{3}t},$

Then: $C_1=\frac{m}{b}=\frac{0.1\×{10}^{-3}}{0.02}=5\×{10}^{-3}$

$C_2=\frac{\mathrm{\μ}{I}_0^2}{4\mathrm{\π}}\frac{b}{x(b-x)}={10}^{-7}\×{(8.3\×{10}^4)}^2\frac{0.02}{x(0.02-x)}=\frac{13.78}{x(0.02-x)}$

$\mathrm{\ω}=\frac{2\mathrm{\π}}{400\×{10}^{-6}}=1.57\×{10}^4$

If during s=0.36,

When getting x=0.001m, t=5.55 * 10 ^-4S, this moment, the spray gun velocity of discharge was:

V=3.77 * 10 ⁴M/s, its tripping speed $v^{*}=\frac{C_2}{4C_1\mathrm{\β}}=4.69\×{10}^{3}m/s$

Wherein: d ₀Diameter for plasma arc;

M is the quality of plasma arc or by the quality of dusty spray;

B is two battery lead plate spacings;

c ₁For the quality of the plasma arc of unit length or unit length by the quality of dusty spray;

T is that plasma arc arrives the required time of spray gun outlet;

X is the distance of any point and a lateral electrode plate on the plasma arc;

S is the length of spray gun; ,

${\mathrm{<figure-callout\; id="3"\; label="C"\; filenames="A20051010597500143.png"\; state="\{\{state\}\}">C</figure-callout>}}_3=\frac{\mathrm{\&mu;}}{4\mathrm{\&pi;}}\frac{b}{x(b-x)}={10}^{-7}\&times;\frac{0.02}{(0.02-x)}$

Pass through aforementioned calculation, powder reaches 3000m/s～4000m/s in the velocity of discharge of secondary spray gun 6, in the present embodiment, the voltage of the current generating apparatus 1 that is connected with spray gun 5 is 5～6KV, the energy storage value of electrical condenser is 15KJ, the voltage of the current generating apparatus 8 that is connected with secondary spray gun 6 is 5～6KV, and the energy storage value of electrical condenser is 20KJ.

Coating mechanism of the present invention is the high-temperature plasma heating high-melting-point ceramic powder that electrical explosion produces, electromagnetic force and high pressure gas promote powder high-speed motion principle and high velocity impact ballistics principle, the coated material particle collision matrix of high-speed flight instantaneous, producing amplitude at the collision interface of particulate and matrix is several ten thousand to tens0000 atmospheric pulse pressure, above-mentioned pressure is the yield strength of any material head and shoulders above, body material and microparticle material are under above-mentioned pressure, all can be considered high-velocity fluid, its mechanical property has been fluid property, under the proal effect of particle behind mass diffusion and the shockwave, can make the matrix top layer count the material melts of micron thickness, the spray material of partial gasification is diffused in the scope of about 5～20 micrometer depth in matrix top layer in ion implantation mode.Molten ceramic grains deposits at matrix surface, because the self-excitation cold-working usefulness of matrix, the melt granules of matrix surface cools off fast with high speed, thus form have ultra-fine crystalline substance, the ceramic coating of nanocrystalline or amorphous structure.

About 2～the 3cm of area of the each spraying of the present invention ², promptly one-level spray gun and secondary spray gun cross-sectional area are at 2～3cm ²Scope, can repeatedly spray to increase coat-thickness at same sprayed surface, the present invention can be used for preparing heat resistant and wear resistant and decreases coating, thermal barrier coating, high temperature oxidation resisting corrosion resistant coating, can be used for mainly containing (1) conductivity ceramics powder or powdered alloy, as TiC, WC-Co, ZrC, TaC, B as the powdered material that applies ₄C, TiB ₂, TiN, HfC, VC, Cr ₃C ₂, etc.; (2) other non-conductive oxide compounds or carbide ceramics powder are as ZrO ₂, TiO ₂, Al ₂O ₃, CBN, Si ₃N ₄Deng; (3) pottery-alloy composite powder is as NiCr-Cr ₂C ₃, NiAl-TiC, ZrO ₂-NiAl etc.; (4) refractory metal powder is as W, Mo, Ta, Nb, Zr etc.In order to make powder reach speed more than the 3000m/s, the diameter of dusty spray material is at 5～15 mu m ranges.

Claims (4)

1. spraying coating process for preparing the high-melting-point ceramic coating, its step is as follows:

A. to the surface to be sprayed of matrix remove contamination, antirust, the conventional pre-treatment of oil removing;

B. material powder to be sprayed (9) is placed in the cavity of close electrode of spray gun (5) of an end band pair of discharge electrodes;

C. apply a heavy impulse current to electrode, the electrode puncture also produces transient high-current between electrode, at spray gun (5) inner chamber generation electrical explosion, high temperature, high pressure plasma that electrical explosion produces preheat and promote the other end harness motion of ceramic powder (9) to the cavity of spray gun (5) to ceramic powder (9) behind the generation electrical explosion;

D. when the ceramic powder (9) of high-speed motion arrives secondary spray gun (6) ingress that is connected with spray gun (5), make the electrode puncture of secondary spray gun (6) and produce big electric current by trigger device (8), formation comprises the plasma body conductive channel of the ceramic powder of componental movement, or be called plasma armature, upper/lower electrode and plasma armature are subjected to the effect of electric power and Lorentz (Lorentz) power respectively, under the effect of electromagnetic force, plasma body travels forward at a high speed, high temperature, high pressure plasma is in high-speed motion forward, and heating also promotes ceramic powder high-speed motion forward;

E. the ceramic powder of high-speed motion forms spray-on coating with the to be sprayed surperficial high velocity impact of the matrix that places secondary spray gun (6) exit.

2. press the spraying coating process of the described preparation high-melting-point of claim 1 ceramic coating, it is characterized in that described discharge electrode is that two negative plate (3) mid-ways of extending relatively are anodal (4), between the positive and negative electrode insulating material, certain tip-shape of positive and negative electrode end tool.

3. by the spraying coating process of the described preparation high-melting-point of claim 1 ceramic coating, it is characterized in that described secondary spray gun (6) is the non-conducting material (7) that there is a spacing two centres of two planar electrode clampings, intermediate formation one strip passage.

4. by the spraying coating process of claim 1 or 2 or 3 described preparation high-melting-point ceramic coatings, it is characterized in that to carry out the high velocity impact spraying of once above high velocity powder to the surface of base material.

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