CN1370852A - Spraying self-reaction composite powder onto metal surface to form composite metal/ceramic coating - Google Patents
Spraying self-reaction composite powder onto metal surface to form composite metal/ceramic coating Download PDFInfo
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Abstract
The present invention relates to the field of ceramic coating preparing technology and aims at solving the problems of preparing refractory ceramic coating, improving performance of ceramic coating and lowering cost of ceramic coating. The main technological point is plasma spraying self-reacton composite powder onto metal surface to form composite metal/ceramic coating. The composite powder is compounded with metal oxide powder with aluminothmics reaction, aluminum powder and adhesive. The present invention is used mainly for the metal surface with both high temperature and wear.
Description
The technical field of the invention is as follows:
the invention belongs to a metal/ceramic coating and a spraying method thereof, and particularly relates to a metal/ceramic composite coating synthesized by spraying self-reaction composite powder on a metal surface.
The background technology of the invention is as follows:
campagne et al in canada use FeTi alloy powder, Ti powder, B powder as raw materials to perform self-propagating sintering, pulverize the sintered product, and then spray-coat the sintered product to prepare TiB2-a Fe coating. The spraying process is not combined with the self-reaction, TiB2Is not easy to melt. G. click and s.dallaire as FeTi alloy powder, Ti powder and graphite powder are used as raw materials to prepare the TiC-Fe coating, and the preparation process comprises the following steps: the FeTi alloy powder and the Ti powder are respectively ground in ethanol, then mixed, washed, dried, added with a binder, a plasticizer and graphite to prepare a comprehensive ingredient, and the comprehensive ingredient is prepared into small particles for spraying by spraying slurry. The graphite is very easy to burn and damage in the spraying process and is not easy to spray. In addition, both FeTi alloy powder and Ti powder are very expensive and difficult to be used industrially.
The high-temperature synthesis by the self-propagating method generally adopted has the advantages of high reaction speed, high temperature, difficult control of the process and poor compactness of the coating.
The coating produced by the general spraying method has poor toughness, abrasion resistance and thermal shock resistance, and high cost.
The technical content of the invention is as follows:
the invention aims to solve the technical problems in the prior art, such as high reaction speed, high temperature, difficult process control and poor compactness of a coating in the high-temperature synthesis by a self-propagating method. And the method is mainly used for preparing the coating on the inner wall of the pipe fitting, and cannot prepare the coating on the outer wall of a workpiece. The coating produced by the general spraying method has poor toughness, abrasion resistance and thermal shock resistance, and high cost. The invention provides a method for synthesizing a metal/ceramic composite coating by spraying self-reaction composite powder on the surface of metal. The metal/ceramic composite coating which has the sintering characteristic and the high-density characteristic is directly prepared by a spraying method, so that the toughness, the wear resistance and the thermal shock resistance of the ceramic are improved. And simultaneously, the cost is reduced.
The technical solution of the invention is as follows:
the metal surface is sprayed with self-reaction composite powder to synthesize the metal/ceramic composite coating, the matrix is metal, the metal surface is an alloy bottom layer, and the coating is arranged on the bottom layer. The coating is a metal/ceramic composite coating synthesized by spraying self-reacting composite powder.
The metal/ceramic composite coating is a composite coating which takes alumina ceramic and hercynite as bases and takes metal and intermetallic compounds as second phases.
The plasma spraying method of the metal/ceramic composite coating comprises the following steps:
(1) sandblasting the surface of a metal matrix to be sprayed to coarsen the surface and expose a fresh metal surface;
(2) putting nickel-aluminum alloy (Ni90) powder into a powder feeder;
(3) switching on a power supply of the control cabinet;
(4) feeding nitrogen and argon;
(5) switching on a spray gun power supply, and spraying a nickel-aluminum alloy bottom layer on the surface of the metal matrix;
(6) and (3) filling the composite powder into a powder feeder, simultaneously feeding hydrogen, and spraying the composite powder on the nickel-aluminum alloy bottom layer to prepare the metal/ceramic composite coating.
The spraying process parameters are as follows:
powder feeding gas flow: 0.4 (m)3/h)，
Arc power: the power of 29-32 KW,
distance of the spray gun: 90-130 mm.
The self-reaction composite powder comprises the following components in percentage by weight: (wt%)
60-85% of metal oxide powder with thermite reaction,
15 to 40 percent of aluminum (Al) powder,
and a proper amount of adhesive.
The metal oxide powder having thermite reaction is Fe2O3Powder of Cr2O3Powder, CrO3Powder, NiO powder and the like, and the granularity is-200 to +400 meshes.
The granularity of the aluminum (Al) powder is-360 to +400 meshes.
The adhesive is polyvinyl alcohol (PVA) with the concentration of 65-85%.
The preparation process of the self-reaction composite powder comprises the following steps:
(1) putting the metal oxide powder and the Al powder with the thermite reaction into a ball mill in proportion, adding a proper amount of ethanol, and mixing for 10-24 hours until the mixture is uniformly stirred;
(2) drying the uniformly stirred mixed powder;
(3) adding an adhesive into the uniform mixed powder, and stirring for 2-3 hours until the mixed powder becomes large-particle composite powder;
(4) placing the prepared large-particle composite powder into a drying oven, and keeping the temperature at 100-150 ℃ for 15-20 hours until the particles are completely dried;
(5) and (3) putting the dried large-particle composite powder into a crusher for crushing, and then screening the composite powder between-60 and +250 meshes for spraying.
Compared with the prior art, the invention has the following beneficial effects:
1. the composite powder has the advantages of rich raw material resources, low price, simple preparation method and low cost.
2. The powder mixing proportion is proper, the components are uniform, and the Al powder is distributed in the metal oxide powder with thermite reaction in a uniform and dispersed mode, so that plasma flame flow ignition and self-reaction continuous operation are facilitated.
3. By controlling the powder feeding amount of the composite powder, the electric arc power can control the self-reaction process, and the defect that the self-propagating reaction degree is difficult to control is overcome.
4. The combined action of the flame flow and the reaction heat can lead the ceramics generated by the reaction to be fully melted, and the melting degree is obviously higher than that of the coating obtained by the common plasma spraying.
5. The ceramic formed by the reaction is Al2O3With harder FeAl2O4Composite ceramics of, FeAl2O4Is formed by plasma spraying Al2O3Phases not possible to obtain.
6. The reaction degree is controlled, the molten metal and intermetallic compounds generated by the reaction are not easy to gather and exist on the ceramic substrate in a dispersion particle shape, so that the stress in the ceramic coating is relieved, and the bonding strength of the coating and the substrate is enhanced.
7. The reaction heat is effective supplement to the energy of the plasma flame flow, thereby realizing the preparation of the ceramic coating with high melting point by using low-power spraying equipment.
8. The composition of the ceramic and the metal overcomes the brittleness of the ceramic to a certain extent and improves the toughness of the ceramic.
9. Self-reaction metal/ceramic composite coating wear resistance ratio Al2O3The ceramic coating is 1.2-1.5 times higher, and the thermal shock resistance is improved by 2-3 times.
The drawings of the invention are illustrated as follows:
FIG. 1 is an optical micrograph 100X of a cross section of a composite powder of-60 to +80 mesh;
FIG. 2 shows the X-ray diffraction results of a composite powder spray coating of-60 to +80 mesh;
FIG. 3 is a back scattering electron image of a-60- +80 mesh composite powder sprayed coating;
FIG. 4 is the result of the energy spectrum analysis at position A in FIG. 3;
FIG. 5 is the result of the energy spectrum analysis at the position B in FIG. 3;
FIG. 6 is the result of the energy spectrum analysis at the position C in FIG. 3;
FIG. 7 is the result of the energy spectrum analysis at the D position in FIG. 3;
FIG. 8 is an optical micrograph 300of a-60- +80 mesh composite powder spray coating;
FIG. 9 shows-60- +80 mesh composite powder sprayed coating, Al2O3The different load abrasion volume change curves of the coating and the NiCrBSi coating;
FIG. 10 shows a metal/ceramic composite coating with Al2O3The relative wear resistance curves of the coating and the NiCrBSi coating are standard samples;
FIG. 11 is an optical micrograph 130 of a cross section of a composite powder of-120 to +150 mesh;
FIG. 12 shows the X-ray diffraction results of a composite powder spray coating of-120 to +150 mesh;
FIG. 13 is a back-scattered electron image of a composite powder spray coating of-120 to +150 mesh;
FIG. 14 is the result of the energy spectrum analysis at position A in FIG. 13;
FIG. 15 is the result of the energy spectrum analysis at position B in FIG. 13;
FIG. 16 is the result of the energy spectrum analysis at the position C in FIG. 13;
FIG. 17 is an optical micrograph 300 of a-120- +150 mesh composite powder spray coating;
FIG. 18 shows-120- +150 mesh composite powder sprayed coating, Al2O3Wear volume change curves of the coating and the NiCrBSi coating at different times;
FIG. 19 shows-120- +150 mesh composite powder sprayed coating, Al2O3The friction coefficient change curves of the coating and the NiCrBSi coating at different times;
FIG. 20 is an optical micrograph 150X of a cross section of a composite powder of-210 to +250 mesh;
FIG. 21 shows the X-ray diffraction results of a composite powder-sprayed coating of-210 to +250 mesh;
FIG. 22 is an SE electron image of a-210- +250 mesh composite powder spray coating;
FIG. 23 is an optical micrograph 300 of a-210- +250 mesh composite powder spray coating;
FIG. 24 shows Al as a composite powder spray coating of-210 to +250 mesh2O3Wear rate profile of different loading of the coating, NiCrBSi coating.
The specific embodiment of the invention is as follows: EXAMPLE 1 Synthesis of a 1.2mm thick Metal/ceramic composite coating by spraying a self-reacting composite powder onto Q235 Steel
1. Preparation of self-reacting composite powder 700g
(1) 1280g of iron oxide (Fe)2O3) Putting the powder and 540g of aluminum (Al) powder into a ball mill, adding a proper amount of ethanol, and mixing for 20 hours until the mixture is uniformly stirred;
(2) drying the uniformly stirred mixed powder;
(3) adding 250ml of adhesive polyvinyl alcohol (PVA) into the uniform mixed powder, and stirring for 2.5 hours until the mixed powder becomes large-particle composite powder;
(4) placing the prepared large-particle composite powder into a drying box, and keeping the temperature at 100 ℃ for 20 hours until the particles are completely dried;
(5) and (3) putting the dried large-particle composite powder into a crusher for crushing, and screening the composite powder between-60 and +80 meshes by using a screen for later use.
2. Plasma spraying on Q235 steel substrate
(1) Sandblasting the surface of Q235 steel to coarsen the surface and expose a fresh metal surface;
(2) the nickel-aluminum alloy powder is loaded into a powder feeder.
(3) Switching on a power supply of the control cabinet;
(4) feeding nitrogen and argon;
(5) switching on a spray gun power supply, and spraying a nickel-aluminum alloy (Ni90) bottom layer on the surface of the metal matrix;
(6) the prepared 100 g-60- +80 mesh composite powder is loaded into a powder feeder, hydrogen is simultaneously fed, the electric arc power is controlled to be 29KW, the distance of a spray gun is 90mm, and the flow of the powder feeding gas is 0.5m3And h, spraying composite powder on the nickel-aluminum alloy bottom layer to prepare the metal/ceramic composite coating.
The test detection is as follows:
1. compound powder:
the optical micrograph of the cross section of the composite powder of-60 to +80 mesh is shown in FIG. 1. It can be seen from FIG. 1 that Al is dispersedly distributed in Fe2O3In (1), the composite powder is internally and uniformly mixed. This structure is advantageous for Fe2O3The powder and the Al powder are fully subjected to oxidation-reduction reaction. Some agglomeration of the aluminum particles was also observed. This will result in Al and Fe2O3The excess of Fe does not allow the self-reaction to proceed sufficiently, and the excess of Fe2O3Is reduced into FeO, the FeO and a self-reaction product Al2O3Reaction to form FeAl2O4( ) The Fe generated by self-reaction forms Fe-Al alloy or FeAl and Fe with the rest Al3An Al intermetallic compound. The presence of these phases is advantageous for improving the coating properties
2. The thickness of the coating is 1.2mm
(1) Composition, texture, structure of coating
The X-ray diffraction results of the coating are shown in FIG. 2, and it can be seen from the X-ray diffraction results that the sprayed composite powder has reacted to form Al2O3、FeAl2O4FeAl alloys, and the like.
The structure of the coating layer observed under a scanning electron microscope is shown in FIG. 3. The energy spectrum analysis of the A, B, C, D region of the coated tissue of FIG. 3 is shown in FIGS. 4, 5, 6, and 7, wherebyThe whole coating is made of metal Fe, iron-aluminum alloy and Al2O3Ceramics, FeAl2O4Spinel is heterogeneous.
The metallographic micrograph of the coating is shown in FIG. 8, and it can be seen from FIG. 8 in combination with FIGS. 3, 4, 5, 6 and 7 that the coating is made of Al2O3Ceramic phase, FeAl2O4The spinel phase, the Fe metal phase and the Fe-Al alloy phase are alternately arranged and staggered with each other, stacked together in a wave form and have a layered structure. FeAl2O4Spinel and Al2O3The ceramic phase constitutes the structural support of the coating. Some of the less hard metal phases and insufficiently reacted species fill the interstices of the stent. The metal phase with high hardness and poor toughness of the bracket and low hardness has higher fracture toughness, and the good matching of the properties ensures that the coating has higher comprehensive strength. Therefore, the coating is generated on the base material by reactive plasma spraying, which is equivalent to coating a layer of shell material with high hardness and higher fracture toughness on the base body with low hardness, and the wear resistance of the base bodymaterial is greatly improved.
(2) The performance of the coating:
A. porosity of the coating:
porosity of metal/ceramic composite coating and pure Al sprayed by plasma2O3The coating and the comparison of the self-propagating prepared coating are shown in table 1. From Table 1, it can be seen that the porosity of the metal/ceramic composite coating is significantly less than that of the self-propagating coating and pure Al2O3And (4) coating.
TABLE 1 Metal/ceramic composite coating, self-propagating coating and Al2O3Comparison of coating porosity
| Coating layer | Density (g/mm)3) | Open porosity |
| Metal/ceramic composite coating | 4.3702 | 0.063 |
| Self-propagating coating | 3.9518 | 0.079 |
| Plasma spraying of Al2O3Coating layer | 3.742 | 0.075 |
B. Microhardness of metal/ceramic composite coating:
table 2 shows the microhardness of different structural morphologies of the metal/ceramic composite coating. The hardness of the ceramic phase in the metal/ceramic composite coating is high, the hardness value reaches 1310HV, cracks appear on sharp corners of diamond-shaped indentations and extend to all directions, which shows that the brittleness is high and the toughness is poor; however, the metal phase has low hardness and high toughness. The structure of the metal/ceramic composite coating with alternate brittle and tough phases ensures good combination of hardness and fracture toughness, so that the toughness of the coating is improved compared with that of a pure ceramic coating, and the coating is very favorable for improving the wear resistance.
TABLE 2 microhardness of different structure morphologies of the metal/ceramic composite coating
| Tissue color | Gray phase (hercynite) | Black phase (Al2O3Ceramic) | White phase (Metal and alloy) |
| Microhardness (HV) | 985 | 1310 | 252 |
C. Frictional wear characteristics of metal/ceramic composite coatings
With Al2O3The coatings and NiCrBSi coatings were standard and wear tests were performed at different loads. FIG. 9 is a graph of wear volume change under different loads for different coatings under no lubrication conditions, where 1 is Al2O3The wear volume curve of the coating, 2 is the wear volume curve of the metal/ceramic composite coating, and 3 is the wear volume curve of the NiCrBSi coating. From the wear volume curve it can be observed that: after a load of more than 392N, Al2O3The abrasion loss of the ceramic coating is 1.5 times of that of the metal/ceramic composite coating; under the load, the volume abrasion loss of the metal/ceramic composite coating is lower than that of the NiCrBSi coating, and the relative abrasion resistance of the metal/ceramic composite coating under the high load is slightly higher than that of the NiCrBSi coating.
FIG. 10 is a graph of the relative wear resistance of a metal/ceramic composite coating relative to two other coatings. FIG. 1 shows the relative Al of the metal/ceramic composite coating2O3The wear resistance curve of the coating, 2 is the wear resistance curveof the metal/ceramic composite coating relative to the NiCrBSi coating. With Al2O3Relative wear resistance of the ceramic coatingPhase (C)The value of (A) is 1.2-1.5, and compared with a NiCrBSi coating, the coating has relative wear resistance epsilonPhase (C)The value of (A) is around 1, which shows that the wear resistance of the metal/ceramic composite coating is better than that of Al2O3High abrasion resistance, equivalent to NiCrBSi coating, but the preparation cost of the metal/ceramic composite coating is far less than that of the NiCrBSi coating.
D. Bonding strength of metal/ceramic composite coating
By adopting an international GB8642-88 dual sample tensile method, tests show that the average value of the bonding strength of 6 pairs of metal/ceramic composite coating samples is 23.12MPa, and pure Al2O3The bonding strength of the coating is 18.17MPa, and the bonding strength of the metal/ceramic composite coating is obviously higher than that of pure Al2O3Coating layer
E. Thermal shock resistance of metal/ceramic composite coating
Tables 3 and 4 show the metal/ceramic composite coating and Al2O3Coating and ZrO2Thermal shock resistance comparison of the coating: metal/ceramicThe thermal shock resistance of the composite coating is best, the coating is not obviously changed after being heated at 800 ℃, water at 20 ℃ is quenched for 1 time, microcracks appear at the edge of the coating after 2 times of circulation, blocky stripping appears at the edge for 3 times, the edge of the coating is completely stripped after 4 times, and the coating is cracked between the bonding bottom layer and the metal/ceramic composite coating. Thermal shock resistance ratio ZrO2The coating is high. Heating at 1000 deg.C, and air cooling for 5 th time to form small pieces at the edge part, and 6 th time to form complete coating peeling. And Al2O3The thermal shock resistance times of the-Ni/Al gradient coating are only 4 times. Thermal shock resistance ratio of Al2O3the-Ni/Al gradient coating is high.
TABLE 3 thermal shock resistance test results for different coatings at 800 ℃ (20 ℃ water quenching)
| Coating layer | Al2O3 | ZrO2 | Metal/ceramic composite coating Layer(s) |
| Number of | 1 | 2 | 4 |
TABLE 4 Heat of 1000 ℃ for different coatingsResults of impact test (air cooling)
Example 2: spraying self-reaction composite powder on low-carbon steel to synthesize a metal/ceramic composite coating with the thickness of 1.0-1.2 mm
| Coating layer | Metal/ceramic composite coating | Al2O3Gradient coating |
| Number of cycles | 6 | 4 |
1. Preparation of self-reacting composite powder 600g
(1)1120g iron oxide (Fe)2O3) Putting the powder and 470g of aluminum (Al) powder into a ball mill, adding a proper amount of ethanol, and mixing for 18 hours until the mixture is uniformly stirred;
(2) drying the uniformly mixed powder;
(3) adding 220ml of adhesive polyvinyl alcohol (PVA) into the uniform mixed powder, and stirring for 2 hours until the mixed powder becomes large-particle composite powder;
(4) placing the prepared large-particle composite powder into a drying box, and keeping the temperature at 150 ℃ for 1 hour until the particles are completely dried;
(5) and (3) putting the dried large-particle composite powder into a crusher for crushing, and screening the composite powder between-120 and +150 meshes by using a screen for later use.
2. Plasma spraying on low carbon steel base material
(1) Sandblasting the surface of the low-carbon steel to coarsen the surface andexpose a fresh metal surface;
(2) the nickel-aluminum alloy powder is loaded into a powder feeder.
(3) Switching on a power supply of the control cabinet;
(4) feeding nitrogen and argon;
(5) switching on a spray gun power supply, and spraying a nickel-aluminum alloy (Ni90) bottom layer on the surface of the metal matrix;
(6) loading 150 g-120- +150 mesh composite powder into powder feeder, feeding hydrogen gas while controlling arc power at 31KW, spray gun distance at 110mm, and powder feeding gas flow at 0.4m3And h, spraying composite powder on the nickel-aluminum alloy bottom layer to prepare the metal/ceramic composite coating.
The test detection is as follows:
1. compound powder:
the optical micrograph of the cross section of the composite powder of-120 to +150 mesh is shown in FIG. 11. It can be seen from FIG. 11 that Al is dispersedly distributed in Fe2O3In (1), the inside of the composite powder is basically and uniformly mixed. This structure is advantageous for Fe2O3Powders andthe oxidation-reduction reaction of the Al powder is fully carried out.
2. The thickness of the coating is 1.1mm
(1) Composition, texture, structure of coating
The X-ray diffraction results of the coating are shown in FIG. 12, from which it can be seen that the sprayed composite powder has reacted to form Al2O3、FeAl2O4、Fe6Al alloy, and the like.
The structure of the coating layer observed under a scanning electron microscope is shown in FIG. 13.
The energy spectrum analysis of the A, B, C part of the coating structure in FIG. 13 is shown in FIGS. 14, 15 and 16, and thus, the whole coating is made of Fe and FeAl metals2O4Spinel, Al2O3Ceramics and FeAl2O4Spinel is heterogeneous.
Metallographic micrographs of coatings such asAs shown in FIG. 17, the coating layer has a structure of Al as shown in FIG. 17 in conjunction with FIGS. 13, 14, 15 and 162O3Ceramic phase, FeAl2O4Spinel equal ceramic is used as a matrix, and Fe metal phase and iron-aluminum alloy are used as a second phase composite coating.
(2) The performance of the coating:
A. porosity of the coating: self-reacting Al2O3Porosity of + Fe composite coating and pure Al of plasma spraying2O3The coating and the comparison of the self-propagating prepared coating are shown in table 5. From Table 5, it can be seen that the porosity of the metal/ceramic composite coating is significantly less than that of the self-propagating coating and pure Al2O3And (4) coating.
TABLE 5 Metal/ceramic composite coating, self-propagating coating and Al2O3Comparison of coating porosity
| Coating layer | Density (g/mm)3) | Open porosity |
| Metal/ceramic composite coating | 4.2605 | 0.064 |
| Self-propagating coating | 3.8988 | 0.080 |
| Plasma spraying of Al2O3Coating layer | 3.756 | 0.076 |
B. Microhardness of metal/ceramic composite coatings
TABLE 6 microhardness of different structure morphologies of metal/ceramic composite coatings
| Tissue color | Gray phase (hercynite) | Black phase (Al2O3Ceramic) | White phase (Metal and alloy) |
| Microhardness (HV) | 970 | 1290 | 260 |
C. Frictional wear characteristics of metal/ceramic composite coatings
With Al2O3The coating and NiCrBSi coating are standard samples, and 196N load is applied to all three coatings at the sliding speedThe coatings were subjected to abrasion tests at a degree of 0.4m/s for various periods of time. FIG. 18 is a graph of wear volume change of different coatings under non-lubricated conditions, wherein 1 is the wear volume curve of the metal/ceramic composite coating, and 2 is Al2O3The wear volume curve of the coating, 3, is the wear volume curve of the NiCrBSi coating. From the wear volume it can be observed: metal/ceramic composite coating ratio Al2O3The coating wear volume is much smaller, the same trend as the wear characteristic curve of the NiCrBSi coating, except that the volume wear is slightly larger than the NiCrBSi coating.
FIG. 19 is a graph of wear coefficient versus time for three coatings, where 1 is the friction coefficient curve for the metal/ceramic composite coating and 2 is Al2O3The friction coefficient curve of the coating, 3, is the friction coefficient curve of the NiCrBSi coating, and the wear of the three coatings tends to be stable and the wear coefficient is reduced along with the time. After 45min the friction torque is substantially unchanged. The coefficient of friction is generally between 0.54 and 0.78. In contrast, Al2O3The most poor friction reducing property. The three coatings were subjected to a steady wear test at a load of 294N, a sliding speed of 0.4m/s and a wear time of 150 min. The test results are shown in Table 7. The wear rates of the metal/ceramic composite coating and the NiCrBSi coating are equivalent as shown in Table 7, however, the preparation cost of the metal/ceramic composite coating is 1/5 of the NiCrBSi coating, and the friction coefficients of the three coatings are smaller after the NiCrBSi coating enters a stable wear stage.
TABLE 7 abrasion characteristics of the three coatings at an abrasion parameter of 294N, 0.4m/s, 2.5h
| Coating layer | Self-reacting recombination Coating layer | Al2O3Coating layer | NiCrBSi Coating layer |
| Rate of wear (10-6mm3/N.m) | 1.6609 | 5.0485 | 1.5471 |
| Stable coefficient of wear | 0.3511 | 0.3614 | 0.3498 |
D. Bond strength of composite coating
By adopting an international GB8642-88 dual sample tensile method, the average value of the bonding strength of 6 pairs of metal/ceramic composite coating samples is 20.92MPa, and pure Al is found in tests2O3The bonding strength of the coating is 18.17MPa, and the bonding strength of the metal/ceramic composite coating is obviously higher than that of pure Al2O3Coating layer
E. Thermal shock resistance of metal/ceramic composite coating
Tables 6 and 7 are the metal/ceramic composite coating with Al2O3Ni/Al coating and ZrO2Thermal shock resistance comparison of the coating: when the metal/ceramic composite coating is heated at 800 ℃ and water quenched at 20 ℃, the thermal shock resistance of the metal/ceramic composite coating is the best, the coating cracks between the bonding bottom layer and the metal/ceramic composite coating, and the coating is heated at 1000 ℃ and then cooled in air, which shows that the 4 th time produces small pieces to be stripped at the edge part and the 5 th time shows that the coating is completely stripped. And Al2O3The thermal shock resistance times of the-Ni/Al gradient coating are only 4 times.
TABLE 8 thermal shock resistance test results for different coatings at 800 deg.C
| Coating layer | Al2O3 | ZrO2 | Metal/ceramic composite coating |
| Number of | 1 | 2 | 4 |
TABLE 9 thermal shock resistance test results for different coatings at 1000 deg.C
| Coating layer | Metal/ceramic composite coating | Al2O3Gradient coating |
| Number of | 5 | 4 |
Example 3 spray coating of self-reacting composite powder on Low carbon Steel to form a 1.0-1.2 mm thick Metal/ceramic composite coating
1. Preparation of self-reacting composite powder 800g
(1)1440g iron oxide (Fe)2O3) Putting the powder and 600g of aluminum (Al) powder into a ball mill, adding a proper amount of ethanol, and mixing for 24 hours until the mixture is uniformly stirred;
(2) drying the uniformly mixed powder;
(3) adding 300ml of adhesive polyvinyl alcohol (PVA) into the uniform mixed powder, and stirring for 3 hours until the mixed powder becomes large-particle composite powder;
(4) placing the prepared large-particle composite powder into a drying box, and keeping the temperature at 120 ℃ for 15 hours until the particles are completely dried;
(5) and (3) putting the dried large-particle composite powder into a crusher for crushing, and screening the composite powder between-210 and +250 meshes by using a screen for later use.
2. Plasma spraying on low carbon steel base material
(1) Sandblasting the surface of the low-carbon steel to coarsen the surface and expose a fresh metal surface;
(2) the nickel-aluminum alloy powder is loaded into a powder feeder.
(3) Switching on a power supply of the control cabinet;
(4) feeding nitrogen and argon;
(5) switching on a spray gun power supply, and spraying a nickel-aluminum alloy (Ni90) bottom layer on the surface ofthe metal matrix;
(6) the prepared 160 g-210- +250 mesh composite powder is loaded into a powder feeder, hydrogen is sent at the same time, the arc power is controlled to be 33KW, the distance of a spray gun is 130mm, and the flow of the powder feeding gas is 0.4m3H on the bottom layer of Ni-Al alloySpraying composite powder to prepare the metal/ceramic composite coating.
The test detection is as follows:
1. compound powder:
the optical micrograph of the cross section of the composite powder of-210 to +250 mesh is shown in FIG. 20. It can be seen from FIG. 20 that Al is dispersedly distributed in Fe2O3In (1), the inside of the composite powder is basically and uniformly mixed. This structure is advantageous for Fe2O3The powder and the Al powder are fully subjected to oxidation-reduction reaction.
2. The thickness of the coating is 1.0mm
(1) Composition, texture, structure of coating
The X-ray diffraction results of the coating are shown in FIG. 21, from which it can be seen that the sprayed composite powder has reacted to form Al2O3、FeAl2O4FeAl alloys, and the like.
The structure of the coating layer observed under a scanning electron microscope is shown in FIG. 22. Therefore, the whole coating is made of metal Fe and FeAl2O4Spinel, Al2O3Ceramics and FeAl2O4Spinel is heterogeneous.
The metallographic micrograph of the coating is shown in FIG. 23, and it can be seen from FIG. 23 in conjunction with FIGS. 21 and 22 that the structure of the coating is Al2O3Ceramic phase, FeAl2O4Spinel equal ceramic is used as a matrix, and Fe metal phase and iron-aluminum alloy are used as a second phase composite coating.
(2) The performance of the coating:
A. porosity of the coating:
porosity of metal/ceramic composite coating and pure Al sprayed by plasma2O3The coating and the comparison of the self-propagating prepared coating are shown in table 10. From Table 10, it can be seen that the porosity of the metal/ceramic composite coating is significantly less than that of the self-propagating coating and pure Al2O3And (4) coating.
TABLE 10 Metal/ceramic composite coatings, self-propagating coatings and Al2O3Comparison of coating porosity
| Coating layer | Density (g/mm)3) | Open porosity |
| Metal/ceramic composite coating | 4.3516 | 0.065 |
| Self-propagating coating | 3.9087 | 0.081 |
| Plasma spraying of Al2O3Coating layer | 3.7906 | 0.077 |
B. Microhardness of metal/ceramic composite coatings
Table 11 microhardness of different texture morphologies of the metal/ceramic composite coatings.
| Tissue color | Gray phase (hercynite) | Black phase (Al2O3Ceramic) | White phase (Metal and alloy) |
| Microhardness (HV) | 980 | 1285 | 250 |
C. Frictional wear characteristics of metal/ceramic composite coatings
With Al2O3The coating and the NiCrBSi coating are used as standard samples, different loads are applied to the three coatings, the sliding speed is 0.4m/s, and FIG. 24 is a relation curve between the wear rate and the load of the different coatings under the non-lubrication condition. In the graph, 1 is a wear rate curve of the metal/ceramic composite coating, and 2 is Al2O3The wear rate curve of the coating, 3 is the wear rate curve of the NiCrBSi coating. From the wear rate profile it can be observed that: the wear rate curve of the metal/ceramic composite coating layer at around 200N shows the lowest point, which shows that the coating layer is relatively suitable for working under the load. The slope of the wear rate of the metal/ceramic composite coating is less than the other two coatings as the load increases. After the load exceeds 392N, the wear rate of the metal/ceramic composite coating is lowest. This indicates that the metal/ceramic composite coating is more capable of withstanding high load wear than the other two coatings.
D. Bonding strength of metal/ceramic composite coating
By adopting an international GB8642-88 dual sample tensile method, the average value of the bonding strength of 6 pairs of metal/ceramic composite coating samples is 22.34MPa, and pure Al is found in tests2O3The bonding strength of the coating is 18.17MPa, and the bonding strength of the metal/ceramic composite coating is obviously higher than that of pure Al2O3Coating layer
E. Thermal shock resistance of metal/ceramic composite coating
Tables 19 and 20 show the metal/ceramic composite coating and Al2O3Ni/Al coating and ZrO2Thermal shock resistance ratio of coatingComparing: the metal/ceramic composite coating has the best thermal shock resistance, the coating cracks between the bonding bottom layer and the metal/ceramic composite coating, and the thermal shock resistance is ZrO2The coating is good. Heating at 1000 deg.C, and air cooling to show that the 4 th time produces small pieces at the edge part, and the 5 th time all the coating is peeled off. And Al2O3The thermal shock resistance times of the-Ni/Al gradient coating are only 4 times.
TABLE 12 thermal shock resistance test results for different coatings at 800 deg.C
| Coating layer | Al2O3 | ZrO2 | Metal/ceramic composite coating |
| Number of | 1 | 2 | 4 |
TABLE 13 thermal shock resistance test results for different coatings at 1000 deg.C
| Coating layer | Metal/ceramic composite coating | Al2O3Gradient coating |
| Number of | 5 | 4 |
The above examples use iron (Fe) oxide2O3) For example, the reaction formula of other metal oxides which can be used for preparing composite powder and spraying with aluminum is as follows, and detailed description is omitted.
Claims (8)
1. A metal surface is sprayed from the compound powder synthesis metal/ceramic composite coating of reaction, its basal body is the metal, the metal surface is the alloy bottom, the bottom is the coating above, characterized by that: the coating is a metal/ceramic composite coating synthesized by spraying self-reacting composite powder.
2. Themetal/ceramic composite coating according to claim 1, wherein: the metal/ceramic composite coating is a composite coating which takes alumina ceramic and hercynite as bases and takes metal and intermetallic compounds as second phases.
3. The plasma spraying method of a metal/ceramic composite coating as claimed in claim 1, which comprises the steps of,
(1) sandblasting the surface of a metal matrix to be sprayed to coarsen the surface and expose a fresh metal surface;
(2) putting nickel-aluminum alloy (Ni90) powder into a powder feeder;
(3) switching on a power supply of the control cabinet;
(4) feeding nitrogen and argon;
(5) switching on a spray gun power supply, and spraying a nickel-aluminum alloy bottom layer on the surface of the metal matrix;
(6) filling the composite powder into a powder feeder, simultaneously feeding hydrogen, and spraying the composite powder on the nickel-aluminum alloy bottom layer to prepare a metal/ceramic composite coating;
the method is characterized in that: the spraying process parameters are as follows:
powder feeding gas flow: 0.4 (m)3/h)，
Arc power: the power of 29-32 KW,
distance of the spray gun: 90-130 mm.
4. The composite powder as claimed in claims 1 and 3, wherein: the composite powder comprises the following components in percentage by weight: (wt%)
60-85% of metal oxide powder with thermite reaction
15-40% of aluminum (Al) powder
Proper amount of adhesive
5. The composite powder of claim 4, wherein: the metal oxide powder having thermite reaction is Fe2O3Powder of Cr2O3Powder, CrO3Powder, NiO powder and the like, and the granularity is-200 to +400 meshes.
6. The composite powder of claim 4, wherein: the granularity of the aluminum (Al) powder is-360 to +400 meshes.
7. The composite powder of claim 4, wherein: the adhesive is polyvinyl alcohol (PVA) with the concentration of 65-85%.
8. A process for preparing a composite powder as claimed in claim 4, characterized in that: the process steps of the powder preparation are as follows:
(1) proportionally adding the metal oxide powder and Al powder with thermite reaction into ball mill while adding proper amount
Mixing ethanol for 10-24 hours until the mixture is uniformly stirred;
(2) drying the uniformly stirred mixed powder;
(3) adding an adhesive into the uniform mixed powder, and stirring for 2-3 hours until the mixed powder becomes large
A composite powder of particles;
(4) placing the prepared large-particle composite powder into a drying box, and keeping the temperature constant at 100-150 DEG C
15-20 hours until the granules are completely dried;
(5) the dried large-particle composite powder is put into a crusher to be crushed and then screened between minus 60 to plus 250 meshes
The composite powder is used for spraying.
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