CN106119762A - A kind of boride cement coating material and preparation method - Google Patents

Abstract

The invention discloses a boride cermet coating material and a preparation method. In the present invention, the method of centrifugal spray drying is used to prepare boride cermet powder, the powder includes _three components of _TiB2 powder, Ni powder and Cr powder, TiB2 powder accounts for 60% to 80% of the total mass, and NiCr powder accounts for the total mass 20% to 40%. The powder has a certain bonding strength through vacuum heat treatment, and the boride cermet powder of the present invention is sprayed on the surface of the metal substrate by using high-speed flame spraying (HVOF). The coating prepared by the above technical scheme has a compact structure, uniform distribution of borides, a typical layered structure, and excellent mechanical properties. Further improve the tribological performance and high temperature oxidation resistance of the metal substrate.

Description

A boride cermet coating material and preparation method thereof

technical field

The invention belongs to the field of surface protection of engineering materials, and relates to a boride cermet coating material and a preparation method thereof, in particular to a method of preparing agglomerated thermal spray powder by using a centrifugal spray drying method, and preparing a boride cermet coating by using a high-speed flame spraying method. Layer process preparation method.

Background technique

At present, the problem of high temperature protection of coal-fired boilers in power stations is still a long-term technical problem in the industry. Protecting the surface of the boiler's high-temperature heating surface can enhance its corrosion resistance, erosion resistance and wear resistance, and reduce the frequency of replacement parts and maintenance outages, which will greatly save boiler maintenance costs. Among many surface protection technologies, thermal spraying technology has very unique advantages, such as flexible process, high production efficiency and wide source of materials, so it has been widely used in surface protection of high-temperature parts of boilers. From the perspective of applied coating materials, the most commonly used ones are still nickel-based alloys with high chromium content, typical representatives such as Ni-50wt%Cr, NiCrMo (Ni-21Cr-9Mo-3.5Nb, 625 alloy), NiCrAl and NiCrSiB Wait. The corrosion resistance of NiCr alloy coatings is usually strong, but the erosion resistance and wear resistance of simple alloy coatings are often poor. Therefore, cermet-based composite coatings containing a certain The comprehensive performance of wear resistance and thermal corrosion resistance has attracted extensive attention, such as NiCr-Cr ₃ C ₂ , Co-WC as the representative cermet coating material.

Boride ceramics have excellent properties such as high melting point, high hardness, high chemical stability, and high wear and corrosion resistance. After the boride is oxidized in the medium temperature region, liquid B ₂ O ₃ is generated, and the film-like B ₂ O ₃ can be attached to the surface of the material to hinder further oxidation. In addition to the above advantages, TiB ₂ also has the advantages of good thermal conductivity, electrical conductivity and high temperature oxidation resistance, and it is also an advanced ceramic material with excellent structural properties and functional properties. For example, EP 074887B1 uses atmospheric plasma spraying to prepare TiB ₂ -NiCr coating with high hardness and good wear resistance, and the preparation method of Ni-based alloy-TiB ₂ nano coating (Chinese invention patent, CN 103589984A) is prepared by supersonic flame spraying A nano-NiCrAl-TiB ₂ coating and so on. The TiB2 _- based cermet coating prepared on the surface of these substrates has greatly improved the wear resistance and oxidation resistance of the material. However, these coating materials are mainly synthesized by self-propagating reaction or alloyed by ball milling. The preparation takes a long time, the batch is small, and the cost is high, so they are not suitable for mass production.

Under the above-mentioned background technology, the present invention proposes a low-cost, large-scale industrially usable boride cermet material and its coating preparation method, which is expected to realize surface protection for high-temperature wear-resistant parts such as boiler inner wall and piston ring.

Contents of the invention

The purpose of the present invention is to provide a preparation method of a high-performance cermet material and its coating, which has low preparation cost, simple operation and strong repeatability, and can be used in large-scale industrial production to protect the high-temperature heating surface of the boiler and improve its resistance Corrosion and erosion wear resistance.

A method for preparing a boride cermet coating material is characterized in that it comprises preparing the boride cermet coating material by means of centrifugal spray drying and heat treatment and preparing the coating by using a flame spraying system.

The boride cermet powder contains TiB ₂ powder, Ni powder and Cr powder with a particle size distribution of 1-5 μm, the TiB ₂ powder accounts for 60%-80% of the total mass, and the Ni powder and Cr powder account for 20%-40% of the total mass .

The inlet temperature of the centrifugal spray dryer is 180°C-200°C, the outlet temperature is 90°C-100°C, the rotation speed of the centrifugal spray disc is 20000rpm-24000rpm, and the feed rate is 0.3-0.5mL/s. The heating rate of the heat treatment is 5°C/min, the temperature is kept at 400°C and 1230°C for 1 hour respectively, and the argon atmosphere is protected.

Spraying process parameters are: spraying distance 355-380mm, oxygen flow rate 870-940L/min, kerosene flow rate 22.7-28.4L/h, _N2 flow rate 10.4±1L/min, powder feeding rate 40g/min.

According to one aspect of the present invention, there is provided a method for preparing NiCr-TiB ₂ cermet coating material, adopting centrifugal spray drying method to prepare cermet powder, using three kinds of Ni powder, Cr powder and TiB powder with unfixed component ratio ₂ powder.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a preparation method of NiCr _- TiB cermet coating material, which is characterized in that Ni powder, Cr powder and TiB ₂ with high purity and particle size of 1-5 microns The powder is used as the raw material, and the centrifugal spray drying technology is used to prepare the agglomerated thermal spray powder. The prepared agglomerated powder has a certain bonding strength after high-temperature heat treatment, and forms a powder suitable for high-speed flame spraying.

According to another aspect of the present invention, a method for preparing a NiCr-TiB cermet coating is provided, which is characterized in that the NiCr-TiB ₂ agglomerated powder with a particle size range of ₁₅ μm to 45 μm prepared by the present invention is used as the spraying material, and the coating is carried out at a high speed The flame sprays the powder onto the substrate to form a dense coating.

Compared with the prior art, the coating prepared by adopting the above technical scheme has the following similarities and differences:

In EP 074887B1, sintering crushing and mechanical alloying are used to prepare NiCr-TiB ₂ powder. The powder preparation cycle is long and the cost is high, which is not suitable for mass production. In CN 103589984A, high-energy ball milling is used to prepare nano-NiCrAl-TiB ₂ powder, and the powder preparation takes a long time , The batch is small, and the particle size of the powder is not easy to control. This technology adopts the method of centrifugal spray drying to prepare thermal spraying materials. The powder particle size is controllable, the fluidity is good, the sphericity is high, and the cost is low, which is beneficial to large-scale industrial use.

Both this technology and the prior art use Ni as the main metal binder phase, and add Cr element in it, this is because Ni is the metal with the best wettability with _TiB2 , and adding Cr can improve the resistance of coating materials to high temperature samples. Ability.

The coating is prepared by supersonic flame spraying. The structure of the coating is dense, the performance is stable, and the oxidation rate of the coating is extremely low. It is suitable for improving the erosion resistance, wear resistance and thermal corrosion resistance of high-temperature parts of the boiler.

Description of drawings

Figure 1a One of the topography images of NiCr _- TiB2 powder prepared by centrifugal spray drying

Figure 1b The _second morphology of NiCr-TiB powder prepared by centrifugal spray drying

Figure 2a HVOF spraying one embodiment of the NiCr-TiB ₂ coating cross-sectional microstructure diagram

Figure 2b HVOF spraying an embodiment of NiCr-TiB ₂ coating cross-sectional microstructure diagram two

Figure 3a HVOF spraying one embodiment of the NiCr-TiB ₂ coating cross-sectional microstructure diagram

Figure 3b HVOF spraying an embodiment of NiCr-TiB ₂ coating cross-sectional microstructure diagram II

Figure 4a HVOF spraying one embodiment of the NiCr-TiB ₂ coating cross-sectional microstructure diagram

Figure 4b HVOF spraying an embodiment of NiCr-TiB ₂ coating cross-sectional microstructure diagram two

Fig. 5 Bright field image and SAD analysis of an example NiCr-TiB ₂ coating sprayed by HVOF

Fig.6 Sliding friction wear scar morphology of HVOF sprayed NiCr-TiB ₂ coating

Fig.7 Sliding friction curves of HVOF sprayed NiCr-TiB ₂ coating

Fig.8 Cyclic oxidation kinetics curves of HVOF sprayed NiCr _- TiB2 coating

Fig.9 Cyclic thermal corrosion kinetics curve of HVOF sprayed NiCr-TiB ₂ coating

Fig.10 Surface 30° erosion wear morphology of HVOF sprayed NiCr-TiB ₂ coating

Fig.11 Surface 90° erosion wear morphology of HVOF sprayed NiCr-TiB ₂ coating

Fig.12 Erosion weight loss of HVOF sprayed NiCr-TiB ₂ coating

detailed description

The present invention will be described in further detail below with reference to the embodiments of the accompanying drawings.

Example 1:

Choose commercially available micron TiB ₂ , Ni, Cr powders with a purity above 99.6%, the weight ratio of TiB ₂ powder, Ni powder and Cr powder in the powder is 60wt.%: 32wt.%: 8wt.%, organic dispersant PAANH ₄ The mass is 0.8%-1.2% of the mass of the mixed powder, and the mass of the organic binder polyethylene glycol is 15%-20% of the mass of the mixed powder.

The following steps are used to prepare high-performance agglomerated and sintered powders:

(1) Put the above materials into deionized water, add the mixed solution into a planetary ball mill and mix at a low speed of 200r/min for 10 hours to form a viscous slurry.

(2) Prepare agglomerated spherical powder by centrifugal spray drying method. The inlet temperature of the spray drying tower is 180°C, the outlet temperature is 90°C, the rotation speed of the centrifugal spray plate is 20000r/min, and the feed rate is 0.4mL/s for constant temperature and constant speed spray drying. powder.

(3) Carry out vacuum heat treatment on the agglomerated sintered powder. Put the agglomerated powder into a vacuum tube furnace, evacuate the corundum furnace tube to 10 ^-2 torr, set the heating rate at 5°C/min, keep it at 400°C for 1 hour, keep it at 1230°C for 1 hour, then cool down to 400°C ℃ to start furnace cooling, when the furnace temperature is lower than 50 ℃, take out the corundum crucible, sieve in the air, and keep the sieves of 325 mesh to 500 mesh.

The agglomerated and sintered powder after sieving is a spherical powder with a smooth surface, and the particle size of the powder is 15-45 μm.

The substrate used for spraying is low carbon steel, and the surface of the substrate is derusted, degreased and sandblasted before spraying.

The spraying equipment is the JP-5000 supersonic flame spraying system produced by the British TAFA company. The main spraying process parameters are: spraying distance 380mm, oxygen flow rate 893L/min, kerosene flow rate 28.4L/h, N ₂ flow rate 10.3L/min min, the powder feeding rate is about 40g/min. The spraying thickness is controlled at 0.25-0.4mm.

In other embodiments, the weight percentage of TiB ₂ powder in the powder can be 70% or 80%, and the weight percentage of NiCr powder can be 20% or 30% accordingly.

In some embodiments, the spraying process parameters can also be 355 mm, the oxygen flow rate is 870 L/min or 940 L/min, and the kerosene flow rate is 22.7 L/min or 24.6 L/min.

The mechanical properties of the coating prepared in Example 1 were tested. The test results are shown in Table 1.

Example 2:

Choose the commercially available purity of more than 99.6% micron TiB ₂ , Ni, Cr powder, the weight ratio of TiB ₂ powder, Ni powder and Cr powder in the powder is 60wt.%: 32wt.%: 8wt.%. Powder preparation process, preparing agglomerated and sintered powder.

The substrate used for spraying is low carbon steel, and the surface of the substrate is derusted, degreased and sandblasted before spraying.

The spraying equipment is the JP-5000 supersonic flame spraying system produced by the British TAFA company. The main spraying process parameters are: spraying distance 380mm, oxygen flow rate 940L/min, kerosene flow rate 24.6L/h, N ₂ flow rate 10.3L/min min, the powder feeding rate is about 40g/min. The spraying thickness is controlled at 0.25-0.5mm.

The mechanical properties of the coating prepared in Example 2 were tested. The test results are shown in Table 1.

Example 3:

Choose the commercially available purity of more than 99.6% micron TiB ₂ , Ni, Cr powder, the weight ratio of TiB ₂ powder, Ni powder and Cr powder in the powder is 70wt.%: 24wt.%: 6wt.%. Powder preparation process, preparing agglomerated and sintered powder.

The substrate used for spraying is low carbon steel, and the surface of the substrate is derusted, degreased and sandblasted before spraying.

The spraying equipment is the JP-5000 supersonic flame spraying system produced by the British TAFA company. The main spraying process parameters are: spraying distance 355mm, oxygen flow rate 870L/min, kerosene flow rate 22.7L/h, N ₂ flow rate 10.3L/min min, the powder feeding rate is about 40g/min. The spraying thickness is controlled at 0.25-0.5mm.

The mechanical properties of the coating prepared in Example 3 were tested. The test results are shown in Table 1.

It can be seen from Table 1 that the microhardness, fracture toughness and porosity of the coating prepared in Example 1 are all excellent. Example 2 has high microhardness and low fracture toughness, and Example 3 has low microhardness, high fracture toughness and high porosity.

Figure 1 schematically shows the micromorphology of the NiCr-TiB ₂ agglomerated powder prepared in Example 1. As shown in Figure 1, the powder has good sphericity and uniform particle size distribution.

Figure ₂ shows the microstructural analysis results of the NiCr-TiB2 coating prepared by Example 1. As shown in Figure 2, the coating is tightly bonded to the substrate, without cracks and other obvious defects, and there is no obvious pores inside the coating. The microstructure is dense, showing a typical sprayed coating-like structure, and the ceramic phase is evenly distributed. It is found that a large number of dark gray polygonal TiB ₂ particles are evenly distributed in the off-white binder phase through partial zoom-in observation.

Figure 3 shows the microstructural analysis results of the NiCr-TiB2 coating prepared by Example ₂ . As shown in Figure 3, the coating is closely bonded to the substrate, without cracks and other obvious defects. There are some pores inside the coating, and the structure is dense, showing a typical sprayed coating structure, with some slender strips of flow-like phase distribution.

Figure 4 shows the microstructural analysis results of the NiCr-TiB2 coating prepared by Example ₃ . As shown in Figure 4, the coating is closely bonded to the substrate, without cracks and other obvious defects. There are obvious pores around the ceramic phase inside the coating, and the microstructure is a typical sprayed coating structure, with some elongated flow-like phase distributions. .

Figure 5 shows the results of TEM analysis of the NiCr-TiB2 coating prepared by Example ₁ . As shown in Fig. ₅ , the TiB2 particles are closely combined with the binder phase, and TiB2 particles with sizes ranging from 0.5 μm to ₅ μm are randomly distributed in the binder phase.

Figures 6 to 9 respectively show the results of analyzing some properties of the NiCr-TiB ₂ coating prepared in Example 1.

Fig. 6 schematically shows the NiCr-TiB ₂ coating that embodiment 1 prepares when the sliding friction pair is a GCr15 steel ball, the radius of rotation is 10mm, the load is 10N, and the sliding friction wear scar morphology of the coating is tested under the conditions of 3600s, Fig. 7 schematically shows a schematic diagram of the sliding friction coefficient of the coating in Example 1. The friction and wear coefficient curve first increases and then stabilizes to about 0.8. It shows that the composite coating has relatively stable anti-sliding friction performance.

Fig. 8 and Fig. 9 have respectively shown the NiCr-TiB ₂ coating prepared by box-type resistance furnace test embodiment 1 in 500 ℃ / 700 ℃ / 900 ℃ static atmospheric pressure atmosphere of high temperature oxidation resistance and hot corrosion resistance result. The results show that the cyclic oxidation weight gain curve and hot corrosion weight gain curve of the coating approximately follow the parabolic law. The coating has good oxidation resistance in an oxidizing environment, because the coating forms a complete and dense oxide layer during the oxidation process, which effectively isolates the coating from the air environment.

Fig. 10 and Fig. 11 respectively schematically show that adopting a caliber of 9.56mm sandblasting gun, using an air pressure of 0.5MPa, and a spray distance of 100mm erosion conditions, the coating prepared in Example 1 along the 30°/90° direction The surface morphology of the coating after eroding 500g of corundum sand with a particle size of 40 mesh to 20 mesh on the coating surface.

Figure 12 schematically shows the weight loss of the coating prepared in Example 1 after 30°/90° erosive wear.

Table 1 Mechanical properties of HVOF sprayed NiCr-TiB ₂ coating

Claims (4)

1. A method for preparing a boride cermet coating material, characterized in that: comprising the method of centrifugal spray drying and heat treatment to prepare the boride cermet coating material and using a flame spraying system to prepare the coating. 2. the preparation method of a kind of boride cermet coating material according to claim 1 is characterized in that: the boride cermet powder comprises TiB ₂ powder, Ni powder and Cr powder of particle size distribution 1～5 μm, TiB ₂ powder accounts for 60%-80% of the total mass, and Ni powder and Cr powder account for 20%-40% of the total mass. 3. The preparation method of a boride cermet coating material according to claim 1, characterized in that: the inlet temperature of the centrifugal spray dryer is 180°C to 200°C, the outlet temperature is 90°C to 100°C, and the centrifugal spray dryer The disc rotation speed is 20000rpm-24000rpm, and the feed rate is 0.3-0.5mL/s. The heating rate of the heat treatment is 5°C/min, the temperature is kept at 400°C and 1230°C for 1 hour respectively, and the argon atmosphere is protected. 4. The preparation method of a boride cermet coating according to claim 1, characterized in that the spraying process parameters are: spraying distance 355-380mm, oxygen flow rate 870-940L/min, kerosene flow rate 22.7-28.4L/min h, N ₂ flow rate 10.4±1L/min, powder feeding rate 40g/min.