A preparation method of a modified cobalt-based plasma cladding coating applied to a high-temperature wear environment

Abstract

The application discloses a preparation method of a modified cobalt-based plasma cladding coating applied to a high-temperature wear environment, and adds WC powder into Stellite21 to prepare a wear-resistant coating by adopting a plasma cladding technology.Taking into account that a large number of holes will appear after adding WC and WC cannot be completely decomposed to form a strengthening phase with Co, the plasma remelting technology is adopted after plasma cladding to make the WC in the coating uniformly distributed and decomposed to form a strengthening phase.The XRD and SEM result analysis shows that the structure obtained after remelting is more uniform, although the surface hardness is lower than that before remelting, the high-temperature wear amount at 600 DEG C is greatly reduced, and the wear resistance is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wear-resistant coating design and performance testing, in particular to the field of inner layer wear-resistant coating design of ore crushers, and relates to a preparation method of a modified cobalt-based plasma cladding coating applied to high-temperature wear-resistant environments. BACKGROUND

[0002] About 70% of all types of damage to electromechanical equipment is caused by various forms of wear.

[0003] Therefore, there is great social and economic benefit in researching the causes of wear failure, developing anti-wear solutions, reducing wear consumables, and improving the safe service life of mechanical equipment and parts. SUMMARY

[0004] In order to improve the bonding strength of the coating and the substrate and reduce the porosity of the coating, the present application provides a preparation method of a modified cobalt-based plasma cladding coating applied to high-temperature wear-resistant environments, which uses plasma remelting technology to make WC in the coating more decomposed and form a strengthening phase with Co.

[0005] The present application is specifically implemented through the following technical means:

[0006] The present application provides a preparation method of a modified cobalt-based plasma cladding coating, which comprises the following steps:

[0007] Step 1): Mix tungsten carbide and Stellite alloy by ball milling to obtain a mixed powder;

[0008] Step 2): Dry the mixed powder, and then use plasma surfacing to cladding the mixed powder on the surface of a substrate plate to prepare a coating;

[0009] Step 3): Perform plasma remelting on the coating obtained in step 2) to obtain a modified cobalt-based plasma cladding coating.

[0010] Preferably, the Stellite alloy in step 1) is Stellite 21 cobalt-based alloy.

[0011] Preferably, the content of tungsten carbide in step 1) accounts for 10%-40% of the total mass of the mixed powder.

[0012] Preferably, the substrate plate in step 2) is Q235 steel.

[0013] Preferably, the plasma surfacing process parameters in step 2) are: welding current 100 A, weld seam spacing 2.5 mm, and walking speed 2.0-2.5 mm / s.

[0014] As preferred, the plasma remelting process parameters in step 3) are as follows: welding current 100 A, welding seam spacing 2.5 mm, and walking speed 2.0-2.5 mm / s.

[0015] The application also provides the modified cobalt-based plasma cladding coating prepared by the method.

[0016] The application also provides application of the modified cobalt-based plasma cladding coating in a wear-resistant coating of an inner layer of a mineral crusher.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] The application uses Q235 plate as a substrate, adds WC powder in Stellite 21, and uses plasma cladding technology to prepare a wear-resistant coating. Considering that a large number of pores will appear after adding WC and WC cannot be completely decomposed to form a strengthening phase with Co, plasma remelting technology is used after plasma cladding to make WC in the coating uniformly distributed and decomposed to form a strengthening phase. Experimental results show that the coating prepared by the process has a more uniform structure, although the surface hardness is lower than that before remelting, the high-temperature wear amount at 600 DEG C is greatly reduced, and the wear resistance is greatly improved. The process has a wide application range, strong operability, small requirement for the use environment, and good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The application is a technical route flowchart.

[0020] Figure 2 The application is a Stellite 21 powder macroscopic morphology diagram.

[0021] Figure 3 The application is a Stellite 21 powder XRD spectrum.

[0022] Figure 4 The application is a WC powder macroscopic morphology diagram.

[0023] Figure 5 The application is a WC powder XRD spectrum.

[0024] Figure 6 The application is a Q235 metallographic structure diagram.

[0025] Figure 7 The application is an SEM diagram of a pure cobalt-based coating before plasma remelting.

[0026] Figure 8 The application is an SEM diagram of a pure cobalt-based coating after plasma remelting.

[0027] Figure 9 The application is an SEM diagram of a cobalt-based coating with 10% WC before plasma remelting.

[0028] Figure 10 SEM image of 10% WC cobalt-based coating after plasma remelting.

[0029] Figure 11 SEM image of 20% WC cobalt-based coating before plasma remelting.

[0030] Figure 12 SEM image of 20% WC cobalt-based coating after plasma remelting.

[0031] Figure 13 SEM image of 30% WC cobalt-based coating before plasma remelting.

[0032] Figure 14 SEM image of 30% WC cobalt-based coating after plasma remelting.

[0033] Figure 15 SEM image of 40% WC cobalt-based coating before plasma remelting.

[0034] Figure 16 SEM image of 40% WC cobalt-based coating after plasma remelting.

[0035] Figure 17 X-ray diffraction spectra of pure cobalt-based coating before and after remelting.

[0036] Figure 18 X-ray diffraction spectra of 10% WC cobalt-based coating before and after remelting.

[0037] Figure 19 X-ray diffraction spectra of 20% WC cobalt-based coating before and after remelting.

[0038] Figure 20 X-ray diffraction spectra of 30% WC cobalt-based coating before and after remelting.

[0039] Figure 21 X-ray diffraction spectra of 40% WC cobalt-based coating before and after remelting.

[0040] Figure 22 Surface hardness of cobalt-based coatings with different WC contents.

[0041] Figure 23 Wear rate of cobalt-based coatings with different WC contents at high temperature. DETAILED DESCRIPTION

[0042] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with embodiments. If specific conditions are not specified in the embodiments, conventional conditions or conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased in the market.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this description, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0044] Embodiments

[0045] Firstly, the base plate material is determined to be Q235 steel, and the wettability of cobalt-based and WC is the best, so the cobalt-based powder is selected as the base powder, and then different contents of WC are added to the cobalt-based powder to improve the hardness and wear resistance of the coating. In the experiment, the Stellite 21 powder and the WC powder are mixed and ball milled for 2 h using a ball mill, and then dried for 2 h (120°C) using a vacuum drying oven. Then, the plasma surfacing machine is used for surfacing, and then the wire cutting machine is used to cut into the experimental size, and then the 240#, 800#, 1200# and 2000# sandpaper are used in turn for polishing, and finally the polishing machine is used for polishing to mirror surface, and then the microhardness and wear resistance are tested, and then the XRD and SEM are used for phase and morphology analysis. Figure 1 The technical route flowchart of the present application.

[0046] Microhardness test: load 200 g, holding time 10 s, test 10 points on the surface, and take the average value as the surface hardness; wear resistance test: test temperature 600°C, rotation speed 2240 r / min, wear radius 5 mm, ball radius 5 mm, before testing, the sample is polished to mirror surface, then ultrasonic cleaning for 10 min, then weighed by a one-hundredth g balance, then wear test, after testing, ultrasonic cleaning again, and calculate the wear amount.

[0047] The main components of Stellite 21, WC and Q235 used in the experiment are as follows.

[0048] Table 1 Stellite 21 composition

[0049]

[0050] Table 2 WC composition

[0051]

[0052] Table 3 Q235 composition

[0053]

[0054] Figure 2 , 4 are macroscopic morphology of Stellite 21 powder, WC powder, respectively; Figure 3 , 5 are XRD patterns of Stellite 21 powder, WC powder, respectively; Figure 6 is the metallographic structure of Q235.

[0055] The plasma surfacing process parameters and the plasma remelting process parameters of the experiment are as follows.

[0056] Table 4 Plasma surfacing parameters

[0057]

[0058] Table 5 Plasma remelting parameters

[0059]

[0060] For pure cobalt-based coating, Figure 7 , Figure 8 are SEM images of pure cobalt-based coating before and after remelting, from which it can be seen that the grain size of the pure cobalt-based coating relatively increases after remelting. The image software is used to calculate the grain size before and after remelting, the average grain size before plasma remelting is 6.7 μm, and the average grain size after plasma remelting is 10.8 μm, which is caused by the input of heat in the remelting process to make the grain continue to grow. EDS analysis shows that the content of iron element in the coating increases after remelting, which is caused by the exchange of elements between the coating and the substrate Q235 steel due to the input of heat in the remelting process, resulting in the increase of the content of iron element in the coating, the solid solution strengthening caused by the fusion of Fe into γ-Co, but the existence of Fe element in the intergranular compound will lead to the decrease of the hardness of the coating, so the surface hardness of the coating is still decreased after remelting. It can be seen from the scanning electron microscope picture that the coating without adding WC is composed of dark solid solution primary phase and intergranular precipitated phase, and the XRD analysis result shows that the coating first forms cobalt-based solid solution during cooling, and then gradually forms intergranular precipitated phase, the primary cobalt-based solid solution is face-centered cubic solid solution, because the cooling speed of the coating is very fast after the surfacing is completed, the γ-Co solid solution cannot be transformed to form ε-Co, so the Co-based solid solution in the surfacing layer is metastable phase γ-Co with face-centered structure, and it also melts into Ni, Cr and C, which has solid solution strengthening effect, forms FeNi phase, and the white intergranular phase is CoCX precipitated phase.

[0061] Referring to the above experimental procedure, first, the Stellite 21 powder and WC powder (90%+10%) were mixed and ball milled for 2 h using a ball mill, then dried for 2 h (120°C) using a vacuum drying oven, and then a 10% WC cobalt-based coating was prepared by surfacing using a plasma surfacing machine. Figure 9 、 Figure 10 The SEM images of the 10% WC cobalt-based coating before and after remelting were compared, and it was found that the grain size of the coating decreased after remelting. The image software was used to calculate the grain size before and after remelting, and the average grain size before plasma remelting was 9.3 μm, and the average grain size after plasma remelting was 5.17 μm; the analysis is that after remelting, the WC particles will dissolve in the high-temperature molten pool to become W and C free atoms, which provides nucleation points for the non-uniform nucleation process and increases the nucleation rate of the nucleation process, resulting in a decrease in grain size; the overall morphology of the cladding coating after adding WC is basically unchanged, but it affects the solidification process of the interdendritic eutectic structure, so the addition of WC will increase the proportion of eutectic structure and generate some other complex products. EDS analysis shows that the content of iron element in the coating after remelting increases slightly, but compared with pure cobalt-based, the change is very small, and the hardness increases instead; the content of eutectic structure in the coating after remelting increases significantly, which is because the input of heat during the remelting process affects the solidification process, resulting in more precipitated phases. It can be seen from the scanning electron microscope picture that the cobalt-based coating with 10% WC is composed of dark solid solution primary phase and intergranular precipitated phase, and combined with the XRD analysis result, it can be known that the solid solution primary phase is γ-Co, and there is a small amount of FeNi phase, and the white intergranular phase is CoCX precipitated phase.

[0062] Referring to the above experimental procedure, first, the Stellite 21 powder and WC powder (90%+10%) were mixed and ball milled for 2 h using a ball mill, then dried for 2 h (120°C) using a vacuum drying oven, and then a 10% WC cobalt-based coating was prepared by surfacing using a plasma surfacing machine. Figure 11 、 Figure 12The SEM images of the cobalt-based coating before and after remelting with 20% WC show that the original interdendritic structure in the coating after remelting is remelted to form a uniform eutectic structure. It can be analyzed by XRD and EDS that Co6W6C and Fe6W6C hard phases are generated in the coating after adding 20% WC. The surface hardness of the coating after remelting increases, which is caused by the generation of a large amount of eutectic structure and the increase of W element content in the grain and intergranular after remelting. The grain radius of W is large, which will enter the crystal lattice during melting, and cannot be precipitated during rapid cooling, so solid solution strengthening will be generated. Before remelting, the coating is mainly composed of γ-Co phase and a small amount of FeNi phase, and the intergranular phase is mainly Co6W6C and Fe6W6C. After remelting, the coating is mainly composed of Co6W6C and Fe6W6C in the eutectic structure.

[0063] Referring to the above experimental steps, the Stellite 21 powder and WC powder (70%+30%) are mixed and ball milled for 2 h using a ball mill, then dried for 2 h (120°C) using a vacuum drying oven, and then a cobalt-based coating with 30% WC is prepared by surfacing with a plasma surfacing machine. Figure 13 、 Figure 14 The SEM images of the cobalt-based coating before and after remelting with 30% WC show that there are white fishbone-like phases, light-colored matrix phases, and dark-colored precipitated phases in the coating before and after remelting. Combined with EDS and XRD analysis, it can be seen that the light-colored phase is mainly the matrix phase of γ-Co, the white fishbone-like phase is Co6W6C and W2C, and the dark-colored eutectic structure precipitated at the phase boundary is a compound formed by Cr, C, and Co. After remelting, the content of the matrix phase increases, and the content of the white W-rich phase and the dark-colored eutectic structure decreases. EDS shows that the content of Fe element in the γ-Co phase after remelting increases significantly compared to other phases, because Fe will solid-solve into the crystal lattice of γ-Co at high temperature, and the atomic radius of Fe element is larger than that of Co element, which cannot be precipitated during cooling, resulting in the increase of Fe element content in the matrix γ-Co phase and solid solution strengthening, thereby increasing the surface hardness of the coating. However, the decrease of the content of white W-rich phase and dark-colored eutectic structure will lead to the decrease of the surface hardness of the coating, and the overall test shows that the surface hardness of the coating is still decreased.

[0064] Referring to the above experimental steps, the Stellite 21 powder and WC powder (60%+40%) are mixed and ball milled for 2 h using a ball mill, then dried for 2 h (120°C) using a vacuum drying oven, and then a cobalt-based coating with 40% WC is prepared by surfacing with a plasma surfacing machine. Figure 15 、 Figure 16The SEM images of the 40% WC cobalt-based coating before and after remelting can be seen from the contrast images. After remelting, the white phase is obviously larger, and the morphology shows that it is not a whole, but is formed by the aggregation of small white phase before remelting. The analysis is that the input of remelting heat increases the fluidity of the coating, and the dispersed white W-rich phase is aggregated to form a network. The XRD and EDS analysis shows that the light gray matrix primary phase in the coating is mainly the γ-Co matrix phase, which also contains (Ni, Fe) phase. The dark gray eutectic precipitated phase is mainly the hard precipitated phase formed by C and Cr, and the white W-rich phase is Co6W6C and W2C, Fe6W6C, and WC also appears. The analysis is that the addition amount of WC is too much, so it cannot be completely decomposed. The Co content in the white network W-rich phase is relatively high, and the XRD and EDS analysis shows that it is Co4W2C.

[0065] The phase analysis of the above coating is shown in Figures 17-21 The Stellite 21 coating without adding WC is mainly the gray matrix phase γ-Co, and Ni, Cr, C are also melted into it, which has a solid solution strengthening effect to form FeNi phase, and the intergranular white color is CoCX precipitated phase. After adding 10% WC, the solid solution primary phase in the coating is γ-Co, and there is a small amount of FeNi phase, and the intergranular white color is CoCX precipitated phase. After adding 20% WC, the coating is mainly γ-Co phase, and there is a small amount of FeNi phase, and the intergranular phase is mainly Co6W6C and Fe6W6C. After remelting, the coating is mainly Co6W6C and Fe6W6C in the eutectic structure. After adding 30% WC, there is no Fe6W6C and FeNi phase in the remelted and unremelted coating, but W2C phase formed by the decomposition of WC appears, and the coating is still mainly γ-Co phase, accompanied by the formation of some W-rich phase (Co6W6C). After adding 40% WC, the coating has more phase types, and the matrix phase is γ-Co phase, but the content of W-rich phase Co6W6C and Fe6W6C also increases, and un-decomposed WC and new Co4W2C phase appear.

[0066] The surface hardness of the above coating is shown in Figure 22As shown, with the increase of WC content, the surface hardness of the coating gradually increases. The surface hardness of the coating with 10% WC is relatively increased by 3% compared with that without WC, and is increased by 3.77 times compared with that of the substrate; the surface hardness of the coating with 20% WC is relatively increased by 18% compared with that without WC, and is increased by 4.3 times compared with that of the substrate; the surface hardness of the coating with 30% WC is relatively increased by 23% compared with that without WC, and is increased by 4.6 times compared with that of the substrate; the surface hardness of the coating with 40% WC is relatively increased by 66.9% compared with that without WC, and is increased by 6.6 times compared with that of the substrate; the analysis is that with the increase of WC content, the content of hard phases Co6W6C, Fe6W6C, Co4W2C and W2C on the surface of the coating gradually increases, and the hardness of the hard phases is much greater than that of the substrate phase, the Vickers hardness of Co6W6C can reach 1200 kg / mm 2 With the increase of WC content, the fine-grain strengthening is more and more obvious, the surface grain is smaller, and the hardness is higher. After remelting, the hardness of the coating with 10% WC and 20% WC is relatively increased compared with that without remelting, and the hardness of the coating with the rest of the components is relatively decreased. The hardness of the coating with 10% WC is increased after remelting, and it is observed from the SEM that the grain size is relatively reduced after remelting, which leads to fine-grain strengthening, and the content of Fe element in the dendrites and intergranular of the coating is basically unchanged, so the hardness of the coating is increased. The hardness of the coating with 20% WC is increased after remelting, and it is observed from the SEM and EDS that a large amount of eutectic structure is generated on the surface, and the content of C element, W element and Cr element in the eutectic structure is increased, the solid solution strengthening is obvious, and the content of Fe element is basically unchanged, so the hardness of the coating is increased. The remelting of the rest of the components reduces the microhardness of the coating to a certain extent, because the fluidity of the elements in the molten pool is improved after remelting, the further diffusion of the elements is accelerated, and the Fe element in the substrate diffuses into the coating at high temperature, but compared with the remelted coating, the composition of the remelted coating is uniform, so the surface hardness value fluctuates little.

[0067] Figure 23 For the wear rate of the cobalt-based coating with different WC contents at high temperature, it can be seen that the wear rate gradually decreases with the increase of WC content, and the wear rate of the coating is also reduced after remelting, which shows that remelting greatly improves the high-temperature wear resistance of the coating, but the effect of remelting gradually decreases with the increase of WC content.

[0068] The above-described embodiments only express several preferred embodiments of the present application, and the description is relatively specific and detailed, but is not used to limit the present application. It should be noted that the present application can also have various changes and modifications for those skilled in the art, and any modification, equivalent replacement, improvement, etc. made within the concept and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a modified cobalt-based plasma cladding coating, characterized in that, Includes the following steps: Step 1): Tungsten carbide and Stellite alloy are mixed and ball-milled to obtain a mixed powder; the Stellite alloy is a cobalt-based alloy of Stellite 21. Step 2): After drying the mixed powder, a coating is prepared by plasma cladding of the mixed powder onto the surface of the substrate. Step 3): Plasma remelting is performed on the coating obtained in Step 2) to obtain a modified cobalt-based plasma cladding coating.

2. The method for preparing the modified cobalt-based plasma cladding coating according to claim 1, characterized in that, Step 1) The tungsten carbide content accounts for 10%-40% of the total mass of the mixed powder.

3. The method for preparing the modified cobalt-based plasma cladding coating according to claim 1, characterized in that, Step 2) The substrate plate is Q235 steel.

4. The method for preparing the modified cobalt-based plasma cladding coating according to claim 1, characterized in that, Step 2) The plasma cladding process parameters are: welding current 100 A, weld spacing 2.5 mm, and travel speed 2.0-2.5 mm / s.

5. The method for preparing the modified cobalt-based plasma cladding coating according to claim 1, characterized in that, Step 3) The plasma remelting process parameters are: welding current 100 A, weld spacing 2.5 mm, and travel speed 2.0-2.5 mm / s.

6. The modified cobalt-based plasma cladding coating prepared by the method according to any one of claims 1-5.

7. The application of the modified cobalt-based plasma cladding coating according to claim 6 in the wear-resistant coating of the inner layer of an ore crusher.

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