In order to enhance the high-temperature wear resistance of the nickel-base alloy, the electron beam is used to clad the WC-CoCr composite coating on the Inconel 617 surface. A six-factor and three-level orthogonal experiment is designed using Minitab software with scanning beam current, frequency, high voltage, beam spot diameter, offset sweep amplitude, and scanning speed as variables, and the variance and range of the test results are analyzed. The optimal cladding process parameters were determined according to the influence of various factors on the quality characteristics of the cladding layer. The wear behavior at 200°C, 600°C, and 1000°C and microstructure and phase composition of coating before and after electron beam treatment were tested. The results show that the ion exchange between the coating and the substrate is carried out after electron beam treatment. The WC, CoCr, (Fe, Ni)C6, Fe3W3C phase, and solid solution of
Inconel 617 alloy is a nickel-base superalloy developed in early 1960s as an advanced alloy for high temperature, high strength, oxidation resistance, and corrosion resistance and used in gas turbine engines [
However, for the electron beam cladding process, the cladding parameters are directly related to the quality of the cladding layer, which then directly affect the coating properties. The main parameters of electron beam cladding are scanning beam current, frequency, high voltage, beam spot diameter, offset sweep amplitude, and scanning speed [
The size of Inconel 617 is 50 × 30 × 10 mm, and the chemical composition is shown in Table
Chemical composition of Inconel 617 alloy (wt.%).
Ni | Cr | Co | Mo | Al | C | Fe | Mn | Si | S | Ti | Cu |
---|---|---|---|---|---|---|---|---|---|---|---|
Balance | 22 | 12.5 | 9 | 1.2 | 0.07 | 1.5 | 0.5 | 0.5 | 0.008 | 0.3 | 0.2 |
The cladding experiment is carried out with SEB(j)6/60/40/30 electron beam machining integrated system. The purpose of the experiment is to optimize the parameters of electron beam processing so that the performance of the cladding layer can be improved. Optimization experiment is based on Minitab software to design different electron beam processing parameters for cladding of WC-CoCr on the surface of Inconel 617 substrate. The main process parameters that affect the quality of cladding layer when the vacuum level and machining distance were fixed are scanning beam, frequency, high voltage, beam spot diameter, and partial scanning amplitude. This experiment chooses L9(36) to design the orthogonal experiment. These six factors are recorded as
Orthogonal experimental factor level.
Level | Factor | |||||
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| |
1 | 80 | 500 | 50 | 8 | 2 | 800 |
2 | 83 | 550 | 55 | 9 | 4 | 1000 |
3 | 85 | 600 | 60 | 10 | 6 | 1200 |
The experimental design table is selected according to the factor level of Table
Cladding orthogonal experiment of WC-CoCr.
Number | Factor | |||||
---|---|---|---|---|---|---|
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|
|
|
|
| |
1 | 80 | 500 | 50 | 8 | 2 | 800 |
2 | 80 | 500 | 50 | 8 | 4 | 1000 |
3 | 80 | 500 | 50 | 8 | 6 | 1200 |
4 | 80 | 550 | 55 | 9 | 2 | 800 |
5 | 80 | 550 | 55 | 9 | 4 | 1000 |
6 | 80 | 550 | 55 | 9 | 6 | 1200 |
7 | 80 | 600 | 60 | 10 | 2 | 800 |
8 | 80 | 600 | 60 | 10 | 4 | 1000 |
9 | 80 | 600 | 60 | 10 | 6 | 1200 |
10 | 83 | 500 | 55 | 10 | 2 | 1000 |
11 | 83 | 500 | 55 | 10 | 4 | 1200 |
12 | 83 | 500 | 55 | 10 | 6 | 800 |
13 | 83 | 550 | 60 | 8 | 2 | 1000 |
14 | 83 | 550 | 60 | 8 | 4 | 1200 |
15 | 83 | 550 | 60 | 8 | 6 | 800 |
16 | 83 | 600 | 50 | 9 | 2 | 1000 |
17 | 83 | 600 | 50 | 9 | 4 | 1200 |
18 | 83 | 600 | 50 | 9 | 6 | 800 |
19 | 85 | 500 | 60 | 9 | 2 | 1200 |
20 | 85 | 500 | 60 | 9 | 4 | 800 |
21 | 85 | 500 | 60 | 9 | 6 | 1000 |
22 | 85 | 550 | 50 | 10 | 2 | 1200 |
23 | 85 | 550 | 50 | 10 | 4 | 800 |
24 | 85 | 550 | 50 | 10 | 6 | 1000 |
25 | 85 | 600 | 55 | 8 | 2 | 1200 |
26 | 85 | 600 | 55 | 8 | 4 | 800 |
27 | 85 | 600 | 55 | 8 | 6 | 1000 |
Electron beam scanning cladding experiments were carried out for each of the experimental design schemes in Table
WC-CoCr orthogonal experiment results.
No. | Factor | Quality characteristic | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
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Number of scores per item | ||||
Surface quality | Cladding phenomenon | Microstructure | Total score | |||||||
1 | 80 | 500 | 50 | 8 | 2 | 800 | 8.0 | 7.0 | 7.0 | 7.4 |
2 | 80 | 500 | 50 | 8 | 4 | 1000 | 9.0 | 8.5 | 8.5 | 8.7 |
3 | 80 | 500 | 50 | 8 | 6 | 1200 | 8.5 | 9.0 | 8.5 | 8.6 |
4 | 80 | 550 | 55 | 9 | 2 | 800 | 8.0 | 7.5 | 8.0 | 7.9 |
5 | 80 | 550 | 55 | 9 | 4 | 1000 | 8.0 | 8.0 | 8.5 | 8.2 |
6 | 80 | 550 | 55 | 9 | 6 | 1200 | 7.5 | 7.0 | 7.0 | 7.2 |
7 | 80 | 600 | 60 | 10 | 2 | 800 | 7.0 | 6.0 | 7.0 | 6.8 |
8 | 80 | 600 | 60 | 10 | 4 | 1000 | 8.5 | 7.0 | 7.5 | 7.8 |
9 | 80 | 600 | 60 | 10 | 6 | 1200 | 9.0 | 7.5 | 8.5 | 8.5 |
10 | 83 | 500 | 55 | 10 | 2 | 1000 | 9.0 | 8.0 | 8.0 | 8.4 |
11 | 83 | 500 | 55 | 10 | 4 | 1200 | 8.5 | 7.5 | 9.0 | 8.5 |
12 | 83 | 500 | 55 | 10 | 6 | 800 | 8.5 | 7.0 | 7.5 | 7.8 |
13 | 83 | 550 | 60 | 8 | 2 | 1000 | 9.0 | 8.5 | 8.5 | 8.7 |
14 | 83 | 550 | 60 | 8 | 4 | 1200 | 8.0 | 8.0 | 8.5 | 8.2 |
15 | 83 | 550 | 60 | 8 | 6 | 800 | 8.5 | 7.5 | 7.5 | 7.9 |
16 | 83 | 600 | 50 | 9 | 2 | 1000 | 9.5 | 8.0 | 8.5 | 8.8 |
17 | 83 | 600 | 50 | 9 | 4 | 1200 | 7.5 | 7.5 | 7.5 | 7.5 |
18 | 83 | 600 | 50 | 9 | 6 | 800 | 8.5 | 8.0 | 7.5 | 8.0 |
19 | 85 | 500 | 60 | 9 | 2 | 1200 | 9.0 | 8.5 | 8.5 | 8.7 |
20 | 85 | 500 | 60 | 9 | 4 | 800 | 9.5 | 8.0 | 9.0 | 9.0 |
21 | 85 | 500 | 60 | 9 | 6 | 1000 | 7.5 | 8.0 | 8.0 | 7.8 |
22 | 85 | 550 | 50 | 10 | 2 | 1200 | 8.5 | 7.5 | 9.5 | 8.7 |
23 | 85 | 550 | 50 | 10 | 4 | 800 | 8.5 | 7.0 | 8.0 | 8.0 |
24 | 85 | 550 | 50 | 10 | 6 | 1000 | 9.5 | 9.0 | 8.5 | 9.0 |
25 | 85 | 600 | 55 | 8 | 2 | 1200 | 9.0 | 8.5 | 8.0 | 8.5 |
26 | 85 | 600 | 55 | 8 | 4 | 800 | 9.0 | 9.5 | 9.0 | 9.1 |
27 | 85 | 600 | 55 | 8 | 6 | 1000 | 9.5 | 9.0 | 8.5 | 9.0 |
The wear resistance of cladding samples was studied by using MPX-2000 vertical universal friction and wear tester. The test was carried out with a load of 20 N and a rotational speed of 200 r/min, and the test distance was 1000 meters (the radius of the sliding path was 5 mm). The wear weight loss is calculated using the equipment AR2130 electronic balance. The microhardness of the cross section between cladding and substrate is measured using HV-1000 microhardness meter. The section structure and element composition of WC-CoCr cladding layer are observed using Quanta 450 FEG field emission scanning electron microscope. The modified phase of the cladding is determined by D8ADVANCE X-ray diffractometer, and the ray source is Cu-K
The results of the range analysis of the quality characteristics of the cladding layer are detailed in Table
Calculation table of range analysis test results.
Number |
|
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|
|
|
|
---|---|---|---|---|---|---|
I |
7.833 | 8.259 | 8.241 | 8.444 | 8.130 | 7.907 |
II |
8.130 | 8.130 | 8.241 | 8.074 | 8.259 | 8.444 |
III |
8.593 | 8.167 | 8.074 | 8.037 | 8.168 | 8.204 |
R |
0.759 | 0.130 | 0.167 | 0.407 | 0.131 | 0.537 |
Trend chart of correlation between factors and quality characteristic values.
The range analysis does not distinguish the data fluctuation caused by the test error from the data fluctuation caused by the change of the test conditions nor does it examine whether the effect of various factors on the test results (indicators) is significant. So we do not know how accurate the analysis is. To make up the shortcomings of the above intuitive analysis, the following uses the method of variance analysis to further estimate the magnitude of the error and accurately estimate the importance of each factor affecting the test results. The variance analysis results of the cladding quality characteristics are shown in Table
Analysis results of quality characteristics of the WC-CoCr cladding layer.
Source | Free degree |
Sum of squares |
Sum of squares of deviations SS | Mean square MS |
|
|
---|---|---|---|---|---|---|
|
2 | 3.18655 | 2.52519 | 1.26259 | 36.926 | 0.005 |
|
2 | 0.00288 | 0.07630 | 0.03815 | 1.1473 | 0.895 |
|
2 | 0.00672 | 0.11630 | 0.05815 | 1.7912 | 0.845 |
|
2 | 0.17316 | 0.58963 | 0.29481 | 8.6975 | 0.044 |
|
2 | 0.00482 | 0.09852 | 0.04926 | 1.4823 | 0.867 |
|
2 | 0.63675 | 1.12963 | 0.56481 | 16.581 | 0.0227 |
Error | 14 | 0.01641 | 0.47918 | 0.03422 | — | — |
Thus, the mean square Ms can be obtained. The influence trend of each factor on cladding characteristics can be compared from the numerical analysis of Ms. And by comparing the magnitude of Ms value corresponding to each factor, the fluctuation results are in agreement with the range analysis. The
Through the above analysis, taking the quality characteristic value of cladding experiment as the evaluation index, it is concluded that the influence of factors on the test index is in the order of scanning beam current > scanning speed > beam spot diameter > high voltage > deviation sweep amplitude > frequency. The optimized level is scanning current 85 mA, high voltage 60 kV, frequency 600 Hz, beam spot diameter 8 mm, offset scan amplitude 4%, and scanning speed 1000 mm/min. Among the factors of “scanning beam,” “scanning velocity,” and “beam spot diameter,”
Test results.
Visual analysis | Variance analysis | ||||
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Primary and secondary order | Optimal parameter | Highly significant | Notable | Quiet | |
Quality characteristic |
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According to the results of orthogonal experiments, the main parameters that have a significant effect on the coating are electron beam current and electron beam scanning speed. And the electron beam spot diameter also has a certain effect on the coating, which is smaller than that of the first two. Figures
Thickness of the coating with different beam current.
Microstructure of coating cross section with different beam current: (a) 80 mA, (b) 83 mA, and (c) 85 mA.
Thickness of the coating with different scanning speeds.
Microstructure of coating cross section with different scanning speeds: (a) 800 mm/min, (b) 1000 mm/min, and (c) 1200 mm/min.
The effect of electron beam current on the cladding of WC-CoCr coating is as follows: with the increase of beam current, the quality of the coating becomes better. And the thickness of the coating increases and becomes uniform (as shown in Figures
The microstructure of the electron beam cladding WC-CoCr alloy layer after optimizing the parameters is compact, and the cladding layer mainly consists of dendritic crystal and a plurality of eutectic compositions. The microstructure and substrate of the cladding layer were analyzed by EDS. The location of the test area is shown in Figure
SEM diagram of cross section of WC-CoCr coating of electron beam cladding; 1: area 1; 2: area 2.
Element percentage (wt.%).
Area | Ni | Cr | Co | Mo | W | C | Fe | Mn | Si | Al | Ti | Cu |
---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | 46.94 | 5.4 | 10.3 | 7.68 | 16.7 | 9.2 | 1.3 | 0.3 | 0.42 | 0.86 | 0.52 | 0.38 |
2 | 6.88 | 2.8 | 13.2 | 1.2 | 66.8 | 8.52 | 0.3 | 0.1 | — | 0.2 | — | — |
Figure
XRD diffraction pattern of the WC-CoCr cladding layer.
The friction coefficient is mainly related to the roughness of the surface and has nothing to do with the size of the contact surface. It can be seen from Figure
The curve of the friction coefficient varies with time of Inconel 617 alloy matrix and cladding at 200°C, 600°C, and 1000°C.
The friction coefficient of the cladding layer and Inconel 617 alloy decreases with the increase in temperature. This is the result of a combination of two factors: (1) With the increase in temperature, the surface of the cladding layer and Inconel 617 alloy softens, and the friction coefficient increases. (2) In the high-temperature environment, the two materials react with oxygen in the atmosphere and form an oxide film on the surface of the material, which can lubricate the friction between the material surface and SiC, and the friction coefficient becomes smaller. The combined effect of these two factors shows that the softening phenomenon is not obvious at the temperature of 200°C to 600°C, the lubricating effect of oxide film is stronger, and the friction coefficient of Inconel 617 alloy decreases faster than that of cladding layer. Between 600°C and 1000°C, the surface softening of the material is serious, and the friction coefficient decreases steadily.
Figure
Wear rate of Inconel 617 alloy substrate and cladding at different temperatures.
Figure
Wear morphology of Inconel 617 alloy substrate and cladding at different temperatures: (a) 200°C, (b) 600°C, and (c) 1000°C. Cladding at (d) 200°C, (e) 600°C, and (f) 1000°C.
The formed Al2O3 and Cr2O3 oxide films cover the substrate surface and play a certain role in lubrication. Thus, the wear on the surface of the matrix is reduced. However, the high-temperature oxidation resistance of Inconel 617 matrix is better. At 200°C, the oxidation resistance grade of Inconel 617 matrix is complete oxidation resistance. The wear scratches of WC-CoCr coatings at 600°C increased compared with those at 200°C (Figure
The optimum cladding parameters of Inconel 617 surface electron beam cladding WC-CoCr are obtained by orthogonal experiment: scanning beam current 85 mA, frequency 60 Hz, high voltage 60 kV, beam spot diameter 8 mm, scanning amplitude 4%, and scanning speed 1000 mm/min. The effects of these parameters on the quality characteristics of the cladding layer are as follows: scanning beam current, scanning speed, beam spot diameter, high voltage, skew sweep amplitude, and frequency, and scanning beam current is very significant, scanning speed and beam spot diameter are significant, and the rest has no significant effect. Compared with the original sprayed powder, new elements such as Ni, Fe, Mn, and Mo appeared in the cladding layer, and the content of the original elements changed. The metallurgical bonding was realized between the coating and the substrate. The rapid heat quenching effect of electron beam treatment results in the formation of new phases such as WC, CoCr, (Fe, Ni)C6, Fe3W3C, and Co in the cladding layer, in which intermetallic compounds and carbides are distributed in the CoCr matrix, which plays a strengthening role. The wear resistance of the cladding layer was 10.14 times of that of the substrate at 200°C. When the temperature exceeds 600°C, the surface softening phenomenon increases, the lubricant film is strengthened, the friction coefficient decreases, and the friction coefficient of the matrix decreases faster than that of the cladding layer. With the increase in temperature, the wear rate of the cladding layer decreases due to the easy oxidation of the substrate and the wear rate of the cladding layer increases by 2.29 times as much as that of the substrate at 1000°C. At the test temperature, the friction coefficient and wear rate of the cladding layer are lower than that of the substrate, and the wear resistance of the cladding layer is improved.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
This work was financially supported by the Foundation Project of the Guangxi Key Laboratory of Manufacturing System and Advanced Manufacturing Technology (17-259-05-0068) and also supported by the Foundation Project of the State Key Laboratory of Metal Material for Marine Equipment and Application (SKLMEA-K201801).