In this paper, the laser cladding is created by using Co50 powder and TiC mixture, covering a H13 hot-working steel substrate. The samples are analyzed by the hardness test, XRD, SEM, and friction test to identify the forming phases, microhardness distribution, and wear-resistant characteristics. The results indicated that hardness reduces from the coating zone to the substrate, achieving the highest value at the coating zone. Increasing the content of TiC results in improving the coating hardness. The coatings with 10%–20% TiC show high-quality surface morphology and macrograph. With 30% TiC, the hardness obtains a higher hardness, but the surface appears to crack. The microstructures of the coatings present a well-mixed and well-distribution of the TiC particle on the Co matrix. The friction coefficient of H13 steel and Co50 coating reaches the maximum value when the load is 50 N and mostly decreases with the increase in the load. The wear rates of H13 steel and Co50 coatings mainly increase with the increase in the load. The temperature has a greater influence on the friction coefficient of the Co50 coating. However, the temperature has a small effect on the friction coefficient of the 20% TiC coating. The wear resistance of 20% TiC coating is higher than that of H13 steel, Co50 coating, and 10% TiC composite coating. At room temperature, the wear mechanism of the coating is mainly brittle spalling, adhesive wear, and ploughing. At 700°C, the wear mechanism is mostly oxidation wear and fatigue wear. After laser cladding, the service life of the coated surface could be greatly improved. The Co + 20% TiC coating has high hardness and wear resistance.
Most machinery failures are caused not by fractures but by wear and damage of friction surfaces in dynamic joints. More than half of the fuel used to run cars, locomotives, and other vehicles is essential to overcome the resistance caused by friction in the engine parts. Similarly, the process of using hot-work mold steels requires the surface must have the same strength and ductility, especially resistance to wear and heat fatigue at high temperatures. Currently, there are many advanced methods of improving surface quality that have been applied, such as carburizing, nitriding, and nitrocarburizing. In general, the harder the material is, the more the brittleness. Researchers are trying to find an ideal material that has both high hardness and high thermal and flexural strength. The machining methods such as milling, lathing, electrical discharge machining, and electroplating change the structure and physical and mechanical features of the surface layers. Recently, surface modification technologies are rapidly developed and applied to create a hard surface while still preserving the flexibility of the substrate. One of those techniques is coating the surface with high hardness and small abrasion coefficient on materials with high flexural strength.
Friction abrasion is a complex process, influenced by many factors. Especially at high temperatures, in addition to the oxygen process, the hardness and durability will be significantly reduced, and thermal expansion will change the organization of the coating. These phenomena are complex but common forms of damage [
In recent years, laser cladding (LC) method has been considered as an advanced material surface modification method, being developed at rapid speed. LC technology is proved to be useful in repairing and restoring the worn surfaces, especially surfaces with a large size [
Co-based alloy has excellent high-temperature performance, high-temperature wear resistance, high-temperature corrosion resistance, good thermal strength, and cold and hot fatigue performance. In addition, it has good thermal conductivity and low thermal expansion coefficient and good performance in shock resistance, creep resistance, wear resistance, and corrosion resistance. It still has good oxidation resistance and abrasion resistance above 600°C, still maintaining a high hardness at 800°C, and having a good antioxidation performance at 1080°C, which are very suitable for hot work of die steel. Xiao-hong et al. and other studies have shown that the H13 hot-work die steel surface after laser cladding Co-based alloy significantly improves the high-temperature hardness and thermal fatigue resistance of the die [
Nowadays, a higher quality is required for the function of coatings, and normally, a single material cannot meet. Recently, the addition of WC, B4C, SiC, Cr2C3, TiN, and other ceramic particles to the Co-based alloy can change the structure of the Co-based alloy and significantly improve the performance of the coating. Zhiyuan et al. reported a cladding Co-based alloy coating and TiN/Co-based composite coating on the surface of low-carbon steel. The results show that TiN has a significant improvement effect on the structure of the cladding layer, which promotes the refinement of its structure, and the dendrite is equiaxed. Crystal transformation can also significantly improve the microhardness and wear resistance of Co-based alloy coatings [
Among carbide ceramic particles, TiC has excellent comprehensive properties with high hardness (3200 HV), good thermal stability, a high melting point of 3150°C, and good resistance to high-temperature oxidation. In addition, TiC has a small coefficient of thermal expansion, good dimensional stability, high elastic modulus, stable thermodynamic properties, and easy dispersion. It has a broad application prospect of wear-resistant ceramic-reinforced phase, and it has been widely used in the fields of wear resistance and high-temperature resistance and has been widely concerned by the material science circle [
Compared with WC, TiC has a lighter weight and higher hardness. Emamian et al. have shown that TiC has a better effect than WC as a reinforcement and can obtain a higher wear resistance [
In order to obtain a high-quality coating, the ratio of the liquid phase to the ceramic phase in the coating should be controlled first. Gao et al. studied the TiC/Ni laser cladding layer on the surface of titanium alloy. The results showed that TiC- and Ni-based alloy powders were laser cladding at a ratio of 1 : 3 (vol.%) to obtain a denser structure, with no pores and cracks. TiC/Ni-based coating hardness is 3 times that of the substrate, and the friction coefficient of the laser cladding layer increases with decreasing environmental pressure [
The way of adding carbide ceramic reinforcing particles in the composite coating is divided into two types: external addition method and in situ self-generation method. Therefore, there are generally two ways to prepare metal-based ceramic composite coatings: adding ceramic reinforcement and in situ ceramic reinforcement. The most difficult problem is the interface problem between the external ceramic phase and the base metal: due to the large difference in thermal physical parameters between the external ceramic phase and the base metal, and there is an obvious interface, the particles are often oxidized and burned or melted and decomposed during the cladding process. It is easy to cause cracks in the coating and the loss of the reinforcing phase and the formation of the brittle phase in the coating, which greatly affects the application of this technology in actual production. In addition, the interface between the external ceramic phase particles and the metal matrix will form undesirable reactants and deposits, making the interface a weak interface with low strength and toughness. The reinforced particles are often susceptible to contamination during processing, which can easily lead to poor wettability of the particles and the matrix and low binding ability, thereby damaging the mechanical properties of the composite material. Many scholars have conducted a lot of research on this problem in order to solve or alleviate the cracking of the coating and have made great progress, but there has been no report on applying this technology to industrial production, and most are still in the laboratory research stage.
The carbide ceramic particle addition method is generally to precoat the reinforcement particles on the surface of the desired reinforcing substrate or mix it with the alloy powder to form the desired spray material. Laser and other heat sources are used to heat and melt the precoating or spraying powder so that the reinforcement particles enter the metal matrix to strengthen the substrate surface to form a metal matrix composite layer. The reinforcing particles are allowed to enter the surface of the metal matrix to strengthen the substrate and form a metal matrix composite layer. According to the temperature of the process, it can be divided into a liquid-phase process and a solid-phase process. Previous research reports on the method of adding particles are still rare, but because of the good effect of the added particles on the refinement and performance of the cladding layer, it has attracted more and more attention. A study by Huang et al. has shown that compared with in situ precipitation, the additive method is more controllable and overcomes the uncertainty and difficulty in the number and size of particles generated by the in situ precipitation method. The refinement of the original austenite grains and the later processing process both play a role [
In addition, the added particles are used as nucleation particles to provide a large number of dispersed particles to promote heterogeneous nucleation. During the solidification and rolling deformation of the molten steel, the structure of the steel material can be refined. You-Wei et al. studied the influence of chemical composition on the structure and properties of TiCp/Fe in situ composites and pointed out that C is a key factor affecting the growth of crystal nuclei [
The method of the mechanical application of ceramic particles is generally to directly add the ceramic phase to the laser melting pool, or the ceramic phase is first made into a mechanically mixed powder or coated powder with the metal powder and then laser cladding. The coated powder is most widely used in Co-coated WC and Ni-coated WC. During laser cladding, the core material is protected by the coating material, which can reduce or prevent the burning of the core material and improve the coating performance. The coated powder is significantly different from the mechanically mixed powder made from powders with different components. The single particles in the powder are composed of two or more solid-phase materials with different compositions and have obvious phase interfaces, and the mechanical components between the phase components are generally mechanical. These aspects will lead to coating cracking or peeling damage during the application process [
This paper focuses on the wear resistance and hardness of Co-based alloy coatings and TiC/Co-based composite coatings at both room and high-temperature conditions. The effects of different TiC contents, loads, rotation speeds, and temperatures on the dry sliding friction and wear properties of TiC particle-reinforced Co-based coatings were studied. Through analysis of wear morphology, microstructure, and high-temperature dry friction and wear properties, the mechanism of high-temperature friction and wear was discussed to provide a reference for the practical applications.
The experiment selected H13 steel, with some main components shown in Table
Chemical composition of the H13 steel sample using in the experiment (weight).
Element | C | Si | Mn | Cr | Mo | V | Fe |
---|---|---|---|---|---|---|---|
% | 0.43 | 1.17 | 0.48 | 4.79 | 1.38 | 0.94 | Bal. |
Chemical composition of Co powder using in the experiment (weight).
Element | C | W | Si | B | Cr | Mo | Fe | Co | Ni |
---|---|---|---|---|---|---|---|---|---|
% | 0.6 | 3.0 | 3.5 | 2.25 | 20.0 | 5.1 | 5.0 | Bal. | 14.0 |
Laser cladding Co50 coating and Co50/TiC composite coating are made at Kunming University of Science and Technology. LC machine is the type of GS-6000 TFL transverse-flow CO2 with the main parameters: the laser power 3.3–4.2 kW, scanning speed 350–500 mm/min, the distance from the laser head to the based steel surface 50 mm, and flow of Argon air protective coating 8 L/h; the remaining technology parameters are given in Table
Technical parameters and samples surface of the LC method applied in the experiment.
Sample | Co50 (wt.%) | TiC (wt.%) | Laser power | Scanning speed | Laser power density |
---|---|---|---|---|---|
S0 | 100 | 0 | 3.3 | 400 | 12.57 |
S1 | 90 | 10 | 3.6 | 500 | 10.97 |
S2 | 80 | 20 | 3.9 | 350 | 16.98 |
S3 | 70 | 30 | 4.2 | 350 | 18.29 |
The experiment chose a hardness testing machine type HMV-WIN, with load 1.961 N (HV0.2), and stopped time is 15 s to test. A bonding zone is selected between the coating and H13 steel as the origin, and then, the samples are measured hardness above and below the origin, in which the top origin is a positive value and vice versa. Wear-by-friction testing machine is used at high-temperature-type MMU-5G to study the wear resistance of coatings from room temperature to high-temperature with pin-on-disc wear of friction pairs (Figure
Pin-on-disc wear of friction pairs and friction testing samples: (a) MMU-5G high-temperature wear tester and its principle; (b) upper specimen; (c) friction pair.
The error range of testing force is ±1%; therefore, the error range of the CoF which is the ratio between the friction force and the normal force is ±2%. Friction torque: the maximum friction torque is 5 N·m; the relative error of the friction torque indication is ±2%. Spindle speed-changing system: single-stage transmission system 0.1–2000 r/min; spindle speed error ±1%. Temperature: the temperature of the cylindrical heating furnace is ∼1100°C; 2 K-type thermocouples (with a cylindrical heating furnace); temperature control accuracy =
In this test, the force experiment value is chosen as 98 N, the speed is 200 r/min, wear time is 2 h, and run out 3 min. The upper sample employed H13 steel, Co-based coating, and TiC/Co-based composite coating with
The friction coefficient is applied as the index of friction and wear performance, and its value is read directly by the testing machine. The upper sample uses the amount of wear as the wear performance index. Relative wear resistance expresses the comparison of the wear resistance of H13 steel, Co-based coating, and TiC/Co
The accuracy of the wear rate mainly depends on the accuracy of the accuracy of measuring
The CoF can be read directly by the tester. By measuring the normal force and frictional force, the machine can calculate the CoF. The normal force is a certain force and is set up with 98 N. Figure
Figure
Screen-display of friction and wear machine testing system.
Figure
Appearances of hardness marks.
Cross section microhardness distribution of the laser cladding.
Effect of the load on the friction coefficient at the speed of 200 r/min: (a) friction coefficient of S0 coating and H13 steel; (b) the average friction coefficient.
The laser cladded region consists of
Microstructure with different shapes of TiC.
S0 coating | S1 coating | S2 coating | S3 coating | |
---|---|---|---|---|
Upper part | ||||
Middle part | ||||
Bottom part |
The hardness of the S0 coating is improved because of the appearance of a high hardness Cr1.12Ni2.88 phase. This phase is well dispersed on the matrix of
S1, S2, and S3 coatings have a higher hardness than S0. As increasing TiC content, the hardness of the coatings increases. The main reason is that TiC which has extremely high hardness is increased, and the newly formed phases have higher hardness and melting points. Additionally, the Ti and C atoms themselves react to form a new TiC with a better structure than before. In addition, the coatings also have nonmelting TiCs and partially melting TiC that retains the main characteristics of carbides. They are fine particles and dispersed uniformly, improving the strength and the hardness of this coating [
The hardness changes and uneven distribution of S1, S2, and S3 coatings appear due to the existence of a large number of incompletely dissolved TiC particles and in situ TiC. During the LC process, the original TiC particles were burnt, contaminated by the interface, and the melting phase of the enhanced phase was deficient. The TiC particles in situ were generated by an in situ reaction, thus solving the problems of enhanced phase thermal stability and interface. When testing the hardness, the hardness value of in situ TiC particles is higher than that of other regions, which is the main reason for the uneven distribution of microhardness of the coating.
The specific laser power density corresponding to each coating is shown in Table
The existence of the coating compounds morphology and macrograph of the coating from the transverse cross section with different component ratios is shown in Table
The surface morphology and macrograph of the coating from the transverse cross section of coatings.
Sample | Surface morphology | Macrograph of the coating from the transverse cross section |
---|---|---|
S0 | ||
S1 | ||
S2 | ||
S3 |
Table
In addition, Table
Figure
Effect of load on the (a) wear weight losses and (b) wear rates.
When the load is less than 100 N, the friction coefficients of the two materials are more different than that of more than 100 N, and the friction coefficient of H13 steel is higher than S0 coating. When a load of H13 steel and S0 coating is 100 N, the friction coefficient is relatively stable, as shown in Figure
Figure
Effect of sliding velocity on the friction coefficient at the load of 100 N: (a) S0 coating and H13 steel; (b) the average friction coefficient.
Figure
Effect of sliding velocity on (a) wear losses and (b) wear rates.
The surface deformation and temperature rise during friction lead to promoting the formation of the surface film. Due to the existence of the surface film, the atomic or ionic bonding force between the friction pairs is replaced by the weaker Van der Waals force. The impact of reducing surface molecular forces reduces the effect of surface molecular forces. In addition, as the mechanical strength of the surface film is lower than that of the base material, shear resistance decreases, and the friction coefficient also decreases. As the sliding speed enhances, the surface film is strongly destroyed, the surface roughness and the wear debris increase, and the friction coefficient also rises.
Figure
Friction coefficients of S0 coating: (a) From room temperature to 700°c and (b) the average friction coefficient
When the sliding speed is less than 150 r/min, the temperature of the surface of the friction pair is not high, and the friction surfaces are not softened. In addition, the surface film will be generated to maintain the friction surface. At lower sliding speeds, the shear and furrow forces are smaller; therefore, the wear rate is lower, as shown in Figure
The improvement in wear resistance of S0 coating is a result of the appearance of strengthening phases such as Cr1.12Ni2.88 which are uniformly distributed in the coating and slows down the wear process of the coating. In addition, the solid solution strengthening and fine-grain strengthening make the microhardness improve and therefore enhance the wear resistance. S0 coating consists of
The effect of temperature on the coefficient of friction of the S0 coating is shown in Figure
Due to the increase in temperature and the effect of frictional heat, the temperature of the friction surface goes up, which often causes the oxidation of the friction surface. At lower temperatures, the presence of an oxide film on the friction surface of the friction pair is beneficial to prevent adhesive wear. As the temperature increases, severe oxidation occurs, and oxidative wear and shedding oxide act as abrasives, which produce secondary wear on the friction pair and reduce the wear performance of the friction pair. If the friction pair is softened, it may cause a sudden change in tribological properties.
Figure
Worn morphologies of the S0 cladding at different temperatures: (a) room temperature; (b) 200°C; (c) 300°C; (d) 400°C; (e) 500°C; (f) 600°C; (g) 700°C; (h) 700°C with high magnification.
The analysis of the wear of the S0 sample is shown in Figure
Effect of temperature on the wear weight losses of S0 coating.
Figure
Friction coefficients of S2 coating at various temperatures: (a) friction coefficient from room temperature to 700°C; (b) average coefficient.
Figure
Worn morphologies of the S2 cladding at different temperatures: (a) room temperature; (b) 200°C; (c) 300°C; (d) 400°C; (e) 500°C; (f) 600°C; (g) 700°C; (h) 700°C with high magnification.
The analysis of the wear weight losses of the lower sample is shown in Figures
Effect of temperature on the wear weight losses of lower specimen.
The wear morphologies of lower specimen at different temperatures: (a) room temperature; (b) 200°C; (c) 300°C; (d) 400°C; (e) 500°C; (f) 600°C; (g) 700°C; (h) 800°C.
Friction coefficient and worn morphology of S2 coating at 800°C.
The bonding between the coating and the substrate plays an important role in the mechanical characteristics of the samples. Induced residual stress is an important factor that strongly affects the mechanical properties of the cladding layer. Especially, too high-induced residual stress may cause the microcrack or fracture during working [
Because S3 coating is not well combined with H13 substrate, the test of the friction and wear performance only selects H13 steel and S0, S1, and S2 samples. The maximum working temperature of hot-work tool steel is 700°C, so the maximum testing temperature is chosen as 700°C. In a certain working environment, the stability of the laser cladding layer decides its performance. Therefore, research on the microstructure and properties of the cladding layer at high temperatures is significantly important.
Figure
Friction coefficient vs. time curves of H13 steel and coatings at room temperature and 700°C: (a) H13 steel; (b) S0 coating; (c) S1 coating; (d) S2 coating.
Under the same test conditions, the friction coefficient of S2 coating is very stable. This value is rather high, indicating that, after adding TiC, the wear resistance of the coating is significantly improved. The wear resistance of S0 coating is mainly based on the strengthening effect of the solid solution and the newly Cr1.12Ni2.88 reinforcement phase. They are uniformly distributed in the coating, having the effect of increasing durability. Besides, their fine microstructure also helps improve the hardness of S0. The hardness of the S0 sample is also as high as the other samples. However, the microstructure of Co50 alloy is characterized by a eutectic structure existing in the form of networks [
Moreover, during the decomposition process of TiC particles, they could combine with other molten elements to product perinatal dendrite solid solution [
In addition, the S2 sample does not show plastic deformation, and its wear mechanism is mainly the adhesion type. In addition, the hardness of S2 is higher than S0, minimizing the surface deformation and thus delaying the time of cracking formation as well as its development speed. These effects result in reducing the risk of cracks failure. The friction coefficient of S2 was stable with a quite high value. Candel et al. [
By adding an appropriate amount of TiC, the wear resistance of the coating has been majorly improved. After laser cladding treatment, the hardness of the coating surface increased, which can reduce the deformation of the coating surface under the force, delay the crack initiation time, and reduce the expansion speed.
In order to further analyze the friction and wear properties of the coating, Table
Wear weight losses of the samples in the friction-wear test at room temperature and 700°C.
Condition | Sample | Wear weight loss (mg) | |||
---|---|---|---|---|---|
H13 steel | S0 | S1 | S2 | ||
Room temperature | Coating | 27.8 | 23.9 | 19.6 | 18.0 |
Cr12MoV | 40.6 | 4.3 | 8.8 | 14.3 | |
700°C | Coating | 3.0 | 5.5 | 5.2 | 5.0 |
Cr12MoV | 4989.7 | 65.1 | 273.0 | 360.5 |
At 700°C, the wear weight loss of H13 steel is only 3.0 mg, which is less than that of S0, S1, and S2 coatings. This is because the peeled metal chips are hot-pressed and could be welded to form larger pieces during the wear process. Moreover, abrasive particles and exfoliated metal will also adhere to the coating surface under stress. This also results in the greatest wear resistance on friction parts of H13 steel. At the same conditions, the wear weight loss of S0, S1, and S2 coatings is about 5.0 mg, while the wear weight losses of S1 and S2 friction parts are much 4 and 6 times larger than that of S0 friction parts. Therefore, it can be concluded that S2 has minimal wear weight loss, and the wear resistance is the best.
From the above analysis, surface modification of H13 steel by laser cladding can highly improve its wear resistance. This is closely related to the hardness, density, and uniformity of the structure and the melting point of the coating. It is generally believed that the main factors affecting the mechanical properties of metal materials are plasticity, hardness, and tensile strength, in which the wear resistance of the surface has a roughly linear relationship with its hardness. The analysis of the weight loss under various conditions shows that the higher the hardness of the material, the smaller the weight loss. S1 and S2 have a higher wear resistance. However, since the strengthening of carbides is not effective as significant as other second-phase particles, therefore, their weight loss is almost the same.
The wear resistance of S1 composite coating is higher than that of S0 coating. The main reason is that, during the process of laser cladding, TiC which melts and precipitates is formed with the matrix elements to generate new carbides. The unmelted or semimelted TiC particles are diffusely distributed in the cladding area and play a hard reinforcement role. S1 coating is composed of unmelted TiC, TiC in situ, TiCo3, Cr2Ni3, and Cr-Ni-Fe-C solid solution with a fine eutectic structure. In addition, the hardness of S1 composite coating is higher than that of S0 coating, and the carbides are finer distributed. In the fine dendrite and eutectic structure, TiC plays as the core-shaped radial carbide which enhances the bonding between the coating structures; thereby, its wear resistance is effectively upgraded.
S2 coating has better antiwear performance as their TiC content is higher. When the S2 coating and the friction part are facing each other, as S2 is mainly composed of carbides, the friction parts are easily embedded in the softer
Secondly, the hardness of the S2 sample is higher than S1 one. In the wear process, increasing the coating hardness can reduce the deformation of the coating surface, decrease the propagation speed, postpone crack initiation time, and delay the chance in crack nucleation. However, the friction coefficient of the S2 coating is higher than S1. It may be due to the existence of hard phases in S2. Under high stress for a long time, the massive hard phase flakes and peels; thus, wear resistance is reduced [
Figures
Worn morphologies of samples at room temperature: (a) H13 steel; (b) S0 coating; (c) S1 coating; (d) S2 coating.
Worn morphologies of samples at 700°C: (a) H13 steel; (b) S0 coating; (c) S1 coating; (d) S2 coating.
Worn morphologies of S0 and S2 coatings at room temperature and 700°C: (a) polishing plastic deformation in S0 coating at room temperature; (b) solid oxide compact layer in S0 coating at 700°C; (c) compound layer removal in S2 coating at room temperature; (d) pitting corrosion in S2 coating at 700°C.
At 700°C, the pits on the worn surface are deep and small, and scratches with raised edges are flattened, as shown in Figure
These above experiments indicate that the S0, S1, and S2 coatings significantly improve the wear resistance of the H13 steel substrate. This H13 steel surface has a lower hardness and poor wear resistance of the substrate. The surface is prone to plastic deformation or even cracks due to severe extrusion. At the same time, the peeling metal chips will also be hot-pressed and welded to form larger abrasives particles during the wear process. Under stress, these larger pieces and abrasive particles without sharp edges produce severe plastic deformation and obvious furrows on the wear surface [
The existence of the coating compounds is studied by using the XRD method. At room temperature, from S0 to S2 samples with different amounts of TiC in the coating, some phases appear such as
XRD patterns of H13 steel and S0, S1, and S2 coatings (a) at room temperature and (b) 700°C.
In order to further analyze the wear mechanism of the coating, Figure
The reason for these phenomena is that, as the temperature rises, the oxidation of the surface sample is intensified. The forming oxide film avoids adhesive wear caused by metal contact and protects the worn surface. However, the oxide film is often brittle and extremely prone to crack initiation and fatigue crack growth under external force; therefore, it is easy to produce fatigue spalling [
After adding TiC, the strength of the microstructures of S1 and S2 is improved, the grains are refined, and various defects in the coating are reduced. In addition, TiC which has a much higher hardness than the matrix and disperse in the ductile matrix enhances the bonding between phases. When the coating is worn, these TiC particles have an extremely strong resistance to deformation. On the one hand, they can support the load, play a uniform load, and reduce friction and wear, so the friction coefficient changes little and the wear resistance is correspondingly improved. On the other hand, they protect the substrate, and thereby, the wear resistance of S1 and S2 coatings with TiC particles is significantly improved. In addition, in the laser cladding layer, some TiC particles are not dissolved; however, there are also some TiC pyrolysis reactions that generate TiC in situ. TiC in situ forms a densely distributed TiC phase on the substrate surface that is tightly bound with the substrate. The modified layer has a much higher hardness than the substrate, which greatly improves the wear resistance [
The hardness reduces from the coating to the substrate, reaching the highest value at the coating zone. In the HAZ, the hardness reduces rapidly. Increasing the content of TiC leads to improving the hardness of the coating. The coatings with 10%–20% TiC present high-quality surface morphology and macrograph. With 30% TiC, the hardness reaches a higher hardness but the surface appears to crack. The microstructures of these coatings indicate a well-mixed and well-distribution of the TiC particle on the Co matrix. The friction coefficient of H13 steel and Co50 coating reaches the maximum value when the load is 50 N and mostly decreases with the increase in the load. The wear rates of H13 steel and Co50 coatings mainly increase with the increase in the load. The temperature has a greater influence on the friction coefficient of the Co50 coating. However, the temperature has a small effect on the friction coefficient of the 20% TiC coating. The wear resistance of 20% TiC coating is higher than that of H13 steel, Co50 coating, and 10% TiC composite coating. At room temperature, the wear mechanism of the coating is mainly brittle spalling, adhesive wear, and ploughing. At 700°C, the wear mechanism is mainly oxidation wear and fatigue wear. After laser cladding, the service life of the coated surface could be greatly improved.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors acknowledge HCMC University of Technology and Education and Kunming University of Technology. They gave them an opportunity to join their team and access the laboratory and research machines. Without their appreciated support, it would not be possible to conduct this research.