Call +86 151 8448 3461sales@huirui-laser.com

Research progress of carbide reinforced laser cladding amorphous coatings

November 1, 2024

Arthur Shaw

Adding carbides to coatings can bring many benefits, especially in improving the hardness, wear resistance, corrosion resistance and stability of coatings under high temperature environments. Today’s industry has specific needs to improve the surface performance of materials and extend the service life of materials, especially in specific working environments with harsh environmental conditions such as high temperature, high pressure, corrosion and wear. The addition of carbides to prepare amorphous alloy coatings by laser cladding is a natural choice. This paper reviews the research status of carbide-enhanced laser cladding amorphous coatings at home and abroad, introduces its technical characteristics, and the research progress of carbide-containing cladding layer performance. Finally, the problems existing in laser cladding amorphous alloy coatings are summarized and the future development direction is proposed.
Keywords Laser cladding Amorphous alloy Friction and wear Corrosion resistance Carbide

Material loss of mechanical parts, such as friction and wear, corrosion and oxidation, mainly occurs on the surface of the material, so the surface performance of the parts directly affects the performance and service life of the material. Various corrosions will cause the energy of the material to be lost, reducing the performance and safety of the material. Surface coating preparation has become one of the hot methods to improve the surface performance of materials. In recent years, many scholars have devoted themselves to coating preparation. In many fields, laser cladding is usually performed on the surface of workpieces to improve service life [1]. Laser cladding is a comprehensive physical metallurgical process that is far from equilibrium and is characterized by rapid heating and rapid cooling [2]. A high-energy flux laser beam is used to irradiate a material with specific properties, rapidly heat it to melt it with a thin layer on the surface of the substrate, and rapidly cool it by relying on the rapid heat conduction of the metal body, so that the inherent excellent properties of the cladding material can be maintained and strengthened, thereby preparing a surface coating that can form a good metallurgical bond with the substrate and has a low dilution rate [3,4]. Laser cladding technology is now relatively mature. Compared with other surface treatment technologies, it can significantly improve the wear resistance and corrosion resistance of the metal surface. Laser cladding instantly melts the cladding material and the surface layer of the substrate to form a fusion zone, and obtains a dense cladding layer between the substrate and the coating, which has good mechanical properties. Using laser cladding to repair parts can avoid the defects caused by traditional repair methods [5]. Compared with thermal spraying, it has higher bonding strength, higher thickness and lower porosity. Laser cladding has high energy density and fast solidification and cooling speed of the cladding layer, which makes the heat source act on the substrate and cladding material for a short time, thereby reducing the thermal deformation, internal stress and dilution rate of the material. In addition, higher cladding heating and cooling speed can also inhibit the nucleation and growth of brittle phases and component segregation, and refine the structure, which is conducive to the optimization of wear resistance and corrosion resistance of the coating [6]. In the laser cladding process, the reasonable selection of cladding materials is crucial [7-10]. In recent years, various types of coating technologies have been developed to improve the corrosion resistance of mechanical parts. Amorphous alloys have the properties of both metals and glasses, and are also called metallic glasses [11]. Due to their unique long-range disordered and short-range ordered organizational structure, lack of grain boundaries and dislocations, they have better performance than most traditional materials [12]. As the research progresses, the amorphous phase content in the amorphous composite coating is maintained at a certain proportion. At the same time, the uniformly distributed crystalline phase in the coating can effectively inhibit the generation of cracks, significantly improving the plasticity and toughness of the coating at room temperature. Due to its superior tribological, chemical and mechanical properties, amorphous composite coatings also show good application prospects in fields such as additive manufacturing [13,14].

1 Performance of carbide-reinforced amorphous alloy coatings

1.1 Friction and wear performance

Friction, wear and corrosion failures of mechanical parts are emerging in various industrial fields. Every year, 80% of the surface failures of mechanical parts in the industrial field are caused by friction and wear. As the research progresses, it is found that an effective way to solve the failure is to prepare wear-resistant coatings on the surface of parts [15].

Amorphous composite coatings exhibit excellent mechanical properties due to their unique microstructure. This coating has been widely recognized for its high hardness, wear resistance, and corrosion resistance. However, under harsh working conditions, simple amorphous coatings cannot meet industrial needs. Therefore, researchers explored adding reinforcing phases in the process of preparing amorphous coatings to improve the hardness of the coatings. The mechanical properties of the coating are directly related to the wear resistance, and the addition of carbides can improve the mechanical properties of the coating, thereby improving the wear resistance. The composition of the cladding powder will have different degrees of influence on the performance of the coating. In the coating preparation process, adding carbides is an effective method to effectively improve the microstructure and phase composition of the coating. These carbides can form a uniformly distributed hard phase in the amorphous alloy matrix, thereby improving its wear resistance and durability. By precisely controlling the type, size and distribution of carbides, the performance of the coating can be further optimized to make it more suitable for specific engineering application requirements. The addition of carbides to the coating composition can also significantly improve the wear resistance and chemical stability of the coating. A large number of studies have shown that the addition of carbide particles as a reinforcing phase to metal coatings mainly improves wear resistance [16]. Carbides usually have a high hardness, and adding them to the coating can significantly improve the overall hardness of the coating. This hardness enhancement can effectively resist surface wear and scratches, thereby extending the service life of the coating. Unlike the direct addition of carbides, the in-situ formed carbides are mainly distributed inside the grains, forming an intracrystalline composite strengthening structure, which is dispersed inside and on the surface of the coating to play a role in fine grain strengthening and dispersion strengthening [17]. Due to the obvious differences between carbides and metal substrates in terms of melting point, elastic modulus and thermal expansion coefficient, the laser cladding process is superior to thermal spraying in terms of mechanical bonding of the coating, which not only improves the surface performance but also enhances the bonding strength between the coating and the substrate. In particular, the laser cladding in-situ ceramic coating technology can combine the high hardness of ceramics with the toughness of metal materials, improve the surface properties of metal materials, and solve the problems of dispersion of ceramic particles and poor bonding with the substrate. While ensuring that the coating is firmly bonded to the substrate, the dilution rate of the coating is controlled to reduce the influence of the substrate on the coating performance [18,19].

1.2 Corrosion performance
It is necessary to improve corrosion resistance while maintaining wear resistance.
Ceramic-based composites are new materials that have gradually developed in the 1980s. They are widely used because of their high temperature resistance, wear resistance, high temperature creep resistance, low thermal conductivity, low thermal expansion coefficient and good chemical corrosion resistance [20]. Under working conditions that resin-based and metal-based composites cannot meet, carbide particles are the most active research field in structural ceramics. Some carbides have the effect of refining the grains of the matrix, and they also have the effect of enhancing the toughness of the matrix. The reinforcing phase formed by carbides can refine the microstructure of the coating, making the grains extremely small, reaching the submicron level or even the nanometer level to a certain extent, greatly reducing element segregation, and further improving the corrosion resistance of the coating [17]. Certain elements enriched in ceramic particles in amorphous alloy coatings are conducive to the formation of passivation films, thereby achieving corrosion resistance [21]. At present, there are relatively many studies on the wear resistance of carbides added to the coatings prepared by laser cladding, but there are few studies on the related corrosion resistance. Because the laser cladding technology under study has a temperature gradient, which causes carbide particles to dissolve and then solidify to form new compounds, and these compounds have relatively high corrosiveness. Academic issues and cutting-edge challenges in this field deserve in-depth study.

2 Effect of carbides on the microstructure and properties of amorphous alloy coatings
There is little research on the role of doped carbide particles in the process of laser cladding to prepare amorphous alloy coatings. In recent years, carbide-reinforced metal-based composite coatings have attracted widespread attention due to their high hardness and excellent wear resistance, and have become a hot topic for many scholars. At present, scholars generally use WC, TiC, SiC, NbC and other particles as reinforcement phases to enhance coating performance in order to achieve an ideal combination of hardness and toughness [22].

2.1 WC particles
WC particles are the most commonly used in coating technology. WC particles have unique properties, such as high hardness, high melting point, high wear resistance and excellent thermal stability. As a reinforcement phase, they can significantly improve the hardness and wear resistance of the coating [23]. Zhang Xinyu et al. [24] prepared Fe-based amorphous composite coatings by laser cladding and introduced fine ceramic particles in situ to prepare Fe-based amorphous composite coatings with high hardness and no cracks. The microhardness of the coatings changed significantly with the increase of WC-14Co addition. The hardness after adding WC reinforcement phase was significantly higher than that of the substrate 04Cr. In the friction and wear experimental test, the wear resistance of all coatings was higher than that of the substrate material. However, when the mass fraction of WC-14Co increased to 5%, the wear surface of the third group of coatings became smoother compared with other coatings, which was the group with the best wear resistance. With the addition of WC-14Co, the number of cracks on the coating surface first decreased and then reappeared, indicating that the addition of WC reinforcement phase had an inhibitory effect on the coating cracks, and the crack inhibition effect was only achieved when the addition amount was appropriate. Xu et al. [25] prepared WC-reinforced Fe-based amorphous composite coatings by laser cladding and laser remelting, studied the effects of laser remelting on the structure and properties of the composite coatings, and focused on the comparative study of the microstructure and corrosion resistance of the composite coatings. WC particles are easily dissolved in molten Fe-based alloys, and the time to completely dissolve in the amorphous alloy solvent is very short. Therefore, the C atoms and W atoms after the WC particles are dissolved can interact with the Fe-based amorphous matrix to precipitate carbides with a blocky morphology, and form a new amorphous phase after rapid solidification. The results show that there are pores and cracks on the surface of the cladding layer, and a large amount of carbides are precipitated. In contrast, the surface after remelting is smooth and has no cracks or pores. The content of amorphous phase and hard phase in the remelted coating increases, which significantly refines the grains, thereby increasing the microhardness of the coating, which is 1.13 times that after laser cladding. Its corrosion resistance and hardness are also significantly improved. Compared with other carbides, WC is widely used in various fields due to its excellent performance, but there are relatively few studies on adding WC particles to laser cladding amorphous alloy coatings. Although significant progress has been made in other fields, there are still many academic issues to be explored.

2.2 TiC particles
TiC particles are also a commonly used hard phase in metal materials. They have the advantages of high hardness, excellent wear resistance, strong thermal stability and elastic modulus.
TiC is used as a reinforcing phase in the coating, and many scholars are committed to related research. Huang Kaijin et al. [26] used laser cladding technology to prepare Zr-Cu-Ni-Al amorphous composite coating doped with TiC powder on the surface of AZ91D magnesium alloy. The study showed that by adding TiC and synthesizing ZrC in situ with Zr atoms, the main components of the cladding layer are amorphous phase and intermetallic compounds. The synergistic effect of the two gives the cladding layer excellent wear resistance. When the TiC content reaches 10%, the wear resistance of the laser cladding layer is improved by 16 times compared with the base material. Ma Liqun et al. [27] prepared TiC particle-reinforced amorphous titanium-based composite materials using Ti45Zr5Cu25Ni20Sn5, the titanium-based amorphous alloy with the strongest amorphous forming ability, as the base, and studied the effect of TiC particles on the thermal stability of titanium-based amorphous alloys. The experiment showed that adding TiC particles to Ti45Zr5Cu25Ni20Sn5 amorphous alloy can not only enhance the hardness of the alloy, but also enhance the thermal stability of the alloy. Puja.K et al. [28] used a 2kW continuous Nd:YAG laser to deposit TiC coating on aluminum alloy. The TiC particles were evenly distributed in the aluminum matrix in the cladding layer, accounting for 50% to 65% of the total volume. The hardness is about 3 times that of the base. Wang Mingwen et al. [29,30] conducted a comparative study on amorphous composite coatings of Fe55Nb15Ti15Ta15 (5%, 10%, 15%, 20% TiC) and Fe55Nb15Ti15Ta15 with different TiC contents. The microscopic morphology of the coatings with different TiC contents showed that the finer the grains, the higher the microhardness of the coatings. When 20% TiC was added, the hardness of the cladding layer reached the maximum, reaching 747.6HV. This is because the addition of TiC promoted heterogeneous nucleation and the generation of carbides with high thermal stability during the crystallization process of the cladding layer. The presence of these carbides hindered the long-range diffusion of amorphous crystallization elements, resulting in grain refinement and precipitation. Therefore, its friction and wear performance is better than that of the alloy coating without TiC. However, as the content of TiC increases, the hard phase formed increases, which hinders the amorphous crystallization. The fewer the crystalline phase in the coating, the more amorphous the phase, which will lead to the decrease of coating hardness or other properties and the decrease of friction coefficient. As one of the reinforcing phases of carbides in ceramic particles, many scholars are committed to the research of adding TiC to coatings. The author believes that in-depth research can be conducted at the level of wear resistance, such as whether the addition of TiC particles in the preparation of amorphous coatings affects dislocations and grain boundaries or the combination of coatings and substrates, whether a composite oxide film is formed, etc. These are all worthy of in-depth research.

2.3 SiC particles
SiC ceramic particles have high hardness, high wear resistance, excellent thermal conductivity, light weight and high strength. They are often used as the hard phase of materials and can
significantly improve the hardness and high temperature oxidation resistance of metal coatings.
Zhang Song, Zhang Chunhua [31] and others used a 2kW continuous Nd:YAG laser to laser clad SiC ceramic powder on the surface of 6061 aluminum alloy. They were able to
prepare metal-based composite materials containing hard phase SiC on the surface of aluminum alloy. The cladding layer also contained a small amount of Al4C3 and Al4SiC4 intermetallic compounds.
SiC ceramic phase has high fracture toughness and hardness, so it is not easy to be destroyed. The corrosion in the sample was observed.
SiC ceramic particles in the matrix were almost unaffected. The experiment showed that the composite coating with SiC particles had significant cavitation resistance and wear resistance.
M.Yue[32] et al. used laser cladding technology to prepare Zr65Al7.5Ni10Cu17.5 cladding layer. In order to enhance the corrosion resistance and wear resistance of magnesium-based cladding layer, SiC particles were added to the amorphous cladding layer to improve the corrosion and wear resistance of magnesium. Huang et al.[33,34] used laser cladding technology to prepare Cu-based amorphous composite coating on magnesium alloy to improve the wear resistance and corrosion resistance of AZ91D magnesium alloy. The mixed powder was Cu47Ti34Zr11Ni8 and SiC. The effect of 20% mass fraction of SiC on the surface of magnesium alloy by laser cladding Cu47Ti34Zr11Ni8 amorphous coating was studied. The results showed that the main components of the coating were amorphous phase and intermetallic compounds. The added SiC can improve the amorphous forming ability through its own decomposition, which means that SiC can be used as a reinforcing phase to increase the hardness and wear resistance of the coating to a certain extent. Many scholars have studied the addition of SiC hard phase to amorphous alloy coatings prepared by laser cladding, which can obtain coatings with good wear resistance and corrosion resistance, but there are also some unpredictable problems. The author believes that research can be strengthened on the bonding strength between SiC particles and amorphous alloy interfaces and the influence of different contents of SiC particles on coatings.

2.4 NbC particles
NbC is one of the most important compounds among refractory metal carbides, with special properties such as high melting point, high hardness, strong chemical stability, good wear resistance and high free enthalpy. The addition of hardening phase NbC can improve the toughness and plasticity of amorphous materials and maintain stable performance under high temperature and harsh environment. This makes NbC particles have important application value in the fields of high temperature tools, coatings and refractory materials.
Zhu et al. [35] used laser cladding to prepare Fe-Co-B-Si-C-Nb amorphous composite coatings and observed and analyzed the microstructure in the amorphous composite coatings. Near the interface between the coating and the substrate, the region presents a layered microstructure, which can be roughly divided into three layers: the first layer (columnar dendrite phase), the second layer (equiaxed dendrite phase) and the third layer (amorphous-particle composite phase). In terms of mechanical properties, the microhardness and wear resistance of the Fe-Co-B-Si-C-Nb amorphous composite coating also show layered characteristics. The microhardness of the third layer is the highest. Because the third layer is doped with some NbC particles as a reinforcing phase, the friction coefficient is reduced and the wear resistance of the coating is significantly improved. Li Ruifeng et al. [36-39] used a composite process of laser cladding and remelting to prepare Ni40.8Fe27.2B18Si10Nb4 amorphous composite coating on low-carbon steel. The results showed that the coating was composed of amorphous phase and NbC phase. The microhardness of the amorphous composite coating was 1227.9HV, which was 6 times that of the substrate, and had good wear resistance. Obviously, NbC in the amorphous phase provides higher hardness, and it also proves that the amorphous composite coating with NbC has strong wear resistance. Jin Yajuan et al. [40] used an in-situ self-generation method to obtain NbC reinforcement phase particles in the cladding layer, thereby achieving an amorphous composite cladding layer with high strength, wear resistance and good toughness and plasticity. The experimental results show that during the friction and wear process, the furrow is forced to change the sliding direction when it contacts the white NbC particles, and the NbC particles inhibit the extension of the furrow. This shows that in the amorphous composite cladding layer, the NbC particles in the amorphous matrix have a relatively high hardness, and the presence of the NbC reinforcement phase inhibits the plastic deformation of the coating substrate, thereby improving the wear resistance of the cladding layer. Zhu Yanyan [41] used laser cladding technology, coaxial powder feeding and one-step method to prepare an iron-cobalt-based amorphous composite cladding layer on the surface of low-carbon steel, and discussed the influence of NbC particles on the performance of the cladding layer. The study found that based on the optimal parameters, the cladding layer is mainly composed of an amorphous phase and dispersed NbC particles. In the performance test of the cladding layer, the phase and microstructure were analyzed by experiments at different temperatures and annealing times. The results showed that the cladding layer began to crystallize at 600°C. With the increase of annealing temperature, the B element around the NbC particles diffused and reorganized, and nano-scale hard and brittle phases such as Fe2B and Fe23B6 were precipitated, resulting in an increase in the microhardness of the cladding layer. The NbC particles were embedded in the amorphous phase, so that the micro-Vickers hardness of the cladding layer reached about 1245HV, which was significantly higher than the dendrite phase in the coating. This shows that NbC particles in the amorphous phase help to improve wear resistance. Compared with other carbides, there are more studies on NbC particle-reinforced amorphous alloy coatings, most of which are dedicated to wear resistance, while few studies on corrosion resistance. The author believes that the addition of NbC to amorphous alloy coatings prepared by laser cladding can be studied in depth in terms of corrosion resistance.

3 Conclusion and Prospect
In recent years, the understanding of the strengthening mechanism of adding particles to amorphous alloy coatings for laser cladding technology has been continuously deepened. In order to further improve the comprehensive performance of amorphous alloy coatings, domestic and foreign scholars have conducted a lot of research. A large amount of experimental data has been accumulated in the development of amorphous material systems, process and performance research. Carbide-enhanced amorphous coatings have both the structural characteristics of amorphous alloys and the excellent performance brought by different carbides, and have significant effects on friction, wear and corrosion resistance. It is necessary to continue to explore the combination of different carbide types and addition amounts to achieve the best coating performance, improve hardness and wear resistance while maintaining the stability of amorphous structure. Secondly, it is necessary to systematically evaluate the long-term stability, wear resistance and corrosion resistance of carbide-containing coatings under extreme working conditions to expand the scope of application.
Although the preparation and research of laser cladding amorphous coatings have developed rapidly, as a surface modification technology, there are still some problems in the research on adding carbides to amorphous coatings prepared by laser cladding.

(1) Few literatures have discussed the reinforcing phase in amorphous coatings in detail, and few literatures have systematically studied the phase and structure of amorphous coatings and comprehensively considered the effect of laser heat input on the phase and structure of amorphous coatings. There are even fewer studies on the effect of carbide particles in the process of laser cladding to prepare amorphous alloy coatings.
(2) Most of the research on adding carbides in the preparation of amorphous alloy coatings is still devoted to wear resistance, and its corrosion resistance is also worthy of in-depth study.
(3) Different types of carbides have different effects on coatings. Selecting suitable carbides and optimizing their amount and ratio is an important research direction.
(4) The uniform distribution of carbides is also crucial to the overall performance of the coating, but during the cladding process, carbide particles may aggregate or be unevenly distributed, and the process needs to be improved to ensure uniformity.
(5) In the actual experimental process, there are some other factors that affect the experimental results, such as process parameters during laser cladding, thermal stress management of coatings and substrates, element content of coating preparation, and compatibility of carbides with amorphous matrix, etc. These directions also need to be studied urgently.