A comprehensive study on tic additions and sliding speed effects governing wear in aluminium matrix composites

Abstract

Particulate-reinforced aluminium matrix composites (PRAMCs) have gained significant attention for their high strength, good ductility, and excellent thermal conductivity, making them suitable for a wide range of modern engineering applications. In this study, micro-sized titanium carbide (TiC) particles were incorporated into an aluminium matrix through liquid-state stir casting, with TiC added at 0%, 3%, 6%, and 9% by weight. The investigation examined the combined influence of TiC content and sliding speed (0.75, 1.5, 2.25, and 3 m/s) on the wear behaviour of the composites when tested against an EN31 steel disc. All wear tests were performed under a constant load of 30 N over a sliding distance of 2000 m. The results show that increasing TiC content leads to a higher wear rate, whereas the coefficient of friction decreases correspondingly. Conversely, increasing sliding speed reduces the wear rate but results in a higher coefficient of friction. These findings demonstrate the coupled effects of TiC reinforcement and sliding velocity on the tribological performance of aluminium matrix composites and provide valuable insights for tailoring their behaviour in industrial applications.

Introduction

Lightweight metal matrix composites (MMCs) are highly prized in the aerospace, automotive, and industrial sectors for their unique blend of low density, high tensile strength, stiffness, and excellent wear resistance^1–3. These attributes make MMCs essential for modern applications where high performance and efficiency are crucial. The rising demand for fuel-efficient, low-emission vehicles has significantly increased interest in MMCs^4–6. Vehicles constructed with lightweight materials like aluminium and magnesium achieve reduced weight, which directly improves fuel economy and decreases emissions. Among the various MMCs, aluminium matrix composites (AMCs) have received notable attention due to their superior properties over pure aluminium, offering enhanced strength, stiffness, and wear resistance^7–9. These traits make AMCs ideal for applications that require both durability and lightness. Depending on the application, different reinforcements such as Titanium carbide (TiC), aluminium oxide (Al₂O₃), zirconium diboride (ZrB₂), boron carbide (B₄C), titanium diboride (TiB₂), and fly ash are used. These reinforcements can be in forms such as fibers, grains, or whiskers, allowing for customization according to performance requirements^10,11. The stir casting method, a commonly used technique for producing MMCs, is particularly valued for its simplicity, cost-effectiveness, and adaptability. This process, performed in the liquid state, involves mixing the matrix and reinforcement materials in specific ratios to achieve the desired composite properties. Research indicates that the stirring speed during this process plays a critical role, influencing the composite’s quality by promoting oxide formation, which helps reduce porosity and enhances structural integrity^12,13. However, challenges such as uneven reinforcement distribution can lead to porosity and agglomeration, negatively impacting hardness and tensile strength. Controlling processing parameters is therefore vital to ensure uniform reinforcement dispersion and optimal performance of the composite¹⁴. The evolution of advanced MMCs is driven by the need for materials that combine superior mechanical properties with lightweight adaptability for various applications. With continuous research into innovative materials and manufacturing techniques, MMCs are set to become increasingly important in high-performance engineering^15–17.

Specific studies highlight the benefits of various reinforcements in AMCs. For instance, Bhowmik et al.¹⁸ found that AA8011 composites reinforced with SiC and TiB₂ particles showed improved wear resistance, particularly at higher sliding speeds, with wear rates decreasing as reinforcement proportions increased. Bakhshizade et al.¹⁹ demonstrated that incorporating AlMgB14 (BAM) nanoparticles significantly enhanced the mechanical and wear-resistant properties of aluminium matrices, with notable increases in hardness, yield strength, and a significant reduction in wear rate. Similarly, Sidharthan et al.²⁰ explored Al11Si₂CuFe composites reinforced with SiC and MoS₂, achieving improved tensile strength and micro-hardness, making them suitable for automotive pistons and cylinder liners. Garg et al.²¹ developed hybrid Aluminium matrix nano-composites with uniformly distributed SiC and graphite particles, achieving an average tensile strength of 258 MPa, hardness of 120 HV, and density of 2.76 g/cm³. Increased graphite content significantly reduced wear rates and friction coefficients. Further research has delved into the impact of different ceramic reinforcements on AMCs. Studies by Yadav and Dixit²² revealed that TiB₂-reinforced composites had lower mass loss compared to those reinforced with SiC. Wang et al. highlighted the uniform distribution of TiB₂ particles in AMCs and their role in improving reinforcement efficiency. Freundl and Jagle²³ exhibits the fabrication of particle-reinforced aluminum-matrix composites (AMCs) using powder mixing and laser powder bed fusion (PBF-LB). Enhanced dispersion of TiC nanoparticles improves grain size, notwithstanding constraints related to TiC loss. SEM/EDS analysis and countermeasures improve comprehension of microstructure and adaptability. Fan et al.²⁴ study employs molecular dynamics simulation to assess TiC particle-reinforced aluminium matrix composite coatings aimed at improving the anti-ablation performance of aluminium armatures in electromagnetic rail launching, offering insights for optimising coating designs to reduce arc-induced material degradation. Ao et al.²⁵ examined the deterioration of 6063 aluminium matrix composites reinforced with TiC and Al2O3, demonstrating that a refined grain structure and AlFeSi phase enhance Cl − absorption, resulting in pitting corrosion and reduced corrosion resistance. Kumar et al.²⁶ examines the corrosion characteristics of Al6061-TiC composites produced using in-situ stir casting with halide salts, then subjected to open die forging. Microstructural study and ASTM B117 salt spray tests demonstrated enhanced corrosion resistance in forged alloys and composites. Dhulipalla et al.²⁷ synthesis and machinability of TiC and MoS₂ reinforced AA7075 composites, demonstrating enhanced machinability, discontinuous chip morphology, decreased ductility, and elevated surface roughness relative to the base alloy as a result of the reinforcing particles. Conversely, Rao and Das²⁸ found that greater SiC content in composites led to reduced wear rates and a higher coefficient of friction. Overall, these studies illustrate the effectiveness of various ceramic reinforcements in enhancing the mechanical and wear properties of aluminium matrix composites, contributing to their suitability for diverse engineering applications.

Materials

Aluminium alloy AA8011 is chosen as the matrix material due to its extensive use in the production of various components, particularly in aluminium extrusion processes. This alloy is highly favoured for visible structural applications requiring a high strength-to-weight ratio, as it facilitates the creation of intricate structures with smooth, highly polished surfaces, making it ideal for anodizing. The chemical composition of AA8011 is outlined in Table 1. Titanium carbide (TiC), with a density of 4.93 g/cm³, is significantly denser than aluminium alloy AA8011, which has a density of 2.7 g/cm³. The matrix metal is infused with varying amounts of TiC powder at concentrations of 0%, 3%, 6%, and 9%. This gradation allows for the systematic study of the impact of TiC reinforcement on the composite’s properties.

Table 1.

Chemical constituents of AA8011 alloy.

Components	Cr	Fe	Si	Mg	Mn	Cu	Ti	Al
Wt. %	0.001	0.72	0.61	0.001	0.002	0.006	0.012	Balance

Experimentation

Aluminium alloy 8011 (AA8011) composites enriched with TiC powder have been effectively manufactured using the stir casting process. Previous research has demonstrated that stir casting produces high-quality aluminium matrix composites (AMCs). Figure 1 illustrates the schematic diagram of the casting process. During the procedure, AA8011 ingots were heated to the required temperature in a graphite crucible while being stirred at 400 RPM for 20 min. To prepare the TiC powder for mixing, it was preheated to 500 °C in a muffle furnace to eliminate oxides and ensure compatibility with the aluminium matrix. To enhance the wettability of the aluminium matrix, 2% magnesium was added before the melting process. A mechanical stirrer was employed during melting to ensure thorough mixing and uniform dispersion of the reinforcement particles. The combination of aluminium’s low weight and TiC’s high strength creates a stir-cast AA8011/TiC composite with enhanced wear resistance and thermal conductivity. Stir casting ensures a uniform distribution of TiC particles throughout the aluminium matrix, providing an efficient and cost-effective method for large-scale production. The resultant AA8011/TiC composite has better mechanical capabilities and a lower density than standard materials, making it a great choice for applications in aerospace, automotive, and other sectors that need high performance and endurance.

Fig. 1.

Flow diagram of the casting process.

Assessing the wear characteristics of AA8011/TiC composites is crucial for optimizing their composition and production methods to meet the specific requirements of various industries, including automotive, aerospace, and industrial machinery. By analyzing these properties, researchers can improve the durability and lifespan of critical components, contributing to the development of lightweight, high-performance materials suited for engineering applications. The wear tests were conducted using a pin-on-disc setup, as illustrated in Fig. 2. In these tests, an EN31 steel disc with a hardness of 62 HRC was rotated, while pins with dimensions of 6 mm in diameter and 40 mm in height were evaluated against the disc, following ASTM G99 standards. Prior to testing, each pin and the counter plate were meticulously cleaned to ensure accuracy. The experiments were carried out under varying sliding speeds of 0.75, 1.5, 2.25, and 3 m/s, with a constant applied load of 20 N and a total sliding distance of 2000 m for each test condition.

Fig. 2.

Wear testing setup.

Results and discussion

Mechanical properties

Microhardness is an essential mechanical characteristic that significantly influences a material’s resistance to indentation, abrasion, and wear. It offers insights into a material’s performance under mechanical stress, especially in applications necessitating durability and resistance to mechanical failure. The microhardness test entails exerting a concentrated force on a tiny surface area of the material, resulting in increased density around the indentation and subsequent localised work hardening. This attribute is especially significant in composite materials, since fluctuations in microhardness indicate changes in the material’s internal structure and the distribution of reinforcing phases. Figure 3 depicts the fluctuation in microhardness corresponding to various weight percentages of titanium carbide (TiC) reinforcement inside an aluminium matrix. As the weight% of TiC rises, the microhardness of the composite markedly enhances in comparison to the unreinforced aluminium alloy. The increase is due to many variables, notably the homogeneous distribution of TiC particles in the matrix, which obstructs dislocation movement and hence improves hardness. The correlation between grain size and hardness in metal matrix composites is elucidated by the Hall-Petch hypothesis, which posits that hardness and strength are inversely related to grain size^29,30. Reduced grain sizes result in an augmented grain border area, which serves as an impediment to dislocation motion. Thus, an increase in grain boundary density results in improved resistance to deformation in the material. In aluminium-TiC composites, TiC particles facilitate grain refinement during solidification, leading to a finer microstructure and enhanced hardness. Furthermore, the enhanced wettability and adhesion characteristics of TiC particles with the matrix AA8011 are pivotal in augmenting the mechanical qualities. The robust interfacial adhesion between TiC and aluminium guarantees effective load transmission from the matrix to the reinforcement under mechanical stress. This durable interface not only improves microhardness but also reduces the risk of stress accumulation at the interface, which may otherwise result in early failure. The enhanced bonding further increases resistance to plastic deformation, as the TiC particles act as impediments to dislocation movement, hence substantially augmenting the overall strength and wear resistance of the composite.

Fig. 3.

Micro hardness of AA8011/TiC composites.

The tensile test, a common mechanical characterisation method, evaluates a material’s tensile strength under certain circumstances. This approach evaluates ultimate tensile strength (UTS), yield strength, and ductility to reveal material mechanical behaviour. Figure 4 shows the UTS of titanium carbide (TiC) powder-reinforced aluminium alloy 8011 composites, which determines load performance. The UTS rises from 150 MPa to 216 MPa with more TiC powder reinforcement. Due to variations in thermal expansion between the reinforcement and matrix, residual stresses strengthen the composite structure and increase UTS. Additionally, increasing the composite’s TiC powder reinforcement weight directly improves UTS. As TiC concentration increases, reinforcing particle spacing reduces, restricting matrix dislocation motion. The Orowan strengthening technique dramatically improves tensile characteristics. Due to homogeneous TiC particle distribution, fine-grained microstructures increase the composite’s fracture stress resistance and ductility. Fine-grained composites have better mechanical characteristics than coarse-grained ones because the high grain boundary density prevents fracture propagation^31,32. Additionally, better interfacial bonding between the TiC powder reinforcement and the aluminium alloy matrix boosts composite tensile characteristics. Strong interfacial connections carry load from matrix to reinforcement efficiently, lowering stress concentrations and fracture initiation. TiC powder provides supplementary reinforcement during bonding, boosting the material’s tensile strength. The interaction between reinforcing particles and dislocations improves mechanical performance and reduces micro-cracking under stress.

Fig. 4.

Ultimate Tensile Strength (UTS) of AA8011/TiC composites.

The impact strength of a material is an essential attribute that determines its capacity to endure abrupt or dynamic loads without shattering. It demonstrates the material’s durability and resilience, which are crucial for applications exposed to shock, impact, or fluctuating loads. Impact strength, offers critical insights into the structural integrity and longevity of a composite under actual loading circumstances. The impact strength of aluminium-based composites reinforced by TiC powder is affected by several parameters, including the type, size, distribution, and concentration of the reinforcing particles. Figure 5 depicts the fluctuation in impact strength corresponding to varying volumes of TiC powder reinforcement. With an increase in TiC powder composition, the impact strength initially increases owing to the dispersion strengthening effect. Nonetheless, above a certain threshold, excessive reinforcing may induce particle clustering or agglomeration, resulting in stress concentration areas that diminish the composite’s overall toughness. The use of TiC (titanium carbide) powder reinforcement is crucial for improving the mechanical characteristics of the composite. TiC particles, characterised by their hardness and wear resistance, enhance the interfacial adhesion between the aluminium matrix and the TiC powder reinforcement. This enhanced bonding reduces the occurrence of microvoids or weak areas at the interface, thereby allowing the composite to absorb and disperse impact energy more efficiently. Thus, the incorporation of TiC reinforcement markedly enhances the material’s resistance to impact pressures by facilitating load transfer and inhibiting fracture start and propagation.

Fig. 5.

Impact strength of AA8011/TiC composites.

Microstructural evaluation

The microstructures that are shown in Fig. 6 demonstrate the differences that may occur in the AA8011 matrix and its composites that are reinforced with various weight percentages of titanium carbide (TiC) particles. In the absence of reinforcement, the microstructure of the pure AA8011 alloy exhibits a reasonably homogenous distribution of aluminium grains in addition to intermetallic phases, as seen in Fig. 6(a). A comparatively smooth matrix with greater grain boundaries is produced as a consequence of the lack of reinforcing particles. Casting flaws, such as micro-porosity, which are normal in as-cast aluminium alloys, may be evident in the material. Significant alterations in the microstructure are brought about by the incorporation of three weight% of TiC particles, as seen in Fig. 6(b). It would seem that the TiC particles are evenly distributed throughout the matrix, carrying out the function as grain refiners. Due to the presence of TiC particles, grain development is inhibited during the solidification process, which ultimately results in finer grains. Dislocation movement is impeded as a result of this refinement, which results in an improvement in mechanical qualities like as hardness and strength. A further improvement in grain refinement is seen in Fig. 6(c) when the TiC level is increased to 6 wt%. The microstructure exhibits a larger density of TiC particles, which further inhibits the movement of grain boundaries. At this reinforcement level, however, there is a possibility that a slight clustering of TiC particles will start to take place. It is possible for this clustering to result in local stress concentration, which may have an impact on the overall performance of the composite material under certain loading situations. The composite exhibits a structure that is greatly refined and tightly packed, as illustrated in Fig. 6(d), which contains 9 weight% of titanium carbide. The TiC particles are more noticeable, and clusters are more obvious than they were before. A material’s homogeneity may be diminished when there is an excessive amount of particle clustering, which might possibly result in brittle failure in some regions. On the other hand, the overall improvement in wear resistance and hardness that might be attributed to the high TiC concentration is still rather considerable. In Fig. 6(e), the EDX (Energy-Dispersive X-ray Spectroscopy) mapping that is shown focusses on the composite material that is composed of AA8011 and 9 wt% TiC. This examination provides information about the distribution of elements, hence validating the existence of TiC particles in the matrix and their dispersion throughout the matrix. The EDX mapping includes the following important points: The main matrix is composed of aluminium, which is the majority of the elements that have been discovered. It is to be anticipated that composites based on AA8011 would include a high concentration of aluminium. The regions that correlate to the TiC reinforcing particles are where the majority of the titanium and carbon are found. Although there is some clustering, the TiC is distributed uniformly, which is an indication of superior interfacial bonding between the matrix and the reinforcement. There is also the possibility of detecting trace elements such as zinc, magnesium, and copper, which were discovered in the original AA8011 alloy. These factors contribute to the strengths of the alloy as well as its resistance to corrosion. The microstructural research sheds information on the impact that increasing the amount of TiC has on the refining of grains and the dispersion of different particles. When the concentration of TiC is smaller, the grain structure is improved evenly; however, when the concentration is larger, clustering occurs, which might have a detrimental impact on the mechanical characteristics. By confirming the effective integration of TiC into the AA8011 matrix, the EDX mapping provides confirmation of the existence of reinforcement particles as well as their dispersion of the particles.

Fig. 6.

Microstructure of (a) AA8011 matrix as casted; (b) AA8011 + 3wt.% TiC composite; (c) AA8011 + 6wt.% TiC composite; (d) AA8011 + 9wt.% TiC composite, and (e) EDX mapping of AA8011 + 9wt.% TiC composite.

Wear resistivity

The wear characteristics of AA8011/TiC composites are shown in Fig. 7 under a range of sliding speeds (0.75, 1.5, 2.25, and 3 m per second) when a constant applied load of 30 N is applied and a sliding distance of 2000 m is maintained. As the sliding speed increases, it has been noticed that the wear rate also increases. This is mostly due to the fact that the higher distance traversed in a given amount of time. The sliding speed plays a crucial role in generating frictional heat at the interface between the pin and the disc. This heat reduces the bond strength between the reinforcement and the matrix, resulting in a rise in shear force. As a consequence of this, a percentage of the hard particles undergo a transformation into wear debris, which results in an increase in the contact surface between the pin and the disc. In addition, composites that have a greater reinforcement content have a lower wear rate when compared to composites that have a lower reinforcement content, and this is seen when the sliding speed is increased. When the load is held constant, the sliding speed becomes the most important component that determines the shear force. The maximum shear stress that is produced as a consequence of this is what causes the material to delamination and wear. The delamination process produces debris, contributing to greater material loss at higher sliding speeds. In contrast, lower sliding speeds reduce shear forces, leading to fewer hard particles detaching from the matrix, which diminishes the ploughing effect in the softer matrix material. Consequently, wear loss decreases when sliding speeds are reduced, assuming the load conditions remain unchanged. With all other factors held constant, higher sliding speeds result in increased frictional heat at the interface between the pin and the disc. This elevated heat facilitates the formation of a mechanically mixed layer, which contributes to higher wear rates.

Fig. 7.

Wear rate of AA8011/TiC composites by variation of sliding speed.

The fluctuation in the coefficient of friction (COF) of AA8011/TiC composites that occurs as a result of variations in sliding speed is shown in Fig. 8. As a consequence of the dynamic construction, destruction, and regeneration of the frictional layer on the contact surface, which is a process that accelerates with speed, the findings reveal that the coefficient of friction (COF) steadily rises with sliding speed. Additionally, the presence of hard reinforcements, in conjunction with the interaction of asperities at the contact locations, has the effect of increasing the frictional force, which ultimately leads to a greater coefficient of friction (COF). On the other hand, the coefficient of friction (COF) drops at any given sliding speed as the weight% of hard reinforcements in the matrix rises.

Fig. 8.

COF of AA8011/TiC composites by variation of sliding speed.

Worn structure

The worn surface characteristics presented in Fig. 9 illustrate the wear behavior of AA8011 composites reinforced with titanium carbide (TiC) particles under a consistent load of 30 kN and a sliding distance of 2000 m. The micrographs capture worn surfaces at varying sliding speeds of 0.75 m/s, 1.5 m/s, 2.25 m/s, and 3 m/s for composites containing 3 wt% and 9 wt% TiC reinforcement. For the AA8011/3 wt% TiC composite, Fig. 9(a) shows the worn surface at a sliding speed of 0.75 m/s. At this speed, the wear is mild, with slight abrasion marks visible. The combination of low speed and moderate reinforcement leads to less severe wear, predominantly governed by an abrasive wear mechanism. Figure 9(b) depicts the worn surface at 1.5 m/s, where more prominent wear features are observed. The increased sliding speed generates more frictional heat, inducing localized surface deformation. This suggests a transition from pure abrasive wear to a mixed mode of abrasion and adhesion. At 2.25 m/s, shown in Fig. 9(c), deeper wear grooves and signs of surface degradation become apparent. The elevated sliding speed results in higher frictional heat, causing matrix softening and intensifying the wear rate. Figure 9(d) illustrates the worn surface at 3 m/s, where significant material loss, larger wear tracks, and potential delamination are evident. The high thermal load at this speed leads to severe adhesive wear becoming the dominant mechanism.

Fig. 9.

Worn Micrograph at constant 30KN Load and 2000 m Sliding distance for AA8011/3 wt% TiC composites where sliding speed of (a) 0.75 m/s, (b) 1.5 m/s, (c) 2.25 m/s, (d) 3 m/s, and AA8011/9 wt% TiC composites where sliding speed of (e) 0.75 m/s, (f) 1.5 m/s, (g) 2.25 m/s, (h) 3 m/s.

For the AA8011/9 wt% TiC composite, the worn surface at 0.75 m/s, as shown in Fig. 9(e), reveals minimal wear with finer abrasion grooves, indicating better wear resistance due to the increased TiC content. The additional reinforcement enhances the composite’s ability to withstand wear at lower speeds. At 1.5 m/s, Fig. 9(f) shows slightly deeper grooves compared to the lower speed but less wear severity compared to the 3 wt% TiC composite at the same speed. The increased reinforcement content helps distribute the load more effectively, thereby reducing wear. Figure 9(g) presents the worn surface at 2.25 m/s, where moderate wear with distinct grooves can be seen. Despite the high sliding speed, the wear resistance remains relatively high, likely due to the well-dispersed TiC particles improving the matrix strength. At 3 m/s, Fig. 9(h) shows a worn surface with noticeable but reduced damage compared to the 3 wt% composite at the same speed. The higher TiC content mitigates the thermal and mechanical stresses, minimizing severe wear and damage. Overall, the wear resistance of the composites increases with higher TiC content. The 9 wt% TiC composite exhibits better performance at all sliding speeds, as the reinforcement particles enhance hardness and reduce material removal. At lower sliding speeds, the primary wear mechanism is abrasion, whereas higher speeds lead to increased frictional heat, promoting adhesive wear and matrix softening.

Conclusion

This research investigates the combined effects of titanium carbide (TiC) reinforcement and sliding velocity on the wear characteristics of AA8011 aluminium matrix composites. Critical results indicate that the integration of TiC significantly improves mechanical qualities, such as microhardness, tensile strength, and wear resistance. The enhancements arise from the uniform dispersion of TiC particles, which facilitate grain refinement, impede dislocation movement, and promote interfacial adhesion between the matrix and reinforcement.

The wear testing findings indicate that a higher TiC content decreases wear rates at all sliding speeds, attributable to the strengthening and hardening properties of TiC particles. Nevertheless, elevated sliding velocities augment wear rates owing to heightened frictional heat, which causes matrix softening and delamination. Moreover, the coefficient of friction (COF) increases with sliding speed owing to the dynamic development and disintegration of frictional layers, but it decreases with greater TiC reinforcement. Microstructural research confirms these findings, demonstrating finer grain structures and enhanced dispersion at appropriate reinforcement levels. Excessive TiC concentration may result in clustering, potentially undermining mechanical integrity under certain situations.

AA8011/TiC composites have exceptional wear and mechanical properties, rendering them appropriate for aerospace, automotive, and industrial applications that need lightweight but resilient materials. Enhancing TiC content and operational parameters, including sliding speed, is essential for optimising the performance of the composites. Future study may concentrate on the amalgamation of hybrid reinforcements and sophisticated production procedures to augment the characteristics and expand the application of these composites.

Future scope

Future study may investigate the amalgamation of hybrid reinforcements, such as the combination of TiC with other ceramics like SiC or TiB₂, to attain an equilibrium between hardness and toughness. Research into new fabrication techniques, including additive manufacturing and in-situ processing, may enhance reinforcement distribution and composite quality. The behaviour of these composites under dynamic and harsh environmental circumstances, including elevated temperatures and corrosive environments, necessitates investigation. Moreover, increasing production methods while ensuring consistent qualities across bigger components might improve their use in industrial manufacturing. These developments will enable the creation of next-generation composites designed for more rigorous and varied technical applications.

Author contributions

Abhijit Bhowmik, Vignesh Packkirisamy: Writing, InvestigationRaman Kumar, N. Beemkumar: Data collection, MethodologyDhirendra Nath Thatoi, Ruby Pant: Figure preparation, SoftwareParveen Kumar, Ankush Mehta, Nagaraj Ashok: Funding, review writing, Conceptualization.

Funding statement

No funding.

Data availability

The data will be available on request to the corresponding author.

Declarations

Competing interests

The authors declare no competing interests.

Conflict of interest

There is no conflict of interest.