Splat Formation Research Articles

Microstructure, property and high-temperature wear performance of Cr3C2-based coatings deposited by conventional and ID-HVAF spray torches: A comparative study

The durability of industrial components exposed to high temperatures can be increased by depositing high-velocity air-fuel (HVAF) sprayed Cr3C2-based coatings. The uniform embedding of wear-resistant Cr3C2 within an oxidation-resistant binder matrix allows HVAF-sprayed Cr3C2-based coatings to be widely used in high-temperature environments. However, consolidating these coatings demands an optimum particle velocity and temperature combination, primarily dependent on the spray torch design. Understanding the role of spray torch variants with altered combustion chamber and nozzle designs is essential, which might influence the coating (splat) formation mechanism and the resultant wear performance. Accordingly, Cr3C2–25NiCr and Cr3C2–30NiCrMoNb were sprayed using different HVAF torches (high-power AK06 and low-power AK05-ID (inner diameter): generate different energy (thermal + kinetic) output) to understand the role of the binder as well as the torch design. The deposited coatings were comprehensively compared based on splat morphology, microstructure, mechanical properties, room and high-temperature erosion and sliding wear behavior. Subsequently, a detailed post-wear analysis was performed to decipher the associated wear mechanism. As inferred from the results, Cr3C2–25NiCr coatings deposited through a high-power AK06 spray torch displayed preferable microstructure, properties and superior wear resistance. The study also offered new insights into HVAF-ID torch-deposited coatings.

Parametric assessment of electrical discharge drilling on plasma sprayed functionally graded Al/Al2O3 coating on Al6061-T6 faceplates

Electrical discharge drilling is a non-conventional machining process that is effective and economical for cutting difficult-to-cut conductive materials. In this work, the parametric assessment of functionally graded Al/Al2O3 coating sprayed by plasma on Al6061-T6 faceplates is investigated. Initially, four different graded layers of Al/Al2O3 (50:50, 40:60, 30:70, and 20:80) were processed through plasma spray and deposited coating morphology, splat formation, and cross-sectional structure were confirmed through a scanning electron microscope. The parametric assessment has been investigated based on the effect of electrical discharge drilling parameters peak current (Pc), pulse-on time (Pon), and gap voltage (Vg) on the material removal rate (MRR), tool wear rate (TWR), machining time (MT), surface roughness (SR), taper angle (TA), and overcut (OC). The selected process parameters were Pc from 8 to 14 A, Pon from 60 to 90 μs, and Vg from 20 to 80 V respectively. The parametric assessment was performed based on the objectives of maximizing the MRR and minimizing the TWR, MT, SR, TA, and OC. The effect of process parameters on various output responses was summarized. From the experimentation, MRR is significantly affected by Vg, and maximum MRR is found at the high levels of Pc and Pon. Reduced TWR was observed at the 2nd level of Pc (0.058 mm3 min−1) and 4th level of Vg (0.076 mm3 min−1) and this same factor has more influence on MT. High level of Pc and Pon exhibits maximum TWR with erosion. The results show that Pon time relatively gives low SR (2.36 μm) and minimum OC (0.0015 mm) was achieved at a high level of Vg. Few un-drilled holes with cracks were witnessed due to high TWR. Many drilled holes exhibit < 2° of TA which indicates good dimensional accuracy.

Splat deposition stress formation mechanism of droplets impacting onto texture

This study focuses on understanding the crucial phenomenon of deposition stress during the splat formation of plasma-sprayed droplets, which is essential for comprehending coating stress in applications such as plasma spraying. A novel three-dimensional coupled fluid–solid and thermo-mechanical model was developed, which employed the volume of fluid method and finite element method. This model was applied to simulate the formation of deposition stress in molybdenum droplets during plasma spraying onto a stainless steel substrate with laser-textured groove patterns. It successfully replicated various stages of the splat formation process, including impacting, spreading, cooling, and solidification, which captured the evolution of temperature, strain, and stress in the splat and groove walls. The accuracy of the model was validated through X-ray diffraction measurements of splat deposition stress on the planar substrate surface. The simulation results revealed that deposition stress was induced during the simultaneous spreading and solidification of the droplet. This stress was attributed to quenching and solidification contraction, which resulted in tensile stress in the splat, with higher stress at the bonding interface edges. By contrast, the groove walls experienced compressive stress, which peaked in the central groove region. The mean isotropic stress and von Mises stress of the splat were quantified as 176 and 141 MPa, respectively. In-situ curvature tests demonstrated that stress relaxation, which was triggered by splat deposition stress, resulted in a 24.6 % reduction in cracking, yielding, and slipping stresses. In addition, a refined theoretical equation for splat deposition stress was proposed, with correction coefficients of 0.119 determined from simulations and experiments. The developed simulation model offers reliable insights into the state of splat deposition stress, which provides valuable information for optimizing plasma-spray processes and enhances our understanding of coating stress in such applications.

Effects of Spray Parameters on the YSZ-Alumina Splat Formation During Solution Precursor High Velocity Flame Spraying

Effects of Spray Parameters on the YSZ-Alumina Splat Formation During Solution Precursor High Velocity Flame Spraying

Microstructural study on the effect of thermo-physical properties for plasma sprayed Ni and Ni[sbnd]20Cr splats formed on Cu substrates

Ni and Ni20Cr powder particles were air plasma sprayed onto polished copper substrates to gain insight into the flattening behaviour of both Ni and Ni20Cr particles (splats) formed on a relatively low melting point material (i.e. copper) substrate. The extent of any interfacial bonding, along with any splat-substrate intermixing derived from the different thermo-physical properties of the sprayed particles were characterised. The plan-view features of the splats were captured using scanning electron microscopy (SEM), while splat-substrate interfacial properties were examined using focused ion beam microscopy (FIB) and transmission electron microscopy (TEM). The chemical characteristics of the splat and substrate were analyzed using energy-dispersive X-ray spectroscopy (EDS). The addition of ∼20 wt% chromium to Ni (i.e the Ni20Cr particles) was observed to significantly influence the spreading behaviour of the particles on impact with the substrate, both the extent of any splat splashing and the splat flattening ratio, as well as the microstructure of the splat-substrate interface, including the degree of substrate melting and the likelihood of material from the substrate jetting into the body of the splat. The evidence of intermixing between the splat and the copper substrate for both feedstocks is an intriguing feature of this study. The presence of a thermodynamically formed copper oxide layer during substrate preheating also influenced both the splat formation behaviour and substrate melting as observed by both microstructural examination and investigation through numerical models.

Effect of polymer substrate elasticity on splat formation during thermal spraying

In this study, we have numerically investigated the effect of elastic properties of polymer substrates on the spreading of the metal droplets. The spreading dynamics of an aluminum droplet on solid substrates with elastic modulus in the range of 50 MPa to 210 GPa has been studied keeping the effects of other physical phenomena like viscosity, surface tension, heat transfer, and solidification unchanged. The results show that the elastic modulus of the substrate has a significant impact on the droplet spread factor owing to the resilience of the substrate. While the substrate behaves like a rigid surface beyond E = 10 GPa, at lower values, the spread is impeded owing to absorption of the energy by the substrate on impact leading to lower spread factors. The introduction of an air jet for cooling the substrate shows that the convective losses are minimal and conduction from the droplet to the substrate remains the dominant mode of heat transfer. As a result, deposition of a bond coat of copper was considered for protection of the substrate from localized heating. It was found that droplet spread was invariant to bond coat thickness in the range of 20 μm and 40 μm as well as any change in surface wettability for the material and range of velocities considered thereby establishing the effectiveness of inserting a Cu bond coat in protecting the substrate without compromising the spreading characteristics of the droplet.

Effect of substrate temperature on the surface and interface properties of NiTi atmospheric plasma sprayed coating

Atmospheric plasma spraying (APS) is one of the most preferred coating processes, which comes under thermal spraying technology. It has a wide range of applications due to its versatility in surface modifications. By the APS technique, different high-temperature application materials like cermets, and ceramics, can be coated on a substrate whose surface properties have to be modified in an extreme environment. Ni50Ti50 (at.%) alloy became more focus of interest for researchers and industrialists due to their two extraordinary smart properties such as shape memory effect (SME), and superelasticity (SE) which can protect any structural materials from catastrophic failure. Compared to various deposition routes, APS is an economical process to apply NiTi on mild steel. NiTi smart alloy also exhibits good wear resistance, corrosion resistance, damping behaviour, and high load-bearing capacity. In terms of mechanical properties, it has high strength and hardness at high temperatures. Owing to these properties, NiTi alloy can be used to protect structural materials such as mild steel from catastrophic failure. In this study, mild steel was coated at 100 °C, 200 °C, 300 °C and 400 °C preheating temperatures by APS techniques using an equiatomic NiTi alloy. The surface and interface characterization were performed using an optical microscope, SEM, XRD, Hardness test and 3D optical profilometer. It was found that along with the desired NiTi phase, some of the intermetallic and oxide phases are responsible for the mechanical strength. The surface and interface morphologies show that NiTi splat formation by APS results in better surface bonding and dense coating. With increase in the substrate temperature, the hardness of a coating interface increases with decrease in the number of pores at coating interface.

Microstructural study of Ni and Ni-20Cr particles plasma sprayed on stainless steel substrate at 300 ˚C

In thermal spray coatings, the bonding and adherence of the spray particles (called splats) to the substrate surface significantly influence the overall quality of the finished coating. In this study, both elemental Ni and Ni-20Cr powders were plasma sprayed onto polished stainless-steel substrates held at 300 ˚C. Splat formation for both feedstock materials was investigated and compared. Detailed studies of the microstructure of single splats as well as the splat-substrate interface were performed using scanning electron microscopy (SEM), focused ion beam (FIB) microscopy and transmission electron microscopy (TEM). The additions of Cr to nickel promoted improved adherence of the splat to the substrate and modified splat formation by improving wettability during spreading. More intriguingly, energy dispersive spectroscopy (EDS) mapping and line scans, performed on TEM cross-sections, revealed splat-substrate inter-diffusion and chemical inter-mixing. Of particular note, a ‘jet’ of iron/chromium-based material, arising presumably from the substrate, was noted to be intimately intermixed into the interior of the nickel splat.

Modeling of liquid detachment and fragmentation during the impact of plasma spray particles on a cold substrate

The flattening of a droplet impacting a solid surface plays a fundamental role in several industrial applications. In plasma spray, the splats resulting from the impact, spreading, and solidification of molten particles are the building blocks of the spray coatings. Fragmented splats are formed on substrates held at room temperature and atmospheric pressure. Although the formation of a fragmented splat is attributed to the presence of adsorbates on the substrate surface, its dynamics have not been adequately addressed. In this study, a numerical model is developed to investigate the formation of fragmented splats during droplet flattening and solidification in plasma spraying conditions. Compressible Navier-Stokes equations are solved, and the volume of fluid (VOF) method is used to capture the liquid and gas interface. In addition, the source term method is used to capture the solidification process during droplet flattening. In addition, a new boundary condition is defined to consider the effect of gas desorption on the substrate surface after droplet impact. The numerical results show that gas desorption from the surface produces a barrier layer between the droplet and the substrate. This high-pressure region detaches the edge of the spreading droplet from the surface and forms a liquid sheet. The liquid sheet rises above the substrate and spreads up to 2 times more than droplets impacting surfaces without gas desorption. The fragmentation of the liquid film follows the overspreading of the droplet. Moreover, the barrier gas layer reduces the heat transfer rate between the molten particle and the substrate. As a result, only a portion of the initial droplet remains at the location of the impact, which forms a small solidified splat.

Investigation into the formation of Ni splats plasma-sprayed on to mild steel and stainless steel substrates

The present study investigates the splat formation behaviour of Ni particles plasma sprayed onto AISI 1008 mild steel and 316 austenitic stainless steel substrates to draw a comparative analysis of splat formation on both surfaces. A range of analytical techniques were used to analyse the surface and cross-sectional characteristics of the splats formed on both substrates. Most of the splats observed on both of the substrates were halo type splats driven by Rayleigh–Taylor instabilities. A linear relationship was identified between the size of the central core of the splats and their outer ring of debris, which was distinct for each substrate. The diffusion profile, obtained through STEM-EDS analysis, revealed a higher degree of diffusion across the interface between splat and stainless steel substrate as compared to mild steel, suggesting a better bond efficiency for stainless steel. Cross-sectional observations, together with theoretical calculations, showed evidence of substrate melting as well as the presence of metallurgical bonds for both mild steel and stainless steel substrates.

Recent Research Advances in Plasma Spraying of Bulk-Like Dense Metal Coatings with Metallurgically Bonded Lamellae.

Although thermal spray metallic coatings have been widely used for materials protection from wear, corrosion and oxidation, its porous feature limits the full utilization of materials potential. Moreover, the oxidation inherent to thermal spraying in the ambient atmosphere is detrimental to interlamellar bonding formation, which further degrades the performance of thermal spray metal coatings. How to tape out the full potential of spray materials in the form of the coating is a still great challenge to thermal spray coating technology. Facing such challenge, recent efforts have been made to deposit dense metallic coatings with sufficiently bonded lamellae by oxide-free molten droplets through atmospheric plasma spraying. In this paper, the strategies for depositing bulk-like metal coatings will be reviewed. The formation of the bulk-like coating through post-spray treatments is briefly reviewed including post-spray heat treatment and laser remelting following the brief introduction to the features of thermal spray metallic coatings. The effect of the substrate preheating temperature on the splat formation and subsequently the adhesion formation was examined to reveal the dominant limitation of resultant oxide scale. Then, the role of the deposition temperature on the formation of bulk-like metal deposits with neglecting the effect of oxidation during spraying by vacuum plasma spraying practices is shortly presented. The recent progress on the new strategies to develop spread-fusing bonding mechanism and in-situ in-flight deoxidizing mechanism through developing ultra-hot metallic droplets will be introduced. The thermodynamics and kinetics requirements for the in-situ in-flight deoxidizing through deoxidizer elements adding to alloy spray powders for achieving oxide-free molten droplets in the ambient atmosphere are examined. The conditions to develop the spread-fusing mechanism during the spreading of impacting molten metal droplet for metallurgical bonding are presented. It is obvious from this review paper that the realization of two mechanisms depends on both the spray materials design and heating control of in-flight particles. Through the generation of ultra-hot droplets by plasma spraying to achieve oxide-free molten droplets, strategically it will be possible to deposit bulk-like dense metallic coating through spread-fusing of splat surfaces with limited post-spray oxidation. Such strategies will tape out the full potential of coating materials and open up the new application fields for plasma spraying.

Microstructure and mechanical properties of plasma transferred wire arc spray coating on aluminum cylinder bores

This study examines the microstructure and mechanical properties of plasma transferred wire arc (PTWA) coating of typical alloyed steel, deposited on diecast aluminum alloy cylinder bores. The coating surface and microstructure were characterized in terms of surface roughness, features (i.e., defects, splats formation mechanisms, distribution of oxides, re-solidified particles, and interfacial metallurgical bonding) using laser scanning confocal microscope, scanning and transmission electron microscope (SEM and TEM). Residual stress through the thickness of the coating was measured using X-ray diffraction (XRD) and hole-drilling method. In post-processed samples, compressive residual stress was measured throughout the coating with a value close to 100 MPa at the interface, resulting from the thermal mismatch between coating and substrate materials. In terms of mechanical properties, coating hardness was estimated at both the micro- and nanoscale and examined the influence of microstructure inhomogeneity on the mechanical performance and failure modes. Three-point bending tests and consequent analysis using the equivalent section method yielded stress-strain properties for both the substrate and coating materials with a maximum coating strength averaging 1480 ± 108 MPa. SEM observation of fracture surfaces showed three modes of failure involving coating delamination and breakage, which is related to the deposition process and the various features within the coating.

Experimental investigation and parameter optimization of Cr2O3 atmospheric plasma spray nanocoatings

In this research, Cr2O3 ceramic nano-sized powder particles were prepared using ball milling and then were granulated to reach the proper size for spraying. Afterward, Cr2O3 nano-coatings were deposited by atmospheric plasma spraying (APS) process onto stainless steel substrates. To optimize APS parameters, spraying was carried out under six conditions with different parameters. Microstructures of the elemental/milled powder and coatings were characterized via a field emission scanning electron microscope (FESEM) equipped with energy-dispersive spectroscopy (EDS). In this research, Cr2O3 coatings were deposited under different spraying conditions to understand the effect of APS parameters on the splat formation, deposition efficiency, and porosities of the coatings. After parameter optimization, spraying was performed under a high deposition efficiency of 46.0±1.3%. The optimized Cr2O3 coatings showed porosity content, Knoop microhardness, and adhesive strengths of 8.7±2.2%, 823±27 HK0.2, and 49±4 MPa, respectively; making them a good candidate for industrial use.

Hollow droplet impact on a solid surface

Droplet impact on a solid surface occurs in many natural phenomena and industrial applications such as raindrop impact on the ground, drip irrigation, spray cooling, spray coating, inkjet printing, etc. Importantly, in several cases such as aerosol transfer from the sea, oxygen dissolution, and thermally sprayed coatings the impinging droplets contain air bubble dealing with liquid-bubble-solid interaction. These hollow droplets upon impacting on the target surface, due to their controllable weight and embedded medium, control the splat properties by triggering the cavitation and releasing the inner substance. To better understand the flattening process of a hollow droplet, in this work a comprehensive experimental and numerical study is performed on water and glycerol droplets impacting on a rigid surface. The experiments are repeated on different types of surfaces including aluminum, sand-blasted steel, and superhydrophobic. The results show that the mechanisms of the post-impact process of hollow droplets are different from those of dense droplets in several aspects. We study the role of surface wettability, liquid properties, and impact velocity on the droplet flattening process. In the numerical work, we compare pressure contours and velocity vectors for dense and hollow droplets that provide an in-depth insight through the formation of splat and counter jets.

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The flattening of a droplet impacting a solid surface plays a fundamental role in several industrial applications. In plasma spray, the splats resulting from the impact, spreading, and solidification of molten particles are the building blocks of the spray coatings. Fragmented splats are formed on substrates held at room temperature and atmospheric pressure. Although the formation of a fragmented splat is attributed to the presence of adsorbates on the substrate surface, its dynamics have not been adequately addressed. In this study, a numerical model is developed to investigate the formation of fragmented splats during droplet flattening and solidification in plasma spraying conditions. Compressible Navier-Stokes equations are solved, and the volume of fluid (VOF) method is used to capture the liquid and gas interface. In addition, the source term method is used to capture the solidification process during droplet flattening. In addition, a new boundary condition is defined to consider the effect of gas desorption on the substrate surface after droplet impact. The numerical results show that gas desorption from the surface produces a barrier layer between the droplet and the substrate. This high-pressure region detaches the edge of the spreading droplet from the surface and forms a liquid sheet. The liquid sheet rises above the substrate and spreads up to 2 times more than droplets impacting surfaces without gas desorption. The fragmentation of the liquid film follows the overspreading of the droplet. Moreover, the barrier gas layer reduces the heat transfer rate between the molten particle and the substrate. As a result, only a portion of the initial droplet remains at the location of the impact, which forms a small solidified splat.

Influence of spray gun parameters on inflight particle's characteristics, the splat-type distribution, and microstructure of plasma-sprayed YSZ coatings

Ceramic coatings, fabricated with specific properties using the atmospheric plasma spray (APS) process, are widely used for many applications in which the porosity and splat interfaces are the main factors affecting the performance. Since the coating microstructure is composed of large numbers of molten and semi-molten particles impinged successfully at the substrate (known as splats), the produced coatings are characterized by the melting degree of these particles and their relative splat-type fractions.In the present work, the effect of process parameters settings has been studied systematically, relating the characteristics of impinging particles to splat formation and eventually to microstructure development and properties of the coating. Therefore, individual splats were collected on mirror-polished substrates and observed using image analysis (IA). These were evaluated and categorized into different splat types, based on their melting degree and morphology, under each combination of spray conditions. It was found that gun current and standoff distance have a profound effect on the characteristics of impinging particles. These, in turn, determine the relative fractions of splat types, layered structure, and final properties of the deposit. The effect of splat-type distribution on the bonding strength between layers, lamellar structure, and coating porosity was investigated.

Ceramic Coatings Deposited from Fine Particles by Different Spraying Processes

Plasma spraying of fine particles promises uniform microstructure and improved properties for ceramic coatings due to the formation of small splats with reduced residual stress and pore size. Although spraying fine particles is challenging due to the poor rheological properties of particles (e.g., low flowability and agglomeration), the potential improvements to the coatings make it an attractive option. In this study, we discussed the feasibility of fine particle spraying via three different spraying techniques, namely low-power direct current (DC) plasma spraying, axial suspension plasma spraying (ASPS), and plasma-assisted aerosol deposition or hybrid aerosol deposition (HAD). Low-power DC plasma was sufficient to melt and deposit fine particles in an ambient atmosphere without using a liquid carrier. The fabricated coatings had similar features to those of ASPS coatings of small splats (5–8 µm in diameter without internal cracks). The fabricated coatings by the low-power DC plasma showed almost equivalent properties to that of the conventional plasma-sprayed coating while providing low energy consumption. Fine particles deposited via the HAD process led to the coatings with improved microstructure without pores or cracks. During the HAD process, particle melting was not required for deposition, and using the plasma assisted the surface activation and improved the deposition efficiency of the aerosol deposition process. The fabricated HAD coating revealed improved microstructure with the highest hardness, Young’s modulus, and adhesion strength and lack of pores or cracks compared to the coatings fabricated by other plasma spray techniques. In addition, similarities and differences among the techniques for spraying fine ceramic particles were investigated.

Investigation on structural, mechanical and tribological properties of plasma sprayed Al2O3-40% TiO2 coating

The present work deals with tribological investigation of Al2O3-40% TiO2 coating deposited using plasma spraying. The structural characterization of coating was done using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD). The micro hardness was measured by vickers micro hardness tester whereas fracture toughness was determined by Indentation Fracture Toughness Test (IFT) method. The sliding wear tests were carried out at different test conditions involving simultaneous variation of load (P) ranging from 5 to 30 N and sliding velocity (V) ranging from 0.1 m/sec to 0.6 m/sec. The sliding wear rate increased with increasing parameter P × V and friction coefficient displayed minima at a load of 20 N and sliding velocity of 0.4 m/sec. The flash temperature showed the increasing trend with P × V parameter. The variation in coefficient of friction and wear rate with varying test conditions was associated with change in wear mechanism from plastic grooving to delamination of splats & splat fracture and formation & removal of tribo layer of Ti2O3 and Ti3O5 on worn surface.

Microstructural investigation of bonding and melting-induced rebound of HVOF sprayed Ni particles on an aluminum substrate

In this study, nickel powder was sprayed on a polished aluminum substrate using the high-velocity oxy-fuel spraying process. Detailed microstructural characterization was conducted to analyse the mechanims of splat formation, with particular attention to the changes occurring at the splat-substrate interface and the subsequent bonding behaviour due to the impact of high thermal and kinetic energy particles with a soft, low melting point substrate. Characterization was performed using scanning electron microscopy, focused ion beam microscopy, transmission electron microscopy, together with the scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that a large number of particles had rebounded upon impact, which was correlated with the degree of substrate melting and the associated time for re-solidification. The remnant splats that adhered to the substrate surface were found to exhibit both mechanical and metallurgical bonding with the substrate. The experimental results were supported by transient finite element based thermal simulation.

Embedding Behavior of Ceramic Particles in Babbitt Coatings and Its Effect on the Tribological Properties of Low-Pressure Cold Sprayed Coatings

The low melting point of Sn-based Babbitt alloys often causes nozzle clogging in the low-pressure cold gas-dynamic spraying (LPCGDS) process, which impacts the process steadiness and the coating quality. Adding hard particles to the feedstock material eliminates this kind of interruption. A certain amount of these particles finds their way in the obtained coatings. These particles also trigger a kind of “hammering effect” due to their impulse forces. These forces are directly dependent on the mass and velocity of the impacting hard particles. However, these forces may lead to a decrease in the porosity and improve the adhesion of the obtained coating. In this study, the effect of the density and size of the hard particle was examined by three different hard materials, Cr3C2, Al2O3, and B4C, which have a material density of 6.68, 3.95, and 2.52 g/cm3, respectively. The used feedstock in this study is a powder mixture that contains 75 vol.% Babbitt and 25 vol.% of either B4C, Cr3C2, or Al2O3. The effect of the size distributions “particles with lower mass” was tested using two different Al2O3. The various hard particles show different embedding behaviors, as well as different effects on the coating build-up. It was found that the blended hard particles were enclosed with the Babbitt matrix, and their interface with Babbitt shows no clear evidence of pronounced diffusion. The size distribution of the blended hard particles has a direct effect on the splat formation and the obtained coating microstructure. It was found that the type of hard particles played a decisive role in the friction behavior. Nevertheless, the hard particle reinforced Sn-Sb-Cu-based composite coatings demonstrated a nearly constant coefficient of friction throughout the load-interval.