Al Alloy Substrate Research Articles

Erosion Wear Behavior of HVAF-Sprayed WC/Cr3C2-Based Cermet and Martensitic Stainless Steel Coatings on AlSi7Mg0.3 Alloy: A Comparative Study

The paper presents a comparative study of the erosion wear resistance of WC-10Co4Cr, Cr3C2-25NiCr and martensitic stainless steel (SS) coatings deposited onto an AlSi7Mg0.3 (Al) alloy substrate by high-velocity air‒fuel (HVAF) spraying. The influence of the abrasive type (quartz sand or granite gravel), erodent attack angle, thickness, and microhardness of the coatings on their and Al substrate’s wear resistance was comprehensively investigated under dry erosion conditions typical for fan blades. The HVAF-spraying process did not affect the Al substrate’s structure, except for when the near-surface layer was 20‒40 μm thick. This was attributed to the formation of a modified Al-Si eutectic with enhanced microhardness and strength in the near-substrate area. Mechanical characterization revealed significantly higher microhardness values for the cermet WC-10Co4Cr (~12 GPa) and Cr3C2-25NiCr (~9 GPa) coatings, while for the SS coating, the value was ~5.7 GPa. Erosion wear tests established that while Cr3C2-25NiCr and SS coatings were more sensitive to abrasive type, the WC-10Co4Cr coating exhibited significantly higher wear resistance, outperforming the alternatives by 2‒17 times under high abrasive intensity. These findings highlight the potential of HVAF-sprayed WC-10Co4Cr coatings for extending the service life of AlSi7Mg0.3-based fan blades exposed to erosion wear at normal temperatures.

Easily Applicable Superhydrophobic Composite Coating with Improved Corrosion Resistance and Delayed Icing Properties

Mitigating the adverse effects of corrosion failure and low-temperature icing on aluminum (Al) alloy materials poses significant research challenges. The facile fabrication of bioinspired superhydrophobic materials offers a promising solution to the issues of corrosion and icing. In this study, we utilized laboratory-collected candle soot (CS), hydrophobic fumed SiO2, and epoxy resin (EP) to create a HF-SiO2@CS@EP superhydrophobic coating on Al alloy surfaces using a spray-coating technique. Various characterization techniques, including contact angle meter, high-speed camera, FE-SEM, EDS, FTIR, and XPS, were employed to investigate surface wettability, morphologies, and chemical compositions. Moreover, a 3.5 wt.% NaCl solution was used as a corrosive medium to evaluate the corrosion resistance of the uncoated and coated samples. The results show that the capacitive arc radius, charge transfer resistance, and low-frequency modulus of the coated Al alloy significantly increased, while the corrosion potential (Ecorr) shifted positively and the corrosion current (Icorr) decreased by two orders of magnitude, indicating improved corrosion resistance. Additionally, an investigation of ice formation on the coated Al alloy at −10 °C revealed that the freezing time was 4.75 times longer and the ice adhesion strength was one-fifth of the uncoated Al alloy substrate, demonstrating superior delayed icing and reduced ice adhesion strength performance.

Mechanically durable resin-based superhydrophobic coating on Al alloy with interface optimization via implanted molecular anchoring

In this study, a mechanically durable resin-based superhydrophobic coating with excellent anti-corrosion, water-repellency, self-cleaning, and anti-reflection properties was fabricated on the Al alloy substrates. The resin-based superhydrophobic coating comprised the polymethyl methacrylate (PMMA) and SiO2 nanoparticles on the anodized Al alloy substrates. The interface between the anodized Al alloy substrates and the superhydrophobic coating was strengthened by linking the rhodamine B (RhB) molecule in Al2O3 and PMMA. The RhB molecule was implanted in the Al2O3 by dissolving the RhB into the electrolyte for the anodization process. Moreover, the porous structure of Al2O3 was also improved significantly due to the existence of RhB. The bonding of N in RhB and Al in Al2O3 enhances the interface contacting of substrate and RhB, and the bonding of carboxyl in RhB and ester group in PMMA enhances the interface contacting of substrate and PMMA coating. As anticipated, the Al2O3-RhB/PMMA-SiO2 composite coating on Al alloy demonstrates significantly enhanced adhesive ability than that of Al alloy with Al2O3/PMMA-SiO2 coating. This interface-strengthening method provides a universal strategy to fabricate mechanically durable protective coating on metallic substrates.

Corrosion resistance and long-term antibacterial performance of ZnO-Al2O3 nanocomposite coatings on aluminum alloy

Anodic aluminum oxide-zinc (AAO-Zn) coatings were prepared on aluminum (Al) alloy substrates through anodization and nZnO deposition. Further heat treatment at various temperature is applied to the composite coatings. Among the samples, AZ-250 sample showed lower corrosion current density (1.127 × 10−8 A/cm2) and higher charge-transfer resistance (4.65 × 105 Ω cm2) compared to the AZ-150 and AZ-350 samples. At 250 °C, a greater incorporation of nZnO into the AAO layer facilitated the fusion of ZnO with aluminum oxide, resulting in a denser and more protective coating. The antibacterial research revealed AZ-250 sample achieved a 100 % reduction of S. aureus and 97.9 % of E. coli within 2 h. Even after 40 days of air exposure, the AZ-250 sample maintained high antibacterial effectiveness due to ZnO attachment and sustained Zn2⁺ release from the nanoporous AAO structure. This nanocomposite is suitable for applications in heat exchangers, medical instrument casings, and transport structure.

Studies on the microstructure and mechanical properties of AlCu4MgSi aluminum alloy repaired via electron beam directed energy deposition

Additive manufacturing (AM) technologies have been used to repair aluminum (Al) alloy components in many engineering structures. However, the use of AM technologies to repair Al-Cu alloys is still very limited, and the repair via electron beam directed energy deposition (EB-DED) has not been reported so far. In this work, the EB-DED repair was performed on AlCu4MgSi-O Al alloy substrate with the specially developed Al-Cu-Si wire (380D). The results show that wall structures with high metallurgical quality were successfully prepared. The deposit exhibits alternating fine grain zones and coarse grain zones. In the bottom layers of deposit, columnar grains growing along building direction dominate, while the middle and top layers mainly consist of equiaxed grains. In the AlCu4MgSi-O substrate, the heat-affected zone (HAZ) close to the fusion line undergoes recrystallization and completely transforms into fine equiaxed grains, while abnormal grain growth occurs and coarse grains are formed in the HAZ slightly away from the fusion line. From substrate to deposit, the intensity of texture gradually decreases. After EB-DED repair, the microhardnesses and strengths of the bottom layers and HAZ are significantly improved. The strengthening of HAZ is entirely attributed to precipitation strengthening, while the bottom layers are affected by both precipitation strengthening and dispersion strengthening. Tensile tests indicate that the repaired structure samples fracture from the interface between HAZ and base metal zone of the AlCu4MgSi-O substrate. EB-DED is demonstrated to be a promising technology to repair AlCu4MgSi alloy components, and this work can serve as a useful reference for the high-quality repair of Al-Cu alloy structural parts.

Enhancing corrosion and wear resistance of a 7075 aluminum alloy via depositing TC4 coating

Aluminum alloys have been widely used in engineering due to their high strength and low density. However, their poor corrosion and wear resistance have largely limited their application in marine equipment. This study successfully improved the corrosion and wear resistance of a typical 7075 Al alloy by depositing a high-performance TC4 titanium alloy coating using in-house annular laser cladding equipment. Microstructural investigations revealed that the defect-free TC4 coating is metallurgically bonded to the 7075 Al alloy substrate along with excellent bond strength. Electrochemical test results showed that compared to the hot-forged 7075 Al alloy and hot-forged double-phase TC4 bulk alloy, the TC4 coating exhibits superior corrosion resistance due to its net-basket α-single-phase microstructure. Further, wear testing results showed that the coefficient of friction and wear volume of the TC4 coating are far lower than that of 7075 Al alloy. The enhanced wear resistance is closely related to the high hardness of the TC4 coating and its excellent fatigue-wear resistance. Therefore, this work can serve as a reference to improve Aluminum alloys' corrosion and wear resistance by depositing Titanium alloy coatings using the annular laser cladding process, which shall widen the potential applications of Aluminum alloys in marine equipment.

Effects of spraying parameters and heat treatment temperature on microstructure and properties of single-pass and single-layer cold-sprayed Cu coatings on Al alloy substrate

Exploring the deposition of single-pass and single-layer pure Cu coatings on Al alloy substrate through high-pressure cold spray technology is a crucial endeavor with significant implications for advancing the utilization of such coatings. Regrettably, research in this specific area remains scarce, highlighting the need for further investigation and understanding. This study examined the characteristics of cold-sprayed Cu coatings deposited on a 6061 T6 aluminum alloy substrate under varying gas temperatures and pressures, and explored the effects of subsequent heat treatment on the microstructure and mechanical properties of the Cu coatings. The morphology, phase composition, surface roughness, thickness, porosity, microstructure, shear strength, and microhardness of the cold-sprayed Cu coatings were systematically analyzed. The findings indicated that the spraying parameters had a substantial impact on the properties of the Cu coatings. Specifically, increased gas pressure led to rougher surfaces and lower porosity, whereas higher gas temperature produced smoother surfaces and also reduced porosity. At 800 °C and 4.0 MPa, the Cu coatings exhibited the lowest surface roughness, measuring 8.03 μm. Conversely, at 800 °C and 5.5 MPa, the Cu coatings demonstrated the lowest porosity, at 0.26 %. Moreover, the microstructure analysis showed evidence of dynamic recrystallization in the deposited Cu particles, contributing to enhanced mechanical properties. Following this, the influence of heat treatment on the microstructure and properties of the cold-sprayed Cu coatings was examined. The results demonstrated that annealing at different temperatures induced changes in the interfacial microstructure, with the formation of intermetallic compounds between the Cu coating and Al alloy substrate. This interdiffusion phenomenon led to improved bonding strength and mechanical properties of the Cu coatings, as evidenced by increased shear strength. After undergoing heat treatment at 400 °C, the Cu coatings exhibited the highest shear strength, measuring 49.89 MPa. However, excessive heat treatment temperatures resulted in the formation of cracks and a decrease in mechanical properties.

Galvanic corrosion behavior of micro-arc oxidation coated Al-Zn-Mg-Cu alloy coupled with 316 L stainless steel in the salt-spray atmosphere

Micro-arc oxidation (MAO) coating with thickness, potential, current density, and impedance of 30 μm, −0.62 V, 7.2×10−8 A/cm2 and 88,730 Ω·cm2 was prepared on the surface of Al–Zn–Mg–Cu alloy to inhibit galvanic corrosion caused by its coupling with 316 L stainless steel. It was found that the MAO coating increased the potential of the galvanic corrosion zone (GCZ) from −0.67 V to −0.43 V, and decreased its current density from 3×10−3 A/cm2 to 4.4×10−7 A/cm2, resulted in a much lower corrosion rate and longer failure time. Salt-spray erosion can cause the MAO coating to detach gradually and formed the stepped corrosion pits at the GCZ. The galvanic corrosion process of the MAO coated 7085 alloy could be divided into three stages: (1) the electrolyte passes through the interconnected defects in the coating, leading to pitting corrosion beneath the coating; (2) the corrosion products block the interconnected defect channels in the coating, reducing the rate of galvanic corrosion; (3) the Al alloy substrate becomes fully exposed and contacts with 316 L stainless steel through the electrolyte, accelerating the galvanic corrosion and corrosion detachment. These findings confirm the effectiveness of MAO coatings in inhibiting galvanic corrosion and clarify the complex corrosion mechanisms involved, providing valuable insights for enhancing the durability of Al–Zn–Mg–Cu alloy in coupled environments.

Sol–gel derived highly hydrophobic Polystyrene/SiO2 spray coatings on polished stainless steel and textured aluminium substrates

ABSTRACT In this study, sol–gel derived spray coatings of highly hydrophobic nature consisting of polystyrene (PS) and SiO2 nanoparticles were developed on polished stainless steel 321 (SS) and textured 6061 aluminium (Al) alloy substrates. The micro-structures on the Al surface were created through ultraprecision machining, known as single-point diamond turning (SPDT) machining. The polished SS and micro-structured Al were coated with PS/SiO2 using a spray coating technique by maintaining a pressure of 4–5 kPa, and positioning the nozzle 20–30 cm away from the substrates. The textured surface of Al was characterised using coherent correlational interferometry (CCI). The PS modified SiO2 nanoparticles and their coatings were characterised using Fourier-Transform Infrared Spectroscopy (FTIR) and field-emission scanning electron microscopy (FESEM). The resulting coating exhibited a micro-nano hierarchical roughness due to the presence of SiO2 nanoparticles and their fine size clusters. The polished SS surface showed static water contact angles of 93.3° and 143.5° before and after coating, respectively. Similarly, the polished and coated structured Al surface exhibited water contact angles of 85.6° and 144.3° before and after coatings. Such coatings can exhibit a great potential particularly in the field of self-cleaning technologies.

Study on the Influence of Metal Substrates on Protective Performance of the Coating by EIS.

The degradation process of a red iron oxide epoxy coating on three kinds of metals under a periodic cycling exposure to 3.5 wt% NaCl solution (45 °C 12 h + 25 °C 12 h) was comparatively studied using electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods. The influence of the metal substrates (carbon steel, brass, and Al alloy) on the protection performance of the coating was analyzed using variations in the electrochemical and chemical parameters. The failure criteria of the coating were discussed. The results show that the coating on the three substrates presents different failure times, with the coating on steel presenting the shortest time and the coating on Al alloy the longest time. The characteristics of metal substrates and their corrosion products influence the coating failure behavior. The corrosion products with loose and hygroscopic properties of steel and brass have promoting effects on the diffusion of water through the coating. The passive film of the Al alloy substrate and the formation of salt film containing Cl- have corrosion-inhibiting effects on the substrate. Evaluation of the coating performance by |Z|0.01Hz should consider the characteristics of the metal substrates.

Microstructural transformation and mechanical properties of Cu-sputtered alumina ceramic/Zn5Al/AA2024 ultrasonic soldering joints

Cu films were deposited on the surfaces of alumina (Al2O3) ceramics via magnetron sputtering, and the ceramics were then joined to AA2024 by using a Zn5Al solder assisted by ultrasonic soldering. Increasing the duration of Cu sputtering led to the continued diffusion of Al from the Al alloy substrate into the solder. This led to the growth of the ZnAl eutectic phase within the solder joint, with the precipitation of CuZn5 diffusing into the ZnAl eutectic and η–Zn phases. The increased formation of the ZnAl eutectic phase enhanced the mechanical strength and stability of the solder. The CuZn5 phase formation suppressed solder shrinkage during cooling, improving the coefficient of thermal expansion to match those of the metallised ceramic and AA2024 alloy. This reduced the residual stress at the joint interfaces in the metallised Al2O3 ceramic/Zn5Al/AA2024 joint. A maximum average shear strength of 65.835 MPa was achieved with 2 h of Cu sputtering, representing a 224.95% increase compared to the joints without Cu. Fractures occurred at the ceramic–solder interface, combining adhesive, cohesive, and mixed failures.

Effect of Substrate Bias on the Microstructure and Properties of Non-Equimolar (AlCrSiTiZr)N Films with Different Cr/Zr Ratios Deposited Using Reactive Direct Current Magnetron Sputtering

To reduce the cost of tools operated in extreme environments, we developed films with excellent corrosion/oxidation resistance. Two high-entropy nitride films, (AlCrSi0.3TiZr)N and (AlCr1.5Si0.3TiZr0.5)N, were deposited using reactive DC magnetron sputtering under different substrate biases. The films exhibited a maximum hardness of 32.5 GPa ((AlCrSi0.3TiZr)N) and 35.3 GPa ((AlCr1.5Si0.3TiZr0.5)N) when deposited at −150 V, corresponding to 27 and 142% increases compared to those deposited at 0 V. This indicates that the bias strengthened (AlCr1.5Si0.3TiZr0.5)N (higher Cr/Zr ratio) more significantly. The enhancement of the mechanical properties was highly correlated with the interstitial point defects and densification of the film microstructures. The corrosion resistance of the films deposited on 6061 Al alloy substrate under different biases was tested in 0.1 M H2SO4. (AlCrSi0.3TiZr)N and (AlCr1.5Si0.3TiZr0.5)N displayed the lowest corrosion currents of 0.75 and 0.19 μA/cm2 when deposited at −100 and −150 V, respectively. These values are two orders of magnitude lower than that of the uncoated substrate. The (AlCr1.5Si0.3TiZr0.5)N film showed better oxidation resistance than the (AlCrSi0.3TiZr)N film and remained partially oxidized after heat treatment at 1000 °C. The (AlCr1.5Si0.3TiZr0.5)N film deposited at −150 V exhibits excellent mechanical properties and corrosion/oxidation resistances, making it suitable for protecting tools operating in harsh environments.

Effects of Electrolyte Compositions and Electrical Parameters on Micro-Arc Oxidation Coatings on 7075 Aluminum Alloy

Aluminum alloys are widely used in a variety of industries nowadays for their high strength-to-weight ratio, good formability, low density, and recyclability. However, their poor corrosion and wear resistance properties restrict their applications. This study investigated the effects of electrical parameters and electrolyte compositions on the microstructures of micro-arc oxidation (MAO) film on a 7075 Al alloy substrate. The morphology, microstructure, and compositions of the MAO coatings were characterized using a scanning electron microscope (SEM), X-ray diffraction (XRD), and an electron probe micro-analyzer (EPMA). Furthermore, measurements of microhardness, corrosion resistance, and wear resistance were also conducted. The cathodic current and duty ratio are proportional to film thickness, which consequently improves the wear and corrosion resistance. The microstructural observations of the aluminate-based coatings revealed that increasing cathodic current reduces the pancake-like structures, and a lot of small pores appear on the top of the coatings, which makes the surface smoother. Moreover, the aluminate-based coatings are mainly composed of α-Al2O3 and γ-Al2O3, while the silicate-based coatings mainly consist of γ-Al2O3 and a small amount of α-Al2O3 phase. Due to the phase compositions, the microhardness of the aluminate-based coatings can reach 1300~1500 HV and exhibit better wear resistance than silicate-based coatings.

Composite laminates reinforced by vertically aligned carbon nanotubes: Detailed manufacturing process, from nanotubes transfer to composite consolidation

Nano-constituent incorporation into composites has been extensively studied in the literature due to its improvement in static and dynamic mechanical properties, as well as its prevention from interlaminar crack initiation and propagation. This work introduces a detailed manufacturing process of nano-engineered composite laminates, from impregnation to consolidation, without damaging the initial morphology of carbon nanotubes transferred on prepreg interfaces. Based on prepreg and vertically aligned carbon nanotubes (VACNTs) synthesized on an aluminium alloy (Al) substrate, the impregnation step allows for the transfer of VACNTs onto the prepreg surface through partial resin-rising capillarity. The Al alloy substrate is then removed from the VACNTs through a separation step, ensuring highly effective and repeatable transfer with more than 80% VACNTs transferred onto the prepreg surface. This paper provides insight into the impregnation and transfer processes and guides the choice of process parameters to ensure minimal VACNTs buckling during the consolidation of the hybrid composites at high pressure in an autoclave.

Crack-Free Copper Alloy Coating on Aluminum Alloy Fabricated by Laser Cladding

Crack-free Cu alloy coating has been fabricated on Al alloy substrate with the existence of a Ag buffer layer. The Cu alloy coating had 12 at.% Al and 45 at.% Ag, which contributed to the formation of Cu solid solution and the eutectic phase (transformation temperature 780 °C). The eutectic phase was characterized as finer Cu solid solution and finer Ag solid solution. The Ag buffer layer had the main contents of Ag2Al and Ag solid solution, and it not only hindered the formation of brittle intermetallic compounds (IMCs)but also reduced the thermal stress as its intermediate coefficient of thermal expansion (CTE). Furthermore, the plastic deformation of Ag solid solution in the Ag buffer layer and Cu solid solution in Cu alloy coating also relieved the thermal stress which was generated during the cladding process. All these three aspects inhibited crack generation. And the hardness of the Cu alloy coating increased to approximately 275 HV due to the strengthening effect of Al solid solution, grain boundary within the finer eutectic phase, and nano twin in the Cu solid solution of the eutectic phase.

Preparation, interface properties and corrosion behavior of nano-modified MAO ceramic film on 5B70 Al alloy

Ceramic film with graphite oxide (GO) particles were prepared on 5B70 Al alloy by micro-arc oxidation（MAO）technique. Effect of GO concentrations on the micro-arc oxidation behavior, ceramic/metal interfacial characteristic and the anti-corrosion performance of MAO ceramic films was studied. The experimental results indicated that the GO additive could decrease the breakdown voltage, enhance the MAO reaction, decrease the surface roughness, reduce the porosity, increase the film thickness, and improve the ceramic/metal interface adhesion. The MAO ceramic film prepared in the electrolyte with 0.15 g/L GO additive had the best corrosion resistance in 3.5 wt% NaCl solution, as manifested by a corrosion current density of 3.72 × 10−8A·cm−2 that was 2 orders of magnitude less than that of the 5B70 Al alloy substrate. The same results of corrosion resistance were also verified by immersion corrosion test.

A smart electroplating approach to fabricate mechanically robust and fluorine-free Ni-W alloys based superhydrophobic coating on Al alloy

In this study, a novel and smart electroplating method was presented to fabricate a mechanically robust superhydrophobic coating on Al alloys. The superhydrophobic coating was composed of Ni-W alloy film with high hardness and stearic acid (STA) with low surface energy, providing excellent abrasive resistance, anti-corrosion properties, and self-cleaning ability. Specifically, a thin transition layer of Al-Ni-W was pre-electroplated on the Al alloy substrate by utilizing Al as anode and Al alloys as cathode in Ni-W ions aqueous solution, which overcome the difficulty of directly electroplating alloys coating on the Al alloys surface. Finally, a robust composite superhydrophobic film was achieved after coating STA layer on Al alloy/Al-Ni-W/Ni-W substrate. As anticipated, the as-prepared Al alloys demonstrates excellent mechanical durability and chemical stability, including wear resistance, hardness, corrosion resistance and self-cleaning with a champion water contact angle of 163° and corrosion protection efficiency of 99.4%. The Leeb hardness of superhydrophobic film coated Al alloys was enhanced by 87.1% compared to the pristine Al alloys, increasing from 325 ± 3 to 608 ± 4. This method provides a universal pathway for fabricating robust superhydrophobic film on the active metallic substrates.

Silicon nitride assisted carbon nanotubes induced stacking faults and twins in aluminum alloy composite joint

The extensive heat input during welding can generally disrupt the meticulously crafted microstructure of the Al alloy substrate, leading to a marked decrease in the mechanical performance of the traditional joint. Here, we conducted a study of adding silicon nitride and CNTs to form Al composite joints, which not only compensated for the microstructural defects caused by welding, but also improved the tensile strength of the joints by 31%. Importantly, microstructural analysis reveals that there are twinning and SFs in both Al and Al4C3 phase. It was contributed to Al4C3 growth and the reduction in Al alloy SFs energy by CNTs. Moreover, the residual CNTs and Al4C3 phase in the composite joints refined the original precipitation phase network. This work is supposed to provide new insights into the strengthening of composite joints based on SFs and twins.

Enhanced corrosion and tribocorrosion behavior of plasma electrolytic oxidized coatings on 5052 aluminum alloy with addition of pullulan to silicate electrolyte

Plasma electrolytic oxidation (PEO) ceramic coatings were fabricated on a 5052 aluminum (Al) alloy using a silicate-based electrolyte with the pullulan addition, and the effects of different pullulan concentrations on the corrosion and tribocorrosion resistance of the coatings were investigated. The morphology, chemical composition, phase structure, and mechanical properties of the coatings were observed via scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and scratching. The corrosion and tribocorrosion properties were evaluated via electrochemical tests and tribocorrosion tests in a 3.5 wt% NaCl solution, respectively. As a result of the pullulan addition, the phase structure of the coatings was slightly affected, but their microstructure and mechanical properties were significantly altered. The PEO coating displayed the smallest pore size and densest structure at a concentration of pullulan addition of 1.0 g/L. The corrosion current density of PEO coating was 2.41 × 10−8 A/cm2, which was two orders of magnitude lower than that of the Al alloy substrate. In addition, under tribocorrosion conditions, the wear rate of PEO coating was only 4.6 × 10−6 mm3N−1m−1, which was 91.8 % lower than that of the substrate, indicating excellent corrosion and tribocorrosion resistance. This study provides guidelines for the development of a sustainable and eco-friendly corrosion inhibitor for PEO coatings on Al alloys.

The Mechanical and Tribological Properties of Cold-Sprayed Cermet Coatings—Al Alloy Substrate Systems

AbstractThe article describes the influence of a solid lubricant such as graphite on the coating-substrate adhesion, susceptibility to cracking during three-point bending tests and tribological properties of the cermet coating-substrate systems. Two types of deposits Cr3C2-25(Ni20Cr) and (Cr3C2-25(Ni20Cr))-5(Ni25C), cold-sprayed on the Al 7075 alloy substrate, were analyzed. The Cr3C2-25(Ni20Cr) coatings showed a homogeneous microstructure with evenly distributed ceramic particles in a Ni20Cr matrix. The (Cr3C2-25(Ni20Cr))-5(Ni25C) deposits also contained graphite placed both between metallic particles and near the crushed ceramic Cr3C2 particles. The force required for the crack that appeared in the coating-substrate system during the three-point bending test under constant velocity was significantly higher in the case of (Cr3C2-25(Ni20Cr))-5(Ni25C) deposit than in that without the solid lubricant. The cracks were observed perpendicular to the coating-substrate interface. The graphite embedded in the cermet coating structure prevented the formation of crack nuclei during three-point bending test under cyclic load at room temperature and reduced the size of cracks in the deposit at 200 °C. Both cermet coatings revealed the same adhesion. The addition of graphite not only did not deteriorate the adhesion of the deposits and thus their quality but also improved their other properties, such as flexural strength and wear resistance. Coatings containing the solid lubricant showed a lower wear index than the Cr3C2-25(Ni20Cr) deposits examined at both room and elevated temperatures. This recommends their use in industry as deposit working in heavy wear conditions. The presented results of mechanical tests effectively fill the gap regarding the properties of the cold-sprayed cermet coatings.