Microstructure Of Coatings Research Articles

Phase composition, microstructure and mechanical properties of CVD Ti–B–N coatings deposited at different temperatures guided by thermodynamic calculations

TiBN coatings, as materials with broad potential applications, have received much attention in surface engineering in recent years. Within this work, the chemical vapor deposition (CVD) phase diagrams of TiBxNy coatings were calculated and the effects of deposition temperature (830–920 °C) on the microstructure, phase composition and mechanical properties of CVD TiBxNy coatings were investigated. The TiB0.61N0.84 and TiB0.61N0.81 coatings deposited at 830 and 860 °C have a particle-like surface, the TiB0.56N0.88 and TiB0.55N0.92 coatings deposited at 890 and 920 °C exhibit needle-like characteristic. XPS and TEM results indicate that TiBxNy coatings consist of nanocrystalline TiN and TiB2 embedded in amorphous TiB and BN matrix. The TiB0.61N0.84 coating exhibits the highest hardness of 40.7 GPa. The hardness of the coatings decreases as the deposition temperature increases. The presently developed approach of thermodynamic calculations and key experiments is equally valid for the efficient deposition of other CVD coatings.

Effect of WC particle size on the microstructure and tribological properties of high-speed laser cladding Ni/WC composite coatings

Ni/WC composite coatings with WC particle sizes of 30–65, 65–100, and 100–145 μm were prepared on 304 steel using high-speed laser-cladding (HSLC). The phase composition, microstructure, and wear mechanism of the composite coatings were studied. The dendrite-growth mechanism around WC with different particle sizes and the effects of WC with different particle sizes on the microhardness and tribological properties of the composite coatings were analyzed. The results demonstrated that the composite coating consisted of intermetallic compound Ni3Fe and secondary carbides W2C and (Cr, Fe)7C3. The composite coating exhibited good macroscopic morphology and uniform microstructure. The WC particle size obviously influenced the columnar and cellular dendrites in the coating. The microhardness values of the three groups of composite coatings were 419.35, 314.64, and 331.65 HV. The average friction coefficients were 0.4876, 0.5693, and 0.5439. The wear volumes were 0.001, 0.0015, and 0.002 mm3. The wear mechanisms included adhesive, abrasive, and oxidation wear mechanisms. The results verified that the WC coating with a small particle size possessed the best microhardness and tribological properties.

Hydrophilic Coating Microstructure Mediates Acute Drug Transfer in Drug-Coated Balloon Therapy.

Drug-coated balloon (DCB) therapy is a promising endovascular treatment for obstructive arterial disease. The goal of DCB therapy is restoration of lumen patency in a stenotic vessel, whereby balloon deployment both mechanically compresses the offending lesion and locally delivers an antiproliferative drug, most commonly paclitaxel (PTX) or derivative compounds, to the arterial wall. Favorable long-term outcomes of DCB therapy thus require predictable and adequate PTX delivery, a process facilitated by coating excipients that promotes rapid drug transfer during the inflation period. While a variety of excipients have been considered in DCB design, there is a lack of understanding about the coating-specific biophysical determinants of essential device function, namely, acute drug transfer. We consider two hydrophilic excipients for PTX delivery, urea (UR) and poly(ethylene glycol) (PEG), and examine how compositional and preparational variables in the balloon surface spray-coating process impact resultant coating microstructure and in turn acute PTX transfer to the arterial wall. Specifically, we use scanning electron image analyses to quantify how coating microstructure is altered by excipient solid content and balloon-to-nozzle spray distance during the coating procedure and correlate obtained microstructural descriptors of coating aggregation to the efficiency of acute PTX transfer in a one-dimensional ex vivo model of DCB deployment. Experimental results suggest that despite the qualitatively different coating surface microstructures and apparent PTX transfer mechanisms exhibited with these excipients, the drug delivery efficiency is generally enhanced by coating aggregation on the balloon surface. We illustrate this microstructure-function relation with a finite element-based computational model of DCB deployment, which along with our experimental findings suggests a general design principle to increase drug delivery efficiency across a broad range of DCB designs.

High-velocity oxy-fuel and high-velocity air fuel sprayed WC-Co-Cr coatings on solution-treated 21-4N steel for slurry and corrosion resistance

This study aims to fabricate WC-Co-Cr coatings on the solution-treated 21-4N steel utilizing high-velocity oxy-fuel (HVOF) and high-velocity air fuel (HVAF) techniques. The microstructure, hardness, surface quality, porosity, slurry erosion, and corrosion resistance of HVOF and HVAF coatings on solution-treated 21-4N steel were investigated and compared. The HVAF sprayed WC-Co-Cr coating exhibited dense structure, more hardness (1582 HV), greater fracture toughness (5.69 MPa m1/2), less decarburization, and lower porosity (0.97 %) as compared to HVOF sprayed coating. Further, slurry jet erosion tests and electrochemical corrosion tests provide a comprehensive evaluation of the coating’s performance under erosive and corrosive conditions. Eventually, the conclusive results of the study affirm the exceptional performance of the high-velocity air fuel sprayed WC-Co-Cr coating, demonstrating its superiority in both erosion and corrosion resistance compared to the high-velocity oxygen fuel sprayed coating.

Effect of La2O3 on hardness, wear resistance and corrosion resistance of WC/Fe90 iron-based composite coatings

In this paper, WC/Fe90 iron-based composite coatings were prepared using plasma spraying technology. The influence of rare earth oxide La2O3 on the microstructure and properties of the composite coatings was studied through microstructural characterization, phase identification, microhardness, wear resistance, and corrosion resistance. The results showed that the composite coatings were mainly composed of α-Fe, M7C3, Fe-Cr, FexCy, and other reinforcing phases. The addition of La2O3 promoted the decomposition of WC particles and improved the uniformity of the coatings. When the La2O3 content reached 1.0 wt%, the hardness was the highest, reaching 885.481 HV, which was 10% higher than that of the untreated coatings. The addition of La2O3 increased the friction coefficient but still improved the wear resistance. Compared to the coatings without La2O3, the mass loss due to wear was reduced by approximately 40%. Moreover, the addition of La2O3 formed a passive film on the surface of the coatings, effectively preventing the penetration of Cl- ions and refining the grain structure of the coatings, significantly enhancing the corrosion resistance. When the La2O3 content was 1.0 wt%, the corrosion resistance of the coatings was the best.

A novel high-temperature FeSiAl/CaO–B2O3–SiO2 microwave absorption coating prepared via atmospheric plasma spraying

In this paper, CaO–B2O3–SiO2 (CBS) is utilized as matrix material of microwave coating for the first time to achieve high-performance microwave absorption under high-temperature. A series of FeSiAl (FSA)/CBS composite coatings were prepared via atmospheric plasma spraying. The impact of spraying power on the microstructure, electromagnetic properties, and high-temperature stability of as-sprayed coatings were studied. The experimental results reveal that CBS could effectively suppress the formation of the lamellar structure of FSA as the low initial melting temperature, also form unexpected Fe2SiO4 structure with FSA during the spraying process. The increase in complex permittivity of the coating is primarily attributed to enhanced coating density and the development of Fe-rich regions within the CBS matrix. Furthermore, the dense coating prevents the oxidation of FSA and exhibits high-temperature stability. Our coating of 1 mm thickness has a reflection loss below −5 dB with frequency range of 7–14.8 GHz at 500 °C.

Investigation on the Microstructure and Micro-Mechanical Properties of Thermal-Sprayed NiCoCrAlY High Entropy Alloy Coating

NiCoCrAlY high entropy alloy (HEA) coating (47.1 wt.% Ni, 23 wt.% Co, 17 wt.% Cr, 12.5 wt.% Al, and 0.4 wt.% Y) was deposited on a stainless steel subtract by atmospheric plasma spraying (APS). The as-deposited coating was about 300 μm thickness with <1% porosity. The microstructure of the coating consisted of dispersed secondary phases/intermetallics in the solid solution. The stress–strain behaviour of this coating was investigated in micro-scale with the help of in situ micro-pillar compression. The experimental results show that yield and compressive stress in the cross-section of the coating was higher (1.27 ± 0.10 MPa and 2.19 ± 0.10 GPa, respectively) than that of the planar direction (0.85 ± 0.09 MPa and 1.20 ± 0.08 GPa, respectively). The various secondary/intermetallic phases (γ′–Ni3Al, β–NiAl) that were present in the coating microstructure hinder the lattice movement during compression, according to Orowan mechanism. In addition to that, the direction of the loading to that of the orientation of the phase/splat boundaries dictate the crack propagation architecture, which results in difference in the micro-mechanical properties.

Construction of Magnesium Phosphate Chemical Conversion Coatings with Different Microstructures on Titanium to Enhance Osteogenesis and Angiogenesis.

Titanium (Ti) and its alloys are widely used as hard tissue substitutes in dentistry and orthopedics, but their low bioactivity leads to undesirable osseointegration defects in the early osteogenic phase. Surface modification is an important approach to overcome these problems. In the present study, novel magnesium phosphate (MgP) coatings with controllable structures were fabricated on the surface of Ti using the phosphate chemical conversion (PCC) method. The effects of the microstructure on the physicochemical and biological properties of the coatings on Ti were researched. The results indicated that accelerators in PCC solution were important factors affecting the microstructure and properties of the MgP coatings. In addition, the coated Ti exhibited excellent hydrophilicity, high bonding strength, and good corrosion resistance. Moreover, the biological results showed that the MgP coatings could improve the spread, proliferation, and osteogenic differentiation of mouse osteoblast cells (MC3T3-E1) and vascular differentiation of human umbilical vein endothelial cells (HUVECs), indicating that the coated Ti samples had a great effect on promoting osteogenesis and angiogenesis. Overall, this study provided a new research idea for the surface modification of conventional Ti to enhance osteogenesis and angiogenesis in different bone types for potential biomedical applications.

Solidification and tribological behaviors of CoCrFeNiSi0.5-(Al,Ti) non-equiatomic high entropy alloy coatings fabricated by direct laser deposition

In order to evaluate the difference in the effects of Al and Ti elements on the microstructure and tribological behaviors of CoCrFeNi-based high entropy alloy (HEA) coatings, CoCrFeNiSi0.5-(Al,Ti) non-equiatomic HEAs coatings were prepared using direct laser deposition (DLD). The phase constitution, solidification microstructure and tribological behaviors of the HEA coatings were investigated. The results indicated that CoCrFeNiSi0.5 HEA coating was composed of face centered cubic (FCC) phase with microstructure of columnar and cellular grains. The addition of Al and Ti led to a columnar-to-equiaxed transition (CET) in the HEA coatings. When only Al was added (CoCrFeNiSi0.5Al0.5), the primary phase transformed into a body centered cubic (BCC) phase (94 vol%). Additionally, Cr3Si formed in the interdendrite (ID) region, and a spinodal decomposition structure emerged in the dendrite (DR) region. Conversely, with the inclusion of Ti alone (CoCrFeNiSi0.5Ti0.5), the matrix maintained its FCC phase, but Ni16Ti6Si7 (G phase, 20.9 vol%) and Cr15Co9Si6 (15.1 vol%) were generated in the ID and DR regions, respectively. Incorporating both Al and Ti (CoCrFeNiSi0.5Al0.5Ti0.5) significantly reduced the G phase content in the ID region to 7.9 vol% and led to the formation of dispersed Fe3Al nanoparticles with an average size of 99 nm in the DR region. The CoCrFeNiSi0.5 HEA coating exhibited the lowest hardness (249 HV0.1), the highest friction coefficient (0.778), and the poorest wear resistance. For the HEA coatings containing Al and Ti, the microhardness significantly increased to over 700 HV0.1, and the friction coefficient decreased to around 0.6. However, the wear resistance of the CoCrFeNiSi0.5Al0.5 HEA coating was almost equivalent to that of the CoCrFeNiSi0.5 with a wear loss of 5.1 mg. By contrast, the HEA coatings containing Ti demonstrated notably improved wear resistance, with wear losses of only 2.2 mg and 2.4 mg for the CoCrFeNiSi0.5Ti0.5 and CoCrFeNiSi0.5Al0.5Ti0.5 HEA coatings, respectively.

Microstructure and mechanical property regulation of plasma-sprayed high-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 thick coatings

The effect of critical plasma spraying parameters (CPSPs) on phase composition, microstructure and mechanical property of (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 thick coatings was investigated. After coating deposition, the phase structure of (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 was transformed from pyrochlore to fluorite in the coating. When the CPSP value increased from 0.83kW/Lpm to 1.17kW/Lpm, the porosity of as-deposited coating was decreased from (16.46 ± 0.65)% to (6.94 ± 0.44)%. As a result, the elastic modulus of the coating was improved from (59.34 ± 2.39) GPa to (79.19 ± 4.78) GPa, and the corresponding micro-hardness was also increased from (2.59 ± 0.30) GPa to (3.39 ± 0.37) GPa. Consequently, the fracture toughness of as-deposited coating was decreased with the increasing CPSP value, while the corresponding residual stress was obtained to be compressive stress and it increased from -(43.00 ± 1.96) MPa to -(70.42 ± 3.89) MPa, indicating that the lower CPSP value was beneficial to reducing the residual compressive stress, which might be in favor of enhancing thermal shock resistance of coating.

Effects of duty cycle on microstructure and mechanical properties of (AlCrNbSiTi)N high-entropy nitride hard coatings deposited by pulsed arc ion plating

High entropy (AlCrNbSiTi)N hard coatings have been deposited by pulsed arc ion plating with various duty cycles. The effects of duty cycles on the morphology, chemical composition, microstructure and mechanical properties of coatings are studied. Higher duty cycles result in the increase of deposited particles and holes on the surface of the coatings. The coatings exhibited a single-phase face centered cubic structure with preferred orientation of (200). Appropriate duty cycle can significantly improve the comprehensive mechanical properties of the coatings. The coating exhibits highest hardness and elastic modulus of 43.4 GPa and 573.4 GPa, respectively. Formation of surface oxides during friction process are observed, which play a self-lubricating role.

Study on Microstructure, Mechanical Properties, Tribological Properties and Service Performance of CrAlN and CrAlBN Coatings Deposited on Powder Metallurgy High-Speed Steel (PM-HSS) and Shaper Cutter by Arc Ion Plating Technique

CrAlN and CrAlBN coatings were prepared on the surface of high-speed steel and shaper cutter by physical vapor deposition (PVD) technique using arc ion source. In the process of coating preparation, the adhesive layers were deposited by low bias voltage (−40 V) and the working layers are deposited by high bias voltage (−130 V). The effects of the addition of B element on the microstructure, hardness, elastic modulus and wear resistance of CrAlBN coating were studied. The results show that B element and its compounds exist in amorphous form in the coating, resulting in lattice distortion of the coating, increase of coating hardness to 37.1 GPa, and decrease of elastic modulus to 406.2 GPa. The addition of B element increases the uniformity of the columnar structure distribution and decreases the width of the columnar structure and grain size. The resistance to elastic deformation and plastic deformation of CrAlBN coating is improved, the wear resistance is improved. The performance of CrAlN and CrAlBN coatings on shaper cutter was studied. It was found that the main failure mode of shaper cutters is boundary wear and the wear mechanism of coatings had changed obviously. CrAlBN coating is mainly due to fatigue induced failure, accompanied by some diffusion wear. The addition of B element makes the CrAlBN coating have excellent resistance to oxidative wear, abrasive wear and diffusion wear during cutting. The results show that the addition of B element can improve the microstructure and mechanical properties of CrAlN coating, and the preparation of CrAlBN coating on the surface of the shaper cutter can significantly improve the service life of the coated shaper cutter, which has significance for the development of the shaper cutter industry.

Effect of Heat Treatment on Microstructure and Wear Behavior of Laser Clad FeCoCrMoNi High-Entropy Alloy Coatings

Effect of Heat Treatment on Microstructure and Wear Behavior of Laser Clad FeCoCrMoNi High-Entropy Alloy Coatings

Effect of appropriate vibration frequency on microstructure and properties of laser cladding Co-based self-lubricating composite coatings

Effect of appropriate vibration frequency on microstructure and properties of laser cladding Co-based self-lubricating composite coatings

Effect of Step potential on the Structure and Properties of Ceramic Coating on the Surface of 2024 Aluminum Alloy thin Sheets

In this paper, a ceramic coating was prepared on the surface of a 2024 aluminum alloy thin sheet via both stepped potential and constant potential methods. This study investigated the effects of different potential modes on the microstructure and properties of ceramic coatings. The analysis included assessments of the microstructure, hardness, corrosion resistance, wear resistance, and mechanical properties of the ceramic coating on the surface of the 2024 aluminum alloy. The findings revealed that the constant potential method tends to result in cracking of the ceramic coating, leading to a decrease in coating quality. The highest hardness achieved with the ceramic coating prepared using the constant potential method was only 308 HV. In contrast, the coating prepared using the stepped potential method at 30 V reached a microhardness of 337 HV, indicating a higher microhardness. When prepared with a stepped potential of 30 V, the ceramic coating showed the best corrosion resistance, with a corrosion potential of -0.53 V and a corrosion current density of 0.20 μA·cm2. The wear volume of the ceramic coating prepared at a step potential of 30 V was also the lowest, measured at 0.025 mm³. The mechanical property results indicate that the ceramic coating reduces the tensile strength and elongation of the material itself. Comparing the two potential modes, the ceramic coating prepared under a stepped potential had a smaller impact on the tensile strength and elongation of the 2024 aluminum alloy, Under the condition of 30 V, the tensile strength decreased by 30.3 MPa, and the elongation decreased by 1.37%.

Microstructure and properties of multicomponent silicide ceramic coatings on Ta substrate prepared by slurry sintering method

High entropy silicide (Mo0.2Cr0.2Ta0.2Nb0.2W0.2)Si2 (named as MeSi2) coating was successfully prepared on Ta substrate by slurry sintering method. Firstly, precursor powders were initially obtained through mechanical alloying of silicide powders. Then powder slurry was coated on Ta substrate, and then the samples were sintered. For comparison, TaSi2 coating prepared by halide-activated pack cementation method was synthesized. Subsequently, the static oxidation resistance of both MeSi2 coating and TaSi2 coating was examined at 1200 °C, results revealing that the MeSi2 coating demonstrates an effective protection time of more than 60 h. The protective effect and duration of the MeSi2 coating on Ta substrate are significantly greater than that of TaSi2, indicating an improvement oxidation resistance due to the high entropy effect of the silicide coating. After oxidation, the coating evolved an outer SiO2 layer, followed by MeSi2, Me5Si3, TaSi2, and Ta5Si3 layers. As the oxidation progressed, MeSi2 gradually transformed into Me5Si3, leading to a loss of the coating's antioxidant capacity.

Tribological behaviour of polytetrafluoroethylene containing plasma electrolytic oxidation coatings on TC4 alloy

Improving the tribological performance of titanium alloys is crucial to expanding their industrial applications. In this study, self-lubricating and wear-resistant coatings for TC4 alloy were achieved by combining plasma electrolytic oxidation (PEO) prepared using compounded electrolytes with incorporation of polytetrafluoroethylene (PTFE) as a solid lubricant. The investigation focused on the comprehensive effects of compounded electrolytes and PTFE on the microstructure and tribological behaviour of PEO coatings. After doping with PTFE, the coating prepared in electrolyte containing silicate, phosphate, and aluminate exhibited lowest wear rate (decreasing by 95.1%) and maximum hardness of 638.6 HV compared to other coatings. Additionally, the coefficient of friction (COF) significantly decreased from 0.8 to 0.16. This can be attributed to the strategy of depositing low-frictional discontinuous layers on hard PEO coatings.

Microstructure and Mechanical Properties of Laser Clad18Ni300 Coatings with La2O3 Addition on ZL205A Aluminum Alloy

Microstructure and Mechanical Properties of Laser Clad18Ni300 Coatings with La2O3 Addition on ZL205A Aluminum Alloy

Effect of Si addition on the microstructure and liquid lead-bismuth eutectic cavitation erosion behaviors of AlCrFeMoTi laser clade coatings

High entropy alloys exhibit high resistance to the lead-bismuth eutectic (LBE), making them promising candidate materials for protective coatings. However, improving their mechanical properties and resistance to cavitation erosion in flowing LBE environment remains a challenge. In this study, AlCrFeMoTi coatings were synthesized using laser cladding, and Si was added to enhance their resistance to cavitation erosion. The results showed that the AlCrFeMoTi coatings mainly contained FeMoTi and Fe-Cr phases. After the addition of Si, a single phase FeMoTi was formed. Moreover, Si increased the hardness of the coatings by 9.6%. After cavitation erosion in LBE at 500 ℃, cracks formed on the surface of the coatings and the main damage mechanism of the coating was lamellar spalling. The addition of Si inhibited crack propagation and reduced the erosion depth of the coatings by 43.5%. It can be attributed to the addition of Si makes the oxidation homogeneous and the strengthening of the single-phase.

Effect of Al3+ on the surface microstructure and film formation mechanism of Zr-based conversion coatings with improved corrosion resistance performance on cold rolled steel

Most Zr conversion coatings are prepared on Al alloys, with Al3+ from the substrate contributing significantly to the film growth process. Thus, the effect of Al3+ on the electrochemical characteristics, surface microstructure and film-formation mechanism of Zr-based conversion coatings on old- rolled steel (CRS) substrates was investigated by growing the coatings with and without Al3+ as an additive. Electrochemical tests indicated that the anticorrosion performance of the Zr-Al coatings prepared in the presence of Al3+ was greatly superior to that of Zr conversion coatings obtained in the absence of Al3+. Field-emission scanning electron microscopy and X-ray photoelectron spectroscopy analysis indicated that adding of Al3+ in the conversion bath changed the surface microstructure of the Zr coating, greatly promoted the deposition of Zr and F on the CRS substrate and increased the film thickness and density. Both coatings were embedded into the etched CRS substrates. The presence of Al3+ additive induced the formation of different coating components. The Zr coating mainly consisted of ZrO2 and some FeFx, whereas the Zr-Al coatings comprised of ZrO2, ZrOxFy, Al2O3, AlFx and some FeFx. The present study results confirm the key role of Al3+ as an additive in the film formation and growth process of Zr coatings and its effect on enhancing the anticorrosion performance of CRS substrates in NaCl solutions.