Annealed Coatings Research Articles

Annealing activated substrate element diffusion and its influence on the microstructure and mechanical properties of CVD TiN/TiCN coatings

TiN/TiCN deposited by chemical vapor deposition (CVD) is widely used as hard coating system for cemented carbide cutting tools, typically under an Al2O3 top layer. During the deposition of the Al2O3 top layer, the underlying TiN and TiCN layers are exposed to high temperatures. Therefore, the present study focuses on the influence of this Al2O3 deposition step, which is mimicked by a vacuum-annealing treatment, on the microstructure and mechanical properties of the TiN/TiCN coating. By applying advanced characterization techniques such as scanning electron microscopy, scanning transmission electron microscopy, transmission Kikuchi diffraction, atom probe tomography, and micro-mechanical bending tests on both, as-deposited and annealed coatings, changes in the microstructure and mechanical properties were studied. It was found that W and Co diffusion occurs along the TiN and TiCN grain boundaries from the substrate into the coating. While the hardness, Young's modulus, and fracture toughness remained unaffected by the annealing treatment, a significant decrease of the fracture stress with increasing annealing time was observed. The present study provides a fundamental understanding of substrate element diffusion in CVD TiN/TiCN coatings deposited on cemented carbide substrates.

Tailoring electroless Ni-W-P polyalloy coatings: Unveiling the synergistic impact of cerium addition and annealing on surface functional properties

Electroless deposition of Ni-based coatings is a cost-effective solution to augment the surface mechanical and electrochemical properties of engineering components. This work explores the influence of addition of rare-earth element Ce on the characteristics of Ni-W-P coatings. The concentration of Ce salt in the deposition bath was varied in the range 0–14 mg/L, and the highest deposition rate was for the solution with 8 mg/L Ce. A homogeneous distribution of Ce over the coated surfaces was observed, and the share of Ce in the composition of the deposition varied monotonically with the Ce concentration in solution. Further, the coating surface compositions also depended on the Ce-content. Coating obtained using 8 mg/L Ce was found to have significantly improved scratch hardness (8.49 GPa), fracture toughness (7.05 MPa.m1/2), specific wear rate (3.1 × 10−6 mm3/N.m) and corrosion protection efficiency (94.16 %) as compared to the coating without Ce (3.87 GPa, 3.39 MPa.m1/2, 9.03 × 10−6 mm3/N.m, and 45.44 %, respectively). Interestingly, the ability of the coating to inhibit biofilm formation on the surface initially increased with increasing Ce content, but this effect also diminished above 8 mg/L Ce. Additionally, annealing the coatings caused further alterations in the microstructures, resulting in improvement in the microhardness, scratch, wear, and biocorrosion resistance, but at the cost of compromised corrosion resistance. Properties of such annealed coatings also depended on the annealing temperature. Therefore, this study indicates that a wide spectrum of combinations of surface physical, mechanical, and electrochemical properties can be achieved by controlling only two processing conditions, i.e., the Ce concentration, and the annealing temperature.

Microstructure and surface morphology change of hydrogenated diamond-like carbon coating with gradient Cr and Si under high temperature and high pressure

A series of annealing treatments were designed to investigate the microstructure structure and surface morphology of hydrogenated diamond-like carbon coating with gradient Cr and Si (DCrSi) in different environments (argon & isostatic pressure) at different temperatures (400°C, 500°C, and 600°C). The pressure effect on the stability of DCrSi coatings was deduced from the analysis of the microstructure structure and surface morphology by using scanning electron microscopy (SEM), surface roughness test, and Raman spectroscopy. The experiment results show that no apparent change to the layer structure can be found in the argon annealed and HIPped coatings. Similar to argon annealed coatings, with increasing HIPping temperature, the surface roughness of coatings increases, and the sp3 content of the coatings reduces. The relatively low roughness of the HIPped surfaces compared with the argon annealed ones could be attributed to the delayed transformation from sp3 carbon bonding to sp2 carbon bonding (i.e., graphitization) by high pressure. Compared with Si-free DCr coating, for Si-containing DCrSi coatings, Si bonded with C from broken C-H bonding and C-C bonding to form SiC quasi compound. Adding silicon into DLC can increase the density of the coatings.

Medium and High Phosphorous Ni-P Coatings Obtained via an Electroless Approach: Optimization of Solution Formulation and Characterization of Coatings

A new lead-free electroless Ni-P plating solution was developed for the deposition of coatings with medium phosphorus content (MP, 6–9 wt%), and its composition was optimized to obtain deposits with high phosphorus (HP, 10–14 wt%). Cleaning and activation treatments were studied in terms of effectiveness and influence on the deposition rate. The concentration of reagents (nickel salt, complexing agent, reducing agent and stabilizer) was studied, and their combined effect on P content and plating rate was investigated. The obtained coatings were analyzed by SEM and XRD and thermally treated at 400 °C and 600 °C to study microstructural evolution. Vickers hardness was measured on as-deposited and annealed coatings to relate hardness evolution to microstructural changes after thermal treatments. Optimal deposition conditions were determined, enabling the production of MP coatings (6.5 wt% P) with a plating rate of 40 µm/h and HP coatings (10.9 wt% P) with a plating rate of 25 µm/h at 90 °C. Samples heat-treated at 400 °C showed improved hardness thanks to crystallization and microprecipitation of Ni3P hard phases, whereas hardness decrease was observed after treatment at 600 °C due to the combined effect of grain growth and coarsening of Ni3P precipitates. No through-the-thickness cracks were detected by the Ferroxyl reagent after heat treatments.

Influence of annealing on the structure and wear resistance of coatings produced by cold spraying of Al–SHS7574 powder mixture

In present work, the possibility of fabricating a composite cold-sprayed coatings consisting of partially amorphous alloy reinforcing particles and an aluminum matrix was studied for the first time. A mixture of pure aluminum and SHS7574 powders in a ratio of 50/50 wt% was deposited on aluminum alloy substrates, which ensured the formation of high-quality coating with a porosity of less than 1%. The ratio of SHS7574 alloy to aluminum in the as-sprayed samples was nearly the same as in the initial powder mixture which indicates a similar efficiency of component deposition. Composite coatings were annealed in a vacuum furnace at 540 °C and 600 °C. Microstructure and phase composition of as-sprayed and annealed coatings were examined with XRD, SEM and EDX mapping. Post annealing of the coatings promoted the formation of a reaction layers around the Fe-based alloy particles consisting of Fe2Al5, Fe4Al13, Fe23B5, and Fe5C2 phases. The effect of annealing on the mechanical properties of the Al–SHS7574 coatings was determined by measuring hardness, nanohardness and wear resistance according to ASTM G 133–05. The increase in the samples’ hardness after annealing was associated with the formation of a reaction layers and increase in its thickness with rising annealing temperature. The coating annealed at 600 °C demonstrated the highest hardness due to the formation of thick brittle reaction layers. The preservation of the aluminum matrix with the simultaneous formation of thin reaction layers after annealing at 540 °C reduced the wear rate of the coating despite the moderate hardness.

Influence of annealing on microstructure and cavitation erosion resistance of iron-based metallic glass coatings synthesized by HVOF thermal spraying

This study aimed to deposit a novel iron-based metallic glass coating onto 316L stainless steel and analyze the microstructures, phases, mechanical properties, and cavitation erosion resistances of the as-sprayed and annealed coatings. The coatings were annealed at temperatures of 540, 640, and 740 °C, resulting in varying crystal contents. As the annealing temperature increased, the amorphous content of the iron-based coatings decreased from 90% to 62%, 35%, and 29%, respectively, while the microhardness increased from 849 HV0.2 to 944, 970, and 860 HV0.2, respectively. The coating annealed at 640 °C exhibited the best resistance to cavitation erosion, whereas the coating annealed at 740 °C had the poorest resistance. Cavitation erosion always initiated from defects in the amorphous/nanocrystal coatings, such as pores, microcracks, or phase interfaces, and then propagated along these defects, eventually causing the stripping of particles. During cavitation erosion, the well-bound particles fragmented under repeated shocks, and the amorphous phase crystallized into nanocrystals, leading to detachment of particles in small sizes.

Advanced diamond-reinforced metal matrix composite (DMMC) coatings via HVAF process: Effect of particle size and nozzle characteristics on tribological properties

High-velocity air fuel (HVAF) spraying is a versatile and cost-effective platform to fabricate wear resistant coatings. In this work, deposition of Nickel–Phosphorus cladded diamond feedstock is explored as a greener alternative to realize highly wear resistant large-area coatings. To the best of authors knowledge. this is the first study that has utilized HVAF technique for developing wear resistant Ni–P coatings reinforced with diamond (NCD). This work also aims to understand the effect of particle size by using coarse (20–30 μm) and fine NCD (10–15 μm) particles as feedstock. The importance of utilizing appropriate processing conditions was also highlighted by using two different nozzle configurations, for which the two powder particle sizes exhibited considerable differences in terms of microstructure, phase characteristics and mechanical properties. Further, the effect of annealing on the above coating characteristics was also examined, and it is shown that optimal spraying conditions can preclude the need for post-treatment. Furthermore, the as-deposited and annealed coatings were subjected to sliding wear tests to assess their tribological performance. Post-wear analysis performed on worn surfaces revealed the associated wear mechanisms. The results ensuing from this work lay the foundation for realizing new generation of HVAF sprayed wear resistant Ni–P/diamond composite coatings for diverse applications.

Improved osteointegration response using high strength perovskite BaTiO3 coatings prepared by chemical bath deposition

A wide range of bioactive materials have been investigated for tissue engineering and regeneration. Barium titanate is a promising smart material to be used as scaffold for bone tissue engineering. Barium titanate coatings are prepared in the present study using chemical bath deposition technique. Coatings are prepared at room temperature with the variation in solution molarity from 0.1 to 1.2 M. Perovskite tetragonal phase is observed after annealing the samples at 300 °C using 1.0–1.2 M solutions. Normal-anomalous dielectric response is observed for annealed coatings. Maximum transmission of ∼55% and ∼82% is observed under as-prepared and annealed coatings, respectivly. Variation in direct band gap, i.e. 3.45–3.64 eV, is observed with varying molarity. High hardness of the coatings (∼1180 HV) is observed at 1.2M with fracture toughness of ∼22 MPam−1/2. Biodegradation studies show smaller values of weight loss even after immersion in simulated body fluid (SBF) after 26 weeks. Barium titanate coatings also show high antioxidant activity. BaTiO3's antibacterial reaction is evaluated against microorganisms such as Escherichia coli (E. coli) and Staphylococcus aureus. Antibacterial activity shows highest zone of inhibition (∼31 mm) against Staphylococcus aureus bacteria. Quantitative real-time PCR is used to assess the gene expression profile in cultivated cells. Thus, coatings produced without the use of hazardous solvents/reagents utilizing CBD technique are a potential material for biomedical applications.

Tribological behavior of Ni-Nb amorphous coating fabricated by mechanical alloying method

In this study, the microstructure, microhardness and tribological behavior of the Ni-Nb amorphous coating fabricated by mechanical alloying method were investigated at three annealing timepoints (30, 120, 240 min) at 650 °C. Annealing of amorphous coating for 30 min led to a reduction in microhardness. However, as annealing continued, the microhardness demonstrated significant growth. The changes were attributed to the formation of Ni3Nb and Ni6Nb7 nanocrystalline intermetallic compounds embedded in the amorphous matrix. The wear resistance of the coatings up to 120 min of annealing showed a similar trend with microhardness but no longer followed the microhardness trend after 240 min of annealing. The delamination and oxidative wear mechanisms were the dominant wear mechanisms for the as-prepared and annealed coatings.

Microstructure and Corrosion Behavior of Atmospheric Plasma Sprayed NiCoCrAlFe High Entropy Alloy Coating.

High entropy alloys (HEAs) are multi-elemental alloy systems that exhibit a combination of exceptional mechanical and physical properties, and nowadays are validating their potential in the form of thermal sprayed coatings. In the present study, a novel synthesis method is presented to form high entropy alloy coatings. For this purpose, thermal sprayed coatings were deposited on Stainless Steel 316L substrates using atmospheric plasma spraying technique with subsequent annealing, at 1000 °C for 4 h, to assist alloy formation by thermal diffusion. The coatings in as-coated samples as well as in annealed forms were extensively studied by SEM for microstructure and cross-sectional analysis. Phase identification was performed by X-ray diffraction studies. The annealed coatings revealed a mixed BCC and FCC based HEA structure. Potentiodynamic corrosion behavior of SS316L sprayed as well as annealed coatings were also carried out in 3.5% NaCl solution and it was found that the HEA-based annealed coatings displayed the best corrosion resistance 0.83 (mpy), as compared to coated/non-annealed and SS 316 L that showed corrosion resistance of 7.60 (mpy) and 3.04 (mpy), respectively.

The Effect of Annealing Temperature on the Microstructure and Properties of Cr–C–Al Coatings on Zircaloy-4 for Accident-Tolerant Fuel (ATF) Applications

Elemental Cr/C/Al multilayers (stoichiometric ratio: 2:1:1) with and without a Cr overlayer have been synthesized on Zircaloy-4 substrates by magnetron sputtering. The effects of annealing temperatures (400 and 550 °C) on phase/microstructure formation, mechanical properties, and oxidation/corrosion performance have been comparatively studied. Annealing of the multilayers at 400 °C led to the formation of nanocrystalline composite consisting of intermetallic and binary carbide phases. Single-phase Cr2AlC was obtained after 550 °C annealing, but with microcracking of the coatings. Both annealed coatings displayed similar mechanical properties, high-temperature oxidation, and hydrothermal corrosion mechanisms. The composite coatings annealed at 400 °C significantly enhance the high-temperature oxidation resistance (α-Al2O3 scale growth) and hydrothermal corrosion (Cr2O3 passivation layer formation) of a Zircaloy-4 substrate without coating microcracking and delamination. Nanocomposite CrCAl-based coatings are promising candidates for coated ATF applications with acceptable processing temperatures and excellent oxidation/corrosion resistances for a zirconium alloy substrate.

Multi-layer MgF2/ITO coatings for electromagnetic interference shielding

Indium tin oxide (ITO) coatings have been found useful for diverse applications including electromagnetic interference (EMI) shielding for defense and aerospace purposes, solar cells, gas sensors, etc. However, the reliability, adhesion, transmittance and control of conductivity are some issues that need to be discussed for EMI shielding. Composite multi-layer coating of magnesium di-fluoride (MgF2) and ITO have been deposited on soda lime glass substrate using electron beam (e-beam) deposition technique at a substrate temperature of 350 °C and annealed in the temperature range of 200–500 °C for 1 h under vacuum. The deposited coatings have been characterized for structural, optical and electrical properties. The deposited coatings were crystalline with a crystallite size in the range of 20–30 nm for ITO and 15–20 nm for MgF2 coatings. The coating thickness of ITO and MgF2 determined by Rutherford backscattering technique were found to be 95 nm and 12 nm, respectively. The maximum transmittance in the visible range is ~92% for as-deposited and annealed multi-layer coatings. The band gap has been found in the range of 3.95–4.02 eV, which is suitable for EMI shielding effectiveness. Raman spectroscopy confirms quantum confinement in MgF2/ITO coatings. The electrical conductivity of as-deposited MgF2/ITO coating has been found to be 200 (Ω-cm)−1 which increased to a value of 1.002 x 103 (Ω-cm)−1 for the sample annealed at 500 °C under vacuum. The multi-layer coating annealed at 500 °C show good EMI shielding effectiveness of 50.4 dB without scarifying the transmittance.

Mechanical, tribological, anti-corrosion and anti-glass sticking properties of high-entropy TaNbSiZrCr carbide coatings prepared using radio-frequency magnetron sputtering

High-entropy TaNbSiZrCr carbide coatings were deposited on WC substrates by radio-frequency unbalanced magnetron sputtering with C2H2 flow rates ranging from 0 to 23 sccm. The microstructure, mechanical properties, tribological properties and anti-corrosion resistance of the coatings were analyzed in both an as-sputtered condition and an annealed condition. The anti-glass sticking performance of the coatings was additionally investigated by annealing the coatings at 750 °C for 1 h on BK7 glass plates. The results showed that the as-sputtered and annealed coatings with a low carbon content (i.e., C2H2 flow rates lower than 8 sccm) had a high hardness (>34.1 GPa). The as-sputtered sample deposited with the maximum C2H2 flow rate (23 sccm) showed the best tribological properties of all the as-sputtered samples. However, the wear rate of the coating increased by a factor of around 10 times after annealing. The annealed coating nevertheless exhibited the highest corrosion resistance of all the coatings. Finally, the glass sticking results showed that the use of an appropriate C2H2 flow rate (4–12 sccm) was beneficial in enhancing the anti-glass-sticking performance of the coatings.

High-temperature oxidation and hydrothermal corrosion of textured Cr2AlC-based coatings on zirconium alloy fuel cladding

Alumina-forming MAX phase coatings reveal great potential for accident tolerant fuel (ATF) cladding applications due to their favorable physical and mechanical properties and excellent high-temperature oxidation resistance. The feasibility of Cr2AlC MAX phase as protective coating on zirconium-alloy fuel claddings was explored focusing on high-temperature oxidation resistance in steam and hydrothermal corrosion performance in autoclave. Single-phase and basal-plane textured Cr2AlC coatings (~6 μm thick) were synthesized on Zircaloy-4 substrate by thermal annealing of specifically designed, magnetron-sputtered Cr/C/Al elemental multilayers at 550 °C for 10 min. Additionally, a second Cr/Cr2AlC bilayer coating design was fabricated aiming to eliminate potential rapid hydrothermal dissolution of Al during normal operating conditions. Micro-cracking appeared on both annealed coatings owing to thermal expansion differences between coating layer and substrate. Growth of an adherent and dense α-Al2O3 scale during high-temperature oxidation in steam and of a thin passivating Cr2O3 layer during hydrothermal corrosion in an autoclave imply excellent combined oxidation and corrosion resistance of the textured Cr2AlC coatings on Zircaloy-4. A self-healing capability via growth of alumina filling the micro-crack (annealing-induced) gaps was observed during high-temperature oxidation. However, partial delamination was seen for both coatings after short autoclave exposure and their mechanical properties (fracture toughness and adhesion strength) need further enhancement. Overall, tailored Cr2AlC-based (multilayered) coatings can be attractive candidates as potential type of coated ATF claddings.

Effects of Different Post-Treatments on Arc Erosion Resistance of Cold-Sprayed AgC Composite Electric Contact

Graphite-silver (AgC) composite materials are widely used in outdoor high-voltage electrical switchgear due to their combining properties of excellent conductivity and outstanding arc-suppressing performance. However, the methods for fabricating AgC composite materials still have some limitations. In this study, the cold spray technique was adopted to deposit AgC composite coatings with the optimized parameters on the copper substrate. Then, AgC coatings were annealed in the furnace and treated by laser scanning, respectively, to further improve the arc erosion resistance performance of the coatings. The results show that the phase structure and electrical resistance of AgC coatings were not influenced by the post-treatment process. Furthermore, excellent hydrophobic performance was obtained after surface laser scanning treatment. The laser scanning treatment exhibited favorable advantages in enhancing the arc erosion resistance of AgC coatings, which indicated the lowest arc erosion rate compared with the cold-sprayed and annealed coatings.

A Novel Oxide Layer Formed on the 800 °C-Annealed CoMoCrSi Coating Significantly Reduced Friction and Wear at Room Temperature

In the present work, we investigated the microstructures and properties of as-sprayed and annealed CoMoCrSi coatings. Specifically, the annealed treatment at 800 °C resulted in good recrystallization, improved microstructure, and enhanced properties of CoMoCrSi coatings. An oxide layer formed on the annealed coating surfaces; it was mainly composed of nano-sized Cr2O3 and micro-sized CoMoO4, and could account for the increased surface microhardness and enhanced anti-wear performance of annealed coatings. In particular, the very hard Cr2O3 played a critical role of resisting press-in and wear during the tests, and the CoMoO4 had a lubricating effect during the friction process. Finally, the annealed coatings exhibited low coefficients of friction (COFs) of 0.4 and wear rates of 0.7–0.8 × 10−6 mm3·N−1·m−1 after a long sliding distance of 1000 m at RT. Consequently, the wear mechanism transferred from brittle fracture coupled with abrasive wear for the as-sprayed coating to slight abrasive wear for annealed coatings.

The Benefit of Superelastic NiTi Addition on Corrosion Performance of Electroless Ni–P Coating During an Accidental Scratch Event

Electroless Ni–P–NiTi composite coatings were prepared on API X100 steel substrates by incorporating Ti particles into Ni–P matrix followed by annealing Ni–P–Ti coatings. The scratch behavior of the as-deposited and annealed coatings under a high load was studied. It was found that the highest scratch resistance is achieved on the annealed 11.8 wt% Ti coating among all the coatings due to the formation of superelastic NiTi particles after annealing. Transformation toughening induced by superelastic NiTi particles significantly improves the toughness and scratch resistance of the annealed 11.8 wt% Ti coating. The effect of scratching on corrosion behavior was also investigated. Potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS) results revealed that the corrosion resistance of pre-scratched annealed Ni–P–Ti coating is higher than both the as-deposited Ni–P and Ni–P–Ti coatings. The highest corrosion resistance is achieved on the pre-scratched annealed 11.8 wt% Ti coating. The addition of NiTi particles into Ni–P matrix prevents crack nucleation and propagation during scratching process, which decreases the available surface area for localized corrosion and improves the corrosion resistance of the annealed 11.8 wt% Ti coating. This research reveals that the corrosion resistance of Ni–P coating is improved by the presence of superelastic NiTi particles within the Ni–P matrix during an accidental scratch event.

Room-Temperature and High-Temperature Wear Behaviors of As-Sprayed and Annealed Cr3C2-25NiCr Coatings Prepared by High Velocity Air-Fuel Spraying

Cr3C2-25NiCr coatings were deposited on stainless steel substrates by high velocity air-fuel (HVAF) spraying. Friction and wear behaviors of as-sprayed and annealed coatings were investigated both at room-temperature (RT) and 600 °C (high-temperature, HT). The results show that annealing at 600 °C in air is effective to enhance the wear performances of the coating both at RT and HT. The enhanced wear resistance of annealed coatings is discussed from the oxide growth and the microstructural evolution of the coatings. The wear behavior of the annealed coating follows the abrasive mechanism at RT and changes to an oxidative wear at HT, in which formation of a tribo-oxide layer plays a critical role to reduce the friction coefficient and to protect the underlying coatings from abrasive damage. The findings of this work reveal the significance of oxide-scale growth and microstructural evolution on the HT wear behaviors of the Cr3C2-25NiCr coating, which provides strategies for enhancing the wear properties of such coatings for HT applications.

Effect of vacuum annealing on initial oxidation behavior and alumina transition of NiCoCrAlY coatings

NiCoCrAlY coatings were prepared using arc-ion-plating on a second generation Ni-base single crystal superalloy, in which some of them underwent vacuum annealing treatment while the others did not. Early oxidation behavior of the two coatings, including phase pattern and morphological evolution of oxide scale during the short term oxidation, has been studied in static air at 1000 °C. The results showed that the vacuum treatment was not only efficient in inhibiting the cavity formation, but also significantly increased the adhesion between oxide scale and coating. Compared with those without vacuum annealing, the NiCoCrAlY coatings with vacuum treatment exhibited slower phase transformation from metastable θ-Al2O3 to stable α-Al2O3. Initial oxidation behavior of as-received and annealed coatings, especially the effect of vacuum annealing on morphology evolution and adhesion of oxide scale, are particularly discussed.

Hertzian Indentation Behavior of Electroless Ni-P-Ti Composite Coatings

Ni-P-Ti composite coatings have been prepared by co-depositing Ni-P and nano-Ti particles which were then annealed. Tensile tests were conducted on standalone coatings to acquire the mechanical properties of the coatings without the effect of the steel substrate. The Hertzian indentation tests were performed on coating-steel substrate bilayer systems to investigate the indentation behavior of the coatings. After annealing, Ni3Ti and superelastic NiTi phases are identified in composite coatings by XRD and EDS. Compared to the as-deposited Ni-P coatings, the toughness of the annealed composite coatings improved significantly. The superelastic effect of NiTi particles was observed in the Hertzian indentation behavior of the annealed composite coatings. The strengthening mechanisms as well as toughening mechanisms such as crack bridging, crack deflection, crack arresting, and transformation toughening were discussed. Recovery ratio (η) values as well as Hertzian indentation stress distribution were computed to analyze and explain the indentation behavior of the as-deposited and annealed coatings.