Corrosion and wear behavior of thermally sprayed nano ceramic coatings on commercially pure Titanium and Ti–13Nb–13Zr substrates

Surface treatments and coatings are the practical approaches used to extend the lifetime of components and structures especially when the surface is the most solicited part of the considered engineering component. Hard thermally sprayed coating is one of the most wear resistance coating widely used in many practical mechanical applications. In the construction of articulating parts of medical devices, titanium and its alloys have to be surface coated to improve their tribocorrosion behavior. In this way, the use of porous thermal coatings is known to be a strategy for better binding bone or tissue on femoral stem for example. It is, thus, important to evaluate the corrosion and the wear behaviors of such materials for biosecurity considerations in the human body. In this study, we investigate the behavior of new nano ZrO₂ and Al₂O₃-13 wt.% TiO₂ thermal sprayed coatings on commercially pure (cp)-Ti (grade 4) and titanium alloy substrates. Friction and wear tests against Al₂O₃ balls showed that the wear resistance of Al₂O₃-13 wt.% TiO₂ is better than that ZrO₂ coating. Both plasma sprayings have similar abrasive wear behavior; however, the average friction coefficient is higher for alumina–titania coating. Electrochemical tests, open circuit potential monitoring and potentiodynamic polarization, were performed in simulated body conditions (Hank’s solution, 37 °C). Results showed that corrosion resistance was appreciably higher for alumina–titania coating.     

Mechanical and tribological performance of Al2O3-TiO2 coatings elaborated by flame and plasma spraying

Mechanical properties and wear rates of Al₂O₃-13 wt.% TiO₂ (AT-13) and Al₂O₃-43 wt.% TiO₂ (AT-43) coatings obtained by flame and atmospheric plasma spraying were studied. The feed stock was either ceramic cords or powders. Results show that the wear resistance of AT-13 coatings is higher than that of AT-43 and it seems that the effect of hardness on wear resistance is more important than that of toughness. Additionally, it was established that, according to conditions used to elaborate coatings and the sliding tribological test chosen, spray processes do not seem to have an important effect on the wear resistance of these coatings.     

Electrodeposition of sol-enhanced nanostructured Ni-TiO2 composite coatings

A novel electroplating method has been developed to produce nanocrystalline metal-matrix nano-structured composite coatings. A small amount of transparent TiO₂ sol was added into the traditional electroplating Ni solution, leading to the formation of nanocrystalline Ni-TiO₂ composite coatings. These coatings have a smooth surface. The Ni nodules changed from traditional pyramid-like shape to spherical shape. The grain size of Ni was also significantly reduced to the level of 50 nm. It was found that the amorphous anatase TiO₂ nano-particles (∼ 10 nm) were highly dispersed in the coating matrix. The microhardness was significantly increased from 320 HV₁₀₀ of the traditional Ni coating to 430 HV₁₀₀ of the novel composite coating with 3.26 wt.% TiO₂. Correspondingly, the wear resistance of the composite coating was improved by ∼ 50%.     

Laser surface cladding of MRI 153M magnesium alloy with (Al+Al2O3)

Laser surface cladding was carried out on a creep-resistant MRI 153M magnesium alloy with a mixture of Al and Al₂O₃ powders using a pulsed Nd:YAG laser at scan speeds of 21, 42, 63 and 84 mm/s. The Al₂O₃ particles partially or completely melted during laser irradiation and re-solidified with irregular shapes in the size range of 5-60 µm along with a few islands as large as 500 µm, within the grain-refined Mg-rich dendritic matrix. More than an order of magnitude improvement in wear resistance after cladding was attributed to the presence of ultra-hard Al₂O₃ particles, increased solid solubility of Al and other alloying elements, and a very fine dendritic microstructure as a result of rapid solidification in the cladded layer. However, corrosion resistance of the laser cladded alloy was reduced by almost an order of magnitude compared to that of the as-cast alloy mainly due to the presence of cracks and pores in the cladded layer.     

Superior performance of high-velocity oxyfuel-sprayed nanostructured TiO<Subscript>2</Subscript> in comparison to air plasma-sprayed conventional Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-13TiO<Subscript>2</Subscript>

Air plasma-sprayed conventional alumina-titania (Al₂O₃-13wt.%TiO₂) coatings have been used for many years in the thermal spray industry for antiwear applications, mainly in the paper, printing, and textile industries. This work proposes an alternative to the traditional air plasma spraying of conventional aluminatitania by high-velocity oxyfuel (HVOF) spraying of nanostructured titania (TiO₂). The microstructure, porosity, hardness (HV 300 g), crack propagation resistance, abrasion behavior (ASTM G65), and wear scar characteristics of these two types of coatings were analyzed and compared. The HVOF-sprayed nanostructured titania coating is nearly pore-free and exhibits higher wear resistance when compared with the air plasma-sprayed conventional alumina-titania coating. The nanozones in the nanostructured coating act as crack arresters, enhancing its toughness. By comparing the wear scar of both coatings (via SEM, stereoscope microscopy, and roughness measurements), it is observed that the wear scar of the HVOF-sprayed nanostructured titania is very smooth, indicating plastic deformation characteristics, whereas the wear scar of the air plasma-sprayed alumina-titania coating is very rough and fractured. This is considered to be an indication of a superior machinability of the nanostructured coating.     

Structural and mechanical properties of nanostructured TiO2 thin films deposited by RF sputtering

This study mainly aims to evaluate the effects of substrate temperatures on the mechanical properties of TiO₂ thin films deposited on glass substrates by radio-frequency (RF) magnetron sputtering. All titania films possess anatase structure having a nodular morphology. AES results reveal that Si and Na ions from glass diffuse into TiO₂ films at higher substrate temperatures. Micro-scratch and wear tests were conducted to evaluate their mechanical and tribological properties. The adhesion critical loads of TiO₂ films deposited at room temperature, 200 and 300 °C are found to be 1.51, 1.54 and 1.08 N, respectively. Scratch hardness also increases from 11.5 to 13.6 GPa with increasing temperature. The wear track width decreases with substrate temperature indicating an improved wear resistance at higher temperatures.     

Effects of critical plasma spray parameter and spray distance on wear resistance of Al2O3-8 wt.%TiO2 coatings plasma-sprayed with nanopowders

Effects of plasma spraying conditions on wear resistance of nanostructured Al₂O₃-8 wt.%TiO₂ coatings plasma-sprayed with nanopowders were investigated in this study. Five kinds of nanostructured coatings were plasma-sprayed on a low-carbon steel substrate by varying critical plasma spray parameter (CPSP) and spray distance. The coatings consisted of fully melted region of γ-Al₂O₃ and partially melted region, and the fraction of the partially melted regions and pores decreased with increasing CPSP or decreasing spray distance. The hardness and wear test results revealed that the hardness of the coatings increased with increasing CPSP or decreasing spray distance, and that the hardness increase generally led to the increase in wear resistance, although the hardness and wear resistance were not correlated in the coating fabricated with the low CPSP. The main wear mechanism was a delamination one in the coatings, but an abrasive wear mode also appeared in the coating fabricated with the low CPSP. According to these wear mechanisms, the improvement of wear resistance in the coating fabricated with the low CPSP could be explained because the improved resistance to fracture due to the presence of partially melted regions might compensate a deleterious effect of the hardness decrease.     

WC和Al2O3对氩弧熔覆FeAlCoCrCuTi0.4高熵合金涂层组织和耐冲蚀性能影响

利用氩弧熔覆技术制备了FeAlCoCrCuTi_0.4,WC/Al₂O₃-FeAlCoCrCuTi_0.4高熵合金涂层,并通过XRD,SEM,EDS,硬度测试和冲蚀磨损测试等方法,探究了WC和Al₂O₃的添加对FeAlCoCrCuTi_0.4高熵合金涂层显微组织和性能的影响.结果表明,通过氩弧熔覆技术所制备的合金涂层表面成形性良好,无孔洞、裂纹等缺陷产生,与基体呈高强度冶金结合.WC和Al₂O₃的添加对涂层稀释率的降低有显著作用.三种涂层都是主要由Bcc相（Fe-Cr固溶体）构成,晶粒以胞状树枝晶形式存在.添加WC后,晶粒细化明显,在各种强化作用下涂层硬度为685.8 HV.且WC和Al₂O₃的添加显著提高了涂层耐冲蚀磨损性能,耐磨性几乎可以达到FeAlCoCrCuTi_0.4高熵合金涂层的2倍.     

Formation of WC-iron silicide (Fe5Si3) composite clad layer on AISI 316L stainless steel by high power (CO2) laser

An attempt was made to produce WC-iron silicide cladded layer on AISI 316L stainless steel by laser processing to obtain high hardness and lesser variations in hardness distribution in the layer. Different compositions of coating materials (WC, Si and Ni) and laser processing parameters were used. A good and defect free cladded layer of WC-iron silicide was obtained for an energy density of 22.5 J/mm² and coating composition of 40WC-40Si-20Ni (wt.%). The layer exhibited average hardness of about 883 HV with lesser variations in the hardness distribution and also higher wear resistance compared to the substrate.     

Effects of the powder manufacturing method on microstructure and wear performance of plasma sprayed alumina-titania coatings

Three Al₂O₃-13wt.% TiO₂ powders, with the same chemical composition but different Al₂O₃-TiO₂ distribution patterns, are plasma sprayed and the resulting coatings are compared in terms of their phase composition, microstructure, hardness, crack growth resistance, and abrasive wear performance. It is demonstrated that the degree of mixing of the Al₂O₃ and TiO₂ ingredients in the feed powder has immense impact on the phase composition, microstructure, hardness, crack growth resistance, and abrasive wear performance of the coatings. A high degree of mixing of Al₂O₃ and TiO₂ in the powder state results in more uniform microstructure, higher hardness, higher crack growth resistance, and consequently better abrasive wear resistance of the coating.     

Microstructure dependent erosion in Cr3C2-20(NiCr) coating deposited by a detonation gun

Cr₃C₂-20(NiCr) coating powder was deposited on a low carbon steel by pulsed detonation spray gun technique. The coated samples were heat-treated at 600 °C for 11/2 h and allowed to cool in air. A systematic microstructural study was carried out using SEM and TEM to understand the microstructural changes. The mechanical properties like hardness, indentation fracture toughness and adhesion strength of the coating in the as-sprayed and heat-treated conditions were also determined. The change in solid particle erosion of the coating was correlated with the microstructural and subsequent mechanical property changes. It was observed that exposure of the as-sprayed coating to elevated temperature improves the wear resistance. It is concluded that crystallisation of the amorphous phase into nanocrystalline composite combined with better bonding between the adjacent splats through sintering contributes to improved hardness, fracture toughness and wear resistance of the heat-treated coating. The deformation characteristics of the binder phase, amorphous vis-à-vis crystalline, also influence the wear behaviour of the coating.     

Properties of High Velocity Suspension Flame Sprayed (HVSFS) TiO2 coatings

TiO₂ coatings were manufactured by the High Velocity Suspension Flame Spraying (HVSFS) technique using a nanopowder suspension. Their microstructure, nanohardness, tribological properties and photocatalytic activity were studied and compared to conventional atmospheric plasma sprayed (APS) and HVOF-sprayed TiO₂ coatings manufactured using commercially available feedstock. The HVSFS process leaves a fairly large freedom to adjust coating properties (thickness, porosity, anatase content, hardness, etc…) according to the desired objective. Layers with higher anatase content and higher porosity can be produced to achieve higher photocatalytic efficiency, better than conventional APS and HVOF TiO₂. Alternatively, dense protective layers can be deposited, possessing lower porosity and pore interconnectivity and better wear resistance than as-deposited APS and HVOF layers. In all cases, HVSFS-deposited layers are thinner (20 µm-60 µm) than those which can be obtained by conventional spraying processes.     

Al2O3-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al₂O₃-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al₂O₃ powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al₂O₃ to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al₂O₃ powder by ball milling to ratios of 0.01 wt.%, 0.03 wt.%, and 0.05 wt.% ND. The water contact angle (CA) of the Al₂O₃-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al₂O₃-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550 nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al₂O₃-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0 wt.% ND. In addition, the Al₂O₃-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.     

MoS2 coated with Al2O3 for Ni-MoS2/Al2O3 composite coatings by pulse electrodeposition

The MoS₂ powders were coated with Al₂O₃ (5 wt.%) through controlling hydrolysis of Al (NO₃)₃·9H₂O. MoS₂ powder coated with Al₂O₃ was written as MoS₂/Al₂O₃ hereinafter. MoS₂/Al₂O₃ powders were put into Ni plating electrolyte bath. Cetyltrimethylammonium bromide (CTAB) — the surfactant was also put into the bath. The experiment proves that MoS₂/Al₂O₃ particles were absorbed onto the Ni plate. The amount of MoS₂/Al₂O₃ deposited on Ni plate rises with the increasing concentration of MoS₂/Al₂O₃ in the bath. The microhardness, micro-surface, phase and the tribological property of the MoS₂/Al₂O₃ multi-plating coating were measured and analyzed. The performances of microhardness and wear resistance of the Ni-MoS₂/Al₂O₃ composite are better than those of Ni-MoS₂ composite.     

Phase constituents and microstructure of laser cladding Al2O3/Ti3Al reinforced ceramic layer on titanium alloy

Laser cladding of the Fe₃Al + TiB₂/Al₂O₃ pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al₂O₃ can react with TiB₂ leading to formation of amount of Ti₃Al and B. This principle can be used to improve the Fe₃Al + TiB₂ laser cladded coating, it was found that with addition of Al₂O₃, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases.     

Dominant microstructural feature over photocatalytic activity of high velocity oxy-fuel sprayed TiO2 coating

TiO₂ photocatalytic coatings were deposited through high velocity oxy-fuel spray using anatase powder and rutile powder as feedstock. The as-sprayed TiO₂ coating was composed of anatase phase and rutile phase. The anatase content in the coating was significantly influenced by fuel gas flow and melting condition of spray powder. A high anatase content of 35% was achieved for the coating deposited using rutile powder. The anatase content in the coating deposited using anatase powder reached 55-65%. The as-sprayed TiO₂ coating was photocatalytically reactive for degradation of acetaldehyde in air. The photocatalytic activity was influenced by spray conditions. The surface morphology and phase structure of coatings deposited at different spray conditions were investigated to clarify the relationship between the coating microstructure and activity. It is found that the photocatalytic activity is significantly influenced by anatase content and surface area.     

Toughening and strengthening mechanism of plasma sprayed nanostructured Al2O3–13 wt.%TiO2 coatings

The starting materials of Al₂O₃, TiO₂, ZrO₂ and CeO₂ nanoparticles were agglomerated into sprayable feedstock powders and plasma sprayed to form nanostructured coatings. There were net structures and fused structures in plasma sprayed nanostructured Al₂O₃–13 wt.%TiO₂ coatings. The net structures were derived from partially melted feedstock powders and the fused structures were derived from fully melted feedstock powders. The nanostructured Al₂O₃–13 wt.%TiO₂ coatings possessed higher hardness, bonding strength and crack growth resistance than conventional Metco 130 coatings which were mainly composed of lamellar fused structures. The higher toughness and strength of nanostructured Al₂O₃–13 wt.%TiO₂ coatings were mainly related to the obtained net structures.     

The performances of TiB2-contained iron-based coatings at high temperature

The TiB₂-contained composite Fe-B-C coatings are deposited by the plasma transferred-arc (PTA) powder surfacing process. The coating's thermal ability, arc ablation resistance and wear resistance at high temperature were analyzed. It is concluded that TiB₂-contained composite Fe-B-C coating having excellent wear resistance at 600 °C and tempering resistance at 900 °C. Furthermore, this coating can effectively resist the arc ablation (120 A arc currents) within 7 s.     

Effect of h-BN addition on the properties of nanostructured Al2O3-TiB2-TiN based coatings developed by combined SHS and laser surface alloying

A hard coating was obtained on AISI1025 steel substrate by the action of a high power laser beam on a powder mixture of Al, TiO₂ and h-BN pre-placed on the substrate surface. The precursor powder mixture underwent self-propagating high-temperature synthesis (SHS) at the high temperatures induced by the incident laser. The products of SHS were subsequently laser alloyed onto the substrate, whereby, a hard, nanostructured coating was formed comprising of Al₂O₃, TiB₂ and TiN. Excess h-BN in the precursor resulted in the presence of free h-BN in the coating. Microhardness and coefficient of friction (with WC-Co as counterbody) of the coating were found to reduce with increase in h-BN content in the precursor. It was possible to develop a coating with a property combination of high hardness, low wear rate and low friction coefficient.     

Al2O3-ZrO2 mixed oxide composite incorporated aluminium rich zinc coatings for high wear resistance

Corrosion resistance and wear resistance are the two important parameters for high performance of zinc galvanic coating. In the present work, the improvement of these two characteristics was achieved by the incorporation of Al₂O₃-ZrO₂ mixed oxide composite in the coating. Al₂O₃-ZrO₂ mixed oxide composite was synthesized from ZrOCl₂·8H₂O. Aluminium rich zinc coatings with high sliding wear resistance was developed from a galvanic bath containing the mixed oxide. Based on the performance of the coating during physicochemical and electrochemical characterization, the concentration of mixed oxide composite in the bath was optimized as 0.50 wt% Al₂O₃-0.50 wt% ZrO₂. While rich in Al-metal content in the coating caused high corrosion resistance, the incorporation of the mixed oxide improved structural characteristics of the coating resulting in high wear resistance also. The coating was nonporous in nature and even the interior layers had high stability. The coatings have potential scope for high industrial utility.