Synthesis and characterization of Ni-W/TiN nanocomposite coating with enhanced wear and corrosion resistance deposited by pulse electrodeposition

To enhance mechanical properties and anti-corrosion capability of Ni-W alloy further, Ni-W/TiN nanocomposite coating has been co-deposited via pulse current co-deposition in this work. The effects of TiN nanoparticles and operating parameters on the structure and properties of the deposited coating were examined. It illustrated that the nanocomposite coatings are uniform, dense and crack-free, exhibiting dome-like or hill-valley like structure. The particles were homogeneously incorporated in the metallic matrix. RTC analysis indicated that the preferred orientation of Ni-W/TiN was (111) texture. The crystallite size was of 10–16 nm, indicating the formation of nanocrystalline structure. TiN concentration, duty cycle and frequency could influence the amount of TiN particle and W element in the coating, then regulating hardness and anti-wear behaviors. The low duty cycle and long deposition time could diminish the roughness of the coating. The inclusion of TiN nanoparticles in the nickel matrix could promote the nucleation of fresh nickel crystals and restrict the growth of already formed nickel grains, favoring the homogeneous growth and grain refinement of Ni-W crystals. The doped TiN particles would favor the preferred orientation (111) plane, enhanced the hardness, wear and corrosion resistance of Ni-W alloy. Electrochemical results illustrated that the best corrosion-resistant properties of the nanocrystalline coating could be obtained at TiN 30 g L⁻¹, duty cycle of 20% and frequency of 60–200 Hz. The enhanced mechanical properties and corrosion resistance of Ni–W/TiN coating benefits its application in harsh corrosive environment.     

Design,thermal shock resistance of dense BaO-Al2O3-SiO2 glass/Si3N4-barium feldspar coating for porous Si3N4 ceramic

Silicon nitride-monoclinic barium feldspar (Si₃N₄-m-BAS) composite possesses great dielectric properties, low density, and low thermal expansion coefficient (CTE). Preparing dense Si₃N₄-m-BAS coating on porous Si₃N₄ ceramic is an effective strategy to improve its water resistance and ensure its dielectric performances. However, this promising coating has not been reported yet, because the synthesis of m-BAS is difficult, and the densification of Si₃N₄-BAS composite requires very high temperature. Here, the BaO-Al₂O₃-SiO₂ glass/Si₃N₄-BAS coating was first fabricated by a manual spray method and pressureless sintering at 1450°C. Combining the influence of Si⁴⁺ on the crystal phase composition of BAS and the volume expansion effect of silicon in N₂, an effective coating structure design scheme was proposed. By changing the content of silicon powder, the CTE and horizontal shrinkage of the coating during sintering were controlled. Besides, the prepared coatings exhibited low water absorption and high bonding strength. During the thermal shock tests, SiO₂ produced by the oxidation of Si₃N₄ healed the cracks in the coating, thus delaying the degradation of the properties. The coating prepared in this work is expected to be applied to radome in extreme service environments.     

Indentation size effect and wear characteristics of spark plasma sintered,hard MWCNT/Al2O3 nanocomposites

Magnesia doped multiwalled carbon nanotube (CNT)/α-alumina nanocomposites have been fabricated by spark plasma sintering at 1500°C under 50 MPa in argon. Owing to combined grain refining effect of nanotube and magnesia, nanocomposites possessed smaller matrix grains and extensively lower matrix crystallites than pure alumina. Thermal expansion mismatch between matrix and filler rendered up to four times higher compressive lattice microstrain to the nanocomposites over pure alumina. Despite very low CNT loading (e.g. 0·13?wt-%), nanocomposites offered considerably higher hardness (as high as 24·42?GPa), negligible indentation size effect (Meyer exponent?=?1·906???1·941) and enhanced elastic response over pure alumina. Up to 0·27?wt-% nanotube loading, much higher wear resistance was observed for the nanocomposites over pure alumina. The presence of uniformly dispersed and structurally intact nanotubes coupled with lower matrix grains and crystallites having compressive lattice strain were the key factors behind achieving such improved mechanical properties of the present nanocomposites.     

Alternant phase distribution and wear mechanical properties of an Al2O3-40 wt%TiO2 composite coating

Al₂O₃-40 wt%TiO₂ (AT40) coating is a low-cost and widely applied ceramic coating. In this article, the phase distribution, micro-hardness and wear mechanism, as well as the spraying conditions optimization, are discussed. Interface defects. Phase distribution and phase composition were analysed using SEM and XRD. The results show that the pre-existing surface morphology mainly determines the phase distribution. Al₂TiO₅ and γ-Al₂O₃ are the main phases in the coating. In this experiment, the highest micro-hardness (1126.2 HV_0.2) was measured using a Vickers tester. Additionally, the wear rate of the highest micro-hardness coating is 0.0387 mg/N m, which is the lowest weight loss rate measured among all the samples. The wear mechanism for this sample is primarily scratches. In conclusion, the compact lamellar phase distribution decreases the number of interface defects, increases the hardness and determines the wear mechanism. Also, the phase distribution is affected by the spraying conditions.     

Influence of hBN content on mechanical and tribological properties of Si3N4/BN ceramic composites

Silicon nitride materials containing 1–5 wt% of hexagonal boron nitride (micro-sized or nano-sized) were prepared by hot-isostatic pressing at 1700 °C for 3 h. Effect of hBN content on microstructure, mechanical and tribological properties has been investigated. As expected, the increase of hBN content resulted in a sharp decrease of hardness, elastic modulus and bending strength of Si₃N₄/BN composites. In addition, the fracture toughness of Si₃N₄/micro BN composites was enhanced comparing to monolithic Si₃N₄ because of toughening mechanisms in the form of crack deflection, crack branching and pullout of large BN platelets. The friction coefficient was not influenced by BN addition to Si₃N₄/BN ceramics. An improvement of wear resistance (one order of magnitude) was observed when the micro hBN powder was added to Si₃N₄ matrix. Mechanical wear (micro-failure) and humidity-driven tribochemical reaction were found as main wear mechanisms in all studied materials.     

The effect of homogeneously dispersed few-layer graphene on microstructure and mechanical properties of Al2O3 nanocomposites

Fully dense few-layer graphene (FG)/Al₂O₃ nanocomposites with homogeneously dispersed FG in matrix are prepared by using a heteroaggregation method followed by spark plasma sintering. It is found that the two dimensional FG has great ability to restrain grain growth in comparison to other inclusions. In addition, the morphology of grain in composite is modified by the addition of FG during densification process compared with monolithic alumina. Thanks to the greatly decreased grain size, the composites are almost as hard as monolithic alumina at low sintering temperature (1573 K) even if graphene content is as high as 1.2 vol.%. However, at higher sintering temperature (1673 K), the hardness of composites decreases further but the change in elastic modulus is very limited. The decline of hardness and elastic modulus mainly arises from the sliding feature of FG, low modulus of reduced graphene oxide in both in-plane and out-of-plane directions.     

Effect of Y2O3-stabilized ZrO2 whiskers on the microstructure,mechanical and wear resistance properties of Al2O3 based ceramic composites

The aim of this study was to improve the mechanical properties of Al₂O₃ ceramics by the addition of Y₂O₃-stabilized ZrO₂ whiskers (designated as Al₂O₃/YSZ_W composite) through the flux method and hot-pressing technology. The effect of YSZ_W content on their microstructure, phase composition and transformability, mechanical properties, and wear resistance was systematically investigated. The Al₂O₃/YSZ_W composites containing 10 wt% YSZ_W exhibited the best mechanical performance, including the highest content of YSZ_W tetragonal phase and transformability as well as the largest values in their relative density (99.5%), hardness (1969 HV), fracture toughness (9.57 MPa m^1/2) and flexural strength (855 MPa). The strengthening and toughening of the Al₂O₃/YSZ_W composites were attributed to the YSZ_W tetragonal-monoclinic phase transformation as well as the whiskers reinforcing effect. Furthermore, the Al₂O₃/YSZ_W composites also showed the highest friction and wearing properties.     

New observations on wear characteristics of solid Al2O3/Si3N4 ceramic tool in high speed milling of additive manufactured Ti6Al4V

Additive Manufacturing (AM) technologies applied to the titanium alloys have attracted attention from industries in recent years. Despite one of the main goals of AM is the reduction of manufacturing steps, semi-finish/finish machining operations are still required so as to obtain the desired geometrical tolerance and surface features. In this study, the solid end mill was manufactured by Al₂O₃/Si₃N₄ (Sialon) ceramic materials and employed in high-speed slot milling of Ti6Al4V alloy fabricated by the Direct Metal Laser Sintering (DMLS) AM technology to study the tool wear characteristics during processing. The Raman spectroscopic method was employed to characterize the molecular structures of Sialon ceramics for the manufacturing of the cutting tool. The morphologies and elemental maps of wear region of the ceramic tool were examined by scanning electron microscope and energy dispersive spectroscopy techniques. The results show that the adhesion wear and diffusion wear are the dominant wear mechanisms, and the chemical stability of Al₂O₃/Si₃N₄ (Sialon) ceramics fabricated as the solid ceramic tool to the attack of the atoms from additive manufactured Ti6Al4V is relatively weak under the atmosphere. The difference of thermal expansion coefficients of diffusion layer and tool substrate accelerates the initiation and propagation of thermal cracks formed on the diffusion interface. Moreover, fracturing and crater-like groves near the tool edge were finally formed due to the removal of adhered workpiece material.     

Comparative study on the corrosion and wear behavior of plasma-sprayed vs. high velocity oxygen fuel-sprayed Al8Si20BN ceramic coatings

Corrosion and wear are common problems encountered in the oil and gas industry. These entail the gradual destruction of materials by mechanical action on the opposite surface, and the chemical and/or electrochemical reaction with their environment. In this research, Al8Si20BN ceramic powder with specific properties against corrosion and wear was selected, and it was sprayed with high velocity oxygen fuel (HVOF) and plasma spray methods onto carbon steel substrates. The coatings were characterized with respect to phase composition, microstructure, microhardness and adhesion strength. Their wear behavior was inspected by applying 5, 10, 15 and 20?N loads by pin-on-disc machine, after which the results of both methods were compared. According to the results, the HVOF-coated models were more durable than the plasma-coated models under different loads in the same condition. In addition, the corrosion deterioration of the coated specimens in both brine (3.5% NaCl) and fossil oil were tested for one month (30 days). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) assessment in 3.5% NaCl solution indicated that the HVOF-sprayed specimens had better corrosion protection than the plasma-sprayed specimens. Generally, the HVOF technique facilitated more durable coats with greater corrosion and tribological resistance compared to the plasma coating technique.     

In situ reaction synthesis and characterization of Ti3Si(Al)C2/SiC composites

The reaction route, microstructure, and properties of Ti₃Si(Al)C₂/SiC composites with 5–30 vol.% SiC content prepared by in situ hot pressing/solid–liquid reaction synthesis process are investigated. In contrast to monolithic Ti₃Si(Al)C₂, the SiC particle-reinforced composites exhibit higher elastic modulus, Vickers hardness, fracture toughness, improved wear, and oxidation resistance, but have a slight loss in flexural strength. The improvement in the properties is mainly ascribed to the contribution of SiC particles, and the strength degradation is due to the residual tensile stresses in the matrix.     

Insight into the adsorption and photocatalytic properties of in-situ synthesized g-C3N4/SnS2 nanocomposite

In this paper, a novel g-C₃N₄/2 wt% SnS₂ nanocomposite was successfully synthesized using an in-situ growth of SnS₂ on g-C₃N₄. X-ray diffraction (XRD), atomic force microscopy (AFM), Brunauer-Emmett-Teller (BET) method, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectrometer were used to characterize the photocatalysts. Exploring adsorption behavior, as an importatnt stage during photocatalytic reactions, is of great importance. Hence, both adsorption and photocatalytic performance of the synthesized photocatalysts have been investigated in detail. The adsorption isotherm fittings exhibited that Freundlich and Langmuir-Freundlich models can be applied to the methylene blue (MB) adsorption on the photocatalysts, indicating surface heterogeneity should be considered. A pseudo-second-order model was fitted to explore the adsorption kinetics. According to the observed redshift in the Fourier transform infrared spectroscopy (FTIR) result of g-C₃N₄/SnS₂ nanocomposite, π-π interaction was dominant during MB adsorption. Also, a slight redshift and significant PL intensity reduction in g-C₃N₄/SnS₂ nanocomposite led to 96% photocatalytic efficiency after 180 min under visible light radiation. The kinetics of photodegradation over g-C₃N₄/SnS₂ was about 9 and 3 times higher than those of g-C₃N₄ and SnS₂ photocatalysts, respectively. The superoxide and hydroxyl radicals were the main reactive species in the photocatalytic degradation with a Z-scheme charge transfer mechanism. The g-C₃N₄/SnS₂ nanocomposite was found to be remarkably stable after three consecutive cycles of MB degradation.     

Effect of nitrogen pressure on the microstructure,mechanical and electrochemical properties of CrAlN coatings deposited by filter cathode vacuum arc

CrAlN coatings were prepared on Al–Si alloys using filter cathode vacuum arc deposition technique with nitrogen as the reactive gas and Cr₂₅Al₇₅ alloy target as the arc source. The effect of nitrogen pressure on the microstructure, mechanical properties and electrochemical properties of the coatings had been systematically studied. The results showed that the composition, structure and performance of the CrAlN coating depended on the nitrogen pressure. As the nitrogen pressure increased, the Al and Cr content decreased while the N content increased slowly in the coating. Meanwhile, the phase structure gradually changed from AlN phase to CrN phase. The hardness of the CrAlN coating increased significantly with the increase of nitrogen pressure from 0.04 to 0.06 Pa due to the formation of CrN phase and grain refinement. However, further increasing the nitrogen pressure to 0.07 Pa, the hardness was reduced owing to the deterioration of the surface quality caused by target poisoning. Moreover, the adhesion strength of the coating gradually decreases, and the corrosion resistance of the CrAlN coating first increased and then decreased with increasing the nitrogen pressure. The CrAlN coating deposited at a nitrogen pressure of 0.05 Pa had the best corrosion resistance, with the highest polarization resistance, charge transfer resistance and pore resistance, which was related to the combined effect of great compactness and AlN-dominant phase structure in the coating.     

Influence of cBN content,Al2O3 and Si3N4 additives and their morphology on microstructure,properties, and wear of PCBN with NbN binder

Polycrystalline cubic boron nitride (PCBN) tool materials with NbN binder without additives and PCBN with Al₂O₃ or Si₃N₄ micropowder and whisker additives were manufactured and compared. PCBN materials with Si₃N₄ whisker reinforcement have the best mechanical properties of all the evaluated materials. Composites reinforced with Al₂O₃ whiskers have the lowest fracture toughness. However, Al₂O₃ whisker-reinforced tools outperform both commercial and Si₃N₄ reinforced tools when machining hardened steel. Thus Al₂O₃ whisker-reinforced PCBN materials are promising for industrial applications, likely due to their higher resistance to oxidation and diffusional wear mechanisms during cutting operations.     

Structural and magnetic properties of Co/Al2O3 cermet synthesized by mechanical ball milling

Cobalt nanoparticles in the alumina matrix were synthesized using high energy mechanical ball milling of Co₃O₄ and Al powders mixture. The effect of ball mill time of 1 up to 12 h on the phase formation and crystalline lattice of the samples was investigated by the fitting of the X-ray diffraction patterns with Fullprof software and Rietveld method. The results show that 6 h milling of the primary powders yields a nanocomposite of Co/Al₂O₃ cermet. The formation of Co/Al₂O₃ nanocomposite was confirmed by a morphological study using scanning electron microscopy and transmission electron microscopy. The prepared nanocomposite by 12 h ball mill time has ferromagnetic properties with a high saturation magnetization value of 118 emu/g. Also, using Henkel plot analysis, it was shown that there are strong dipole-dipole magnetic interactions between the prepared cobalt nanoparticles in the Al₂O₃ matrix.     

Structural properties and mechanical behavior of SWCNTs and MWCNTs reinforced Al2O3 fabricated by spark plasma sintering

Carbon nanotubes due to their structural and mechanical properties are good candidates as the second phase to improve the mechanical properties of alumina-based ceramics. In the present study, the effects of single wall and multi-wall carbon nanotubes on structural and mechanical properties of alumina were investigated. SWCNTs and MWCNTs were dispersed in alumina powder via a conventional method using 1 wt % PVA water solution as media. Sintering process for two different composite powders, alumina-2 wt. % SWCNTs and alumina 2 wt % MWCNTs was performed by spark plasma sintering technique at 1500 °C and 20 MPa for 10 min. Results showed that the presence of CNTs in alumina caused a considerable amount of porosity in final bodies. SEM images of fracture surfaces revealed the agglomeration of SWCNTs which played a dominant role in the deterioration of mechanical properties. MWCNTs reinforced alumina obtained higher Vickers hardness and bending strength values (12.91 GPa and 291 MPa, respectively) compared to that of SWCNTs (9.18 GPa and 276 MPa, respectively), due to sever agglomerate of SWCNTs throughout sintered composites. Typical load-displacement (P/h) curves were obtained from bending strength test and discussed. It was concluded that the addition of MWCNTs to alumina represented better densification and mechanical properties compared to SWCNTs.     

Corrosion properties of ceramic coating on pure titanium by pack boronizing with Nd2O3

In this work, the corrosion behaviors and mechanisms of the pure titanium by pack boronizing with different Nd₂O₃ contents in 3.5 wt% NaCl and 5.0 vol% H₂SO₄ solutions were characterized and analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), electron probe microanalyzer (EPMA), and electrochemical tests. The results showed that the sample boronized with 4 wt% Nd₂O₃ has the smoothest surface, the densest ceramic coating with a thickness of 52 μm, and the best corrosion resistance. Nd₂O₃ can react with B to generate Nd–B active group, which promotes ceramic coating growth and turns local corrosion into uniform corrosion.     

Corrosion resistance of Al2O3-Y2O3-SiC coating on depleted uranium prepared by cathode plasma electrolytic deposition

Al₂O₃-Y₂O₃-SiC composite coatings were prepared on depleted uranium by cathode plasma electrolytic deposition in Al(NO₃)₃, Y(NO₃)₃, SiC nanoparticles and anhydrous ethyl alcohol mixture. The resulting coating consisted of an inner barrier layer and an outer porous layer. The SiC nanoparticles were incorporated into the composite coating and decreased the coating porosity by filling the pores. The potentiodynamic polarization test and neutral salt spray test revealed that the corrosion resistance of depleted uranium was enhanced by the composite coating. Moreover, with increasing the content of SiC nanoparticles in the coating, the coating corrosion resistance was improved gradually.     

热压烧结Al2O3/Si3N4复相陶瓷的研究

采用热压烧结工艺制备了Al2O3/Si3N4复相陶瓷材料,对不同温度下、不同氮化硅用量时所制备的材料进行了硬度、断裂韧性等力学性能的测试,运用X射线衍射分析(XRD)和扫描电镜(SEM)技术对材料的微相组成与显微形貌进行表征.结果表明1600 ℃,30 MPa,保温1 h,Si3N4用量为3wt%时所制备的材料的各项力学性能达到了最佳值.     

The effect of Ti and Si on the mechanical and electrochemical behaviors of the AlCrN coating deposited by CAPVD on 304SS

This study aimed to investigate the effect of adding titanium (Ti) and silicon (Si) elements on the mechanical and electrochemical properties of the AlCrN-based coating. For this purpose, a cathodic arc physical vapor deposition machine was used. Scanning electron microscopy, X-ray diffraction, and nanoindentation tests were utilized for morphological, microstructural, and mechanical characterization of the coatings. The hardness value and plastic deformation index of CrAlN-based coating increase with the presence of Si element. The mechanical properties improvement is attributed to the reduction of crystallite size as well as to the tendency of the coating structure to become amorphous. The specimens were subjected to 3.5 wt% NaCl solution to electrochemical impedance corrosion and potentiodynamic polarization tests. The results showed that by increasing the coatings’ titanium content, the coatings’ corrosion resistance improved. Moreover, by adding 3% and 5% of Si elements to the coatings’ composition, the corrosion resistance of the AlCrTiSiN coatings was enhanced by 35% and 78%, respectively. Improving the corrosion resistance of the AlCrN-based coatings by adding the Si element is attributed to the change in the microstructure and reduction in the porosity of the coatings.     

Effect of mechanical properties on the ballistic resistance capability of Al2O3-ZrO2 functionally graded materials

Because Al₂O₃ exhibits high strength and hardness, it is prevalently used as a ceramic material. ZrO₂ is often added to increase the toughness of such a material. Therefore, this study mixed Al₂O₃ and ZrO₂ to formulate functionally graded materials (FGMs). four-layer and eleven-layer Al₂O₃-ZrO₂ FGM_S were produced from Al₂O₃ and ZrO₂ mixtures by sintering at 1500 °C. Moreover, testing sheets were created by mixing various ratios of Al₂O₃ and ZrO₂ to analyze their fracture toughness and hardness. The results revealed the 90% Al₂O₃-10% ZrO₂ sheet to exhibit a hardness of 15.12 GPa, and the 50% Al₂O₃-50% ZrO₂ sheet to attain a fracture toughness as high as 4.7 MPa m^0.5. The impact resistance test involved analyzing various types of testing sheets, including the four-layer Al₂O₃-(0%, 10%, 20%, 30%) ZrO₂ FGM, eleven-layer Al₂O₃-(0–100%) ZrO₂ FGM, 100% Al₂O₃ composite material, 90% Al₂O₃-10% ZrO₂ composite material, 70% Al₂O₃-30% ZrO₂ composite material, and 50% Al₂O₃-50% ZrO₂ composite material. The ballistic tests showed that FGMs of the same areal density (4.64 g/cm²) or thickness (11 mm) attained the highest energy absorption. The experimental results confirmed that FGMs can delay the formation and propagation of ceramic cones. Specifically, toughened alumina materials prevent the growth of radial and circumferential cracks, delay the formation of ceramic cones, decrease cones hitting against the back plane, and increase the penetrating resistant capability of the ceramic materials experiencing bullet impact, features important for applications in fields such as aerospace, aviation, automobile, the military industry, and biomedicine