Corrosion,wear and wear–corrosion behavior of graphite-like a-C:H films deposited on bare and nitrided titanium alloy

This work presents a comparative wear, corrosion and wear–corrosion (the last one in a simulated physiological solution) study of graphite-like a-C:H (GLCH) films deposited on bare and nitrided Ti6Al4V alloy. Films, deposited by r.f. PACVD, presented low porosity and promoted high corrosion resistance. The friction coefficient of the films was very low with appreciable wear resistance at room conditions. However, due to the simultaneous action of both load and the corrosive environment in wear–corrosion tests a marked reduction in the coating lifetime was observed. Unexpectedly, films deposited on the nitrided alloy presented a lifetime at least ten times shorter than that of films on bare alloy. We explain such a result in terms of film/substrate interaction. The weak GLCH/nitrided alloy interaction facilitates fluid penetration between the film and the substrate which leads to a fast film delamination. Such an interpretation is supported by force curve measurements, which show that the interaction between GLCH and nitrided alloy is four times weaker than that between GLCH and bare alloy.     

Corrosion behavior of nanohybrid titania–silica composite coating on phosphated steel sheet

Corrosion resistance behavior of sol–gel-derived organic–inorganic nanotitania–silica composite coatings was studied. Hybrid sol was prepared from Ti-isopropoxide and N-phenyl-3-aminopropyl triethoxy silane. The structure, morphology, and properties of the coating were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermo gravimetric analysis. The corrosion performances of the sol–gel-coated samples were investigated by electrochemical impedance spectroscopy (EIS) and standard salt spray tests. The hybrid coatings were found to be dense, more uniform, and defect free. In addition, the coatings also proved its excellent corrosion protection on phosphated steel sheet.     

Effect of temperature on friction and wear behaviour of CuO–zirconia composites

Results of wear tests using an alumina ball sliding against 5 wt% copper oxide doped tetragonal zirconia polycrystalline (CuO-TZP) ceramics are reported as a function of temperature up to 700 °C. The specific wear rate and friction coefficient are strongly dependent on temperature. Below a critical temperature (T < 600 °C), CuO-TZP showed a high coefficient of friction as well as a high wear rate. This was ascribed to the formation of a rough surface, caused by brittle fracture and abrasive wear, based on observations by scanning electron microscopy (SEM), laser scanning microscopy (LSM) and X-ray photoelectron spectroscopy (XPS). However, above 600 °C a self-healing layer is formed at the interface and results in low friction and wear. The mechanism of layer formation and restoration is discussed and rationalized by onset of plastic deformation caused by a reduction reaction of CuO to Cu₂O at high temperatures.     

A review on application of structural adhesives in concrete and steel–concrete composite and factors influencing the performance of composite connections

This paper chronicles the use of structural adhesives in civil engineering construction since its inception. The usage of structural adhesives as effective and popular strengthening agents has been discussed. The application of structural adhesives as connecting agents, especially in cases of steel–concrete composites has also been discussed in detail. Various factors influence the bond strength of interfaces, such as the physical, mechanical and chemical properties of structural adhesives and adherends, the shape of adherends, water immersion, adhesive layer thickness, bonded area geometry, relative humidity and temperature of the environment during curing and service life, the amount and type of fillers and surface finishing of adherends.     

Effect of suspension stability on bonding strength and electrochemical behavior of electrophoretically deposited HA–YSZ nanostructured composite coatings

In the present study, HA–YSZ nanostructured composites were deposited on Ti–6Al–4 V substrates by electrophoretic deposition of suspensions containing 0, 10, 20 and 40 wt% YSZ. The stability of each suspension was determined by applying response surface methodology, DLVO theory and zeta potential measurement for different YSZ contents and dispersant concentrations. The maximum zeta potential and electromobility of suspended particles was obtained for the suspension with 20 wt% YSZ. The electrophoretic deposition of HA–YSZ nanostructured composites was carried out at a constant voltage of 20 V for 120 s. The deposition kinetics was studied based on a mass-charge correlating approach under ranges of voltage (20–60 V), time (30–300 s) and wt% YSZ (0–40). The as–deposited and sintered HA–YSZ coatings were characterized by SEM, XRD, DSC–TG and FT–IR analyses. The micro-scratch behavior of coated samples indicated the highest critical contact pressures of crack initiation, P_c1 = 4.50 GPa, crack delamination, P_c2 = 5.14 GPa and fracture toughness, K_IC = 0.622 MPa m^1/2 for HA-20 wt% YSZ sample. The results of potentiodynamic polarization measurements showed that the implementation of 20 wt% YSZ could efficiently decrease the corrosion current density and corrosion rate of coated samples, while corrosion potential and linear polarization resistance were increased.     

Microstructure and mechanical properties of Ti–C–TiN-reinforced Ni204-based laser-cladding composite coating

In situ Ti(C, N), ring phase, and multi-phase enhanced Ni204-based alloy coating were prepared by adding various Ti/C/TiN ratios particles. The effects of the reinforcement phase on the microstructure, microhardness, tribological property, and microstructure characteristics at the interface between the coating and substrate were investigated. The results show that the coatings with a 5:1 mass fraction ratio of TiN/C exhibits the highest microhardness, which is 3.78 times higher than that of the original Ni204 coating. While, the coating with 21:7:2 mass fraction ratio of TiN/Ti/C exhibits the lowest friction coefficient, which is 4.44 times smaller than that of the original Ni204 coating. The addition of Ti and C particles promotes the precipitation of ring phase and carbides, reduces ceramic agglomeration, alleviates the floating of ceramic particles, and improves the bonding strength of reinforcement phases. Owing to the good mutual solubility among Fe, Ni, and, Cr elements, the diffusion happened at the interface between the coating and substrate.     

Tool life and wear of WC–TiC–Co ultrafine cemented carbide during dry cutting of AISI H13 steel

WC–5TiC–10Co ultrafine cemented carbides were prepared and used for the cutting tool for AISI H13 hardened steel. The effect of cutting parameters on the tool life and tool wear mechanism was investigated, and conventional cemented carbide with the same composition and medium grain size were prepared for comparison. The results showed that WC–5TiC–10Co ultrafine cemented carbides possess higher hardness and transverse rupture strength, and showed better cutting performance than conventional insert with the same cutting condition. Tool life was analyzed by an extended Taylor's tool life equation, indicating that cutting speed played a profound effect on the tool life and wear behavior of both cutting inserts. SEM and EDS analysis revealed that there were major adhesive wear and minor abrasive wear on the rake of WC–5TiC–10Co ultrafine inserts, and increase of cutting speed resulted in a transition from abrasion predominant wear mechanism to adhesive wear on the flank face. As for the conventional inserts, there were combination of more serious abrasive and adhesive wear on the rake and flank. The favorable cutting performance of ultrafine WC–5TiC–10Co inserts was attributed to the higher hardness and less thermal softening during machining.     

Electrosynthesis and protection role of polyaniline–polvinylalcohol composite on stainless steel

Polyaniline–polyvinyl alcohol (PANI–PVA) composite has been electrodeposited on stainless steel surface from aqueous sulfuric acid solution of aniline monomer in presence of soluble PVA at different concentrations. The PVA increased the rate of electropolymerization where 4 g/L PVA formed a composite of 37 wt% PANI and 63 wt% PVA composition. The composite layer exhibited more adhesion to the steel surface in comparison with PANI layer but with less thermal stability. It has higher protection role for the stainless steel (SS) against general and pitting corrosion. It enhanced the passivation of the SS surface by increasing the thickness of oxide film and improving the composition.     

Synthesis of polyaniline nanofiber and anticorrosion property of polyaniline–epoxy composite coating for Q235 steel

Polyaniline (PANI) nanofibers were prepared by direct mixed oxidation in four kinds of inorganic acids. The characterization of scanning electron microscopy (SEM) showed that high quality PANI fibers with uniform diameter and several microns length can be obtained by direct mixed oxidation, especially in a sulfuric acid system. Structural characteristics of PANI products through IR and UV spectra indicated the consistent peak distribution with the classic spectrum of the doped PANI. In addition, composite coatings of PANI–epoxy resin were prepared by mechanical grinding. The effect of PANI’s content on anticorrosion property of the composite coatings for Q235 steel was studied by the electrochemical impedance spectroscopy (EIS). Results showed that the best shielding protective effect was obtained when the amount of PANI was around 0.5% (wt%). More importantly, the effects of four different inorganic acids on anticorrosion property of the composite coatings were studied by the EIS and Tafel polarization curve. Experiments showed that the different composite coatings of PANI doped by different inorganic acids provided different protective abilities for the Q235 steel. It can be concluded that both the morphology and counter-anion would impact the anticorrosion effect of the doped PANI.     

Enhanced bonding strength and thermal cycling performance of MoSi2–CrSi2–SiC–Si coating for carbon/carbon composites by surface modification via blasting treatment

Before the preparation of MoSi₂–CrSi₂–SiC–Si coating, blasting treatment of carbon/carbon (C/C) composites, as a surface modification method, was conducted under oxyacetylene torch. MoSi₂–CrSi₂–SiC–Si coating was prepared on the treated C/C composites by pack cementation, where an interlock interface was formed between the coating and the C/C substrate. After blasting treatment, the thermal expansion coefficient mismatch between the coating and C/C substrate was alleviated efficiently, and the bonding strength of the coating was increased by 45.6% and reached 26.2 MPa. To simulate the real working condition, thermal cycling test was conducted under oxyacetylene torch from 1600 °C to room temperature to construct an environment of combustion gas erosion. Due to the improvement of bonding strength and the alleviation of thermal expansion coefficient mismatch between the coating and the C/C substrate, thermal cycling performance of MoSi₂–CrSi₂–SiC–Si coating was enhanced. After 25 thermal cycles, the mass loss of the coated C/C composites without blasting treatment was up to 2.4%, and the C/C substrate was partially exposed. In contrast, the mass loss of the coated C/C composites with blasting treatment was only 1.1%.     

Hydroxyapatite–Titania nanotube composite as a coating layer on Co–Cr-based implants: Mechanical and electrochemical optimization

Inadequate mechanical properties of pure hydroxyapatite (HA) coating layers make it an unsuitable candidate for many load-bearing orthopedic implants. In this study, Titania nanotubes (TNT) and HA were synthesized using Rapid Breakdown Adonization (RBA) and sol–gel methods, respectively. The sintering process at different temperatures was then conducted for the phase transformation of titanium. HA–TNT mixtures in different quantities and phases were prepared for coating on Co–Cr-based substrates. To optimize the coated HA–TNT composite layer in term of hardness, bonding strength and corrosion potential, empirical models based on Response Surface Methodology (RSM) were developed. The synthesized TNT and HA–TNT coated samples were characterized using X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopy (TEM). The predicted models generated by RSM were compared with the experimental results, and close agreement was observed. While the models demonstrate that TNT quantity is a more significant factor than sintering temperature in improving hardness (H), bonding strength (P) and the corrosion potential (E_corr) of a coated substrate, sintering temperature still has a considerable effect on H and E_corr. The optimum HA–TNT composite coating layer in terms of the mechanical and electrochemical properties were obtained with a TNT ratio of 1.07 (wt%) at a sintering temperature of 669.11 °C.     

Tribological behavior and wear mechanism of C/C–SiC brake discs based on third-body layer

C/C–SiC composites are promising candidates for heavy-duty tracked vehicle brake discs. A third-body layer (TBL) can be formed on the surface of C/C–SiC self-mated brake discs, which has an important impact on tribological behavior and wear mechanism of brake discs. Herein, the formation conditions and evolution process of TBL and its effect on friction and wear properties were investigated. An appropriate braking pressure and speed (P and V) are beneficial to the cutting of asperities and refinement of wear debris on the contact surface, which are preconditions for the formation of original TBL. The original TBL can be formed under the P·V of 12, 15, and 16, which effectively improve braking stability and reduce the wear rate. During the continuous braking process, the original TBL undergoes growth, stabilization, destruction, and regeneration. Under the frictional heat and compressive stress, wear debris gradually evolves into a uniform and dense TBL. The average coefficient of friction and wear rate reach to the lowest value of .446 and 38.5 × 10⁻³ cm³/MJ, respectively. A continuous high temperature in the later stages of braking leads to severe oxidative wear. The newly formed TBL covers the original surface to form a multilayered structure, indicating the TBL undergoes destruction and regeneration.     

Microstructure,interfacial characteristics,and wear performances of Cu–Fe–SiC cermet composites

The Cu–Fe metal-based ceramic grinding wheel material with SiC as abrasive was prepared by the powder metallurgy process of ball milling and hot pressing sintering. Cu–Fe–SiC cermets with Cu:Fe mass ratios of 4:1, 1:1, and 1:4 were designed by changing the composition of metal binder. The phase composition, microstructure, mechanical properties, and grinding properties of Cu–Fe–SiC cermets were systematically studied. The effect of Cu–Fe binder ratio on the microstructure and properties of cermets was analyzed. The results show that with the increase of Fe content, the density and hardness of cermets increase gradually, indicating that the mechanical properties are improved. Because the Fe in the adhesive can react with the abrasive SiC to form the reaction bonding interface, the Cu–80Fe–SiC cermets with higher Fe content have better adherence. The grinding test results of Cu–80Fe–SiC cermet show that the friction coefficient is .341, the surface roughness is 6.64 μm, the residual stresses parallel to the grinding direction are 353.3 MPa, and the residual stresses perpendicular to the grinding direction are 140.9 MPa. With the increase of Fe content, the wear mechanism changes from ploughing and cutting to friction.     

Hydrogen embrittlement of Zn-, Zn–Ni-, and Cd-coated high strength steel

Sacrificial coatings, such as Zn and Cd, are used to protect steel against corrosion. During the electrodeposition of metals, hydrogen is evolved due to electrolysis. The evolved hydrogen may diffuse outward and become trapped in the substrate/coating interface or migrate inward into the steel lattice causing delayed embrittlement when the component is subjected to stress. This study reports two principal variables for Zn, Zn–Ni, and Cd coatings: (i) the quantity of hydrogen absorbed by the coating and substrate by vacuum thermal desorption and (ii) the permeability of the coating material to hydrogen by electrochemical permeation. The findings were analyzed in correlation with the microstructural characteristics of both the coating material and the coating/substrate interface. With Zn–Ni, both coating process and coating material combined to significantly reduce the risk of internal hydrogen embrittlement by (i) introducing the least amount of hydrogen during the electrodeposition process and (ii) by the ease with which hydrogen can be extracted by baking due to the presence of cracks in the coating.     

Influence of temperature on the bending stiffness and tensile-shear strength of composite–metal joints

The temperature effect on bending and shear strength of single lap joints, composed by metal–composite substrates with fixed geometry, was evaluated in this paper. The tests provide analysis associated with a system frequently used in the oil and gas industry, characterized by the use of polymeric composite materials with adhesives for repairing and reinforcing pipelines. The results revealed that the tensile behavior of the composite is highly affected by temperature and can be predicted by a linear function with good agreement. The bending stiffness and tensile-shear strength of composite–metal single lap joints are also dependent of the test temperature. The first can be represented by a linear equation and the second by a power law, both with good agreement.     

Characterization and adhesion strength study of detonation-sprayed MoB–CoCr alloy coatings on 2Cr13 stainless steel substrate

A novel MoB–CoCr alloy coating was deposited onto stainless steel (2Cr13) substrate using a detonation gun (D-gun) spraying technique. Microstructures of the powder and coating were investigated by X-ray diffraction (XRD), scanning election microscopy (SEM), and transmission electron microscopy (TEM), and a quantitative determination of the adhesion strength of the coating was calculated by combination of modified four-point bending (4PB) test and finite element analysis (FEA) simulation. The results show that the coating mainly consists of ternary transition metal boride matrix phases (CoMo₂B₂, MoCoB) and binary borides (MoB and CrB). Nanocrystalline grains with a size of 50–100 nm were observed in the coating. The average energy release rate and phase angle are 191.2 J m⁻² and 41.7o, respectively, which show strong bond strength compared to other reported values.     

Wear and corrosion properties of a B–Al composite layer on pure titanium

A boriding and aluminizing two-step method was used to fabricate a B–Al composite layer on the surface of pure titanium. The composite layer was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoindentation, wear tests, and electrochemical experiments. For comparison, single boriding and single aluminizing treatments were performed on pure titanium. The results show that the surface morphology characteristics from the single boriding and single aluminizing treatments were transferred to the composite sample. The XRD pattern reveals that the B–Al composite layer also has XRD peaks of Al₃Ti+TiB₂+TiB. The SEM results revealed that the B–Al composite layer is composed of an outermost TiB₂ layer, a TiB+Al₃Ti sublayer, an Al₃Ti layer, and an internal diffusion layer. The corrosion resistance of the composite sample is slightly better than that of the matrix, and the hardness is approximately 3 times higher than that of the matrix. The wear type is mainly abrasive wear, and the wear resistance is improved; with increasing temperature, the wear on the surface of the sample is intensified, and the wear resistance is reduced.     

Microstructure and performance of brazed diamond segments with NiCr–x(CuCe) composite alloys

Novel multi-layer brazed diamond segments were fabricated using NiCr–x(CuCe) composite alloys. Differential scanning calorimetry curves of the composite alloys were measured and analysed. The microstructures of the alloy segments and surface topographies of the brazed diamond segments were characterised. Performance tests of the alloy segments and brazed diamond segments were performed. The undercooling degree of the Ni–Cr alloy in the composite alloy increased with the Cu–Ce alloy addition, which led to coarse NiCu-rich regions and Ni₃Si phases. A brazed diamond segment with a 5% Cu–Ce alloy addition exhibited the highest wear resistance and machining performance and the best surface morphology after a wear test. An excessive Cu–Ce alloy addition led to a rapid decrease in wear resistance of the brazed diamond segment owing to the large number of coarse NiCu-rich phases falling off from the composite alloy. The mechanism of the reduction in thermal damage to diamonds by the Cu–Ce alloy is elucidated. Initially the Cu–Ce particles melted and mainly Ni atoms diffused into the Cu–Ce liquid, thereby leading to the formation of NiCu-rich regions and Ce₂Ni₇ and CeNi₂ phases, which in turn promoted the diffusion. The melting temperature of the Ni–Cr composite alloy was significantly reduced by the addition of the Cu–Ce alloy.     

Microstructure and oxidation behavior of Si–MoSi2 functionally graded coating on Mo substrate

The Si–MoSi₂ functionally graded coating on Mo substrate consisting of a Si–MoSi₂ layer (2.5 µm), a MoSi₂ layer (18 µm) and a Mo–Mo₅Si₃–Mo₃Si layer (2–4 µm) was prepared by a liquid phase siliconizing method. The siliconized coating has a dense layered structure and no micro-cracks and holes. The Si element mainly enriches on the surface with the highest content of about 50 wt%, and inhibits the formation of Mo₅Si₃ and volatile MoO₃ and improves the high-temperature oxidation resistance of the coating. The mass gain of Si-MoSi₂ coating is only 0.17 wt% after oxidized at 1600 ℃ for 70 h. The Si–MoSi₂ functionally graded coating exhibits better high temperature oxidation resistance than pure MoSi₂ coating.     

Effect of iron content on the wear behavior and adhesion strength of TiC–Fe nanocomposite coatings on low carbon steel produced by air plasma spray

In this study, the effect of Fe content on the abrasion behavior of TiC–Fe nanocomposite coatings applied on the CK45 steel substrate by air plasma spray method was investigated. For this purpose, milled TiC powder was prepared at 1, 2, 3 and 4 h milled TiC powder for 4 h was selected as the suitable sample. In the next step, a suitable sample mixture with different iron powder concentrations of 5, 10, 15, 20 and 25% was prepared by mechanical milling. The granulated mixture was applied to the substrate using air plasma spray technique. Microstructural and phase analyzes were performed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). According to the results of Williamson-Hall calculations, the TiC crystallites' size decreased by 49 nm–29 nm, and network strain reached 0.16% by increasing milling time from 1 h to 4 h. Studies have shown that the coatings contain titanium carbide, iron oxide, and titanium oxide, with the number of phases formed depending on the amount of iron in the chemical composition. Investigation of the tribological properties of the coating layer showed that with increased iron content in the coating, the wear resistance of the samples is reduced. Hardness tests on coatings indicate that adding iron to nanocomposite from 5 to 25% reduces hardness from 1025 to 699 Hv. It can be argued that a slight increase in the adhesion strength of the coating to the substrate is due to increased wettability because of the formation of molten iron in the coating.