Reusing oxide-based pulverised fly ash and medical waste particles to develop electroless nickel composite coatings(Ni–P/fly ash and Ni–P/SiO_2–Al_2O_3)

Recycling and reusing materials from waste have become a nexus in the development of sustainable materials, leading to more balanced technologies. In this study, we developed a composite coating by co-depositing recycled ceramic particles, pulverised fly ash(PFA) and medical ceramics(MC), into a nickel–phosphorus matrix using a typical electroless plating process. Scanning electron microscopy(SEM) images indicated well-dispersed particles in the Ni–P matrix. However, compared with the MC particles, the PFA particles were distributed scantily with a lower content in the matrix, which could be due to the less impingement effect during the co-deposition. A modified microstructure with refined grains was obtained for the PFA-incorporated composite coating, as seen in the SEM micrograph. The X-ray diffraction result of the MC-incorporated composite coating showed the formation of Nix Siy phases in addition to the typical Ni3 P phases for the heattreated electroless Ni–P coatings. Upon heat treatment, the PFA-reinforced composite coating, due to a modified microstructure, exhibited a higher microhardness up to HK0.05 818, which is comparable to that of the traditional SiC particle-embedded composite coating(HK0.05 825).The findings can potentially open up a new strategy to further advance the green approach for industrial surface engineering.     

Fabrication of Fe–TiC–Al2O3 composites on the surface of steel using a TiO2–Al–C–Fe combustion reaction induced by gas tungsten arc cladding

The aim of the present study was to fabricate Fe–TiC–Al₂O₃ composites on the surface of medium carbon steel. For this purpose, TiO₂–3C and 3TiO₂–4Al–3C–xFe (0 ≤ x ≤ 4.6 by mole) mixtures were pre-placed on the surface of a medium carbon steel plate. The mixtures and substrate were then melted using a gas tungsten arc cladding process. The results show that the martensite forms in the layer produced by the TiO₂–3C mixture. However, ferrite–Fe₃C–TiC phases are the main phases in the microstructure of the clad layer produced by the 3TiO₂–4Al–3C mixture. The addition of Fe to the TiO₂–4Al–3C reactants with the content from 0 to 20wt% increases the volume fraction of particles, and a composite containing approximately 9vol% TiC and Al₂O₃ particles forms. This composite substantially improves the substrate hardness. The mechanism by which Fe particles enhance the TiC + Al₂O₃ volume fraction in the composite is determined.     

H2O2溶液对钛种植体表面的处理

The surface treatment is important for titanium and its alloys as promising candidates for dental implantation due to their bioinert surface. Titanium surface samples were modified using H₂O₂ solution at different times up to 72 h to boost their bioactivity. According to the results of the field emission scanning electron microscopy test, some nanostructures are formed on the surface of treated titanium samples and increased in size by increasing the time of treatment up to 24 h. After 24 h of application, the sharpness of nanostructures decreased and the micro-cracks and discontinuity in the coating surface increased. The results of the X-ray diffraction study and Raman spectroscopy revealed that anatase (TiO₂) was formed on the surface of treated titanium samples. The peak intensity of Raman spectroscopy increased with an improvement in treatment time of up to 24 h and then decreased due to the discontinuity of the coating. Full wettability and ability to form apatite were reached at 6 h of treatment. It is clear that the treatment time has a significant effect on the surface treatment of titanium using the H₂O₂ solution.     

碳包覆Ti3AlC2增强银基复合材料的制备与性能

Ti₃AlC₂-reinforced Ag-based composites, which are used as sliding current collectors, electrical contacts, and electrode materials, exhibit remarkable performances. However, the interfacial reactions between Ag and Ti₃AlC₂ significantly degrade the electrical and thermal properties of these composites. To diminish these interfacial reactions, we fabricated carbon-coated Ti₃AlC₂ particles (C@Ti₃AlC₂) as reinforcement and prepared Ag–10wt%C@Ti₃AlC₂ composites with carbon-layer thicknesses ranging from 50–200 nm. Compared with the uncoated Ag–Ti₃AlC₂ composite, Ag–C@Ti₃AlC₂ was found to have a better distribution of Ti₃AlC₂ particles. With increases in the carbon-layer thickness, the Vickers hardness value and relative density of Ag–C@Ti₃AlC₂ gradually decreases. With a carbon-layer thickness of 150 nm, we obtained the lowest resistivity of Ag–C@Ti₃AlC₂ of 29.4 135.5×10?9 Ω·m, which is half that of Ag–Ti₃AlC₂ (66.7 × 10?9 Ω·m). The thermal conductivity of Ag–C@Ti₃AlC₂ reached a maximum value of 135.5 W·m?1·K?1 with a 200-nm carbon coating (~1.8 times that of Ag–Ti₃AlC₂). These results indicate that the carbon-coating method is a feasible strategy for improving the performance of Ag–C@Ti₃AlC₂ composites.     

Microstructure of Ni–Al powder and Ni–Al composite coatings prepared by twin-wire arc spraying

Ni–Al powder and Ni–Al composite coatings were fabricated by twin-wire arc spraying (TWAS). The microstructures of Ni-5wt%Al powder and Ni-20wt%Al powder were characterized by scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the obtained particle size ranged from 5 to 50 μm. The morphology of the Ni–Al powder showed that molten particles were composed of Ni solid solution, NiAl, Ni₃Al, Al₂O₃, and NiO. The Ni–Al phase and a small amount of Al₂O₃ particles changed the composition of the coating. The microstructures of the twin-wire-arc-sprayed Ni–Al composite coatings were characterized by SEM, EDS, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that the main phase of the Ni-5wt%Al coating consisted of Ni solid solution and NiAl in addition to a small amount of Al₂O₃. The main phase of the Ni-20wt%Al coating mainly consisted of Ni solid solution, NiAl, and Ni₃Al in addition to a small amount of Al and Al₂O₃, and NiAl and Ni₃Al intermetallic compounds effectively further improved the final wear property of the coatings. TEM analysis indicated that fine spherical NiAl₃ precipitates and a Ni–Al–O amorphous phase formed in the matrix of the Ni solid solution in the original state.     

Preparation of electroless Ni–P composite coatings containing nano-scattered alumina in presence of polymeric surfactant

Ni–P electroless coating was applied on low carbon steel with the incorporation of different amounts of nano Al2O3 powder (ranging from 3 g/l to 30 g/l) in electroless bath. Corrosion properties and microstructures of the coating were studied. The dispersion stability of alumina colloidal particles stabilized by polymeric (non-ionic) surfactants in an electroless bath was also investigated. The surface morphology and the relevant structure were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of the coated steel was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques. The results showed that increasing alumina concentration not only changed the surface morphology, but also promoted the corrosion resistance. Addition of surfactants has an indirect effect on the amount of the incorporated particles. Meanwhile, in the presence of surfactant, corrosion resistance of Ni–P coating containing even a small quantity of alumina was improved since a stabilized bath was obtained.     

Microstructure and mechanical properties of Nb–Mo–ZrB2 composites prepared by hot-pressing sintering

Nb–Mo–ZrB₂ composites (V(Nb)/V(Mo)=1) with 15vol% or 30vol% of ZrB₂ were fabricated by hot-pressing sintering at 2000℃. The phases, microstructure, and mechanical properties were then investigated. The composites contain Nb-Mo solid solution (denoted as (Nb, Mo)ss hereafter), ZrB, MoB, and NbB phases. Compressive strength test results suggest that the strength of Nb–Mo–ZrB₂ composites increases with increasing ZrB₂ content; Nb–Mo–30vol%ZrB₂ had the highest compressive strength (1905.1 MPa). The improvement in the compressive strength of the Nb–Mo–ZrB₂ composites is mainly attributed to the secondary phase strengthening of the stiffer ZrB phase, solid-solution strengthening of the (Nb, Mo)ss matrix as well as fine-grain strengthening. The fracture toughness decreases with increasing ZrB₂ content. Finally, the fracture modes of the Nb–Mo–ZrB₂ composites are also discussed in detail.     

PTA clad (Cr,Fe)7C3/γ-Fe in situ ceramal composite coating

A wear-resistant (Cr, Fe)₇C₃/γ-Fe in situ ceramal composite coating was fabricated on the substrate of 0.45wt%C carbon steel by a plasma-transferred arc cladding process using the Fe-Cr-C elemental powder blends. The microstructure, microhardness, and dry-sliding wear resistance of the coating were evaluated. The results indicate that the microstructure of the coating, which was composed of (Cr, Fe)₇C₃ primary phase uniformly distributed in the γ-Fe, and the (Cr, Fe)₇C₃ eutectic matrix was metallurgically bonded to the 0.45wt%C carbon steel substrate. From substrate to coating, the microstructure of the coating exhibited an evident epitaxial growth character. The coating, indehiscent and tack-free, had high hardness and appropriate gradient. It had excellent wear resistance under the dry sliding wear test condition.     

Corrosion behavior of Ni–P/nano-TiC composite coating prepared in electroless baths containing different types of surfactant

In current research, in order to enhance the incorporation of nano-sized TiC particles into electroless Ni–P (EN) coating, different types of surfactant (cationic, anionic, and polymeric) were added to the plating bath. The effects of addition of the surfactants on surface morphology, deposition rate, TiC and P contents of the prepared coatings were investigated. The surface morphology was evaluated by scanning electron microscopy (SEM). It was demonstrated that in the presence of the anionic, polymeric and somehow cationic surfactants, TiC nano-particles were embedded in the matrix which influenced the surface morphology. The effect of surfactant types on the corrosion properties of Ni–P/TiC coated steel was also studied. Corrosion behavior of the coated steel was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) which affected by the incorporation of TiC particles into the Ni–P matrix. The level of corrosion resistance improvement depended largely on the phosphorous and TiC concentration of the applied coating.     

18wt%Cr–8wt%Ni不锈钢中增塑性MnO–Al2O3–SiO2基非金属夹杂物的演变及其浸泡性能

The properties of MnO–Al₂O₃–SiO₂-based plasticized inclusion are likely to change during soaking  process due to its low melting point. In this study, the evolution of the MnO–Al₂O₃–SiO₂-based inclusion of 18wt%Cr?8wt%Ni stainless steel under isothermal soaking process at 1250°C for different times was investigated by laboratory-scale experiments and thermodynamic analysis. The results showed that the inclusion population density increased at the first stage and then decreased while their average size first decreased and then increased. In addition, almost no Cr₂O₃-concentrated regions existed within the inclusion before soaking, but more and more Cr₂O₃ precipitates were formed during soaking. Furthermore, the plasticity of the inclusion deteriorated due to a decrease in the amount of liquid phase and an increase in the high-melting-point-phase MnO–Cr₂O₃ spinel after the soaking process. In-situ observations by high-temperature confocal laser scanning microscopy (CLSM) confirmed that liquid phases were produced in the inclusions and the inclusions grew rather quickly during the soaking process. Both the experimental results and thermodynamic analysis conclude that there are three routes for inclusion evolution during the soaking process. In particular, Ostwald ripening plays an important role in the inclusion evolution, i.e., MnO–Al₂O₃–SiO₂-based inclusions grow by absorbing the newly precipitated smaller-size MnO–Cr₂O₃ inclusions.     

Preparation and properties of the Ni-Al/Fe-Al intermetallics composite coating produced by plasma cladding

A novel approach to produce an intermetallic composite coating was put forward. The microstructure, microhardness, and dry-sliding wear behavior of the composite coating were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS) analysis, microhardness test, and ball-on-disc wear experiment. XRD results indicate that some new phases FeAl, Fe_0.23Ni_0.77Al, and Ni₃Al exit in the composite coating with the Al₂O₃ addition. SEM results show that the coating is bonded with carbon steel metallurgically and exhibits typical rapid directional solidification structures. The Cr₇C₃ carbide and intermetallic compounds co-reinforced composite coating has a high average hardness and exhibits an excellent wear resistance under dry-sliding wear test compared with the Cr₇C₃ carbide-reinforced composite coating. The formation mechanism of the intermetallic compounds was also investigated.     

Fabrication and character ization of electrospun TiO2/CuS micro–nano-scaled composite fibers

A process to fabricate a kind of novel micro–nano scaled TiO2/CuS composite fibers by electrospinning technique and chemical precipitation method was developed in the present study. The microstructures and photoelectronic properties of the fibers were characterize d using SEM, FT-IR, UV–vis and fluorescence spectroscopy. The results revealed that the TiO2 portion in the composite fibers was a mixture rutile and anatase phases while TiO2 and CuS had been fully composite. The fibers had smooth surface with a diameter of 50–300 nm. Comparing with pure TiO2 fiber, the TiO2/CuS micro–nano-scaled composite fibers exhibited a strong absorption in the visible light region and the efficiency of photo-induced charge separation were enhanced. This composite system is of widely potential applications in the areas such as solar cells, supercapacity, photocatalysis, etc.     

Microstructure characteristics of Ni/WC composite cladding coatings

A multilayer tungsten carbide particle (WCp)-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology. The morphology, microstructure, and formation mechanism of the coating were studied and discussed in different zones. The microstructure morphology and phase composition were investigated by scanning electron microscopy, optical microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. In the results, the coating presents a dense and homogeneous microstructure with few pores and is free from cracks. The whole coating shows a multilayer structure, including composite, transition, fusion, and diffusion-affected layers. Metallurgical bonding was achieved between the coating and substrate because of the formation of the fusion and diffusion-affected layers. The Ni-based alloy is mainly composed of γ-Ni solid solution with finely dispersed Cr₇C₃/Cr₂₃C₆, CrB, and Ni+Ni₃Si. WC particles in the composite layer distribute evenly in areas among initial Ni-based alloying particles, forming a special three-dimensional reticular microstructure. The macrohardness of the coating is HRC 55, which is remarkably improved compared to that of the substrate. The microhardness increases gradually from the substrate to the composite zone, whereas the microhardness remains almost unchanged in the transition and composite zones.     

Microstructure and properties of Ag–Ti3SiC2 contact materials prepared by pressureless sintering

Ti₃SiC₂-reinforced Ag-matrix composites are expected to serve as electrical contacts. In this study, the wettability of Ag on a Ti₃SiC₂ substrate was measured by the sessile drop method. The Ag–Ti₃SiC₂ composites were prepared from Ag and Ti₃SiC₂ powder mixtures by pressureless sintering. The effects of compacting pressure (100–800 MPa), sintering temperature (850–950℃), and soaking time (0.5–2 h) on the microstructure and properties of the Ag–Ti₃SiC₂ composites were investigated. The experimental results indicated that Ti₃SiC₂ particulates were uniformly distributed in the Ag matrix, without reactions at the interfaces between the two phases. The prepared Ag–10wt%Ti₃SiC₂ had a relative density of 95% and an electrical resistivity of 2.76×10-3 mΩ·cm when compacted at 800 MPa and sintered at 950℃ for 1 h. The incorporation of Ti₃SiC₂ into Ag was found to improve its hardness without substantially compromising its electrical conductivity; this behavior was attributed to the combination of ceramic and metallic properties of the Ti₃SiC₂ reinforcement, suggesting its potential application in electrical contacts.     

In-situ fabrication of Al(Zn)-Al2O3 graded composite using the aluminothermic reaction during hot pressing

In this study, the fabrication of multilayer Al(Zn)–Al₂O₃ with different volume fractions of Al₂O₃ was investigated. Al and ZnO powders were milled by a planetary ball mill, after which five-layer functionally graded samples were produced through hot pressing at 580℃ and 90 MPa pressure for 30 min. Formation of reinforcing Al₂O₃ particles occurred in the aluminum matrix via the aluminothermic reaction. Determination of the ignition temperature of the aluminothermic reaction was accomplished using differential thermal and thermogravimetric analyses. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometery analyses were utilized to characterize the specimens. The thermal analysis results showed that the ignition temperatures for the aluminothermic reaction of layers with the highest and lowest ZnO contents were 667 and 670℃, respectively. Microstructural observation and chemical analysis confirmed the fabrication of Al(Zn)–Al₂O₃ functionally graded materials composites with precipitation of additional Zn in the matrix. Moreover, nearly dense functionally graded samples demonstrated minimum and maximum hardness values of HV 75 and HV 130, respectively.     

Effects of SiO2 on the preparation and metallurgical properties of acid oxidized pellets

The effects of SiO₂ content on the preparation process and metallurgical properties of acid oxidized pellets, including compressive strength, reduction, and softening–melting behaviors, were systematically investigated.Mineralogical structures, elemental distribution, and pore size distribution were varied to analyze the mechanism of the effects.The results show that with an increase in SiO₂ content from 3.51 wt%to 7.18 wt%, compressive strength decreases from 3150 N/pellet to 2100 N/pellet and reducibility decreases from 76.5% to 71.4%.The microstructure showed that pellets with high SiO₂ content contained more magnetite in the mineralogical structures.Additionally, some liquid phases appeared, which hindered the continuous crystallization of hematite.Also, the softening–melting properties of the pellets clearly deteriorated as the SiO₂ content increased.With increasing SiO₂ content, the temperature range of the softening–melting zone decreased, and the maximum differential pressure and the comprehensive permeability index increased significantly.When acid oxidized pellets are used as the raw materials for blast furnace smelting, it should be combined with high basicity sinters to improve the softening–melting behaviors of the comprehensive charge.     

The strain ampli tude-controlled cyclic fatigue behavior of Al2O3 fiber reinforced Al–Si alloy composite at elevated temperatures

The strain amplitude-controlled fatigue characteristics of an Al–Si casting alloy and itscomposite reinforced with 17 vol% Al₂O₃ fibers (Al–Si/Al₂O₃) are studied at three different temperatures. Both the alloy and the composite showed different degrees of cyclic softening at elevated temperatures. Increasing the temperature, fatigue damage of either the alloy or the composite occurred with varying mode from brittle fracture of silicon particles to their separation from the aluminum matrix. This is explained by the different thermal expansion coefficients of silicon particles and the aluminum matrix. The reinforcement Al₂O₃ fibers in the composite showed a similar damage behavior with those silicon particles despite temperature variation     

Microstructure and wear resistance of PTA clad Cr7C3/γ-Fe ceramal composite coating

A wear resistant Cr₇C₃/γ-Fe ceramal composite coating was fabricated on substrate of the hardening and tempering C degree steel by PTA (plasma transferred arc) cladding with (wt%) Fe-25Cr-7C elemental powder blends. Microstructure of the coating was characterized by OM, SEM, XRD and EDS. Wear resistance of the coating was tested under dry sliding wear condition at room temperature. The results indicate that the PTA clad ceramal composite coating has a rapidly solidified fine microstructure consisting of Cr₇C₃ primary particles uniformly distributed in the γ-Fe matrix and is metallurgically bonded to the C degree steel substrate. The PTA clad Cr₇C₃/γ-Fe ceramal composite coating has high hardness and excellent wear resistance under dry sliding wear test conditions. The excellent wear resistance of the Cr₇C₃/γ-Fe ceramal composite coating is attributed to the coating’s high hardness, strong covalent atomic bonding and refined microstructure.     

Microstructure and wear resistance of PTA clad Cr7C3/γ-Fe ceramal composite coating

A wear resistant Cr₇C₃/γ-Fe ceramal composite coating was fabricated on substrate of the hardening and tempering C degree steel by PTA (plasma transferred arc) cladding with (wt%) Fe-25Cr-7C elemental powder blends. Microstructure of the coating was characterized by OM, SEM, XRD and EDS. Wear resistance of the coating was tested under dry sliding wear condition at room temperature. The results indicate that the PTA clad ceramal composite coating has a rapidly solidified fine microstructure consisting of Cr₇C₃ primary particles uniformly distributed in the γ-Fe matrix and is metallurgically bonded to the C degree steel substrate. The PTA clad Cr₇C₃/γ-Fe ceramal composite coating has high hardness and excellent wear resistance under dry sliding wear test conditions. The excellent wear resistance of the Cr₇C₃/γ-Fe ceramal composite coating is attributed to the coating’s high hardness, strong covalent atomic bonding and refined microstructure.     

Effect of pickling processes on the microstructure and properties of electroless Ni–P coating on Mg–7.5Li–2Zn–1Y alloy

The electroless plating Ni–P is prepared on the surface of Mg–7.5Li–2Zn–1Y alloys with different pickling processes.The microstructure and properties of Ni–P coating are investigated.The results show that the Ni–P coatings deposited using the different pickling processes have a different high phosphorus content amorphous Ni–P solid solution structure,and the Ni–P coatings exhibit higher hardness.There is higher phosphorus content of Ni–P amorphous coating using 125 g/L Cr O3and 110 ml/L HNO3(w68%)than using 180 g/L Cr O3and 1 g/L KF during pre-treatment,and the coating structure is more compact,and the Ni–P coatings exhibit more excellent adhesion with substrate(Fcup to22 N).The corrosion potential of Ni–P coating is improved and exhibits good corrosion resistance.As a result,Mg-7.5Li-2Zn-1Y alloy is remarkably protected by the Ni–P coating.