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There is a growing interest in enhancing the bioactivity of TC4-based metallic biomaterials, which are known for their excellent biocompatibility. Bioactive glass (BG) has been recognized for its high potential in promoting bioactivity, particularly in osteo tissue engineering. This study focuses on investigating the influence of BG addition on the microstructure and electrochemical properties of TC4 coatings. The TC4/BG composite coatings were fabricated through laser cladding, and their microstructure was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical properties of the coatings were assessed through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in three different solutions. The results revealed that the incorporation of BG had a significant impact on the microstructure of the TC4 coatings, leading to the formation of a well-defined interface between the TC4 matrix and the BG aggregates. The distribution of BG aggregates within the TC4 matrix coating was found to be random and unrelated to the specific regions of the coating. The metallographic microstructure variations were attributed to different heat dissipation conditions during the laser cladding process. Furthermore, the electrochemical corrosion behavior of TC4/BG composite coatings reveals that they exhibit stability similar to that of passive films and good resistance against media corrosion compared to TC4, while also showing enhanced corrosion resistance in 3.5 wt% NaCl and Dulbecco's modified Eagle medium (DMEM) solutions, indicating their potential for biomedical applications; however, the corrosion resistance decreases gradually in all solutions, potentially due to the elevated Cl− concentration. Further research can explore bioactivity enhancement of TC4/BG composite coatings and investigate the long-term stability and biological response of these coatings in diverse physiological environments. [ABSTRACT FROM AUTHOR]

Two kinds of layered double hydroxides inhibition materials were synthesized on graphene oxide, and applied to strengthen the Ni-based coating on Mg-Li alloy. The composition and release properties of corrosion inhibition materials were studied. The formation of passivated film and the corrosion resistance mechanism of coating were summarized. The results show that two kinds of corrosion inhibition materials had good release properties. The addition of corrosion inhibition materials was helpful to form Ni-based composite coatings with fine and dense cell clusters, which strengthened the corrosion resistance of the coating, especially for a long time. • Two kinds of graphene-based corrosion inhibition materials were synthesized. • Corrosion resistance of Ni-based coatings in different soaking time was studied. • Inhibition materials enhanced the corrosion resistance of coatings on Mg-Li alloy. • Passivation film formation and corrosion resistance mechanism were studied. [ABSTRACT FROM AUTHOR]

For the application of lightweight alloys, the corrosion and wear problems of magnesium-lithium (Mg-Li) alloys have always been important problems that cannot be ignored. The coupling protection of multiple technologies has gradually become a new trend. In this study, layered double hydroxides (LDH) nanosheet arrays were in-situ grown on Ni-P coating by the electroless plating technology combined with hydrothermal synthesis technology. The optimum deposition conditions (temperature-time-pH) were selected by orthogonal test. The surface morphology, structure, corrosion resistance and wear resistance of LDH/Ni composite coatings under different conditions were systematically studied by SEM, XRD, FT-IR, DSC, electrochemical and tribological tests. The growth mechanism of LDH suitable for Ni-P coating surface was proposed by analyzing the growth process of LDH nanosheet arrays. The results showed that the condition of 125 °C-12 h-13 was conducive to the growth of LDH nanosheet arrays. Compared with the Ni-P coating and the composite coating under other conditions, the LDH 125°C-12h-13 /Ni composite coating has the lowest self-etching current density (7.50 × 10−7 A·cm−2) and the average friction coefficient (0.35). The defect sealing effect and Cl− barrier property of LDH effectively improved the corrosion resistance of the coating. The frictional properties were improved by lubrication and heat absorption properties of LDH. In addition, it was found that the growth of LDH on the Ni-P coating surface followed the mechanism of "deposition nucleation-diffusion growth". • Nanosheet arrays in-situ coupled Ni-based coatings on Mg-Li alloy were prepared. • Optimum growth conditions of nanosheet arrays were selected by orthogonal test. • The composite coating had better corrosion and wear resistance for Mg-Li alloy. • Wear mechanism and growth mechanism of LDH nanosheet arrays were studied. [ABSTRACT FROM AUTHOR]

In this paper, the oxidation behavior and high-temperature tribological properties of laser cladding Ti-Al-Si-SiCx system coatings at 800°C in the air were studied. The results demonstrated that these coatings had Ti 5 Si 3 /Ti 3 Al eutectic structure before oxidation. The results of oxidation resistance suggested that the oxidation weight gain conformed to the parabolic law. An appropriate increase in SiC content is beneficial to lower the oxidation rate. The Ti 5 Si 3 phase has excellent oxidation resistance. TiC phase forms CO 2 product during the oxidation process. In addition, the diffusion rates of Ti and Al elements in the oxide layer are different. The combined effect of the two eventually leads to the gradual formation of pores in the oxide layer. The TiC-reinforced phase improves the friction coefficient of high-temperature friction, but its introduction significantly improves the high-temperature wear resistance. Additionally, the adhesion of the oxide film in the high-temperature wear process exerted a great influence on the wear mechanism. Ti-Al-Si-SiC 3 exhibited the lowest wear rate of 6.73 × 10−7 mm3 N−1 m−1. The wear mechanism is primarily adhesive wear, abrasive wear, and oxidative wear. • Ti-Al-Si-SiC 3 coatings are mainly composed of Ti 3 Al, Ti 5 Si 3 , and TiC phases. • The improvement of oxidation resistance of Ti-Al-Si-SiCx coating is the result of the interaction of Al and Si. • An appropriate amount of Si can promote the formation of Al 2 O 3 oxidation products. • Compared with Ti-Al-Si,the Ti-Al-Si-SiC 3 coating has excellent oxidation resistance and wear resistance. [ABSTRACT FROM AUTHOR]

The metastable materials have attracted the attention of researchers due to their promising physicochemical properties, but the thermal stability limits their practical application. In this paper, Ni-B/La 2 O 3 amorphous/nanocrystalline composite coatings were prepared on AISI 1045 steel substrate by electro-brush plating technique. The surface morphology, component and the phase structure of coatings were observed by Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD), respectively. The coatings were further analyzed by Transmission Electron Microscope (TEM). Then the thermal stability of coatings with different content of La 2 O 3 was also analyzed under different annealing temperature. It was found that the coating had a unique microstructure consisting of amorphous and nanocrystalline structures. The addition of La 2 O 3 does improve the thermal stability of metastable Ni-B coatings when the annealing temperature is over 355 °C. In addition, the thermal stability of the amorphous/nanocrystalline coatings depends on the percentage of amorphous phase and grain sizes. [ABSTRACT FROM AUTHOR]

Fe/MWCNTs (multi walled carbon nanotubes) composite coatings with varying-content MWCNTs (0, 0.1, 0.2, 0.5 and 0.9 g/L) on the surface of AISI 1045 steel were produced by electro-brush plating technique. The effect of MWCNTs concentration in the plating solution on the microstructures and of the composite coatings was discussed in detail. The co-deposition of MWCNTs with Fe atom occurs in the Fe-based coating, which can decrease the number of through-wall cracks and increase the deposition velocity whereas the phase structure of the composite coatings cannot be affected. When the content of MWCNTs added in the plating solution is 0.2 g/L, the microhardness (612 HV 0.3 ) of coating is much higher than that of pure Fe coating (489 HV 0.3 ). The friction coefficient and weight loss of all Fe/MWCNTs composite coatings are significantly lower than that of pure Fe coating, which is attributed to the effect of reinforcement and lubrication of MWCNTs. [ABSTRACT FROM AUTHOR]

In the pursuit of high performance development of alloy materials, it is a long-standing problem to enhance strength and toughness simultaneously. In this study, by selecting heterogeneous high-entropy alloy (HEA) materials and conducting structural design and laser process optimization, an external-hard internal-tough HEA composite coating with an in-situ dual-phase interface layer was successfully prepared. For the microstructure, the phase structures at the top, middle, and bottom of the coating are single-phase body-centered cubic (BCC), dual-phase BCC/face-centered cubic (FCC), and single-phase FCC, respectively. Among them, the dual-phase interface layer gives priority to the FCC phase (79.4 %), supplemented by the BCC phase (16.7 %). In terms of mechanical properties, the hardness of the coating from the top to the bottom is 9.85 GPa, 5.53 GPa, and 4.86 GPa, respectively. As demonstrated by employing the three methods of K, H/E, and H3/E2, the HEA composite coating has favorable integrated characteristics of strength and toughness. Meanwhile, due to the in-situ generated dual-phase interface layer, the structural and performance differences between the high-hardness layer and the high-toughness layer are effectively alleviated, and the stress concentration is reduced, thus stabilizing the overall structure of the coating. Hence, the HEA composite coating designed and prepared in this study possesses better erosion resistance (mass erosion rate = 0.141 × 10−3 g.cm−2 s−1), tribological properties (wear rate = 0.30 × 10−6 mm3/(N · m)), and impact resistance (AKU = 103.5 ± 2.8 J). The study results can provide new methods and new theories for new HEA composite coatings with integrated strength and toughness, and can be used in guiding the development and design of similar HEA composite coating structures. [Display omitted] • The FCC/FCC + BCC/BCC HEA composite coating with gradient structure is successfully prepared. • The FeCoCrNiAl interface layer is formed in situ by FeCoCrNi and FeCoCrAl. • The interface layer alleviates the structural and performance differences between the surface and bottom layers. • The HEA composite coating possesses good strength and toughness. • The HEA composite coating has better erosion resistance, preferable tribological properties, and superior impact resistance. [ABSTRACT FROM AUTHOR]

As a lightweight material, the wide application of Mg-Li alloy is restricted by its corrosion resistance. Focusing on this, an innovative superhydrophobic composite coatings of nickel-based metal coupled with layered double hydroxides (LDHs) was prepared on Mg-Li alloy. The microstructure, hydrophobic property and corrosion resistance of coatings were investigated by SEM, TEM, XRD, FT-IR, AFM, contact angle tester and electrochemical test. The results indicated that the MgAl LDHs uniformly grown in situ on the NiP coating deposited on Mg-Li alloy through electroless plating and hydrothermal treatment. The MgAl LDHs with a complex honeycomb micro-nano structure improved the surface roughness of the composite coating to 126 nm. The two-step treatment achieved an excellent coupling between the metal-based coating and inorganic compounds. The low surface energy treatment of micro-nano structure on NiP coating surface with stearic acid (@SA) realized the superhydrophobic transition of the composite coating (WAC=154.27° ± 2.56°). Besides, MgAl LDHs showed better trapping properties for Cl-. Under the synergistic effect of anion capture and hydrophobic effect, the corrosion current density (1.35 ×10−7 A⋅cm−2) and impedance modulus of NiP/MgAl LDHs@SA coating were significantly better than those of NiP and NiP/MgAl LDHs coating. The superhydrophobic composite coating provided a better anticorrosion choice for Mg-Li alloy. [Display omitted] • A new superhydrophobic double-layer coatings were prepared on the Mg-Li alloy. • MgAl LDHs with uniform honeycomb structure were in situ grown on the NiP coating. • Modified by stearic acid, the double-layer coatings had good superhydrophobicity. • The superhydrophobic double-layer coatings showed excellent corrosion resistance. [ABSTRACT FROM AUTHOR]

One of the vital problems limiting the application of multi-layer cladding coating is that there appears a coarse grain structure at interface between different layers. In order to refine the grain and increase the bonding strength, Nb was added to Co50 composite coating in this study. The multi-layer Co50 composite coating was fabricated by plasma cladding. Microstructure was investigated by scanning electron microscopy (SEM) with energy dispersive spectrum (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). And the effect of Nb on bonding strength was investigated using tensile test and first-principles calculations based on density functional plane-wave ultrasoft pseudopotential method. The results show that when Nb is added, a few in situ synthesized NbC with very small grain size appears on the grain boundaries, restraining those movements which results in the grain and microstructure refinement. Besides that, the strength bonding between different layers increases, which is attributed to the fine-grain strengthening and dispersion strengthening effect of NbC. Further, the strong Co-C covalent bonds in the NbC/Co interface and the Co-Co metallic bond in the internal coating might be why the NbC can serve as an obstacle and have a strong drag and pinning effect on the grain boundary according to the first principle calculations. [ABSTRACT FROM AUTHOR]

The Ni-based WC coatings enhanced by WC particle were fabricated on FV520B by plasma cladding device. The influence of magnetic force on the microstructure and performance of the coating was investigated. If the magnetic field does not exist, the microstructure of coating is a cluster of block-shaped structures; it is observably different from the dendritic and crumbling snowflake-like structures formed under transverse and longitudinal magnetic fields. The WC particles were distributed at the grain boundary. With the effect of longitudinal magnetic field, wear resistance and erosion resistance of coatings improved markedly. When axial magnetic field intensity came to 38 mT, the microhardness of coatings reached a maximum value, 720 HV0.2. Electron probe microanalyzer (EPMA) indicates the metallurgical combination at the interface and element interdiffusion happened between the coating and substrate. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiB/Ti 50 Zr 25 Al 15 Cu 10 medium-entropy alloy composite coating (MEACC) was successfully prepared on the surface of magnesium alloy by laser cladding. • La rare earth element was added into the self-designed Ti 50 Zr 25 Al 15 Cu 10 non-equiatomic medium-entropy alloy in the form of LaB 6. • The strengthening mechanism with LaB 6 addition was investigated. • The corrosion and wear resistance of magnesium alloy got huge improvement. The improvement of corrosion resistance and wear resistance levels is of great significance because of the far-ranging impacts of them on the further application of magnesium alloys. In this work, a novel TiB/Ti 50 Zr 25 Al 15 Cu 10 medium-entropy alloy composite coating (MEACC) was successfully prepared on the surface of magnesium alloy by laser cladding. The effect of LaB 6 content on microstructure, micro-hardness, wear resistance and corrosion resistance of Ti 50 Zr 25 Al 15 Cu 10 coatings was studied in detail. The results show that TiB/Ti 50 Zr 25 Al 15 Cu 10 MEACCs are mainly composed of α-Ti, BCC and TiB phases. With LaB 6 content increased, the microstructure of the coating is refined and homogenized. And when the addition amount is excessive, Cu 2 La clusters appear. The lattice distortion caused by La3+ with large ion radius leading to the formation of hard BCC solid solution, as well as the dispersion strengthening of TiB in-situ, the coating presents high micro-hardness and excellent wear resistance. Especially, the average micro-hardness values of Ti 50 Zr 25 Al 15 Cu 10 coating with 4 wt% LaB 6 is ∼679.4 HV 0.3 , which is about 11 times than that of the substrate (∼61.6 HV 0.3). Besides, TiB/Ti 50 Zr 25 Al 15 Cu 10 MEACC displays excellent corrosion resistance. The minimum corrosion current density is 8.52 × 10−7 A·cm−2, and the oxidation phenomenon emerged in the coating. The oxide film is mainly composed of the oxidation state of Ti, Zr, Al, Cu and the sub-oxide state of Cu. [ABSTRACT FROM AUTHOR]

[Display omitted] • CeO 2 nanoparticles modified GO composites were synthesized by hydrothermal method. • Electroless Ni-P coatings enhanced by modified GO were prepared on Mg-Li alloys. • The microstructure of coatings became uniform and dense after adding modified GO. • Adding modified GO was conducive to improving the wear resistance of coatings. • Modified GO significantly improved the corrosion resistance of coatings. A new strategy of CeO 2 nanoparticles integration with GO nanosheets (CeO 2 @GO composites) was adopted for reinforcing Ni-P coating on Mg-Li alloys. Besides, the effect of GO nanosheets and CeO 2 @GO composites as reinforced particles on the microstructure, corrosion resistance and wear resistance of Ni-P coating were investigated. CeO 2 nanoparticles with average size of 4.19 nm were uniformly synthesized on GO nanosheets by hydrothermal method. The cellular nodules of coatings were refined after adding GO nanosheets and CeO 2 @GO composites. Moreover, the compactness and flatness of CeO 2 @GO-Ni-P composite coating were better than that of GO-Ni-P composite coating. The average friction coefficient of CeO 2 @GO-Ni-P composite coating (0.331) was decreased by 17%, 35.5%, and 39.6% than that of GO-Ni-P composite coating, Ni-P coating and Mg-Li substrate, respectively. The addition of GO nanosheets and CeO 2 @GO composites both improved the corrosion resistance of coatings, while CeO 2 @GO-Ni-P composite coating has the best corrosion resistance. Compared with Mg-Li alloys, the self-corrosion potential of CeO 2 @GO-Ni-P composite coating (-0.35 ± 0.006 V) shifted to positive potential by 1.28 V, and the self-corrosion current density was reduced by two order of magnitude (1.41 ± 0.13 × 10-6 A⋅cm−2). This was mainly attributed to the synergistic effect of the CeO 2 nanoparticles on the GO nanosheets. [ABSTRACT FROM AUTHOR]

NiTi, NiTi-4Si, and NiTi-4Si-2YF 3 coatings were prepared on Ti-6Al-4V substrate by laser cladding to obtain composite multilayer protective coating for composite structure. The effects of Si and YF 3 addition on the microstructure, phase composition, microhardness, and phase transformation of the coatings were systematically analyzed. The coatings are mainly composed of NiTi, NiTi 2, and TiN phases. The addition of YF 3 results in the decrease of the dendrite TiN phase in the coating. TEM results show that the core-shell structure is observed in NiTi-4Si coating. The β -Ti phase was surrounded by the shell NiTi 2 phase. After the addition of YF 3 , the core-shell structure was found to disappear. With the addition of the Si element, the eutectic structure was found in the coatings. The eutectic structure is mainly composed of NiTi (B2) and Ti 2 Si phases. According to the SEAD result, there are crystallographic orientation relationships (ORs) between NiTi (B2) phase and Ti 2 Si phase as follows: 1 ¯ 11 B 2 / / 1 ¯ 23 Ti 2 Si. The average microhardness of the NiTi, NiTi-4Si and NiTi-4Si-2YF 3 coatings were at 468.33 HV 0.5 , 499.86 HV 0.5 , and 433.65 HV 0.5 , respectively. At the same time, the uniformity of the NiTi phase in NiTi-4Si-2YF 3 coatings is improved, which is conducive to a more complete phase transition. [Display omitted] • With the addition of Si element, the eutectic structure was found in the coatings. • The addition of YF 3 results in the decrease of the dendrite TiN phase in coatings. • the core-shell structure (NiTi 2 @ β -Ti) is observed in NiTi-4Si coating. • The NiTi-4Si-2YF 3 coating exhibits the lowest microhardness. [ABSTRACT FROM AUTHOR]

Refractory high entropy alloy (RHEA) coatings containing W and Ta elements at the same time usually have excellent performance at high temperature, which are promising candidate materials for high temperature protective coating materials. In this work, the effects of W and Ta on the microstructure and performance evolution of TiMoCrW x Ta y RHEA coatings have been investigated. Experimentally, TiMoCrW x Ta y coatings are mainly composed of BCC phase, Laves phase and Ti-rich phase, with W and Ta atoms preferably dissolved in BCC phase. The W atoms promote the formation of dendrites and the growth of rod-like and equiaxed crystals and the Ta atoms promote the formation of cellular crystals and produce the effect of fine crystal strengthening. W and Ta atoms have significant influence on the tribological properties of TiMoCrW x Ta y coatings. The tribological properties of TiMoCrW x Ta y coatings at 800 °C are better than those at room temperature. TiMoCrW x Ta y RHEA coatings follow near-linear oxidation kinetics during the oxidation of 50 h at 800 °C.The oxidation resistance of the coatings first increases and then decreases with the increase of Ta content. Ta 2 O 5 , TiO 2 and other oxides may have a shielding effect on the oxidation of W. In particular, The W 0.3 Ta 0.5 shows the best tribological properties and oxidation resistance, and the mass gain of W 0.3 Ta 0.5 is only 13.4 mg/cm2 after the oxidation test for 50 h. It indicates that TiMoCrW x Ta y coatings can obtain good high temperature performance by optimizing the content of W and Ta in RHEA coatings. This work can provide guidance for the research and application of TiMoCrW x Ta y RHEA coatings. • The Ta atom is preferentially dissolved in the BCC phase and it significantly affects the BCC lattice. • The variable content of W and Ta elements significantly affects the crystal growth rate and precipitation sequence of phases. • The tribological properties of the coatings can be improved by controlling the content of W and Ta elements. • Appropriate addition of W and Ta elements can improve the oxidation resistance of the coatings. [ABSTRACT FROM AUTHOR]

• High quality Ni-coated graphene powders were prepared by electroless plating. • Modified graphene was preserved in laser cladded coatings. • Modified graphene was conducive to improving the wear resistance of coatings. • Modified graphene significantly improved the corrosion resistance of coatings. In recent years, graphene (Gr) has attracted much attention owing to its excellent reinforcement effects. However, the application of Gr in laser cladded coatings remains a challenge due to the agglomeration of Gr and poor wettability between Gr and the molten metals. To overcome these problems, in this study, Ni modified Gr (Ni@Gr) powders were synthesized by electroless plating method, and Ni@Gr powders reinforced Ni60 (Ni60-Ni@Gr) composite coatings were prepared on the surface of AISI 1045 steel by laser cladding technique. The microstructure, existential state of Gr nanosheets, micro-hardness, wear resistance and corrosion resistance of Ni60-Ni@Gr coatings, Ni60-Gr coatings and Ni60 coatings were studied by SEM, TEM, XRD, Raman, micro-hardness tester, wear tester and electrochemical tester. The results showed that the wettability between the metal matrix and Gr was improved after modification, which promotes the dispersion of Gr nanosheets. The average micro-hardness value of Ni60-Ni@Gr coating was 920.79 HV 0.2 , which was higher than that of Ni60-Gr coatings (843.80 HV 0.2) and Ni60 coatings (777.13 HV 0.2). Compared with Ni60-Gr coatings and Ni60 coatings, the Ni60-Ni@Gr coatings have the lowest friction coefficient and weight loss, indicating the best wear resistance of Ni60-Ni@Gr coatings. The potentiodynamic polarization test and EIS test indicated that the corrosion resistance of Ni60 coatings was significantly improved after adding Gr. More notably, compared with the Gr without modification, the addition of modified Gr contributes to the further improvement of the corrosion resistance of Ni60 coating, which was related to the excellent barrier property of uniformly dispersed Ni@Gr powders in coatings. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) as nano reinforcement has been extensively used to improve the overall performance of metal-based composite coatings. In this work, GO nanosheets with surface modification and magnetic field (MF) assisted electro-brush plating (EBP) technique were employed to construct Ni-based composite coatings with biomimetic structure to improve the corrosion resistance of coatings. The preparation, deposited behavior and some properties of coatings were investigated. The results showed that after surface modification, GO surface carried numerous Co 7 Fe 3 magnetic nanoparticles with the size of 40–50 nm. During the MF assisted EBP process, the co-deposition of CoFe@GO magnetic powders with the reduced Ni atoms contributed to the formation of Ni-CoFe@GO composite coatings with stripe-like structure that resembled the surface morphology of conch. Besides, induced by the synergistic action of MF and electric field, most magnetic powders were distributed regularly in the stripe-like areas. After two weeks exposure to air, Ni-CoFe@GO composite coatings changed spontaneously from hydrophilic for fresh coatings to hydrophobic. This transformation was mainly attributed to the high surface roughness and the adsorption of a lot of hydrocarbons on the stripe-like surface. Moreover, air pockets that resulted from these hydrocarbons formed on the coating surface impeded the diffusion of corrosive media into coatings. Consequently, Ni-CoFe@GO composite coatings exhibited good corrosion resistance. Therefore, the preparation proposed in this work is desirable and has a prospect in further improving the corrosion resistance of GO reinforced Ni-based composite coatings. • A composite method was employed to prepare a new GO-reinforced Ni-based coating. • This coating presented the stripe-like structure similar to conch surface. • GO changed from non-magnetic to magnetic via surface modification. • Ni-CoFe@GO coatings exhibited hydrophobicity and good corrosion resistance. [ABSTRACT FROM AUTHOR]

As reinforcements, carbonaceous nanomaterials (CNMs) especially multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO), have attracted increasing attention in the application of electrodeposition. In this work, Ni-based nanocomposite coatings with MWCNTs and GO were prepared by electro-brush plating technique (EBP). The results showed that adding MWCNTs and adding GO both significantly improved the compactness of Ni coatings, however, the latter contributed more uniform microstructure and morphology of nanocomposite coatings owing to the excellent dispersion of GO. In addition, MWCNTs and GO could not only provide numerous nucleation sites for Ni primary crystals contributing the grain refinement, but also co-deposited with Ni atoms to form a strong interfacial bonding with Ni matrix. The addition of MWCNTs and GO can significantly reduce the worn volume of coatings from 7.52 × 107 μm3 to 3.49 × 107 μm3 and 2.82 × 107 μm3, respectively. Moreover, Ni nanocomposite coatings adding GO exhibited better wear resistance and friction stability than that of adding MWCNTs. Microstructural characterizations revealed that during wear testing, the agglomerated MWCNTs in nanocomposite coatings were destroyed severely and transformed into the shorten MWCNTs or the unfolded sidewalls, thereby leading to the instability of the wear process. In contrast, the damage degree of rGO was relatively slight. The nanosheets of rGO uniformly distributed in nanocomposite coatings became smaller and some of them were stacked between each other, which promoted the stability of friction process. Image 1 • Comparison study of MWCNTs and GO reinforced Ni composite coatings was conducted. • Both MWCNTs and GO significantly improved the compactness of pure Ni coatings. • HRTEM characterization provided evidences for grain refinement of MWCNTs and GO. • Adding GO promoted the stability of friction process compared with MWCNTs. • Structural variations of MWCNTs and GO after wear testing were investigated. [ABSTRACT FROM AUTHOR]

Graphene (Gr) has been regarded as the promising reinforcement for metal matrix composite coatings. However, it is hard to mix nano-scale Gr with micron-scale metal powders effectively at present, restricting the extensive application of Gr in engineering field. Therefore, this work proposed a new two-step method to in-situ synthesize multilayer Gr on the surface of Ni60 powders by combining ultrasonic and wet milling. Under protective atmosphere, Ni60 + Gr coatings were fabricated using laser cladding technique. In-situ synthesized multilayer Gr were successfully incorporated into Ni60 coatings, but part of them were transformed into the fullerene-like structures. In addition, a new matrix phase of Ni-Cr-Fe with bcc structure was generated in Ni60 + Gr coatings owing to the super adsorption effect of Gr on Ni, Cr and Fe atoms. The second phases such as chromium carbides in Ni60 + Gr coatings were refined and distributed more uniformly compared with that of Ni60 coatings. Furthermore, Ni60 + Gr coatings showed excellent tribological performance than that of Ni60 coatings, which was attributed to the synergistic effect between the lubrication of Gr or fullerene-like structures and the superior dispersion strengthening of the second phases. • Multilayer Gr on the surface of Ni60 powders by combing ultrasonic and wet milling was in-situ synthesized. • Multilayer Gr were incorporated into Ni60 coatings, but part of them were transformed into the fullerene-like structures. • Ni-Cr-Fe with bcc structure was generated in Ni60+Gr coatings. • The second phases in Ni60+Gr coatings were refined and distributed more uniformly compared with that of Ni60 coatings. [ABSTRACT FROM AUTHOR]

The friction and wear of bearing cages, sealing rings and other transmission components working in harsh environments such as high vacuum and heavy load directly affect the operational stability and safety reliability of the equipment. Therefore, it is vitally important to improve the tribological properties of machine components. In this paper, NiCrBSi alloy coating, NiCrBSi-30 wt% WS 2 coating and double-layer NiCrBSi-30 wt% WS 2 coating were prepared on 38CrMoAl steel by laser cladding. The results show that a metal sulfide layer is formed on the double-layer NiCrBSi-30 wt% WS 2 coating compared to NiCrBSi-30 wt% WS 2 coating. The NiCrBSi-30 wt% WS 2 coating consists of γ-(Ni,Fe) solid solution, (Fe,Ni) 9 S 8 , Cr 7 S 8 and M 7 C 3 phases. The metal sulfide layer consists of γ-(Ni, Fe) solid solutions, Fe 3 S 4 , Cr x S y and M 7 C 3 phases. The double-layer NiCrBSi-30 wt% WS 2 coating is 4 mm thicker than the NiCrBSi-30 wt% WS 2 coating. The average microhardness values of NiCrBSi coating, NiCrBSi-WS 2 coating and double-layer NiCrBSi-WS 2 coating are 412.6 ± 15.2HV 0.3 , 383.9 ± 14.5HV 0.3 , and 368.6 ± 13.3HV 0.3 , respectively. The average coefficient of friction of the double-layer NiCrBSi-30 wt% WS 2 coating is 0.29, which is 37 % and 14.7 % lower than that of the NiCrBSi coating (0.46) and the NiCrBSi-30 wt% WS 2 coating (0.34), respectively. The wear rate of the double-layer NiCrBSi-30 wt% WS 2 coating is 1.51 × 10−5 mm3/(N·m), which is 47.6 % and 34.9 % lower than that of NiCrBSi coating (2.88 × 10−5 mm3/(N·m)) and NiCrBSi-30 wt% WS 2 coating (2.32 × 10−5 mm3/(N·m)), respectively. Therefore, double-layer NiCrBSi-30 wt% WS 2 coating has the best wear resistance and friction reduction performance at room temperature. A more continuous lubricating film was formed on the surface of the double-layer NiCrBSi-30 wt% WS 2 coating, which explains its lowest coefficient of friction and wear rate. • A metal sulfide layer was formed on top of double-layer NiCrBSi-30 wt.% WS 2 coating. • Formation mechanism and tribological behavior of metal sulfide layer were studied. • A more continuous lubricating film is formed on the metal sulfide layer, resulting in the lowest coefficient of friction(0.29) and wear rate(1.51×10-5 mm3/(N·m)). [ABSTRACT FROM AUTHOR]

Based on the influence of Mo and Nb content on the eutectic degree of FeCoCrNi high-entropy alloy (HEA), this study prepared in-situ HEA composite coatings with a gradient eutectic degree using the principle of element diffusion in the molten pool under a laser beam, namely Mo-CC and Nb-CC. Both of the two coatings were composed of the face-centered cubic (FCC) phase and Laves phase. Within the coating, there was a gradual decrease in the Laves phase and an increase in the FCC phase from top to bottom. The Laves phase in Mo-CC was rich in Mo (21.36 at.%) element and exhibited an orientation relationship with the FCC phase of [ 0 1 ¯ 1 ] Laves //[ 0 1 ¯ 1 ] FCC. The phase interface was a non-coherent crystal plane. The Laves phase in Nb-CC is enriched with Nb (36.15 at.%) element and demonstrated an orientation relationship with the FCC phase of [ 1 ¯ 2 ¯ 1 ] Laves //[ 0 0 1 ] FCC. The phase interface was a semi-coherent crystal plane. Furthermore, the process and mechanism of FCC phase transformation into FCC + Laves phase were elucidated by examining the mixing enthalpy, lattice distortion, and atomic radius difference. In terms of properties, the hardness of Mo-CC and Nb-CC from the top to the bottom section gradually decreased from the outer to inner section. Nb-CC possessed a higher surface average hardness (773.66 HV 0.3) and superior tribological properties compared to Mo-CC. The gradient control method for HEA and the phase structure formation mechanism presented in this study provided valuable insights for the research and development of new HEA coatings. [Display omitted] • Mo-CC and Nb-CC with eutectic gradient were prepared in situ, which were composed of FCC phase and Laves phase. • The difference between Δ H AB mix and δ lead to a transition from the FCC phase to the FCC + Laves phase. • The Laves phase was enriched in Mo or Nb elements, and the strain was concentrated in the Laves phase. • The Laves phase and the hardness gradually decreased from the top to the bottom of the coating. • Compared with Mo-CC, Nb-CC exhibited better tribological properties. [ABSTRACT FROM AUTHOR]

The embrittlement of thermal barrier coatings (TBCs) in a high-temperature service environment inhibits the ability of the top-coat to resist crack initiation and propagation, in which the cracks are generated by erosion or wear of particles, limiting the service durability of TBCs. This study was based on the preparation of SiC whiskers (SiC w) / Y 2 O 3 partially stabilized ZrO 2 (YSZ) integrated composite powder, and the SiC w /YSZ composite TBCs was prepared through the atmospheric plasma spraying (APS) to improve the toughness of the top-coat. The effects of SiC w on the fracture toughness, tribological properties, erosion resistance and bending strength of the coatings were studied. The results showed that the fracture toughness of the composite coating with a SiC w length-to-diameter ratio (L/D ratio) of 250 was 24.6 % higher than the YSZ coating. Moreover, the composite coating presented excellent performance in wear, erosion, and resistance to crack propagation and spallation. The low amplitude of the Weibull modulus m of hardness distribution of the doped coating proved the stability effect of SiC w on the reinforcement and toughening of the coating. • A SiC whiskers/Y 2 O 3 partially stabilized ZrO 2 (YSZ) composite coating was successfully deposited. • The toughening mechanism of SiC whiskers in thermal barrier coatings (TBCs) was revealed. • SiC whiskers can significantly improve the wear resistance and bending strength of TBCs. • Promote the application process of SiC whiskers toughened TBCs under extreme service environments. [ABSTRACT FROM AUTHOR]

The improvement of wear resistance has a profound effect on the far-ranging application of aluminum alloy. In this study, the Al–Cu-based in-situ reinforced composite coating was successfully manufactured on the AlSi10Mg substrate by laser cladding. The microstructure, microhardness and wear resistance under gradient loading (3 N, 6 N, 9 N, 12 N and 15 N) and thermal conditions (200 °C, 300 °C and 400 °C) of the composite coating were studied. The research results showed that the composite coating exhibited a gradient distributed microstructure due to the different diffusion degrees of Cu and Al atoms. The composite coating was mainly composed of Al 4 Cu 9 , Al 7 Cu 4 Ni and α-Al in the bottom, center and top area, respectively, and Al 2 Cu evenly distributed in each area. The microhardness showed gradient distribution owing to the gradient microstructure. Compared with the AlSi10Mg substrate, the composite coating possessed higher microhardness and better wear resistance contributed by the gradient Al–Cu intermetallic compounds. At room temperature, the main wear mechanisms of the composite coating changed from abrasive wear to adhesive wear with the increase of loading condition. At high temperatures, the main wear mechanisms of the composite coating were adhesive wear and plastic flow. During the wear process, Al–Cu intermetallic compound was the key to improving the wear resistance and stabilizing the friction coefficient. • The Al–Cu-based composite coating with gradient distribution on Al alloy was prepared. • The diffusion properties of Al and Cu elements were briefly analyzed. • The friction property of the coating is improved than the substrate at room and high temperatures. • The increase of Al–Cu intermetallic and the transformation of microstructure make the coating have better properties. [ABSTRACT FROM AUTHOR]

FeCoCrNiCu is a face-centered cubic (FCC) high entropy alloy (HEA) with good dislocation storage capacity, ductility, and toughness. FeCoCrNiAl is a body-centered cubic (BCC) HEA whose phase is hard and brittle with high strength and low toughness. In this study, a FeCoCrNiCu/FeCoCrNiAl composite HEA coating was prepared by laser cladding technology. After preparation, the microstructure and mechanical properties of the composite HEA were evaluated. A new two-phase (FCC + BCC) HEA was generated in situ between FCC and BCC HEA, achieving a good transition from hard to soft. The composite coating has the best wear resistance, the friction coefficient is about 0.3, the wear rate is 4.2 × 10−5 mm3/ N·m, and the wear mechanism is abrasive wear. While maintaining high hardness and good wear resistance, the composite coating has good compression properties. The FeCoCrNiCu cladding layer reduced the energy of the FeCoCrNiAl cladding layer by storing dislocations, which reduced its tendency to crack during compression, thus extending the service life of the coating surface. • FeCoCrNiCu/FeCoCrNiAlCu/FeCoCrNiAl composite high entropy alloy coating was successfully prepared by laser cladding. • In-situ generation of FeCoCrNiAlCu dual-phase high-entropy alloy. • Gradient distribution of coating hardness. • The composite HEA coating achieved an effective strength-toughness balance. [ABSTRACT FROM AUTHOR]