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• A novel Cu 2.3 Al 1.3 Ni 1.7 SnCr 0.3 multi-principal element alloy (MPEA) and a multi-step ultrasonic assisted (UA) laser remelting technology were proposed. • An unusual ultrafine lamellar eutectic structure exists in Cu 2.3 Al 1.3 Ni 1.7 SnCr 0.3 UA-MPEA coating. • The effect of the FCC and eutectic phases on the corrosion behavior of the Cu 2.3 Al 1.3 Ni 1.7 SnCr 0.3 MPEA coatings was studied. • The passive films formed on the Cu 2.3 Al 1.3 Ni 1.7 SnCr 0.3 MPEA coatings exhibits duplex semiconductor behavior in NaCl solution. The evaporation and dilution of substrate seriously limit the performance of laser cladding coatings on magnesium alloys. In order to overcome the above shortcomings, a multi-step ultrasonic assisted laser remelting technology was proposed to improve the performance of the coating. In this work, a novel Cu 2.3 Al 1.3 Ni 1.7 SnCr 0.3 multi-principal element alloy coating (MPEAC) was prepared on the surface of magnesium alloy. Characterization techniques such as transmission electron microscopy (TEM), electron back scatter diffraction (EBSD) and scanning electron microscopy (SEM) were employed to characterize the microstructure and phase composition of the coatings. And the phase structure and morphology at the interface between the coating and the substrate were also studied via focus ion beam (FIB) and TEM method. In addition, the corrosion and wear resistance ability of the coatings were monitored by potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS), hardness and friction tests. The results show that Cu 2.3 Al 1.3 Ni 1.7 SnCr 0.3 MPEAC with ultrasonic assisted is composed of FCC phase and eutectic phases (Cu 10 Sn 3 and Cu 2 Ni 3 Sn 3). Due to the forced convection generated by ultrasonic waves, some Cu and Ni phases are precipitated around Cu 2 Ni 3 Sn 3 phases, which is beneficial to enhance the corrosion resistance. Because of the grain refinement effect caused by ultrasonic, the wear resistance of the coating is also improved. Furthermore, ultrasonic vibration can effectively weaken and eliminate the texture density of the Cu 2.3 Al 1.3 Ni 1.7 SnCr 0.3 MPEAC fabricated by laser cladding. [ABSTRACT FROM AUTHOR]

The (La0.5Eu0.25Y0.25)2Zr2O7(LEYZ) ceramic powder for spraying was prepared and synthesised by combining spray granulation and solid phase reaction phase, and a double ceramic layer structure with (La0.5Eu0.25Y0.25)2Zr2O7ceramic surface coating and YSZ intermediate coating was prepared by atmospheric plasma spraying. Experimental characterisation revealed that the moulding state of spray granulated powders was significantly influenced by the solid content. When the solid content is small, the viscosity of the slurry is insufficient, and the prepared powder has poor formability and small overall particle size. When the solid content is large, the slurry is too viscous, which easily leads to unfavourable conditions such as sticky walls. The best formability of the pelletised powder was obtained with a solid content of 55 wt-% and a binder content of 2.0 wt-%. Compared with La2Zr2O7(LZ) ceramics, the fracture toughness of the rare-earth co-doped modified LEYZ ceramic coating was increased by 8.4% and the bond strength was increased by 49.9%, showing good toughness and crack resistance. Moreover, LEYZ coating has significantly better resistance to solid phase particle erosion than LZ coating, with 46.3% and 45.4% reduction in erosion rate at 45° and 90°, respectively.

Cobalt-based coatings were fabricated on FV520B substrate by plasma cladding technology. Evolution of performance and microstructure of cobalt-based coating and interface under thermomechanical coupling action was studied. Results elucidated that the nano-hardness of the compressed material changes obviously, but the interface structure can maintain good hardness stability. Wear resistance of coatings subjected to high-temperature compression is significantly enhanced, and the higher compression temperature further increases the wear resistance of the coating. Torsion and deformation of microstructure occur with the increasing of deformation amount. Obvious plastic deformation occurs at the interface. The original dendrite morphology in the coating completely disappeared with the increase of temperature and deformation amount, and there is a series of microstructure changes contribute to the improvement of performance.

ABSTRACTCobalt-based coatings were fabricated on FV520B substrate by plasma cladding technology. Evolution of performance and microstructure of cobalt-based coating and interface under thermomechanical coupling action was studied. Results elucidated that the nano-hardness of the compressed material changes obviously, but the interface structure can maintain good hardness stability. Wear resistance of coatings subjected to high-temperature compression is significantly enhanced, and the higher compression temperature further increases the wear resistance of the coating. Torsion and deformation of microstructure occur with the increasing of deformation amount. Obvious plastic deformation occurs at the interface. The original dendrite morphology in the coating completely disappeared with the increase of temperature and deformation amount, and there is a series of microstructure changes contribute to the improvement of performance.

Magnesium, as a biodegradable metal, is a promising candidate for biomedical applications. To modify the degradation behavior of magnesium and improve its osteocompatibility, chemical conversion and spin coating methods were combined to develop a diammonium hydrogen phosphate-pretreated/poly(ether imide) (DAHP/PEI) co-coating system. The diammonium hydrogen phosphate pretreatment was employed to enhance the attachment between PEI coatings and the magnesium substrate; meanwhile, it could serve as another bioactive and anticorrosion layer when PEI coatings break down. Surface characterization, electrochemical tests, and short-term immersion tests in DMEM were performed to evaluate DAHP/PEI coatings. Electrochemical measurements showed that DAHP/PEI coatings significantly improved the corrosion resistance of pure magnesium. No obvious changes of the chemical compositions of DAHP/PEI coatings occurred after 72 h of immersion in DMEM. An in vitro cytocompatibility study confirmed that viability and LDH activity of human osteoblast-like cells on DAHP/PEI coatings showed higher values than those on the DAHP-pretreated layer and pure magnesium. The DAHP-pretreated layer could still enhance the ALP activity of MG-63 cells after the degradation of PEI in DAHP/PEI coatings. Besides that, the in vitro cellular response to the treated magnesium was investigated to gain knowledge on the differentiation and proliferation of human adipose-derived stem cells (hADSCs). Cell distribution and morphology were observed by fluorescence and SEM images, which demonstrated that DAHP/PEI coatings facilitated cell differentiation and proliferation. The high level of C-terminals of collagen type I production of hADSCs on DAHP/PEI coatings indicated the potential of the coating for promoting osteogenic differentiation. Positive results from long-term cytocompatibility and proliferation tests indicate that DAHP/PEI coatings can offer an excellent surface for hADSCs.

One of the problems limiting the application of Stellite 6 coating is the residual stress resulting in cracks in the coating easily. In order to reduce the residual stress and increase the nano-indentation hardness, La2O3was added to Stellite 6 coating in this study, and the influence on the microstructure, nano indentation hardness and residual stress of the coatings were investigated by scanning electron microscopy (SEM) with energy dispersive spectrum (EDS), X-ray diffraction (XRD) and nano-indentation tester. Results indicate that the addition of La2O3leads to the phenomenon that the dendrite is partly transformed into the equiaxed grain, which results in the grain refinement. The nano-indentation hardness of coatings is improved, which is attributed to the fine-grain strengthening and dispersion strengthening effect of La2O3. With the addition of La2O3, the residual stress in coatings is decreased significantly. Especially, when the content of La2O3is 0.8 wt%, the nano indentation hardness increases by 1.31 times and residual stress decreases to 20 percent, compared with coating without La2O3.

ABSTRACTIn this work, a nanocrystallisation surface layer with an average grain size of 29 nm was fabricated on the 12Cr2Ni4A steel by the supersonic fine particles bombarding (SFPB). The vacuum carburising process was carried out on the original and the SFPB pre-treatment samples. X-ray diffraction, scanning electron microscopy and hardness tester were employed to study the phase constituents, grain size, hardness and residual stress of the two carburised samples. Experimental results showed that compared to the coarse-grain carburised layer (without SFPB), the carburised layer with SFPB pre-treatment has smaller martensite and carbide, and its thickness, hardness, compressive residual stress and wear resistance have been significantly improved. The dominant wear mechanisms of the two carburised samples were both abrasive wear and fatigue wear.

The microstructure of cerium-based conversion coatings with and without microcapsules containing Ce(NO3)3or La(NO3)3on magnesium alloys were investigated and the corrosion resistance was evaluated as well. The gelatin–chitosan microcapsules were prepared by complex coacervation. Microcapsules can effectively avoid the traditional porous state, namely, by releasing active and repairing material immediately after changes in coating integrity. Microcapsules distribute in the tiny cracks of coating deposited on magnesium alloys. The electron probe micro-analyser results characterise the element distribution of coating. The potentiodynamic polarisation curve and impedance spectra show that the conversion coating with microcapsules can enhance the corrosion resistance of magnesium alloys. The microcapsules containing La(NO3)3show a better corrosion resistance so as to promote a self-healing performance.

In this work, a nanocrystallisation surface layer with an average grain size of 29?nm was fabricated on the 12Cr2Ni4A steel by the supersonic fine particles bombarding (SFPB). The vacuum carburising process was carried out on the original and the SFPB pre-treatment samples. X-ray diffraction, scanning electron microscopy and hardness tester were employed to study the phase constituents, grain size, hardness and residual stress of the two carburised samples. Experimental results showed that compared to the coarse-grain carburised layer (without SFPB), the carburised layer with SFPB pre-treatment has smaller martensite and carbide, and its thickness, hardness, compressive residual stress and wear resistance have been significantly improved. The dominant wear mechanisms of the two carburised samples were both abrasive wear and fatigue wear.

ABSTRACTThe microstructure of cerium-based conversion coatings with and without microcapsules containing Ce(NO3)3or La(NO3)3on magnesium alloys were investigated and the corrosion resistance was evaluated as well. The gelatin–chitosan microcapsules were prepared by complex coacervation. Microcapsules can effectively avoid the traditional porous state, namely, by releasing active and repairing material immediately after changes in coating integrity. Microcapsules distribute in the tiny cracks of coating deposited on magnesium alloys. The electron probe micro-analyser results characterise the element distribution of coating. The potentiodynamic polarisation curve and impedance spectra show that the conversion coating with microcapsules can enhance the corrosion resistance of magnesium alloys. The microcapsules containing La(NO3)3show a better corrosion resistance so as to promote a self-healing performance.

As bearing parts, 12Cr2Ni4A is expected to have high hardness and excellent fatigue strength, so carburizing is employed to improve the inherit properties of 12Cr2Ni4A. However, the traditional carburizing is limited by poor microstructure distribution and low rate of carburizing. The rare earth ion implantation is known to help improving the properties of tribology, corrosion resistance and oxidation resistance of metal. In this article, the RE implantation is employed to assist the carburizing. Lanthanum and cerium ion implantations are initially used to assist 12Cr2Ni4A low pressure vacuum carburization. The microstructure, content of retained austenite, hardness, thickness of layer and carbon diffusion were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Rockwell/Vickers hardness tester, respectively. It was shown that lanthanum and cerium implantations can improve structure of the vacuum carburizing layer, and enhance the uniformity of carbon element distribution on the carburized surface. Meanwhile the RE implantation plays a positive role in promoting the surface hardness and carburized rate. The lanthanum element has more significant effect on surface hardness and content of retained austenite than cerium element. The surface hardness of lanthanum element implanted layer was 62.9 HRC with 9.6% content of retained austenite, while the carburizing rate of cerium implanted layer increased by 12.4%.

The effect of rare earths (La, Ce and Pr) addition on residual stress in iron coatings prepared by brush plating was investigated. The results showed that the addition of rare earth transformed the residual stress in the coating from tensile to compressive. To relieve the residual stress, on the one hand, RE elements segregated at the grain boundaries which restricted the coalescence of the grains and provided more capability of grain deformation. On the other hand, RE elements could purify detrimental element and absorb hydrogen atoms in the coating. Among the three rare earths, elements lanthanum showed the most significant effect on surface morphology and residual stress.

The service condition determines the Rolling Contact Fatigue(RCF) failure mechanism and lifetime under ascertain material structure integrity parameter of thermal spray coating. The available literature on the RCF testing of thermal spray coatings under various condition services is considerable; it is generally difficult to synthesize all of the result to obtain a comprehensive understanding of the parameters which has a great effect on a thermal spray coating’s resistance of RCF. The effects of service conditions(lubrication states, contact stresses, revolve speed, and slip ratio) on the changing of thermal spray coatings’ contact fatigue lifetime is introduced systematically. The effects of different service condition on RCF failure mechanism of thermal spray coating from the change of material structure integrity are also summarized. Moreover, In order to enhance the RCF performance, the parameter optimal design formula of service condition and material structure integrity is proposed based on the effect of service condition on thermal spray coatings’ contact fatigue lifetime and RCF failure mechanism. The shortage of available literature and the forecast focus in future researches are discussed based on available research. The explicit result of RCF lifetime law and parameter optimal design formula in term of lubrication states, contact stresses, revolve speed, and slip ratio, is significant to improve the RCF performance on the engineering application.

Grain morphology control is a challenging issue for additive manufactured NiTi alloy, which directly affects the functional properties. In this work, La2O3addition was applied to control microstructure and improve functional properties of directed energy deposited (DED) NiTi alloy. The results showed that the DEDed NiTi alloy mainly consisted of NiTi (B2) columnar grains and some coarse NiTi2phases within and at the boundaries of NiTi grains. The addition of La2O3led to the promotion of columnar-to-equiaxed transition and grain refinement of NiTi (B2) phase. La2O3and LaNi secondary phases can be found in the DEDed NiTi alloy with La2O3addition. The La2O3precipitate could act as the effective heterogeneous nucleation site and the NiTi2or LaNi precipitates could pin the grain boundaries contributing to the grain refinement and the formation of equiaxed grains of NiTi(B2) phase. The introduction of La2O3could also refine the phase size and adjust morphology of NiTi2phase, which was attributed to the increase of nucleation sites and more dispersed L(Ti-rich).The temperatures and latent heat of phase transformation evidently increase with La2O3addition due to the decrease in the Ni content and La dissolved into NiTi(B2) phase. Improved superelasticity property was achieved after La2O3addition owing to the promotion of grain order and yield strength of NiTi(B2) phase and the reduction of resistance from NiTi2phase for the interface movement.