Design and characterization of a novel Cu_(2.3)Al_(1.3)Ni_(1.7)SnCr_(0.3) multi-principal element alloy coating on magnesium alloy by laser cladding

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 mag-nesium 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.

Influence of La2O3 addition on nano indentation hardness and residual stress of Stellite 6 coating prepared by plasma cladding

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,La2 O3 was 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 La2 O3 leads 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 La2 O3. With the addition of La2 O3, the residual stress in coatings is decreased significantly. Especially, when the content of La2 O3 is 0.8 wt%, the nano indentation hardness increases by 1.31 times and residual stress decreases to 20 percent, compared with coating without La2 O3.

Vacuum carburization of 12Cr2Ni4A low carbon alloy steel with lanthanum and cerium ion implantation

As bearing parts, 12 Cr2 Ni4 A is expected to have high hardness and excellent fatigue strength, so carburizing is employed to improve the inherit properties of 12 Cr2 Ni4 A. 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 12 Cr2 Ni4 A 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%.

Hydrodynamic performance and structural response characteristics of the double-slotted vertical cambered V-Type otter board

Vertical cambered V-type otter boards are widely used in large and medium-sized trawlers for their good stability and adaptability to various water layers.However,limited numerical studies on the hydrodynamic performance and structural strength of this type of otter board have been published.In this study,we established the three-dimensional numerical model of the double-slotted vertical cambered V-type otter board according to its special structure and stress feature.We compare the hydrodynamic performance results of our model with those of previous experiments.Using this model,we analyzed the influence of parameters such as attack angle,aspect ratio,dihedral,and deflector angles on its hydrodynamic performance.Moreover,the structural response characteristics of the otter board under typical working conditions were studied.We believe our results will provide theoretical reference for the structural design and optimization of the vertical cambered V-type otter board.