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Fe-based coatings were fabricated on GCr15 bearing steel by laser cladding assisted by ultrasonic vibration. Microstructural evolution and wear resistance of the cladding layers were investigated s...

Graphene reinforced titanium (Ti-Gr) nanocomposite was prepared by laser sintering of the mixture of PVA bonding graphene sheets and titanium powders. During laser sintering process, the survival and uniform dispersion of graphene have been demonstrated, which embedded in Ti matrix, and formed Ti-Gr nanocomposites. Microstructures and components of the nanocomposites were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. The survival of graphene sheets in nanocomposite is due to rapid heating/cooling in laser sintering process. Hardness measurements showed that the laser sintered Ti-Gr nanocomposites achieved more than 2-fold Vickers Hardness value of barely sintered Ti.

The laser surface melted layers were fabricated on AZ31B magnesium alloy by ultrasonic vibration-assisted using with different vibration amplitude. Microstructural evolution and corrosion resistance were studied systematically. The uniformity and compactness of the microstructure can be get further improved with the increase of vibration amplitude, while the coarse microstructure is observed at an even higher vibration amplitude. The melted layer with a reasonable vibration amplitude at the maximum outputs of 80% possess the highest microhardness, and the lowest corrosion current density as well as the minimal corrosion rate than the substrate. The results of electrochemical impedance spectra (EIS) and corrosion morphology are in agreement with potentiodynamic polarisation measurements, the charge transfer resistance (Rct) and corrosion area of the sample at 80% vibration amplitude are highest and smallest, respectively. Experimental results revealed that the melted layer fabricated at 80% of the ...

Laser surface melting (LSM) with alternating magnetic field was applied to the AZ91D magnesium alloy using a 2 kW fiber laser. The microstructure and phase composition of melted layer with and without alternating magnetic field were studied by optical microscopy (OM) and X-ray diffraction (XRD) measurement. The micro-and nano-hardness, wear and corrosion resistance of the modified layers and as-received magnesium alloy were measured by microhardness tester, nanoindenter, pin-on-disc wear tester and electrochemical workstation, respectively. Results showed that the LSM treatment resulted in a highly homogeneous modified layer with refined grains. Compared to the melted layer without electromagnetic stirring (EMS), the microstructure of melted layer became finer and more uniform, the dendritic crystal was changed to an approximately equiaxial crystal under the action of EMS application treatment. The microhardness of the melted layer with and without EMS (70.8Hv0.1 and 62.9Hv0.1) is higher than the as-received magnesium (55.53Hv0.1) microhardness, regarding especially the melted layer with EMS.·The friction coefficient and wear mass loss of the melted layer with EMS were 0.2175 and 0.1616 g accordingly, subsequently having decreased by 14.8% and 6.1% compared to the melted layer without EMS. From the worn-out appearance of the melted layer without and with EMS, the wear mechanism turning from a slight abrasive wear into a slight plastic deformation during EMS-assisted. The corrosion potential and corrosion current density of the melted layer with EMS were increased by 18.7% and decreased by 4% compared to the corresponding effects without the EMS-assisted, respectively. Experimental results showed that the melted layer assisted by EMS displayed the best wear and corrosion resistance properties.

Transient temperature field distribution is important for quality control of laser sintering graphene (Gr) reinforced nickel matrix (Ni-Gr) nanocomposites and the optimization of sintering parameters. To date, it is difficult to measure the temperature field directly. Thus, numerical simulation was utilized to study the distribution and evolution of temperature field. Finite element models were employed to simulate the sintering process of Ni-Gr coatings on AISI 4140 steel. The temperature distribution, the depth of the melting pool, the width of metallurgical bonding and the parameter optimizing method for laser sintering were investigated. In order to verify simulation results, single-track experiments were performed with the same laser sintering parameters as simulation. Simulated results reveal that convection and radiation heat transfer, and the latent heat of phase transition play a major role in the sintering process. Simulation output is consistent with experiments under the same processing parameters. Based on simulation results, substrate melting depth, metallurgical bonding width and thermal accumulation effects can be predicted. Thus, according to these guidelines, the optimal laser sintering parameters can be decided.

Single layer graphene oxide (SLGO) reinforced titanium (SLGO-Ti) nanocomposites have been achieved by laser sintering. This study focuses on the graphene oxide dispersion and survival in titanium matrix during laser sintering process. Through laser sintering, graphene oxides were dispersed uniformly into titanium matrix to fabricate SLGO-Ti nanocomposites. Microstructures and components of the nanocomposites were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy-dispersive X-Ray spectroscopy (EDS) and Raman spectroscopy. It was confirmed by XRD patterns, EDS maps and Raman spectrum that graphene oxide survived in SLGO-Ti nanocomposites after laser sintering. Nanoindentation measurements showed the laser sintered SLGO-Ti nanocomposites hardness was improved by more than 3-folds than that of pure titanium counterpart.

Thick Fe901 coatings were prepared on Cr12MoV substrates using electromagnetic field (EMF)-assisted multi-layer laser cladding. The effect of the EMF on surface topography, microstructure, multi-layer strategy, phase composition, and wear resistance in the multi-layer laser cladding Fe901 coatings were investigated. The results indicate that the application of EMF decreased the number of defects in coatings produced with laser cladding. Dendrites or cellular crystals oriented perpendicular to the interface were observed in the coatings with and without EMF-assisted growth. The microstructure of the coating formed with the applied EMF gradually transitioned from columnar dendrites to fine dendrites and equiaxed dendrites as the number of cladding layers increased. The coatings with and without an applied EMF primarily contained α-(Fe), α-(Fe,Cr), (Cr,Fe)7C3, CrFeB and FeCrMo phases. The EMF did not affect the phase composition of the coatings, although the intensity of X-ray diffraction peaks from the coating produced in an EMF were changed from those in the coating produced without the field. In addition, the coating produced in the EMF exhibited higher fatigue and abrasion resistance. The coatings prepared in an EMF also displayed narrower, shallower wear tracks, with 78.2% lower mass loss than the conventional coating.

Graphene reinforced titanium (Ti-Gr) nanocomposites have been prepared on AISI 4140 base plate by laser sintering process. The dispersion and survival of graphene in the Ti matrix after laser treatment were discussed. Through laser sintering, graphene sheets were dispersed uniformly into Ti matrix to form Ti-Gr nanocomposites. Microstructures and components of the nanocomposites were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. It was proved by SEM images, XRD patterns and Raman spectrum that graphene survived in Ti-Gr nanocomposites after laser sintering. Hardness measurements showed the laser sintered Ti-Gr nanocomposites got more than 2-fold higher in Vickers Hardness value than that of laser sintered Ti.