CALCULATION AND EXPERIMENTAL INVESTIGATION OF ELECTRIC FIELDS INDUCED BY ELECTRODES IN ELECTROSTATIC CHARGED POWDER SPRAYING TECHNIQUE

Electric fields induced by ring and pin electrodes in electrostatic charged powder sprayingtechnique are analysed. The fundamental formulae to deseribe these fields have been built up. Theseformulae could be used to design electrostatic charged podwer spraying system. The chargingeffectiveness of ring and pin electrode is experimentally investigated and compared each other. Theperformance of ring electrode is better than that of pin electrode.

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, Ni_3Al, Al_2O_3, and NiO. The Ni–Al phase and a small amount of Al_2O_3 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 Ni Al in addition to a small amount of Al_2O_3. The main phase of the Ni-20wt%Al coating mainly consisted of Ni solid solution, Ni Al, and Ni_3Al in addition to a small amount of Al and Al_2O_3, and Ni Al and Ni_3Al intermetallic compounds effectively further improved the final wear property of the coatings. TEM analysis indicated that fine spherical NiAl_3 precipitates and a Ni–Al–O amorphous phase formed in the matrix of the Ni solid solution in the original state.

An investigation on plasma spraying with artificial bone powder and bonding characteristics of coating

Artificial bone powder is satisfactorily deposited onto the surface of synthetic metal arthrosis(Co-Cr-Mo) with plasma spraying process. Factors influencing the quality of coating are investigated. Bond of artificial bone powder coating sprayed with different parameters is measured. and the coatings are anlyzed with metallographic examination and electron probe analysis. Experiments show that artificial bone powder coating sprayed onto synthetic metal arthrosis with satisfactory bond strength can be obtained by manipulating plasma spraying.

In-situ formation of Ni-Al intermetallics-coated graphite/Al composite in a cold-sprayed coating and its high temperature tribological behaviors

In this study, cold spraying（CS） was used to deposit a mixture of nickel-coated graphite and 40 vol.% Al powder（Ni-Gr/Al） on a steel substrate aiming to effectively preserve a certain volume fraction of graphite in the deposited Ni-Gr/Al composite coating. The microstructure of the as-sprayed coating and the effect of post-spray heat-treatment（PSHT） temperatures on the in-situ formation of Ni-Al intermetallic phases in coating were studied. The tribological behaviors of the as-sprayed coating and the PSHTed coating under 450？C were tested at 25？C, while the as-sprayed coating was tested at 450？C for comparison.As a result, the Ni-Gr particles showed a homogenous distribution in the coating. The multilayer Ni-Al intermetallics-coated graphite/Al composite coating was achieved in situ after the PSHT of 450？C, where the graphite did decompose at 550？C leaving big pores in the coating. The coefficients of friction（COF）of the CSed coating and the PSHTed coating were measured at 450？C as well as 25？C, which showed a similar tendency, much higher than that of the CSed coating tested at 25？C. The lubrication phase（graphite） improved the formation of a graphite film during sliding friction and decreased the COF, while the hard Ni-Al intermetallic phases contributed to the increase of COF.