| Deposit formation dynamics and microstructure development during thermal spray is based on spreading and solidification of individual droplet. The many individual molten droplets impacting on the substrate flatten to form"splats"which pile one-on-top-of-other creating the deposit. In the reality, however, depending on the spraying condition,the droplet may have a more regular'disk'- like shape, or may be less regular, with an appearance like a'splash'. This phenomenon also has important implications on the deposit microstructure and tensile adhesion properties. Consequently, deposit micro structural integrity improves, and a number of properties are significantly enhanced with concomitant implications for coating performance.Three different substrate pre-temperatures(25℃,150℃,250℃)were applied in this study. Plasma sprayed NiAl splats on polished and blasted magnesium alloys substrates,the flattening behaviour of the spray particles and the related bonding mechanisms of coating was investigated in correlation with the substrate pre-heating temperature. The microstructures and peoperties of plasma sprayed ceramic coatings on Mg-alloy have been investigated by means of X-ray diffraction and scanning electronic mocroscope etc..The results indicate that the central solidification area of droplets is gradually enlarged with the substrate temperature's increase. NiAl-particles could well melt the substrate on the surface and deform it locally,and the dominating bonding mechanism for NiAl-coatings could be attributed to a metallurgical bonding,enhanced the adhesion of coating.And NiAl particles could well melt the substrate at the surface and deformed it locally, and form a main metallurgical bonding. The ceramic coating exhibited typical lamellae characteristic. Al2O3 ceramic coating microstructures are primarity composed of metastableγ-Al2O3 and stable phaseα-Al2O3. the microhardness of the coating between 800-1000HV0.3, and has a good property of corrosion resistances.
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