Application of Plasma Cladding Ni60A+35wc (4)

       When the coating is preset by plasma,
The coating absorbs heat and melts and transfers a part of the heat to the substrate. This part of the heat can heat the substrate to a certain temperature, but it is not enough to melt the substrate.
When the arc leaves the molten pool, the molten pool begins to solidify.
Since the liquid metal in the molten pool is still at a very high temperature at this time, the matrix itself has good thermal conductivity. In this way, when the molten pool metal is condensed, it is beneficial to start to grow dendrites at the liquid-solid interface, and primary dendrites
The crystal is also relatively coarse.
As the solidification progresses, the temperature gradient becomes smaller and smaller, but the direction of heat conduction is still dominated by the matrix.
Although dendrites in the direction of heat flow are still formed at this time, due to the presence of a large amount of carbides, these carbides also refine the coarse dendrites during the solidification process.
The liquid metal in the molten pool solidifies to the outermost layer. At this time, through the air convection heat dissipation and the cooling effect of argon, some parts of the surface layer begin to nucleate. At this time, a layer of disordered fine dendrites is observed on the metallographic photo.
And equiaxed crystal.