Study On Preparing Sub-micron Grain Coating Using Electrothermal Explosion Spraying Method

Electrothermal explosion directional spraying[EEDS] is a new thermal spray technology, which can prepare the sub-micron grain coating.The properties of the coatings with sub-micron grain sprayed by EEDS and electric characteristics are studied in detail in this thesis. And the temperature fields of coatings are simulated with numerical calculation.Results show that no laminar structure occurs in all coatings. The grain of coating is refined and is in the range between a few tens nm and 500nm.The coating is dense and the porosity is little. The distinct diffusion occurs in the interface between coating and substrate. The mechanism of coating-substrate is metallurgy bond. Hardness of coating is increased greatly, about 1.3-4.0 times of the sprayed materials. There is a tendency of gradual descent for hardness, modulus and elastic recovery parameter. XRD shows that no new phase occurs in Mo coating, but decarburisation occurs in WC-Co coating during spraying. There are no cracks in the composite coatings except the NiCr/WC-Co coating.Vickers indentation tests have been used to analyse the cross section fracture behavior of various coatings deposited by EEDS process. It is found that the fracture toughness of the coating is anisotropic, which means crack propagating is much easier transverse to the coating/substrate interface than parallel to it. The fracture toughness of coatings is ranked as follows: Mo/WC-Co