Materials processing using an electromagnetic railgun

Intense materials heating and accelerating by an electromagnetic railgun were applied to conduct a high-velocity thermal spraying and a high-density plasma deposition.

Firstly, molten particles of tungsten and titanium were produced and sprayed in the velocity range of more than 1km/s using a conventional railgun. An unique microstructure was observed in the interface between tungsten coating and steel substrate, where various sizes of tungsten particles were embedded in W-Fe fine mixture over a thickness range of about 100µm. However, titanium coating did not show such a mixing structure, indicating that the mechanical properties of coated materials played an important roll in the material mixing. One possible mechanism of the material mixing observed in the high-velocity tungsten spraying was a jet formation of the coated material and its penetration into the substrate. Two-dimensional hydrodynamic calculation showed the penetration depth of tungsten into steel could be about 100µm when the particle particle collision velocity was l.5km/s, and the penetration depth strongly depended on both particle material and collision velocity.

Secondary, a dense mixture of titanium and aluminum plasmas was produced by a railgun-type ablation arc plasma generator, in which numbers of titanium and aluminum electrode rods were ablated to form arc plasmas of various Ti/Al compositions. Quenching of those plasmas on the copper substrate under the stagnation pressure of about lOMPa resulted in direct synthesis of Ti-Al intermetallic compounds including Ti₃Al, Ti₂Al, TiA1₂ and TiAl₃. Microstructures of the deposits showed that the reaction mainly occurred in the liquid phase on the substrate, however main compound did not clearly correspond to equilibrium phase expected from the Ti/Al composition of the plasma.

Unique features of deposits such as a fine structure of the intermetallic phase, high-hardness and considerable diffusion of substrate material into matrix were observed.