Structure and Mechanical Properties of a Three-Dimensional Capillary Porous Titanium Coating

The effect of two types of abrasive treatment and preliminary arc discharge heating of a titanium coating on the shear strength of a three-dimensional capillary porous (3DCP) titanium coating is found to exist. The coatings are deposited by plasma spraying of a wire in a protective argon atmosphere. The efficiency of deposition of the 3DCP titanium coatings is determined by the application of three arc discharges, which are induced between cathode and anode, cathode and wire, and cathode and substrate. Before the action of an arc discharge on a substrate, the shear strength is 195 MPa after treatment by Al2O3 particles and 72 MPa after treatment by glass balls, which is explained by the 2.7 times larger specific surface area of the substrate subjected to treatment by Al2O3 particles. In case of preliminary treatment of the substrate by Al2O3 particles and glass balls, the 9-s action of an arc discharge on the substrate increases the shear strength to 250 and 230 MPa, respectively. For this arc-discharge action time, the microhardness of the titanium substrate increases gradually from 1.9 to 8 GPa from the volume to the boundary with the coating; in the middle of the coating, the microhardness decreases to 2.9 GPa and increases subsequently to 4.7 GPa at the coating surface. The high shear strength and microhardness at the 3DCP titanium coating/substrate interface is explained by plasma and arc-discharge activation of the substrate material and its reaction with residual oxygen and nitrogen in the spraying chamber.