Intensification of nitriding by ultrasonic vibration

Conclusions

• 1. Ultrasonic vibration accelerates the process of liquid nitriding in a neutral bath through which ammonia is circulated. Ultrasonic vibration increases the depth of the hardened layer and the microhardness in the nitrided layer.

• 2. Direct ultrasonic vibration of the samples makes it possible to obtain greater microhardness in the case of gas nitriding than in the case of liquid nitriding.

• 3. Ultrasonic vibration accelerates the rate of nitriding not only when applied directly to the metal but also when applied to the medium surrounding the metal. The increased rate of nitriding in the liquid medium is explained by the fact that ultrasonic vibration: a) promotes mixing of the salts and therefore a fresh supply of the liquid to the surface of the metal; b) eliminates the reaction products from the surface of he metal; and c) cleans the treated surface, activating it, and thus affecting the adsorption of surface-active elements.

• 4. The diffusion of nitrogen in the liquid medium is apparently promoted by high pressures as the result of closing the cavitational bubbles at the surface of the metal.