Effect of duty cycle on surface properties of AISI 4340 using a pulsed plasma nitriding process

 

J. C. Díaz-Guillén, A. Campa-Castilla, S. I. Pérez-Aguilar, E. E. Granda-Gutiérrez, A. Garza-Gómez, J. Candelas-Ramírez, R. Méndez-Méndez

 

Corporación Mexicana de Investigación en Materiales Ciencia y Tecnología N. 790, Col. Saltillo 400, Coahuila, México.

 

Recibido: 26 de septiembre de 2008.
Aceptado: 9 de enero de 2009.

 

Abstract

Plasma nitriding is a glow discharge technique, which is widely used to improve the surface properties of steel and its alloys, such as wear, corrosion resistance and hardness; additionally, it can increase fatigue strength. The aim of this work is to evaluate the effect of duty cycle on the surface properties of AISI 4340 low alloy steel, in a pulsed plasma nitriding process. The effect of duty cycle (applying a 10 – 80 % tON interval) on the surface hardness, treatment depth, compounds zone width and crystalline phase composition will be discussed. It has been found that for nitriding process at 540 °C in a gas mixture 50 % N₂ – 50 % H₂ at a constant pressure, using a discharge voltage of -800 V, duty cycle has a negligible effect on crystalline phase composition, even though the influence on surface hardness, treatment depth and compounds zone width is evident.

Keywords: Surface modification; Plasma nitriding; White layer control.

 

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