Nitretação por plasma em furos de diferentes relações geométricas

Abstract

Parts that contain holes and/or grooves are commonly used in assembly of mechanical components and operate, in many cases where the pressures are high in the holes . To raise the hardness and wear resistance of these holes, treatments such as nitriding can be made. The liquid nitriding, and even gaseous nitriding, have limitations in holes, and these restrictions that may be harmful in the results obtained. Thus, it is necessary to study and understand the nitriding on holes. This study evaluated the results of plasma nitriding on parts that contain no holes passers of different ratios of height and diameter and different treatment pressures. Aiming to establish the influence of gas pressure in the treatment, were nitrided parts containing length/diameter set at 1, 3 and 9 relations . The diameters, fixed at 2 and 7 mm, gives the geometric difference between the samples. Pressures of 1 and 5 Torr were used, making this the only parameter to be modified in both treatments. The results showed the large influence of pressure nitriding on holes, and the length/ diameter ratio was not a decisive factor in the occurrence of nitrided layer. The Hollow Cathode phenomenon, giving rise to an undesirable overheating in the samples, was observed for samples especially 7 mm diameter nitrided at 1 Torr. Furthermore, it was verified, through pictures during nitriding, the decrease in thickness of the cathode sheath was higher the pressure treatment. Finally, a significant result was a complete nitriding of samples of 2 mm in diameter nitrided to 5 Torr, while samples 2 mm nitrided at 1 Torr, didn’t developed white or a diffusion layer. Thus, it was observed that there is a relationship between pressure and the part geometric conditions, which may confer a nitrided layer on pieces of small diameter and deep holes.