Low temperature plasma immersion ion implantation of nitrogen on a steel mould

In the injection moulding of polymers the mould is a critical element; in addition to obtaining the correct shape of the moulded part, it is required to let the produced object getting out without damaging it. During ejection, the polymer can get stuck to the mould. The plasma-immersion ion implantation (PI3) treatment produces a surface modification, which can improve mould properties in the following way; nitrogen implantation allows to obtain a very thin nitrided layer, which can reduce the adhesion between polymer and steel and avoid the packing during component extraction. In this work the efficacy of this treatment is evaluated considering the decrease on adhesion and friction between polymer and steel. Moreover, the influence of the nitriding PI3 process on corrosion behaviour of mould steel was also evaluated. The experimental data showed that the PI3 process strongly reduces the adhesion and the friction between polymer and 35NCD16 steel. It was clearly observed the influence of treatment on the corrosion resistance of mould walls. The treatment promoted the formation of a stable passive layer. Moreover, this oxide layer decreased the passivity current density by more than 10 times. It was not possible to establish which was the best implantation dose to obtain the best corrosion performance. Even when chlorides were present the treated steel tended to passivate. It was possible to observe some beneficial effect of treatment on the pitting corrosion resistance and passivity current density. © 2002 Elsevier Science B.V. All rights reserved.