NGHIÊN CỨU CÔNG NGHỆ PHỦ PVD TRÊN NỀN THÉP AISI 420 THẤM NITƠ

A RESEARCH ON PVD COATING TECHNOLOGY ON NITRIDED AISI 420 STAINLESS STEELThis article presents the technologies of vacuum heat treatment, gas nitriding and TiN, CrN deposition using PVD cathode arc method for the AISI 420 martensite stainless steel, a favourite steel grade in manufacturing plastic die mould. The nitrided layer and the coating were analyzed using various techniques: Analysis of the phase composition using X-ray diffraction, metallographic analysis using an optical microscope and scanning electron microscope with the EDS probe, determination of the surface hardness, the coating adhesion, the potentiodynamic polarization corrosion test and the “ball on flat” wear test. The experimental results showed that the nitrided layer was formed with a thickness of about 50 µm and with a hardness of 1010 HV0.1 to 1250 HV0.1. The TiN and CrN coatings thickness reached a value of 1÷2 µm with significantly improved hardness. The XRD and EDS analyses showed that the CrN and TiN coatings were formed on the substrate. Other coating properties such as the adhesion, corrosion resistance and coefficient of friction were significantly improved when the substrate was nitrided before coating deposition in comparison with the substrate that has only undergone heat treatment. The TiN coating has a greater hardness than the CrN coating. Nevertheless, the CrN coating exhibited better corrosion resistance and coefficient of friction than TiN coating.