Sponsored Student: Cast alloy soldering tendency and corrosion resistance of duplex PVD coatings for application on die casting tools for aluminum alloys processing

Wear resistance of die casting tools used for aluminum alloys processing is nowadays successfully increased by application of duplex PVD nitride coatings. However, their performance greatly depends on few surface characteristics which are often overlooked. These are coatings topography, growth defects morphology and variable nature of surface chemistry. This investigation concerned H11 steel, plasma nitrided steel, CrN and TiAlN PVD coatings deposited in form of duplex layers, all prepared to different grades of surface roughness. Soldering and corrosion behavior in cast Al-Si-Cu alloy was evaluated by ejection test performed with conventional and delayed alloy solidification. Investigated coatings outperformed steel and nitrided layers and exhibited no reaction with the cast alloy in both experimental configurations. By decreasing the coating roughness ejection force from the conventionally solidified castings considerably increased. However, the highest ejection force that was recorded for post deposition polished coatings, in the test with the delayed solidification decreased as a consequence of coatings oxidation. Corrosion of nitrided substrate developed through the defects in the coatings, but the observed damage does not endanger the coatings integrity. Achieving the highest coating performance requires that, except the coating type, consideration also focuses on surface morphology and transformation of the coatings during exploitation.