Dissolution and soldering behavior of nitrided hot working steel with multilayer LAFAD PVD coatings

Soldering and corrosive dissolution are the primary causes of die non-perfo rmance in permanent mold and die casting production of net shape parts for the transportation industry. At worst, these corrosive reactions result in core pin or sprue dissolution, and at the least. some soldered cast metal r emains behind when the casting is ejected. The objective of this work was t o explore the possibility of surface engineering of the die steel surface t o reduce the dissolution and soldering tendencies of the surface. This pape r presents a duplex surface treatment approach for dissolution resistance t hat consists of nitrided hot working die steel substrate coated by multi-la yer titanium-based coatings applied by the large area filtered arc depositi on technique. The dissolution behavior of the coating candidates is evaluat ed by measuring weight loss after dipping them in molten aluminum for a pre determined time. Results are compared with those of single layer coatings a nd surface treatments. The chemisorption and adhesion behavior is evaluated by measuring ejection force of the soldered material. The duplex coating i s found to significantly reduce both the dissolution and adhesion tendencie s of the coated steel surface. (C) 2001 Elsevier Science B.V. All rights re served.