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-performance 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 remains behind when the casting is ejected. The objective of this work was to explore the possibility of surface engineering of the die steel surface to reduce the dissolution and soldering tendencies of the surface. This paper presents a duplex surface treatment approach for dissolution resistance that consists of nitrided hot working die steel substrate coated by multi-layer titanium-based coatings applied by the large area filtered arc deposition technique. The dissolution behavior of the coating candidates is evaluated by measuring weight loss after dipping them in molten aluminum for a predetermined time. Results are compared with those of single layer coatings and surface treatments. The chemisorption and adhesion behavior is evaluated by measuring ejection force of the soldered material. The duplex coating is found to significantly reduce both the dissolution and adhesion tendencies of the coated steel surface. (C) 2001 Elsevier Science B.V. All rights reserved.