Deposition of Oxides as Tool Protection for Large Thixoforming Dies by Using the Pulsed MSIP-PVD Process

Abstract

Oxide coatings offer great potential for their use in forming operations in the semi-solid state. Advantages of these types of coatings are high resistance against abrasive wear, high hot hardness and low thermal conductivity. Nevertheless deposition by pulsed Magnetron Sputter Ion Plating-PVD for oxide coatings is quite challenging: deposition rates are low and insulating layers on the target surface can cause arcing. On laboratory scale it was possible to deposit γ-Alumina using PVD in a temperature range, where hot working steel can be utilized. The next important step in the development towards an industrial application for larger forming tools is the upscaling process to larger coating units. In this work the process development of oxide coatings on an industrial coating unit for large tools was described. To increase adhesion of oxide top-layer additional bond coats were applied. Different process parameters like oxygen content, total pressure and substrate bias were varied, to improve the performance. The relationship between coating properties and process parameters of the deposited films were characterized by X-Ray-diffraction, Nanoindentation and Scanning Electron Microscopy (SEM). By using reactive pulsed PVD-process it was possible to deposit γ-Al2O3 on large steel tools for semi-solid melt protection. The developed coatings showed for thixoforging processes of X210CrW12 an extraordinary stability in field tests. The lifetime of the permanent moulds was increased by using PVD thin film coatings as a tool protection.