Papers by Author: Kirsten Bobzin

Abstract: Over the last decades demands for optical systems and complex optical products made of glass increased steadily. Precision glass moulding has a great potential for the bulk production of complex lenses with high precision and low costs. To prevent sticking or reactions between hot glass and moulding, and to reduce abrasive wear of the die a protective coating is deposited on the tool. In this research two coating systems suitable for this application are compared by analysing their behaviour under an impact load. The PVD (Physical Vapor Deposition) coating PtIr with two different bond coatings Ni or Cr is analysed. During impact test number of impacts and loads are varied. Compared to industrially used coating system PtIr with a Ni interlayer the adhesion can be improved by using a Cr interlayer. The PtIr-based coating with Cr as bond coating shows an excellent endurance even at very high loads causing Hertzian stresses in the range of 10 14 GPa. An impact load of 600 N which corresponds to a contact pressure of app. 13.2 GPa generates almost no damage after 200,000 impacts.

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.

Abstract: The process of semi solid metal forming with permanent moulds combines the advantages of the process technologies casting and forging. Semi solid metal forming of steel is a challenge with respect to very high thermal, mechanical and tribological stresses of tools. Alumina based ceramics show a very high potential for tool protection. Alumina occurs in different known meta stable phases. First experiments show that the high temperature γ-phase exhibits high strength and toughness. Various methods and technologies have examined γ-phase stabilisation by using different thin film process technologies. By using Physical Vapor Deposition (PVD) it was possible to deposit γ-Alumina in a temperature range, where hot working steel can be utilized. The properties of the by pulsed reactive magnetron sputtering deposited films were analyzed by common thin film techniques revealing hardness, Young´s modulus and coating adhesion. By using the reactive pulsed PVD-process it was possible to stabilize γ-Al2O3 on steel substrates for semi-solid melt protection. The γ-Al2O3 coatings showed an extra ordinary stability for thixoforging of X210CrW12 and 100Cr6 in field tests. The durability of the permanent moulds was increased by using PVD thin film coatings as a tool protection.