Alumina PVD tool coatings for the use in semi solid metal forming of steel

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 gamma-phase exhibits high strength and toughness. Various methods and technologies have examined gamma-phase stabilisation by using different thin film process technologies. By using Physical Vapor Deposition (PVD) it was possible to deposit gamma-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 gamma-Al2O3 on steel substrates for semi-solid melt protection. The gamma-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.