CrAlON CAE-PVD coatings for oxidation and wear protection of TZM alloys in FAST sintering applications

CrAlO and CrAlO/CrAlN multilayers deposited by cathodic arc evaporation were developed as protective films in metal and ceramic powder FAST sintering tool dies fabricated in titanium-zirconium-molybdenum (TZM). The films have been characterised in terms of their composition, microstructure, mechanical properties and thermal stability in air at high temperatures between 800 C and 1100 C; in addition the tribological performance has been analysed at room temperature and at 400 C. The crystalline structure and composition of the CrAlO based coatings are compatible with the formation of a mixture of a-corundum and a cubic fcc (Cr,Al)2O3. The crystalline structure of the multilayer is, on the other hand, dominated by the cubic fcc lattice plane reflections of the CrAlN. The deposited specimens have high hardness, between 25 and 30 GPa, which are stable even after annealing at 1000 C. Even more, the multilayer coating also exhibited good mechanical stability at 1100 C. The multilayer coating also exhibited an excellent behaviour against wear at 400 C. Sintering trials using coated TZM dies have been carried out using Ti90Sn10 and Al2O3 high energy ball milled powders. The experimental results show that the oxide based coating formulations are potentially able to protect the tools from wear, sticking and oxidation of their surfaces. This may allow for the use of TZM material as an alternative to other substrates such as graphite for high-temperature dies.