Synthesis of Tribologically Favorable Coatings for Hot Extrusion Tools by Suspension Plasma Spraying

Up to now, no coating systems have been marketed in the field of direct hot extrusion, which provide both surface protection of the parts in contact with the billet (i.e., container and die) as well as a significant reduction of the frictional losses induced by the billet passing over the container walls. To dispense with the use of lubricants and to enhance the usable forming capacity and therefore the efficiency of the process, different oxide ceramics were prepared in one suspension and plasma sprayed to produce coatings. The aim was to reach a sufficient level of feedstock mixing to obtain deterministic solid solutions of the oxide phases in coatings resulting in a reduction of their coefficient of friction under dry sliding conditions. To achieve this objective, the high specific surface area of nanosized feedstock with primary particle sizes below 100 nm was used. By means of x-ray diffraction it could be proven, that the desired phases could be synthesized to varying ratios regarding the different coating systems considered here. Besides the experimental work, the fundamentals of the mixing process of different oxides are discussed with regard to the crystallographic aspects.