Combined surface treatment for generation of multi functional surface by means of electron beam cladding (EBC) and thermochemical treatment (TCT) on an austenitic corrosion resistant steel (KomET)

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Corrosion resistant steels are distinguished by an excellent corrosion resistance, but are afflicted with considerably limitations related to wear resistance. Numerous treatments to eliminate these disadvantages led only partially to positive results. The submitted project is based on a combined surface treatment with an electron beam cladding (EBC) as first process step and a subsequent plasma nitrocarburizing (PNC). Own preliminary investigations showed that in principle it is possibly to raise hardness and wear resistance and to maintain the corrosion resistance at one. Aim of the project is to generate layer/matrix compounds useable under increased loading conditions in corrosive media. Using the example of steel X6CrNiMoTi17-12-2 initially there are to indentify optimum EB parameters to produce one- but especially multi-pass Co-based EBC coatings, free of cracks and pores, as well as a faultless metallurgical connection. Hardness and wear resistance should be improved considerably. The corrosion resistance at least should be nearly the same as that of base material. Basis for these investigations is one selected Co-base additive, which have to be investigated concerning the effect of Cr and Fe content on EBA coating formation (microstructure) and the degree of mix up , i.e. the element content of the prior deposited cladding layer, especially in the multi-pass EBA coating. In connection with the combination EBC+PNC, the metallurgical compatibility and the effect of coating configuration (microstructure) on the mechanisms of PNC layer formation in relation to a compact material as well as the supporting effect of the EBA coating for the subsequently generated thin PNC layer (expanded austenite) should be methodically investigated. The occurring processes during EBA (interaction EB/material) respectively PNC (N/C layer formation on Co-base EBA coating) will be fundamentally analyzed and interpreted. On the basis of selected reference specimens the load characteristic of the layer/matrix compounds, i. e. which wear and corrosion mechanisms occur in case of different application specific load conditions will be basically investigated. For that purpose should be carried out wear tests (Tribometer) on different load levels (normal force 5-500 N) and/or at different temperatures (24-300 °C) as well as corrosion tests in different acid media (potentiodynamic measurements in 0.05M acid sulfur, and long term tests in 30% citric acid or 20% acid sulfur). In result of the project should be obtained new basic knowledge about the project relevant combined surface treatment and created generalized conclusions for the process design.