Fundamental research on deposition of amorphous coatings on surfaces of inner geometries and evaluation of phase stability under tribological loading

• Applicant: Professorin Dr.-Ing. Kirsten Bobzin
• Subject Area: Coating and Surface Technology ; Joining and Separation Technology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419126987

Various metallic glass alloys are the subject of research for potential use as wear-resistant metallic thermal barrier coatings (TBC). As part of our own preliminary work, a particularly resource-efficient, low-alloy, iron-based metallic glass (MG) was developed. Two approaches were pursued in parallel to develop the alloy. On the one hand, shallow neural networks were used to produce data-driven predictions about areas of high glass forming ability (GFA). On the other hand, samples of metallic ribbons were produced by melt spinning (MS) and examined with regard to the GFA. The low content of alloying elements of x_alloy ≈ 15 wt.-% enabled manufacture as cored wire for thermal spraying. The supplied cored wires were processed using various thermal spraying (TS) techniques and the resulting layer structures were characterized. High hardness levels in the range of HV0.1 = 900 and high proportions of amorphous phases were demonstrated for arc wire-sprayed coatings. The high wear resistance of the sprayed coatings was also demonstrated in tribological tests. However, for later use as a wear-resistant TBC, further investigations of the coating properties are necessary. Firstly, the thermal conductivity of the coating produced by TS must be determined and compared with that of the metallic ribbons. The fracture toughness KIC is of interest for an application with alternating mechanical loads. In contrast to ceramic TBCs, metallic TBCs usually have a higher fracture toughness. In preparation for use as a TBC, the thermal application limit must also be determined. In this respect, the crystallization of the coating as the upper application temperature is decisive. The various crystallization phases can be undergone and measured in situ using high-temperature XRD tests. This project lays the foundations for transferring the research results to corresponding applications. A later application could be in the area of reducing greenhouse gas emissions of marine diesel engines. The newly developed coating would then be used in the future as a thermally sprayed TBC on cylinder liners to increase the fuel efficiency of marine diesel engines and ensure sufficient robustness of the combustion engine against alternative, more sustainable fuels.

• DFG Programme: Research Grants