Materials and Corrosion

The demand for environmentally and resources-friendly processes as well as higher efficiency in thermal plants and machinery requires an increase of operating temperatures. However, processes conducted at high temperatures and often in complex atmospheres lead to increasing demands on the high temperature corrosion resistance of the materials used. The main research objectives of the "high temperature corrosion" team at DFI are material analysis and development in the field of aggressive, high temperature environments. Within this research field, we focus on the development of metallic and ceramic protective coatings and innovative material systems appropriate for extremely aggressive service conditions (e.g. chlorine, sulphur, bromine, vanadium, and carbon-rich environments) and operation temperatures up to 1800 °C. The team also works on conceptionalising, developing and producing novel alloying systems that withstand more aggressive conditions.

Main Research Fields

• Diffusion Coatings: modification of the material surface by enrichment with protective elements, which prevent substrate corrosion during high temperature exposure.
  Methods: Pack cementation (in-pack, out-of-pack, slurry).
  Examples: protective coatings for a better oxidation resistance of materials at high temperature in environments rich in water vapour, typical for gasification and combustion atmospheres, slurry-based coatings for application on-site in plants or on machine parts.

• Computational modelling of coatings and their lifetime: prediction of material behaviour during manufacturing as well as their lifetime during operation at high temperatures.
  Examples: modelling of layer growth and phase formation in the pack cementation process, modelling the influence of defects on the mechanical properties of thermal barrier coatings and oxide layers.

• Functional high temperature coatings: combining high temperature protective coatings with additional properties such as self-cleaning, thermal insulation or improved aerodynamics.
  Examples: self-healing "shark skin" coatings for turbines, foam-like ceramic thermal barrier coatings.

• "Minimally-invasive" high temperature corrosion protection: targeted changes in the chemical composition near the surface for improved corrosion behaviour at high temperatures.
  Examples: development of stable and protective alumina layers by using the halogen effect, Sn-modified surfaces for catalytic poisoning in metal dusting environments, controlling chlorine corrosion by selective doping of coatings.

Methods

• Isothermal, cyclic and thermogravimetric experiments in various environments
• Extensive analytics for investigating metallic phases, alloy compositions, oxide scales, and reaction products
• Pack cementation methods, slurry coatings

Achieving a carbon-neutral economy requires increased efficiencies of green technologies and thus increases the demand on materials to reach higher operating temperatures and survive more aggressive conditions. The aerospace, transportation, process and energy industries, among others, are desperate for alloys that can endure high temperature and extreme (HX) environments. The “High Temperature Alloys” team at DECHEMA Research Institute designs, develops and produces such alloys and coatings. We optimize alloy oxidation and corrosion resistance in addition to mechanical properties, analyzing microstructure, heat treatment and processing (additive manufacturing, AM) influences.

Main Research Interests

• Development and understanding of next generation high temperature alloys:
  Ni-based alloys, Fe-based alloys, refractory metal alloys (Cr, Mo), Ti alloys, multiple principal element (MPEA) and high entropy (HEA) alloys

• Improving the AM buildability of current state-of-the-art alloys:
  Additively manufactured Ni-based alloys, Al-based alloys and MPEAs/HEAs

• Development of protective coatings, especially for novel alloying systems:
  Pack cementation and slurry coating of Al, Cr, Si and more on novel alloys

Laboratory Methods

• Production of customized alloy compositions in an electric arc furnace and centrifugal caster
• Heat treatment, microstructure development and optimization up to 1800°C
• Isothermal, cyclic and thermogravimetric experiments in extreme environments
• Extensive analytics for investigating phases, alloy compositions, oxide scales, and reaction products
• Pack cementation, slurry coatings

The research team focusses on the one hand on the mechanistic investigation of corrosion processes of new materials as well as in various technologies. On the other hand the focus is on corrosion protection by different types of coatings. In both fields light alloys (aluminium, magnesium, titanium as well as high-strength steels) play an important role. Furthermore actual topics in the field of cathodic protection are adressed. Most profiting industrial branches are automotive, aviation, medical technologies, the structural-facings sector and pipeline construction.In addition the research team is responsible for corrosion investigations, materials selection tasks and corrosion failure analysis in the frame of the DECHEMA Corrosion Center.

Main Research Fields

• Development of inorganic coating systems via anodising, application of ultrasound and use of nanoparticles or nanocapsules (see projects PhotoEloxal, MagPEO2, PEO-TBC, AlUlIMP)

• Antimicrobial surfaces and biocorrosion (see project Antimicrobial Peptides)

• Mechanistic corrosion investigations and modelling (see projects AC-Corrosion, Al-Grinding, SLM-Titanium)

Specific investigation methods used are:

Electrochemical measurements

• Stationary current density – potential curves
• Electrochemical Impedance Spectroscopy (EIS)
• Rotating discs/cylinders and ring-disc electrodes
• Hydrogen permeation measurements
• Scanning Kelvinprobe (SKP) / Scanning Kelvinprobe Force Microscopy (SKPFM)

Materials characterisation methods

• Scanning Electron Microscopy (SEM) with EDX
• Electron Beam Microanalysis (EBMA) with WDX
• X-ray Diffraction (XRD)
• Scanning Force Microscopy (AFM, EC-AFM)
• Tribometry / Tribocorrosion
• Contact angle measurements
• Adhesion testing

Spectroscopic/analytical methods

• Confocal Raman microscopy
• FT-IR spectroscopy
• Particle size analysis and Zeta potential measurement
• Instrumental chemical analysis (AAS, GC-MS, IC, ICP-MS)