Corrosion Behavior of Detonation Gun Sprayed Fe-Al Type Intermetallic Coating
The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior of Fe-Al type coatings under air atmosphere. The oxide layer ensures satisfying oxidation resistance, even at 950 and 1100 °C. Hematite, α-Al2O3 and metastable alumina phases were noticed on the coatings top surface, which preserves its initial thickness providing protection to the underlying substrate. In general, only negligible changes of the phase composition of the coatings were noticed with simultaneous strengthening controlled in the micro-hardness measurements, even after 10-hours of heating at 1100 °C. On the other hand, the electrochemical corrosion tests, which were carried out in 200 ppm Cl− (NaCl) and pH ~4 (H2SO4) solution to simulate the acid-rain environment, reveal higher values of the breakdown potential for D-gun sprayed Fe-Al type coatings than the ones for the bulk Fe-Al type alloy and Cr21Mn9Ni4 austenitic valve steel. This enables these materials to be used in structural and multifunctional applications in aggressive environments, including acidic ones.
TEM Microstructure of Fe-Al Coatings Detonation Sprayed Onto Steel Substrate
The microstructure analysis of Fe-Al intermetallic coating deposited by detonation-gaseous spraying (DGS) on the 045 carbon steel substrate was presented in the paper. The microstructure was investigated using scanning (SEM) and transmission (TEM) electron microscopy, as well as selected area electron diffraction (SAED) techniques. The chemical concentration in microareas was revealed using the energy dispersive X-ray (EDS) spectroscopy technique. The TEM technique was applied to the analysis across the coating as well as close to the coating/substrate interface. The vicinity of the substrate was composed of an amorphous phase and columnar crystals as a result of rapid solidification of the partially melted FeAl powder. The Fe3Al phase was identified inside the coating, while at its surface Fe2Al5, Fe3Al and FeCrAl phases were found. Their occurrence and also the FeAl2O4 phase and aluminium oxide were confirmed by the X-ray diffraction method.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.