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.
Processing and characterization of graded metal/intermetallic materials: The example of Fe/FeAl intermetallics
Abstract In this work, a novel processing routine for the fabrication of graded metal/intermetallic materials is shown. It is a combined process that begins with “layer by layer” manufacturing of the 3-D components from the elemental metal powders under computer-aided design and manufacturing (CAD/CAM), followed by low-temperature uniaxial pressing under cycle loading and subsequent sintering at high temperature. The ability to fabricate heterogeneous metal-intermetallic materials with a continuous and/or discrete intermetallic gradient was demonstrated by producing graded Fe/FeAl materials as an example. The microstructure of the graded Fe/FeAl materials was investigated with X-ray diffractometer (XRD) and scanning electron microscope (SEM) coupled with a backscattered electron detector (BSE) and an energy dispersive spectrometer (EDS). In both of the investigated materials, Fe and FeAl intermetallic compounds with different amounts of Al and aluminum oxides were found. The mechanical properties of the graded Fe/FeAl materials were examined with a static compression test. The Fe/FeAl material with a continuous gradient exhibited higher compression strength than the material with a discrete gradient.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.