Ultrasonic cavitation erosion of gas nitrided Ti-6Al-4V alloys.
Ultrasonic cavitation erosion experiments were performed on Ti-6Al-4V alloys samples in annealed, nitrided and nitrided and subsequently heat treated state. The protective oxide layer formed as a result of annealing and heat treatment after nitriding is eliminated after less than 30 min cavitation time, while the nitride layer lasts up to 90 min cavitation time. Once the protective layer is removed, the cavitation process develops by grain boundary erosion, leading to the expulsion of grains from the surface. The gas nitrided Ti-6Al-4V alloy, forming a TixN surface layer, proved to be a better solution to improve the cavitation erosion resistance, compared to the annealed and nitrided and heat treated state, respectively. The analysis of the mean depth of erosion rate at 165 min cavitation time showed an improvement of the cavitation erosion resistance of the nitrided samples of up to 77% higher compared to the one of the annealed samples.
Low-temperature plasma nitriding of titanium layer on Ti/Al clad sheet
A nanostructured surface layer was fabricated on titanium layer of a Ti/Al clad sheet composite by means of the surface mechanical attrition treatment (SMAT). The low-temperature plasma nitriding treatment of the SMAT sample was investigated in comparison with the coarse-grained sample by using structural analysis (X-ray diffraction, scanning electron microscopy, and transmission electron microscopy) as well as mechanical and corrosion property measurements. Results showed that the nitriding kinetics of the SMAT sample with the nanostructured surface layer was greatly enhanced, so that the nitriding temperature could be as low as 550 degrees C, which is significantly lower than the melting point of the aluminum layer on Ti/Al clad sheet (conventional nitriding can lead to melting of the aluminum layer due to higher temperature about 800 degrees C). The nitrided layer of the SMAT sample was composed of nanostructured epsilon-TiN and gamma-Ti2N phase with high supersaturation of nitrogen. The surface hardness and the hardened surface layer thickness as well as the wear and corrosion resistances of the nitrided SMAT sample were all substantially enhanced relative to the nitrided coarse-grained sample. (C) 2012 Elsevier Ltd. All rights reserved.
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.