Surface Segregation of Ti in a V-4Cr-4Ti Alloy and Its Influence on the Surface Reaction Rates of Hydrogen Isotopes

Abstract

The change in the chemical surface state of a V-4Cr-4Ti alloy after heat treatments in vacuum at temperatures from 573 to 1273 K was investigated by means of X-ray photoelectron spectroscopy. Before heating, the surface of the as-polished alloy was covered with a V oxide film. Diffusion of oxygen into the bulk started at around 673 K, and the alloy surface gradually became metallic. Oxygen, however, did not disappear from the surface completely. Surface segregation of Ti was observed as the temperature increased. The concentration of Ti reached 20 at% at 1273 K. No significant segregation of Cr or other impurities were observed. This surface segregation of Ti significantly reduced the surface reaction rates of H 2 and D 2 . The isotope effect on the surface reaction rates of H 2 and D 2 was not observed under the present experimental conditions.

Friction Stir Processing of Particle Reinforced Composite Materials

“…Unfortunately, welded structures are more prone to fracture because of the presence of residual stresses, non-equilibrium microstructure, cracks and other metallurgical defects. Vanadium alloy joins produced using gas tungsten arc, laser and electron beam welding have been found to have low fracture toughness due to the embrittlement of heat affected zone [ 80 , 81 ]. It is obvious that current practices used to process vanadium alloy joints are not good enough for engineering applications.…”

Microstructure and texture evolution during accumulative roll bonding of aluminium alloy AA5086

“…The sub-structure formation in a polycrystalline material is thus highly orientation dependent. The situation is further complicated since multiple slip systems are needed in order to meet five independent slip system criterion [52][53][54][55][56][57][58]. It is possible that the deformation of certain regions of the grain is limited to only the primary slip, although the von Mises' criterion is satisfied globally through poly-slip at other regions, especially near the grain boundaries.…”

Development of membranes for hydrogen separation: Pd coated V–10Pd

“…12 The activation energy for hydrogen permeation through the V -1 OPd membrane at < 400°C as determined from V-6Ni-5Co membranes. I 1, 16,20,27,48 It is likely that this mechanism is also occurring here and by the end of the test period may be beginning to cause a noticeable flux decline.…”

“…The foil was washed with warm water and soap, rinsed with methanol, blown dry with nitrogen, mounted by clamping the ends of the foil strip, and loaded into the physical vapor deposition (PVD) chamber. After evacuation of the chamber to -1 x 10'5 Pa, argon was bled into the chamber to a pressure of 2 x 10'2 Pa and the ion-gun was set to a power of 1 keY and 20 25 rnA to ion-mill each side of the foil for 60-90 min. The foil was visually inspected through a window during ion-milling to ensure removal of remaining surface contaminants.…”