Existence Of Surface Layer Research Articles

The Effects of the Oxygen-enriched Surface Layer on Mechanical Properties of .ALPHA.+.BETA. Type Titanium Alloys

The effects of heat treating conditions on thickness of the oxygen-enriched layer or α-case in Ti-4.5%Al-3%V-2%Fe-2%Mo alloy were studied in comparison with Ti-6%Al-4%V alloy, and then the effects of these layers on the mechanical properties were investigated. The higher heating temperature and an extended heating time increased oxygen-enriched layer or α-case thickness in Ti-4.5%Al-3%V-2%Fe-2%Mo alloy, and atmospheric heating using high purity argon gas with 99.999% purity could not prevent formation of the oxygen-enriched layer even by heating at such a low temperature as 998 K. The 30 μm thick oxygen-enriched layer without α-case was formed by heat treating at 1048 K for 3.6 ks in use of 99.9% purity argon gas which corresponded to the typical heating conditions adopted in a practical superplastic forming (SPF) operation using Ti-4.5%Al-3%V-2%Fe-2%Mo alloy. The thickness of both surface layers in Ti-6%Al-4%V alloy was much thicker than Ti-4.5%Al-3%V-2%Fe-2%Mo alloy because of its higher heating temperature. Tensile elongation, fatigue strength and bendability were deteriorated with the increase of oxygen-enriched layer or α-case thickness, and removal of these layers by pickling treatment fully recovered these properties to an original level. Deterioration of the mechanical properties was exerted by existence of the surface layer with high hardness, and in particular, the oxygen-enriched layer with α-case decreased fatigue strength more pronouncedly compared with the surface layer without α-case. Existence of brittle surface layer with high hardness and the coarse grain size in α-case appeared to be responsible for accelerated formation of microcrack at the surface of the mechanical testing specimens, resulting in deterioration of various properties.

Specific properties of ferroelectric thin films

Ferroelectric thin films have some specific properties such as low dielectric constant, high coercive force and presenting of polarization above Curie point, etc. These properties can be explained by the existence of surface layer and internal stresses in the films. The surface layer has lower dielectric constant and large spontaneous strain than in the bulk. The internal stresses will cause the shift of Curie point and create an internal bias field in the films.

Surface impedance investigations of superconducting niobium

AbstractMeasurements of the surface resistance derivative dR/dH in dependence on magnetic field strength H are presented as observed at pure superconducting niobium single crystals. At crystals not annealed after preparation procedure the measured impedance spectra do not represent the phase transitions appearing at critical fields indicating thus the existence of surface layers with properties different from the bulk of pure niobium. At annealed crystals the critical magnetic field strengths are marked as characteristic discontinuities in the spectra. The spectra observed at recently annealed crystals being in Meissner state can be interpreted by means of magnetic surface states.

“Controlled” surface layers in BaTiO3 single crystals

In spite of the fact that the existence of surface layers in ferroelectric materials has been verified by numerous experiments, their physical nature still remains obscure.1