Hydride precipitation in Nb and some properties of NbH

Precipitation of hydrides in high purity niobium after different treatments

“…36,37 It is known that strong plastic deformation at hydride formation sites produces large dislocation densities. 13,29 This leads to the formation of Cottrell clouds, less uniform local hydrogen concentration after the first cryocycle, and a smaller amount of free hydrogen. Higher concentrations around the dislocations then may explain the observed higher temperatures of the hydride formation upon the subsequent cool downs.…”

“…29 This creates a lot of dislocations, especially at the interface between a and b phases. 13 b-phase inclusions can range in size from hundreds of nanometers 15 to hundreds of microns, 13,30 and usually their size depends on the cooldown rate-the faster the cooldown the smaller the hydrides. 17 The inclusions have a tendency to be bounded by low index planes such as [100] or [110].…”

“…14,15 Numerous studies 13,[16][17][18][19] showed the effectiveness of different optical techniques-hydrides were observed by bright field and dark field imaging, in polarized light and by using interference techniques. Of importance is a fact that the samples must be virtually free of deformation layers.…”

“…[13][14][15][16][17][18][19] Neutron diffraction experiments 20 showed that it is formed by ordering of the hydrogen interstitials on tetrahedral interstitial sites and has a face centered orthorhombic structure of host niobium atoms. The a-b solvus line was determined by using resistivity, [21][22][23] internal friction 24 and DTA 25 methods.…”

The effect of stress on hydride precipitation

“…An equation describing the solvus is given by in a = const. -AHs/RT (1) where AH is known as the solvus enthalpy. Alternatively, the hydride phase can be precipit, Sol ed in an open system by the addition of H 2 (g) to the hydrogen-saturated solution, i.e.,…”