Atomic-scale Ab-initio study of the Zr-H system: I. Bulk properties

A model of slow crack propagation based on the delayed hydride cracking (DHC) mechanism in hydride-forming alloys has been critically examined and evaluated to take account of recent experimental and theoretical advances in the understanding of hydride fracture and terminal solid solubility (TSS). The model predicts that the DHC velocity is a sensitive function of the hydrogen concentration induced in the bulk of the material as a result of the direction of approach to test temperature. For test temperatures approached from below, factors such as the hydridematrix accommodation energies, the stress state at the crack tip, and the value of the yield stress have a strong effect on the DHC arrest temperature in the technologically interesting temperature range of 400 to 600 K. A fracture criterion is explored based on the need to achieve a critical hydride length in the plastic zone at the crack tip. A necessary condition for DHC is that the crack tip hydride must grow to this critical length. An approximate estimate is made for the steady-state growth limit of the crack tip hydride as a function of the direction of approach to temperature and the crack tip stress state. For temperatures approached from below, growth of the crack tip hydride is limited to just outside the plastic zone boundary at low temperature, gradually receding toward and inside the plastic zone boundary with increasing temperature. At lowK
 I
 values, this limits the crack tip hydride lengths to below their critical values for fracture. This could be one condition forK
 IH
 . For test temperatures approaches from above, the growth limit is significantly increased, and the sensitivities to the above parameters become less evident.

Effects of crack tip stress states and hydride-matrix interaction stresses on delayed hydride cracking

Environmentally-induced cracking of zirconium alloys — A review

Synchrotron diffraction study of dissolution and precipitation kinetics of hydrides in Zircaloy-4

The first step for delayed hydride cracking in zirconium alloys

DILATION OF h.c.p. ZIRCONIUM BY INTERSTITIAL DEUTERIUM

Time-of-flight neutron diffraction has been used to measure the dilation of h.c.p. Zr by interstitial deuterium at 727 and 777 K. The dilation per atom of D is 2.78 Â3, and the partial molai volume is 1.67 cm3/mol. The lattice strain in the 〈c〉-direction is 1.65 times greater than in the 〈a〉-direction, and assuming tetragonal symmetry, the components of the A-tensor are found to be ⋌1 = 0.032 and ⋌3 = 0.052.

C.E. Ells

Papers

DILATION OF h.c.p. ZIRCONIUM BY INTERSTITIAL DEUTERIUM

DILATION OF h.c.p. ZIRCONIUM BY INTERSTITIAL DEUTERIUM