Hydrogen in zirconium alloys: A review

The terminal solid solubility of hydrogen and deuterium in Zr-2.5Nb alloys

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

The hydride embrittlement in ZIRCALOY-4 was studied at room temperature and 350 °C. Sheet tensile specimens of two fabrication routes in the stress-relieved, recrystallized, andβ-treated states were hydrided with or without tensile stress. It was found generally that the effect on strength of increasing hydrogen content was not important. However, for the tensile tests at room temperature, there is a ductile-brittle transition when the hydrogen content is higher than a certain threshold. The prior thermomechanical treatment shifts this transition considerably.In situ scanning electron microscopy (SEM) tests, fractography, and fracture profile observations were carried out to determine the fracture micromechanisms and the microscopic processes. At 20 °C, the fracture surfaces are characterized by voids and secondary cracks for low and medium hydrogen contents and by intergranular cracks and decohesion through the continuous hydride network for high hydrogen contents. This phenomenon disappears at 350 °C, and the hydrogen seems to exert no more influence on the fracture micromechanism even for very high hydrogen contents (up to 1500 wt ppm). A full-coverage model is proposed to estimate the critical hydrogen content that makes ZIRCALOY-4 totally brittle. The effect of microstructure on hydride embrittlement in different metallurgical states is thus explained according to the modeling. Special attention is devoted to relating the micromechanisms and the modeling in order to propose the possible measures needed to limit the hydride embrittlement effect.

Hydride embrittlement in ZIRCALOY-4 plate: Part I. Influence of microstructure on the hydride embrittlement in ZIRCALOY-4 at 20 °C and 350 °C

Dissolution and precipitation behavior of hydrides in Zircaloy-2 and high Fe Zircaloy

Experimental studies of mechanical properties of solid zirconium hydrides

Fracture strength of hydride precipitates in Zr–2.5Nb alloys

The effect of metallurgical factors on hydride phases in zirconium

On the consequences of hydrogen supersaturation effects in Zr alloys to hydrogen ingress and delayed hydride cracking

Delayed hydride cracking in zirconium alloys in a temperature gradient

M.P. Puls

Papers

Experimental studies of mechanical properties of solid zirconium hydrides

Fracture strength of hydride precipitates in Zr–2.5Nb alloys

The effect of metallurgical factors on hydride phases in zirconium

On the consequences of hydrogen supersaturation effects in Zr alloys to hydrogen ingress and delayed hydride cracking

Delayed hydride cracking in zirconium alloys in a temperature gradient