Non-Pd BCC alloy membranes for industrial hydrogen separation

Mechanisms which have been formulated to describe delayed hydrogen cracking in hydride-forming metals are reviewed and discussed. Particular emphasis is placed on the commercial alloy Zr-2.5 pct Nb (Cb) which is extensively used in nuclear reactor core components. A quantitative model for hydrogen cracking in this material is presented and compared with available experimental data. The kinetics of crack propagation are controlled by the growth of hydrides at the stressed crack tip by the diffusive ingress of hydrogen into this region. The driving force for the diffusion flux is provided by the local stress gradient which interacts with both hydrogen atoms in solution and hydrogen atoms being dissolved and reprecipitated at the crack tip. The model is developed using concepts of elastoplastic fracture mechanics. Stage I crack growth is controlled by hydrides growing in the elastic stress gradient, while Stage II is controlled by hydride growth in the plastic zone at the crack tip. Recent experimental observations are presented which indicate that the process occurs in an intermittent fashion; hydride clusters accumulate at the crack tip followed by unstable crack advance and subsequent crack arrest in repeated cycles.

Mechanisms of hydrogen induced delayed cracking in hydride forming materials

Elastic and plastic accommodation effects on metal-hydride solubility☆

An electron-optical study of β-hydride and hydrogen embrittlement of vanadium

Low temperature hydrogen embrittlement of niobium II—Microscopic observations☆

The embrittlement of vanadium and tantalum by hydrogen has been investigated with the ultimate goal being to answer three specific questions concerning ductility behavior in different temperature ranges. Torsion pendulum internal friction and another technique using the torsion pendulum as well as visual observations have been used to establish the solid solubility curve in the V-H and the Ta-H systems. The primary variables studied in this work were tensile strain rate, test temperature and hydrogen content. The results have been analyzed and tentative hypotheses have been set forth to explain the ductility behavior of the hydrogen charged metals.

Relation between hydrogen embrittlement and the formation of hydride in the group V transition metals

SAE 1020, 1040, and 1095 steels were shock-loaded to 158 and 283 kbar peak pressures by the mousetrap flyer plate technique. Post-shock mechanical properties, optical microscopy, and comparison with data from the literature indicated that shock pressure duration, is critical to strengthening by the α→e pressure induced transformation. It is suggested that the critical pressure duration is related to a time required for completion of the transformation process and that the required duration is inversely dependent on the volume percent carbide present in the steel.

T. E. Scott

Papers

Relation between hydrogen embrittlement and the formation of hydride in the group V transition metals

Effects of initial microstructure and shock method on the shock-induced transformation strengthening of carbon steels