Review of the initiation and arrest temperatures for delayed hydride cracking in zirconium alloys

Based on Kim's delayed hydride cracking (DHC) model, this study reanalyzes the critical temperatures for DHC initiation and arrest in zirconium alloys that had previously been investigated with Puls DHC model. In an unratcheting thermal cycle where DHC crack tip hydrides were dissolved fully at the peak temperature, the DHC initiation was suppressed, which required a supercooling or ΔT from the terminal solid solubility for dissolution (TSSD) temperatures. At a hydrogen concentration as 7 ppm H, the DHC initiation temperatures coincided with the TSSD, which is in conflict with Puls' DHC model. In a ratcheting thermal cycle, where the hydrides precipitated at the DHC crack tip were not fully dissolved, the DHC initiation was enhanced, so as to require a lesser ΔT, compared to that of the unratcheting thermal cycle. Therefore, the DHC initiation temperatures are concluded to depend upon at what temperatures the hydrides can nucleate in the zirconium matrix with the supersaturated hydrogen concentration. The DHC arrest temperatures were governed by the critical supersaturated hydrogen concentration or ΔC regardless of the thermal cycle treatment, providing further supportive evidence that Kim's DHC model is feasible.