Volume 30, Issue 3-4

Basic aspects of stress corrosion cracking (SCC) in metallic materials are outlined, followed by a summary of the numerous mechanisms that have been proposed for SCC. The characteristics of transgranular and intergranular SCC in model systems, e.g., pure metal and single-phase alloy single crystals and bicrystals under testing conditions that facilitate discrimination between mechanisms, are then described. The applicability of the various proposed mechanisms, such as those based on dissolution, hydrogen embrittlement, film-induced cleavage, and adsorption, are discussed in detail for these systems. Mechanisms of SCC in complex commercial alloys are then considered in light of these studies on model systems.

Mechanisms of hydrogen embrittlement in steels and other materials are described, and the evidence supporting various hypotheses, such as those based on hydride formation, hydrogen-enhanced decohesion, hydrogen-enhanced localised plasticity, adsorption-induced dislocation emission, and hydrogen-vacancy interactions, are summarised. The relative importance of these mechanisms for different fracture modes and materials are discussed based on detailed fractographic observations and critical experiments.

This study describes corrosion behaviour and microstructure evolution of 17-4 PH stainless steel foam, which was produced for biomedical implant applications. 17-4 PH stainless steel foam was produced by the space holder-sintering technique. The effect of boron addition, aging, sintering temperature and sintering time on the corrosion behaviour and microstructure of the 17-4 PH stainless steel foam was investigated. Microstructure of the 17-4 PH stainless steel foams was examined by using scanning electron microscope (SEM) and optical microscope. The corrosion behaviour of the 17-4 PH stainless steel foam was investigated by using neutral salt spray (fog) and accelerated aging tests. The 17-4 PH stainless steel foams were exposed to salt spray solution, which consisted of 5% NaCl with pH of 6.68, in a closed cabin at 35°C. The surface of the foams after the corrosion test was observed by optical microscope and the digital photographs were analysed by an image analyser. The corrosion resistance of boron-added foams was higher than boron-free 17-4 PH stainless steel foams. Aging heat treatment slightly decreased the corrosion resistance of the 17-4 PH stainless steel foams. Increasing sintering temperature and sintering time increased the corrosion resistance of the stainless steel foams.