Corrosion features fatigue

Fig. 8.59 Features of a corrosion fatigue crack growth curve...

Some of the investigations involving electrochemical measurements have been concerned with relating easily determined quanities such as corrosion potential and corrosion current with the behaviour of a material in corrosion fatigue, so that this behaviour can be rapidly assessed without the necessity of the laborious collection of data which was the feature of McAdam s approach. Endo and Komai have derived an expression relating the increase... 

Undue static or cyclic stressing and other features which give rise to stress concentrations should be avoided as these may lead to premature failure by stress-corrosion cracking or corrosion fatigue. 

Environmentally induced cracking consists of (i) stress corrosion cracking (ii) corrosion fatigue and (iii) hydrogen-induced cracking. The general features of these modes of failure are given below ... 

When one talks about reversibility of the Rehbinder effect, the presence of a thermodynamically stable interface between mutually saturated solid phase and the liquid, as well as complete disappearance of these effects upon the removal of the medium (e.g. by evaporation) are implied. These features emphasize principal difference between the Rehbinder effect and corrosive action of the medium. At the same time, one has to realize that it is not possible to draw here a distinct border line. The term disintegration covers a broad range of processes from idealized cases of purely mechanical breaking to destruction by corrosion or dissolution. The Rehbinder effect, i.e. the lowering of strength due to adsorption and chemisorption, stress-caused corrosion, and corrosion fatigue, occupies some intermediate place between these extremes. All these phenomena represent a certain degree of combination between the mechanical work performed by external forces and chemical (physico-chemical) interaction with the medium. 

Physically based, using detailed thermodynamics and kinetics of phase transformations, cahbrated on direct measurement of micro-structural features and able to predict hardness and strength, with the potential for extension to ductility, fracture toughness, fatigue, and corrosion properties. 

Since mechanical valves provide a physical barrier to the backflow of combustion products through the combustor inlet during the positive-pressure phase of the pulse combustion cycle, the unidirectional flow is the fundamental feature of valved pulse combustors. There are, however, certain problems associated with the design of mechanical valves, such as minimizing valve inertia, protection from corrosion, and resistance to material fatigue due to thermal stress. These specific problems are of major importance in heavy-duty pulse combustors operated at large pressure amplitudes (Kentfield, 1993). 

Stress corrosion cracking and corrosion fatigue may have common features and there is a continuum of morphology and mechanisms between the two phenomena, CF becoming similar to SCC as the loading frequency is decreased. In the same way, the distinction between HE and SCC or CF is... 

Corrosion fatigue tests under a controlled potential have been conducted in the passive region at the rest potential of the duplex alloy (Eq=- 2Q raVsce) d at a more anodic potential ( anod.=+150 mVsc ) for a given strain rate e=10 s . This strain rate has been chosen because it corresponds to the more marked corrosion fatigue life reduction at both applied potentials. The Coffin-Manson curves under such conditions are given in Fig. 5-36. The following features can be observed ... 

These findings suggest that the failure mechanism is a combination of low-cycle corrosion fatigue and stress-induced corrosion. Extensive oxide formation relative to the depth of cracking is a key feature. The formation of oxide was associated with corrosion attack of the ferrite phase. The lamellar pearlite phase remained relatively intact and was contained within the oxide product. The oxide itself exhibited numerous cracks, allowing aqueous corrosion of fresh metal to occur at the oxide/metal interface. 

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