Electrochemical methods are currently used to characterize the corrosion properties of metals. However, because of the easy use of these methods, the interpretation of the results could be sometimes difficult or wrong in terms of the metal corrosivity. This paper presents some precautions concerning the use of electrochemical methods devoted to characterize, to compare and to control metals. The discussion about these methods is a good way to establish the electrochemical criteria that they can produce.

Various phenomena occur during the high temperature corrosion of materials: the formation of a scale or of volatile products, the change of the weight and of the size of the samples, the development of mechanical stresses, the variation of the structure and/or the composition of the substrate or of the corrosion products, Specific experimental methods are devoted to the recording of the variations of these different parameters. In this paper some of the most frequently used methods will be described and discussed.

In spite of its shortcomings, the salt spray test is universally used to characterize the corrosion resistance of zinc based coatings. A working group has tried to improve its reliability by the introduction of a new calibration method of the equipment. The outcome of the work is the definition of a new testing procedure, presently adopted in France for the control of coated products delivered to the automobile industry.

Coatings are widely applied to improve the durability of components. In order to understand how corrosion protection is obtained, the behaviour of coatings in aggressive environments must be characterized. Factors responsible for an increase of the susceptibility to corrosion are indentified and methods available to characterize these factors are reviewed. These are indirect methods as they do not concern the measurement of corrosion rates, nor the study of corrosion mechanisms. They deal with morphology, composition, crystallographic structure and mechanical properties of the coating.

Two specific examples are presented to describe the experience gained in the use of mechanical tests for the study of stress corrosion cracking and corrosion-fatigue: 1) the design of tension test platforms and low-frequency fatigue machines, having cross-head displacement rates of the order of 1 μm/h; 2) the use of curved tension test pieces to take into account heterogeneities of the material microstructure, in the case of cracking phenomena in burried pipelines.

The civil engineering structures considered in this paper are reinforced concrete structures and cables. Corrosion tests are used to select the steel grades having the best corrosion resistance. Furthermore, electrochemical techniques, like the measurement of the electrode potential and of the polarization resistance, are applied to structures in service to characterize the condition of the reinforcing elements in the concrete.

Paleocorrosion, a new domain in science of materials, refers to the understanding of the processes of degradation of the “ancient” metal materials. Objectives are to decipher technical, ethnological or simply historic information inherent in them. It is not only a question of allowing their reading, but also to estimate their state of degradation to ensure their durability. The understanding of the deteriorated structures requires physical chemical characterizations (analytical, structural or even functional), often with a high level of performance, according to a very particular approach. The main methods of investigation to study these problems are presented and illustrated with some specific archaeological samples.

The influence of Cd, Sn and Ge on the kinetics of the Guinier-Preston (GP) zones formation has been studied for the Al-7 %Zn-3 % Mg-0,05 % Cd(0,05 %Sn) and Cu-2 % Be-0,3 %Cd(0,3 % Ge) solid solutions. The volumic fraction of the formed GP zones is determined by a method based on microhardness measurements. Traces addition of Cd and Sn cause, respectively, a delay in the GP zones formation and an elimination of these zones, in Al-Zn-Mg-Cd(Sn). For the Cu-Be-Cd(Ge) alloys, the added Cd atoms accelerate the GP zones formation, while Ge atoms at a concentration of 0.3 % have no influence.

Continuous (CDRX) and discontinuous (DDRX) dynamic recrystallizations in the hot working range are compared on the basis of large strain flow curves and EBSD measurements. The same basic mechanisms occur in the two cases, but with different kinetics leading to distinct textures and microstructures. Furthermore, a transition from CDRX to DDRX may occur in high stacking fault energy metals at very high levels of purity.

A natural kaolin material, which contains 45 wt % of alumina and less than 1 wt % of metal oxide impurities, has been submitted to thermal treatments in the temperature range 1 000-1 450 °C. The cristobalite development is studied by X-ray diffraction, using the broadening of line {101}. The apparent grain sizes of cristobalite, measured by the integral width of the line, change as a function of thermal treatment. Nevertheless, the apparent total content of the cristobalite remains constant. In the case of a chamotte material, which contains 42 wt % alumina and 3 to 4 wt % of metal oxide impurities, the apparent cristobalite grain sizes are of order of magnitude of the nanometer and the total apparent content is slightly lower. Finally, the thermal expansion coefficient, α (T), of the first material is higher, during the cristobalite transformation α → β, than that of the chamotte material.