Dislocations produced during plastic deformation tend to gather in well defined patterns. Both the shape and the structuring degree of these clusters depend on material parameters and on loading conditions. The present work analyzes these relations and classifies the observations in a schematic structural map. While a strong correlation exists between dislocation patterns and mechanical behaviours, it is shown that there is no direct effect of the substructure on either the stress level or the work-hardening rate of the material.

During the normal growth of recrystallized grains in the metastable beta titanium alloy called Beta III, several parameters have an influence on the size of the recrystallized grains. The parameters considered in this study are: the amount of cold work, the initial grain size, the annealing temperature and time. The grain size distribution is determined by image analysis. The influence of each parameter is identified using a Taguchi type of experimental planning. From the results, the growth constants A and n are derived, as well as the activation energy Q of a growth model of the beta grain size as a function of annealing time and temperature for fixed initial conditions (amount of cold work, initial grain size).

The evolution toward equilibrium of the supersaturated Pb-1.5%Cd-0.15%Ag-1.25%Sn alloy has been studied by various techniques, such as hardness, optical microscopy, scanning electron microscopy and electron microprobe. The explored temperatures are 20 and 80°C. The precipitation hardening mechanisms of this alloy are similar to those of silver-free alloys. The as-quenched structure transforms toward equilibrium in a two stage process. In the first stage, called ageing, two transformations take place at the same time: a continuous hardening precipitation and a discontinuous, incomplete, softening transformation. The second stage is characterized by a discontinuous lamellar reprecipitation. The microstructure of this alloy is characterized by the presence of Ag5Cd8 precipitates and of zones corresponding to the eutectic mixture. The main effect of silver is to increase hardness by about 2 HV.

The high temperature oxidation behaviour of cast superalloys strengthened by carbides has been studied as a function of their grain fineness and their dendritic orientation near the surface. These microstructural features have both a significant influence on the oxidation kinetics. The effect depends on the nature of the base metal of the superalloy, on the overall chemical composition or on the types of carbides.

Because of the effects that they produce, grinding operations may modify significantly the surface of a material and change its properties. The major part of the plastic work of cutting is tranferred to the part being ground as heat. In the case of the austenitic stainless steel studied here, grinding leads to an increase in hardness which can be attributed to the superficial plastic deformation of the material. However, for the most severe grinding conditions, a change in the deformation process is observed leading to dynamic recrystallization. This process is characterized by grain growth and dislocation rearrangement under the combined effect of the temperature and the stress level reached during grinding.

After two previous reconsideration steps on cathodic charging and hydrogen stress cracking, then permeation measurements, a third step is presented on the SOHIC mechanism, and more generally any interaction between internal hydrogen and moving dislocations. This results in a unified mechanism for all forms of hydrogen damage, built ex-nihilo from the mere data on metal electronic structure, the physical state of the H+ ion in water, steel micrographic structure and dislocations movement. There are already many practical and theoretical consequences.

Tests were performed on austenitic stainless steels. In order to investigate thermal fatigue resistance of quasi-structural specimens, test facilities enforcing temperature variations similar to those found under the operative conditions have been developed. Multiple cracking networks similar to those detected during in-service inspections have been reproduced. Experiments and simulations deal with crack initiation and crack growth. In the case of multiple cracking simulation, a Skelton's modelling has been used. A shielding effect between cracks is evidenced. It leads to a dramatic reduction of crack growth rate. Such effect is also crucial for the crack network stability under additional loading.

In Valchiusella, near Traversella on the left side of the Chiusella river, some rivets in steels were found and they can be dated at the end of the 18th century and the beginning of the 19th one. The chemical analysis has pointed out that the steel is very poor in carbon, but in the essentially ferritic structure, some significant pearlitic zones have been observed by metallography in the core of the product, as it could be expected if a forging carburizing treatment was applied. Some fragments of entrapped slags have been detected within the analyzed steel products and have been chemically analyzed by EDS as well as the slags found in the rivet and the non-metallic inclusions of the steel. The chemical composition of the non-metallic compounds has been investigated by the software ThermoCalc. The data obtained have been compared with the results of the metallographic analysis of the steel. The thermodynamic conditions for the production of the investigated steels have been underlined in order to improve the knowledge of the features of the reduction process used during that period.