Anomalous slip in body-centred cubic metals.

Crystal strength and plastic flow are controlled by the motion and interaction of dislocations, the line defects carrying atomic shear increments. Whereas, in most crystals, deformation develops in the crystallographic planes in which the glide force acting on dislocations is maximum, plasticity in body-centred cubic metals is more complex. Slip systems in which the resolved shear stress is not the highest can dominate at low temperature, leading to anomalous slip.

Dislocation locking versus easy glide in titanium and zirconium.

The ease of a metal to deform plastically in selected crystallographic planes depends on the core structure of its dislocations. As the latter is controlled by electronic interactions, metals with the same valence electron configuration usually exhibit a similar plastic behaviour. For this reason, titanium and zirconium, two transition metals of technological importance from the same column of the periodic table, have so far been assumed to deform in a similar fashion.

The Hall-Petch law investigated by means of in situ straining experiments in lamellar TiAl and deformed Al.

Dislocation-boundary interactions are studied in TiAl and Al by means of in situ straining experiments in transmission electron microscopes (TEM). The results in TiAl allow us to measure the strength of domain boundaries against the motion of ordinary dislocations and twins. The results in Al are used to analyze the interaction between dislocations and cell walls.

The structure of titanate nanobelts used as seeds for the nucleation of hydroxyapatite at the surface of titanium implants.

The sequence of steps of a chemical treatment having as its goal the induce of nucleation and the growth of hydroxyl carbonated apatite (HCA) at the surface of titanium implants was studied by scanning and transmission electron microscopy in cross-section. In the first step, an acid etching forms a rough titanium hydride layer, which remains unchanged after subsequent treatments. In the second step, soaking in an NaOH solution induces the growth of nanobelt tangles of nanocrystallized, monoclinic sodium titanate.

In situ observations of unusual dislocation mechanisms in the intermetallic alloy Ti3Al.

In situ straining experiments in a transmission electron microscope have been carried out on a Ti3Al intermetallic alloy, with the aim of determining the microscopic mechanisms controlling glide in prism, basal and pyramidal planes. Five different antiphase boundary energies have been measured and compared with the corresponding densities of incorrect first nearest neighbour atoms. The determination of a tension-compression asymmetry in pyramidal slip, and the detailed analysis of the complex microscopic mechanisms involved illustrate the efficiency of in situ experiments to solve complex problems in plasticity.

Dislocation mobility and electronic effects in semiconductor compounds.

In situ transmission electron microscopy experiments provide a unique way to investigate in real time the dislocation behaviour at a microscopic scale and to decide which elementary process controls the dislocation glide in semiconductors. In this review the experimental results obtained on different semiconductors are presented and discussed. Particular attention is devoted to the radiation-enhanced glide process.

Quantitative measurements in in situ straining experiments in transmission electron microscopy.

Several examples of recent studies by in situ straining experiments in a transmission electron microscope performed in the Toulouse group (France) are presented. In particular, quantitative measurements of the features of the dislocation motion are described. These examples deal with individual or collective propagation of dislocations, which are submitted to various types of obstacle.