Tem study of twin boundary dislocations in cadmium

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A DISLOCATION MECHANISM FOR THE GROWTH OF TWINS IN DEFORMED HCP METALS

Des macles mécaniques ont été examinées par MET dans les métaux hexagonaux comme Zn, Cd, Zr, Ti. En particulier, les joints contenant des dislocations intrinsèques ont été examinés. Les caractéristiques de ces dislocations ont été étudiées à partir de leur contraste et par diffraction électronique. Il est déduit que dans les cas du Zn et du Cd, les macles mécaniques croissent par le mouvement de dislocations dont les vecteurs de Burgers sont déduits des caractéristiques des macles mécaniques. Dans le Zr et le Ti des familles de dislocations intrinsèques parallèles à la direction de coincidence sont observées.Deformation twins in hexagonal metals are examined by TEM. The materials studied are Zn, Cd, Zr, Ti. The observations are focussed on the twin boundaries that contain intrinsic dislocation structures. The characteristics of these dislocations are analysed using contrast and electron diffraction techniques. It is deduced that in Zn and Cd deformation twinning proceeds by a dislocation mechanism in which the glide of the dislocation as well as its Burgers vector are connected with the crystallographic elements of the twinning mechanism. In Zr and Ti parallel arrays of intrinsic dislocations, with lines along coincident direction in both grains, are also observed

COINCIDENCE IN HEXAGONAL MATERIALS

L'analyse de joints de grains a été réalisée sur des métaux à structure hexagonale compacte après recuit (zirconium) ou après recuit et déformation (zinc, cadmium, magnésium) et sur des céramiques (carbure de tungstène-cobalt, carbure de silicium, nitrure de silicium). Dans les métaux hexagonaux, des joints en coïncidence ou proches de la coïncidence sont fréquemment observés. Pour les céramiques : le carbure de tungstène-cobalt, à la différence des deux autres céramiques, présente une très forte proportion de joints en coïncidence.Grain boundaries have been analyzed in different hexagonal materials : hexagonal close packed metals after annealing (zirconium) or after annealing and deformation (zinc, cadmium, magnesium), hexagonal ceramics (tungsten carbide-cobalt, silicon carbide, silicon nitride). For the hexagonal metals, coincidence or near coincidence grain boundaries are often observed. In the case of ceramics, tungsten carbide-cobalt, unlike silicon carbide and silicon nitride, exhibits a great deal of coincidence grain boundaries

Evolution of Relationships Between Dislocation Microstructures and Internal Stresses of AISI 316L During Cyclic Loading at 293 K and 573 K (20 °C and 300 °C)

The evolution of dislocation densities and of dislocation microstructures during cyclic loading of AISI 316L is systematically evaluated. In addition, internal stresses are also measured for every cycle and comprehensively analyzed. These observations are made in order to establish relationships between the evolution of dislocation condition and internal stresses, and ultimately to obtain a thorough insight into the complex cyclic response of AISI 316L. Moreover, the dependencies of established relationships on the variation of temperature and strain amplitude are investigated. The back stresses (long-range stresses associated with the presence of collective dislocations over different length scales) are mainly responsible for the cyclic deformation response at high strain amplitudes where dislocations tend to move more quickly in a wavy manner. In contrast, the effective stress, coupling with short-range dislocation interactions, plays an insignificant role on the material cyclic response for wavy slip conditions, but increasingly becomes more important for planar slip conditions. The additionally strong short-range interactions between dislocations and point defects (initially with solute atoms and later in life with corduroy structure) at 573 K (300 °C) cause dislocations to move in more planar ways, resulting in a significant increase in effective stress, leading to their influential role on the material cyclic response.ISSN:1073-5623ISSN:1543-194