Search

The generalized stacking fault energies of magnesium and their alloys have been calculated using density functional theory. It is shown that the deformation tendency caused by partial dislocations emission varies with alloying elements. Three slip systems have been considered: (0001)[1120], {1 00}[ 20] and (0001)[1100]. It has been shown that Pb and Sn strongly change the generalized stacking fault energy of Mg, thus reducing the stacking fault energy. [ABSTRACT FROM AUTHOR]

Owing to their stimulating effects on bone cells, ceramics are identified as expressly promising materials for fabrication of tissue engineering (TE) scaffolds. To ensure the mechanical competence of TE scaffolds, it is of central importance to understand the impact of pore shape and volume on the mechanical behaviour of the scaffolds, also under complex loading states. Therefore, the theory of continuum micromechanics is used as basis for a material model predicting relationships between porosity and elastic/strength properties. The model, which mathematically expresses the mechanical behaviour of a ceramic matrix (based on a glass system of the type SiO2–P2O5–CaO–MgO–Na2O–K2O; called CEL2) in which interconnected pores are embedded, is carefully validated through a wealth of independent experimental data. The remarkably good agreement between porosity based model predictions for the elastic and strength properties of CEL2-based porous scaffolds and corresponding experimentally determined mechanical properties underlines the great potential of micromechanical modelling for speeding up the biomaterial and tissue engineering scaffold development process—by delivering reasonable estimates for thematerial behaviour, also beyond experimentally observed situations. [ABSTRACT FROM AUTHOR]

Plastic deformation can produce materials with different structural states. Strained BCC-metals have been shown to undergo internal structural developments during plastic deformation. The interaction between quasi-cleavage crack and substructure was studied. The details of the influence of substructure on stress near the crack tip, structure rebuilding near the crack tip and the energy of dislocation movement were analyzed. The essential influence of the deformation substructure on the force and energy parameters of fracture processes was established. [ABSTRACT FROM AUTHOR]

Severe plastic deformation by torsion was applied to refine the structure of Ni3Al intermetallic compound. Transmission electron microscopy (TEM) observations revealed that in as-deformed state the intermetallic crystal structure was disordered. In order to investigate the dynamics of the transition from the disordered to the L12 lattice structure, in situ TEM annealing experiments were performed. These experiments and studies of the bulk material have revealed details of the processes taking place during annealing of severely deformed Ni3Al. [Copyright &y& Elsevier]

The generalized stacking fault energy for aluminium and some of its alloys have been calculated using density functional theory. It is shown that the deformation tendency caused by emission of partial dislocations varies with alloying element. The twinnability of aluminium is also modified by the presence of alloying element in the deformation plane. The results suggest that Al–Mg and Al–Ga alloys are the most susceptible for the deformation by partial dislocations and twining. [ABSTRACT FROM AUTHOR]

Abstract: The structure and mechanical properties of Ni subjected to severe plastic deformation by means of equal channel angular pressing (ECAP) followed by cold rolling or high-pressure torsion were investigated. A material with uniform ultra-fine-grained (UFG) microstructure and mean grain size in the range from 100 to 600nm, depending on the processing procedure, was obtained. Tensile tests at room temperature revealed ultimate tensile strength values in the range from 840 to 1270MPa and an elongation to fracture in the range from 7 to 12% depending on the processing method. Annealing at 200°C of the sample deformed by ECAP and cold rolling led to the best combination of strength and plasticity. The strength of the material was well above the level expected from the Hall–Petch rule. We explained this high strength by taking into account dislocations trapped at grain boundaries (TLDs). In ultra-fine-grained (UFG) materials the specific surface of grain boundaries is high and therefore the TLDs density is high as well. The fracture and deformation relief indicate an important role of grain-boundary sliding and grain rotation as deformation mechanisms. The UFG high-strength Ni with relatively good ductility has a potential for applications in particular in microsystems, where the cross section of the material is in the micrometer range but still must cross a sufficient number of grains to look structurally uniform. [Copyright &y& Elsevier]