Behavior Of Nanocrystalline Materials Research Articles

In situ neutron diffraction study of drawn pearlitic steel wires upon tensile deformation

Abstract The strengthening mechanism of heavily cold-drawn pearlitic steel wires was studied using the highresolution neutron diffraction experiment performed in situ upon tensile deformation. Microstructural parameters of lattice strain, microstrain and coherent block size, the evolution of which evidences the deformation mechanism of this ultrahigh strength steel, were extracted from the position, width and shape of the in situ recorded neutron diffraction profiles, respectively, using a newly proposed method of profile shape analysis. It was found that the deformation mechanism of cold-drawn pearlitic steel wires resembles the behavior of nanocrystalline materials.

Disclination Mechanism of Plastic Deformation of Nanocrystalline Materials

A model describing mechanical behaviour of nanocrystalline materials (NC) obtained by crystallization from amorphous precursor is presented. In the framework of this model a structure of such NCs is represented as a composite consisting of amorphous matrix and absolutely rigid inclusions corresponding to crystalline phase. Dependencies of stress concentration coefficient and yield stress of NCs on the average grain size are obtained. It is shown that the dependence of the yield stress has a point of inflection at the critical grain size in the range of 20–25 nm and is inverse to the Hall-Petch relationship at grain sizes smaller than the critical one. The model predicts a formation of a superlattice from disclinations located in triple junctions of grains on the stage of NC plastic flow. A process of the plastic flow of NC's amorphous matrix and amorphous metallic alloys is described as a go-ahead mechanism of dislocation movement, which includes emission, absorption and reemission of dislocations by disclinations.

Disclination-Dislocation Model of the Mechanical Behaviour of Nanocrystals Prepared by Crystallization from Amorphous Precursor

A model of plastic deformation of nanocrystalline materials as an evolution of a space network of disclinations located in triple junctions of grains is developed. The plastic deformation is executed as a result of plastic rotation of grains, mismatch of which causes an appearance of partial disclinations in joint intergranular boundaries. A process delaying the increase of capacity of Frank vectors at the stage of plastic flow is a go-ahead mechanism of dislocation movement, which includes emission, absorption and reemission of dislocations by disclinations. It is shown that important peculiarity of mechanical behaviour of nanocrystalline materials is a deviation of yield stress from the Hall-Petch relation up to the critical size of grain in the range of 25-30 nm.

Remark to the magnetocaloric behavior of nanocrystalline materials

Remark to the magnetocaloric behavior of nanocrystalline materials

A modified model for hall-petch behavior in nanocrystalline materials

A modified model for hall-petch behavior in nanocrystalline materials

Low temperature magnetization behavior in nanocrystalline materials: spin waves

The low-temperature magnetization behavior of ferromagnetic ribbons with the composition Fe/sub 73.5/Si/sub 13.5/B/sub 9/Cu/sub 1/Nb/sub 3/ in amorphous, and partially and fully crystallized states was studied in the high applied field regime (5T) using a SQUID (superconducting quantum interference device) magnetometer. The experimental data can be explained by means of the usual spin waves model. The spin wave stiffness constant D was determined. The values of D depend strongly on the degree of crystallization.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>