Papers by Keyword: Dislocation Density

Abstract: The recrystallization behavior of the cold-rolled AA3003 aluminum alloy with the reduction rate of 20%, 50% and 90% during annealing at the temperature ranging from 300°C to 400°C was investigated. As increasing reduction rate, the cold rolled specimens exhibit deformation bands with elongated grain microstructure consisting of straight grain boundary parallel to rolling direction. Therefore, large density of nucleation sites for recrystallization would be expected with increase of strain energy. The grain size of the cold-rolled specimens decreased with increase of reduction rate, c.f., as the rolling reduction increased to 90%, grain size along the direction normal to the sheet decreased to about 8μm in thick. When the sample annealed at 350°C for 5s, the first recrystallized grains were observed in the vicinity of the grain boundary. The relaxation and recrystallization kinetics under different annealing conditions were characterized in terms of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model. The apparent activation energies of recrystallization for the cold-rolled specimens with reduction rate of 20%, 50% and 90% were determined as 332 kJ/mol, 239 kJ/mol and 115 kJ/mol, respectively. XRD analysis by using modified Williamson–Hall plots revealed that the tendency of the change in dislocation density is varied depending on reduction rate. These results indicate that the apparent activation energy for recrystallization and the crystallites size decrease with increase of the reduction rate, which leads to a decrease in the size of the recrystallized grains.

Abstract: Dislocation densities of GLIDCOP®, dispersion-strengthened copper with ultra-fine particles of aluminum oxide, were evaluated by employing the X-ray line profile analysis using the modified Williamson-Hall and modified Warren-Averbach methods. X-ray diffraction profiles for GlidCop samples with compressive strains applied at 200oC were measured with synchrotron radiation. The dislocation densities of GlidCop with compressive strain ranging from 0.6 to 4.3% were in the order of 3.2 × 10¹⁴–5.8 × 10¹⁴ m^-2. The dislocation density increased with increasing the compressive strain within the measured strain range.

Abstract: The mechanical properties and deformation mechanism of nickel nanowire of dimension 100 Å (x-axis) × 1000 Å (y-axis) × 100 Å (z-axis) containing a single linear surface defect is studied at different temperatures using molecular dynamics simulations. The defect is created by deleting a row of atoms on the surface and is inclined at 25° to the loading axis. The tensile test is carried out at 0.01 K, 10 K, 100 K and 300 K temperature and 10⁸ s^-1strain rate. To determine the effect of temperature on the stress-strain curves, fracture and failure mechanism, a thorough investigation has taken place. Maximum strength of 21.26 GPa is observed for NW deformed at 0.01 K temperature and the strength decreased with increase in temperature. Through slip lines, the deformation relief pattern taken place by developing the extrusion areas along with intrusion over the surface defect area in all NWs deformed at respective temperatures. Further it is observed that fracture strains decrease with increase in temperature. After yielding, stacking faults associated with dislocations are generated by slip on all four {111} planes. Different type of dislocations with both intrinsic and extrinsic stacking faults are noticed. Out of all dislocation densities, Shockley partial dislocation densities has recorded a maximum value.

Abstract: The evolution of structure, strength and ductile properties of M001 grade copper wire after the coarse and medium drawing were studied using the metallography, micro-indentation and tensile testing. Coefficient for evaluation the ultimate tensile strength from the micro-indentation data was determined. The formula was proposed for estimation the dislocation density the stress strain curves and from the data on the grain size in the transverse section of the wire.

Abstract: Dislocation densities of dispersion-strengthened copper with aluminum oxide, namely GlidCop were evaluated employing the X-ray line profile analysis using the modified Williamson-Hall and modified Warren-Averbach method. X-ray diffraction profiles for GldCop samples with compressive strains applied at ambient temperature were measured with synchrotron radiation. The dislocation densities of GlidCop with compressive strain ranging from 0 – 2.7 % were on the order of 1.5×10¹⁴ – 6.6×10¹⁴ m^-2.

Abstract: X-ray line profile analysis was performed to evaluate the microstructural characteristics of low-cycle fatigued austenitic stainless steel, AISI 316. Strains were frequently applied to the specimens with three levels of the total strain ranges, 0.01, 0.02, and 0.03. The dislocation densities at the number of cycles for each strain condition were obtained by X-ray line profile analysis. In the case that the strain range was small, that is Δε = 0.01, dislocation densities were slightly increased until 53% of life time with the cycles, and then decreased. In the case that the strain ranges were 0.02 and 0.03, the dislocation densities were steeply increased during the first stage of the life time until around 10%. However, the variations after n/N_f ≃ 10% were different each other. In the case of Δε = 0.02, dislocation density did not increase significantly until the end of the life. But in the case of Δε = 0.03, the dislocation density monotonously increased until the end of the life. These tendencies agreed with the variations of stress amplitude. The relationship between dislocation density and stress amplitude could be expressed as Δσ/2 = 1.14ρ^1/2 + 207 (Δσ [MPa], ρ^1/2 [m⁻²]).

Abstract: This study evaluated the effect of a heat treatment on the potential application of AlMg5Si2Mn die casting alloy as a substitute for wrought aluminium alloy products. The proposed heat treatment was intended to increase the workability of the AlMg5Si2Mn alloy, which is typically not malleable due to the presence of interconnected brittle phases. By disintegrating interconnected eutectic Mg2Si phases into fragmented particles and dissolving Mg-rich phases the workability was increased. Subsequently, heat treated samples were subjected to high-pressure torsion process. The microstructure of the heat treated and deformed samples were characterized using light and electron microscope. Hardness measurements were used to investigate the influence the number of HPT revolutions on mechanical properties.

Abstract: Variation of hardness and microstructure evolution in a solution treated AlMg3 aluminium processed by equal channel angular pressing and subjected to subsequent artificial ageing are investigated. The microstructure features of the UFG aluminium alloy are studied by light, electron microscopy and using X-ray diffraction analysis. Microstructural observations showed significant grain refinement. After four ECAP passes microstructure consist of elongated grains with average widths of shear bands of ∼100 nm. A significant increase in the microhardness was observed in the ECAPed samples due to the grain refinement and strain hardening. Prior ECAP solution treatment and a short time artificial ageing can additionally increase the strength of AlMg3 aluminium alloy.

Abstract: The present work investigates about the effect of pre-ageing on hardening behavior of Al-Mg-Si alloys processed by cryorolling and its age hardening behavior. Ageing conditions were examined at natural ageing for 2days and pre-ageing at 100 °C, 130°C and 170 °C for 4 hours, 2 hours and 30 minutes respectively. The observations revealed that, the pre-ageing before cryorolling is useful to enhance the dislocation density during cryorolling. However artificial ageing of cryorolled samples is not influenced much with pre-ageing. It is revealed that, maturing at room temperature of CR samples for 30 days has resulted better hardening response during artificial ageing.

Abstract: A new model to predict the structure evolution of 30Cr2Ni4MoV steel is proposed based on the dislocation density in this research. Hot compression of 30Cr2Ni4MoV steel is carried out on Gleeble 1500 at different temperatures from 1233 K to 1473 K with a strain rate of 0.01 s^-1 and the deformed samples are immediately quenched by water to frozen the austenite structure. The recrystallization kinetics model of 30Cr2Ni4MoV steel is successfully established by inverse analysis of the flow curve based on the relation between flow stress and dislocation density. In order to validate the proposed model, comparison between the predicted values and experimental values obtained by metallographic analysis is implemented. It is shown that the predicted results agree with the experimental results well.