The effects of post annealing on the mechanical properties, microstructure and texture evolutions of pure copper deformed by twist extrusion process

X-ray diffraction peak broadening analysis showed that performing a proper heat treatment between the twist extrusion passes of commercially pure copper decreased the coherent domain size and increased the microstrain. Moreover, SEM micrographs illustrated that annealed material contained new formed grains that could not grow due to lack of sufficient time. Under such circumstances, the ultimate strength was elevated about 45 MPa. The deformed material showed texture of simple shear deformation, changing by applying the post annealing.     

Grain refinement of HAZ in multi-pass welding

A technique named Impacting Trailed Welding (ITW) was proposed, aimed at refining the grain size of the HAZ in multi-pass welding. The key idea of ITW is to obtain a large deformation in the HAZ during one weld pass, and get it recrystallized during the next weld pass. Theoretical analysis suggests that the deformed HAZ can get completely recrystallized and the degree of the successive grain growth is lower than the normal grain growth, so that the grains can be dramatically refined. The average grain size was reduced by a factor 2 through the application of the ITW technique, and remained close to the grain size of the base material. The results are consistent with the theoretical analysis.     

A study of manufacturing tubes with nano/ultrafine grain structure by stagger spinning

A new method of manufacturing tubes with nano/ultrafine grain structure by stagger spinning and recrystallization annealing is proposed in this study. Two methods of the stagger spinning process are developed, the corresponding macroforming quality, microstructural evolution and mechanical properties of the spun tubes made of ASTM 1020 steel are analysed. The results reveal that a good surface smoothness and an improved spin-formability of spun parts can be obtained by the process combining of 3-pass spinning followed by a 580 °C × 0.5 h static recrystallization and 2-pass spinning with a 580 °C × 1 h static recrystallization annealing under the severe thinning ratio of wall thickness reduction. The ferritic grains with an average initial size of 50 μm are refined to 500 nm after stagger spinning under the 87% thinning ratio of wall thickness reduction. The equiaxial ferritic grains with an average size of 600 nm are generated through re-nucleation and grain growth by subsequent recrystallization annealing at 580 °C for 1 h heat preservation. The tensile strength of spun tubes has been founded to be proportional to the reciprocal of layer spacing of pearlite (LSP), and the elongation is inversely proportional to the reciprocal of LSP. This study shows that the developed method of stagger power spinning has the potential to be used to manufacture bulk metal components with nano/ultrafine grain structure.     

Twinning, dynamic recovery and recrystallization in the hot rolling process of twin-roll cast AZ31B alloy

Hot-rolling experiments with a reduction from 10% to 60% in single pass were conducted on AZ31B twin-roll cast sheets. Optical microscope (OM), electron backscattered diffraction (EBSD) tests and transmission electron microscope (TEM) were used to investigate twinning and DRV/DRX behaviors at different stage in the hot-rolling process. Two types of twinning occurred in the initial stage of hot-rolling process. DRV and discontinuous recrystallization dominated at moderate strain while continuous DRX took place homogeneously throughout original grains at the largest strains.     

Measurement,Correlation and Thermodynamics of Solubility of 2,6‐Diamino‐3,5‐Dinitropyrazine‐1‐Oxide (LLM‐105) in Eight Solvents

The solubility of insensitive explosive 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) in dimethyl sulphoxide (DMSO), N,N‐dimethylformamide (DMF), N‐methyl‐2‐pyrrolidone (NMP), N,N‐diethylformamide (DEF), 1,4‐dioxane, 1,4‐butyrolactone, ethyl acetate and 1‐butyl‐3‐methylimidazolium trifluoromethanesulfonate ([Bmim]CF₃SO₃), were measured by a polythermal method in the temperature range of 293.15 K to 375.15 K at the atmospheric pressure. The solubility of LLM‐105 decreased in the order of DMSO, NMP, DMF, DEF, 1,4‐butyrolactone, [Bmim]CF₃SO₃, 1,4‐dioxane, ethyl acetate. With higher temperature, the solubility of LLM‐105 increased in all solvents. The solubility data was correlated against temperature with the modified Apelblat equation and Ideal solution model. In addition, the dissolution enthalpy, entropy, and mole Gibbs free energy of LLM‐105 in each solvent were also calculated from the experimental solubility data by using van′t Hoff equation with the temperature dependence. The results show that the dissolution process of LLM‐105 in these solvents is endothermic and the mechanism is the entropy‐driving. DMSO is suggested as the appropriate solvent for the cooling crystallization or drowning‐out crystallization of LLM‐105.     

On the room-temperature annealing of cryogenically rolled copper

The electron-backscatter-diffraction (EBSD) technique was applied to investigate room-temperature annealing processes in cryogenically rolled copper during long-term (∼1.5 years) storage at ambient temperature. Static recrystallization appeared to be nucleated as result of both grain-boundary bulging and recovery. A bimodal recrystallized grain size distribution appeared to be a result of these two competing mechanisms. The ultra-fine grain copper produced via cryogenic deformation was deduced to be prone to abnormal grain growth after long static storage at room-temperature.     

Surface grain structure evolution in hot rolling of 6061 aluminum alloy

During hot deformation of Al–Mg–Si alloys, a non-uniform microstructure is developed due to differences in localized strain. Physical simulations were performed to examine the effects of processing parameters such as deformation temperature, total reduction, rolling schedule and alloying additions on the grain structure evolution. Overall, the kinetics of recrystallization followed the traditional trends predicted by JMAK kinetics. Electron backscatter diffraction (EBSD) was used to quantify the difference in recrystallization kinetics at the sample surface and mid-thickness. The results showed that the surface showed elevated kinetics when compared to the sample mid-thickness.     

Observation of Coalescence Process of Silver Nanospheres During Shape Transformation to Nanoprisms

In this report, we observed the growth mechanism and the shape transformation from spherical nanoparticles (diameter ~6 nm) to triangular nanoprisms (bisector length ~100 nm). We used a simple direct chemical reduction method and provided evidences for the growth of silver nanoprisms via a coalescence process. Unlike previous reports, our method does not rely upon light, heat, or strong oxidant for the shape transformation. This transformation could be launched by fine-tuning the pH value of the silver colloidal solution. Based on our extensive examination using transmission electron microscopy, we propose a non-point initiated growth mechanism, which is a combination of coalescence and dissolution–recrystallization process during the growth of silver nanoprisms.     

Ultrasonic velocity measurements for characterizing the annealing behaviour of cold worked austenitic stainless steel

Precise measurements of shear wave velocities have been made in 20% cold worked and annealed samples of alloy D9 (Ti-modified austenitic stainless steel) to characterize the microstructural changes during annealing. The variation in wave velocity with annealing time exhibited a three stage behaviour. In the first stage, a slight increase in the velocity during recovery regime has been observed. This is followed by a significant increase in the velocity in the recrystallization regime (second stage) and reaching saturation on completion of recrystallization (third stage). Microstructural observations using optical metallography confirmed these three stages. The maximum variation in velocity is observed only when the polarization or the propagation direction of the shear wave is alingned with the cold working direction. Variation in shear wave velocity during annealing process, in general, is just opposite to that of the variation in longitudinal wave velocity. A number of velocity measurements were made by changing the propagation and polarization directions of the shear waves with respect to the cold working direction. Based on these measurements, a suitable velocity ratio parameter is suggested for determining the degree of recrystallization during annealing of cold worked alloy D9.     

Automatic determination of recrystallization parameters based on EBSD mapping

A new automatic algorithm for determining the recrystallization parameters V_V, S_V and <λ> based on EBSD mapping is presented in this paper. The algorithm is validated on aluminium deformed to high strains. The algorithm is also compared with other methods using the exact same sets of samples, and it is found that the present method gives better results for S_V.