Papers by Keyword: Dynamic Recrystallization (DRX)

Abstract: The process of new fine grain formation was studied in compression of a Ni-20%Cr alloy at temperatures ranging from 500°C (0.46Tm) to 950°C (0.73 Tm) at a strain rate of 710-4 s-1. Two types of deformation behaviors with different features of microstructure evolution were observed, depending on processing conditions. The deformation behavior under flow stresses below about 500 MPa (relatively high temperatures) was typical for hot working associated with discontinuous dynamic recrystallization (DRX). The extensive local migration (bulging) of both initial and deformation induced high angle boundaries (HAGBs) resulted in the development of nuclei, which grew out leading to the formation of recrystallized structure with grain size of D > 1 m. Numerous annealing twins were observed within these DRX grains. On the other hand, continuous DRX gave a major contribution to the formation of new grains at applied stresses above 500 MPa (relatively low temperatures). This fact was attributed to a low mobility of grain boundaries. The new grains with size of D < 1 m were evolved due to gradual transformation of deformation induced low angle boundaries (LAGBs) into HAGBs.

Abstract: On the basis of generalization of research results obtained at the Institute for Metals Superplasticity Problems, principles of fabrication of bulk ultrafine-grained and nanostructured materials by multiple isothermal forging are formulated. Multiple isothermal forging is shown to be a universal high-performance deformation technique for the grain refinement in metals and alloys maximally exploiting the potential of dynamic recrystallization.

Abstract: The major problem restricting universal employment of intermetallic phase base alloy is their low plasticity which leads to hampering their development as construction materials. The following work concentrates on the analysis of microstructure and plasticity of ordered Fe3Al (D03) and FeAl (B2) during hot plastic deformation process.. The microstructure analyses applying optical electron microscopy and EBSD method have revealed the structure reconstruction processes occurring in Fe3Al and FeAl alloys. It has been shown that different mechanisms of the structural changes ensue from the thermal plastic strain in the investigated alloys, which influences their technological plasticity.

Abstract: Composite systems composed of nanocrystalline apatites and oligolactide-based polymer networks were prepared resulting in malleable and even injectable formulations which can be cured to compact materials at body temperature. Porous devices with inter-connective porosity were obtained after addition of suitable foaming agents to the composite mixtures. Setting time, porosity and mechanical properties of the composites can be properly adjusted by varying the educt composition. The determined compressive strengths and Young’s moduli of the porous composites perfectly match the mechanical characteristics of cancellous bone material. Preliminary in vitro cell culture experiments with compact composite materials demonstrated their good cytocompatibility. Based on these findings, the synthesized nano-structured composites represent promising candidates for the development of new biomaterials usable in hard tissue regeneration.

Abstract: Dynamic recovery (DRV) and dynamic recrystallization (DRX) play important roles during thermomechanical processes of light metals and alloys because they have obvious influence on microstructure evolution and finally on the mechanical properties of the worked material. Hot compression tests of 7050 aluminum alloy was carried out on Gleeble1500D thermomechanical simulator to modeling multi-pass hot rolling process. Microstructure evolution features of the alloy deformed to a reduction up to 80% were investigated through OM, TEM and EBSD observations. DRX behavior of the alloy during hot compression was emphasized. Some evidence of continuous DRX can be found in the alloy deformed at different temperatures and reductions. The main nucleation mechanisms of DRX are subgrain coalescence and subgrain growth. However, static recrystallization takes place in the material during slow cooling after hot compression.

Abstract: The hot deformation behavior of Nb-V-Ti microalloyed steel in the temperature range of 850°C～1100°C and the strain rate range of 0.001s-1～30s-1 was investigated by establishing the processing maps. The strain rate sensitivity (m), power dissipation efficiency (η) and instability parameter were calculated based on the experimental compression data and are plotted in the temperature–strain rate plane to obtain power dissipation and instability maps. The processing maps exhibit that the deformation at 1000°C and 2s-1 is one peak efficiency of power dissipation of 21%, the deformation at 1050°C and 0.01~0.001 s-1 is another peak efficiency of power dissipation of 45%. The optical microstructure observations show that they represent two dynamic recrystallization domains. Based on the above processing maps, the hot working parameters were optimized.

Abstract: The metallurgical observations of microstructure characteristics of the adiabatic shear bands(ASB) within the primary shear zones of the serrated chips produced during high speed machining high strength steel have been performed by using optical microscope, SEM and TEM. The observations showed that the microstructure between the matrix and the center of the ASB gradually was changed, the fine equiaxed grains appeared with size of about 0.4～0.6μm in the center of the adiabatic shear band. The serrated chip formation was likely due to material softening that occurred in the primary shear zones. The microstructural development of dynamic recovery and rotational dynamic recrystallization is the dominant metallurgical process leading to material softening in primary shear zone during high speed machining. A model of microstructural development in primary shear zone during serrated chip formation in high speed machining was suggested by analyzing material softening mechanism.

Abstract: The ternary system has been built by the deposit of two metal coats (layers), Gold and Palladium on a monocrystalline Silicon substrate of orientation (111). The whole system has been subjected to a vacuum heat treatment, the range of temperatures starts from 100 °C up to 600°C by steps of 50°C and with an annealing time being fixed at 30 min. Both metal layers were successively deposited without breaking the vacuum within the evaporator. The Silicon substrate had undergone beforehand a chemical treatment by the method in the CP4 to prevent it from the Oxygen barrier effect. So, we obtained few series of samples of which the characterization has been carried out by various techniques, namely: the spectroscopy of retrodiffusion of Rutherford (RBS), the diffraction of the X-rays (XRD), the scanning electronic microscopy (SEM) and its incorporated technique of Energy Dispersive X-rays (DEX). These analyses allowed us to fulfil a study of the interdiffusion

Abstract: The characteristic of dynamic recrystallization (DRX) in Mg-Y-Nd-Gd-Zr magnesium alloy had been investigated by compression test at temperatures between 523 and 723K and the strain rates ranging from 0.002 to 1s-1with maximum strain of 0.693. The flow behavior was described by a power exponent function. Processing map of this alloy was established on the basis of dynamic material model. Microstructure observations suggested that the peak value of dissipation factor was 0.36 at the temperature of 673K and the strain rate of 1s-1. The map exhibits flow instabilities as two domains, one is at the lower temperatures but higher strain rates, and the other is at higher temperatures and lower strains.The region at an intermediate temperature and a high strain rate is the region of the optimal mechanical working properties.

Abstract: A model for describing the plastic flow has been developed. The model is based on a strain dependent Garofalo equation and predicts the variation with strain of grain size refinement by dynamic recrystallization using non-linear optimization methods. The predictions have been applied to two wrought magnesium alloys, AZ31 and AZ61 and are in good agreement with experimental data.