Influence Of Initial Grain Size Research Articles

A new cellular automata model for hot deformation behavior of AZ80A magnesium alloy considering topological technique

In this paper, the CA model of grain topological deformation technique (T-CA) and the physical constitutive model considering strain are introduced to study the hot deformation behavior of extruded AZ80A magnesium alloy. The isothermal compression test of extruded AZ80A magnesium alloy was carried out on the Gleeble-3800 thermal simulator. The deformation temperature and strain rate were 598 K∼723 K and 0.001 s−1∼1 s−1, respectively. According to the experimental results, a phenomenological constitutive model of flow stress considering strain was constructed. The reliability of the model was verified by comparing the experimental and predicted flow stress. The influence of thermal deformation parameters, i.e., deformation temperature, strain rate, and strain, on the DRX kinetic curve and grain size evolution was studied based on the CA model with the introduction of grain topological (T-CA) deformation technology. Meanwhile, the influence of initial grain size on dynamic recrystallization was studied using the conventional CA model (C-CA) and the CA model with topological deformation (T-CA) technology. Finally, the accuracy of the T-CA model was verified by combining physical experiments and electron backscatter diffraction (EBSD) technology. At the temperature of 598 K, the strain rate of 0.1 s−1, and the strain of 0.91, the error between the average grain size simulated by the topological CA (T-CA) model and the experimental results is 7.6 %, which is consistent with the experimental results. When the initial grain size is 43 µm, compared with the conventional CA simulation method (C-CA), the CA simulation method with the introduction of grain topological deformation can promote the occurrence of recrystallization, improving the simulation speed and accuracy. The error between the percentage of recrystallization and the experiment is 4.5 % and 3.2 %, respectively, indicating that the simulation method with the introduction of grain topological deformation (T-CA) can accurately predict the dynamic recrystallization behavior of AZ80A magnesium alloy.

The role of initial grain size on bimodal-grained microstructure and mechanical properties of an extruded Mg-Gd-Y-Nd-Zr alloy

Influence of initial grain size on the formation of bimodal-grained microstructure and mechanical properties of a Mg-11Gd-3Y-0.5Nd–Zr alloy was investigated. The results indicate that the fraction of unrecrystallized (un-DRXed) grains in bimodal-grained microstructure was governed by the initial grain size, and the fraction increases with the increasing of initial grain size. Formation of un-DRXed grains in samples with a small initial grain size is induced by the uneven distribution of grain size, in which coarser grains is more difficult to recrystallize. However, the recrystallization behavior in samples with large initial grain size is mainly affected by the difference in orientation among grains, and grains with orientation that are not favored for slip are difficult to recrystallize. The strength increases while the elongation decreases with the increasing of initial grain size. The sample with the highest initial grain size (178 μm) accordingly shows the best ultimate tensile strength of 459 MPa. The higher strength is mainly due to the higher texture strengthening and hetero-deformation induced (HDI) strengthening provided by higher fraction of un-DRXed grains.

Grain-size affected mechanical response and deformation behavior in microscale reverse extrusion

The continuing demand on device miniaturization has motivated the interest in micro metal forming technologies for manufacturing metal parts with sub-mm characteristic dimensions. In this work, axisymmetric reverse extrusion experiments were conducted on Cu 110 and Al 1100 alloy rod specimens with widely varying initial grain sizes, achieved through equal channel angular pressing (ECAP) and post annealing. Accompanying crystal plasticity finite element (CPFE) simulations were carried out. At a characteristic extrusion dimension (CED) of ∼100 µm, defined by the sidewall thickness of the extruded cup-shaped structures, the deformation characteristics of the reverse extrusion process were investigated. Specifically, the characteristic plastic strain for extrusion and the influence of initial grain size on the extrusion mechanical response and shape of extruded parts were examined in detail through scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), in combination with CPFE simulations. The mechanical response of extrusion showed deviations from continuum scaling behavior as the CED became small as compared to the initial grain size. The present study serves as a baseline for further studies of metal forming at the meso to micro scales.

Investigation on initial grain size and laser power density effects in laser shock bulging of copper foil

Laser shock bulging process is a promising flexible microforming method in which the laser shock wave pressure is employed to cause plastic deformation and fabricate microfeatures on thin sheet metals. However, the influence of initial grain size and laser power density on the forming quality of bulged parts has not been well understood. In this paper, three various initial grain sizes as well as three levels of laser power densities were provided, and then, laser shock bulging experiments of T2 copper foil were conducted. The characteristics of bulging height, thickness distribution, microhardness, surface morphology, and microstructure were examined. It is revealed that the bulging height increases with the increase of grain size and the enhancement of laser power density. The exhibiting good formability of pure copper foil in laser shock bulging process is attributed to the inertial effect on necking stabilization and strain-rate effect on material constitutive behavior. The overall thickness of bulged parts decreases compared with its original thickness. Moreover, the microhardness in the laser-shocked region increases due to the strain hardening effect, but the microhardness distribution is nonuniform because of the inhomogeneous plastic deformation. The grain sizes of bulged parts are slightly refined with the increase of laser power density, especially for the coarse-grained part. The grain refinement in laser shock bulging forming process is attributed to the large plastic deformation at high strain rates under laser shock.

The Influence of Initial Grain Size and Strain Sequence of Slab Hot Rolling on the Austenite Evolution of Peritectic Microalloyed Plate Steels

The influence of the strain sequence during slab hot rolling (also known as “roughing”) on the evolution of austenite in plain carbon, C-Mn-V and C-Mn-Nb-Ti-V steels was investigated. Reheating and roughing simulations were conducted in a Bähr deformation dilatometer using a constant austenitising temperature, constant soaking time and various heating rates and roughing strain sequences. Stress analysis was used to quantify the austenite softening behaviour and the prior austenite grain size was measured from quenched specimens. The austenite grains of the plain carbon steel were coarser than those of both microalloyed steels, with the C-Mn-Nb-Ti-V grade being the finest due to effective pinning of the grain boundaries. Pass strains greater than 0.2 were sufficient for initiation of dynamic recrystallisation (DRX) for the C-Mn and C-Mn-V steels and led to uniform austenite microstructure with austenite grain sizes less than 40µm after the roughing stage.

Warm Forming of FCC Poly Crystals: The Effect of Grain Size under Different Forming Conditions on the Softening Behavior

Ingot breakdown is the most significant process for achieving high-quality billets in the cogging process. Especially microstructure evolution and grain refinement during the plastic deformation are of technical interest for the metal forming industry. To obtain refined and uniform microstructures after processing, it is necessary to understand deformation mechanisms as well as recovery-and recrystallization phenomena. Polycrystalline pure nickel and cast structured austenitic stainless steels were deformed by a compression test at different warm forming temperatures (800-1200°C) to investigate the influence of initial grain size, strain and strain rate on the structural refinement process. To get rid off static-and postdynamic softening processes the samples were immediately water quenched after deformation. By using the electron back scatter diffraction technique, the microstructural evolution and the crystallographic orientations were captured after deformation.

Effect of grain size in compression deformation on the microstructural evolution of an austenitic stainless steel

Abstract The influence of initial grain size on the dynamic recrystallization behavior has been investigated in a commercial austenitic stainless steel. Compression tests were performed at constant temperatures of 810, 980 and 1150 °C at an average strain rate ϵ ˙ of 0.01 s −1 and 0.1 s −1 . In order to capture the microstructural evolution after the deformation the electron back scatter diffraction technique (EBSD) was used. The results show that nucleation of new grains is strongly grain size dependent. Increasing the grain size of the material reduces the stored energy measured in terms of kernel average misorientation, well known as driving force for dynamic recrystallization. This leads to the problem of grain refinement in coarse structured materials. Applying large plastic strains or using static recrystallization in a double hit forming process seems promising for an efficient refinement strategy.

Processing map for hot working of Inconel 718 alloy

Cylindrical specimens of Inconel 718 alloy with grain size of 90 μm were used in the compression tests and processing maps at the strains of 0.1, 0.3, 0.5 and 0.7 were developed at 950–1150 °C in the strain rate range 0.001–100 s −1. Only one unstable region for adiabatic shear bands and one small dynamic recrystallization zone in the stable region are exhibited in the processing map at 0.1 strain. As the strain is beyond 0.3, there exist three unstable regions in the processing maps where one is for adiabatic shear bands and the other two are for intergranular cracking. At the same time, the zone of dynamic recrystallization with a peak efficiency of 0.39 at about 950 °C and 0.001 s −1 in the stable region is enlarged and the distribution of which is from lower temperature and lower strain rate to higher ones. Optical micrographs of the specimens compressed to 0.7 strain show good agreement with the processing maps and main hot working schedules have been designed. Influence of initial grain size from 10 μm to 90 μm on the occurrence temperature of adiabatic shear bands and intergranular cracking has been analyzed at a strain rate of 100 s −1 and in the temperature range 900–1200 °C.

Effect of Initial Austenite Microstructure on the Softening – Precipitation Interaction in a Low Nb Microalloyed Steel

The influence of initial grain size on the softening-precipitation interaction in a low niobium microalloyed steel has been investigated. The study has revealed that for the largest initial grain size (1000 μm), the recrystallised fraction remains lower than the softening fraction until relatively long times are reached. In contrast, for the smallest initial grain size (166 μm) both magnitudes are similar. As a result, precipitation interacts with recrystallisation in the case of the finest austenite grain size, whereas for the coarsest one, since recrystallisation is significantly retarded, interaction with recovery process is observed. Apparently, the initial austenite grain size does not affect precipitation kinetics.

Cube Textured Substrates for YBCO Coated Conductors: Influence of Initial Grain Size and Strain Conditions During Tape Rolling

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The realization of high critical current density YBCO-based coated conductors in the RABiTS approach is primarily related to the sharpness of cube texture developed in the substrate. Among the various proposed Ni-based tapes, Ni-W alloys have attracted a particular interest either because of the enhanced mechanical properties and reduced magnetism with respect to pure Ni, or of the sharp and almost pure cube texture that can be induced. The only other remarkable component associated with cube orientation consists of its twins, whose formation is known to be primarily determined by the stacking fault energy, which is a characteristic of the material. Despite this fact, the obtained textures for a given material can significantly vary, suggesting that the deformation regime, as well as the initial bulk conditions, have a role in influencing twins formation. In this contribution, the effect of the strain conditions during mechanical deformation and initial bulk grain size on the final recrystallization texture are evaluated. EBSD and x-ray analyses evidence the influence of the initial grain size on the recrystallization texture, since sharper cube textures with reduced non-cube components develop in finer-grained starting material. Conversely the condition of plane strain deformation plays no role in determining the recrystallization texture. </para>

Influence of thermomechanical treatments on the production of rheocast slurries by partial melting

This work deals with the influence of thermomechanical treatments on the production, by partial melting, of rheocast structures of Al–3.35wt.%Cu alloy. Two types of treatments are performed: recrystallization and partial melting (RAP), in which the alloy is submitted to cold work at room temperature prior to heating to the semi-solid state; and overaging treatment (OAT), where the alloy is submitted to homogenisation and controlled precipitation of second phase followed by deformation at room temperature and heated to temperatures above Tsolidus. The influence of initial grain size, degree of cold work and overaging conditions in the resulting microstructure is investigated. Results are presented in terms of Cu distribution, solid fraction, globule diameter and shape factor. For both processes there are substantial reductions in the globular primary phase size compared to initial grain sizes, this reduction being more significant for rheocast produced via the OAT than the RAP route. The degree of previous deformation only influences the final globule diameter of the rheocast structure obtained by the OAT process, while initial grain size influences globule diameter in both processes. Changes in shape factor with process parameters show that different mechanisms are operative during rheocasting, such as recrystallization coarsening and coalescence; the predominance of one of them depending on the initial microstructure of the material. In general, OAT produces more rounded and smaller globules than RAP, mainly from higher deformed and coarser raw material, due to the predominance of recrystallization.

Ductility of nanocrystalline zirconia based ceramics at low temperatures

The ductile behavior of nanophase yttria doped zirconia ceramics was investigated during low-temperature deformation experiments. Ceramics were produced by following a standard processing route of mechanical compaction of the dispersion mixed nanoparticles synthesised by the inert gas condensation or chemical vapor condensation technique and pressureless sintering. Uniaxial forming in tension has been performed in air at temperatures below 0.5 T m. The influence of initial grain size and porosity on strain and strain-rate has been a topic of interest as well as the microstructural evolution during deformation. Constant load tests and tests with stress- and temperature-jumps have been carried out to estimate the thermomechanical parameters, strain-rate-sensitivity exponent, activation energy and grain-size exponent of 10 wt.% yttria partially stabilized zirconia. A maximum elongation of about 60 % has been achieved with a ZrO 2 + 10 wt.% Y 2O 3 + 12 wt.% A 2O 3 composite ceramic at 1250 °C. The results were related to a deformation model based on mesoscopic grain boundary sliding.

Evolution of the Microstructure in the Processes of Hot Compression and Drawing-Rolling.

The paper deals with the problem of the prediction of the microstructure evolution during the hot deformation of carbon-manganese steels. The objective of the work is the validation of the approach which incorporates an advanced thermal-mechanical finite-element model with the conventional closed form equations describing processes of static recrystallization and grain growth. Two types of the experiments are performed. The first is a typical multistage hot compression test for the axisymmetrical samples. The second is hot drawing of the flat samples through a set of the roller dies. An influence of initial grain size, starting temperature, strains and interpass times is investigated. The results include validation of various equations describing austenite grain size and kinetics of static recrystallization for the carbon-manganese steels.

Superplastic forging procedures for manufacture of ceramic yttria stabilised tetragonal zirconia products

AbstractThe influence of initial grain size and density on the deformation behaviour of fine grained yttria stabilised tetragonal zirconia (YTZ) polycrystals has been studied. The presence of very fine (0·2–0·25 μm) grains at the start of straining, together with appreciable initial porosity, leads to an increase in the formability of these usually brittle ceramics. As a result, relatively high strains can be applied at sufficiently low temperatures and high strain rates, such that products of complex shape can be manufactured from YTZ compacts.

Effect of composition and initial grain size on the dynamic recrystallization of austenite in plain carbon steels

The effect of composition on the dynamic recrystallization behavior of plain carbon steels has been examined in the temperature range 850 to 1300 °C and the strain-rate range 6 × 10-6 to 2 × 10-2 s-1. With increasing solute content, the onset of dynamic recrystallization is delayed and the rate of recrystallization is decreased. At 1000 °C the elements can be ranked in order of increasing effectiveness as C, Ni, Mn, Si, P. At higher temperatures the effect of composition is complicated by its effect on grain coarsening, which itself postpones the onset and slows the rate of recrystallization. Similarly, for steels in which precipitation may occur, a fine-grain structure can promote the earlier onset and faster rate of recrystallization. Thus, out of an examination of the effect of composition comes an appreciation of the influence of initial grain size. Another factor which can complicate any explanation of the compositional dependence of dynamic recrystallization is grain-boundary segregation, which is probably responsible for the strong retarding influence of phosphorus.