Retardation Of Recrystallization Research Articles

Annealing hardening of the pre-deformed Cu-56at.%Au alloy due to retardation of recrystallization by L1o-type ordering

The evolution of the microstructure, physical and mechanical properties of pre-deformed samples of the non-stoichiometric alloy Cu-56at.%Au in the process of the L1o-type atomic ordering was studied. The duration of annealing at 250 °C ranged from 1 h to 2 months. Changes in microhardness and electrical resistivity at various stages of the disorder→order transition were found out, the microstructure was examined using a transmission electron microscope, XRD-scans and tensile tests were performed. Based on the resistometric results and XRD-analysis, the dependence of the fraction of the ordered phase vs. the annealing time was plotted. Consecutive changes in structural states observed during long-term annealing were considered through the competition between the energy of the elastic stresses, the surface energy and the energy of the dislocation structure. An abnormal increase in the strength properties of the alloy during annealing was found: the yield strength and microhardness of the initially deformed samples significantly increase (at 15 % and 30 %, respectively), at the same time there is a drop in electrical resistivity and an increase in plasticity. An attempt was made to describe the observed phenomena considering mutual effect of ordering and recrystallization. Discovered annealing hardening was explained in terms of the suppression of recrystallization by ordering, which is confirmed by the preservation of a high density of inherited dislocations in an ordered matrix and low plasticity of the annealed samples. The retardation in the recrystallization rate with an increase in the preliminary deformation strain of the alloy was discovered.

Retarding ice recrystallization by tamarind seed polysaccharide: Investigation in ice cream mixes and insights from molecular dynamics simulation

Food hydrocolloids, such as naturally sourced polysaccharide stabilizers, are becoming potential candidates for retarding ice recrystallization in frozen desserts. Tamarind seed polysaccharide (TSP) and its depolymerized fraction (DTSP) possessed ice recrystallization retardation (IRR) activity by a splat cooling assay. This study is a follow-up work aiming to investigate their application effects to retard ice recrystallization in ice cream mixes (ICMs) and delve into the ice-binding behavior at the ice/water interface. Native TSP worked for or against IRR in the ICMs depending on the concentration, while DTSP possessed an increased IRR effect under the addition of higher concentration (3.0%). Compared to TSP, adding DTSP caused less of an increase in the viscosity of the ICMs. Molecular dynamics was used to simulate ice growth in the presence of TSP (oligomer) and showed that the TSP possessed activity for retarding ice growth along the prismatic planes. During the propagation of ice crystals, the TSP was bound onto the ice and caused evident structural defects of ice layers. The findings of this study proved that TSP and DTSP have a promising application to retard ice recrystallization in ice cream and shed new light on understanding the mechanism of natural polysaccharides to retard ice growth.

Unveiling the effects of Ti microalloying and thermomechanical processing on recrystallization behavior and mechanical properties of type 316 stainless steel

For the titanium-stabilized austenitic stainless steels, the interaction of precipitation due to the addition of Ti and the recrystallization process is an important aspect of grain refinement, which needs more systematic investigations. Accordingly, in the present work, the effects of Ti microalloying and thermomechanical processing on the recrystallization behavior and mechanical properties of type 316 stainless steel were investigated. It was revealed that the strain-induced α′-martensitic transformation in these metastable alloys is sensitive to the presence of Ti and C in solid solution or their presence as TiC carbides in the aged condition, as well as the temperature of rolling and reduction in thickness. During annealing, the reversion of deformation-induced α′-martensite to austenite and primary recrystallization resulted in the formation of fine-grained equiaxed microstructures, where the precipitation of TiC and sigma-phase was found to be important in the retardation of recrystallization and grain growth (by Zener pinning mechanism) as well as refining the grain size. Annealing the cold rolled 316Ti stainless steel at 800 °C led to a fine grain size of ∼2.5 μm with the precipitation of sigma-phase; while annealing at 900 °C resulted in a coarser grain size of 4 μm but without the presence of the unfavorable sigma-phase. The yield stress of 476 MPa, ultimate tensile strength of 805 MPa, and total elongation of 68 % were obtained for the latter, revealing the merits of Ti addition and thermomechanical processing for the improvement of mechanical properties.

Influence of starting microstructure on the microstructure evolution during annealing and the yield strength in Nb-Ti microalloyed cold-rolled steel

The microstructure evolution of cold-rolled microalloyed steel during annealing at different soaking temperatures was investigated, with emphasis on the influence of the starting microstructure prior to annealing. The starting microstructure of cold-rolled martensite exhibited the fastest recrystallization kinetics, followed by the cold-rolled ferrite-pearlite initial microstructure, while the recrystallization was nearly suppressed in the cold-rolled ferrite-cementite microstructure. The different recrystallization kinetics appear to be influenced by the competing effects of the driving pressure for recrystallization and the solute drag of microalloying elements, which leads to dissimilar post-annealing microstructures even with comparable fractions of new ferrite originating from the reversely transformed austenite. The yield strength following annealing was found to be affected by the starting microstructure. In addition to the dislocation strengthening associated with recrystallization retardation, contributions from other strengthening mechanisms, such as grain refinement and precipitation, varied depending on the starting microstructure. Consequently, the strengthening effects are subject to interplay between the starting microstructure and microalloying elements during annealing, which requires quantitative evaluation for a comprehensive understanding of changes in yield strength.

Achieving high heat-resistant property in dilute Mg-0.2Ce wrought alloy by retarding recrystallization process

Conventional heat-resistant Mg alloys always involve a high concentration of rare-earth solutes to produce amounts of thermostable second phases. In this work, however, the high heat resistance is achieved in a dilute Mg-0.2Ce (wt%) alloy, exhibiting a high ultimate tensile strength of ∼ 181 MPa at 250 ℃, which is superior to those of benchmark Mg alloys including ZK60, AZ80 and other rare-earth element containing Mg alloys. The high-temperature strength of present Mg alloy can be attributed to the suppressed recrystallization process due to the minor Ce addition, since the softening mechanism of grain boundary sliding at high-temperature can be effectively suppressed in the elongated un-recrystallized grains and the texture hardening is always effective in the deformed regions. In addition, the present Mg alloy exhibits excellent thermal stability during the long-term heating on account of the sluggish static recrystallized process. The high temperature strength decreases gradually with the annealing time, which can yet exceed 145 MPa after annealing at 300 ℃ for 6 h. Generally, the present work would provide important insight into developing novel low-alloyed and heat-resistant Mg wrought alloys.

Analysis of Recrystallization Kinetics Concerning the Experimental, Computational, and Empirical Evaluation of Critical Temperatures for Static Recrystallization in Nb, Ti, and V Microalloyed Steels

Recrystallization kinetics and two critical temperatures—the non-recrystallization temperature TNR and the static recrystallization critical temperature TSRCT—of five Nb, Ti, and V microalloyed steel grades are evaluated. The experimental examination is realized by employing isothermal double-hit compression tests and continuous hot torsion tests, both performed on a Gleeble® 3800 thermo-mechanical simulator. The experimental results are used for the critical assessment of predicted TNR using four empirical equations from the literature, and for the validation of simulated TNR and TSRCT. The thermokinetic computer simulations are realized using the mean-field microstructure modeling software MatCalc. Analysis shows that higher microalloying contents increase both critical temperatures, TNR and TSRCT, whereby the effect of recrystallization retardation of Nb is more pronounced than that of Ti or V. The most accurate reproduction of the experimental recrystallization behavior of the five examined steel grades is realized by the employed physics-based simulation approach.

Comparison of K-doped and pure cold-rolled tungsten sheets: Microstructure restoration in different temperature regimes

For tungsten in divertor parts of future fusion reactors, a fine-grained microstructure is preferred to reduce its brittle-to-ductile transition temperature and minimize cracking events due to cyclic thermal and mechanical loading. In our ongoing study on tungsten sheets with different degree of deformation by warm- and cold-rolling, the potential of potassium-doping to stabilize the microstructure at high operation temperatures is assessed. Successful production of technically pure and equivalently rolled potassium-doped tungsten sheets up to very high logarithmic strains of 4.6 was already shown in the past with in-depth analysis of the evolution of microstructure and mechanical properties after rolling steps. Our current study investigates the microstructure changes in the same material batch by recovery, recrystallization and grain growth in temperature regimes between 600 °C and 2400 °C. Annealing studies with subsequent microhardness and SEM analysis reveal increased retardation of recrystallization in potassium-doped tungsten with higher rolling strain, but abnormal grain growth at high temperatures is also increased. However, potassium-doped tungsten with low rolling strain shows promising results with much less grain growth than its pure tungsten counterpart.

Role of Microalloying Elements on Recrystallization Kinetics of Cold-Rolled High Strength Low Alloy Steels

The recrystallization kinetics of two cold-rolled high strength low alloy steels with the addition of Ti and Ti-V, respectively, during annealing were investigated by means of modeling and experimental validation. The recrystallization kinetics of the Ti-V steel were hindered compared to the Ti steel. Based on solid solution theory, mass conservation law and classical nucleation, growth and coarsening theory, the precipitation behavior of Ti and Ti-V steels was predicted. The radius of TiC is larger, and its number density is lower than (Tix, V1−x)C. On this basis, by considering the comprehensive effect of recrystallization on stored energy, the effect of the microalloyed precipitates and microalloying solute on the driving force and grain boundary mobility, the model of the recrystallization kinetics was proposed, which could well reproduce the effect of microalloying elements on recrystallization. Moreover, it was indicated that solute drag is more effective in retarding recrystallization than the pinning effect of precipitates.

Synergistic effect of precipitation strengthening and multi-heterostructure on the improvement of strength and ductility in NbC-reinforced FeMnCoCr high entropy alloys

An appropriate multi-heterostructure NbC-reinforced Fe48Mn30Co10Cr10NbC (at%) high entropy alloy (HEA) was obtained by adjusting the annealing parameter. Nb addition can lead to static recrystallization retardation, additionally, shear bands and micro-sized NbC as nucleation sites led to the heterogeneous of recrystallization nucleation, which is conducive to the regulation of multi-heterostructure. The multi-heterostructure contained ultrafine recrystallized grains, micron-sized recrystallized grains, large un-recrystallized grains with dense dislocations, and micron-, submicron-, and nano-sized NbC particles, with the grain size exhibiting a bimodal distribution. The sample with 41.8% (volume fraction) ultrafine recrystallized grains exhibited excellent comprehensive mechanical properties with yield strength of 843 MPa and uniform elongation of 30.8%. The high yield strength was attributed to precipitation strengthening and multi-heterostructure, which is about 1.5 times that of other HEAs with similar uniform elongation. The samples with high recrystallization volumes (>70%) exhibited three-stage work hardening behavior, and the increase in the work hardening rate was primarily related to dislocation strengthening and the transformation induced plasticity (TRIP) effect. Twinning induced plasticity (TWIP) effect preferentially occurred in the coarse grain, and lower dislocation density in the un-recrystallized grain was beneficial to TRIP effect. This new design strategy of the multi-heterostructure NbC-reinforced HEA provides a theoretical basis for the development of high-performance HEAs.

Effect of ι-carrageenan and its acidic and enzymatic hydrolysates on ice crystal structure changes in model sucrose solution

The aim of the study was to compare the effects of ɩ-carrageenan and its hydrolysates on ice recrystallisation inhibition (IRI) in model solutions. Acid hydrolysis of ɩ-carrageenan was carried out using hydrochloric acid (HCl). Enzymatic hydrolysis was conducted using the enzymes β-galactosidase and commercial lactase. Hydrolysates were used as a stabiliser in model system solutions. The recrystallisation process was analysed on the basis of images of ice crystals in 50% sucrose and 50% sucrose with the addition of sodium caseinate after 24, 48, 72 and 96 h of storage at − 8 °C. The molecular mass after hydrolysis of ɩ-carrageenan was decreased by around 16% after hydrolysis with β-galactosidase use, around 3% after hydrolysis with commercial lactase use and 24% after acid hydrolysis. Furthermore, using the hydrolysates of ɩ-carrageenan had a strong impact on the recrystallisation process. Significant retardation of recrystallisation in the sucrose solution was observed for the addition of both types of hydrolysates (after acid and enzymatic hydrolysis). However, in sucrose with the addition of sodium caseinate, the oligosaccharides obtained after hydrolysis with commercial lactase use were more effective in recrystallisation inhibition – the average diameter of ice crystals was 16.92 µm. The spectra obtained with Fourier Transform Infrared Spectroscopy (FTIR) show changes in the absorption bands, which confirms that functional groups changes could lead to the IRI activity of gained hydrolysates.

Tailormade Wheat Arabinoxylan Reveals the Role of Substitution in Regulating Gelatinization and Retrogradation Behavior of Wheat Starch.

To elucidate the role of substitution of arabinoxylan (AX) in the characteristics of wheat starch, this study prepared AX with a well-defined structure by targeted enzymatic hydrolysis and comparatively investigated the effects of AX with different degrees of substitution on gelatinization and retrogradation behavior of starch. Removal of major arabinofuranosyl (Araf) of mono- or disubstituted xylopyranosyl (Xylp) of both low-molecular-weight (Mw: 62.5 kDa, Araf/Xylp: 0.61) and high-molecular-weight AX (Mw: 401.2 kDa, Araf/Xylp: 0.61) reversed the decreased gelatinization viscosity and recrystallization of amylose induced by AX to a similar extent. Upon retrogradation for 30 days, the Araf of mono- and disubstituted Xylp contributed to the water distribution and the effect depended on the molecular chain length. The C3-linked Araf of disubstituted Xylp was more involved in prohibiting the retardation of recrystallization of amylopectin, while the presence of Araf of monosubstituted Xylp might hinder the interactions between AX and amylopectin.

Effect of Sc microalloying on microstructure evolution and mechanical properties of extruded Al–Zn–Mg–Cu alloys

The effect of microalloying Sc on the microstructure and mechanical properties of Al–Zn–Mg–Cu alloys was experimentally investigated through X-ray diffraction, optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy characterizations and tensile tests. The presence of Sc caused the formation of the primary Al3Sc phase and behaved a significant modifying effect on the cast microstructure with an equiaxed microstructure attained in the Sc-bearing alloys rather than the dendrites in Sc-free alloys. In the subsequent thermal extrusion processing, a remarkable grain refinement and retardation of recrystallization occurred, because the nano-sized Al3Sc dispersoids contributed to the pinning effect on the dislocation movement and grain boundary migration in the Sc-bearing alloys. The mechanical properties were significantly improved with the addition of Sc. The superior comprehensive mechanical properties in the Sc-bearing alloys were achieved via the optimal extrusion at 350 °C with the yield strength and ultimate tensile strength of 373.7 ± 3 MPa and 490.3 ± 5 MPa, respectively. The strong strengthening behavior of the Sc addition in the extruded alloys is mainly attributed to the grain refinement and the dispersoid strengthening from the Al3Sc particles. The corresponding contributions to the increase in yield strength derived from the grain refinement and the dispersoid strengthening were estimated, which indicated that the highest particle density attained by extrusion at 350 °C resulted in the excellent mechanical properties of the Sc-bearing alloys.

Evolution of Zr-Bearing Dispersoids during Homogenization and Their Effects on Hot Deformation and Recrystallization Resistance in Al-0.8%Mg-1.0%Si Alloy

The precipitation behavior of Zr-bearing dispersoids in an Al-0.8%Mg-1.0%Si alloy was investigated for different homogenization treatments (450-550 °C). The effect on the recrystallization resistance of the alloy was also studied during post-deformation annealing. With an addition of 0.2 wt.% Zr, two different Zr-bearing dispersoids were observed depending on the homogenization conditions. Homogenization at 450 °C for 2 h resulted in the precipitation of fine and dense L12-Al3Zr dispersoids (8-10 nm), which were found to be coherent with the matrix. In contrast, extended homogenization times, such as 12 h at 450 °C, or increasing the homogenization temperature to 500-550 °C produced elongated DO22-(Al,Si)3Zr dispersoids with a larger size. During hot compression testing, the addition of 0.2 wt.% Zr combined with homogenization at 450 °C increased the high-temperature flow stress by 20% relative to the base alloy free of Zr, revealing their potential to inhibit dislocation motion and dynamic recovery. Both dispersoids were found to have positive impact on the retardation of recrystallization during post-deformation annealing, but the fine and coherent Al3Zr dispersoids were more effective than the coarse and incoherent (Al,Si)3Zr dispersoids.

Microstructure, texture, and mechanical properties of the extruded and multi-directionally forged Mg–xGd alloys

The microstructural and textural evolutions as well as room-temperature mechanical properties of three binary Mg–Gd alloys with 1, 2, and 3 wt% of Gd were studied in the as-extruded condition and after two, four, and six passes of multi-directional forging (MDF). Microstructural observations of the extruded samples were indicative of partial dynamic recrystallization resulting in bimodal grain structures comprised of elongated un-recrystallized patches and fine recrystallized grains. After six passes of the MDF process, the fraction of the un-recrystallized regions decreased because of dynamic recrystallization, and thus, relatively uniform microstructures were achieved in all alloys. The greater fraction of the un-recrystallized patches and the finer grains in the recrystallized regions of the Mg–3Gd alloy confirmed the more pronounced retardation of recrystallization via solute drag mechanism at the higher Gd concentrations. Evaluation of crystallographic texture revealed that by applying the MDF process, the conventional fiber texture of the extruded condition was replaced with a new randomized texture, in which the basal planes had a tendency to rotate at angles of lower than 90° to the transverse direction. Mechanical properties were evaluated using shear punch testing (SPT) and the results showed that with increasing the number of MDF passes in each alloy, the achieved finer grain structure was responsible for improving the shear strength. In addition, increasing the Gd content of the alloys resulted in finer grain size, more solute atoms, and higher fraction of Mg 5 Gd second phase particles, all of which led to the enhancement in shear strength.

Effects of Pressure on Microstructure and Residual Stresses during Hot Isostatic Pressing Post Treatment of AISI M50 Produced by Laser Powder-Bed Fusion

Laser powder-bed fusion (LPBF) enables the production of difficult-to-machine materials with near-net shape and complex geometries. Components made of tool steels produced by LPBF, even using high preheating temperature, tend to show residual porosity, cracks, and high residual stresses. Hot isostatic pressing (HIP) is able to densify components and modify their microstructure. Moreover, compared to conventional heat treatment at ambient pressure, rapid cooling within the HIP vessel can alleviate thermal stresses, warping or cracking during quenching. In this study, the effects of isostatic pressure on microstructure evolution and residual stresses are investigated. Samples were produced by LPBF. Partly, they were conventionally heat treated by austenitizing, quenching, and tempering, partly using a HIP-device with an integrated quenching facility. The microstructure was characterized by optical microscopy, scanning electron microscopy employing energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis. The results showed that besides the densification of the material to the porosity of 0.001%, HIP influenced the microstructure evolution by retarding recrystallization during austenitization due to the pressure and led to slight compressive residual stresses around 11 MPa on the surface of components.

On the Thermal Stability of Dislocation Cellular Structures in Additively Manufactured Austenitic Stainless Steels: Roles of Heavy Element Segregation and Stacking Fault Energy

The thermal stability of dislocation cellular structures in three additively manufactured (AM) austenitic stainless steels (SSs), 316L SS, 304L SS, and Al modified 316L SS (316L(Al)), were studied. Minor alloying elements, Mo and Al, were found affecting the stability of the cellular structures in AM austenitic SS, resulting in a stability ranking of AM 316L SS > AM 304L SS > AM 316L(Al) SS. As a result, their abilities towards recrystallization also differed. Owing to the high stacking fault energy (SFE) due to Al addition, AM 316L(Al) SS had the least stable subgrain cellular structure and exhibited the lowest recovery temperature. Although 316L SS possessed slightly higher SFE than 304L SS, the pinning effect due to Mo segregation at the cellular walls in AM 316L SS significantly enhanced its thermal stability. While the low-SFE AM 316L SS and AM 304L SS recovered their cellular structures via the equiaxed cell growth, the dislocation cellular walls in high-SFE AM 316L(Al) SS continuously vanished along a preferred direction. The fast recovery of cellular structures led to recrystallization retardation. The Hall–Petch model was found incapable of correlating cell size to strength because of the continuous weakening of cellular walls during heat treatment.

Ultra-high strength attributed to retardation of recrystallization during intercritical annealing in cold-rolled (V,Nb) microalloyed 5Mn steel

The effects of V and Nb addition on the microstructure and mechanical properties of a cold-rolled and intercriticallly annealed 5Mn steel were investigated. Compared to a steel without V or Nb the recrystallization in microalloyed steel was retarded significantly from the beginning of annealing, which resulted in a 100–200 MPa increase in both yield and tensile strength while the degradation of ductility was not observed. Negligibly small change in elongation was attributed to a larger degree of carbon enrichment due to the smaller volume fraction of retained austenite and accelerated Mn transport through high density dislocations, which may well have operated to increase the austenite stability.

Study on high temperature strengthening mechanism of ZrO2/Mo alloys

ZrO2/Mo alloy bars are fabricated by hydrothermal method and powder metallurgy process, with their microstructures, density, hardness, strength, reduction of area and elongation under ambient temperature investigated experimentally. The high temperature deformation stress of these alloy bars are tested through thermomechanical simulator. Results show that the second phase (ZrO2) in the microstructure was fine. As addition amount of the second phase increases, the microstructures of the matrix are refined, the density decreased while the hardness and strength are enhanced. Under high temperature, the second phase in ZrO2/Mo alloy bars can improve compressive stress of the alloy effectively by fine-grain strengthening and intra-granular and grain-boundary strengthening. At 1400 °C, the deformation stress of Mo alloy bars with 1.5% ZrO2 can be 20% higher than that of pure molybdenum. The strengthening effect of the second phase at high temperature are analyzed. The increase of strengthening effect is actually the manifestation of the pinning effect on hindering recrystallization behavior. It is shown that the improvement of mechanical properties of alloys at elevated temperatures should be mainly attributed to the retardation of recrystallization by the second phase.

Some aspects of physical metallurgy of microalloyed steels

Some aspects of deformation, precipitation, and recrystallization behavior in medium carbon V-microalloyed and low carbon Nb/Ti-microalloyed steels are presented in the paper. Changes in microstructure are explained together with methods of quantification. The temperature of No-recrystallization (Tnr) is defined as a milestone to show the onset of retardation of recrystallization while the apparent activation energy for hot working shows the extent of this retardation. In the case of high cooling rates, this method is not sufficiently sensitive and Trl (recrystallization limit temperature) and Trs (recrystallization stop temperature) must be evaluated from softening data. Paper presented the possibility to estimate Tnr temperature on six stands finishing train at Hot Strip Mill in HBIS Iron and Steel Serbia, Smederevo as well as the activation energy for static recrystallization, QSRX, derived from Tnr temperatures.

Effects of Si and Zr addition on strength and recrystallization behavior of Al-Mn alloy fin stocks for automotive heat exchanger

For an Al-Mn alloy heat exchanger fin stocks which continuous casting was simulated in, the effects of Si and Zr addition on strength and recrystallized grain structures after brazing heat treatment were investigated. As a result of tensile test, pre-brazed tensile strength was increased with increasing Si and Zr contents in the Al-Mn alloy. On the other hands, Zr addition have a small effect on post-brazed tensile strength regardless of Si contents. This was attributed the dissolution of Al3Zr or (Al,Si)3Zr precipitates during brazing heat treatment. Post-brazed grain structure were refined with increasing Si contents. Meanwhile, Zr addition led to larger post-brazed grain structures. It was found that Al3Zr or (Al,Si)3Zr precipitated during intermediate annealing played to major role in retarding recrystallization during brazing heat treatment.