Recrystallization Temperature Research Articles

High Strain Rate Deformation Behavior of Gradient Rolling AZ31 Alloys

A dynamic impact test was performed on as-rolled AZ31 alloys with gradient microstructure under various strains. The microstructural evolution and mechanical properties were systematically investigated. As the strain rate gradually increased, an increasing number of twins were formed, facilitating dynamic recrystallization (DRX), and the mechanical properties were also gradually improved. The microstructure became heterogeneous at higher strain rates, but the peak stress decreased. The impact process resulted in a significantly higher performance due to microstructural refinement, work hardening by dislocations, and precipitates. In addition, both the adiabatic shear band and the adjacent crack experienced a temperature rise that exceeded the recrystallization temperature of the alloys. This observation also explains the presence of ultrafine recrystallized grains within the adiabatic shear band and the appearance of molten metal around the crack.

High Strain Rate Deformation Behavior of Gradient Rolling AZ31 Alloys

A dynamic impact test was performed on as-rolled AZ31 alloys with gradient microstructure under various strains. The microstructural evolution and mechanical properties were systematically investigated. As the strain rate gradually increased, an increasing number of twins were formed, facilitating dynamic recrystallization (DRX), and the mechanical properties were also gradually improved. The microstructure became heterogeneous at higher strain rates, but the peak stress decreased. The impact process resulted in a significantly higher performance due to microstructural refinement, work hardening by dislocations, and precipitates. In addition, both the adiabatic shear band and the adjacent crack experienced a temperature rise that exceeded the recrystallization temperature of the alloys. This observation also explains the presence of ultrafine recrystallized grains within the adiabatic shear band and the appearance of molten metal around the crack.

Biodegradable polybutylene succinate: Purified method and oligomers investigation

The oligomers found in polybutylene succinate (PBS) have a significant impact on its properties. It is crucial to qualitative and quantitative analyze oligomers in PBS and remove them effectively. Three kinds of solvent dissolution/precipitation methods were used to extract oligomers from PBS. Ten oligomer components were identified in the molecular weight in a range of 200–1400 g/mol for each extraction method, and the component with molecular weight of 236 g/mol in PBS could be effectively extracted by hexafluoroisopropanol/tetrahydrofuran (HFIP/THF) method, accounting for 51.4 %. Oligomers have almost the same chemical structure as PBS, mainly cyclic structure with 2–6 repeating units. The thermal stability of the three oligomers is weaker than that of PBS, showing two-step decomposition. The recrystallization temperature of PBS is increased from 92.1 °C to 95.6–97.8 °C after purification. The findings in this study will significantly contribute to the purification and subsequent commercial application of PBS.

Effects of carbon concentration on the local atomic structure of amorphous GST.

Ge-Sb-Te (GST) alloys are leading phase-change materials for data storage due to the fast phase transition between amorphous and crystalline states. Ongoing research aims at improving the stability of the amorphous phase to improve retention. This can be accomplished by the introduction of carbon as a dopant to Ge2Sb2Te5, which is known to alter the short- and mid-range structure of the amorphous phase and form covalently bonded C clusters, both of which hinder crystallization. The relative importance of these processes as a function of C concentration is not known. We used molecular dynamics simulation based on density functional theory to study how carbon doping affects the atomic structure of GST-C. Carbon doping results in an increase in tetrahedral coordination, especially of Ge atoms, and this is known to stabilize the amorphous phase. We observe an unexpected, non-monotonous trend in the number of tetrahedral bonded Ge with the amount of carbon doping. Our simulations show an increase in the number of tetrahedral bonded Ge up to 5 at.% C, after which the number saturates and begins to decrease above 14 at.% C. The carbon atoms aggregate into clusters, mostly in the form of chains and graphene flakes, leaving less carbon to disrupt the GST matrix at higher carbon concentrations. Different degrees of carbon clustering can explain divergent experimental results for recrystallization temperature for carbon doped GST.

Intergranular Attack of Low Carbon Steel in Molten Aluminum Chloride

AISI 1018 carbon steel exhibits intergranular attack in molten aluminum chloride. To explore grain boundary corrosion initiation and propagation, tests have been conducted on several iron-based alloys, heat treated to recrystallization temperature, and using molten aluminum chloride and its mixture with other molten chlorides environments. Pure iron, A106, and AISI 1018 carbon steel have been exposed to both pure aluminum chloride and ferric chloroaluminate melt in both their recrystallized and as-received, cold-worked conditions. Intergranular corrosion is observed in both 1018 and A106 carbon steels in all the salts whereas pure iron only shows pitting. Materials processing has varying effects on the corrosion depths of 1018 and A106 carbon steels. The grain boundary microchemistry of 1018 carbon steel is examined with in situ fracture Auger spectroscopy where molybdenum and carbon segregation are found, and a mechanism is proposed to explain the present corrosion phenomenon.

Hot compression bonding of a 9Cr oxide dispersion strengthened alloy and a 9Cr reduced-activation ferritic/martensitic alloy

An innovative method of hot compression bonding is proposed in this work for the joining of 9Cr oxide dispersion strengthened (ODS) alloy and 9Cr reduced-activation ferritic/martensitic (RAFM) alloy. The microstructural evolution of the bonding interface was investigated by scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM). The results verify that the pinning effect of nano-oxides particles (NPs) in 9Cr ODS alloy significantly enhances its dynamic recrystallization (DRX) temperature and deformation resistance. Continuous DRX (CDRX) first occurred on the 9Cr RAFM alloy side, and the areas near the bonding interface were composed of recrystallized grains. With increasing strain, CDRX also showed up on the 9Cr ODS alloy side. Inevitable slight oxidation occurred at the bonding interface during the hot compression bonding (HCB) process, and the interfacial oxides transformed from initial coarse CrO to TiO and finally to Y-Ti-O nanoparticles with sizes comparable to pre-existing NPs dispersed in the 9Cr ODS alloy matrix. It is believed that interfacial oxide transformation and grain structure consistency contributed to the excellent interface healing of the two dissimilar alloy pieces. The effectiveness of the bonding was tested by tensile tests and fractography analysis, revealing that ideal metallurgical bonding could be achieved under a controlled strain level of 10 % at 800 °C followed by soaking at 1000 °C for 4 h.

The impact of precipitation on recrystallization in a severely plastically deformed CoCrFeMnNi multi–principal element alloy

The present study investigated the rate-controlling mechanism for recrystallization kinetics in a severely plastically deformed (SPD) multi–principal element alloy. For this purpose, an equiatomic Cantor alloy (CoCrFeMnNi) was subjected to equal channel angular processing (ECAP) at room temperature and annealed at 773–973 K. The major recovery process was found to be concurrent recrystallization with precipitation. The recrystallization kinetics, investigated in the frame of the Johnson–Mehl–Avrami (JMAK) theory, gives a retarded recrystallization with a high recrystallization temperature of above 0.54Tm and an anomalous low JMAK exponent value of 1.1–1.8. The measured apparent activation energy for recrystallization exhibited a steady increase over the duration, with initial values of 220.8 ± 7.5 kJ/mol rising to 313.9 ± 23.8 kJ/mol towards the end. The systematic analysis leads to the conclusion that the rate-controlling mechanism for recrystallization in ECAP processed CoCrFeMnNi MPEA is the grain boundary migration-determined grain growth instead of nucleation. During this process, the Zener pinning effect exerted by precipitates from the concurrent precipitation with recrystallization plays the dominant role.

Comparative study of microstructural evolution in W-3Re alloy under high-temperature conditions: High heat flux loading versus furnace heating

In tokamak devices, tungsten (W), as the main candidate for plasma facing material, will suffer from the simultaneous challenges of high heat flux (HHF) and neutron irradiation. This study involved annealing experiments on W-3Re alloy using two distinct heating methods: furnace heating and electron beam heating. The evolution of hardness and microstrure of tungsten-rhenium (W-3Re) alloy after isochronous annealing and isothermal annealing has been analyzed and compared with pure tungsten (PW). The recrystallization kinetics of W-3Re alloy have been obtained employing the Johnson Mehl-Avrami Kolmogorov (JMAK) equation. Experimental results showed that recrystallization kinetics during electron beam annealing were faster than those in furnace annealing. This phenomenon can be attributed to the rapid heating process of electron beam annealing, which preserved more deformation energy within the material, thus providing more driving force for recrystallization at high temperatures. Additionally, Re appeared to inhibit grain boundary migration in W-3Re alloy, causing the recrystallization temperature to be approximately 100 °C higher than in pure tungsten, and also resulted in a smaller average grain size compared to pure tungsten. This research provides experimental data and reference for predicting the microstructural evolution of tungsten-rhenium alloy in future fusion reactor environments.

Sensitivity of reduction rate on the mechanical response of boron-doped Fe50Mn30Co10Cr10 high entropy alloy

Phase transformation induced plasticity (TRIP) effect is an effective technical solution to enhance the strength and ductility of alloys, represented by Fe50Mn30Co10Cr10 high entropy alloy (HEA). Introducing heterostructures into alloys is also an effective synergistic method for enhancing the strength and ductility of alloys. Combining element doping, heterostructures, and the TRIP effect of the alloy itself can enable the alloy to achieve both high strength and high ductility. In this work, the boron doped Fe50Mn30Co10Cr10 HEA were prepared by cold rolling with different reduction rates followed by recrystallization annealing processes. Different reduction rates result in different heterogeneous structures. The large rolling reduction weakens the advantage of heterogeneous structure for introducing large stress concentration, resulting in the low ductility of the alloy. The sample with small rolling reduction shows excellent strength and ductility, which comes from the synergistic effect of large-small grains matching and TRIP effect. In summary, the TRIP effect combined with the appropriate amount of reduction and low recrystallization temperature annealing induced heterostructure is an effective solution to overcome the strength ductility trade-off.

Formation mechanism of recrystallisation internal friction peak and its application to determine the recrystallisation temperature of deformed pure Cu

ABSTRACT The formation mechanism of a recrystallisation internal friction (IF) peak superimposed on a grain boundary (GB) IF peak for deformed copper was studied. The P1 peak, associated with the recrystallisation process, was observed at ∼ 599 K (2 K/min) during the first heating process. Subsequently, the P2 peak, located at ∼ 510 K (0.2 Hz), corresponded to GB relaxation during the cooling process. The P1 peak showed minor relaxation at higher frequencies owing to the influence of GB relaxation. To accurately determine the temperature of the P1 peak in this scenario, two methods were used: fitting the measured IF spectra and performing IF measurements at lower frequencies and/or with faster heating rates to minimise the impact of GB relaxation. This work investigated the formation mechanism of the recrystallisation peak and supplemented the method for determining the recrystallisation temperature through IF measurements when the GB peak occurs at a nearby temperature.

Consideration of tungsten recrystallization in plasma facing components design

Tungsten recrystallization leads to a modification of material properties including a reduction in hardness, strength and thermal shock resistance. The recrystallization assisted material degradation compared to the as-received state has made it very undesirable as demonstrated in high heat flux testing. Consequently, tungsten recrystallization temperature has been widely used as the upper limit of material surface temperature under steady state loading conditions. However, this study shows that recrystallization is inevitable where steady state or transient loads are high enough. The efforts to retard recrystallization will only reduce the recrystallized depth but cannot completely avoid it. While it is demonstrated the material will be weakened by recrystallization, the recrystallized depth plays a relatively small role in deciding the fatigue lifetime once it is recrystallized. Therefore, it is recommended that the geometry and fracture toughness of the design is optimised to reduce crack growth into the component. The design criterion against tungsten recrystallization under steady state loading conditions has also been proposed for engineering design stages.

Waste chicken feather biofiller reinforced bioepoxy resin based biocomposites — A waste to wealth experimental approach

Utilizing poultry wastes, particularly chicken feathers, in biopolymer composites is seen as an important aspect in lowering the environmental pollution and paving a new path to sustainability. The main objective of this experimental study is to develop polymer composites reinforced with waste chicken feather fillers and evaluate their physical, mechanical, and thermal characteristics. The composites were fabricated through an open mold casting process using bio epoxy (SR-33 Greenpoxy) as the matrix and chicken feather filler as a reinforcement in three distinct weight fractions (2.5, 5, and 7.5 wt%). To evaluate the effects of filler content on the mechanical properties of the fabricated bio-epoxy composites, they were subjected to tensile, flexural, impact, and hardness tests. The findings from the experimental studies demonstrated that the composites containing 2.5 wt% of chicken feather filler had improved mechanical properties, thermal stability, and crystallization behaviour. The thermal attributes of samples included a greater melting point, lower recrystallization temperature, higher glass transition temperature, and quicker crystallization rates. The Scanning Electron Microscope analysis of the fracture surface morphology of the biocomposites showed a better interfacial adhesion between the filler and matrix. It could be concluded from the results that the waste chicken feather can be used as potential filler reinforcements for begetting natural composites for various low- and medium-density structural and non-structural applications.

Experimental and optimization studies of friction stir processed Cu-TiB2 surface composites

The present study aims to fabricate different Copper surface composites (Cu-SCs) such as Copper-Silicon Carbide (Cu-SiC), Copper-Boron Carbide (Cu-B4C), Copper-Titanium Diboride (Cu-TiB2) with enhanced mechanical properties using friction stir processing. The Cu-SCs were fabricated at different levels of tool rotational speed (TRS), traverse speed (TS), and Vol. % of micro-sized Boron Carbide (B4C), Silicon Carbide (SiC), and Titanium Diboride (TiB2) reinforcements using blind hole method. The mechanical characteristics such as ultimate tensile strength (UTS), yield strength (YS), percentage of elongation (%EL), impact toughness (IT), and microhardness (H) of the Cu-SCs were evaluated and analyzed. In the next stage, the process parameters were optimized using a graph theory algorithm and utility concept and the TRS, and TS were 1120 rev/min, and 40 mm/min respectively. The Cu-SCs fabricated by using taper threaded cylindrical tool pin profile at four Vol.% of TiB2 possess enhanced the mechanical characteristics such as UTS, YS, % EL, IT, and H up to 282.07 MPa, 197.76 MPa, 12.96%, 16.67 J, and 168.6 HV. This was happened due to the increased recrystallization temperature, the pining effect, and restricting the grain boundary sliding. The microstructure in the stir zone of Cu-SCs fabricated with 4 Vol. % of SiC, 4 Vol. % of B4C, and 4 Vol. % of TiB2 particles exhibit fine grains. This is attributed to uniform distribution of the particles in the copper surface composites. The mechanical characteristics were also correlated with microstructures and fracture features.

A roadmap for tailoring the microstructure and mechanical properties of additively manufactured commercially-pure titanium

In recent years there has been a growing interest in using additive manufacturing to produce near net-shape parts from titanium alloys. Most of these studies have focused on the fabrication of various high-strength alloys such as Ti5553 and Ti–6Al–4V, but there is also a desire to produce parts out of lower-strength and higher elasticity alloys such as commercially pure titanium (CP–Ti). In this work, we have shown the effects on various properties of CP-Ti Grade 2 produced via the Laser Powder Bed Fusion (L-PBF) manufacturing process and subsequent heat treatments. Samples with 99.98 % density were produced. Microstructure and phase evolution was characterized by X-ray and electron backscatter diffraction and polarized light microscopy. Oxygen was found to be incorporated during manufacture and processing by Inert Gas Fusion (IGF). Heat-treatment of the samples resulted in recrystallization of the acicular microstructure. By testing the mechanical properties throughout the recrystallization temperatures, it was observed that the grain recrystallization lead to a reduction in mechanical strength without a significant improvement in ductility, therefore making a low temperature heat-treatment that retains the AM microstructure an interesting alternative to strengthen CP-Ti.

Study on Softening Resistance of Cu-Sn-Fe-P alloy for Advanced Electrical Connectors

The effect of adding iron element in tin bronze on the microstructure and properties of Cu-Sn-Fe-P alloy is studied by means of phase diagram calculation and microstructure observation. The work hardening curve of Cu-Sn-Fe-P alloy is plotted by cold deformation of the alloy with different reduction rates. The test and microstructure observation are conducted for tensile strength and ductility of the alloy sample annealed at different temperatures, so as to determine the recrystallization temperature of the alloy. The results show that the addition of iron element plays a significant role in grain refinement and improves the subsequent working performance. After the cold rolling deformation, an obvious work hardening effect is imposed on the alloy. With the increase of the deformation, the alloy presents a trend of increasing first and then becoming stable in the tensile strength, while a reverse trend in ductility. Cu-Sn-Fe-P alloy has a softening resistance equivalent to that of QSn6.5-0.1 high-tin bronze, both of which will be softened at 400ºC; therefore, Cu-Sn-Fe-P alloy can replace QSn6.5-0.1 alloy at high temperature.The present study proposes how to maintain the original properties of the tin-phosphorous bronze alloy while reducing the content of the tin, and achieve the more effective industrialized production.

Restoration kinetics and microstructural evolution of moderately warm-rolled yttria dispersion-strengthened tungsten plate during annealing at high temperatures

The thermal stability of an yttria particle dispersion strengthening tungsten (W-2vol%Y2O3) plate with 67 % rolling thickness reduction (WY67) fabricated by powder metallurgy and warm rolling is investigated through isochronous annealing and isothermal annealing. Hardness testing of annealed specimens allows tracking the degradation of the mechanical properties and electron backscatter diffraction (EBSD) was used to characterize the corresponding microstructure. Isochronous annealing for 1 hour between 1150 °C and 1450 °C indicates that the recrystallization temperature of WY67 is about 1400 °C. Herein, the recovery kinetics, recrystallization kinetics, and the evolution of microstructure and texture of WY67 during isothermal annealing at temperatures ranging from 1300 ℃ to 1450 ℃ were investigated in detail. The effect of both the heterogeneity of the deformed microstructure and the yttria particles on the recovery and recrystallization was further studied. The results show that the stored energy of the deformed grains of yttria dispersion strengthened tungsten is texture-dependent and the grain with γ-fiber (normal direction // <111>) texture has the largest stored energy of 546 KJ/m3. The grains with higher stored energy are conducive to recrystallized nucleus/grain growth rather than nucleation during subsequent annealing. The recrystallized texture inherits the deformed texture and is mainly composed of γ-fiber texture. There are more pre-existing potential recrystallization nuclei in the elongated grains with larger deformation in the as-rolled microstructure. Micron-sized yttria particles can stimulate the formation of recrystallization nuclei through particle-stimulated nucleation mechanism, nevertheless, this is not the dominant nucleation mode for WY67 during recrystallization in this study. Fine (submicron) yttria particles hinder the recovery and recrystallization processes through the Smith–Zener pinning effect.

The coupling effect of particle and electric current on the grain refinement of Al–Cu–Li alloy by an improved thermo-mechanical treatment with electrically-assisted annealing

An improved thermo-mechanical treatment with electrically-assistant recrystallization annealing (EARA) was proposed for Al–Cu–Li alloy with the fine and equiaxed grains. The Al–Cu–Li alloy strips were subjected to the different overaging times, asymmetric rolling and EARA. The size and number of particles had a significant effect on the average grain size. The critical particle size for particle-stimulated nucleation (PSN) was determined. The introduction of electric current did not change the critical size, however, the efficiency of PSN triggered by coarse particles was improved by 3.6 times, compared with the conventional recrystallization annealing (CRA). By the optimized overaging time, the grains were refined and the texture was weakened. The recrystallization mechanism for the specimens containing coarse particles was the discontinuous static recrystallization (DSRX) by PSN and the continuous static recrystallization (CSRX). At the constant current density and annealing time, the critical temperature for rapid recrystallization for EARA decreased by 40 °C, compared with CRA. The results were due to the local Joule heating effect, the activation energy reduction and atomic diffusion rate increase by the athermal effect of electric current. The improved RI-ITMT with EARA would be an ideal candidate for rapid grain refinement in Al–Cu–Li alloy alloys.

Effect of recrystallization annealing on microstructure and properties of cold-deformed CoCrCu1.2FeNi high entropy alloy

In this paper, CoCrCu1.2FeNi high entropy alloy (HEA) was prepared by vacuum suspension melting. After 50 % cold-deformation, recrystallization annealing experiments involving the annealing temperatures of 650–950 ℃ and the annealing times of 30–120 min were carried out on the cold-deformed HEA. The microstructure and properties of the alloy were compared before and after annealing. The results showed that with the extension of annealing time and temperature, the microstructure of the alloy was gradually uniform and coarsening occurred after spheroidization. In addition, fusion and engulfment occurred in the microstructure and the microstructure size decreased first and then increased. Both the fracture strength and fracture strain of the alloy increased first and then decreased. The alloy had the best compression performance at 850 ℃/60 min. Compared with the alloy after cold-deformation, the fracture strength was increased by 79.3 %, the fracture strain was increased by more than 1 time, and the comprehensive mechanical properties were the best at 750–850 ℃. The average hardness decreased with the increase of temperature and annealing time, and the initial recrystallization temperature of the alloy was determined to be about 650 ℃. The formation of annealing twins refined the microstructure and improved the properties of the alloy.

Unveiling the optimal selenization temperature for enhancing efficiency in flexible Cu(In,Ga)Se2 thin film solar cells

This work is centered on the growth of metallic precursors (Cu/In/Ga) through sequential evaporation, followed by a controlled ramping step selenization process aimed at synthesizing thin films based on copper indium gallium diselenide (CIGSe) on stainless steel substrates. Selenization temperatures ranging from 475 to 525 °C were employed to optimize the most suitable recrystallization temperature. A comprehensive characterization was conducted, covering structural, morphological, topographical, optical, and electrical aspects, revealing the distinct role of selenization temperature. Subsequently, solar cells were fabricated using the synthesized absorbers, resulting in an impressive efficiency of 15.89 % for the absorber selenized at 525 °C. This observation underscores the pivotal role of selenization parameters in shaping the quality of CIGSe, directly influencing the performance of solar cells. Consequently, this research not only focuses on refining the growth process of CIGSe through a modified approach but also provides valuable insights for the advancement of flexible solar cell technology.

Effects of thermal ageing time and temperature during heat-treatment on the mechanical properties of fiber laser welded Nb-1%Zr-0.1%C alloy in continuous wave mode

The effects of thermal ageing time and temperature used during heat-treatment were studied on tensile strength, elongation, and microhardness of the laser welded Nb-1%Zr-0.1%C alloy in continuous wave mode. Post-weld heat treatment (PWHT) was carried out by varying the temperature and time in the ranges of (850–1050) °C (that is, about the recrystallisation temperature) and (0.5–4) h (as the weld samples were prepared in the form of sheets), respectively. The grain sizes of fusion zone (FZ), and FZ heat treated at 850 °C for 4 h and that at 950 °C for 2 h were found to be equal to 52.85 μm, 84.89 μm and 116.43 μm, respectively. The segregation of zirconium, carbon and oxygen increased grain boundary energy and induced brittleness to the grain boundary, resulting in loss of ductility. The micro-hardness and Young's modulus values were observed to increase in the FZ compared to that of the base metal (BM), but their decreasing trends were noticed during the heat-treatment due to the grains' softening. For the PWHT samples, the plasticity was found to decrease to about 57% of that of BM. This was attributed to the precipitation of carbides, grain growth, and dislocation pinning during the ageing process. During the heat-treatment of the welded samples, both Yield Strength (YS) and Ultimate Tensile Strength (UTS) were found to decrease to 77% and 86%, respectively, of that of the BM.