Occurrence Of Recrystallization Research Articles

Investigation of the Softening Resistance Behavior and Its Mechanism in Cu-Ni-Si Alloys with Discontinuous Precipitates.

In this study, isothermal annealing experiments were conducted on copper-nickel-silicon alloys containing continuous precipitates (CP) and discontinuous precipitates (DP) to investigate the effects of different types of precipitate phases on the microstructural evolution and softening temperature during annealing, as well as to analyze the differences in softening mechanisms. The experimental results revealed that the softening temperature of the CP alloy, subjected to 75% cold deformation, was 505 °C. In contrast, the DP alloy achieved softening temperatures of 575 °C and 515 °C after 75% and 97.5% cold deformation, respectively. This indicates that the DP alloy exhibits significantly superior softening resistance compared to the CP alloy, attributed to the distinct softening mechanisms of the two alloys. In the CP alloy, softening is primarily influenced by factors such as the coarsening of the precipitate phase, the occurrence of recrystallization, and the reduction in dislocation density. In the DP alloy, the balling phenomenon of the DP phase is more pronounced, and its unique microstructure exerts a stronger hindrance to dislocation and grain boundary motion. This hindrance effect reduces the extent of recrystallization and results in a smaller decrease in dislocation density. In summary, the DP alloy, due to its unique microstructure and softening mechanisms, demonstrates better softening resistance, providing higher durability and stability for high-temperature applications.

Ameliorating the microstructure and properties of a Cu[sbnd]Cr alloy by introducing a high-temperature short-time treatment into the thermo-mechanical process

The optimization of process is essential for improving the overall properties of high-strength and high-conductivity Cu alloys. This study introduces a high-temperature short-time treatment (HTSTT, 850 °C/5 min) into the thermo-mechanical process of a CuCr alloy. Following the process of “solid solution - cold rolling - HTSTT - cold rolling - aging”, the tensile strength of the alloy increases from 450 MPa to 508 MPa, with the electrical conductivity increasing from 82.2 %IACS to 86.4 %IACS when compared to the conventional process of “solid solution - cold rolling - aging” under the same total deformation condition. The reasons for the improvement in the comprehensive properties of the alloy after introducing HTSTT are analyzed through microstructural characterization. The results indicate that the HTSTT promotes the occurrence of recrystallization, leading to grain refinement, which results in smaller grain sizes during subsequent processing. Additionally, the introduction of HTSTT changes the main texture of the alloy from 〈100〉//X to 〈111〉//X during the process, which is beneficial to enhancing the alloy's strength and electrical conductivity. More importantly, the HTSTT facilitates the precipitation of solute Cr atoms, leading to the formation of a significant quantity of nanoscale Cr particles, most of which are spherical with an average size of 27 nm. During the subsequent cold rolling process, these Cr particles effectively pin dislocations and promote their proliferation, leading to the precipitation of a large number of smaller Cr particles during the aging process, with an average size of 4.8 nm. These finer Cr particles are crucial for precipitation strengthening. This paper offers valuable insights into the microstructural optimization and performance enhancement of high-strength and high-conductivity Cu alloys.

Study on the grain development and dislocation evolution from dynamic to post-dynamic stage in IN718Plus superalloy; the role of second-phase

The introduction of hexagonal η-Ni3(Al,Ti)0.5Nb0.5 phase can refine and homogenize the microstructure of IN718Plus superalloy during hot working, but produces more complicated recrystallization behavior associated with second-phase modified structural mechanisms. Derived from this perspective, the role of η phase on recrystallization mechanisms and grain development from dynamic deformation to post-dynamic dwell was systematically investigated. The results indicated that η phase delayed the throughout recrystallization procedure and grain development. During dynamic deformation, boundary η inhibited discontinuous dynamic recrystallization via preventing the bulging of original grain boundaries, while intragranular lamellar η promoted heterogeneous strain concentration, stimulated random dislocations for continuous dynamic recrystallization and dislocation walls for banded dislocation substructures, which limited recrystallization occurrence in dynamic stage. During post-dynamic dwell, boundary η dissolution increased the nucleation sites for discontinuous static recrystallization, and η phase restricted grain boundary migration to provide abundant nucleation sites for continuous static recrystallization (CSRX). The banded dislocation substructures slowly evolved into subgrains to further form banded CSRX grains, which reduced grain size during early post-dynamic stage. After fully recrystallization, the residual η protected the small grains and impeded grain growth, meanwhile controlled the grain distribution. As a result, η phase induced sluggish dislocation evolution and recrystallization nucleation, consequently suppressed grain development and obtained the more homogeneous and fine grain configuration.

Effect of Y2O3 on high temperature thermal compression performance of Cu–10W composites and microstructure analysis

In this study, Cu–10W and 2 wt%Y2O3/Cu–10W composites were successfully prepared via mechanical ball milling and spark plasma sintering. Hot compression experiments on the two materials were carried out in the temperature range of 300°C-600 °C and in the strain rate range of 0.01 s−1–10 s−1. The hot deformation activation energy of the two materials was calculated and a constitutive equation was established. The optimum hot deformation process parameters were obtained according to a hot processing map. The effects of Y2O3 on the thermal deformation behavior of the Cu–10W composites and their microstructures were investigated, and the results showed that Y2O3 could enhance the stability of Cu–10W at high temperatures. The activation energies of thermal deformation of Cu–10W and 2 wt%Y2O3/Cu–10W were 159.56 kJ/mol and 129.85 kJ/mol, respectively. Moreover, Y2O3 improved the interfacial bonding strength of Cu and W in the Cu–10W material, effectively preventing the generation of microcracks and pores during the high-temperature compression process; Y2O3 provides more nucleation sites in the recrystallization process, which is favorable for the excitation of recrystallization. A low strain rate at high temperatures favors the occurrence of recrystallization, and the 2 wt%Y2O3/Cu–10W composites tend to exhibit discontinuous dynamic recrystallization (DDRX) under high-Z-value conditions and continuous dynamic recrystallization (CDRX) under low-Z-value conditions.

Study on the microstructure and mechanism of stress relaxation behavior of Cu–Ni–Si alloy by two-stage rolling deformation

In this paper, the effect of the second-stage rolling deformation of Cu–Ni–Si alloy on its stress relaxation resistance was studied, and the mechanism of the change in microstructure and properties before and after stress relaxation was explored. The results show that the tensile strength and yield strength of Two-stage rolling peak aging (TRPA) 43.7 %, TRPA68.8 %, TRPA80.3 % and TRPA96.1 % alloys at 150 °C are close. After stress relaxation, the stress relaxation rates of these alloys are 7.7 %, 11.24 %, 14.69 % and 19.4 %, respectively. It is found that the smaller the second-stage rolling deformation, the better the stress relaxation resistance of the alloy, especially the stress relaxation resistance of the TRPA43.7 % alloy, which is 60.31 % higher than that of the TRPA96.1 % alloy. According to EBSD analysis, it was found that the increase in the number of twins can improve the stress relaxation resistance of the alloy. However, the occurrence of recrystallization reduces the stress relaxation resistance. Additionally, it was determined that the precipitated phase is the δ-Ni2Si phase with an orthogonal structure. Before stress relaxation, the size of the precipitated phase of the alloy with TRPA96.1 % is larger than that of the alloy with TRPA43.7 %, and after stress relaxation, the precipitated phase further grows. The influence of the interface relationship between δ-Ni2Si phase and Cu matrix on the stress relaxation properties of TRPA43.7 % and TRPA96.1 % alloys before and after stress relaxation was investigated using the mismatch theory. In summary, this study reveals that the size of δ-Ni2Si phase, dislocation density and recrystallization are the key factors affecting the stress relaxation resistance of Cu–Ni–Si alloy.

Effect of grain orientation angles and compressive parameters on the deformation characteristics and corrosion property of 6061 Al alloy

The influence of grain orientation angle and processing parameters on the compressive flow stress and corrosion behaviour of 6061-T6 Al alloy was investigated in this study by altering the grain orientation angles in relation to the compressive direction. At relatively low processing temperatures (≤ 300 °C), an increase in the grain orientation angle from 0° to 90°reduced flow stress at low strain ranges (< 0.1) due to the facilitated slip of Al grains. As strain and processing temperature increased, changes in orientation angles had a negligible effect on the flow stress, attributed to the enhanced contribution of intermetallic particles (IMPs) and the occurrence of recrystallisation. Microstructural analysis revealed that higher processing temperatures resulted in a diverse range of IMPs, including Mg2Si (β phase) and Al15(Fe,Mn)3Si2 phases. When the Al alloy was compressed at a high strain rate (25 s−1) and processed at 500 °C, submicron-scale β”, β’, and β phases coexisted. Corrosion tests indicated that a wider distribution of Al15(Fe,Mn)3Si2 phases reduced the corrosion resistance of the Al alloy. This led to the formation of connected corrosion sites in specimens compressed at 500 °C, where a larger corrosion area and enhanced charge transfer ability were confirmed by equivalent circuit fitting. However, no significant variation in corrosion resistance was observed for Al alloys with various grain orientation angles, due to similar grain structure and precipitation behaviour at similar processing temperatures.

A multi-scale experimental investigation on fatigue crack propagation rate behavior of powder bed fusion-laser beam 316L stainless steel subjected to various heat treatments

In this study, three heat treatments referred to as heat treatment 1 (HT1), HT2, and HT3 were applied to tune the microstructure of powder bed fusion-laser beam (PBF-LB) 316L stainless steel. Furthermore, the fatigue crack propagation rate (FCPR) of as-built PBF-LB 316L specimens and specimens subjected to the three aforementioned heat treatments was thoroughly investigated. To this end, the FCPR was evaluated by a fatigue testing machine combined with an infrared thermal camera, and the Paris law was established to quantitatively assess the FCPR of PBF-LB 316L. In addition, a systematic investigation of microstructural evolution, residual stress, tensile properties, and fatigue crack propagation (FCP) fracture surfaces as well as their effect on the FCPR in function of various heat treatments were carried out. The results indicate that the release of residual stresses, the annihilation of the cellular structure, and the occurrence of recrystallization are obtained through the application of HT1, HT2, and HT3 respectively. Furthermore, it is shown that although all three heat treatments can improve the FCPR behavior of PBF-LB 316L to some extent, HT3 PBF-LB 316L presents the lowest FCPR mainly due to its most pronounced plasticity-induced crack closure effect, indicating its highest resistance to FCP even though the recrystallization obtained by HT3 results in the lowest yield strength (YS). Finally, some recommendations about adequate heat treatments concerning fatigue life are suggested.

Controllable Si micro-structuring by temporally modulated single-shot femtosecond pulse lithography

Micro-structured silicon surface plays a significant role in the electronics industry. Crystalline and amorphous phases of silicon, which have significantly different physical properties, can be transformed into each other using femtosecond laser, and assisted chemical etching enables the easy fabrication of various micro-structures. However, efficient and controllable fabrication of micro-cylinders, micro-rings, and micro-ring grooves on silicon surfaces still remains a challenge. Here, we propose a temporally modulated single-shot femtosecond pulse lithography technology, combining laser-induced silicon modification and chemical etching. In this technology, the occurrence of recrystallization allows for the flexible manipulation of the shape of the modified area, transitioning from circular to annular shapes by adjusting the laser fluence. This corresponds to the formation of micro-cylinders and micro-rings after etching. In the case of temporally shaped pulses, with an increasing pulse delay, the micro-rings formed after etching gradually transform into micro-ring grooves, as the recrystallization area created by the first sub-pulse is reacted by the second sub-pulse. Due to the characteristics of the single shot, the technology, when combined with the flying punch method, can be used for the high-efficiency fabrication of large-area silicon surface micro-structure arrays.

Synergistic effects of trace silicon, calcium and cerium on the microstructure and properties of a novel Cu–Cr–Nb–Si–Ca–Ce alloy

In this paper, a novel Cu-0.60Cr-0.20Nb-0.05Si-0.02Ca-0.02Ce (CCNSCC, wt.%) alloy is designed. By comparing the differences in the properties and microstructure with the Cu-0.60Cr-0.20Nb (CCN, wt.%) alloy under the same process, the effects of trace Si, Ca, and Ce elements on the CCNSCC alloy are disclosed. After undergoing cold rolling by 80% and aging at 450 °C for 60 min, the CCNSCC alloy exhibits a tensile strength of 524 MPa and a softening temperature of 600 °C. These values represent an increase of 104 MPa and 90 °C respectively compared with the CCN alloy. After a multi-stage combined thermo-mechanical treatment including preaging at 400 °C for 30 min, the tensile strength and electrical conductivity of the CCNSCC alloy reach 618 MPa and 75.2%IACS respectively. Microstructure analysis shows the existence of rod-like and polygonal Cr8Nb3Si particles, as well as globular, ellipsoidal, and crescent-shaped (Ca,Ce)Cu5 particles. During the process of aging, the precipitation of the Cr phase occurs at the phase boundaries of Cr8Nb3Si particles. Additionally, significant quantities of fine Cr particles at the nanoscale surround the Cr8Nb3Si particles, exerting a beneficial influence on the strength and electrical conductivity of the CCNSCC alloy. Besides, the CCNSCC alloy has finer Cr particle size and lower volume fraction of recrystallized grains after aging in comparison to the CCN alloy. This indicates that the addition of trace Si, Ca, and Ce elements significantly inhibits the growth of Cr particles and occurrence of recrystallization. Plenty of dislocations are observed in different states of the CCNSCC alloy, and their interaction with the Cr precipitates is the primary factor contributing to the excellent mechanical properties of the CCNSCC alloy. The findings of this study provide valuable insights for improving the properties and microstructure of Cu–Cr–Nb alloys.

An investigation into the softening behavior of cast A356 alloy in the solid and semisolid deformation regimes

The current work deals with the hot deformation behavior of A356 aluminum alloy starting with the cast structure and an emphasize on the capability of flow softening. Toward this end, the hot compression tests were performed at temperatures of 150, 250, 350, 450, 500 and 550 °C in the solid range and 580 °C in the semisolid range under the typical strain rate of 0.01s−1. The materials represent high protentional for the occurrence of softening mechanism in solid state regime. During thermomechanical processing (above 250 °C), after reaching the peak stress, the dynamic recrystallization prevails over the deformation behavior and the stress level reaches a steady state regime. The α-dendritic arms are crushed and refined, and the silicon blades are mechanically fragmented and spread irregularly through the microstructure. Being in the semi-solid temperature range, the eutectic silicon phase is melted and causes a sharp decrease in the resistance against deformation. The penetration of the liquid phase along the developed sub-boundaries give rise to grain partitioning and resembles the occurrence of dynamic recrystallization. The presence of the liquid phase during semisolid forming, in addition to the lubricated flow mechanism, facilitates the deformation by providing proper condition for the occurrence of recrystallization. In the present case, a stable stress level as below as 1 MPa was recorded for the experiment cast structure.

Achieving recrystallization of prior β in Ti-6Al-4V alloy by electroshock

Fine grain strengthening is an important approach to improve mechanical properties in titanium alloys. The martensite (α′) of Ti-6Al-4V alloy generally shows fine acicular grain and has high strength. However, the grain size of martensite is influenced by the prior β grain, thereby affecting the overall strength-plasticity combination of the alloy. Generally, the prior β grains grow rapidly above β-transus temperature (∼1000 ℃). It is difficult to refine the prior β grain through traditional heat treatment alone if it coarsened. In this work, we found that electroshock treatment could directly recrystallize the coarse prior β grain in α+β titanium alloy without plastic deformation process. EBSD and TEM analyses found that the prior β grain size reduced from 44 µm to 29 µm and the remained textures had been eliminated after electroshock, therefore the tensile strength and elongation were simultaneously improved from 1196 MPa and 4.7 % to 1259 MPa and 10.4 %. The residual subgrain boundaries within prior β grain, electric current-induced extra driving force and extremely high heating rate (106 ℃/s) are the main reasons for the occurrence of recrystallization as well as no grain growth of prior β. These findings may be used for repairing the mechanical properties of coarse overheated microstructure or eliminating the anisotropy of columnar grain that produced in additive manufactured α+β titanium alloy without deformation processing.

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.

Effect of cold rolling on aging precipitation and mechanical properties of magnesium-aluminum alloy

Although magnesium-aluminum alloys, such as AZ80 and AZ91 have promising application potential in automotive, high-speed train and aerospace fields, their age-hardening response is generally not very appreciable. In this work, the aging-hardening response of AZ80 alloy was effectively enhanced by applying cold-rolling deformation before conducting conventional aging treatment at 200 °C. Compared to the directly aged sample, the yield strength of the pre-rolling and aged sample was increased by 35 MPa. Electron microscope examination confirmed that profuse {101¯1} and {101¯1}-{101¯2} twins, consisting of high density of dislocations and stacking faults, were generated by cold rolling. Blocky or ellipsoidal Mg17Al12 precipitates formed at the twin boundaries (TBs) during subsequent aging treatment. Crystallographic analysis indicated that the precipitates at {101¯1} TBs always held an identical Potter OR with both the matrix and twin, while the precipitates at {101¯1}-{101¯2} TBs exhibited three different ORs: Burgers OR, Potter OR and P-S OR with either the matrix or the twin. Moreover, recrystallized grains were found inside {101¯1}-{101¯2} double twins after peak-aging at 200 °C, implying that precipitation and recrystallization might occur concurrently along TBs at a relatively low temperature. It was speculated that the highly stored energy inside twins and the high elastic energy between the precipitates and twins were driving factors for the occurrence of recrystallization.

Improving mechanical properties and achieving structural stability of large-size molybdenum single crystal during hot deformation by adding Nb element

The occurrence of recrystallization will cause catastrophic damage to the structure of the metallic single crystal, which can be avoided by alloying reasonably. In this work, a new strategy is proposed to improve mechanical properties and achieve the structural stability of Mo single crystal during hot deformation. Thermal simulation tests show that the mechanical property of Mo single crystal is significantly improved by adding the Nb element. The Nb element is beneficial to inhibit the dynamic recrystallization of Mo single crystals through blocking the development of high-angle grain boundaries and dislocation cells, leading to Mo-Nb alloy single crystals still retaining monocrystal structure.

High-temperature oxidation of Haynes 282 microtubes in CO2

ABSTRACT The oxidation characteristics of Haynes 282 microtubes measuring 1 mm in diameter and 200 µm thick exposed to CO2 at elevated temperature are reported. After 215 hours at 700°C and 1 atm, a thin, protective chromia scale accumulates up to 2.03 µm from the outer surface, approximately 1% of the thickness, and internal aluminum oxidation is observed 2.59 µm from the inner surface. The results suggest that oxidation is limited by oxygen diffusion through the growing oxide scale layer. The average grain size in the microtube is 10 µm, and it decreases to 5 µm closer to the inner surface. Severe plastic deformation and variable dynamic recovery and recrystallization from the manufacturing process were observed throughout the microtube. Overall grain size and distribution in the microtube were found to be independent of thermal exposure, despite the occurrence of recrystallization. The superalloy microtube geometry shows promising performance in high-temperature thermal applications.

Microstructure evolution and deformation behaviors of pulse electro-assisted deformation in M50 bearing steel

M50 bearing steel, as a typical high-carbon and high-alloy steel, exhibits low cold working capacity with high susceptibility to produce voids during the ring rolling process. In this paper, the deformation behavior and microstructure evolution during the pulse electro-assisted tensile of M50 bearing steel was studied. The results show that the maximum flow stress of the pulse electro-assisted deformation (PEAD) specimen decreases by 24.4% compared with that of the traditional deformation (TD) specimen. However, the section shrinkage rate of the PEAD specimen is increased by 32.2%, which is even higher than that of the hot deformation (HD) specimens. This indicates the positive role of pulse current on the increase of plasticity. Besides, a constitutive model of the PEAD process was established by fitting the experimental data. With the assistance of pulse current, the deformation resistance and work hardening are reduced, so the number of voids is significantly reduced due to the easier metal flow. Moreover, the energy barrier of recrystallized grain nucleation is decreased, while the nucleation rate is increased under pulse current. As a result, the occurrence of recrystallization leads to the reduction of average grain size from 4.51 μm to 1.62 μm. According to the high-resolution transmission electron microscopy (HRTEM) and electron backscatter diffraction (EBSD) characterizations, the dislocation density decreases by 24% under the applied current, which should be ascribed to the increase of atomic flux and lattice diffusion coefficient. This work provides a new idea for solving the plastic deformation problem of M50 bearing steel.

Dynamic recrystallization and constitutive equation of 15Cr-10Mn-Ni-N steel under hot deformation

Hot working as one of the indispensable processes for all metal materials can effectively refine the grain to improve the material properties. However, the study on the hot-deformation process of low-Ni austenitic stainless steel is scarce. In this study, we conducted single-pass compression tests to explore the dynamic recrystallization process of a low-Ni austenitic stainless steel with the chemical compositions of 15Cr-10Mn-Ni-N during deformation at various temperatures and strain rates. According to the experimental data, the true stress-strain curves are drawn and constitutive equation is established to predict the variations of stress and strain, accompanied with high accuracy. The microstructural characterizations show that the increase of deformation temperature leads to the occurrence of recrystallization in spite of the enhanced softening effect. In particular, the increase of strain rate promotes the refinement of grain size, and the average grain size significantly decreases from 200 µm to 20 µm under the compression condition of 1100 ℃ and 10 s−1. The decreasing grain size can compensate the sacrificing strength due to the reduction of Ni addition. The peak stress of 15Cr-10Mn-Ni-N austenitic stainless steel is 186 MPa at 1000 °C and 0.1 s−1, which is basically similar with the conventional austenitic stainless steel. Evidently, the austenitic stainless steel in this study has a cost-effective advantage because of its low Ni addition, i.e., we have the advantage of reducing material costs while maintaining the identical mechanical properties. Here the recrystallization process of 15Cr-10Mn-Ni-N austenitic stainless steel provides a basis for the selection of thermal processing parameters and a general understanding of the microstructure evolution.

Statistical analysis and recovery behaviors of dislocations in cold‐rolled and annealed reactor pressure vessel steels

AbstractThe statistical analysis and recovery behavior of dislocations in cold‐rolled and annealed reactor pressure vessel steels with a thickness reduction of 50 % were investigated by using x‐ray diffraction and electron backscattered diffraction analysis in this study. A new modified Kubin &amp; Mortensen's method was proposed to evaluate the geometrically necessary dislocation density, and this method could effectively improve the accuracy of geometrically necessary dislocation evaluation by eliminating the effect of step size and measurement noises. Comparison analysis between modified Williamson‐Hall and modified Kubin &amp; Mortensen's methods was also performed in this study, which shows different recovery behavior of dislocations. The electron backscattered diffraction results show that geometrically necessary dislocation density remained unchangeable after annealing treatment below and at 550 °C, and it occurred to decrease above 550 °C due to the occurrence of recrystallization. However, dislocations started to migrate and annihilate at 340 °C according to x‐ray diffraction results. A possible explanation is a difference in the effect of pairwise dislocation annihilation on statistically stored dislocations and geometrically necessary dislocations.

Using Defect Control To Break the Stability-Activity Trade-Off in Enzyme Immobilization via Competitive Coordination.

Immobilization of enzymes within metal-organic frameworks is a powerful strategy to enhance the long-term usability of labile enzymes. However, the thus-confined enzymes suffer from the trade-off between enhanced stability and reduced activity because of the contradiction between the high crystallinity and the low accessibility. Here, by taking laccase and zeolitic imidazolate framework-8 (ZIF-8) as prototypes, we disclosed an observation that the stability-activity trade-off could be solved by controlling the defects via competitive coordination. Owing to the presence of competitive coordination between laccase and the ligand precursor of ZIF-8, there existed a three-stage process in the de novo encapsulation: nucleation-crystallization-recrystallization. Our results show that the biocomposites collected before the occurrence of recrystallization possessed both increased activity and enhanced stability. The findings here shed new light on the control of defects through the subtle use of competitive coordination, which is of great significance for the engineering application of biomacromolecules.

EBSD Analysis of Hot Deformation Behavior of Oxide-Doped Molybdenum Alloys

Hot compression tests of Mo–1.5 wt% Al2O3/ZrO2 molybdenum alloys were carried out using the Gleeble–1500 simulator at 0.01 s−1−5 s−1 strain rates and 1000–1500 °C deformation temperatures. The microstructural changes of the alloy at 1000–1500 °C were studied. The changes in the hot deformation process for the Mo−1.5 wt% Al2O3/ZrO2 molybdenum alloys were analyzed by means of EBSD. The ZrO2 particles had a greater effect on improving the thermal deformation resistance of molybdenum alloys than did the Al2O3 particles. The activation energy of the molybdenum alloy doped with ZrO2 (403.917 kJ/mol) was lower than that of the molybdenum alloy doped with Al2O3 (440.314 kJ/mol). Due to the occurrence of recrystallization, the intensity of {100} the texture first increased and, then, dropped down with increase in the temperature, while the change law of {111} texture was the opposite. Above 1200 °C, the higher deformation temperature made the texture more random by lowering the texture intensity. The dislocation density was sacrificed to promote recrystallization. When dynamic recrystallization occurred, the sub–grain boundaries absorbed dislocations and transformed them into high–angle grain boundaries, resulting in a decrease in dislocation density and an increase in high–angle grain boundaries at high temperatures and low strain rates. At 0.01 s−1 strain rate, the average grain size of Mo–1.5 wt% ZrO2 alloy increased from 2.38 μm to 4.67 μm, and the proportion of large angle grain boundaries increased from 59.8% to 86.6%.