Grain Boundary Motion Research Articles

Effect of isothermal multidirectional compression on microstructure and mechanical properties of Al–Zn–Mg–Cu–Zr alloy with minor Sc addition

Sc microalloying and isothermal multidirectional compression (IMC) are important methods to refine grains and improve the mechanical properties of Al–Zn–Mg–Cu–Zr alloys. Herein, EBSD, SAXS and TEM have been carried out to investigate the effect of IMC and minor Sc on the microstructure, especially for grain boundary wetting, and mechanical properties of aged Al–Zn–Mg–Cu–Zr alloys by melting and hot compression process parameter optimization. The results show that the strength and plasticity can be obviously improved simultaneously by minor Sc addition and IMC. Especially, stripy GBs (one kind of typical GB complexion) have been widely observed for alloy samples after microalloying Sc and IMC, which indicates the occurrence of GB wetting for Al–Zn–Mg–Cu–Zr alloy. And the GB wetting degree gradually increases for alloys with only microalloying Sc, only IMC and (microalloying Sc + IMC). Combined with GB wetting, the formation of Al3(Sc, Zr) due to Sc addition could inhibit the motion of dislocation and grain boundary, which promotes formation and inhibit growth of recrystallized grains, leading to further grain refinement. Besides, GB wetting degree would affect the precipitate distribution, especially for grain boundary precipitates. Also, GB wetting probably promote grain bridging, which is beneficial to improve the yield strength and ductility of Al–Zn–Mg–Cu–Zr alloys. The concurrent effect of grain refinement, the precipitate including finer Al3(Sc, Zr) particles, dislocation strengthening and grain bridging contribute to the simultaneous improvement of the strength and ductility of Al–Zn–Mg–Cu–Zr alloys under IMC and Sc. This study provides a new understanding on microalloying Sc combined with IMC on the microstructure and properties of Al–Zn–Mg–Cu–Zr alloys.

Purification of copper foils driven by single crystallization

High-purity copper (Cu) with excellent thermal and electrical conductivity, is crucial in modern technological applications, including heat exchangers, integrated circuits, and superconducting magnets. The current purification process is mainly based on the zone/electrolytic refining or anion exchange, however, which excessively relies on specific integrated equipment with ultra-high vacuum or chemical solution environment, and is also bothered by external contaminants and energy consumption. Here we report a simple approach to purify the Cu foils from 99.9% (3N) to 99.99% (4N) by a temperature-gradient thermal annealing technique, accompanied by the kinetic evolution of single crystallization of Cu. The success of purification mainly relies on (i) the segregation of elements with low effective distribution coefficient driven by grain-boundary movements and (ii) the high-temperature evaporation of elements with high saturated vapor pressure. The purified Cu foils display higher flexibility (elongation of 70%) and electrical conductivity (104% IACS) than that of the original commercial rolled Cu foils (elongation of 10%, electrical conductivity of ∼100% IACS). Our results provide an effective strategy to optimize the as-produced metal medium, and therefore will facilitate the potential applications of Cu foils in precision electronic products and high-frequency printed circuit boards.

Exceptional improvement in the yield strength of AZ61 magnesium alloy via cryo-stretching and its implications on the grain growth during annealing

This study explored the influence of pre-stretching temperature on the microstructural characteristics and deformation behavior of AZ61 magnesium alloy and its implications on grain growth during subsequent annealing. AZ61 alloy was stretched to 5% plastic strain along rolling (RD) and transverse direction (TD) at room (RT) and cryogenic temperature (−150 °C, CT) followed by annealing at 320 °C for 1 h to investigate the twinning and dislocation evolution and its consequent effect on the flow stress, plastic strain and strain hardening rate. Compared to RT-stretched samples, significant improvement in yield stress, strain hardening rate and moderate reduction in elongation to failure were witnessed for CT-stretched samples along RD and TD. The subsequent EBSD analysis revealed the increased fraction of fine {10−12} twins and nucleation of multiple {10−12} twin variants caused by higher local stress concentration at the grain boundaries in CT-stretched samples as manifested by the kernel average misorientation. This higher twin fraction and twin-twin interaction imposed the strengthening by restricting the mean free path of dislocations leading to higher flow stress and strain hardening rate. During annealing of the RT/CT-stretched samples, the residual strain energy and twin boundaries were decreased due to static recovery leading to a coarse-grained twin-free microstructure. Strain induced boundary migration (SIBM) was found to be the predominant mechanism governing the grain growth during annealing via movement of high angle grain boundaries.

The Dynamic Recrystallization in a Hot‐Compressed Al–Zn–Mg–Cu–Sc–Zr Alloy: The Role of Strain Rate

The effects of strain rates (0.001–1 s−1) on the microstructures and mechanical performance of the novel Al–Zn–Mg–Cu alloy through hot compression at 300 °C are investigated in detail. With the increase of strain rate, the dislocation density increases from 0.06 × 1013 to 3.77 × 1013 m−2, which promotes the dynamic precipitation kinetics. And the volume fraction of η precipitates is calculated by the differential scanning calorimetry curves increasing from 1.36% to 3.94%. Both dislocations and precipitates promote to increase the hardness of the Al–Zn–Mg–Cu alloy. The large number of η precipitates in high‐strain‐rate samples hinders the recrystallization process by impeding the movement of dislocations and grain boundaries, decreasing the volume fraction of recrystallized grains to 3.1%. Continuous/discontinuous dynamic recrystallization occurs preferentially at low strain rates, and discontinuous dynamic recrystallization is rarely observed in high‐strain‐rate samples. In addition, because the process of continuous dynamic recrystallization promotes the transformation from low‐angle grain boundaries to high‐angle grain boundaries, more continuous dynamic recrystallized grains and less low‐angle grain boundaries can be observed in low‐strain‐rate samples.

Mechanistic understanding of strengthening in a novel MXene/AlSi10Mg matrix composite processed by laser powder bed fusion

The fabrication of high-performance two-dimensional nanosheets strengthened Al matrix composites (AMCs) is challenging due to the agglomeration issue of traditional nanosheets (graphene) and their high reactivity with Al powder. To address these concerns, Ti3C2 MXene nanosheets with superior chemical stability were employed as a substitute for graphene in this study. Furthermore, a novel MXene/AlSi10Mg composite powder for the laser powder bed fusion (LPBF) was synthesized using a powder coating strategy. The approach involves three steps, including intercalation treatment of MXene flakes, uniform dispersion of the delaminated MXene nanosheets in aqueous solution, followed by the powder coating treatment using a solid-liquid fluidized bed. Differing from conventional methods for making powder mixtures, such as mechanical blending and ball milling, our powder coating approach achieved uniform distribution and high purity of MXene on the surface of AlSi10Mg powder, while maintaining the original sphericity and flowability of powder. The MXene-coating exhibited exceptional stability under intense conditions of high-energy laser exposure and high-temperature Al melt, enabling the successful retention of MXene nanosheets after LPBF processing. Experimental results show that the retained MXene effectively strengthened the Al matrix through load transfer from Al matrix, pinning effect on the movement of grain boundaries, and inhibiting effect on the deformation and fracture of eutectic Si. Consequently, compared to the bare AlSi10Mg sample processed by LPBF, a small addition of MXene (0.25 wt%) yielded a significant improvement in tensile strength (over 60%), while maintaining an acceptable ductility.

Quasi-in-situ observation and analysis of grain boundary evolution of GH4169 nickel-based superalloy during the micro-strain stage of thermal deformation

A systematic study was conducted to analyze the grain boundary microstructure evolution of GH4169 nickel-based superalloy during the micro-strain stage of thermal deformation. A quasi-in-situ EBSD (electron backscatter diffraction) approach was used for observation. Moreover, at a temperature of 1100 °C and a strain rate of 0.1 s−1, a continuous strain uniaxial compression experiment was carried out. We observed the development of the grain boundary structure and the grain boundary deformation. The experimental findings revealed that GH4169 underwent locally inhomogeneous thermal deformation during the micro-strain stage, and the simultaneous occurrences of grain boundary slip, grain rotation, and grain boundary migration, exhibiting microstructural diversity. The grain boundary structure changed continuously as a result of the random movement of high-angle grain boundaries. Twin grains displayed a stable structure during the migration of grain boundaries, and their content indicated a considerable decrease as the strain increased. This provides a basis for directing the design of grain boundary engineering since it suggests that twin boundaries are easier to migrate during thermal deformation. In addition, no evidence of dynamic recrystallization was found throughout the entire micro-strain stage and a <101>/<111> micro-texture was observed, which is compatible with common dislocation slips in face-centered cubic crystals. Then, on the basis of the transmission electron microscope images of the microstructure, the numerous forms of grain boundary deformation were rationally explained from the standpoint of the relation mechanisms among grain boundaries and dislocations. Finally, the synergistic mechanism of grain boundary slip and migration is established as the primary mechanism of thermal deformation in the micro-strain stage.

Effect of pre-aging on microstructure, activation energy, texture evolution of Mg–9Gd–4Y–2Zn–0.5Zr alloy during compression deformation

This paper illustrated the effects of pre-aging on the microstructure, texture evolution, and deformation behavior of Mg–9Gd–4Y–2Zn–0.5Zr alloy during hot compression. Dynamic recrystallization (DRX) behavior, texture evolution, stress-strain curve, and activation energy of the solid solution and pre-aged alloy were evaluated. The results showed that the second-phase particles of the pre-aged samples exhibit combination of two types particles structure, which is composed of coarse dynamic precipitation particles and fine nanoparticles. The combination of these two types particles showed the best grain refinement effect by accelerating the DRX process, as the coarse dynamic precipitation particles promoted DRX through the PSN mechanism and the fine granular phase pinned dislocations and inhibited grain growth. As a result, the pre-aged samples had a higher DRX grain volume fractions and smaller average grain sizes than the solid solution alloys. In addition, the pre-aged sample had higher deformation activation energy (Q = 294.8 kJ/mol) than solid solution sample (Q = 223 kJ/mol) because β-phase pin dislocations formed during deformation restrained the movement of grain boundaries. The pre-aged alloys also showed a more concentrated texture than the solid solution alloys, with the c-axis of the coarse grains distributed from the compression direction (CD) at 30° inclination to the normal direction (ND). The c-axis distribution of the coarse grains was more scattered in the solid solution alloys. A hot processing map was constructed for the pre-aged alloy and used for evaluation. The optimal deformation parameters for the pre-aged Mg–9Gd–4Y–2Zn–0.5Zr alloy were between 0.001 and 0.1 s−1 at 400 °C–480 °C. These significant observations not only provide theoretical guidance but also practical application for setting plastic forming deformation parameters in industrial production.

Influence of homogenization treatment on microstructure and recrystallization behavior of 2195 Al–Li alloy

The microstructural evolution during homogenization treatment and the recrystallization behavior caused by Al3Zr precipitate in 2195 alloy were investigated via scanning electron microscopy, X-ray diffraction, transmission electron microscopy and electron backscatter diffraction. The severe dendrite segregation in the as-cast alloy was removed during homogenization, but the process was limited by the slower dissolution of Al–Cu phases. Moreover, the Al3Zr dispersoids precipitated in the sample homogenized by ramp heating rate of 30 °C/h (H30) were finer and denser compared to the samples subjected to other homogenization treatments (single-step, double-step, and ramp heating rate of 60 °C/h). The movement of dislocations and (sub)grain boundaries was resisted by the stronger Zener drag of finer and denser Al3Zr dispersoids. Thus, a higher recrystallization resistance during the hot compression and subsequent solution treatment was achieved for H30 sample. This work can provide theoretical guidance for optimizing the heat treatment parameters of the as-cast 2195 Al alloy.

Understanding and control of Zener pinning via phase field and ensemble learning

Zener pinning refers to the dispersion of fine particles which influences grain size distribution via movement of grain boundaries in a polycrystalline material. Grain size distribution in polycrystals has a significant impact on their properties including physical, chemical, mechanical, and optical to name a few. We explore the use of Phase-field modeling and machine-learning techniques to understand and improve the control of grain size distribution via Zener pinning in polycrystalline materials. We develop a machine learning model that determines the relative importance of various parameters to exercise microstructure control via Zener pinning. Our workflow combines high-throughput phase-field simulations and machine learning to address the computational bottlenecks associated with large-scale simulations as well as identify features necessary for microstructure control in polycrystals. A random forest (RF) regression model was developed to predict grain sizes based on five Phase-field model parameters, achieving an average prediction error of 0.72 nm for the training data and 1.44 nm for the test data. The importance of the input parameters is analyzed using the SHapley Additive exPlanations (SHAP) approach which reveals that diffusivity, volume fraction, and particle diameter are the most important parameters in determining the final grain size. These findings will allow us to select the best second-phase particles, optimize grain size distributions and thus design microstructures with the desired properties. The developed method is a highly versatile and generalizable approach that can be used to assess the combined effects of individual features in the presence of multiple variables.

The Atomic Observation of the Structural Change Process in Pt Networks in Air Using Environmental Cell Scanning Transmission Electron Microscopy.

The structural change in Pt networks composed of multiple chain connections among grains was observed in air at 1 atm using atomic-resolution environmental cell scanning transmission electron microscopy. An aberration-corrected incident electron probe with a wide convergence angle made it possible to increase the depth resolution that contributes to enhancing the signal-to-noise ratio of Pt network samples in air in an environmental cell, resulting in the achievement of atomic-resolution imaging. The exposure of the Pt networks to gas molecules under Brownian motion, stimulated by electron beams in the air, increases the collision probability between gas molecules and Pt networks, and the Pt networks are more intensely stressed from all directions than in a situation without electron irradiation. By increasing the electron beam dose rate, the structural change of the Pt networks became significant. Dynamic observation on an atomic scale suggested that the structural change of the networks was not attributed to the surface atomic-diffusion-induced step motion but mainly caused by the movement and deformation of unstable grains and grain boundaries. The oxidized surface layers may be one of the factors hindering the surface atomic step motion, mitigating the change in the size of the grains and grain boundaries.

Effects of grain boundaries and temperature on spinodal decomposition in a binary Fe-Cr alloy: A phase-field simulation

Due to its excellent oxidation resistance, corrosion resistance and mechanical properties, Fe-Cr based stainless steel is a promising candidate for advanced nuclear power systems. At the temperature of 300–600 °C, spinodal decomposition usually occurs in Fe-Cr alloys. However, irradiation can greatly accelerate this process. Fe-Cr based stainless steel decompose into a Cr-enriched α′ phase and a Fe-enriched α phase during spinodal decomposition, and the Cr-enriched α′ phase plays an important role in the hardening/embrittlement of Fe-Cr based stainless steels. In the present work, the evolution of vacancy and the Cr-enriched α′ phase in Fe-Cr alloy is investigated using phase-field method. The simulation results show that the vacancy concentration has a great influence during the spinodal decomposition. The Cr-enriched α′ phase occurs initially at the positions with high vacancy concentration. During spinodal decomposition, the vacancy forms a defect concentration loop around the Cr-enriched α′ phase. In addition, with the increase of temperature, the concentration of Cr atoms in the center of the Cr-enriched α′ phase decreases, and the coarsening rate increases, while the number of the Cr-enriched α′ phase formed in the alloy decreases. At low temperature, α′ phase is mainly coarsened by interlinking; while at high temperature, α′ phase is mainly coarsened by Oswald maturation. Moreover, the Cr-enriched α′ phase occurs at the grain boundary (GB) and the Fe-enriched α phase occurs at both sides of the GB during the spinodal decomposition. At the same time, in polycrystalline system, GB movement during grain growth is inhibited during the spinodal decomposition.

Inhibition effect of segregation and chemical order on grain boundary migration in NbMoTaW multi-principal element alloy

The impacts of solute segregation and chemical order on grain boundary (GB) migration are investigated by atomistic simulations in the NbMoTaW multi-principal element alloy (MPEA). Assisted by a contrived Nb-rich model, it is found that solute segregation and chemical order synergistically inhibit GB migration. Nb segregation increases the critical stress for GB migration, and the presence of chemical order further enhances the resistance of GB to plastic deformation. The destruction of local ordering structures is responsible for the difficult GB migration. Transition pathway analyses show that GB modified with both Nb segregation and chemical order requires high migration barrier, and the prior migration of GB sites tends to avoid regions with heavier chemical order. These results provide new insight into how chemical complexity affects elementary GB motion and contribute to manipulating the stability of MPEAs.

Direct atomic-scale observation of thermally driven grain-boundary migration associated with triple-junction motion

The internal structure of metals is defined by a complex network of grain boundaries (GBs) and their intersections---triple junctions (TJs). Heat or stress forces GBs to migrate, thus altering many physical properties of the material, and TJs play a key role in this migration as they control GB edges. The GB-TJ interaction strongly depends on the local crystallography, so it can only be properly described at the atomic scale. Although recent direct atomic-scale imaging of GB migration provides some insight into their dynamic behavior, the nanoscale details of the coupled motion of TJs and GBs in a natural nanocrystalline system remain elusive. Here, using in situ transmission electron microscopy (TEM) imaging, we describe the dynamics of the GB-TJ system in a nanocrystalline Co film with mixed fcc and hcp crystal phases during thermal annealing at both the mesoscale and the atomic scale. Our observations reveal that GB evolution proceeds through destabilization and displacement of TJs followed by GB relaxation within the new TJ geometry, which modifies the dihedral angles. This process is mediated by atomic-scale disconnection dynamics, where TJs serve as their sources and sinks. These findings advance our understanding of grain evolution in metal nanostructures, which is crucial for engineering their properties.

In-situ analysis on defect evolution in potassium-doped tungsten during synergistic He+ and H2+ dual-beam irradiation

Potassium-doped tungsten (KW), as an advanced candidate for first wall material, was developed to mitigate intrinsic embrittlement of bulk W. The addition of gaseous potassium bubbles (KBs) was known to act as effective barrier to the motion of irradiation damage and grain boundaries (GBs). The irradiation response to the He/H synergistic effect and the role of KBs on damage defects were two key issues when evaluating the performance of KW in future fusion reactors. In this work, KW was in-situ irradiated by 30 keV He+ and H2+ with He/H ratios of 2.5, 0.5, and 0.1 at 823 K. The synergy of He, H, and damage defects were discussed. The number density and the average size of irradiation-induced loops and bubbles nearby KBs, nearby GBs, and within the matrix was quantified. Increasing the ratio of H to He enhanced the nucleation sites of loops and promoted the accumulation rates of bubbles. The formation of a loop denuded zone nearby a KB was related to the KB size. The difference between the loop denuded zones nearby KBs and GBs was found. The estimated sink strengths of KBs and GBs were in line with our experimental results.

Abnormal grain growth under solution-aging treatments enables convergence mechanical properties of a Fe-Ni-Cr based austenitic alloy

In this study, systematic heat treatment routes including solution (980 °C to 1130 °C) and aging (675 °C to 775 °C) processes were used to tailor the microstructural evolution and mechanical performance of a Fe-Ni-Cr based austenitic alloy, strengthened by a γ′ phase (Ni3(Ti, Al)). Grain growth was observed with increasing solution treatment temperature from nearly 90 μm (980 °C) to nearly 200 μm (1130 °C). Grain refinement during solution heat processes was found to ascribe to the solute drag effect and the pinning effect of nickel-titanium-enriched segregates and precipitates. During aging, the precipitation behavior of γ′ is found to be almost independent of solution treatment temperatures. Interestingly, abnormal grain growth during aging was observed. The motion of grain boundaries was ascribed to the formation of nickel-titanium-enriched γ′ in the austenitic matrix, thereby contributing to the dissolution of the previously enriched segregates and precipitates from grain boundaries. The studied alloy shows a wide range of mechanical properties, from tensile strength of 1131 MPa with ductility at 36%, to tensile strength of 880 MPa with ductility at 50%. The current study demonstrates that grain refinement of the alloy at solution treatment may not benefit the final mechanical properties.

Zn–0.8Mn alloy for degradable structural applications: Hot compression behaviors, four dynamic recrystallization mechanisms, and better elevated-temperature strength

• Hot deformation behavior of Zn-0.8Mn alloy are revealed. • Constitutive equation and processing map of the alloy are established. • Four DRX mechanisms, i.e., DDRX, CDRX, TDRX and PSN, are activated. • The alloy exhibits excellent elevated-temperature strengths. Environmentally degradable Zn-0.8Mn alloy is highly ductile, which lays the foundation for developing high-performance Zn-Mn-based alloys. However, not only constitutive equation of this alloy is unknown, but also its dynamic recrystallization (DRX) behavior is unclear, which makes optimization of hot processing parameters of this alloy almost dependent on trial-and-error. This work aims to tackle these problems. The constitutive equation was deduced to be ε ˙ = 1.38 × 10 12 × [sin h (0.009 σ )] 8 exp(–135150/ RT ). A processing map of the alloy was obtained for the first time, which shows that it has excellent hot formability with narrow instability zones. At a final true strain of 0.8, the volume fraction of DRX grains increased from 37% to 79% with temperature increasing from 150 °C to 350 °C and strain rate decreasing from 10 s –1 to 10 –3 s –1 . Discontinuous DRX (DDRX), continuous DRX (CDRX), twinning-induced DRX (TDRX), and particle stimulated nucleation (PSN) were activated during hot compressions. DDRX was always the main mechanism. TDRX was completely suppressed at 300 °C and above. PSN arose from dispersed MnZn 13 particles. Furthermore, Zn-0.8Mn alloy exhibited elevated-temperature strengths better than pure Zn and Zn-Al-based alloys. At 300 °C and 0.1 s –1 , its peak stress was 1.8 times of pure Zn, owing to MnZn 13 particles of 277 ± 79 nm impeding the motion of grain boundaries and dislocations.

The dual role of hydrogen in grain boundary mobility

The effect of solute hydrogen on shear-coupled grain boundary (GB) migration is investigated with the dislocation-array type Σ25(430)[001] GB and a dual role of hydrogen on GB mobility is unraveled. In the low temperature and high loading rate regime, where hydrogen diffusion is substantially slower than GB motion, GB breaks away from the hydrogen atmosphere and transforms into a new stable phase with highly enhanced mobility. In the reverse regime, hydrogen atoms move along with GB, exerting a drag force on GB and decreasing its mobility. These findings provide rationale for the coexistence of hydrogen hardening and softening observed experimentally in polycrystalline materials.

A nucleation rate limited model for grain boundary creep

The motion of grain boundary (GB) dislocations, via a combination of glide and climb, mediates GB plasticity during processes such as creep and GB stress relaxation. Creep within the low stress regime, where non-Newtonian GB creep occurs, remains poorly understood. Models for GB dislocation nucleation rate limited creep, however, have not been sufficiently developed previously in the literature. Herein, a model for nucleation rate limited kinetics is developed and demonstrated to describe existing creep data reasonably well, using physically realistic materials properties as inputs to the model.

Weak solutions to an initial-boundary value problem for a continuum equation of motion of grain boundaries

&lt;p style='text-indent:20px;'&gt;We investigate an initial-(periodic-)boundary value problem for a continuum equation, which is a model for motion of grain boundaries based on the underlying microscopic mechanisms of line defects (disconnections) and integrated the effects of a diverse range of thermodynamic driving forces. We first prove the global-in-time existence and uniqueness of weak solution to this initial-boundary value problem in the case with positive equilibrium disconnection density parameter &lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}$ B $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt;, and then investigate the asymptotic behavior of the solutions as &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ B $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt; goes to zero. The main difficulties in the proof of main theorems are due to the degeneracy of &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ B=0 $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt;, a non-local term with singularity, and a non-smooth coefficient of the highest derivative associated with the gradient of the unknown. The key ingredients in the proof are the energy method, an estimate for a singular integral of the Hilbert type, and a compactness lemma.&lt;/p&gt;

Microstructure evolution and hot deformation characteristics of 15Cr-22Ni iron-base superalloy

The hot deformation behavior and microstructure evolution of a newly designed 15Cr-22Ni iron-based superalloy containing 0.6 wt %Nb was studied. The strain-compensated constitutive equations were established, which can accurately predict the high-temperature flow behavior of the superalloy. The dynamic recrystallization kinetic model was developed. The degree of dynamic recrystallization gradually increases with decreasing strain rate and increasing deformation temperature. The hot processing map of designed superalloy was developed and the optimum hot processing range has been determined to be 1050–1150 °C/0.01 s−1. Hot deformation induces the precipitation of nano-sized NbC at grain boundaries and dislocations in the designed superalloy. Nano-sized NbC particles act as nucleation sites for dynamic recrystallization. The dynamic recrystallization behavior is compared with that of 15Cr-22Ni-1 Nb alloy. The starting of dynamic recrystallization of designed superalloy is later than that of 15Cr-22Ni-1 Nb alloy, which is attributed to the lack of active sites in the early recrystallization nucleation. However, the recrystallization kinetics of designed superalloy is faster than that of 15Cr-22Ni-1 Nb alloy. Due to the weak pinning force of nano-sized NbC precipitates to the grain boundaries and dislocations, the movement of grain boundaries and dislocations is less hindered, which is beneficial to the growth of dynamic recrystallization grains.